imhotep
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Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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It's been almost a year since the idea to build this telescope first came about. Ideally this thread would have appeared several months ago when I first began working on the project. Technically it started back in October, but the concept and determination to build this instrument originated circa February of 2008. I spent the summer doing my homework, researching materials, construction methods, optical suppliers and various options for newtonian components. Then the project finally started moving.
In September I settled on a finalized set of dimensions using NEWT.
NOTE: This drawing contains errors and is now obsolete.
I've done my best to juggle the various needs/wants on my list while respecting the limitations of my mount and budget. I wanted a native (unbarlowed, sorry for the made-up terminology) focal length of at least 800mm but probably no more than 1250mm. I chose an 8" aperture at f/5 and worked with NEWT to find an arrangement that can fully illuminate the CCD chip in my QHY8.
Edited by imhotep (03/09/09 01:58 PM)
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imhotep
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Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Later in October I pulled the trigger and ordered an 8" f/5 Royce conical primary, which is scheduled for delivery around March 18th. At the time I ordered my mirror (and to my knowledge this is still the case) there was only one commercially manufactured mirror cell that featured a center hole for mounting a Royce conical primary - http://astronomy-mall.com/regular/products/cpt/13inchshortclips.jpg
I think it's an impressive piece of engineering, but I wanted something simpler and if possible, homegrown. I started working on designs for a custom mirror cell with the intention to have the plates precision-cut on a Flow-Jet machine. The assembly would then be doable at home.
CAD drawings of the mirror cell:
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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imhotep
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Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Both halves of the mirror cell were cut from a single 12"x12" plate of 6061 aluminum.
I took the material and my CAD drawings to a local metal fabricator. The DXF files were used to drive a water-jet machine. The owner permitted me to snap some photos of the machine while it cut the aluminum. I was also able to chat with the technician about the whole process. The mahcine pictured below uses a 60,000 PSI jet of water measuring 0.030 inches in diameter.
I was very pleased with the result:
The hardware for my mirror cell all came from McMaster-Carr. Pictured below from left to right, top row first:
- 1/4-28 stainless knurled thumbscrews, 1.75" shank (collimation bolts)
- Stainless compression springs, 1.5" long, 0.375" OD, 17.68 lb/inch
- Stainless compression springs, 1.25" long, 0.6" OD, 37.49 lb/inch
- 1/4-20 stainless knurled thumbscrews, 1.5" shank, (locking bolts)
- 8-32 stainless socket-head machine screws, 0.75" shank, (mounting bolts)
For lack of experience building mirror cells I ordered two different sets of compression springs to feel them out. One set is substantially stiffer than the other, but both are fully capable of lifting the combined weight of the upper plate plus mirror with as little as 0.25" of deflection.
I threaded varous holes myself and assembled the mirror cell with each set of springs. The following photos show the 0.6" OD springs, but eventually I decided to use the 0.375" OD springs. The both seem fully adequate to lift a 3.5 lb mirror. I chose the narrower springs because they are a better fit to the collimation bolts.
Oblique view:
Bottom view:
Top view:
The project basically halted after finishing the mirror cell. I was waiting on two very important packages to arrive. Just recently one of them did, so the past ten days have seen lots of progress.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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imhotep
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Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Initially I wantd this instrument to have a CF tube. After researching the process of rolling your own CF I felt like it would be taking on too much at once. I've decided to make the CF tube a long-term goal and use a Hastings tube for the near future. Several folks in this community have done some amazingly good jobs on their own CF upgrades and I look forward to following in their footsteps later this year.
A fellow ATM/astorphotographer gave me the idea to build a dry-run OTA using a cheaper tube material in order to confirm that my camera reaches focus using all of the spacings and dimensions shown in NEWT. The purpose of this exercise is to ensure that I only drill one set of holes in the Hastings tube. A 10" sonotube will be used to build the dry-run OTA. All components will be installed followed by a rough collimation before having first light with a QHY8 CCD camera.
I knocked together this cradle which bolts to my drill press. The cradle provides support and aids in carefully positioning the tube under the bit. The tube can also be clamped or strapped to the cradle.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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One of my goals for the astrograph was to fill a wishlist of bells of whistles that my previous imaigng scope lacked. I chose Moonlight's motorized CR newtonian focuser because it will add several additional technologies to my imaging workflow. Motorized focusing will allow me to stay at the laptop and adjust focus remotely rather than having to lean way over and shake up the mount by manually adjusting focus with my hand. I can also employ various automated focusing utilities, create focusing profiles for multiple cameras and filters, and lastly have the benefit of automated temperature compensation.
Several controller options are available with Moonlight's motorized focusers. I chose the Cercis controller because it can control two focuser simultaneously while running separate temperature profiles for each one. In fact, I believe the Cercis controller is the only choice for those who want temperature compensation. Two temperature probes can be connected as well.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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imhotep
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Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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The focuser hole was cut using a 2-3/8" hole saw attached to a corded hand-drill. I wasn't able to use the drill press because the hole saw is too tall.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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imhotep
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Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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My plan for mounting the mirror cell has evolved over time. Originally I was going to drill and tap threaded holes into the edges of the lower plate. The problem was that it required me to know the ID of the Hastings tube within a very small margin of error. After talking to Andy over at Hastings Pipe CO I realized this was asking too much of irrigation pipe. I opted to leave somewhere between 0.10" and 0.25" of space between between the arms of the mirror cell's base plate and the inner walls of the tube. I had to make this decision back when the mirror cell was being designed in CAD. The revised plan for mounting the mirror cell is as follows.
Mounting brackets for the mirror cell were fabricated using three 1" sections of aluminum L-channel. I bought these pieces at the local metals supplier for less than a dollar each. One side is longer than the other, measuring 1.5" and 0.75" respectively. The brackets are fastened to both the tube wall and the mirror cell using 10-32 screws. I wanted a small amount of adjustablility with respect to the tube's inner diameter, so I routed slots in the face that abuts the mirror cell (rather than single holes).
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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imhotep
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Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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The spider I ordered from Protostar features a couple of bells and whistles. It comes with an integrated dew heater that runs off a 12V power source. Two of the vanes actually act as positive and negative conductors. Wires can be attached on the outside of the tube and then run to the power source. In my case I'll be using a standard RCA plug so I can connect the integrated secondary dew heater right alongside my other dew heater strips (for guidescope, telrad, etc).
The second enhancement is built-in offset. I simply took the offset amount provided by NEWT and requested that Protostar build it into the spider. This is a standard option they offer and well worth it IMHO.
I haven't glued the secondary to the holder yet. This will probably get done either tonight or tomorrow.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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Mike I. Jones
Carpal Tunnel
Reged: 07/02/06
Posts: 1572
Loc: Fort Worth TX
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Curt,
For a fully illuminated field diameter of 1.313", your diagonal should be offset 0.106" away from the focuser and toward the primary. That centers your FOV on the diagonal aperture (see attached diagram).
Your tube wall thickness looks to be a lot more than the 0.064" value you used in NEWT. But as long as the distance from the primary vertex to the focuser hole plane is 32.45" as you used in NEWT, the diagonal offset of 0.106" is right.
S'gonna be a nice instrument!
Mike
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56 mirrors, lenses, 16" f/6 Newt, 6" f/10 refractor, TOA-130S, Tinsley 5" f/15 Mak, 6" f/4 RFT, Coronado PST. Still to build: 24" f/10 Modified Dall-Kirkham, 10" f/26 Mak, 8" f/12 apo, spectrohelioscope, Herrig, Schupmann, and others.
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imhotep
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Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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The sonotube dry-run has already paid off. Yesterday when I drilled holes for the spider I forgot to account for the built-in offset. The holes I drilled in the sonotube are spaced 90º apart, but the spacings will be a little off from 90º for this custom spider. The two vanes on either side of the focuser are slightly longer than the other two which accounts for the offset. I'm not sure exactly how far off from 90º the other spacings will need to be, but I can already see my current holes aren't correct. The vanes are flexed slightly to reach them.
Here's the dry-run OTA sitting next to the Hastings tube.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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With all of that said, there's not a whole lot left to do between now and March 18th. I'll have the secondary installed and aligned to the focuser by then. First light will probably be somewhat anticlimactic. I'll confirm that the QHY8 reaches focus, then start transferring the hole pattern to the Hastings tube.
Knock on pyrex for a timely delivery of the primary 
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Mike, thanks for posting the illustration. I'm glad you did because it made me realize I posted the wrong NEWT drawing! I've edited the original post to show the correct one. That drawing went through several revisions and I got mixed up when I posted it.
Using the correct drawing, I'm curious if you come up with the same offset of 0.13" that I did.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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charles genovese
super member
Reged: 02/04/06
Posts: 132
Loc: Madisonville Louisiana
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To adjust the amount of back focus you simply drill more than one set of holes for the primary mirror - can slide it back and forth to adjust parameters. I would suggest setting the focal plane .5" above the minimum focuser height and have a smaller secondary for planets/visual - a 1.6 or 1.8" secondary (all you need is about .5" 100% illumination). For the astrograph you will need a secondary 2.1 to 2.6 inches , and I would suggest being able to get 3.5 " of back focus (ie the second set of primary mirror mount holes will be 3" farther foreward) to allow for a coma corrector and possibly an off axis guider. Would also suggest the tube extend at least 5-6" of tube beyond the focuser so the imager can't "see" any light from outside the tube. A (Also helps keep the secondary from dewing). Flock the tube- baffles are unnecessary.
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Mike I. Jones
Carpal Tunnel
Reged: 07/02/06
Posts: 1572
Loc: Fort Worth TX
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Don't forget to take the real, fabricated mirror focal length into your design. Royce should be able to tell you the final focal length to 1mm accuracy or better.
Your transverse offset is 0.106", but with your vanes rotated 45 degrees to the focuser, the spider vane mounting hole offsets are (0.106)sin(45)=.075" away from the focuser, not much but enough to keep from bending the spider vanes.
REALLY good idea to prototype-drill a disposable Sonotube before final drill on the Hastings tube. I need to go tell Frank in the Yahoo Astrograph group about your idea. He's putting together a 10" f/3.8 astrograph that uses an MPCC to correct the coma, and neither of us are 100% sure how much the MPCC shifts the DSLR focus position. Sonotubing it together first will answer that question with confidence.
Mike
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Chris Curran
scholastic sledgehammer
Reged: 06/14/05
Posts: 827
Loc: Brandon, FL
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0.064 is correct for the final Hastings OTA. The Sonotube of course is not 0.064....
Quote:
Your tube wall thickness looks to be a lot more than the 0.064" value you used in NEWT.
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cheers & beers,
Chris
Homepage | Over 40?
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Chris Curran
scholastic sledgehammer
Reged: 06/14/05
Posts: 827
Loc: Brandon, FL
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Nice work Curt.
BTW, you can use a hand drill and hole saw for the Hastings tube. It'll actually cut easier than the cardboard sonotube...
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cheers & beers,
Chris
Homepage | Over 40?
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Mike I. Jones
Carpal Tunnel
Reged: 07/02/06
Posts: 1572
Loc: Fort Worth TX
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I changed the ZEMAX model to the 31.74" mirror spacing and reduced the FOV diameter to 1.194", as you show in the new diagram. I'm getting the transverse offsets to be 0.112" to the nearest thousandth. The elliptical aperture offset in the plane of the diagonal face is 0.158", and 0.158cos(45)=0.112". Did NEWT do the calculation for the offset? It may be using an approximate formula for decentration rather than using exact raytracing. At lower focal ratios, like Frank's 10" f/3.8 astrograph over in Yahoo, the extra precision of raytracing really matters.
Here's a ZEMAX shaded layout of your astrograph using the values from NEWT above. I only drew half the tube for clarity.
I am getting disturbing results that don't jive with NEWT, though. Using all the values in your NEWT graphic, I'm only getting a focal plane clearance of 0.618 inches above the 2.0125" focuser at its minimum height. Let's go through the math:
Focal length = 1000mm = 39.37 inches
Spacing to diagonal face = 31.74 inches
Diagonal face to focus = 7.63 inches
Tube ID = 9.872, so ID radius = 4.936 inches
Wall thickness = 0.064 inches, so
Tube OD radius = 5.000 inches
So the image plane is 7.63-5.00=2.63 inches above OD
Focuser minimum height = 2.0125 inches,
So image plane clearance above the focuser is 2.63-2.0125=0.6175 inches, which agrees with the ZEMAX model exactly.
Is this enough clearance for you? Or, are there any errors remaining in the NEWT graphic?
Jus' checkin', seems kind of low.
Mike
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Strgazr27
Vendor - Deep Space Mods and Composites
Reged: 10/04/04
Posts: 6984
Loc: StonyHill Observatory
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Curt,
I'm working on a similiar design only F/4 so this is perfect timing. Looking at your NEWT drawing I see a 100% FOV of 1.19 inches which is roughly 30mm. This is still smaller than the diagonal distance of the QHy's chip. I know it's only about 2mm shy but will this make a difference to you? I will be using an MPCC with mine and was curious if my 100% FOV needs to be bigger than your 1.19. Maybe Mike could answer this.
That hastings tube is nice! When your ready for a CF tube for it let me know.
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Bobby
StonyHill Observatory
Skywatcher EQ6 Pro (On it's way)
AT 130 F/6 Prototype
Royce 10" f/4 Astrograph (Under Construction)
Self Modded 40D
70-200 F2.8 L IS
SSAG
YAHOO TMB 130SS Group
Astronomy Technologies Yahoo Group
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Mike I. Jones
Carpal Tunnel
Reged: 07/02/06
Posts: 1572
Loc: Fort Worth TX
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Found some information on the MPCC at http://www.baader-planetarium.com/pdf/mpcc_e.pdf. It says the MPCC doesn't change the primary EFL, but didn't indicate if the position of the primary focal point is shifted or by how much.
Losing a little illumination out in the corners isn't a big deal as it can be compensated for by flat fielding, up to around 1 to 1 1/2 stops max.
If you have any detailed information on the MPCC that would be most helpful here.
Mike
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Strgazr27
Vendor - Deep Space Mods and Composites
Reged: 10/04/04
Posts: 6984
Loc: StonyHill Observatory
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Mike,
Baader says it adds about 10mm to the backfocus but doesn't change the in focus requirement. That and it supposedly will produce 12 micron stars at the edge of a 35mm chip is about all I could dig up.
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Bobby
StonyHill Observatory
Skywatcher EQ6 Pro (On it's way)
AT 130 F/6 Prototype
Royce 10" f/4 Astrograph (Under Construction)
Self Modded 40D
70-200 F2.8 L IS
SSAG
YAHOO TMB 130SS Group
Astronomy Technologies Yahoo Group
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Thanks everyone for the great feedback. Right now it's a bit late so bear with me if I miss-state something or misunderstand some of the potential concerns that have been raised. I'm really glad for the help on this, and I'll admit to being a little scared by some of the disagreeing specs that came from ZEMAX. I probably should've started this thread a long time ago, but fortunately it's not too late to make some last minutes changes if necessary.
I'll go through these one at a time.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Mike...
Quote:
Don't forget to take the real, fabricated mirror focal length into your design. Royce should be able to tell you the final focal length to 1mm accuracy or better.
Arg...I didn't think about that, but I'm trusting that it'll be pretty stinkin' close. I can call Royce tomorrow and ask him, then plug the adjusted FL into my model.
Quote:
Your transverse offset is 0.106", but with your vanes rotated 45 degrees to the focuser, the spider vane mounting hole offsets are (0.106)sin(45)=.075" away from the focuser, not much but enough to keep from bending the spider vanes.
I'm not quite following this part. How do I use the 0.075" value when it comes time to redrill holes for the spider (or for drilling them in the hastings tube)?
Quote:
REALLY good idea to prototype-drill a disposable Sonotube before final drill on the Hastings tube. I need to go tell Frank in the Yahoo Astrograph group about your idea. He's putting together a 10" f/3.8 astrograph that uses an MPCC to correct the coma, and neither of us are 100% sure how much the MPCC shifts the DSLR focus position. Sonotubing it together first will answer that question with confidence.
Chris Curran gets the credit for this idea. I did have to search far and wide for a 10" OD sonotube though. Lowe's and Home Depot only carry 8" and 12" down here, and those numbers are used very loosely. I saw four 12" sonotubes telescops inside each other on the shelf.
Quote:
I changed the ZEMAX model to the 31.74" mirror spacing and reduced the FOV diameter to 1.194", as you show in the new diagram. I'm getting the transverse offsets to be 0.112" to the nearest thousandth. The elliptical aperture offset in the plane of the diagonal face is 0.158", and 0.158cos(45)=0.112". Did NEWT do the calculation for the offset? It may be using an approximate formula for decentration rather than using exact raytracing. At lower focal ratios, like Frank's 10" f/3.8 astrograph over in Yahoo, the extra precision of raytracing really matters.
Yes, NEWT gave me the 0.13" offset value. I can't comment on the method it uses to output any of the dimensions in my drawing.
Should I have used ZEMAX instead of NEWT? How much does ZEMAX cost?
Moving along...
Quote:
I am getting disturbing results that don't jive with NEWT, though. Using all the values in your NEWT graphic, I'm only getting a focal plane clearance of 0.618 inches above the 2.0125" focuser at its minimum height. Let's go through the math:
Focal length = 1000mm = 39.37 inches
Spacing to diagonal face = 31.74 inches
Diagonal face to focus = 7.63 inches
Tube ID = 9.872, so ID radius = 4.936 inches
Wall thickness = 0.064 inches, so
Tube OD radius = 5.000 inches
So the image plane is 7.63-5.00=2.63 inches above OD
Focuser minimum height = 2.0125 inches,
So image plane clearance above the focuser is 2.63-2.0125=0.6175 inches, which agrees with the ZEMAX model exactly.
Is this enough clearance for you? Or, are there any errors remaining in the NEWT graphic?
Jus' checkin', seems kind of low.
Mike
Yeah.... this may be a real problem. I need to take some time and review my NEWT model one more time. I may have made a mistake or two.
The good news is that it isn't too late to straighten this out. Mike, thanks for taking the time to run my dimensions through ZEMAX. I never even doubted NEWT or looked for a second opinion as it were.
Stay tuned, I'll get back to you after I rerun this thing.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
Edited by imhotep (03/08/09 10:48 PM)
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Quote:
Curt,
I'm working on a similiar design only F/4 so this is perfect timing. Looking at your NEWT drawing I see a 100% FOV of 1.19 inches which is roughly 30mm. This is still smaller than the diagonal distance of the QHy's chip. I know it's only about 2mm shy but will this make a difference to you? I will be using an MPCC with mine and was curious if my 100% FOV needs to be bigger than your 1.19. Maybe Mike could answer this.
That hastings tube is nice! When your ready for a CF tube for it let me know.
Hi Bobby,
I calculated the QHY8's chip diagonal to be 1.11". Maybe I did something wrong. I got this number by multiplying the pixels on each side by the pixel size, and I came up with a diagonal of 28.11mm. What did I miss?
Thanks for the encouragement. I'm looking forward to learning from you on rolling a CF tube later on down the line.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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FYI on the other thing and then I'm back to the drawing board with NEWT to see if I screwed something up....
I'm planning on using the Televue Paracorr (older model called the PLA) for coma correction. What I don't know is what effect, if any, the PLA has on the focusing distance. I called TV to ask about this and acutally got Al on the phone. He didn't give me a super clear answer actually. He said he didn't think it would change the focusing distance at all. I'll find out soon enough.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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Mike I. Jones
Carpal Tunnel
Reged: 07/02/06
Posts: 1572
Loc: Fort Worth TX
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ZEMAX is pretty pricey (think buying about five Ethos eyepieces at once) but OSLO-EDU is free, no strings attached, available at http://www.lambdares.com/education/oslo_edu/. Download it and I can send you the OSLO file for your scope. OSLO's 10-surface limit can do Newtonians in its sleep.
But it doesn't take ZEMAX or OSLO to do the simple sanity-check calculations I showed you. Either the height of your focuser is less than 2.0125", or you're going to have to move the diagonal closer to the primary and push the focal plane farther out so you can reach focus.
The guy that wrote NEWT sent me his source code a couple of years ago, but I haven't had time to plow through it. I've started writing my own version of NEWT I'll call NEWT2 to keep the name continuity. NEWT2 is going to be based on exact 3D raytracing and fix a lot of the problems and approximations NEWT apparently has. It will have a much easier GUI as well, but I make no promises about when I'll have it ready. I still need to get CassDesign2 finished up and released.
Meanwhile, get OSLO-EDU, but also just do the simplest calculations like I did here to make sure things make sense. And don't drill any holes until you get the real mirror!
Mike
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Okay, I went back to check some of my work. Couple of things...
First of all, it seems I made a mistake when I determined the minimum focusing distance. According to the maker of the QHY8 camera, the distance measured from the chip surface to the top of the t-thread bezel on the camera is 21mm. What I neglected to account for is the extra 10mm of distance from that point to the lip on my T-adapter (2" nosepiece). So 31mm has to be added to the minimum focuser height of 2.0125, giving me a revised minimum focusing distance of 3.2325"
Secondly, a correction -- I did NOT get the offset value from NEWT like I said previously. Sorry for the brain malfunction there. I got it using an online offset calculator. A few minutes ago I revisited the site and plugged in my new-found value for the minimum height of the image plan (again, measured from the outer tube wall), and I got Mike's value of 0.112".
Even scarier -- if I plug in the previous value I came up with for secondary-to-image distance, it doesn't even give me the 0.13" I wrote down, so somehow I came up with that one via a typo or some other mistake.
Correct dimensions agree with you Mike. Convert this to inches and you get 0.1125"
So to summarize...
1. My custom-made spider's built-in offset is OFF by 0.18". 
2. The correct minimum focusing distance (measured from tube's OD to image plane) is 3.2325"
Mike, here I've plugged the corrections into NEWT. Does this agree with ZEMAX, or is there still a mystery or two?
NOTE: This drawing contains errors and is now obsolete.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
Edited by imhotep (03/09/09 01:59 PM)
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Going back to the issue about the QHY8's diagonal....if it really is 32mm across then that converts to 1.26".
In the revised NEWT drawing above, I've got 1.147" for the 100% illuminated area. This also assumes padding the focusing height with an extra 0.25" of in-travel. I got curious about the effects of adding or subtracting in-focus to the size of the 100% illuminated area. Here's what NEWT gave me for the following extra in-travel:
0.00" extra in-travel -- 1.201" 100% illuminated area
0.25" extra in-travel -- 1.147" 100% illuminated area
0.50" extra in-travel -- 1.092" 100% illuminated area
I think it's useful to put this in the context of actual pixels. Plugging in the 7.8 micron pixels of the QHY8 I get the following:
0.00" extra in-travel -- a circular perimeter measuring 192 pixels wide lies outside the 100% illuminated area
0.25" extra in-travel -- a circular perimeter measuring 367 pixels wide lies outside the 100% illuminated area
0.50" extra in-travel -- a circular perimeter measuring 547 pixels wide lies outside the 100% illuminated area
Yikes. To me this seems like a badly vignetted image plane.
Granted, that perimeter will mostly overlap with the corners and less so at the edges.
What do you guys think about this? Are those numbers deplorable for an instrument bearing the name 'astrograph'?
One option for me is to go up to a 3.1" secondary. According to NEWT, doing so would put my 100% illuminated area about 0.5" larger than the QHY8's chip diagonal. There are two big problems with this...
1. Doing so would require at least a 2.5" focuser barrel. To my knowledge Moonlight only offers large format focusers for refractors, so I'd have to see about returning mine and finding an alternative.
2. I started to say that I wouldn't be able to use my custom-made spider, but it might still be usable since I'm gluing the secondary onto the holder vs installing the 2.6" shroud around it. I'd have to get Bryan Greer's input on this and see if the spider is even robust enough to use a 3.1" secondary.
Well, all is not lost, but man what a bust  I made some mistakes for sure, but I'm optimistic that solutions can be found.
Thanks everyone for your patience in reading through so much verbage. I look forward to your feedback on this first round of trouble-shooting the design.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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Mike I. Jones
Carpal Tunnel
Reged: 07/02/06
Posts: 1572
Loc: Fort Worth TX
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Simple-math sanity check on the above:
Focal length = 1000mm = 39.37 inches
Spacing to axial diagonal face and focuser hole = 31.52 inches
Diagonal face to focus = 39.37-31.52 = 7.85 inches
Tube ID = 9.872, so ID radius = 4.936 inches
Wall thickness = 0.064 inches, so
Tube OD radius = 5.000 inches (same as before)
So the image plane is 7.85-5.00=2.85 inches above OD
(See? I still can't get the 3.2325" value...)
Focuser minimum height = 2.0125 inches,
So image plane clearance above the focuser is
2.85 - 2.0125 = 0.8375 inches, or about 21.27 mm.
Almost makes me think NEWT is including the diagonal offset in the separation calculation, which is 100% wrong. The offset is along the surface of the diagonal and doesn't change where the optical axis intersects the diagonal plane.
Did you get OSLO? I'll attach this latest rev to your design in OSLO *.len format, perhaps tomorrow night when I get home.
Mike
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Vincent Becker
super member
Reged: 09/16/08
Posts: 198
Loc: France
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Really nice project. Your mirror cell looks really good. You've got the biggest Dremel I've ever seen 
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Vincent Becker
10" dobsonian on EQ platform (home-made by my father)
8" string newtonian as travelscope (home-made by myself )
Orion 80ED and GSO 200/1000 on Atlas EQ-G for astro-imaging
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Quote:
Simple-math sanity check on the above:
Focal length = 1000mm = 39.37 inches
Spacing to axial diagonal face and focuser hole = 31.52 inches
Diagonal face to focus = 39.37-31.52 = 7.85 inches
Tube ID = 9.872, so ID radius = 4.936 inches
Wall thickness = 0.064 inches, so
Tube OD radius = 5.000 inches (same as before)
So the image plane is 7.85-5.00=2.85 inches above OD
(See? I still can't get the 3.2325" value...)
Focuser minimum height = 2.0125 inches,
So image plane clearance above the focuser is
2.85 - 2.0125 = 0.8375 inches, or about 21.27 mm.
Almost makes me think NEWT is including the diagonal offset in the separation calculation, which is 100% wrong. The offset is along the surface of the diagonal and doesn't change where the optical axis intersects the diagonal plane.
That all makes perfect sense to me. I'm annoyed with myself for letting NEWT be my crutch during this process. The simple math just doesn't check out as you've illustrated.
Quote:
Did you get OSLO? I'll attach this latest rev to your design in OSLO *.len format, perhaps tomorrow night when I get home.
I downloaded OSLO-EDU and saw that the start-up options all have to do with lenses and refractive optics. I skimmed the manual's TOC and found the section on reflecting systems. At present I haven't the slightest clue how to use this software, so I'll definitely need a tutorial of some kind to get started.
Mike, thanks again for your helpful feedback. I'm all ears for any other tools I could/should be using to remodel this astrograph. I look forward to seeing what OSLO can do, but again I'll have to spend some time learning the software. I also thought about Krieg and Berry's book which I own, but it doesn't deal with 100% illuminated areas (I don't think). It does discuss how to choose a secondary size based on the eyepieces you intend to use with the scope, so I wondered if that principle could be transferred to a camera.
I'm still a little shocked by the basic arithmetic that doesn't add up with NEWT's output. To think I was using it as my sole design tool for this telescope....
Curt
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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Chris Curran
scholastic sledgehammer
Reged: 06/14/05
Posts: 827
Loc: Brandon, FL
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Guys - take it easy on Curt - he spooks easily!
Curt - sanity check time. The 100% zone is not 100% across the entire field. It's not like you have 100% illumination across some portion of the field and then it suddenly drops off to 75%. You have 100% at the dead center - it falls off from there. You will use/need flats no matter what. Even my precious FSQ-106N requires a flat. Just because a few pixels lie in the 75% zone doesn't mean they are vignetting your image...
Psst: once you complete your focus testing, there's little chance there will be anything as severe as 0.25" extra in-travel (or more), so stop worrying about it.
Quote:
0.00" extra in-travel -- 1.201" 100% illuminated area
0.25" extra in-travel -- 1.147" 100% illuminated area
0.50" extra in-travel -- 1.092" 100% illuminated area
...
Yikes. To me this seems like a badly vignetted image plane.
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cheers & beers,
Chris
Homepage | Over 40?
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Mike I. Jones
Carpal Tunnel
Reged: 07/02/06
Posts: 1572
Loc: Fort Worth TX
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Let's take a different direction here by designing exactly what you want regardless of what NEWT says.
You need your minimum image plane distance above the tube OD to be 3.2325". Let's just round it to 3.25".
Your nominal mirror focal length is 1000mm or 39.37". We know that the real one delivered to you could be plus or minus a few millimeters, but we'll use 39.37" for now.
Your tube OD is 10" even, so its OD radius is 5".
The total path from the optical axis up to the image is thus 5.00 + 3.25 = 8.25".
That puts the intersection of the optical axis and the plane containing the diagonal face at 39.37 - 8.25 = 31.12" from the primary vertex.
Thus you cut the focuser hole at a distance of 31.12" from the primary vertex.
Notice I'm saying "vertex" (the mirror center) rather than "edge". The edge is closer to the diagonal and focuser by the sag formula R-SQR(R^2-r^2), which for your mirror becomes 78.74-SQR(78.74^2-4^2)=0.102". But don't measure from the edge; measure from the mirror center.
If your focuser really is 2.0125" high at its racked in position (and you should probably check that), then your image clearance is 3.25 - 2.0125 = 1.2375". If you say that's enough, fine, but you may want to put the image another 1/4" to 1/2" higher to allow focusing either side of infinity.
Just remember that the Primary focal length = Primary/diagonal spacing + Tube OD radius + Image height above OD.
I'll figure the diagonal offset for the 31.12" spacing later today.
Mike
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Mike I. Jones
Carpal Tunnel
Reged: 07/02/06
Posts: 1572
Loc: Fort Worth TX
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OK - took all of 15 seconds to update your astrograph OSLO file to the 31.12" design. Here - have fun, I'll talk to you later today.
Mike
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Strgazr27
Vendor - Deep Space Mods and Composites
Reged: 10/04/04
Posts: 6984
Loc: StonyHill Observatory
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Curt,
I spent some more time with it last night and realized my dimensions were for a Canon based DSLR. You are correct with your measurements for the QHy's chip as 28mm so you should be fine and as Chris says, it's a gradual fall off.
I'm going back a redoing mine also with some updated measurements.
Hang in there! I think you'll be fine!
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Bobby
StonyHill Observatory
Skywatcher EQ6 Pro (On it's way)
AT 130 F/6 Prototype
Royce 10" f/4 Astrograph (Under Construction)
Self Modded 40D
70-200 F2.8 L IS
SSAG
YAHOO TMB 130SS Group
Astronomy Technologies Yahoo Group
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Strgazr27
Vendor - Deep Space Mods and Composites
Reged: 10/04/04
Posts: 6984
Loc: StonyHill Observatory
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Does vignetting of the 75% ray at the front aperture have any impact on the design? I ask as with a 10" tube it shows vignetting but going to a 10.5 inch tube removes that issue?
Curt,
Hope you don't think I'm hijacking your thread  Just have a few questions..
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Bobby
StonyHill Observatory
Skywatcher EQ6 Pro (On it's way)
AT 130 F/6 Prototype
Royce 10" f/4 Astrograph (Under Construction)
Self Modded 40D
70-200 F2.8 L IS
SSAG
YAHOO TMB 130SS Group
Astronomy Technologies Yahoo Group
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Strgazr27
Vendor - Deep Space Mods and Composites
Reged: 10/04/04
Posts: 6984
Loc: StonyHill Observatory
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Quote:
1. Doing so would require at least a 2.5" focuser barrel. To my knowledge Moonlight only offers large format focusers for refractors, so I'd have to see about returning mine and finding an alternative.
Curt,
Ron is making me a large format based on their refractor setup. They will be ready next month. They will feature a recessed mounting base which will add no height to the focuser. Total focuser height is 2.38 inches with a drawtube ID of 2.5 inches. I'm going with a 1" drawtube. They will feature 8 bearings and be able to carry around 12lbs of gear. Should be perfect for what you and I are doing. Ron says price should be somewhere around $365. I just spoke to him to confirm all the info.
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Bobby
StonyHill Observatory
Skywatcher EQ6 Pro (On it's way)
AT 130 F/6 Prototype
Royce 10" f/4 Astrograph (Under Construction)
Self Modded 40D
70-200 F2.8 L IS
SSAG
YAHOO TMB 130SS Group
Astronomy Technologies Yahoo Group
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walt r
Post Laureate
Reged: 02/13/07
Posts: 3463
Loc: Doylestown, PA
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I have found that Mel Bartel's diagonal calculator handy for field illumination drop off.
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Walt
Obsession 18" f/4.45 #1370 AN/SC
MK67 Deluxe 6" f/12 Mak-Cass, Super Polaris GEM, JMI MicroMax DSC
DIY 60mm f/6 Achromat
Cookbook 245 CCD
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Mike,
Thanks for the OSLO file and for all your time and help. I looked at the model in 2D and 3D, but I’m still a little lost with the interface. I would love to learn this software.
This morning I discovered the problem with my NEWT model. The confusion over focusing height is all my fault. As a control I opened NEWT and looked at the dimensions for the default 6” f/8 it displays on startup. The arithmetic for this model all checks out, so I went back to mine and looked harder for a mistake. The FL of my mirror is not 1000mm, it's actually more like 1016mm (40" X 25.4mm = 1016mm), so the numbers I’ve been feeding you were based on an FL that’s over half an inch off. I rounded to 1000 in my head months ago when I first used NEWT and never caught it. Sorry about that!
While we're on the subject, I called Royce and he dug out the papers for my mirror. To quote Bob, "it tested at 40" right on the button". So plugging in 1016mm, here's yet another revised NEWT model:
I lowered the drawtube on my focuser all the way down and physically measured the height. It looks like a hair over 2.00” so I think 2.0125” is legit.
Sanity check….
Focal length = 1016mm = 40 inches
Spacing to axial diagonal face and focuser hole = 31.52 inches
Diagonal face to focus = 40-31.52 = 8.48 inches
Tube ID = 9.872, so ID radius = 4.936 inches
Wall thickness = 0.064 inches, so
Tube OD radius = 5.000 inches (same as before)
So the image plane is 8.48-5.00=3.48 inches above OD
Focuser minimum height = 2.0125 inches,
So image plane clearance above the focuser is
3.48 - 2.0125 = 1.4675 inches, or about 37.3 mm.
Phew! I ought to be banned from the ATM forum for running a thread about building an astrograph in which I missed the FL by 16mm. Maybe I should work for NASA….
So…crisis averted? Looks like my camera will reach focus with 0.24” of spare in-travel ahead of it. My NEWT model calls for 0.25”, close enough.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Bobby,
Hijack all you want. I'm learning too, and I was curious about the question you asked anyway.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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Mike I. Jones
Carpal Tunnel
Reged: 07/02/06
Posts: 1572
Loc: Fort Worth TX
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Just checking CN during lunch break. YEAH! That's more like it. 16mm makes a load of difference. And three cheers for validating using the sanity check calculations.
I'll look at the diagonal offset tonight once more. I think you've converged on a good design now, especially with the Royce report on your mirror EFL. It should work perfectly in the Sonotube mockup.
But this was also a great side trip opportunity for you to start into using OSLO. Several of us are here to help you learn to use it. You can do everything in OSLO you can do in NEWT, but go well beyond NEWT's limited capability, including vignetting calculations, spot diagrams, MTF curves, aberration ray fans, everything. It's limited to 10 surfaces, but almost any ATM project can be fit into that range. It just takes a few evenings to get the hang of it, once you learn the basics of optical system modeling (sign conventions, etc.).
Talk tonight,
Mike
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Bobby, here's my tube weight calculator (attachment). Later this year I hope to have a website up and running, and my goal is to turn this tool into a simple online applet for others to use. It's like a lot of other form-field tools out there....based on simple math that's doable with a calculator, but it sure is nice to have a program that spits it out quicker.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
Edited by imhotep (03/09/09 01:13 PM)
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Quote:
Just checking CN during lunch break. YEAH! That's more like it. 16mm makes a load of difference. And three cheers for validating using the sanity check calculations.
I'll look at the diagonal offset tonight once more. I think you've converged on a good design now, especially with the Royce report on your mirror EFL. It should work perfectly in the Sonotube mockup.
But this was also a great side trip opportunity for you to start into using OSLO. Several of us are here to help you learn to use it. You can do everything in OSLO you can do in NEWT, but go well beyond NEWT's limited capability, including vignetting calculations, spot diagrams, MTF curves, aberration ray fans, everything. It's limited to 10 surfaces, but almost any ATM project can be fit into that range. It just takes a few evenings to get the hang of it, once you learn the basics of optical system modeling (sign conventions, etc.).
Talk tonight,
Mike
Thanks Mike. I'm looking forward to learning OSLO and using it in the future. This won't be my last ATM project, and I'm mostly a reflector guy.
Speaking of which, you mentioned another program - CassDesign. I've never played with a Cassegrain modeler but it's only a matter of time I've been yearning for one of Royce's Cass sets for awhile now. Is CassDesign your own project? How is it obtained?
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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Mike I. Jones
Carpal Tunnel
Reged: 07/02/06
Posts: 1572
Loc: Fort Worth TX
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Good news, everything checks out in ZEMAX, including the decentration value. I am getting a little bit of vignetting at the extreme edges of the FOV from the diagonal, but only amounting to a few percent. Like Chris said, you need to flat-field your camera before taking astrophotos anyway, so that will compensate for this slight rolloff at the extreme field edges. I attached the modified OSLO file.
I wrote CassDesign almost 25 years ago (the original was in FORTRAN). It included a paraxial baffle tube optimization routine I developed that worked great for what we were doing. I converted CassDesign to Visual Basic 6.0 in the 90's, emailed it to a few ATM folks, they thought it was pretty helpful and had some good inputs, and I started making improvements. The latest version is one I'm still trying to find the time to finish, that of exact ray-based optimization of Cassegrain baffle tubes with no approximations. I did an article in Astronomy Technology Today last November on the algorithm I came up with, which runs wonderfully in a ZEMAX macro. I'm working to implement the ZEMAX macro in VB6. I dabble at it now and then, mostly on flights and rare weekends, and hope to get CassDesign2, or CD2, out and running this spring. So it should be up and running by the time you want to get into it. Besides, you've got an astrograph to build now
I'll post CD2 on the Yahoo Astronomy Technology Today website when I get it running so everyone can access and download it.
Mike
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Thank Mike. I'll see if I can at least get started understanding OSLO using this file.
I forgot ask one last question - the built-in offset in my spider is 0.130 which we've learned is off by 0.019. Is this a big deal?
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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Mike I. Jones
Carpal Tunnel
Reged: 07/02/06
Posts: 1572
Loc: Fort Worth TX
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Naah. Might change the vignetting at the extreme edges of the FOV a percent or three, that's all. And the spider vanes shouldn't be a tight fit to your tube ID anyway so it could be shifted back toward the focuser by just loosening and tightening the screws a little.
If you put a collimation target, sticky washer, etc. on the diagonal, be sure it's NOT at the center of the diagonal. Offset the collimation target toward the top of the diagonal nearest the focuser by 0.158", as shown in the diagram. That will help get your diagonal placed properly with respect to the focuser.
Mike
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fetoma
Pooh-Bah
Reged: 09/26/06
Posts: 1094
Loc: NW Ohio
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Curt,
What was your price for having the mirror cell cut on the waterjet machine?
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Frank in NW Ohio
Vixen CF VC200L and R200SS
Meade SN-10
Celestron 9.25" SCT
Meade 8" f/6.3 SCT
Intes-Micro M73
Stellarvue 80/480 LOMO Triplet
Takahashi FS-60C
Celestron CGE
QHY8 and SXV-H16
www.jerseydevilastronomy.com
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Quote:
Curt,
What was your price for having the mirror cell cut on the waterjet machine?
The metal shop charged me about $135 for the water-jet process. They were able to cut both pieces of the cell from one 12"x12" tile of 6061. The tile cost me $22 from a local metal supplier. The three pieces of L-channel (mounting brackets) were less than $1 each from the same supplier. The hardware is from McMaster-Carr and IMHO was way too expensive but it's really nice stuff so I cringed and paid for it.
I think the shop with the water-jet fleeced me, but I'm not exactly sure. Maybe someone else can comment on that. I know the machine uses a variable that is set by the shop owner to calculate cost per linear inch. That variable changes with thickness as well. It just seemed a little high to me, but again I bit the bullet.
My goal was to spend less on making mine than the cost of this mirror cell. In the end I only beat it by about $5.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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dawsonian2000
professor emeritus
Reged: 07/26/06
Posts: 563
Loc: Riverview, FL, USA
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Curt,
Congrats! Your 8" astrograph is coming along just great. I can't wait to see the end results of your hard work. I know how you feel when it comes to spending you hard earned cash. But, it is the thrill and passion of building something with your own two hands that is just priceless.
So don't worry about the milk you have already poured, because later on it will either turn into butter, or cheese. ...and that's not a bad thing at all my friend.
Mel
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Clear Skies, Forever!
The Vega Sky Center
10" (254mm) F/5.65 Home Built Fork Mounted Newtonian Reflector
5" (127mm) F/9.4 Home Built Refractor (under construction)
3.5" (90mm) F/11.1 "Vixen-Spec Modified" Konus Refractor
3.1" (80mm) F/6 Scopos ED APO Refractor
4.5" (114mm) F/8 Tasco 11te-5 Newtonian (under restoration)
2.4" (60mm) F/16.7 Tasco 7te-5 Refractor
2.4" (60mm) F/15 Jason Discoverer 313 Refractor
http://www.vega-sky-center.com
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Dennis Sakva
Pooh-Bah
Reged: 10/19/04
Posts: 1309
Loc: Kiev, Ukraine
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Great idea on water jet cutting! It forced me to look for one locally. They charge around $10/yard of cutting (3/8" aluminum) So unless you cut 13.5 yards... 
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Quote:
Great idea on water jet cutting! It forced me to look for one locally. They charge around $10/yard of cutting (3/8" aluminum) So unless you cut 13.5 yards...
I just tallied up the total length of all cuts in my mirror cell. It comes to 98.4855 inches, or 2.7357 yards.
Sounds like the shop you found is a pretty good deal compared to what I paid.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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dawsonian2000
professor emeritus
Reged: 07/26/06
Posts: 563
Loc: Riverview, FL, USA
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Hey Curt,
So what color are you planning on powder coating the OTA? You may have mentioned it earlier, but I did not read every post yet.
Oh BTW - I am hosting my progress on the 127mm f/9.4 on this CN thread: http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/2922528/page/0/view/collapsed/sb/5/o/all/fpart/all/vc/1
The thread was initial openned by Scubaguy, but several of us have used it to post our project notes. Check it out when time permits.
Keep up the awesome work you are doing. I hope to be see it at FOO on the 28th.
Mel
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Clear Skies, Forever!
The Vega Sky Center
10" (254mm) F/5.65 Home Built Fork Mounted Newtonian Reflector
5" (127mm) F/9.4 Home Built Refractor (under construction)
3.5" (90mm) F/11.1 "Vixen-Spec Modified" Konus Refractor
3.1" (80mm) F/6 Scopos ED APO Refractor
4.5" (114mm) F/8 Tasco 11te-5 Newtonian (under restoration)
2.4" (60mm) F/16.7 Tasco 7te-5 Refractor
2.4" (60mm) F/15 Jason Discoverer 313 Refractor
http://www.vega-sky-center.com
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Mel, I'm leaning towards a plain gloss black for both the astrograph and the guiescope. Which reminds me, I haven't run a thread about that project yet.
The powder coater I'm thinking of specializes in motorcylces, so I might ask about flames. Cost will probably kill that idea but it never hurts to ask.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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dawsonian2000
professor emeritus
Reged: 07/26/06
Posts: 563
Loc: Riverview, FL, USA
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Flames are cool, but how about celestial objects? If you are serious able applying flames, you may want to have them placed at the primary's end of the tube. Since you are going with a black base color, you don't want to have highly reflective, contrast robbing embellishments near or around your focuser. Any updates from the coaters yet?
Mel
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Clear Skies, Forever!
The Vega Sky Center
10" (254mm) F/5.65 Home Built Fork Mounted Newtonian Reflector
5" (127mm) F/9.4 Home Built Refractor (under construction)
3.5" (90mm) F/11.1 "Vixen-Spec Modified" Konus Refractor
3.1" (80mm) F/6 Scopos ED APO Refractor
4.5" (114mm) F/8 Tasco 11te-5 Newtonian (under restoration)
2.4" (60mm) F/16.7 Tasco 7te-5 Refractor
2.4" (60mm) F/15 Jason Discoverer 313 Refractor
http://www.vega-sky-center.com
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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I haven't heard squat from the coaters, but Royce did tell me to expect the mirror on or around March 18th. He sent it to them via express or rush delivery.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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Chris Curran
scholastic sledgehammer
Reged: 06/14/05
Posts: 827
Loc: Brandon, FL
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Quote:
The powder coater I'm thinking of specializes in motorcylces, so I might ask about flames. Cost will probably kill that idea but it never hurts to ask.
Well, I'm a sucker for a good flame job. Here's a '92 Meade 127 APO with a flame job:
http://www.planetcurran.com/img/allyScope-00.jpg
http://www.planetcurran.com/img/allyScope-20.jpg
The paint job was $650 (he painted cycles too!). Yea, I know - the paint is probably worth more than the scope. Long story... A "wrap" may be an option too.
I don't see how the paint job can affect anything at the focuser. A) Presumably the scope is being used at a location where there are no lights around to be reflecting, and B) with the camera firmly attached to the focuser nothing on the outside of the scope is going to adversely impact what's going on inside the scope and lastly, C) aren't all (commercial) scopes "shiny" up there around the focuser?
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cheers & beers,
Chris
Homepage | Over 40?
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Chris Curran
scholastic sledgehammer
Reged: 06/14/05
Posts: 827
Loc: Brandon, FL
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Quote:
I haven't heard squat from the coaters, but Royce did tell me to expect the mirror on or around March 18th. He sent it to them via express or rush delivery.
Is he still using Spectrum? They're in Deltona ya know. Not that far of a drive...
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cheers & beers,
Chris
Homepage | Over 40?
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Quote:
Is he still using Spectrum? They're in Deltona ya know. Not that far of a drive...
Nope, the coater he uses is located in California.
Based on the size of your Meade flame job I'm betting it would be more expensive for a 10"x43" tube. Probably a no-go for me, but man, am I jealous. I'll still get a quote on flames when I take it in.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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Owen
professor emeritus
Reged: 06/21/07
Posts: 514
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Having seen the photos, I'd spring for the flames. That is one gorgeous scope
Owen
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dawsonian2000
professor emeritus
Reged: 07/26/06
Posts: 563
Loc: Riverview, FL, USA
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Quote:
I don't see how the paint job can affect anything at the focuser. A) Presumably the scope is being used at a location where there are no lights around to be reflecting,
I should have clarified. Using the scope at a remote dark location, even if the tube is white, or chrome plated  would not matter. There is no extraneous light to contend with. But, using it visually in urban areas it could be an issue if the flame job is bright and reflective around the focuser. If the flame job is subtle, like the one on your awesome 127mm APO, flame on baby!
Actually it won't matter anyway since it will be used primarily for astrophotography.
Mel
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Clear Skies, Forever!
The Vega Sky Center
10" (254mm) F/5.65 Home Built Fork Mounted Newtonian Reflector
5" (127mm) F/9.4 Home Built Refractor (under construction)
3.5" (90mm) F/11.1 "Vixen-Spec Modified" Konus Refractor
3.1" (80mm) F/6 Scopos ED APO Refractor
4.5" (114mm) F/8 Tasco 11te-5 Newtonian (under restoration)
2.4" (60mm) F/16.7 Tasco 7te-5 Refractor
2.4" (60mm) F/15 Jason Discoverer 313 Refractor
http://www.vega-sky-center.com
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dawsonian2000
professor emeritus
Reged: 07/26/06
Posts: 563
Loc: Riverview, FL, USA
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I hope Spectrum are the coaters, as Chris pointed out. I have heard great things about them. They use quartz overcoatings instead of the silicon monoxide.
Mel
--------------------
Clear Skies, Forever!
The Vega Sky Center
10" (254mm) F/5.65 Home Built Fork Mounted Newtonian Reflector
5" (127mm) F/9.4 Home Built Refractor (under construction)
3.5" (90mm) F/11.1 "Vixen-Spec Modified" Konus Refractor
3.1" (80mm) F/6 Scopos ED APO Refractor
4.5" (114mm) F/8 Tasco 11te-5 Newtonian (under restoration)
2.4" (60mm) F/16.7 Tasco 7te-5 Refractor
2.4" (60mm) F/15 Jason Discoverer 313 Refractor
http://www.vega-sky-center.com
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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When I got home today there was a package waiting for me 
Barring any unexpected hiccups I should have the sonotube OTA finished tomorrow evening. If time allows I'll go ahead and have a pseudo-first light right away, or possibly the day after if weather permits. Failing that it'll be early next week sometime.
She's getting there!
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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Strgazr27
Vendor - Deep Space Mods and Composites
Reged: 10/04/04
Posts: 6984
Loc: StonyHill Observatory
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Curt,
Now that is BEAUTIFUL!! Congrats! I spoke to Bob today and he starts my mirror next week hopefully. She's going to be a killer scope when your done.
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Bobby
StonyHill Observatory
Skywatcher EQ6 Pro (On it's way)
AT 130 F/6 Prototype
Royce 10" f/4 Astrograph (Under Construction)
Self Modded 40D
70-200 F2.8 L IS
SSAG
YAHOO TMB 130SS Group
Astronomy Technologies Yahoo Group
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Mike I. Jones
Carpal Tunnel
Reged: 07/02/06
Posts: 1572
Loc: Fort Worth TX
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Nice mirror, great looking cell, Curt! Can't wait to hear about first light. We're gonna have to start calling you Preston!
Mike
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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I'm still fascinated by the conical design. The thin rim all the way around seems impossible somehow, yet these mirrors hold their figure just as well as flat blanks.
Well, it did what new optics always do and brought me some cloudy/rainy weather. Looks like pseudo-first light will be Sunday March 22 at the earliest.
In the meantime I'm struggling a bit with this Protostar spider and secondary holder. The shaft on the secondary holder has a VERY snug fit into the spider, so snug that it takes a lot of effort to rotate it. This is hard to describe, but imagine having to use so much force that when it finally budges it shoots past the point you needed. It basically clicks or pops from one orientation to the next. So far it hasn't been bad enough that I'm risking damage or anything like that, but it's bad enough that I had a lot of trouble trying to get it aligned to the focuser using my sighttube as a guide. Bryan Greer may have some insight for me on this. It may be that I need to sand or trim down the OD of that shaft just slightly to get the adjustability I need.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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Strgazr27
Vendor - Deep Space Mods and Composites
Reged: 10/04/04
Posts: 6984
Loc: StonyHill Observatory
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PICTURES !!
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Bobby
StonyHill Observatory
Skywatcher EQ6 Pro (On it's way)
AT 130 F/6 Prototype
Royce 10" f/4 Astrograph (Under Construction)
Self Modded 40D
70-200 F2.8 L IS
SSAG
YAHOO TMB 130SS Group
Astronomy Technologies Yahoo Group
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Chris Curran
scholastic sledgehammer
Reged: 06/14/05
Posts: 827
Loc: Brandon, FL
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Quote:
I'm still fascinated by the conical design.
Yea, everything about that conical design is brilliant. That single bolt in the back simply rocks...
Quote:
The shaft on the secondary holder has a VERY snug fit into the spider, so snug that it takes a lot of effort to rotate it.
That's odd. Stupid question: you did loosen the nut on that bolt before adjusting it, right? Assuming you did, it might be easier to bore out that hole a bit on your lathe...
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cheers & beers,
Chris
Homepage | Over 40?
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dawsonian2000
professor emeritus
Reged: 07/26/06
Posts: 563
Loc: Riverview, FL, USA
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Simply beautiful, Curt! You must be bouncing off of walls at this point. Will it be ready to showcase at the next observing session? Sorry I have not been on your thread of late. Been working odd hours with only limited time for pastimes.
Mel
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Clear Skies, Forever!
The Vega Sky Center
10" (254mm) F/5.65 Home Built Fork Mounted Newtonian Reflector
5" (127mm) F/9.4 Home Built Refractor (under construction)
3.5" (90mm) F/11.1 "Vixen-Spec Modified" Konus Refractor
3.1" (80mm) F/6 Scopos ED APO Refractor
4.5" (114mm) F/8 Tasco 11te-5 Newtonian (under restoration)
2.4" (60mm) F/16.7 Tasco 7te-5 Refractor
2.4" (60mm) F/15 Jason Discoverer 313 Refractor
http://www.vega-sky-center.com
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gatorengineer
scholastic sledgehammer
Reged: 02/28/05
Posts: 882
Loc: Hellertown, PA
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Beautiful scope, if you dont mind me asking what did the local metal shop charge for the cut outs?
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20" F5 Dob
16" Dob in pieces
Comet Catcher
MN71
12" Doc Clay Sky Patrol MEADE SCT
12.5" F4 Newt under construction
Siebert 45mm Binoviewers
Lots of binos---
Optics Past - 8" Stf Mak, 4" B&W triplet, 6"Schmidt newt, 12"LX200, C8, Meade LX10-10", 10" MEADE ACF, SN8, TAL150K, Orion 150MC, Jason 60mm refractor, ATM 6" F8, WO 110FLT, 92mm Off Axis Newt, Televue Genesis, Nikon 20x120 bino's, 15x110 Boarderguards, Kuhne Flaks
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Quote:
That's odd. Stupid question: you did loosen the nut on that bolt before adjusting it, right? Assuming you did, it might be easier to bore out that hole a bit on your lathe...
I have yet to even install the bolt. I 'think' what's going on is friction between two coats of black paint. The shaft and the inside of the hole in the spider are both painted black and it has a slightly tacky feel to it. Machining a few mils off the inside of the hole may indeed be necessary. I still need to call Bryan about this actually. Sanding might do it though if it's the paint that's doing it. The paint would get removed, but not a big deal since it'll be inside the hole.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Quote:
Beautiful scope, if you dont mind me asking what did the local metal shop charge for the cut outs?
Thanks, and I don't mind a bit. Scroll back a ways. It's been discussed.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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Luigi
Post Laureate
Reged: 07/03/07
Posts: 4940
Loc: MA
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Very nice work. IMO, for max rigidity and lightest weight, mounts for center-mounted mirrors should be construced with the main supporting members parallel to and passing through the optical axis of the the primary, much as you'd support a secondary, rather than plates perpendicular to the axis. Of course, with a secondary you try to minimize width of the the vanes but behind the primary it doesn't matter, and because they can be thicker, tension isn't needed to keep them straight.
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17.5" f/5 Dob. IM-715 MCT. 120ED. Lunt 60mm Ha.
Zeiss, Leica, Fujinon, Nikon, Pentax, Bushnell bins
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Yesterday I had one of those experiences where you knew it was a good story in the making. My goal was to test focus using the newly assembled sonotube OTA. I call this…
A PRACTICAL GUIDE: How NOT to test focus with a newly assembled astrograph OTA.
Step 1. Start with a pile of equipment that requires electrical power to get anything done.
Step 2. Drive to a location with no electrical power.
Step 3. Spend a solid hour fumbling around in the dark.
Step 4. Go home, get 4 hours of sleep, and go to work the next morning.
Last night I had a window of opportunity to get this done. After much consternation and deliberation I decided to strap the sonotube to my dovetail bar and test focus on Sirius. Other options were considered, but ultimately I wanted the ability to aim and track during this process. Going into this fiasco I had four devices requiring power:
- Atlas EQ-G
- QHY8 & power supply
- Laptop
- Motorized moonlight focuser
Kevin and I have access to a semi-dark site on a friend’s farm property. There’s always been electrical power inside a nearby shed. For the past two years we’ve been going there and plugging in with no issues. Last night I slapped everything into the sonotube and drove out to meet Kevin around 10:30pm. Skies looked beautiful. I setup and plugged in.
No power.
Flipped breaker. Still no power.
ARGGHHH!!!!!!!!!
I acknowledge that driving to the dark site was totally unnecessary. We were just trying to make an event of it, that’s all. We kept trying to think of ways to power stuff off our car batteries. Every idea came up short by one little missing part or adapter. The bottom line is that I came prepared to plug in and fate had other plans.
However, we succeeded in getting a fairly collimated visual image using various EP/Barlow combinations. I defocused on Sirius through a 26mm super plossl and 2x Barlow. Diffraction rings looked ‘good’ but not perfect. We also looked at Saturn with a UO 7mm ortho. Using some a make-shift project screen we basically measured where the image plane was relative to the top of the fully racked-in drawtube. Camera or not, it’s looking very good!
Lastly we took some photos of the most retarded-looking telescope in the world. How do ya’ll like these ratchet straps?
Everyone should be jealous of my voice-command GOTO system....
"Ok....Kevin, engage the clutchezzzz......NOW"
Hopefully I can test properly in my backyard very soon. Next step is to start popping holes in the hastings tube…..
Also, more to come on that issue with the secondary holder sticking. I talked to Bryan at Protostar and he recommended I ream out the hub gradually until it turns more freely. I did so using a sharp ½” bit in a corded drill. After four or five iterations I’m getting less sticking, but it’s still nowhere near the point of fine adjustability. I’ll work on it again for the final product, but for the sonotube testing I didn’t fuss over it any further.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
Edited by imhotep (03/25/09 03:45 PM)
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Chris Curran
scholastic sledgehammer
Reged: 06/14/05
Posts: 827
Loc: Brandon, FL
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LOL... Love it!
Psst: try putting a little lithium on that bolt before drilling out some more...
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cheers & beers,
Chris
Homepage | Over 40?
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Mike I. Jones
Carpal Tunnel
Reged: 07/02/06
Posts: 1572
Loc: Fort Worth TX
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Hey Curt!
How far above the racked-in focuser did the focal plane finally end up? Did it agree with the sanity-check calculations OK?
Mike
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Vincent Becker
super member
Reged: 09/16/08
Posts: 198
Loc: France
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Nice first light anyway!
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Vincent Becker
10" dobsonian on EQ platform (home-made by my father)
8" string newtonian as travelscope (home-made by myself )
Orion 80ED and GSO 200/1000 on Atlas EQ-G for astro-imaging
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Quote:
Hey Curt!
How far above the racked-in focuser did the focal plane finally end up? Did it agree with the sanity-check calculations OK?
Mike
It looked like about 1.25" - 1.5", so that's right where it should be, give or take a small bit.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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The results are in...
These captures were done without the Paracorr first.
Can you guys check me on the following observation? There's a 0.125"" discrepancy between where I was expecting the focuser travel to be and where it actually was when focus was achieved. My final NEWT model shows a camera height of 1.00" with 0.25" of extra in-travel built into the spacing. I was expecting the camera to reach focus with the drawtube racked out about 0.25" from minimum. Instead it was racked out about 0.125". Then I realized I didn't account for the height of the T/2" lip, so I need to measure it again and see if that's where the missing 0.125" got eaten up. But...that value of 1.00" for the camera height is actually a little too generous. The actual back-focus for the QHY8 is 21mm, or about 0.827", so the lip on the T/2" would have to be nearly 0.5" thick to account for all the missing space and I know for a fact it isn't.
I'm also wondering if being off by 1/8" is anything to be concerned about? I would be more worried if it were off in the opposite direction because that might suggest some vignetting at the secondary mirror, would it not? But in this direction it means there's 0.125" of extra space between the primary and focal plane. Is this a big deal? I'm guessing no.
Now on to the Paracorr...
I attached an older TV PLA to the QHY8 with 35mm of extension between the rear element and the camera's top T-threads. This adds to the 21mm gap from that point to the chip and gives me the 56mm of spacing that's suggested by TV for the PLA.
The big difference is that the PLA is a completely uniform 2" tube, and the extenders are uniform as well, so there's no lip or edge to rest flush against the top of the drawtube. So I inserted the PLA into the focuser and made the back edge flush with the top edge of the drawtube (i.e. the Paracorr is now completely inside the focuser). Then I attempted to reach focus and found it with about an inch racked out.
So....I think I'm good....??? The PLA reaches focus!
I'm officially in new territory. Please point out any problems I am missing.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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A couple things just hit me...
1. I'm using a much thicker tube right now than what is specified in my NEWT model.
2. The secondary isn't perfectly centered yet.
I haven't taken a tremendous amount of care in slapping the sonotube OTA together because I just wanted to test focus with it and nothing more. So I think 0.125" of gap could very easily get absorbed in the above two factors, plus there are probably others that all add together.
The thicker tube may actually be the kicker. It think this sonotube may be right at 0.125" thick
I'll look for the focuser travel to be closer to 0.25" with the final hastings tube build.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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Chris Curran
scholastic sledgehammer
Reged: 06/14/05
Posts: 827
Loc: Brandon, FL
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Curt,
Yes, the thicker tube is effecting your measurements.
1) Do I read the above correctly in that you reach focus with your focuser racked mostly in (~0.125" out now). Yes?
2) Where is the bottom of that PLA once you reach focus? Is it hanging over your primary?
--------------------
cheers & beers,
Chris
Homepage | Over 40?
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dawsonian2000
professor emeritus
Reged: 07/26/06
Posts: 563
Loc: Riverview, FL, USA
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Yes, differences in tube thickness between your Sonotube and Hastings aluminum tube will affect where your focal plane will fall. Especially if you are placing the optics in the same position from one tube to the other. Compensations or adjustments can be done by moving the primary, but not to the point that would cause vignetting, or spillage of light aroung the minor axis of the secondary.
In any case, I believe your thinking is leading you in the right direction. So continue to use the force, my friend. You have done a great job.
--------------------
Clear Skies, Forever!
The Vega Sky Center
10" (254mm) F/5.65 Home Built Fork Mounted Newtonian Reflector
5" (127mm) F/9.4 Home Built Refractor (under construction)
3.5" (90mm) F/11.1 "Vixen-Spec Modified" Konus Refractor
3.1" (80mm) F/6 Scopos ED APO Refractor
4.5" (114mm) F/8 Tasco 11te-5 Newtonian (under restoration)
2.4" (60mm) F/16.7 Tasco 7te-5 Refractor
2.4" (60mm) F/15 Jason Discoverer 313 Refractor
http://www.vega-sky-center.com
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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With all that's going on I forgot to check my thread for a few days.
Quote:
1) Do I read the above correctly in that you reach focus with your focuser racked mostly in (~0.125" out now). Yes?
Correct, but this is without the PLA, just camera mated to focuser with a T/2" adapter.
Quote:
2) Where is the bottom of that PLA once you reach focus? Is it hanging over your primary?
Yes it hangs over the primary by about 0.5" when focused as in #1 above. However, using the PLA changes that. This is hard to describe....the PLA is a continuous metal tube with no lip on either end of it to abut the drawtube's edge, so I can slide it as far into the focuser as I want. I'm not exactly sure at what point that will cause a problem with this scope, so to play it safe I've inserted it until the upper edge of the PLA tube is flush with the drawtube's edge. With it positioned like this, focus happens with the focuser racked out about an inch with no protrusion into the light path.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Sorry I haven't updated in awhile folks. Various woes with my mount have taken precedence. I find myself with a fully functional brand-new astrograph and a problematic Atlas to mount it on. More on that later.
The OTA is now assembled inside the hastings tube. I was holding off on posting some final photos until after powder-coating was done but recently I decided to forgo the powder-coating altogether in favor of a CF tube. My order with Bobby goes in today. The CF will make this monster much lighter and look better too.
I won't go on about the Atlas. Short version - all of the problems I'm aware of have been dealt with. The 'hypertuned' mount will be run with PEC and pulseguiding for my first serious imaging session with the astrograph. With any luck I hope to have some first-light images to share following new moon this month.
Stay tuned for photos of the scope as it looks right now.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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dawsonian2000
professor emeritus
Reged: 07/26/06
Posts: 563
Loc: Riverview, FL, USA
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Look forward to hearing good results, Curt. I hope the CF tube will aid in resolving the issues with your Atlas. Any plans to apply a finish to the new tube, or will you leave it as is?
Mel
--------------------
Clear Skies, Forever!
The Vega Sky Center
10" (254mm) F/5.65 Home Built Fork Mounted Newtonian Reflector
5" (127mm) F/9.4 Home Built Refractor (under construction)
3.5" (90mm) F/11.1 "Vixen-Spec Modified" Konus Refractor
3.1" (80mm) F/6 Scopos ED APO Refractor
4.5" (114mm) F/8 Tasco 11te-5 Newtonian (under restoration)
2.4" (60mm) F/16.7 Tasco 7te-5 Refractor
2.4" (60mm) F/15 Jason Discoverer 313 Refractor
http://www.vega-sky-center.com
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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I'll probably leave the CF as-is, unless there's a way to apply flames to the outside of cured CF...?
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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Strgazr27
Vendor - Deep Space Mods and Composites
Reged: 10/04/04
Posts: 6984
Loc: StonyHill Observatory
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Quote:
I'll probably leave the CF as-is, unless there's a way to apply flames to the outside of cured CF...?
Silly ATM'ers..........Flames belong on cars.........NOT scopes.
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Bobby
StonyHill Observatory
Skywatcher EQ6 Pro (On it's way)
AT 130 F/6 Prototype
Royce 10" f/4 Astrograph (Under Construction)
Self Modded 40D
70-200 F2.8 L IS
SSAG
YAHOO TMB 130SS Group
Astronomy Technologies Yahoo Group
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Strgazr27
Vendor - Deep Space Mods and Composites
Reged: 10/04/04
Posts: 6984
Loc: StonyHill Observatory
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Curt,
The outside can be painted same as any other object. Scuff the finish down, tack rag it, prime it, sand it etc......Paint will stick like glue to the resin topcoat.
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Bobby
StonyHill Observatory
Skywatcher EQ6 Pro (On it's way)
AT 130 F/6 Prototype
Royce 10" f/4 Astrograph (Under Construction)
Self Modded 40D
70-200 F2.8 L IS
SSAG
YAHOO TMB 130SS Group
Astronomy Technologies Yahoo Group
|
Jason Glass
sage
Reged: 06/27/05
Posts: 238
Loc: 36°33'9.19"N, 86°40'7.36"W
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Quote:
Silly ATM'ers..........Flames belong on cars.........NOT scopes.
? The flames on my 8" F/5 ain't too bad!
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Best wishes,
Jason Glass 
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Strgazr27
Vendor - Deep Space Mods and Composites
Reged: 10/04/04
Posts: 6984
Loc: StonyHill Observatory
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I was waiting for you to throw that pic up Jason 
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Bobby
StonyHill Observatory
Skywatcher EQ6 Pro (On it's way)
AT 130 F/6 Prototype
Royce 10" f/4 Astrograph (Under Construction)
Self Modded 40D
70-200 F2.8 L IS
SSAG
YAHOO TMB 130SS Group
Astronomy Technologies Yahoo Group
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Wow. That's quite a paint job.
I don't know Bobby, I've seen some pretty sweet looking flame jobs on telescopes. I'm not 100% set on it yet, but we'll see.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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Chris Curran
scholastic sledgehammer
Reged: 06/14/05
Posts: 827
Loc: Brandon, FL
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Quote:
Silly ATM'ers..........Flames belong on cars.........NOT scopes.
Cars? Flames? Isn't that getting just a bit over-done and boring?
--------------------
cheers & beers,
Chris
Homepage | Over 40?
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Jason Glass
sage
Reged: 06/27/05
Posts: 238
Loc: 36°33'9.19"N, 86°40'7.36"W
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Chris,
That is a killer flame job! It's truly one of the nicest I've seen, including the hot rod and custom chopper guys'.
Curt,
I went the "wrap" route. I cut the flames out of a giant sheet of adhesive backed, laser-etched aluminized Mylar film and wrapped the polished aluminum Hastings tube. It's a real pain to apply it without forming bubbles or wrinkles. The black part is an accessory semi-rigid HDPE dew/light shield and the flames are cut out of the trailing edge.
You can find lots of different colored fiber-weave adhesive backed films on Ebay, both genuine and simulated. A multicolor fiber on carbon fiber flame job would be new, interesting, and wicked-awesome!
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Best wishes,
Jason Glass
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Gene Hunter
sage
Reged: 12/29/07
Posts: 288
Loc: SC
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I think that if it excites the general public perhaps it might be a good thing, But I would spend the money on actual performance. If I spent a lot of time on a scope and it was a custom scope I would probably do something to make it look special so people at the star party knew it was hand made and not a factory made scope.
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Clear Skies
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Chris Curran
scholastic sledgehammer
Reged: 06/14/05
Posts: 827
Loc: Brandon, FL
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Quote:
I think that if it excites the general public perhaps it might be a good thing, But I would spend the money on actual performance. If I spent a lot of time on a scope and it was a custom scope I would probably do something to make it look special so people at the star party knew it was hand made and not a factory made scope.
Well, I did spend the money on performance - note the $8500 mount it's sitting on. It was a project that me and my (then) 11 year old daughter worked on. It was worth every penny. "Priceless" as they say in the commercials...
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cheers & beers,
Chris
Homepage | Over 40?
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Jason, I'm going to look into the wrap options. Application does sound tricky but I'm interested all the same. Can't be worse than applying adhesive-backed flocking to the inside of a tube, and I survived it a couple of times.
What I'm picturing is something subtle, preferably a dark red that matches the anodizing on my focuser and mirror-cell (whenever I get around to anodizing it). Semi-transparency would be awesome.
Sorry for not posting new photos yet. I took them last night and then didn't get around to posting them. I'll get them up here tonight.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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Gene Hunter
sage
Reged: 12/29/07
Posts: 288
Loc: SC
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I do understand, especially in light of your daughter working on it with you. Kids love flames. It is important to get people excited sometimes ( using Flames ) before they can truly appreciate the instrument, and then what they are looking at. I have found that my appreciation of an instrument goes hand in hand with the experience of what I am looking at. The finer the scope, the more time I take appreciating the view. Scopes themselves are just objects, but you have to take into account the human experience as well. people do immediately recognize the craftsmanship in a scope and they all want to look through that scope that looks well crafted.
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Clear Skies
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dawsonian2000
professor emeritus
Reged: 07/26/06
Posts: 563
Loc: Riverview, FL, USA
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As Bobby pointed out, if you prep the surface well (sand, tack, prime, etc.), paint will stick to it like glue. If you plan to paint it yourself, Krylon has spray paint (called Fusion) that adheres to plastic quite well. I used some to refinish the star diagonal housing of my 8x50 GSO right-angle finder and it worked great.
Mel
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Clear Skies, Forever!
The Vega Sky Center
10" (254mm) F/5.65 Home Built Fork Mounted Newtonian Reflector
5" (127mm) F/9.4 Home Built Refractor (under construction)
3.5" (90mm) F/11.1 "Vixen-Spec Modified" Konus Refractor
3.1" (80mm) F/6 Scopos ED APO Refractor
4.5" (114mm) F/8 Tasco 11te-5 Newtonian (under restoration)
2.4" (60mm) F/16.7 Tasco 7te-5 Refractor
2.4" (60mm) F/15 Jason Discoverer 313 Refractor
http://www.vega-sky-center.com
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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I am way overdue for posting some photos of recent progress. The past few weeks have seen little work on the OTA and much effort to work the kinks with my Atlas mount.
Awhile back I ran a thread asking for advice on drilling the focuser hole. My first thought was to use a 2-3/8" hole saw with my drill press. The replies to my thread ranged from "yeah that's the best way" to "NEVER use a hole saw on a curved tube surface". The latter opinion cautioned me against the teeth grabbing under the tube wall as they punched through. I briefly considered buying a diamond-sugared hole-saw but they are way too expensive for a one-use tool.
I've learned that in the ATM world, there are at least two ways (often times more) to do something and get good results. I decided to give the hole saw a try since I already own a 2-3/8". Unfortunately I don't have enough clearance under my drill press you fit the Hastings tube and the chucked hole-saw, so I opted to use a corded hand-drill instead.
Here's a video of how it went. This is only meant as proof-of-concept, and NOT as a how-to. I got so many warnings about using a hole-saw....and yet my experience was completely uneventful. I was so pleased with the results that I wanted to post this quick video for others who may have similar fears or reservations about it. I carefully scored both sides of the hole area on low speed before going for it. Try to overlook the rough start and one or two hops. The end result was just about perfect.
http://www.youtube.com/watch?v=YBslPcwJcjs
I used my homemade cradle to drill the focuser's mounting holes with my drill press:
Ready to receive the focuser:
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Here's a few shots of the fully assembled OTA mounted to the Atlas. Also pictured is the 80mm f/5 guidescope I built/machined to ride piggyback with the astrograph.
I've procrastinated like a champ on running a thread for the guidescope's build. It's probably not worth the attention actually. It features a custom-made lens cell for a Surplus Shed 80/400, and a GSO 2" crayford with custom-made tube adapter. The tube is also a Hastings (4").
  
 
Tonight I'm taking her out for a serious test run. I'll be autoguiding and running PEC via EQMOD. If all goes well with my mount I should be able to capture a short series using the QHY8 for appraisal. Right now the tube is temporarily flocked with black art paper
This is as far as I'm going to go with the Hastings tube. In hindsight I wish I'd just planned on buying one of Bobby's CF tubes from the start as it would've saved by about $80, but no biggie.
Well, she's almost a done deal!
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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Chris Curran
scholastic sledgehammer
Reged: 06/14/05
Posts: 827
Loc: Brandon, FL
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Quote:
I got so many warnings about using a hole-saw....and yet my experience was completely uneventful.
??? A hole saw cuts that aluminum tube like bwutta... I was actually surprised at how easy it was. How about you?
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cheers & beers,
Chris
Homepage | Over 40?
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Chris Curran
scholastic sledgehammer
Reged: 06/14/05
Posts: 827
Loc: Brandon, FL
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Quote:
Well, she's almost a done deal!
That looks GREAT!!!
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cheers & beers,
Chris
Homepage | Over 40?
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dawsonian2000
professor emeritus
Reged: 07/26/06
Posts: 563
Loc: Riverview, FL, USA
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Curt, she's a beaut! I still would like you to send it to the VSC Test Labs for final confirmation.
As for cutting the focuser hole using a standard hole saw, I would never thought you would have an issue. I have used them on many occasions to cut holes in car body panels. All it takes is a good quality saw blade. The center bit generally keeps the hole true to center. Like Chris said:
Quote:
??? A hole saw cuts that aluminum tube like bwutta...
Great job!
Mel
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Clear Skies, Forever!
The Vega Sky Center
10" (254mm) F/5.65 Home Built Fork Mounted Newtonian Reflector
5" (127mm) F/9.4 Home Built Refractor (under construction)
3.5" (90mm) F/11.1 "Vixen-Spec Modified" Konus Refractor
3.1" (80mm) F/6 Scopos ED APO Refractor
4.5" (114mm) F/8 Tasco 11te-5 Newtonian (under restoration)
2.4" (60mm) F/16.7 Tasco 7te-5 Refractor
2.4" (60mm) F/15 Jason Discoverer 313 Refractor
http://www.vega-sky-center.com
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Last night Chris was very generous to allow me to mount the OTA on his AP1200GTO and conduct an imaging session. I managed to leave the house with my DSLR but no CF card inside, so I had to snap a photo with my camera:
I haven't had time to process the data, but hopefully I can get to it sometime in the next couple of days. The ST-8XE amazed me. I watched as Chris fired up the focusing window with the camera set for 1-second exposures binned 3x3. Clear spiral structure in M51 was visible with a ONE SECOND exposure. This is probably old news for some, but to me it was pretty amazing. That guider chip is wicked sensitive too. Again Chris, thanks for the test-drive and demo.
I came away from this experience with a huge morale boost to say the least. My mind is made up on a few things that were bugging me:
1. I'm going to follow through with my Mach1GTO purchase. Circa June/July of this year I should have it.
2. As soon as funds allow I'm going to make the transition away from OSC and simultaneously away from a separate guidescope/camera configuration. I think it'll be an ST-2000XM for me.
Fortunately this astrograph was designed for the large chip in a QHY8. I should have less vignetting and coma at the edges of the ST-2000XM's chip.
Progress is good
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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dawsonian2000
professor emeritus
Reged: 07/26/06
Posts: 563
Loc: Riverview, FL, USA
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Curt,
I am happy that the use of Chris' AP1200GTO solidified your decision on getting the APMACH1GTO. I knew it would. Please get to work on generating those images so I can put my drool cup to use.
Man! I can't wait to see the paint job you are going to put on the bad boy! See you later today!
Mel
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Clear Skies, Forever!
The Vega Sky Center
10" (254mm) F/5.65 Home Built Fork Mounted Newtonian Reflector
5" (127mm) F/9.4 Home Built Refractor (under construction)
3.5" (90mm) F/11.1 "Vixen-Spec Modified" Konus Refractor
3.1" (80mm) F/6 Scopos ED APO Refractor
4.5" (114mm) F/8 Tasco 11te-5 Newtonian (under restoration)
2.4" (60mm) F/16.7 Tasco 7te-5 Refractor
2.4" (60mm) F/15 Jason Discoverer 313 Refractor
http://www.vega-sky-center.com
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astrokwang2
super member
Reged: 05/06/04
Posts: 160
Loc: Florida
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Love it! Great work, Curt! 
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18" Obsession
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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I have finally made good on my threats to use this astograph. Over the weekend I took it to CAV in northern Florida. The night started out a bit rocky with some EQASCOM crashes, but eventually I got a fresh batch of PE recorded and got PEC + Pulseguiding running. Collimation was poor at best, but I'm not quite setup for a super accurate collimation yet. More on that later.
Here are there images from my all-nighter at CAV:
I'll get the stinker out of the way first. This is 12x300 of M8:
http://picasaweb.google.com/curt.walker/Astrophotography#5329093309355914274
I'm not sure why my guiding fell apart on this series. All night long I'd been second guessing myself on the RA and DEC aggressiveness in the pulseguiding panel of EQASCOM. None of the subs from this two-hour effort had anything resembling good tracking, but I picked about half and went with it. I was sleeping for most of this series :-/
Here's 3x300 of M51:
http://picasaweb.google.com/curt.walker/Astrophotography#5329093323274970962
Lastly, here's 13x120 of Omega Centauri:
http://picasaweb.google.com/curt.walker/Astrophotography#5329093336967499394
Overall I'm pleased. Considering the tube isn't properly flocked, collimation was off, and the backend is still wide open to stray light, I think the results are promising.
For collimation I'm using a Glatter laser with several attachments. FWIW I have not been impressed with the holographic grid attachment. The concept behind this thing is to align the secondary to an unspotted primary via the grid that reflects off it's surface. I did my best to align the secondary such that the pattern was symmetrical across the primary's face, but in all honesty it is still what I call eyeballing something. My next step is to spot the primary and align the traditional way from that point forward.
Other than that I LOVE the Glatter laser, especially the barlowed BLUG attachment for aligning the primary with a closed-tube OTA. Works like a champ.
Next steps:
- Spotting the primary
- Paint job for the Hasting tube or CF tube from Bobby.
- Installing the flocked insulating tube liner
- Anodizing the mirror cell
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
Edited by imhotep (04/27/09 08:51 AM)
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Mike I. Jones
Carpal Tunnel
Reged: 07/02/06
Posts: 1572
Loc: Fort Worth TX
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Curt, those are GREAT beginning shots! I was expecting M8 to be a blurred mess from your description, but it actually looks pretty good. The tracking error is visible and can be improved on, but the nebulosity is well captured with plenty of detail for IP'ing. Omega is SWEET. How are you focusing? Looks pretty close.
Like I wrote and plotted several posts back, be sure you offset the collimation spot on the diagonal where I showed so you don't vignette the lower part of the field. Yes it can be flatted out but you shouldn't lose the light when it's easy to fix with the right amount of offset.
Well done!
Mike
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Thanks Mike. Here are some answer and a couple more questions for you...
I used a Bahtinov mask to focus, so it was dead-on at the beginning of each series. I refocused between each series and did notice some shift each time. Very soon I plan on switching to either MaximDL or CCDSoft for my catpure/autoguiding software so I can take advantage of automatic focusing with FWHM. My understanding is that there's also a way to have it automatically refocus whenever it detects a certain amount of temperature shift (in other words, if in the middle of a capture the temperature changes by a set amount it will pause after that capture to refocus and then continue with the next sub), or you can set it to refocus between every single shot as was recommended to me by the Moonlight staff (I think I'll pass on this one though). A third option would be to program a profile that moves the stepper motor progressively as temperature changes. I'm not sure I like this third option because I've noticed a fair amount of vibration coming from the Moonlight stepper motor and I'm concerned it would mess up my images if it moved in the middle of a capture. So to sum up, my first choice would be to setup MaximDL or CCDSoft so it will simply run a new focusing routine between subs whenever the temperature changes 1 degree F.
About collimation, I'm in desperate need of some guidance on rotating and aligning the seconday. I am confused on a couple of points:
1. This is hard for me to explain.....Sight tubes are recommended for rotating the secondary such that it is square to the focuser and also for moving it up and down the right amount as well. I can see this getting it pretty close, but you are still having to eyeball the edges of the secondary as you rotate it to a position that "looks" square. This really bugs me. I'd rather not let it go at what "looks" square because it'll be off by a small amount, and with range of acceptible focus being so small on an f/5 scope, if I'm off by a fraction of a millimeter it'll produce uneven focus across my image. I'm pretty sure this is already an issue because I've got some strange stuff going on in those three I posted. Focus and/or collimation is different in the top half of those images than it is in the bottom half. So to me this method of using a sight tube doesn't seem accurate enough because you're still having to eyeball it a bit. I am sure to be off by at least a fraction of a millimeter when I use a sight tube. Does this make sense? Maybe I'm doing something wrong. Ideally shouldn't there be a way to measure the distance from the edges of the drawtube to the edges of the secondary and rotate until they are equal?
2. About spotting the secondary, is this intended to make rotating the secondary into position a bit more accurate? It means losing a bit of light doesn't it?
Sorry for blasting you with questions Mike. Thanks again for all your help.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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Chris Curran
scholastic sledgehammer
Reged: 06/14/05
Posts: 827
Loc: Brandon, FL
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... What Curt didn't tell you:
I hadn't had the 1200 out in about a year, and, I was using a new power supply I put together at the last minute with bailing wire and duck tape (an old PC power supply rigged up in a battery box). We fire up the mount and the hand controller refused to go past the first display - it kept "rebooting". Great. Here I've been singing the praises to Curt of how AP gear is "rock solid" and "just works" and mine isn't working. Hmm. OK. The battery in the HC is about 5 years old, so I assume that's the problem. You don't "need" a hand controller to run an AP mount, so we unplug the hand controller and initialize the mount via the laptop. Curt, like myself, has no finder on his scope. We spend the next ten minutes gun-sighting Sirius - without a hand controller to move the mount - all by hand. Whew!
Things are starting to look better. We're hooking up all the right wires to the right places. I get the right adapter on the camera for Curt's scope - complete with MPCC. We then try to focus - no go. Curt then remembers that he forgot his Paracorr. We take the MPCC and all spacers out of the image train. Still can't quite get to focus - we're close, but oh so far. Curt then has the brilliant idea of moving the mirror forward by using the collimation bolts. I doubt it'll work, but why not? Well, it WORKED! Yea, collimation was "out" once we got focus, but it wasn't horrible. I've seen new (consumer) scopes with worse collimation...
I was trying to demonstrate three things to Curt:
1) Self guiding camera operation. Curt had some reservations about being able to find a guide star in self guiding cameras (SBIG). I think we addressed those concerns.
2) The difference between NABG and ABG cameras. His is color ABG, mine is mono NABG. Yea, big difference in sensitivity. However, I did mention to Curt numerous times that trying to shoot M42 or M45 with a NABG camera is murder... but I'll eat the lunch of that ABG color camera on something like the Helix.
3) Guiding accuracy of AP mounts. Curt was impressed, but we didn't perform up to snuff here. We had three problems:
a) I forgot to re-balance the scope/mount after adding the camera to the mix. Worse yet - the imbalance was on the "wrong" side of the mount. I had to slide the 18lb'er out about another 14-16 inches before it reached balance, which of course I didn't remember/do until after the testing!
b) The balance issue above wouldn't normally be a problem, except I was running the mount on a weak power supply. However, I didn't learn this until the next morning. Remember the hand controller issues above? Well, a quick call to AP tech support (Fri morning) and the first thing out of Christine's mouth was "power supply". She assured me it wasn't the battery in the HC - it was probably a bad PS or a corroded connection. I pulled out my mutimeter and checked my bailing wire PS rig - 11.4 volts! Holy *BLEEP* Batman. Once I replaced that PS the hand controller worked flawlessly. And that got me to thinking... with the mount so far out of balance, and the volts so low, I wouldn't be surprised to find out that I was choking those servos during a move... resulting in tracking jitter. I replaced the PS and did some imaging of my own the next day. The tracking swing of +/-1 pixel we saw with Curt's scope went back to near zero. Sure, +/- 1 pixel *is* good - but not when you know it should be near zero.
c) Too short of an exposure for the tracking star. I had it set for 5 seconds - and that was working fine, until we hit the blue filter. Maxim had to search for that guide star a few times...
All things considered, the evening went well. We almost got shut down a few times, but overcame the issue at hand. It was a cool evening though - almost "cold" for us Florida boys. I was OK as my 65lb lap dog (Lucy) kept me warm. Curt found a new heater he just has to have too: http://mednet-store.stores.yahoo.net/presheatdise.html (I got mine @ Costco for $49 two years ago). Remove the "footlight" bulb and you're ready to go.
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cheers & beers,
Chris
Homepage | Over 40?
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Chris, I went to Costco on my way out of town to CAV and they gave me a snicker about shopping for heaters at the start of summer. It won't be in stock again until next fall/winter which makes sense. Even in late April I still get chilly at 2am.
Your comments about the +/- 1 pixel of guide corrections being poor performance for an AP mount is what I wanted to hear Can't wait to join the club.
Now I just need to learn how to colimate. Right now a blind midget missing three fingers on each hand could do a better job than me.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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After several months of no activity on this project I have finally put on the finishing touches. The plan all along was to anodize the mirror cell red. Sometimes my camera and subsequently RAW settings do weird things with red, but this actually came out extremely close to the Moonlight focuser's shade of red. Here are some shots of the result:
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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APM America
Vendor - APM America
Reged: 11/07/05
Posts: 2775
Loc: Madison. NJ. USA
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Sweet!
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Morris Bagnall
Sales Manager
www.apmamerica.com
A whole room full of APM refractors......
Seymor Rosin F/4.5 Astrograph in the making
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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