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Equipment Discussions >> ATM, Optics and DIY Forum

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Chuck Hards
Post Laureate
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Reged: 05/03/10

Loc: The Great Basin
Re: Jaeger 114mm f/4.5 ATM frefractor help please [Re: bvillebob]
      #6600793 - 06/25/14 08:10 AM

Quote:



Regarding the sketch, the fully illuminated area is 18mm, it's just a preliminary proof of concept sketch, it still needs to be optimized.




Thanks for clarifying that.


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dan_h
Carpal Tunnel


Reged: 12/10/07

Re: Jaeger 114mm f/4.5 ATM frefractor help please new [Re: Chuck Hards]
      #6600848 - 06/25/14 09:07 AM Attachment (20 downloads)

Here's a layout I have used for an RFT refractor to maximize illuminated FOV using a small mirror and an inexpensive low profile focuser.

dan


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Chuck Hards
Post Laureate
*****

Reged: 05/03/10

Loc: The Great Basin
Re: Jaeger 114mm f/4.5 ATM frefractor help please new [Re: dan_h]
      #6600855 - 06/25/14 09:14 AM

I like that, dan. A lot. Effective yet inexpensive.

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woodscavenger
sage


Reged: 08/20/13

Loc: Boise, ID
Re: Jaeger 114mm f/4.5 ATM frefractor help please new [Re: Chuck Hards]
      #6600897 - 06/25/14 09:56 AM

So last night I stuffed the lens cell in place, bolted on my cheap focuser and jumped out the the partly cloudy skies. Pinpointed Acturus and took a peek. Nice orange color. As I rolled in and out of focus the star would flatten then going the other direction would rotate 90 degrees and flatten again. Am I dealing with colimation issues or pinched optics? When I put the lens in this time I used a few more layers of tape and it was a bit tighter fit.

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Chuck Hards
Post Laureate
*****

Reged: 05/03/10

Loc: The Great Basin
Re: Jaeger 114mm f/4.5 ATM frefractor help please new [Re: woodscavenger]
      #6601013 - 06/25/14 10:55 AM

Pinched optics sounds very likely.

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figurate
super member


Reged: 02/09/13

Loc: Metro North Texas
Re: Jaeger 114mm f/4.5 ATM frefractor help please new [Re: Chuck Hards]
      #6601734 - 06/25/14 06:38 PM Attachment (25 downloads)

This is a simple autocollimator made from a spice bottle lid; on the underside is an accurately centered boss (artifact of the molding process) that makes it easy to locate a hole dead center. I used an awl to make an indentation and then drilled the hole. (Since that hole is precisely centered, a hole at any other location will constitute a radius). The nose of the mini-maglight bulb is small enough to fit partway into the hole, and to use I simply unscrew the flashlight lens and position the light in one hole and view the reflections through the other. I'm not sure if this model of flashlight is still available, but I have been using this system for many years on all my refractors for rough collimation and it has saved a lot of time. I have another collimator that is 1 1/4" and made from scratch, but this 2" diameter lid (shimmed with one layer of tape) makes it super easy.

This can give a quick answer to your question, "collimation or pinched optics?". Line up the reflections, using five or so different orientations of the autocollimator in the focuser, and take it outside to check the diffraction pattern. Any astigmatism then will indicate pinching. I have a 80mm triplet, that turned out to be out of collimation, that showed pretty noticeable astigmatism. But that's another story!

Fred


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zeehas
member


Reged: 08/06/11

Loc: Tucson, AZ
Re: Jaeger 114mm f/4.5 ATM frefractor help please new [Re: figurate]
      #6603012 - 06/26/14 02:50 PM

Here's another idea for a low cost tube assembly. For mine I used 4" black ABS plumbing pipe. The objective sits nicely against the end of the pipe held on by an ABS coupler and a large metal ring. The focuser end consists of an ABS end cap with a hole drilled in it. A 2" Newtonian focuser is attached to the end cap. The inside of the tube is simply flocked for glare reduction. Very simple, cheap, and robust. I can post a photo if anyone wants to see it.

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Chuck Hards
Post Laureate
*****

Reged: 05/03/10

Loc: The Great Basin
Re: Jaeger 114mm f/4.5 ATM frefractor help please new [Re: zeehas]
      #6603102 - 06/26/14 03:34 PM

Interesting idea.

Whats the ID of the ABS pipe? How much aperture do you lose to wall thickness?

Normally I don't like to use plastic pipe due to warpage over time, but one this short is probably going to remain stable for much longer.


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zeehas
member


Reged: 08/06/11

Loc: Tucson, AZ
Re: Jaeger 114mm f/4.5 ATM frefractor help please new [Re: Chuck Hards]
      #6603155 - 06/26/14 04:05 PM Attachment (15 downloads)

For ABS pipe the ID is 4", OD is 4.5". So it winds up being stopped down to 4". The lip on the coupler isn't quite large enough to secure the lens, so I had to make a metal ring to hold it. ID on the ring is about 4.25".

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figurate
super member


Reged: 02/09/13

Loc: Metro North Texas
Re: Jaeger 114mm f/4.5 ATM frefractor help please new [Re: zeehas]
      #6603486 - 06/26/14 07:07 PM Attachment (14 downloads)

I built several PVC refractors at one time or another and never saw any warpage. What is clear from my experience is that without a lot of bracing, it is structurally flimsy, especially in the larger diameters. This is a 120mm f8 OTA I made about 15 yrs ago using a secondhand early chinese doublet (not very good, as it turned out). The tube is 6" diameter and 32" in length, and is stiffened by the focuser plug. the rings in the center. and an internal ring that mounts the collimatible cell (which is birch ply) in front.

This has been under a sheet for 10 years and I am surprised by how lightweight it is in comparison to my D&G. I might look for another optic and put it back in operation.

Fred


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zeehas
member


Reged: 08/06/11

Loc: Tucson, AZ
Re: Jaeger 114mm f/4.5 ATM frefractor help please new [Re: figurate]
      #6603507 - 06/26/14 07:15 PM

Nice looking scope Fred.

I choose ABS over PVC because the ABS pipe is thicker and more rigid. It's possibly heavier too, but that didn't make much difference with a short 4" scope.


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figurate
super member


Reged: 02/09/13

Loc: Metro North Texas
Re: Jaeger 114mm f/4.5 ATM frefractor help please new [Re: zeehas]
      #6603628 - 06/26/14 08:27 PM

Thanks. I have a 4" (110mm) f/10 Jaegers set and I may try your system for the front end. A 40" long ABS tube, I assume, would be pushing it.

The wall thickness on that PVC tube of mine is only 1/8", so it is unusually flexible compared to other sizes, and more like a load-bearing shroud than anything else. I did, at the time, give some thought to using longitudinal struts inside.

Fred


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Chuck Hards
Post Laureate
*****

Reged: 05/03/10

Loc: The Great Basin
Re: Jaeger 114mm f/4.5 ATM frefractor help please new [Re: figurate]
      #6603788 - 06/26/14 10:29 PM

That is a fine looking scope. I may have to tackle PVC or ABS on a larger scope once again.

I once made an 80mm refractor using PVC as the main tube. It turned into a banana after about 3 years. Since then I've avoided it on larger OTAs but still use plastic for smaller scopes. There may be an "aspect ratio" where long tubes are prone to warp but shorter scopes with larger diameters are more resistant.

Both of the small scopes below are all plastic, with flocked tube interiors.

Here is a 50mm f/9. ABS tube, PVC cell made from fittings turned on the mini-lathe. Slide-on dewcap made from a coupler. Commercial R&P that I attached to a lathe-turned rear flange. The tube rings are PVC, routed from 5/8" sheet. Lathe-turned aluminum clamp knobs. I use this one for white-light solar observing, tandem mounted with my PST.


Another view, home made eyepiece. 2-part automotive paint finish.


Cell detail.


Slide-on solar filter, made from grey (electrical) PVC fittings turned on the mini lathe. Baader film.


Focuser detail. It's an Orion plastic Newtonian focuser, with the tube mounting base cut-off and turned round in the lathe, then glued into the sheet PVC end piece with industrial high-temp adhesive, bodyworked, painted & textured. Home made 23mm WA eyepiece, aluminum barrel turned on a Sherline mini lathe.


Slip-on dust cover. PVC & acrylic.


55mm finder. Again, an ABS tube, with PVC cell and 1.25" eyepiece holder.


Dust cover removed, showing the slide-on dewcap.


55mm cell detail, dewcap removed.


Dust cap. Grey electrical PVC with ABS face piece. All dewcaps and dust covers are felt-lined and slip-on.


Tail piece/eyepiece holder detail, lathe-turned sheet PVC. Commercial star diagonal.


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zeehas
member


Reged: 08/06/11

Loc: Tucson, AZ
Re: Jaeger 114mm f/4.5 ATM frefractor help please new [Re: Chuck Hards]
      #6603796 - 06/26/14 10:37 PM

That's very professional looking work Chuck.

I just took a closer look at the ABS I used and compared it to some PVC I had laying around. I think the ABS is actually less dense than PVC and hence lighter.


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Chuck Hards
Post Laureate
*****

Reged: 05/03/10

Loc: The Great Basin
Re: Jaeger 114mm f/4.5 ATM frefractor help please new [Re: Chuck Hards]
      #6603814 - 06/26/14 10:48 PM

I built ten of these for some of our club members for the annular eclipse and Venus transit two years ago. I call it the "SunSpotter". 50mm objective, PVC tube and countercell, commercial 1.25" focuser. Automotive finish. Home made aluminum tripod mounting block.
There is a piece of Baader film in contact with the front objective element, held in place with the lens retaining ring. The countercell is a PVC coupler that captures the plastic, commercial objective cell.











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Chuck Hards
Post Laureate
*****

Reged: 05/03/10

Loc: The Great Basin
Re: Jaeger 114mm f/4.5 ATM frefractor help please new [Re: zeehas]
      #6603817 - 06/26/14 10:51 PM

Quote:

That's very professional looking work Chuck.

I just took a closer look at the ABS I used and compared it to some PVC I had laying around. I think the ABS is actually less dense than PVC and hence lighter.




Thank you!

I've been doing this a long time, and having spent a career in manufacturing has exposed me to a lot of materials and techniques.
Regarding ABS tubing, I think you're right. I want to examine a cut section under a microscope. It almost seems like it has a "foamed" interior, or cellular in some fashion. Maybe that's what contributes to it's relative lightness.


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figurate
super member


Reged: 02/09/13

Loc: Metro North Texas
Re: Jaeger 114mm f/4.5 ATM frefractor help please new [Re: Chuck Hards]
      #6604973 - 06/27/14 06:42 PM Attachment (10 downloads)

You're getting pretty good with that Sherline lathe, Chuck. Amazing work, and I share your interest in home-built finderscopes but with a slightly different approach (I can't touch your level of craftsmanship). When I started using telescopes seriously in the 1980s, I developed a dislike for everything associated with finders: clunky mounting rings, mediocre optics, a general lack of imagination overall. Since then I use my own stuff exclusively. My finders rival or exceed the optical performance of my scopes, and all use various kinematic mounting schemes.

I call this composition "Still life with two finderscopes". The shorter one on the right is a detachable model, originally built for the telescope pictured above, and features angled aluminum bases that interface with two fixtures on the tube, held in by a swing-arm on one side and a knurled nut on the other. The aluminum brackets are pinned to the PVC cradle which was slotted to allow this. (one of my better ideas, but I never really used the scope) The 40mm optics are from an autocollimator made by Wild, a swiss company, and are beautiful.

The long-tubed finder is my current favorite, used on my 5" D&G, and has a Zeiss 50mm E-type objective. This one, if anything, out-performs the main scope. I use an old Jaegers 35mm symmetrical eyepiece with it (17 or 18 power). The collet focuser was scavenged from the finder on the right. The cradle system uses unorthodox adjusters (!!!) and is another example of trying to do things differently; tweaking alignment takes seconds instead of minutes. The tube was made from an old aluminum fishing pole case.

I think your warped tube may have come from a bad batch, Chuck. Wiki articles indicate both ABS and PVC are fairly stable materials. They fine-tune the properties of the mixture with additives, and as you know, any manufacturing process can get fouled up on occasion. The article says clarinets are being made out of PVC and bass flutes out of ABS. I think both can be affected by UV exposure eventually, like other plastics.

Fred


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Chuck Hards
Post Laureate
*****

Reged: 05/03/10

Loc: The Great Basin
Re: Jaeger 114mm f/4.5 ATM frefractor help please new [Re: figurate]
      #6605389 - 06/28/14 12:46 AM

Those are two really nice finders! I have a home-made 50mm f/20 with aluminum tube and 1.25" R&P that I use as a primary instrument not infrequently.

My old Sherline died after 20 years and 3 motors, I gave it to a friend with a similar model, for parts. I now use a Harbor Freight mini-lathe, and miss the Sherline terribly. Much smaller capacity, but the Sherline is a better-made lathe. I may get another one of these days.

Thanks for the kind words!


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figurate
super member


Reged: 02/09/13

Loc: Metro North Texas
Re: Jaeger 114mm f/4.5 ATM frefractor help please new [Re: Chuck Hards]
      #6606539 - 06/28/14 09:02 PM

Funny, I probably have the same model Harbor Freight lathe. Looks like it was designed by a committee, but has huge speed variations; comes in very handy every so often for these little refractors. And those long-focus small achromats are something special. A 2" f/20 would have to have perfect color correction.

Fred


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Chuck Hards
Post Laureate
*****

Reged: 05/03/10

Loc: The Great Basin
Re: Jaeger 114mm f/4.5 ATM frefractor help please new [Re: figurate]
      #6606796 - 06/29/14 01:49 AM

Quote:

Funny, I probably have the same model Harbor Freight lathe. Looks like it was designed by a committee, but has huge speed variations; comes in very handy every so often for these little refractors. And those long-focus small achromats are something special. A 2" f/20 would have to have perfect color correction.

Fred




I'm actually on my 2nd HF mini lathe. The first was returned after only a few days due to a burned-out relay. The handle on the toolpost broke on the second, and I replaced with a 1/4-20 carriage bolt. So far the lathe and I are getting along otherwise...I've been experimenting with the threading gears, something the Sherline didn't have.

The 2" f/20 is a remarkable lens! It's cemented, and of unknown provenance. I've had it about ten years and can't for the life of me recall where I bought it. It has a nice, purple AR coating. The full moon shows no color fringes, it is well-corrected. When I was building it, I first looked at PVC pipe, but every piece I looked at was bent slightly, over a 1-meter-long length, so I decided on 2" aluminum. I turned-down the base on a 1.25" refractor focuser to slip-fit into the tube, secured with 3 stainless-steel allen screws. The focuser was purchased from Meridian, who are no longer in businness, and I haven't found another source. Aftermarket knobs from Orion.

Here's a shot of the OTA, alongside (coincidentally), my Jaegers 110mm f/4.5 build, in progress in the pic, from last year. PVC cell and dewcap on the 50mm (aluminum on the Jaegers). I've since painted the dewcap black on the 50mm. You can just see the HF lathe at the extreme left of this photo.


And I also found this shot of the of the "SunSpotter" 50mm PVC scopes under construction. I made at least ten of them, IIRC, maybe twelve, for club members to view the Venus transit and annular eclipse.



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