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Binoviewer or Binoculars

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#1 CapnRon

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Posted 22 June 2020 - 10:30 AM

I enjoy night sky viewing and I have been into Astrophotography for some time, with modest success.  It is being out under the stars and being able to "see" more that I like the most.  I have been contemplating adding either binoviewers or an all sky binocular viewing setup for some time.  The decision as to which way to go is just too difficult, so I think I will do both!  

 

The easiest approach to start with is the binoviewer.  I have two Celestron SCT's; a 9.25" on a CGEM mount and a 5" on a table top mount (the table top mount has battery driven RA motion, but is manual otherwise).  The smaller scope is great for quickly taking outside and setting up on a table for parties or just quick viewing, while the larger scope on the CGEM has goto and tracking capability.  I have a Baader click-lock adapter that threads directly to the back of each scope and is 2" on the clamping side.  I think I will start with a WO binoviewer and grow from there.  I have read thru several threads here and I believe with the proper prism assembly (that I can thread the WO binoviewer directly two) it will allow me to reach focus on both scopes.  But I also remember reading somewhere that some newer binoclular viewers do not allow you to unscrew the front extension tube.  Can anyone here enlighten/remind me what I will need to enable binoviewing with both of these scopes?

 

And while I am at it we might also discuss the pros's and con's of bino vs binocular setups.  I have also read some remarks that say the parallelogram setups for binoculars can be finicky, while the bino/telescope approach does limit  you to sitting at a table to be able to rest/lean forward to view.  I am in my mid 70's so comfort and ease of setup are becoming more important.

 

thanks,

Ron

 

 

 


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#2 eyeoftexas

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Posted 22 June 2020 - 10:44 AM

One thing to consider is what you want to observe with the binos.  If you want to see what the C5 shows in terms of field of view and magnification, then adding binoviewers makes sense.  If you want to see a much wider field of view, then binoculars is the choice.  I have a pair of 8x42's for wide field (~8°) and 20x80's for narrower view (~3°).  For closer, narrower views I use my AT115EDT or 12" Dob.  The 20x80's are mounted on a parallelogram, but the smaller ones fit on a monopod.  You could also put the larger binoculars on a monopod for very quick grab-n-go use, just make sure it is rated to hold them.

 

Clear Skies!


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#3 CapnRon

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Posted 22 June 2020 - 11:00 AM

Thanks, yes FOV is important.  My hesitance in just pulling the trigger on Binoviewers is exactly because I am not sure how much they will improve the viewing in the C-5.   I have CCDCalc to show example FOV's for telescope/Camera combinations, but I don't know of a similar program for binocular views; is there one?

 

I believe the Binoviewers on the C-5 would be great for SolarSystem viewing, star clusters, doubles and maybe Comets (if you can find them).  But I have no expectations on DSO's, even with the C-9.25 as most people (I read here) seem to use them with larger scope (at least 11").  While I envision binoculars to be good for just lying out on the deck, looking up comfortably and catching the "Bigger" picture.



#4 markb

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Posted 22 June 2020 - 11:07 AM

I sold off all of my straight through binoculars, although I am experimenting with a couple of long unused mirror tables for my remaining general use binoculars.

 

Once I used a 45 degree eyepiece binocular I sold all the rest. I have WWII flak 10x80 binoculars, and an APM 100.  Zero regrets and much happiness.

 

Easy on the aging neck too.

 

The Vixen BT80, or whatever the correct designation is for their 45-degree 80 mm binocular, would be a very easy and very affordable way to get into a 45 degree bino. Conventional wisdom has it approximately equivalent to a 110 aperture, the brain at work.

 

With the obstruction on a C5, that either put you even or ahead with just a BT80. An APM 100 what you close to a 6in in light grasp.

 

I also have a Baader Maxbright that has been waiting for my upcoming move, and for me to resolve my mount limitations. I very much look forward to using it on the GPS 11 as well as the C8.

 

 

Baader FINALLY released the maxbright 2, which has interface advantages using their system. Frankly the original Maxbright with glass path correctors is just fine for all but the widest views. A want ad should scare one up pretty easily, often with one GPC.

 

Check Baaders literature, the GPC's are designed to minimize any back focus changes, so you may not even have to use any of their t2 system.

 

If you go the 45 degree binocular route, send me a PM and I will send you some information on my balancing setup. I attached it to the mount with a very inexpensive Orion L bracket. I have the Vixen L plate but it has not proved necessary so I use it for other purposes.


Edited by markb, 22 June 2020 - 11:36 AM.


#5 eyeoftexas

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Posted 22 June 2020 - 11:21 AM

Thanks, yes FOV is important.  My hesitance in just pulling the trigger on Binoviewers is exactly because I am not sure how much they will improve the viewing in the C-5.   I have CCDCalc to show example FOV's for telescope/Camera combinations, but I don't know of a similar program for binocular views; is there one?

 

I use SkySafari, and it's let you enter both telescopes and binoculars to give indications of FOV.  You should be able to calculate FOV for the C5 for a given eyepiece, and compare that the FOV listed for any binoculars in which you might have interest.  Binoculars often list their TFOV (angular).  My Celestron 20x80's are listed as 3.2°, and it seems to be correct because the view I see matches what is shown in SkySafari (I can just get the entire belt on Orion in view).

 

I definitely see the attraction of the 45 degree eyepiece binocular.waytogo.gif


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#6 Eddgie

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Posted 22 June 2020 - 12:17 PM

First, be aware that both the C5 and the C9.25 can very easily be pushed into aperture reduction using binoviewers with an un-optimized configuration.  

 

Now that does not mean they won't work with binoviewers.  Both should reach focus with no problem and you will be able to see stuff with the binoviewers, but the question is really does it bother you to not work at full aperture?  If not, just stick the BVs into a 1.25" Prism diagonal and away you go.  Aperture loss on the C5 with this setup will be about 10mm depending on the model of binoviewer. 

 

Otherwise, if you want to avoid aperture loss, I recommend going to the Baader T2 diagonal and a T2 connected binoviewer with the Baader SCT to T2 connector, you can get the C5 and the C9 to both work at full aperture (or very close to full depending on the size of the binoviewer).

 

A binoviewer will also raise the focal length of the scope.  Once gain, a more optimized configuration will minimize this, but the focal lenght gain will be similar for each scope if the same configuration is used (150mm to 400mm depending on the configuration).



#7 CapnRon

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Posted 22 June 2020 - 08:51 PM

Eddgie,

You always seem to get right to the important trade-off issues and knowledgeably.   As usual the answer on "will aperture matter" is "it depends."   With the C5 I don't have any great expectations outside of Solar System objects, etc; so the aperture there may not matter so much.  But if I put the BV on the C9, then I may want as much aperture as I can get to see those barely visible fuzzies (assuming more aperture equates to brighter object, not just finer detail).   The other side of the trade-off coin is cost.  It looks like a full kit of Baader Maxbright Binoviewer with T-2 diagonal, SCT-adapter, a couple pair of eyepieces (all when available, soon maybe) would run around a boat-buck (yeah, Break Out Another Thousand).  Which means I should be 'serious' about using this.  To complicate matters that also puts me up in the Binotron atmosphere.  While a (drop it in and you get what you get) WO BV is a around third of that cost and I can afford to be less "serious."   And they are available now.  Of course, in this hobby area, you can usually count on getting what you pay for in the form of mechanical stability and quality.

 

There is actually a lot to consider here (as he preaches to the choir); the increased focal length/magnification of the scope, the reduction of aperture due to working past the ideal back focus of the scope, the reduction of the eyepiece FOV with the increased magnification and then all the issues of using 2 eyepieces instead of one; the physical size of the eyepiece and your required IPD as well as eyepiece selection for different magnifications.

 

I think I will drop back and punt.  I will start by using the C5 with an eyepiece again until I sort some of this out (what targets and how comfortable can I make the setup and viewing, knowing that 2 eye viewing will enhance it).    I have used the C5, in the past,  as a lighter alternative to lifting the C9 in place, but I now have a semi-permanent but mobile setup for the C9.   I keep the C9 with OAG, FW and camera all setup on the CGEM which is mounted on a home made dolly that I roll out of the garage down the driveway to image.  While in the garage it is under a Telegizmo cover with its own personal mini-dehumidifier.  It would not be hard to remove the camera gear and drop in a BV as long as I don't have to remove the C9 scope.  

 

As with most people here I tend towards being a 'numbers' person; so I need to make sure I understand all the issues and how they impact the 'numbers' and then crank thru a few 'numbers.'

 

thanks,

Ron



#8 Cali

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Posted 24 June 2020 - 11:34 AM

One thing to consider is what you want to observe with the binos.  If you want to see what the C5 shows in terms of field of view and magnification, then adding binoviewers makes sense.  If you want to see a much wider field of view, then binoculars is the choice.  I have a pair of 8x42's for wide field (~8°) and 20x80's for narrower view (~3°).  For closer, narrower views I use my AT115EDT or 12" Dob.  The 20x80's are mounted on a parallelogram, but the smaller ones fit on a monopod.  You could also put the larger binoculars on a monopod for very quick grab-n-go use, just make sure it is rated to hold them.

Agree with eyeoftexas.

 

Here is an Oberwerk 20x80LW binocular (serving as spotters), hosted on a Farpoint UBM parallelogram, sitting atop an Oberwerk 5000 Series Tripod, hovering over an Orion 127mm Mak, outfitted with an Arcturus Binoviewer and resting upon a modified Twilight I Mount & Tripod. (I think the only thing I'm missing is a Flux Capacitor.)

 

I had to save up for this rig but man, it works for me. And yeah, its pretty much grab and go.

 

- Cal

 

p.s. When I need to lean back after a long, strenuous night of star hopping, I do what eyeoftexas does. I whip out a pair of 8x40's. (See the space.com video review at the bottom of the link.) Best glass in the house for wide views.

 

You can have a whole lotta fun at low powers.

.

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Edited by Cali, 24 June 2020 - 02:23 PM.

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#9 CapnRon

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Posted 24 June 2020 - 08:46 PM

OK, so my drop back and punt formation did not last very long.  I added few eyepieces to the Ocular view in Stellarium to go with the C5-f10 telescope and 'viewed' a number of objects in the night sky to get a feeling for the FOV.  I used 10, 18 and 24 mm eyepieces and those seemed to work for most star clusters (it seems that time of the year for them).  

 

Then unlikely (as my luck does not usually run this way) I found a pair of used Denkmeier II bino's with eyepieces for sale in the Classified's here.  From what I have read the Denk's are right up there with some of the other top brands, so I bought them!  And they are on their way, as I write.  

 

I have never used PayPal before and that was a little unsettling, but so far no problems.

 

The Denk's come with (if I recall correctly) a pair of 21 and 25 mm eyepieces as well as a pair of 8-24 zoom eyepieces (no power switch), also with some corrector optics and both the 1.25 and 2" nose-pieces.  This will allow me to get introduced to 2-eye viewing for half the cost of something new, which I think is a good deal.

 

I have a 1.25" Astro-Tech Dielectric Diagonal, which should work well initially to get as bright a view as I can.  If I really enjoy the BV viewing (which I believe I will) then I will consider getting the SCT to T2 adapter, a Baader T2 Diagonal and some adapter to connect the Denk's to it, so I can operate at full aperture of my SCT's.

 

This will be a lot of first's for me; first used equipment purchase, first PayPal experience and first Bino-viewing.

 

On the Binocular side I have a pair of Pentax 10x50's and Canon 10x30 stabilized binoculars.  Both are pretty easy to use to scan the sky and get wide views, but neither go particularly deep and they are both hand held (at this time).  I think I need to find a real comfortable chair first and then figure out how to 'hang' binoculars in front of it.

 

thanks,

Ron



#10 eyeoftexas

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Posted 24 June 2020 - 11:24 PM

Congratulations and Clear Skies. Enjoy the two eyed views!

#11 CapnRon

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Posted 27 June 2020 - 08:01 PM

OK, I received the Denkmeier Bino's with eyepieces today.  All items look in good order, so I dropped (sorry bad choice) I mounted them into the 1.25" prism diagonal on the C-5 and viewed across the backyard, because it is cloudy tonight (how likely is that!) but I was able to see clearly, bring distant objects into focus, with no issue with the IPD or merging the images (so far).   I am surprised at how heavy they are, but my CGEM and the table top C-5 mount have both handled my SBIG with FW and OAG hanging off the end of the scope so I don't anticipate any problems there.  I am more concerned about the set screws on the visual back and diagonal being able to hold them as I move the scope around.  All the more reason to think about going to the 2" imaging train.

 

There is nothing (well almost) quite like a new toy to bring out the kid in us again.  Now I just need clear skies, seems I read that somewhere before.

 

Ron

Oh and I need to update my profile.



#12 CapnRon

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Posted 03 July 2020 - 11:24 PM

Finally got to try out the, new to me, Denk's tonight.  Not the best night for anything but Solar System objects; hot, humid and full Moon. I first focused on Vega (I have limited sky from my deck due to trees) and checked the scope collimation with a single eyepiece and it looked pretty good.  Then I used the BV's with the SvBony 20 mm UltraWide eyepieces and at first it looked like it was off, but the BV was not fully seated in the diagonal.  Once I corrected that they looked pretty good also.  Focusing both eyepieces and merging the image was not a problem.  

 

Not much to see around Vega, so I had to wait for the Moon to clear the trees.  When it did finally clear it was an astonishing view.  It filled the image (more about that) and felt like I could reach out an touch it.  The craters at the limb were sharp and the details of the surface did take on a 3-D effect; I felt I could actually see the height of the crater walls and the depths of the scars on the surface.  I have never spent a lot of time looking at the moon, but now I want to learn the surface.  I had to stand on tip toes as the scope was sitting on a high table and now my calves hurt.  

 

The image of the Moon seemed to NEARLY fill the view.  Obviously it drew my attention looking thru the BV and I did not spend a lot of time trying to judge how much I could see 'around' the Moon, but I can say it was not much.  I would guess my FOV was .6 - .7 degrees, which is way off from the almost 1.1 degrees that Stellarium or Astronomy-Tools says it should be for the 5" SCT with an fl of 1270 at f/10 and that eyepiece.  I would have to increase the fl by over 800 mm to have that small of a FOV.  Eddgie indicated that the fl might increase by up to 400 mm but not 800?  Anyone care to comment on why the FOV was that much smaller?

 

As I am totally new to BinoViewing I can see that there are a number of things to consider to make it easier and better to use.  It is clear that the table top mount is useful for only the most casual viewing.  I need a mount that is stable and will allow me to position the scope at a more comfortable viewing position and still be able to aim it at a target.  I could track the object easily with manual motion, so it does not need to have any drive nor even equatorial, but the motion controls should be easily accessible.  The weight of the scope and BV is around 8 lbs.  Other thoughts are that it would be nice to have a 45 degree diagonal and also some filters (I assume they can be screwed into the 1.25" nose piece or can these Denkmeier II be adapted to use some sort of filter changer? )

 

I am open to suggestions for further reading on how to best use my BV's.

 

thanks,

Ron



#13 CapnRon

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Posted 04 July 2020 - 12:22 AM

I waited up for Jupiter to clear the trees.  Nice view of 4 moons and 2 bands on Jupiter.  I took 2 min and 23 seconds for the farthest moon to drift across my FOV in the same arrangement as above (C5 SCT, BV with 20mm UltraWide Eyepieces.)  That gives around a .6 degree FOV, Stellarium show it drifting across that same Ocular in 4 minutes.  So obviously the fl is longer, buy why by so much?

 

Ron



#14 eyeoftexas

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Posted 04 July 2020 - 07:43 AM

Did your Denk come with the power switch?  It has Barlows to change the magnification.  There is also a separate Barlow that screws onto the nose of the Denk to allow it to be used in Newtonian scopes to compensate for the back focus.  If either of those are in place, that will shorten the focal length and narrow the FOV.

 

BTW, yes the Moon looks stunning close up and with two-eyed viewing.  When you get a chance, get a good Moon Atlas so you can identify the craters you see and hunt down where the Apollos landed, etc.

 

Clear Skies!



#15 CapnRon

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Posted 04 July 2020 - 10:17 AM

The Denkmeier II Bino's that I purchased did not come with any extra optics (other than the 3 sets of eyepieces), it only came with the 2" and 1.25" nose piece adapters.   I believe I can purchase the other optics as needed.  There is nothing wrong with a .6 FOV for my intended use of the BV's with SCT 5", I am just trying to understand where it comes from.  It was mentioned that using the BV's with a standard 1.25" diagonal there would be aperture loss (maybe 10 cm) and the f/l will increase because of the added optics and the extended back focus; so my question is whether the increased magnification is a combination of both of these.  Are both effects (fl increase, aperture loss) pushing the f# higher and increasing the magnification or is one the consequence of the other?

 

In any event I will be looking to add a 2" (45 degree probably) diagonal for multiple reasons; eliminate the aperture loss, provide a more stable connection to the scope, make it a bit more comfortable to view (I envision a zero gravity chair with some sort of solid arm mount for the scope and BV's) and hopefully get the BV's away from the SCT focus knob.  

 

Saturn eventually came into view and it was so nice not to have to squint to see the rings, but it was a bit to hazy to make out any moons.

 

Ron



#16 Eddgie

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Posted 04 July 2020 - 01:52 PM

The amount of focal length gain will depend on the back focus and remember, when the focal lenght changes, you have to recaluclate not just the magnfication, but also the true field the eyepiece can give.

 

If you used a standard visiual back and standard 1.25" prism diagonal (not the mirror, but a prism), the telescope used with a regular eyepiece should be around 1270mm and f/10.

 

If you added a binoviewer with 120mm light path, the focal length would be increased by about 375mm, for a total of 1645mm.

 

Now I don't know the size of the field stop in your eyepiece but it is probably in the range of 21mm to 22mm so let's use 21mm.  If the field stop is 21mm then the true field would be .73 degrees.   This is the moon in a .7 degree field, which is as close as Sky Safari lets me get. Last night, the moon was a tad over .5 degrees. 

 

thumbnail_Sky Photo - Sat Jul 04 13_37_33 CDT 2020.jpg

 

Now suppose the focal lenght was increased by 800mm.  Now the focal length would be  of an eyepiece with a 21mm field stop would be 1270 = 800) 2070, so the true field of an eyepiece with a 21mm field stop would be .58 degees.

 

Here is a field with .6 degrees. 

 

.6 moon.jpg

 

Now I don't know how big the moon was, but these images should let you estimate about what your true field was.

The first thing you should do is measure your field stop.  If it is smaller than 21mm, that is going to do a whole lot to change things.  

 

Are you using the factory visual back and the factory Prism diagonal?  If you are using anything other than this combination with a longer light path, for every 10mm of light path you add, the focal length will increase by 31mm.   So, if you were using a 1.25" mirror diagonal, then the focal length would be about 31mm greater.  

 

If you were using a visual back like the Baader, that adds about 30mm to the focal length.

 

So, we did not see what you saw, and your description of not having a lot of space, is not really something that any us can visualize with any accuracy, so the above images will help. If you put a 31 arc minute circle inside an 45 arc minute circle, there is not going to be a lot of space around the outside.

 

If you have done anything to alter your configuration from the stock visual back and stock prism diagonal, that can have an effect as well.

 

It is highly unlikely that you added 800mm of focal length though.

 

Even if the aperture is reduced, that will not change the true field size. 

 

 

 

 

 

 

 

 



#17 CapnRon

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Posted 04 July 2020 - 03:48 PM

Thanks,

How does the field stop size of the eyepiece impact the overall FOV?  I mean I understand it does but how do you calculate it?

 

I actually did a drift measurement using Jupiter and its moons and the FOV came out around .6 degree, so my estimate was about right.

 

I was using an AstroTek dielectric mirror diagonal with a standard SCT 1.25" visual back and the BV with the 1.25" nose piece seated in the diagonal eyepiece holder.  

 

I agree I did not think I added that much focal length, but the drift measurement seems to confirm the FOV; unless I am missing something about how the ultra wide (68 degree) eyepieces play a roll in all this.



#18 markb

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Posted 04 July 2020 - 04:42 PM

There are formulas for calculating actual field of view based on field stop, but this page from wilmslow has an automatic calculation script

 

http://www.wilmslowa...re/formulae.htm

 

The second gives you a maximum field of view for the particular telescope and field stop.

 

The first gives you actual field of view for a particular eyepiece.

 

If you are doing a particular task like looking for maximum field of view in a 28 mm wide 1.25 barrel, you can punch in numbers to figure it out. 20mm at 82 degree apparent fov should be a barrel limited maximum for 1.25 barrels, as an example. 

 

One I actually use because that is one of my go to eyepieces, an old 20mm Widescan. Barrel limited field-of-view for 1.25. As is 32mm at 82 degrees for a 2 inch barrel, I use a 30mm 82 degree, and never worry about what I'm missing, and that is the only 2 inch barrel eyepiece I regularly use now, besides a 20mm APM 100, IIRC 27mm is the 2 " barrel limit at 100 degrees. Punch the numbers in and find out


Edited by markb, 04 July 2020 - 04:46 PM.


#19 Eddgie

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Posted 04 July 2020 - 05:29 PM

To calculate true field, divide the field stop diameter by the focal length and multiply by 57.3.

 

If your true field is really .6 degrees, then you would divide 57.3 by .6 and you get 95.5, and if you multiply that by 21 (if this is your field stop size, but we don't know what your field stop size really is) then the focal length would be 2005mm

 

(21 / 2005 = .00105 then x 57.3 for that, and that gives you .6). 

 

So, not sure at all how you could get your focal length to be over 2000mm. 

 

If you are using a 1.25" mirror, that is going to add only about 30mm to the focal length.

I am going to guess that the problem is that the diagonal is hard vignetting the light path.  These diagonals do not really have a 1.25" opening.  I owned one, and unless they have changed it, if you measure the front opening it is only about 26mm.   

 

You have a diagonal with a light path from the front opening to the top of the eyepiece holder that is about 60mm ahead of the opening in the front of the binoviewer and that means that this opening is something like 170mm ahead of the focal plane.  
 

I will confess to not knowing exactly what is happening, but I don't think it is a function of focal lenght increase  Your focal length is probably in the neighborhood of 400mm longer than it would be with the factory diagonal and visual back and the aperture is almost for sure being reduces, but if your field is only .6 degrees, I have to think that the front of the diagonal housing is 100% vignetting the outside of the field.

 

But again, I confess to this just being a guess, but if you unscrew the nose of your diagonal and measure inner diameter of the end that goes into the front of the housing, I think you are going to see it is only something like 25mm or 26mm, and being that far in front of the focal plane, I am now just guessing that the vignetting is so strong that it is over-riding the fields stop.   But that is just a guess.  Your primary mirror would probably not go forward enough to increase the focal lenght of the scope to 2000mm. Maybe.  But I have measured enough SCTs to know that the gain is about 3.1mm or so for every extra mm of rearward focal plane displacement, so my money is now on the discrepency being hard vignetting caused by the tiny little hole in the front of the Astro Tech diagonal. I had one of these and found it to be too small for binoviewer us. 

 

Just a guess though, but  if that is not it, I am at a loss, and you will have to figure it out on your own or with others on teh forum that are smarter than I am. 



#20 Eddgie

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Posted 04 July 2020 - 05:37 PM

And again, this is all based on a field stop size of 21mm, but we really don't know how big it is. If it is more like 18mm, then that will make a big difference.



#21 CapnRon

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Posted 04 July 2020 - 08:20 PM

Thanks,

I am puzzled by this also, I don't think I have every actually measured my C5 FOV before, I just accepted whatever it was.  At some point I will measure it at the proper back focus using a camera.  I have unscrewed the 1.25 mount tube on the diagonal and the eyepieces that I have and measured what looked to be the limiting aperture down in the barrel.  None of them are less than 22 mm, the AstroTek looking more like 27mm.

 

I guess what I did not write up was that I did the drift measurement with the same (20mm 68 degree) eyepiece and just the AstroTek diagonal and it took nearly 4 minutes for Jupiter and moons to drift across the FOV (so I just contradicted myself because this was a measurement of the C5 FOV).  Which indicates a 1 degree FOV, which is what is expected with that eyepiece (well 1.086 degree FOV according to Stellarium).  When I added the Denk BV and did the same drift measurement it was 2 minutes and 23 seconds.  I just assumed that the extended back focus and reduced aperture of the 1.25 arrangement is what was increasing the f/l.  But those numbers did not compare to what Eddgie had indicated previously.  So the BV is either limiting the aperture and/or increasing the fl because I am beyond the 127 ideal back focus of position of the scope.  An analysis done by Ken Hutchinson in 2007 (for the C8 not the C5) showed that an increase of 100 mm beyond ideal back focus increased the fl by 400 mm which is only half of what I need to end up with the reduced FOV?  

 

This is all interesting and good to know, but the fact of the matter is that "I got what I got."  And that is fine (I don't think there is anything defective here - just optics).  I still think I want to get one of these:  Baader 2" 45° Erecting Amici Prism SCT Diagonal w/ 1.25" Adapter because of the reasons I mentioned earlier and then I need to start to figure out how to mount the optics for ease of viewing.

 

I guess what I really wanted was a set of 20x100 45 degree binoculars, but they run several grand.  I had the SCT 5" scope and picked up the BV's for less than half price, so I am trying to make the best of what I have.

 

Ron



#22 CapnRon

CapnRon

    Mariner 2

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Posted Yesterday, 11:11 PM

I have the capability to make more measurements, but it is not convenient to do so now (besides cloudy skies).  I have a Baader 2" clicklock and a 1.25" clicklock adapter with which I can add many mm to the back focus location for a single eyepiece and redo the the drift measurement.  The Celestron 5" SCT may be a bit different than the larger (6", 8", 11" and 14") versions in that it was sold as a spotting scope for terrestrial use as well as astronomical use (some came with a 45 degree erecting prism, mine did not).  I have not seen any analysis of the increased FL with back focus for the 5" SCT and it may just not follow the same 'rules.'  

 

What I recall from my observation during the drift measurement of Jupiter and its moons, was that the image I monitored during the drift was not limited in the sense of looking thru a tunnel.  Each view, single eyepiece or BV view, filled the field of what I could see shifting my eye from side to side.  So it 'seemed' like just an increase in magnification rather than a 'limited' FOV.  Which I think indicates increased FL over limited aperture.  I will try to make more measurements when I can.

 

The 2"  Baader 45 degree Amici prism has a optical path of 121 mm, not much different than the normal visual back and 90 diagonal, so I don't expect any changes to the FOV from what I already see.  The Baader T2 diagonal optical path is only 40 some mm (plus adapters) and my provide a 'truer' FOV for the SCT 5", but I think my reasons for wanting a 45 degree diagonal are more relevant to me than having the scope operate at its optimum FL.  Unless someone can convince me that doing so will really degrade the visual image of the "usual' targets.  I really enjoyed the movie, "The Usual Suspects."

 

I really do appreciate being able to 'bounce' my thoughts/ideas over more experienced people and get relevant feedback.

 

thanks,

Ron




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