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NVD with a Diagonal

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#1 GeezerGazer

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Posted 13 September 2019 - 03:42 PM

Using camera lenses and some other prime objectives like finder scopes with NV is great because they provide such wide FoVs to see enormous areas of nebulosity or to see how different structures that we think of as individual deep space objects, actually fit together.  But hand holding the NVD with these objectives does become bothersome because as we fatigue, which doesn't take long, jitters set in, or we set it down for a rest.  I thought it would be great to have a diagonal attached to my NVD for more convenient use with my camera lenses.  After Jeff Morgan recently posted about his excellent "sky window," I decided to see if I could attach a diagonal to the ocular of my Mod 3C.  

 

I designed an adapter that would work and I thought I was going to need Precise Parts to make it; but it turns out I already have an adapter that works sufficiently for my needs.  The RAF Envis to T2 adapter is all that's needed to attach a T2 diagonal to the ocular of all the popular NVD's used for NV astronomy.  The threads at the back of the ocular (under the metal eye guard ring) are the same as the front of the Envis lens!

 

To make it work, the aluminum ring that holds the rubber eye guard, at the very back of the NV ocular must be unscrewed.  Some of these rings are screwed in VERY tight, so use care not to damage the ring.  Once it is removed, screw in the RAF Camera, Envis to T2 adapter, found here:  

https://www.rafcamer...f-to-m30-3x0-8m

then screw in the male threads on the T2 diagonal and you are set.  I use a T2 15mm extension tube on the other side of the diagonal to keep my eyelashes away from the prism in my diagonal, but it is not essential.  

 

I said that it is "sufficient for my needs" which means that it is not "perfect" but it is really close... there is slight vignetting at the very edge of the image because the inside diameter of the Envis side of the adapter intrudes ever so slightly on the image from the NV ocular.  I took an image to show the effect, but it is pretty minor and probably not even visible at night. 

 

I would like to hear from anyone else who tries this.  I know many already have the RAF adapter because it allows the use of 2" filters in front of an Envis lens (with a step up adapter ring), I also use it for a hard connection between certain eyepieces and the Envis lens for AFOCAL.  But I don't know how many have a T2 diagonal AND a camera lens or finder that already attaches to their NVD.  I'd like to hear a confirmation before others invest in this effort.  The hardest part of this might be removing the eye guard ring from the ocular to expose the Envis (M30.3 x .8mm) threads.  

 

Here are some photos to help.  This one shows the metal eye guard ring removed and the RAF adapter between the NVD and the T2 diagonal.

IMG_5617.jpg

 

This shows the T2 diagonal actually attached to the NVD

IMG_5615.jpg

 

Here, it is shown with the NVD attached to my Nikon 300mm lens on my larger alt/az mount

IMG_5619.jpg

 

And this shows the Envis lens removed and the T2 diagonal attached to the NVD with a Nikon 105 lens for a 10° FoV

IMG_5625.jpg


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#2 GeezerGazer

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Posted 13 September 2019 - 03:46 PM

This is the 105mm lens attached to NV and mounted on my small CF tripod and alt/az mount

IMG_5627.jpg

 

I attach my NVD to the mount using a bracket I made with a short Vixen style dovetail

IMG_5629.jpg

 

And this is a photo using the Envis lens at 1x, 40° FoV, looking into my darkened kitchen with the diagonal attached, showing the tiniest bit of vignetting.  

IMG_5632.jpg


Edited by GeezerGazer, 13 September 2019 - 04:18 PM.


#3 AllanDystrup

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Posted 14 September 2019 - 06:34 AM

     Interesting setup waytogo.gif

 

     I’d be tempted to add a binoviewer (T2 QuickChange ring/bayonet) to the Baader diagonal there... grin.gif

 

     (Of course if max FOV is the goal, that’s hardly the way to go. — But could be interesting trying...)

 

     — Allan


Edited by AllanDystrup, 14 September 2019 - 06:43 AM.


#4 slavicek

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Posted 14 September 2019 - 01:57 PM

Wow. This will solve my latest problem before it even happens. Instead of mounting the diagonal between the fast Nikon lens and the NV, I am going to mount the diagonal at the end - hence there will be no issue with having enough back focus. Exellent.

And, to get rid of the vignetting, how about using 2 inch Badder diagonal indstead of T2 diagonal... I will have to give it a try.


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#5 Jeff Morgan

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Posted 14 September 2019 - 04:24 PM

I'm loving this idea Ray! The Baader T2 Zeiss spec prism was already on the Buy list for planetary use.

 

Regarding the 15mm extension ring on the eye side, how critical is eye positioning? I had in mind the idea of re-mounting the NVD rubber eyecup there.



#6 GeezerGazer

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Posted 14 September 2019 - 06:23 PM

Wow. This will solve my latest problem before it even happens. Instead of mounting the diagonal between the fast Nikon lens and the NV, I am going to mount the diagonal at the end - hence there will be no issue with having enough back focus. Exellent.

And, to get rid of the vignetting, how about using 2 inch Badder diagonal indstead of T2 diagonal... I will have to give it a try.

I think this is a potential solution to problems including back focus dilemmas.  The vignetting is NOT caused by the T2 diagonal... a 1.25" diagonal could actually be used and still get a compete image.  I unscrewed the nose and eyepiece holder from my Tak 1.25" diagonal and placing it over the ocular displays an unimpeded view.  The vignetting occurs at the inside edge of the Envis threaded adapter.  When I place the T2 diagonal directly over the ocular, with the eye guard ring removed, there is NO vignetting.  It is the adapter that is intruding on the perimeter of the image emitted from the ocular.  

 

I'm loving this idea Ray! The Baader T2 Zeiss spec prism was already on the Buy list for planetary use.

 

Regarding the 15mm extension ring on the eye side, how critical is eye positioning? I had in mind the idea of re-mounting the NVD rubber eyecup there.

 

Eye position did not seem critical at all.  Moving my head around at the T2 opening did not matter.  The prism (or a mirror) is simply re-directing the image at 90°.  The image at the top end of the diagonal is a little smaller than it would be at the ocular; the light path through the T2 prism diagonal is about 47mm.  It's like pulling your eye farther back from the ocular (without the diagonal).  My 15mm T2 spacer is simply to keep my eyelashes away from the prism... a 5-10mm spacer would work too.  Using a mirror diagonal (like the BBHS) would not need the spacer at all, IMO.  

 

The existing RAF Envis to T2 adapter screws onto the male T2 threads on the diagonal, which are on the outside of the diagonal housing.  My adapter design would screw into the female T2 threads on the diagonal, moving the diagonal closer to the ocular.  When I figured out that the threads at the back of the ocular are the same as the threads at the front of the Envis, I tried the RAF adapter which works pretty well.  My adapter design would put the front side of the diagonal prism a little closer (+/- 5mm) to the eye lens of the ocular.  But it might not make any difference at all.  

 

Today, I screwed the Envis to 1.25" filter holder (the tiny RAF adapter) into the ocular threads, then I placed the diagonal about where the proposed adapter would hold it and I saw the same vignetting.  I then removed the nose & eyepiece holder from my Tak 1.25" diagonal and set it as close as possible to the ocular... same results.  When I place my eye up to the ocular, no vignetting, even with the adapter in place.  If I understand this correctly, the inside diameter of any Envis adapter will cause visible vignetting when adding the additional light path of a diagonal.  As Eddgie might say, "it's simple geometry."  

 

I'll try the diagonal attached using one of my camera lenses to see how mild or severe the vignetting is at night.  This might take a few days.  



#7 Jeff Morgan

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Posted 14 September 2019 - 09:59 PM

If I understand this correctly, the inside diameter of any Envis adapter will cause visible vignetting when adding the additional light path of a diagonal. 

 

A small price to pay for the convenience I would say. The band shift from extremely narrow filters looks worse than this IMHO.



#8 The Ardent

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Posted 14 September 2019 - 10:55 PM

It's seems like 99% of NV is having the right adapters.


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#9 Jeff Morgan

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Posted 14 September 2019 - 11:40 PM

It's seems like 99% of NV is having the right adapters.

 

Early on I searched the RAF Camera site for the word ENVIS and bought one of everything. In comparison to the cost of the NVD, peanuts.



#10 slavicek

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Posted 14 September 2019 - 11:51 PM

If it's the Envis  adapter which is causing the vignetting then all is needed is different adapter. Rather than unscrewing rings from the NV occular, I am thinking about some kind of -clamp on- adapter. But I am abroad for few weeks so I will have to wait till I get back to the US. You guys will probably figure it out by then. Aslo, the 1.25 inch Tak diagonal has short light path and it is also is very light, which would be another advantage of it - that is if it works with the NV.


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#11 GeezerGazer

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Posted 15 September 2019 - 12:15 AM

It's seems like 99% of NV is having the right adapters.

99% of getting things to work right does involve the right adapter.  The Mod 3C is versatile, so adapters are a necessary component of that versatility.  If it was not versatile, no adapters would be required.  Calling upon a NVD to produce good results with a variety of prime lenses, all sorts of telescopes, to perform afocally, and adding a diagonal does require adapters, but the result is a more useful device... for which I am grateful.  I keep my NV adapters in a single box and the current count is 14... but I have more duplicate adapters for some specific uses, like the C2TT adapter from ScopeStuff, or the Envis to 1.25" adapter from RAF.  And this number does not include the many 2" and TT extension tubes I have for reducers that require a specific working distance to the focal plane.  I know what you are saying, but I believe the adapters are a small price to pay for the versatility.  



#12 GeezerGazer

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Posted 15 September 2019 - 12:27 AM

If it's the Envis  adapter which is causing the vignetting then all is needed is different adapter. Rather than unscrewing rings from the NV occular, I am thinking about some kind of -clamp on- adapter. But I am abroad for few weeks so I will have to wait till I get back to the US. You guys will probably figure it out by then. Aslo, the 1.25 inch Tak diagonal has short light path and it is also is very light, which would be another advantage of it - that is if it works with the NV.

The good thing about threaded components is that they do not often come apart unexpectedly.  And I'm not sure there would be sufficient purchase (surface area) to secure a clamping adapter.  I am not willing to risk dropping my Zeiss prism diagonal to the ground!  I'll try to test for night time vignetting using the RAF adapter to see how much it intrudes.  I am not fond of vignetting, so I'll be direct about the results.  



#13 jdbastro

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Posted 15 September 2019 - 12:49 AM

Another way to do this and avoid removal of the ocular's eyecup ring would be to use this part and then have a custom M46 to T2 male thread adapter made via Precise Parts.


Edited by jdbastro, 15 September 2019 - 12:50 AM.

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#14 Jeff Morgan

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Posted 15 September 2019 - 12:45 PM

Another way to do this and avoid removal of the ocular's eyecup ring would be to use this part and then have a custom M46 to T2 male thread adapter made via Precise Parts.

 

Baader makes all kinds of T2 parts, I'll see if I can hunt down a M46->T2.


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#15 GeezerGazer

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Posted 15 September 2019 - 03:52 PM

Another way to do this and avoid removal of the ocular's eyecup ring would be to use this part and then have a custom M46 to T2 male thread adapter made via Precise Parts.

I have a TNVC afocal camera adapter.  It would push the diagonal farther from the ocular... instead of bringing it closer.  And, that adapter requires that the eye guard ring remain in place to support it.  It's all about the light path from the ocular.  When used visually, your eye is close enough to see a complete image, even with the adapter or the eye guard ring in place.  Move your eye 47mm away from the ocular (light path of the T2 diagonal) and you will see vignetting because the Envis adapters are acting like a field stop.  The inside diameter of the Envis adapter OR the eye guard ring, is slightly smaller than the eye lens in the ocular.  Moving your eye farther away from the ocular reveals vignetting.  If like slavicek suggests, a clamping device could be used, then removing the eye guard ring would reveal a slightly bigger clear path for the image.  

 

Take a metal washer and look through the hole in the center, move it closer to your eye and you see a bigger FoV, move it away and the FoV becomes smaller.  That's what's happening with the Envis adapters when screwed into the ocular.  Move your eye close enough and the FoV is sufficient to see the entire image from the ocular.  Move your eye away and the FoV becomes smaller until the inside diameter of the Envis adapter intrudes on the image.  

 

The diameter of the exposed eye lens on the NV ocular is 29.1mm, which matches the clear aperture from the ocular housing WITHOUT an Envis adapter screwed in.  The inside diameter of the metal eye guard ring is 24.9mm (it has a raised center edge).   The inside diameter of the RAF Envis to T2 adapter is 27.5mm.  The vignetting I see is caused by the difference in size between the diameter of the eye lens and the inside diameter of the RAF adapter... just 1.6mm.  With an Envis adapter in place on the ocular, the farther from the adapter your eye is, the less FoV you see... it is a small amount and is unlikely to be a problem for visual use.

 

Although the Tak 1.25" diagonal has a shorter light path than the T2 diagonal, it would require a special adapter to be made to fit the female metric threads in the diagonal (that the nose and eyepiece holder screw into).  The light path of the Tak 1.25" diagonal is 64mm, but without the eyepiece holder (or the nose), the light path is only 30mm.  So there is a savings of 17mm when compared to the Baader T2 Zeiss prism diagonal.  

 

I think a bigger concern than vignetting for most will be the size of the image at the other end of the diagonal when installed... it's smaller because your eye is farther away from the ocular, by the distance of the light path for the diagonal that is used.  Some might object to the smaller visual image.   I definitely see a difference, but for the convenience of using a right angle diagonal, it would be worth the tradeoff, especially with a big, heavy lens like my Nikon 300 which weighs 6 lbs.  

 

Baader makes all kinds of T2 parts, I'll see if I can hunt down a M46->T2.

 

I have a 46 to 42 adapter.  The addition of another adapter will push the diagonal farther from the ocular, which is opposite of what we need.  

 

Tonight, skies are below average for seeing and transparency.  Tomorrow looks OK, so I should be able to test what I have.  I'll take a couple of photos to see if I can accurately demonstrate the two primary concerns; vignetting and image size.



#16 Jeff Morgan

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Posted 15 September 2019 - 06:38 PM

 If like slavicek suggests, a clamping device could be used, then removing the eye guard ring would reveal a slightly bigger clear path for the image.  

 

Along those lines I tried to slip-fit a T2 adapter over the diopter ring of my Mod 3. Just a bit tight. Perhaps a 43mm or 44mm ID sleeve with a male T2 thread would work?

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#17 GeezerGazer

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Posted 16 September 2019 - 12:34 AM

A sleeve with T2 threads might work very well!  It would eliminate the threaded adapter that creates the restriction.  



#18 GeezerGazer

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Posted 18 September 2019 - 04:30 PM

Today, I did some experimenting to see differences using the T2 diagonal.  I took 4 photos through different assemblies to show differences in the image that was presented.  The only editing was to rotate the images using the diagonal so they were also upright, although they are not flipped, so look backwards when compared to the first image where no diagonal was used.  

 

1.  Using the NVD/ocular straight through with phone adapter attached to the the back of the ocular, having removed only the rubber eye guard, but leaving the eye guard ring in place.  This is how I normally attach the phone to the Mod 3C to take images.

 

IMG_5646.JPG

 

2.  With the RAF, Envis to T2 adapter screwed into the back of the ocular, the male threads on the T2 diagonal were screwed into the RAF adapter for a solid connection; I hand held the phone over the top of the diagonal for a very close, unobstructed image.  The camera lens was about where my eye would be if using this system visually.  Although, my eye was close to the prism when used in this manner, my eyelashes did not touch the prism.  

 

IMG_5647.jpg

 

3.   With the phone held against the male T2 threads on the diagonal, I hand held the diagonal with the female thread side against the ocular, to simulate a sleeve adapter that would place the female threaded side of the diagonal slightly closer to the ocular.  This was a bit awkward but the image came out OK, and when compared to the other images, probably does present the best of the possibilities.  So I worked on an adapter design today, using a sleeve to slip over the diopter adjuster ring, that would be tightened with two nylon thumbscrews.  The adapter would place the diagonal 2mm farther from the ocular than is represented by this photo.  

 

IMG_5648.jpg

 

4.  Using the RAF, Envis to T2 adapter between the diagonal and ocular, I added a 10mm extension tube to the top and attached my phone adapter with my phone in the adapter.  The extension did allow the phone bracket to securely attach, but at the cost of a smaller image because it extends the light path.  This represents less image size shrinkage than I saw when adding the 15mm extension to the top of the diagonal, discussed in post 15.  

 

IMG_5649.jpg

 

Based on my findings, I'd probably be happy using either the RAF adapter or the sleeve adapter suggested by Jeff, for visual use with the T2 adapter (see images #2 & 3, above).  I probably won't be using this system for imaging because it does extend the distance from the NV ocular too much, which means I'd lose resolution.  

 

If anyone is interested in having a sleeve adapter with T2 threads made, please PM me.  If I decide to have one made, it would probably be about the same price for two; maybe even for three.  Most of the machining labor costs are for the time it takes to set up to make such things.  Based on my experience, one adapter would probably cost $130 to be made (bare aluminum, no anodizing).  To make 4 would probably be $150, so that would be split 3-4 ways.  This adapter might not require removal of the eye guard ring for an non-vignetted image.  It'll be really close.  

 

I have not yet been able to test the RAF adapter at night; clouds tonight until early morning... tomorrow looks promising for a short test with a couple of images.  

Ray

 

 


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#19 GeezerGazer

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Posted 19 September 2019 - 03:15 AM

Tonight I found a sucker hole amongst the clouds and took a couple of photos and compared visually using the RAF, Envis to T2 adapter between the Mod 3C ocular and the T2 diagonal.  The photos were taken handheld, with the phone's camera lens held on the top of the diagonal.  They are good enough to show the FoV. 

 

Both images were taken through a Nikon f:2.8, 300mm lens from my red zone home.  The first image shows the star field around Deneb and reveals the minor vignetting, which shows up as a fuzzy or indistinct edge of field.  It is very minor and not bothersome to me.  For the second image, I added a 1.25" 7nm H-a filter.  Again, vignetting is not really noticeable.  There is a little falloff of nebulosity at the very EoF because of band shift and that edge is a little fuzzy.

 

IMG_5656.JPG

 

IMG_5658.JPG

 

Visually, I was disappointed to find that I could not see the entire image unless I moved my eye and head to see around the internal restriction caused by the Envis adapter.  Basically, I could not get my eye close enough to the top of the prism in my T2 diagonal to see the entire image being emitted through the ocular, even though my cheek was against the diagonal housing.  The phone camera lens could get close enough, but my eye could not.  

 

Tomorrow I go to the machine shop to see about making a T2 Sleeve Adapter.  I think it is about the only way that the diagonal can be attached so that the restriction created by Envis adapters is eliminated for visual use.  



#20 GeezerGazer

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Posted 09 November 2019 - 12:23 AM

Here is follow-up info, after making a 15mm Baader T2 extension ring into an adapter that slides over the NVD diopter ring.  It works very well with one drawback.  The image is +/- 23% smaller than without the diagonal.  Below are 4 images, three showing the adapter and its function on the NVD and one showing the difference in size as compared to an image without the diagonal and adapter on the NVD.  In use, the aluminum eye guard ring must be removed to get the largest clear aperture from the NVD ocular.  

 

Jeff Morgan and Slavicek collaborated on this project, so they each have adapters.  Perhaps they will be able to provide opinions as to the function and performance in their use.  

 

When I took a design for an adapter to the machine shop, the cost to produce it was very high, at $400.  But using a Baader 15mm T2 extension ring, the machine shop charged $20 to bore out the female end to 42mm diameter extending 13mm into the extension ring.  Then I drilled and tapped a hole for a very small, aluminum set screw so it would not rotate on the diopter ring.  I did have to chuck the adapter in my shop lathe to reduce the inside diameter by a few thousandths of an inch to properly fit onto the diopter ring.  During this process, I found that the synthetic material used for the diopter ring is slightly tapered with a smaller diameter at the end.  

 

I used this adapter for visual use in Utah last month with my 300mm Nikon lens and it worked fine, showing no vignetting.  I do find the smaller image (because my eye is 47mm farther from the NVD ocular) a bit annoying, but the tradeoff is a much more comfortable user experience.  The f:2.8 - 300mm is a 6 lb. lens crammed into an 11" package; it is far too heavy to hand hold and the magnification (11x) makes it near impossible to get a steady glimpse of anything.  The objective is 4.25" so this is like using a 100mm APO in a very short/convenient size.  The adapter makes it possible to use this large camera lens (or ANY C-mount lens) mounted with a diagonal for 90° viewing... much easier on the neck than straight through... even if the image is smaller! 

 

Here is the adapter screwed into the Baader T2 diagonal

IMG_5665.jpg

 

This is the adapter fitted to the NVD (without the diagonal)

IMG_5667.jpg

 

This is the adapter attached to the diagonal and the NVD... now any C-mount lens can be used at 90°.

IMG_5660.jpg

 

This photo was taken to show the difference in image size; photos taken with and without the diagonal.  The image is of a ruler on the wall.  The FoV is the same; only the size of the image changed because of the distance from the NVD ocular.  Measuring these two image circles reveals a 23% shrinkage.  

comparison.jpg

 

 


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#21 slavicek

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Posted 10 November 2019 - 05:31 PM

Here is my experience with the diagonal adapter:

As you know, when you use NV device you need to focus two things:

a) the telescope to the focal point of NV device and

b) set the NV ocular to your eye prescription

 

I were glasses of -5 Diopries. I do all my regular observing without glasses, using the telescope focuser to compensate for my prescription. However I've run into one problem with this diagonal set up. When I observed with this diagonal I could not get the image into focus. I could not figure out what was going on until it hit me - my eyes are just too far away from the NV screen to be able to focus on the screen, even thou the NV ocular is set at -5 D. So I had to put my glasses on and then I could focus on to the NV screen again. The problem is that now my eyes are even further away from the NV device, hence I get even smaller FOV. The solution to this problem will be installing -5 D lens into the "eye side" of the diagonal.

But I just want to mention this for those who will consider this set up and are wearing (like me) strong negative glasses.

I will still use this 90 deg set up as planned = as a finder scope on my DOB and with my very wide FOV telephoto lens. Just be aware of the this fact. There's always few tweaks to be made... smile.gif

 

The convenience of the 90 deg diagonal and not having one's neck sored is, in my opinion, worth all the troubles.


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