Stereo microscope photo port projection lens not parfocal with eyepieces

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ClassMSpecie
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Stereo microscope photo port projection lens not parfocal with eyepieces

#1 Post by ClassMSpecie » Sat Nov 06, 2021 5:00 am

Hello All,

I can't make my stereo microscope's photo pot optical path and eyepieces parfocal to each other. I can raise the eyepiece height a bit by adjusting the diopter to make the eyepieces parfocal with the photo port's optical path, but this makes the continuous zoom range not parfocal to each other. I have a CF PL5X projection lens on the photo port, but currently don't know a way to vary the distance between the projection lens and the photo port. I can easily vary the distance between my camera sensor to the projection lens, but that does not solve this eyepiece to projection lens parfocal problem.

Any input would be much appreciated.

ClassMSpecie
Last edited by ClassMSpecie on Thu Dec 23, 2021 4:57 pm, edited 1 time in total.

Scarodactyl
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Re: Stereo microscope photo port projection lens not parfocal with eyepieces

#2 Post by Scarodactyl » Sat Nov 06, 2021 3:59 pm

Which stereo microscope do you have?

ClassMSpecie
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Re: Stereo microscope photo port projection lens not parfocal with eyepieces

#3 Post by ClassMSpecie » Sat Nov 06, 2021 6:16 pm

It's a Nikon SMZ-U with a trinocular module add-on. I read somewhere that removing a lens in front of a prism would create infinity optics, but I can't entertain a super long photo tube. I'd prefer to use a projection lens.

Thanks.

ClassMSpecie

Scarodactyl
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Re: Stereo microscope photo port projection lens not parfocal with eyepieces

#4 Post by Scarodactyl » Sat Nov 06, 2021 7:43 pm

That is odd. I have set one up with a pl 2.5xa and it was dead on parfocal just like you'd expect. The 5x is a bit of an unusual choice, and it's the only one I haven't tried--any particular reason for that one? The 8x and 10x pl eyepieces are actually not projective and are meant to be used afocally, not sure about the 5x though.

ClassMSpecie
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Re: Stereo microscope photo port projection lens not parfocal with eyepieces

#5 Post by ClassMSpecie » Sun Nov 07, 2021 6:46 am

It came with the unit. At first glance, I thought I can use it with a wee 1/3" sensor camera for video. With my DSLR, the mag is too much; I need lower mag like 2.5x. Did you have to raise the eyepieces just a tad bit to make it parfocal or do your eyepieces sit flush (all the way down) inside eyepiece tubes?

Thank you.

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Last edited by ClassMSpecie on Thu Dec 23, 2021 4:59 pm, edited 1 time in total.

Scarodactyl
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Re: Stereo microscope photo port projection lens not parfocal with eyepieces

#6 Post by Scarodactyl » Sun Nov 07, 2021 8:42 am

The 2.5x sitting flush in the camera port produced a parfocal image when the camera was the right height above it.
Honestly I would ditch the 5x and get a pl 2.5xa or a pli 2.5x (if you can find the 23mm variant, not the 30mm). The original pl 2.5x doesn't perform very well, at least from what few copies I have tested.

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Re: Stereo microscope photo port projection lens not parfocal with eyepieces

#7 Post by MichaelG. » Sun Nov 07, 2021 8:51 am

I am pretty sure that the 5x projection lens was intended to cover either Polaroid or 5x4 sheet film.

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ClassMSpecie
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Re: Stereo microscope photo port projection lens not parfocal with eyepieces

#8 Post by ClassMSpecie » Sun Nov 07, 2021 11:09 pm

Ok, thanks. I"ll research more on the pl 2.5xa and pli 2.5x lenses.
Last edited by ClassMSpecie on Thu Dec 23, 2021 5:00 pm, edited 1 time in total.

jpl
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Re: Stereo microscope photo port projection lens not parfocal with eyepieces

#9 Post by jpl » Mon Nov 15, 2021 5:43 pm

What is the right distance from the top of the PLI lens to the image plane(sensor level)? Have tried to find some info but have not yet

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Re: Stereo microscope photo port projection lens not parfocal with eyepieces

#10 Post by Scarodactyl » Mon Nov 15, 2021 9:01 pm

I think somewhere in the neighborhood of 180mm, based on measuring my DI adapter.

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Re: Stereo microscope photo port projection lens not parfocal with eyepieces

#11 Post by MichaelG. » Mon Nov 15, 2021 9:13 pm

jpl wrote:
Mon Nov 15, 2021 5:43 pm
What is the right distance from the top of the PLI lens to the image plane(sensor level)? Have tried to find some info but have not yet
.

It doesn’t actually answer your question, but … Looking at the system diagram on the final page of this : http://www.tsn.org.uk/KC/teachers%20not ... 0notes.pdf

is rather scary :o
.
Note the reference to H-III
Note the reference to H-III
96314531-AC46-4979-BF83-9DC00E1B724A.jpeg (66.67 KiB) Viewed 7142 times
.

Try a google [images] search for nikon hiii

.
Here’s one configured for large format: https://www.labx.com/item/nikon-h-iii-p ... escription
… but there are also 35mm versions

MichaelG.
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Too many 'projects'

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Re: Stereo microscope photo port projection lens not parfocal with eyepieces

#12 Post by jpl » Mon Nov 15, 2021 11:06 pm

Scarodactyl wrote:
Mon Nov 15, 2021 9:01 pm
I think somewhere in the neighborhood of 180mm, based on measuring my DI adapter.
Ok that was quite long distance. I found some data for the 1x TV projection lenses, they seems to have 71mm from the top of the lens to the image plane. Do you know if the differnt projection lenses have different image plane distances? Like the 2x, 2.5x, 5x….

Would be nice to find a similar spec/drawing for the PLI 2.5x

5754E32A-8771-4678-A1D4-E0212F4F67F7.jpeg
5754E32A-8771-4678-A1D4-E0212F4F67F7.jpeg (77.29 KiB) Viewed 7222 times
Last edited by jpl on Tue Nov 16, 2021 10:11 am, edited 1 time in total.

Scarodactyl
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Re: Stereo microscope photo port projection lens not parfocal with eyepieces

#13 Post by Scarodactyl » Tue Nov 16, 2021 1:45 am

The 1x is different from the others, yeah.

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Re: Stereo microscope photo port projection lens not parfocal with eyepieces

#14 Post by patta » Tue Nov 16, 2021 9:36 am

I have the PLI 4 ; measured/estimate
eye relief 23mm (distance to aperture)
barrel height from tube 42.5

distance to cover full frame sensor: 128 mm +(23 + 42.5) = 193.5 mm
distance to cover aps-c: 78mm + (23 + 42.5) = 143.5 mm
This distance is like the 115mm in the drawing above, tube-to-image
When projecting at different distances, yes also the intermediate image is moved upwards by a few mm, and that #%%## up parfocality

the 115mm may be the right distance to cover a 1" sensor , with intermediate image exactly where should be, where the eyepiece field stop is.
You can try to put your camera nearer, at those 115mm, won't cover the whole sensor but may fix the parfocality issue.

One way to understand something:
remove the camera, turn lights on
use a piece of paper over the projection eyepiece; move it up and down until the projected light circle has sharp border
that is its "design projection distance"
if it is 115mm, yeah, maybe is where your sensor should be and with some luck is also the parfocal distance.

My PLI4 seems to do this at the 200 ~193 mm, so guess was designed for full-frame film.
I have APS-C, and if I mount it nearer so to get max field, parfocality is ##### up.
but then, put a spacer to raise the eyepiece some 3 mm, parfocality back in business.

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Re: Stereo microscope photo port projection lens not parfocal with eyepieces

#15 Post by Scarodactyl » Tue Nov 16, 2021 2:50 pm

Moving the eyepiece out of position to change the size of the image will have an effect on the image. It will be parfocal when set up correctly.

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Re: Stereo microscope photo port projection lens not parfocal with eyepieces

#16 Post by jfiresto » Tue Nov 16, 2021 4:11 pm

Scarodactyl wrote:
Tue Nov 16, 2021 2:50 pm
Moving the eyepiece out of position to change the size of the image will have an effect on the image....
As in, degrade the image / add aberrations?
-John

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Re: Stereo microscope photo port projection lens not parfocal with eyepieces

#17 Post by Scarodactyl » Tue Nov 16, 2021 4:21 pm

Yes, to some extent anyway, since the optics are being pushed out of spec in a way they typically don't appreciate. It may or may not cause a problem for a given usecase, but it is something to be aware of.

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Re: Stereo microscope photo port projection lens not parfocal with eyepieces

#18 Post by viktor j nilsson » Tue Nov 16, 2021 4:41 pm

jfiresto wrote:
Tue Nov 16, 2021 4:11 pm
Scarodactyl wrote:
Tue Nov 16, 2021 2:50 pm
Moving the eyepiece out of position to change the size of the image will have an effect on the image....
As in, degrade the image / add aberrations?
Here's the only decent test of this that I can thing of:
https://www.krebsmicro.com/NFK_lowermag/index.html

Not the same eyepiece, but the principle is the same

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Re: Stereo microscope photo port projection lens not parfocal with eyepieces

#19 Post by viktor j nilsson » Tue Nov 16, 2021 4:49 pm

The CF PL and PLI eyepieces are designed to be used with 202.5mm from the shoulder to the image plane.

This is according to Azuma Kosall and verified by several others in the Nikon microscope user group on Facebook when I asked about it a couple of years ago.

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Re: Stereo microscope photo port projection lens not parfocal with eyepieces

#20 Post by jfiresto » Tue Nov 16, 2021 5:24 pm

viktor j nilsson wrote:
Tue Nov 16, 2021 4:41 pm
jfiresto wrote:
Tue Nov 16, 2021 4:11 pm
Scarodactyl wrote:
Tue Nov 16, 2021 2:50 pm
Moving the eyepiece out of position to change the size of the image will have an effect on the image....
As in, degrade the image / add aberrations?
Here's the only decent test of this that I can thing of:
https://www.krebsmicro.com/NFK_lowermag/index.html

Not the same eyepiece, but the principle is the same
Thank you. That was quite interesting and suggests what to watch out for when you image out of position.
-John

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Re: Stereo microscope photo port projection lens not parfocal with eyepieces

#21 Post by jpl » Tue Nov 16, 2021 8:33 pm

Thanks for the helpful replies.
viktor j nilsson wrote:
Tue Nov 16, 2021 4:49 pm
The CF PL and PLI eyepieces are designed to be used with 202.5mm from the shoulder to the image plane.

This is according to Azuma Kosall and verified by several others in the Nikon microscope user group on Facebook when I asked about it a couple of years ago.
Just to confirm, the 202.5mm would correspond to the 71mm for the 1x lens in the picture above?

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Re: Stereo microscope photo port projection lens not parfocal with eyepieces

#22 Post by viktor j nilsson » Tue Nov 16, 2021 8:41 pm

jpl wrote:
Tue Nov 16, 2021 8:33 pm
Thanks for the helpful replies.
viktor j nilsson wrote:
Tue Nov 16, 2021 4:49 pm
The CF PL and PLI eyepieces are designed to be used with 202.5mm from the shoulder to the image plane.

This is according to Azuma Kosall and verified by several others in the Nikon microscope user group on Facebook when I asked about it a couple of years ago.
Just to confirm, the 202.5mm would correspond to the 71mm for the 1x lens in the picture above?
No, the 115mm.

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Re: Stereo microscope photo port projection lens not parfocal with eyepieces

#23 Post by Scarodactyl » Tue Nov 16, 2021 9:49 pm

Oh yeah, my measurement was from the top of the eyepiece rather than the shoulder. I'd recommend using extension tubes with a helicoid so you can finely adjust the position of the camera to get exact parfocality anyway.

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Re: Stereo microscope photo port projection lens not parfocal with eyepieces

#24 Post by ClassMSpecie » Wed Nov 17, 2021 4:22 am

Yeah, raising eyepiece height will not make zoom ranges parfocal, so that's is not recommended.

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Re: Stereo microscope photo port projection lens not parfocal with eyepieces

#25 Post by jpl » Sun Nov 21, 2021 3:37 pm

I tried the setup with the PLI 2.5x using the 202.5mm from shoulder of lens to image plane, posted an update in this thread.

viewtopic.php?f=9&t=8710

When compared to direct projection the viewalble diameter becomes roughly 1.8 times less (is using a SONY and Canon apps-c, sensor sizes is slightly different, but will still give 1.8). I thought the difference should be 2.5. How do you calculate the increase in image size? Have I got it wrong?

When using direct projection I dont get any vignetting and the diagonal of the Canon aps-c sensor is 27mm, so I guess the diameter of the image is somewere 28-30mm at the image plane. If you take this times 2.5, you get an image diameter of 75mm, much larger than the 43mm diagonal for a full frame sensor.

Or is the PLI lens cropping the image, the input diameter on the PLI lens is only about 20mm. Taking this times 2.5 gives 50mm close to the 43mm of the full frame. Anyone know if this is what is happening, and if so, why is the photo port limiting the image that much.

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Re: Stereo microscope photo port projection lens not parfocal with eyepieces

#26 Post by viktor j nilsson » Sun Nov 21, 2021 4:04 pm

Not sure what "1.8 times less" means in this context.

Using a stage micrometer, it would help to know 1) how wide is the field (in mm) that you see through the viewing eyepieces with 10x eyepieces at low magnification; 2) how wide is the field with direct projection; 3) how wide is the field with the 2.5x PLI; 3) are both photographic setups exactly parfocal with the viewing eyepieces? And 4) does the view through the viewing eyepieces remain sharp when you zoom to a higher magnification?

Any deviation from perfect parfocality (and thus, tube length) can really throw off the magnification from that expected.

Edit: forgot it was a stereo microscope, edited to make more sense :D

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Re: Stereo microscope photo port projection lens not parfocal with eyepieces

#27 Post by jpl » Sun Nov 21, 2021 4:36 pm

I think i did a misstanke in the calculations, the 1.8 times refered to the difference in field of view (diagonal) between direct projection and using the projection lens. In the measurements below it becomes around 2.5.

Here is the different measurements, all data in parfocal mode.

1) 33mm diameter (through 1 eyepiece)
2) 31x19mm (diagonal 37mm) no vignetting
3) 13x8mm (diagonal 15mm) no vignetting
4) Yes all through the zoom range.

Measured the distance from the top of the beam splitter port to the shoulder of the PLI lens and the lens shoulder sits 39mm above, that is 10mm above the image plane. When using direct projection, the sensor sits 29mm above the top of the beam splitter port, and is parfocal. Since I dont get any vignetting and the sensor diagonal is 27mm the image diameter must be more than that.

When the PLI lens is inserted the lens tube at 29mm above the beam splitter port, is only 19.8mm internal diameter (23.2mm external). Am I right in assuming that the available picture diameter the PLI lens can project is then only 19.8mm out of 28-30mm available.

Any idea why the projection lens / photo port design limits the image area that much?
Last edited by jpl on Sun Nov 21, 2021 8:01 pm, edited 1 time in total.

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Re: Stereo microscope photo port projection lens not parfocal with eyepieces

#28 Post by Scarodactyl » Sun Nov 21, 2021 7:02 pm

Yes, the photo eyepiece crops the FoV on top of resizing. This is a common and frustrating issue with basically all microscope makers--many of them make optics that cover large or even huge FoVs with good quality and thrn have no official way to take advantage of it. The reason is probably that they make objectives with smaller good fields as well (ie, nikon plan s fluors are only rated to 22mm) and it's easier to design a system that works for all of them than to maximize the performance of their best systems in photography.

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Re: Stereo microscope photo port projection lens not parfocal with eyepieces

#29 Post by jpl » Sun Nov 21, 2021 8:59 pm

Ok, that might very well be one reason.

So it seems using direct projection with aps-c for a SMZ-U or similar system seems like the best option.

What would be the reason for using projection lenses today? Get a cropped picture, less camera pixel resolution needed?

Have also tried finding information on what camera resolution is needed for APS-C camera sensor to match the SMZ-U system resolution with 1x ED plan optics. Most information I have found on how to calculate needed resolution seems to cover compond microscops, very little about how to calculate for stereo zoom microscopes.

Would like to understand what is needed for these two cases(with sensor at its intended image plane):

1) Direct projection on to APS-C sensor

2) Using 2.5x projection lens onto APS-C sensor.

What resolution is needed for the two cases and how to calculate it, taking objective, zoom optics, beam splitter optics and optionally projection lens optics inte account. Cloud anyone help explain how to figure out what is needed?

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Re: Stereo microscope photo port projection lens not parfocal with eyepieces

#30 Post by Scarodactyl » Sun Nov 21, 2021 11:00 pm

The ED plan 1x probably has an NA around 0.1 (but stopped down to lower resolution at lower mags, and likely lower at the image periphery particularly beyond the 24mm spec). That would typically translate to about 300 lp/mm of resolution on subject. At the max mag of 7.5x that translates to an approximately 3mm horizontal fov on aps-c, so about 900 lp or 1800 lines/pixels in very approximate terms. Long story short it isn't a very high res system (as stereos generally aren't, even excellent ones) and 18mp is likely getting every drop of good image out of it with direct projection, even taking bayer sensor stuff etc etc into account.

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