Reichert 410 "Microstar IV" head -- corrective element present in binocular path but not trinocular camera port

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hans
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Reichert 410 "Microstar IV" head -- corrective element present in binocular path but not trinocular camera port

#1 Post by hans » Wed Jul 29, 2020 2:56 am

(For additional context, see this thread.)

After some more experimentation I conclude that the telan lens alone leaves a lot of transverse CA and what looks like a thick glass plate at the base of the eye tube is actually a "biplanar doublet" (not sure if there is a term for that) which corrects it while having average optical power near zero:
reichert-410-corrector.jpg
reichert-410-corrector.jpg (114.29 KiB) Viewed 3820 times
There is somewhat of a recess but the glass surface actually protrudes slightly beyond the mounting face. I added the adhesive rubber feet figuring it would not be long before I forgot and set it glass-down on my workbench. Looking through it at distant objects shows significant transverse CA which I don't think would be possible with a simple glass plate. Presumably the official Photostar stuff either includes this same element or integrates the corrections into the relay lens. In an afocal camera setup the corrective effect on the image from the camera port is dramatic and gives a result much closer to what is seen through the eyepieces in the binocular optical path:
afocal-181-only.jpg
afocal-181-only.jpg (98.47 KiB) Viewed 3820 times
afocal-complete.jpg
afocal-complete.jpg (92.53 KiB) Viewed 3820 times
It would be interesting to try direct projection from the camera port with only the corrector and no eyepiece but I suspect the distance from corrector to intermediate image plane is important and the corrector is cemented into the base of the eye tube. It may be possible to get it close enough to be sensor by reversing the eye tube. Here are photos of the afocal setup without and with the corrector:
afocal-181-only-setup.jpg
afocal-181-only-setup.jpg (148.86 KiB) Viewed 3820 times
afocal-complete-setup.jpg
afocal-complete-setup.jpg (142.42 KiB) Viewed 3820 times

BrianBurnes
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Re: Reichert 410 "Microstar IV" head -- corrective element present in binocular path but not trinocular camera port

#2 Post by BrianBurnes » Wed Jul 29, 2020 5:46 am

Phenomenal work hans! That explains a lot about the optical issues I have been seeing in my setup.

I've looked into the heads before but did not think to check the base of the eyepiece tube, and sure enough, both tubes contain a correcting glass plate. I am quite interested in a direct projection setup, and mounting this piece seems like a challenge (at least, without rudely removing it from the eyepiece tube). I wonder how critical the distance to the intermediate image plane is - it sits in a fixed location even in the eyepiece tube with the diopter adjustment, so there seems to be some leeway as to the location. I have not yet checked how chromatic aberration is affected through the eyepiece as the diopter adjustment is turned, and this would be a good experiment to check whether direct projection would be possible.

I do not know the precise details of how the element operates, but if it does correct for CA I have doubts that it would be reversible.

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Re: Reichert 410 "Microstar IV" head -- corrective element present in binocular path but not trinocular camera port

#3 Post by MichaelG. » Wed Jul 29, 2020 6:52 am

Excellent stuff, chaps

I am not familiar with the ‘scope but you are certainly onto something interesting

... You have an enthusiastic spectator :geek:

MichaelG.
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hans
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Re: Reichert 410 "Microstar IV" head -- corrective element present in binocular path but not trinocular camera port

#4 Post by hans » Wed Jul 29, 2020 7:51 am

BrianBurnes wrote:
Wed Jul 29, 2020 5:46 am
I am quite interested in a direct projection setup, and mounting this piece seems like a challenge (at least, without rudely removing it from the eyepiece tube).
I have one with some spotty damage to the anti-reflective coating, which probably loses a bit of contrast but otherwise seems ok, that I was considering sawing the tube part off for testing.
BrianBurnes wrote:
Wed Jul 29, 2020 5:46 am
I wonder how critical the distance to the intermediate image plane is - it sits in a fixed location even in the eyepiece tube with the diopter adjustment, so there seems to be some leeway as to the location. I have not yet checked how chromatic aberration is affected through the eyepiece as the diopter adjustment is turned, and this would be a good experiment to check whether direct projection would be possible.
At one point, before I was aware of the corrector, I did see some of the transverse CA while intentionally moving the objective away from the intended working distance, but if I remember correctly it was only really noticeable going beyond the normal eyepiece diopter adjustment range. One difficulty is that it is hard to judge the CA without maintaining focus, but maintaining focus involves changing both the objective working distance and corrector-to-eyepiece distance simultaneously, so there is ambiguity.
BrianBurnes wrote:
Wed Jul 29, 2020 5:46 am
I do not know the precise details of how the element operates, but if it does correct for CA I have doubts that it would be reversible.
Yeah, not sure what is expected theoretically. I did notice that the color fringing when looking through it at distant objects is roughly the same when reversed, which gave me some hope it may work well enough even if the behavior is not perfectly symmetric.

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Re: Reichert 410 "Microstar IV" head -- corrective element present in binocular path but not trinocular camera port

#5 Post by MichaelG. » Wed Jul 29, 2020 9:10 am

hans wrote:
Wed Jul 29, 2020 2:56 am
... what looks like a thick glass plate at the base of the eye tube is actually a "biplanar doublet" (not sure if there is a term for that) which corrects it while having average optical power near zero:
Just curious ... Do you mean something like this ?
.
2EA4FCDB-3CF7-45CB-8697-85914184C21C.jpeg
2EA4FCDB-3CF7-45CB-8697-85914184C21C.jpeg (38.01 KiB) Viewed 3778 times
... if so, can you offer any estimate of that internal curvature ?
... or is it invisible ?

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Hobbyst46
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Re: Reichert 410 "Microstar IV" head -- corrective element present in binocular path but not trinocular camera port

#6 Post by Hobbyst46 » Wed Jul 29, 2020 9:15 am

MichaelG. wrote:
Wed Jul 29, 2020 6:52 am
Excellent stuff, chaps

I am not familiar with the ‘scope but you are certainly onto something interesting

... You have an enthusiastic spectator :geek:

MichaelG.
Me too ! waiting for image results !
Zeiss Standard GFL+Canon EOS-M10, Olympus VMZ stereo

apochronaut
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Re: Reichert 410 "Microstar IV" head -- corrective element present in binocular path but not trinocular camera port

#7 Post by apochronaut » Wed Jul 29, 2020 2:53 pm

This is a really interesting project. The " correcting plates" or whatever they might be deemed have for some time been a mystery to me. Especially the glass column in the photo port section, which is for sure a cemented doublet. It's purpose is most likely to equalize the light paths , I have presumed since the path to the eyepieces passes through equivalent glass structures......but using optical windows in the optical tubes as corrector plates?

So, most binocular heads have optical windows there. While it would be possible for someone to engineer an optical window to function in that purpose, is it likely and why?

I tested 4 or maybe more optics for this system. The critical factor in getting the chromatic difference in magnification to settle down is to get the photo lens at the correct focal distance from the telan lens. It has been a while since I used a # 181 as a photo eyepiece so I don't 100% remember the distance. I think I may have told Zuul it was about 150mm but I
apologize Zuul, it may have been more like 250 or so to the top of the eye lens .... that sticks in my mind but I haven't done a measure for a while and my Diastars are not here now. You are trying to get the eyepiece to focus on the intermediate image at the correct or close to the reference length .
Initially, I tend to mention using a #181 as a photo eyepiece because I am trying to make it easy, since I know that everyone who has bought a Microstar IV has one , so can get a basic photo system up and running quickly but I shifted over to a #145 a while ago. It seemed a little easier to get it to work in my adapted , gutted, photo star based photo tube. I think it just fit somewhere nicely that the the 181 didn't and nestled into a nice distance too. I recall that the 181 needs more distance from the telan lens to evaporate the ca
One thing I notice is that , a lot of people seem to think that the optical tube and projection distances should be quite tight. I don't know where this is coming from?

Anyway, what I found was that too close and you wil get ca and some pincushion distortion too.

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Re: Reichert 410 "Microstar IV" head -- corrective element present in binocular path but not trinocular camera port

#8 Post by hans » Wed Jul 29, 2020 5:09 pm

MichaelG. wrote:
Wed Jul 29, 2020 9:10 am
Just curious ... Do you mean something like this ? ... if so, can you offer any estimate of that internal curvature ? ... or is it invisible ?
Yes, exactly. I think I can see a joint around the perimeter, which I was trying to show in the first photo, but obviously much harder to interpret the photo than in person. I can't see any sign of an interface internally, though, even shining a bright flashlight through. Nice diagram, what software are you using for ray tracing? Does it model dispersion?
apochronaut wrote:
Wed Jul 29, 2020 2:53 pm
Especially the glass column in the photo port section, which is for sure a cemented doublet.
As far as I can tell the column is just straight glass. I see no evidence of a joint, and in the test I posted in the linked thread, no significant difference in transverse CA when removing it. I suspect the effect would be more on spherical aberration and axial CA which I have not looked at carefully.
apochronaut wrote:
Wed Jul 29, 2020 2:53 pm
...but using optical windows in the optical tubes as corrector plates? While it would be possible for someone to engineer an optical window to function in that purpose, is it likely and why?
Maybe this is just stating the obvious, but I would speculate that in the overall system design the necessary correction is easier to achieve, with lower total cost and fewer other adverse effects, with the element close to the intermediate image plane. Otherwise, I agree, duplicating the corrector (if that is what it is) across both eyepiece paths makes no sense. It would almost certainly be more expensive than two simple glass plates so the correction would have been implemented before the splitter if practical.
apochronaut wrote:
Wed Jul 29, 2020 2:53 pm
The critical factor in getting the chromatic difference in magnification to settle down is to get the photo lens at the correct focal distance from the telan lens. It has been a while since I used a # 181 as a photo eyepiece so I don't 100% remember the distance.
Without changing the objective working distance, I had little success with the 181 alone at any distance, from image circle close to APS-C all the way to projecting ~2 meters onto the ceiling, but I stopped experimenting once I noticed the corrective element. (Direct ceiling projection works surprisingly well with the 10 W LED I now have hooked up.)
Last edited by hans on Wed Jul 29, 2020 6:15 pm, edited 1 time in total.

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Re: Reichert 410 "Microstar IV" head -- corrective element present in binocular path but not trinocular camera port

#9 Post by MichaelG. » Wed Jul 29, 2020 5:44 pm

hans wrote:
Wed Jul 29, 2020 5:09 pm
MichaelG. wrote:
Wed Jul 29, 2020 9:10 am
Just curious ... Do you mean something like this ? ... if so, can you offer any estimate of that internal curvature ? ... or is it invisible ?
Yes, exactly. I think I can see a joint around the perimeter, which I was trying to show in the first photo, but obviously much harder to interpret the photo than in person. I can't see any sign of an interface internally, though, even shining a bright flashlight through. Nice diagram, what software are you using for ray tracing? Does it model dispersion?
.

It's an App on my iPad, called RayLab [by Kamyar Ghandi]

To be honest, I'm still 'exploring the foothills' of its capability ... but it's already better than I could ever have expected.

If you could give me the diameter and thickness of the plate, and your best estimate of where the join lies, I will happily have a play with some curvatures and glass types.

MichaelG.

.

Ref. https://apps.apple.com/gb/app/raylab/id710190065
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Re: Reichert 410 "Microstar IV" head -- corrective element present in binocular path but not trinocular camera port

#10 Post by hans » Wed Jul 29, 2020 6:41 pm

MichaelG. wrote:
Wed Jul 29, 2020 5:44 pm
If you could give me the diameter and thickness of the plate, and your best estimate of where the join lies, I will happily have a play with some curvatures and glass types.
A bit difficult to measure thickness, but subtracting I get something very close to 7 mm, maybe +/-0.2 mm. Diameter is 24.0 mm. The position of the joint, assuming it is even a joint in the first place, is very hard to judge due to the distortion looking through the glass, but I don't see it on the ~2.5 mm of edge that sticks out beyond the mounting recess.

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Re: Reichert 410 "Microstar IV" head -- corrective element present in binocular path but not trinocular camera port

#11 Post by hans » Wed Jul 29, 2020 6:57 pm

apochronaut wrote:
Wed Jul 29, 2020 2:53 pm
So, most binocular heads have optical windows there. While it would be possible for someone to engineer an optical window to function in that purpose, is it likely and why?
Actually, if you don't mind having to redo binocular alignment, there should be an easy test staying purely within the binocular path which I have not tried yet -- just remove the eye tube and hold the eyepiece in front of the hole. If the difference is as dramatic as in the afocal camera port photos it should be plainly visible even with imperfect, hand-held alignment of the eyepiece.

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Re: Reichert 410 "Microstar IV" head -- corrective element present in binocular path but not trinocular camera port

#12 Post by MichaelG. » Wed Jul 29, 2020 7:45 pm

hans wrote:
Wed Jul 29, 2020 6:41 pm
A bit difficult to measure thickness, but subtracting I get something very close to 7 mm, maybe +/-0.2 mm. Diameter is 24.0 mm. The position of the joint, assuming it is even a joint in the first place, is very hard to judge due to the distortion looking through the glass, but I don't see it on the ~2.5 mm of edge that sticks out beyond the mounting recess.
Thanks, Hans ... that should be enough to get me started

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Re: Reichert 410 "Microstar IV" head -- corrective element present in binocular path but not trinocular camera port

#13 Post by MichaelG. » Wed Jul 29, 2020 10:13 pm

This is just a wild guess ... but we have a near life-size virtual image, and chromatic compensation
.
DBF2B066-B6EC-4771-9DAA-7C68DAA09471.jpeg
DBF2B066-B6EC-4771-9DAA-7C68DAA09471.jpeg (174.76 KiB) Viewed 3685 times
.

Let me know what you want adjusted

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Re: Reichert 410 "Microstar IV" head -- corrective element present in binocular path but not trinocular camera port

#14 Post by hans » Wed Jul 29, 2020 10:47 pm

Thanks for making the diagrams, Michael. I did some more measuring and it looks like the distance from the intermediate image plane to the nearest surface of the element is pretty close to 30 mm. I am not too familiar with the common lens mounts, but just looked up flange-to-focal-plane distances of 46.5 and 44 mm for Nikon and Canon, so seems pretty questionable whether this element could be mounted close enough for direct projection to a tradition SLR without interfering with the mirror. I don't own and have no experience with any of the mirrorless systems.

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Re: Reichert 410 "Microstar IV" head -- corrective element present in binocular path but not trinocular camera port

#15 Post by MichaelG. » Wed Jul 29, 2020 11:07 pm

hans wrote:
Wed Jul 29, 2020 10:47 pm

I am not too familiar with the common lens mounts,
.
You might find this page useful, Hans
https://cameramarket.eu/data/pdf/camera ... tances.pdf

MichaelG.
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Re: Reichert 410 "Microstar IV" head -- corrective element present in binocular path but not trinocular camera port

#16 Post by Zuul » Thu Jul 30, 2020 12:18 am

apochronaut wrote:
Wed Jul 29, 2020 2:53 pm

One thing I notice is that , a lot of people seem to think that the optical tube and projection distances should be quite tight. I don't know where this is coming from?

The commonly shared technique for eyepiece projection:

1) Locate the distance where the eyepiece provides a sharp view to your eye
2) Lift the eyepiece several millimeters further
3) Position the camera where the image has the desired framing/crop
4) Tweak the eyepiece location to achieve perfect focus

That is how I arrived at the location, and it seems Hans arrived at a very similar location.

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Re: Reichert 410 "Microstar IV" head -- corrective element present in binocular path but not trinocular camera port

#17 Post by apochronaut » Thu Jul 30, 2020 1:50 am

Is that practice commonly employed with telescopes or microscopes?

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Re: Reichert 410 "Microstar IV" head -- corrective element present in binocular path but not trinocular camera port

#18 Post by Zuul » Thu Jul 30, 2020 2:16 am

apochronaut wrote:
Thu Jul 30, 2020 1:50 am
Is that practice commonly employed with telescopes or microscopes?
I said commonly shared. It’s described on Charles Krebs‘ site and repeated frequently in other places. Like many things on the internet, in the absence of better information, you use what you can find. To be fair, he says this is a “good start”, not the golden rule.
Last edited by Zuul on Thu Jul 30, 2020 2:24 am, edited 1 time in total.

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Re: Reichert 410 "Microstar IV" head -- corrective element present in binocular path but not trinocular camera port

#19 Post by hans » Thu Jul 30, 2020 2:23 am

Zuul wrote:
Thu Jul 30, 2020 12:18 am
... That is how I arrived at the location, and it seems Hans arrived at a very similar location.
Just to clarify, none of the photos I posted in this thread or Brian's are direct projection through an eyepiece. As I mentioned to apochronaut I did experiment with it crudely (181 only through the camera port without the corrective element) but saw similar transverse CA over a wide range of projection distances. I used an afocal setup for the test in this thread because I wanted to keep everything (including the eyepieces) operating as close as possible to their intended working distances. I focused through the binocular as usual, trying to stay near the infinity end of my eye's range then focused the eyepiece over the camera port to match. As a sanity check I also manually focused the camera on a distant object (the 35mm 1:1.8G, as is common with inexpensive lenses I think, doesn't have an accurate mechanical stop at infinity) and verified that very little refocusing was necessary going to the eyepiece.

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Re: Reichert 410 "Microstar IV" head -- corrective element present in binocular path but not trinocular camera port

#20 Post by Zuul » Thu Jul 30, 2020 2:28 am

hans wrote:
Thu Jul 30, 2020 2:23 am
as is common with inexpensive lenses I think, doesn't have an accurate mechanical stop at infinity
It’s common because many of the materials used to build modern lenses have disparate coefficients of thermal expansion. The “slop” is so the lens can still focus to infinity in extreme temperatures. It’s found on expensive glass, too.

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Re: Reichert 410 "Microstar IV" head -- corrective element present in binocular path but not trinocular camera port

#21 Post by hans » Thu Jul 30, 2020 3:25 am

Just remembered I have one of those cheap eye-unsafe violet laser pointers, which appears to elicit some fluorescence from the cement in the presumed doublet:
reichert-410-corrector-cement.jpg
reichert-410-corrector-cement.jpg (109.13 KiB) Viewed 3650 times

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Re: Reichert 410 "Microstar IV" head -- corrective element present in binocular path but not trinocular camera port

#22 Post by MichaelG. » Thu Jul 30, 2020 5:08 am

hans wrote:
Thu Jul 30, 2020 3:25 am
... which appears to elicit some fluorescence from the cement ...
Very effective check, Hans
Nicely done !

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Re: Reichert 410 "Microstar IV" head -- corrective element present in binocular path but not trinocular camera port

#23 Post by hans » Thu Jul 30, 2020 5:11 am

Realizing the photo with violet laser pointer may be confusing without the benefit of messing with it in person, there are five distinct bands I am interpreting as:
  1. blue, scattering from first external surface
  2. greenish tint, scattering plus fluorescence from internal interface
  3. blue, scattering from opposite external surface
  4. dim reflection of #2 from opposite external surface
  5. dim reflection of #1 from opposite external surface
Also, less confident in this, but pretty sure I can see the depth of the spot from the internal surface varying consistent with spherical curvature as I move the laser radially. Difficult to judge, as with the position of the seam at the edge, because looking through the glass compresses the apparent distance, but I would very roughly guess a curvature corresponding to ~1 mm difference from center to edge.

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Re: Reichert 410 "Microstar IV" head -- corrective element present in binocular path but not trinocular camera port

#24 Post by hans » Thu Jul 30, 2020 5:49 am

Here is the direct projection to ceiling I mentioned earlier, using 181 eyepiece without corrector and Samsung LH351D series LED running at ~6 W if I remember correctly. Going to need a catchy phrase for this new camera coupling method... "diffuse afocal" maybe? The ceiling is slanted but the depth of focus at that distance is pretty large. Same transverse CA is visible:
direct-181-only-ceiling.jpg
direct-181-only-ceiling.jpg (113.34 KiB) Viewed 3625 times

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Re: Reichert 410 "Microstar IV" head -- corrective element present in binocular path but not trinocular camera port

#25 Post by MichaelG. » Thu Jul 30, 2020 6:09 am

hans wrote:
Thu Jul 30, 2020 5:11 am
... but pretty sure I can see the depth of the spot from the internal surface varying consistent with spherical curvature as I move the laser radially. Difficult to judge, as with the position of the seam at the edge, because looking through the glass compresses the apparent distance, but I would very roughly guess a curvature corresponding to ~1 mm difference from center to edge.
So that’s about half what I used in my last sketch

MichaelG.

.

Edit:
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Re: Reichert 410 "Microstar IV" head -- corrective element present in binocular path but not trinocular camera port

#26 Post by Zuul » Thu Jul 30, 2020 6:39 am

hans wrote:
Thu Jul 30, 2020 5:49 am
Here is the direct projection to ceiling I mentioned earlier, using 181 eyepiece without corrector and Samsung LH351D series LED running at ~6 W if I remember correctly. Going to need a catchy phrase for this new camera coupling method... "diffuse afocal" maybe? The ceiling is slanted but the depth of focus at that distance is pretty large. Same transverse CA is visible:
Before you apply for the patent, check out Ken-A-Vision. They made a business of projecting microscopes.

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Re: Reichert 410 "Microstar IV" head -- corrective element present in binocular path but not trinocular camera port

#27 Post by hans » Fri Jul 31, 2020 3:17 am

MichaelG. wrote:
Thu Jul 30, 2020 5:08 am
Very effective check, Hans
Nicely done !
Thank you, but probably giving me too much credit. The fluorescence was actually a surprise, I was originally just trying to think of anything I had brighter than an LED flashlight that might highlight imperfections at the interface. For completeness, here is the glass cylinder in the camera port showing no sign of any internal interface:
reichert-410-cylinder.jpg
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Re: Reichert 410 "Microstar IV" head -- corrective element present in binocular path but not trinocular camera port

#28 Post by hans » Fri Jul 31, 2020 4:08 am

hans wrote:
Wed Jul 29, 2020 6:57 pm
Actually, if you don't mind having to redo binocular alignment, there should be an easy test staying purely within the binocular path which I have not tried yet -- just remove the eye tube and hold the eyepiece in front of the hole. If the difference is as dramatic as in the afocal camera port photos it should be plainly visible even with imperfect, hand-held alignment of the eyepiece.
I just tried this and would say the difference is similar to what is seen in the afocal camera port photos. Once the eyepiece is reasonably locked in place with hands braced on the head a pretty good side-by-side comparison is possible moving one eye back and forth between the two eyepieces. Probably the most straightforward way, with the fewest other confounding factors, to observe the corrective effect.

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Re: Reichert 410 "Microstar IV" head -- corrective element present in binocular path but not trinocular camera port

#29 Post by apochronaut » Fri Jul 31, 2020 11:20 am

hans wrote:
Wed Jul 29, 2020 2:56 am
(For additional context, see this thread.)

After some more experimentation I conclude that the telan lens alone leaves a lot of transverse CA and what looks like a thick glass plate at the base of the eye tube is actually a "biplanar doublet" (not sure if there is a term for that) which corrects it while having average optical power near zero:
reichert-410-corrector.jpg
There is somewhat of a recess but the glass surface actually protrudes slightly beyond the mounting face. I added the adhesive rubber feet figuring it would not be long before I forgot and set it glass-down on my workbench. Looking through it at distant objects shows significant transverse CA which I don't think would be possible with a simple glass plate. Presumably the official Photostar stuff either includes this same element or integrates the corrections into the relay lens. In an afocal camera setup the corrective effect on the image from the camera port is dramatic and gives a result much closer to what is seen through the eyepieces in the binocular optical path:
afocal-181-only.jpg
afocal-complete.jpg
It would be interesting to try direct projection from the camera port with only the corrector and no eyepiece but I suspect the distance from corrector to intermediate image plane is important and the corrector is cemented into the base of the eye tube. It may be possible to get it close enough to be sensor by reversing the eye tube. Here are photos of the afocal setup without and with the corrector:
afocal-181-only-setup.jpg
afocal-complete-setup.jpg
I' m curious why the ca is so skewed to the right side? In the shot using the optical window, the far left of the image is the most highly corrected?

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Re: Reichert 410 "Microstar IV" head -- corrective element present in binocular path but not trinocular camera port

#30 Post by hans » Fri Jul 31, 2020 3:43 pm

apochronaut wrote:
Fri Jul 31, 2020 11:20 am
I' m curious why the ca is so skewed to the right side? In the shot using the optical window, the far left of the image is the most highly corrected?
Sorry, forgot to say they are cropped the same as the previous test I posted in Brian's thread, showing just the upper right quadrant with the optical center in the lower left corner. The CA is well centered and the lower left quadrant looks very similar so I cropped them like that to make the most of the 1024x1024 resolution limit. I will see if I can find a reasonable way to host and link to the original Nikon NEF files.

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