Eyepieces, photoeyepieces and Teleconverters; what are the similarities and differences? Should we care?

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seta666
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Eyepieces, photoeyepieces and Teleconverters; what are the similarities and differences? Should we care?

Post by seta666 »

Because if optimized at the end the final result seems to be pretty much the same...a central crop of the image

In the last couple of weeks I have been looking for a way to magnify the image from nikon CFN lenses on a microscope via direct projection. I am not looking for a permanent solution as direct projection works very well , I just want to have an option when working with very small subjects.

- First I thought of a Teleconverter as I had good results in my vertical set up with them in the past, I run some tests only to realize later on that I can not use the teleconverter I have on my scope. My phototube adaptation is 11mm long, Sony E-mount flange distance 18mm and nikon F mount flange distance is 46.5mm, teleconverter should sit inside the trinocular head. There is a sony teleconverter but is priced 500$, pass.

- Also tried afocal method with a Konika Hexanon 40mm f1.8 lens I have but depending on the situation gives a hot spot in the middle of the frame, something common with analog era manual lenses on digital sensors. One thing about this set up I do not like is there is too much glass which may bring new defects; maybe a modern pancake lens would work perform better. Canon 40/2.8 for example

- The nikon CF PL2x would be another but it is not cheap and I do not know how does it perform; 2x is more than I would like to get though..

- I also tried using a Nikon SC 10x eyepiece as a photo eyepiece (10x/18), this so far is working pretty well. First I did set the eyepiece parfocal and then placed a extension tube so that there was not vigneting. I realized later parfocality was lost buy playing with placement of both camera and eyepiece I can get the system completely parfocal even though eyepiece is higher than it should be for a 160mm tube length system. There is not just one correct setting, different placement of the eyepiece/camera gives you different magnification ratios while keeping parfocality.

This image was taken with such set up and the CFN 40/0.70 and this one with the CF Fluor 20/0.75, no crops Sony NEX-5N camera and that was before I realized system was not parfocal. I would say performance is good corner to corner

I thought normal eyepieces could not be used this way; why is it working then? what makes a photo eyepiece different then?

Is it wrong to think as long as the system is parfocal the set up is correct? The way I see it is the aberrations created by misplacement of the eyepiece are corrected somehow by the position of the camera. Something similar happens with the Teleconverter but I can not get it completely parfocal


And yet just run another test with Sony NEX-5N, CFN 40/0.70 and nikon SC 10x/18 eyepiece , Afocal with Konika Hexanon 40mm 1.8 vs SC as a photo eyepiece. Both set ups parfocal, 1.80X aprox

Shot with same settings, JPGs from camera raw with no other adjustments than WB; crops have global levels applied

Image

Guess which is which?
Image

Full size

Direct Zerene outputs for any one who wants to check them.
A Pmax
B Pmax
A DMap
B DMap

What would I need to get lower magnification like 1.5X? would a low power neutral eyepiece work? Better a WF one?

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Re: Eyepieces, photoeyepieces and Teleconverters; what are the similarities and differences? Should we care?

Post by Pau »

I am not looking for a permanent solution as direct projection works very well , I just want to have an option when working with very small subjects.
If you can't switch to a higher magnification/NA objective this is almost for sure a case where you are in empty magnification zone, so you don't need smaller pixels.
If you have a camera with a good sensor (and you have) just cropping the image will do. If in most cases you can cover APSC with good quality, a crop up to 4/3 format will not be too much.
Is it wrong to think as long as the system is parfocal the set up is correct? The way I see it is the aberrations created by misplacement of the eyepiece are corrected somehow by the position of the camera. Something similar happens with the Teleconverter but I can not get it completely parfocal
Yes, it is wrong. For high NA objectives the distance from the objective shoulder and the primary image placement is very important to avoid spherical CA.
Parfocality is important only because it is practical and the microscope objectives of the same standard are designed to be parfocal when al the other parameters are correct, and the whole microscope system also is.

If you have not parfocality it is a symptom that there is mismatch, although I don't think that the inverse needs to be true.
I thought normal eyepieces could not be used this way; why is it working then? what makes a photo eyepiece different then?
A visual eyepiece at its right position projects the image to infinite to have a relaxed vision with your eye, this is the base of afocal with an infinite focused camera lens. But when you raise it, it focuses the image closer, so you can place a sensor to capture the secondary image. This is a very classical approach, very popular in the 70s-90s with adapters for film SLRs
Projective eyepieces like CF PL 2.5X or Oly NFK project the secondary image at closer than infinite with the primary image at its right position.
There are also "photoeyepieces" of the visual type but specially corrected for afocal photography like the Zeiss S-KPL, Leitz "red dot" Periplan and the "Nikon CF photo" 8X and 10X. I own the the former two and are excellent, I have no experience with the Nikons, any one could comment?
The nikon CF PL2x would be another but it is not cheap and I do not know how does it perform; 2x is more than I would like to get though.
Does it exist? I think the PLI is pretty good.
(Yo tengo un PLI 2X (para tubo de 30mm). Cuando nos veamos te lo puedo dejar para probarlo.)
Pau

Ichthyophthirius
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Re: Eyepieces, photoeyepieces and Teleconverters; what are the similarities and differences? Should we care?

Post by Ichthyophthirius »

seta666 wrote:
Thu Mar 25, 2021 4:20 pm
- I also tried using a Nikon SC 10x eyepiece as a photo eyepiece (10x/18), this so far is working pretty well. First I did set the eyepiece parfocal and then placed a extension tube so that there was not vigneting. I realized later parfocality was lost buy playing with placement of both camera and eyepiece I can get the system completely parfocal even though eyepiece is higher than it should be for a 160mm tube length system. There is not just one correct setting, different placement of the eyepiece/camera gives you different magnification ratios while keeping parfocality.

This image was taken with such set up and the CFN 40/0.70 and this one with the CF Fluor 20/0.75, no crops Sony NEX-5N camera and that was before I realized system was not parfocal. I would say performance is good corner to corner

I thought normal eyepieces could not be used this way; why is it working then? what makes a photo eyepiece different then?
That's called eyepiece projection. A visual eyepice that is lifted slightly above the designed position (image at infinity) will produce an image at a defined position above the eyepiece. But that changes the tube length and leads to spherical aberration, as Pau said. It's actually quite usable but can lead to problems in critical applications.

In afocal adapations, the eyepiece remains in its designed position with the correct tube length.

Afocal can work with almost any eyepiece. Some photo eyepieces are special designs (Zeiss S-Kpl), others are probably just selections (Leitz red dot) where the factory tested a batch after assembly: the worst ones are discarded, the ones that pass QC are the regular eyepieces and the best ones are labelled as photo eyepieces. It's probably things like coma correction at the edge of the image that are the criteria for photo eyepieces over the regular ones and some might well be unnoticible except on a factory test bench.

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Re: Eyepieces, photoeyepieces and Teleconverters; what are the similarities and differences? Should we care?

Post by rjlittlefield »

Ichthyophthirius wrote:
Fri Mar 26, 2021 8:37 am
A visual eyepice that is lifted slightly above the designed position (image at infinity) will produce an image at a defined position above the eyepiece. But that changes the tube length and leads to spherical aberration
To clarify, the optical tube length changes only if the eyepiece as used in projection is not parfocal with the eyepiece used normally. If it is parfocal, then the optical tube length has not been changed.

Getting it parfocal is a matter of matching the distance between eyepiece and camera with the amount the eyepiece is raised, so as to leave the intermediate image in the same place it would be with a normal eyepiece.

In that configuration there will be no added spherical aberration due to the objective. From the standpoint of the objective, nothing has changed.

But there will be some spherical aberration introduced by the eyepiece being used far away from its design point. It's the same problem you get when repurposing a landscape lens to shoot closeup/macro by just adding extension.

--Rik

Ichthyophthirius
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Re: Eyepieces, photoeyepieces and Teleconverters; what are the similarities and differences? Should we care?

Post by Ichthyophthirius »

rjlittlefield wrote:
Fri Mar 26, 2021 9:47 am
But there will be some spherical aberration introduced by the eyepiece being used far away from its design point.
Yeah, that's what I was getting at. For eyepiece projection, a 10x eyepiece has to be lifted by 5 mm (for k = 125 mm camera length); a tube length increase of 5 mm would just about be acceptable for purists but certainly something you can get away with.

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Re: Eyepieces, photoeyepieces and Teleconverters; what are the similarities and differences? Should we care?

Post by rjlittlefield »

Ichthyophthirius wrote:
Fri Mar 26, 2021 10:39 am
rjlittlefield wrote:
Fri Mar 26, 2021 9:47 am
But there will be some spherical aberration introduced by the eyepiece being used far away from its design point.
Yeah, that's what I was getting at. For eyepiece projection, a 10x eyepiece has to be lifted by 5 mm (for k = 125 mm camera length); a tube length increase of 5 mm would just about be acceptable for purists but certainly something you can get away with.
Again to clarify, this "tube length increase of 5 mm" is not the same tube length increase that is depicted in the classic graph titled "Tolerance to tube length change versus objective N.A."

In the case of a parfocal raised eyepiece, there is no change in the optical tube length as seen by the objective. The intermediate image will be just as free of spherical aberration, regardless of N.A., as it would be with a normal eyepiece used visually. The increase in spherical aberration with the raised eyepiece is entirely due to the eyepiece, and that increase will actually be less with a high NA, high magnification objective, due to the narrower light cones coming from the objective.

I note that in the demo by seta666, he's using a 40X NA 0.70 objective. That makes f/28 at the intermediate image, which also makes life pretty simple for the eyepiece even used far away from its normal design point.

--Rik

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Re: Eyepieces, photoeyepieces and Teleconverters; what are the similarities and differences? Should we care?

Post by Ichthyophthirius »

Ah, I see. So you're maintaining the correct position of the intermediate image (at 150 mm) and only the distance between intermediate image and eyepiece changes (from 10 mm to 15 mm). I described that incorrectly above.

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Re: Eyepieces, photoeyepieces and Teleconverters; what are the similarities and differences? Should we care?

Post by rjlittlefield »

Right. Maintaining parfocality with a visual eyepiece implies that the intermediate image remains in the same place.

--Rik

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Re: Eyepieces, photoeyepieces and Teleconverters; what are the similarities and differences? Should we care?

Post by viktor j nilsson »

I'm trying to wrap my head around what's going on when you raise a normal viewing eyepiece but can't really figure it out on my own. But if I understand what you say, Rik, then if you move the camera away from the eyepiece just the right amount, and raise the eyepiece just the right amount, then you create a situation where i) the eyepiece still pick up the intermediate image at the original location (so you have basically increased the "working distance" of the eyepiece?); and 2) projects a real image at the sensor plane (instead of being focused at infinity as it would be if the eyepiece wasn't raised). Is this correct?

Do you know of any visualizations of what the light path looks like when you raise the eyepiece this way?

Although I have a decent grasp of how microscope optics work from the illuminator and up to the intermediate image, this discussion made me realize that I don't really understand what's going on where the eyepiece meets the eye.

Edit: I noticed that you guys already clarified part of this as I was typing on my phone. Glad I got that right!

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Re: Eyepieces, photoeyepieces and Teleconverters; what are the similarities and differences? Should we care?

Post by Ichthyophthirius »

viktor j nilsson wrote:
Fri Mar 26, 2021 12:34 pm
Do you know of any visualizations of what the light path looks like when you raise the eyepiece this way?
Yes, this graphic shows common camera adaptations: https://www.mikroskopie-forum.de/pictur ... 766975.jpg
I: Visual lightpath (visual eyepiece and human eye)
II: Afocal (eyepiece and camera lens)
III: Refocussing (not recommended)
IV: Eyepiece projection (lifting eyepiece while maintaining the intermediate image location O')
V: Projective

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Re: Eyepieces, photoeyepieces and Teleconverters; what are the similarities and differences? Should we care?

Post by seta666 »

Pau wrote:
Fri Mar 26, 2021 4:52 am
If you can't switch to a higher magnification/NA objective this is almost for sure a case where you are in empty magnification zone, so you don't need smaller pixels.
.....
Maybe using the whole sensor helps regarding noise, and this could be very useful for video too. A good 1.5X eyepiece would give you half step magnification setting for the scope, sometimes 10x is too little and 20X too much.
Does it exist? I think the PLI is pretty good.
(Yo tengo un PLI 2X (para tubo de 30mm). Cuando nos veamos te lo puedo dejar para probarlo.)
Yes, it does; there are some on ebay right now. And yes ..we have to meet one day, would be nice.. :D
Ichthyophthirius wrote:
Fri Mar 26, 2021 10:39 am
Yeah, that's what I was getting at. For eyepiece projection, a 10x eyepiece has to be lifted by 5 mm (for k = 125 mm camera length); a tube length increase of 5 mm would just about be acceptable for purists but certainly something you can get away with.
Where does this 5mm number come from? In those test images the eyepiece is raised around 13mm above the viewing point and the camera sensor is 43mm away from the eyepiece optics. My goal is minimum magnification without vignetting, 1.6 to 1.7x seems doable with a 10/18 eyepiece. If I could finetune the OEM 10/22 eyepiece ( which seems to work OK too)I have I could get down to 1.3-.1.4x without vignetting
rjlittlefield wrote:
Fri Mar 26, 2021 11:55 am
In the case of a parfocal raised eyepiece, there is no change in the optical tube length as seen by the objective. ..................

I note that in the demo by seta666, he's using a 40X NA 0.70 objective. That makes f/28 at the intermediate image, which also makes life pretty simple for the eyepiece even used far away from its normal design point.
So, if the system is parfocal everything is OK on the objective end; however rising up the eyepiece will create spherical aberrations, maybe this is what I see on the binocular loupe eyepiece. Would be possible for an overcorrected eypiece to become kind of neutral when rising it?

Would this also be the case with a teleconverter, if you could keep an image focused to infinity by changing the position of lens, TC and camera relationship?

Do you mean the high f number is helping the eyepiece minimise the aberrations, correct? I have the impression it performs better with the 40x than with the 10x, this could explain it.

To fine tune parfocality I am using now a Nex-M42 helicoid, I may get a M42 helicoid for precise placement of the eyepiece; now I have to play with too many step up/down rings and those add 2mm or 3mm minimum
viktor j nilsson wrote:
Fri Mar 26, 2021 12:34 pm
Do you know of any visualizations of what the light path looks like when you raise the eyepiece this way?
I found this, should be similar to what a projection eyepiece does

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Re: Eyepieces, photoeyepieces and Teleconverters; what are the similarities and differences? Should we care?

Post by Pau »

rjlittlefield wrote:
Fri Mar 26, 2021 11:55 am
Again to clarify, this "tube length increase of 5 mm" is not the same tube length increase that is depicted in the classic graph titled "Tolerance to tube length change versus objective N.A."

In the case of a parfocal raised eyepiece, there is no change in the optical tube length as seen by the objective. The intermediate image will be just as free of spherical aberration, regardless of N.A., as it would be with a normal eyepiece used visually. The increase in spherical aberration with the raised eyepiece is entirely due to the eyepiece, and that increase will actually be less with a high NA, high magnification objective, due to the narrower light cones coming from the objective
Ichthyophthirius wrote:
Fri Mar 26, 2021 1:03 pm
...
this graphic shows common camera adaptations: https://www.mikroskopie-forum.de/pictur ... 766975.jpg
...
III: Refocussing (not recommended)
IV: Eyepiece projection (lifting eyepiece while maintaining the intermediate image location O')
...
I must recognize that I had not clear enough the difference between #III and #IV, cases.

Thanks Rik and Ichthy for the clarifications! I've not used this method since my student times, several decades ago.

So, if I have it now right you're only forcing the eyepiece optics to work outside its design. I guess that if your sensor size is wide enough you will have the eyepiece diaphragm out of focus when the sample image is in focus, am I right?

And... could be doable to use a macro lens in place of the eyepiece to capture the objective primary image?
Pau

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Re: Eyepieces, photoeyepieces and Teleconverters; what are the similarities and differences? Should we care?

Post by rjlittlefield »

viktor j nilsson wrote:
Fri Mar 26, 2021 12:34 pm
I'm trying to wrap my head around what's going on when you raise a normal viewing eyepiece but can't really figure it out on my own. But if I understand what you say, Rik, then if you move the camera away from the eyepiece just the right amount, and raise the eyepiece just the right amount, then you create a situation where i) the eyepiece still pick up the intermediate image at the original location (so you have basically increased the "working distance" of the eyepiece?); and 2) projects a real image at the sensor plane (instead of being focused at infinity as it would be if the eyepiece wasn't raised). Is this correct?
Yes, exactly.
seta666 wrote:
Fri Mar 26, 2021 3:17 pm
So, if the system is parfocal everything is OK on the objective end; however rising up the eyepiece will create spherical aberrations, maybe this is what I see on the binocular loupe eyepiece. Would be possible for an overcorrected eypiece to become kind of neutral when rising it?
Certainly possible. I have no idea whether any eyepiece is designed so that would happen in practice.
Would this also be the case with a teleconverter, if you could keep an image focused to infinity by changing the position of lens, TC and camera relationship?
In principle, yes, you can keep the objective from seeing any change. On quick study, it looks like you would need to move the teleconverter forward (less distance to front lens) while moving the camera sensor back (more distance from the teleconverter).
Do you mean the high f number is helping the eyepiece minimise the aberrations, correct? I have the impression it performs better with the 40x than with the 10x, this could explain it.
Yes.
Pau wrote:
Sat Mar 27, 2021 6:03 am
I guess that if your sensor size is wide enough you will have the eyepiece diaphragm out of focus when the sample image is in focus, am I right?

And... could be doable to use a macro lens in place of the eyepiece to capture the objective primary image?
Yes and yes.

I actually have used the macro lens approach in one difficult situation, where I wanted to capture a 100X NA 1.25 image that needed to form 10 mm inside the microscope tube and I didn't have the right equipment to work afocal. That is described in the thread at https://www.photomacrography.net/forum/ ... .php?t=835 . The note says "Olympus 80mm f/4 bellows macro used as 2.5X relay lens". The camera model is not recorded, but at that time -- 2006, almost 15 years ago now -- it would have been a 6.3 megapixel APS-C sensor, the original Canon EOS Digital Rebel.

--Rik

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Re: Eyepieces, photoeyepieces and Teleconverters; what are the similarities and differences? Should we care?

Post by seta666 »

rjlittlefield wrote:
Sat Mar 27, 2021 11:25 am
I actually have used the macro lens approach in one difficult situation, where I wanted to capture a 100X NA 1.25 image that needed to form 10 mm inside the microscope tube and I didn't have the right equipment to work afocal. That is described in the thread at https://www.photomacrography.net/forum/ ... .php?t=835 . The note says "Olympus 80mm f/4 bellows macro used as 2.5X relay lens". The camera model is not recorded, but at that time -- 2006, almost 15 years ago now -- it would have been a 6.3 megapixel APS-C sensor, the original Canon EOS Digital Rebel.
Thanks Rik for the clarifications; that last bit of information looks interesting, I may try the Canon 60mm 2.8 macro as a relay lens. As I remember the Canon 60mm changes focal length as it gets close to 1:1. Maybe I could get down to 1.5X with this set up.

EDIT: I have tried that with both Olympus 80mm and canon 60mm, I get a circular image, does not fill the frame (is this supposed to happen?). Adding 25mm extension to the 60macro almost fills the frame but there is still vignetting and corner quality is pretty bad

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Re: Eyepieces, photoeyepieces and Teleconverters; what are the similarities and differences? Should we care?

Post by JKT »

I wasn't too happy with EF-S 60mm either, though I tried it reversed as taking lens. The quality just wasn't there.

As far as black corners are concerned, it could be the tube lens or it could be your objective. In general, photographic lenses tend to vignette very easily. The entrance pupil is likely quite far inside. I thought that 135mm f/2 would not vignette easily, but it does.

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