Strain free eyepiece

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75RR
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Strain free eyepiece

#1 Post by 75RR » Sun Jul 12, 2020 7:21 am

Have been toying (again) with direct projection using a 'raised' 12.5x kpl normal eyepiece, it is a little too much magnification so I would like to try using either a 10x or an 8x.

I would need to purchase one.

Is there any advantage to using a Strain free kpl eyepiece over a normal one as a projection lens?
Zeiss Standard WL (somewhat fashion challenged) & Wild M8
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Re: Strain free eyepiece

#2 Post by Hobbyst46 » Sun Jul 12, 2020 10:04 am

PM sent

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ImperatorRex
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Re: Strain free eyepiece

#3 Post by ImperatorRex » Sun Jul 12, 2020 11:07 am

Hi 75RR,
what do you consider as "normal" Eyepiece? Beside the KPL for Zeiss standards there have been "C" and "CPL" eyepieces. But image quality of the C or CPL type ocular will suffer, so certainly not recommended for a photo adaption.
So you would use KPL oculars. Since you do not use a Camera objective (relais optic) you will not need to worry on the exit pupil distance of the ocular, so it could be any KPL, not necessarily a KPL Br (for spectacles) or the wide field KPL W type oculars.

Actually I wonder what is the camera length / distance with your photo adaption? With a 125mm distance the magnification factor of a 10x Objective will be 5x. So still a lot of the intermediate image will be cropped on a APS-C DSLR chip?

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Re: Strain free eyepiece

#4 Post by 75RR » Sun Jul 12, 2020 11:22 am

Hi ImperatorRex, agree Kpl for the high NA objective corrections is the way to go.

By normal I meant not strain free. Just wondered if there was any advantage to using a strain free Kpl vs a non strain free Kpl.

As to the distance (eyepiece to camera sensor), I will have to get back to you on that.

I still have the camera attached to a tripod and due to limited space have to dismantle it after every use. I did not think to measure it.
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Re: Strain free eyepiece

#5 Post by ImperatorRex » Sun Jul 12, 2020 11:52 am

Hi 57RR,
not sure actually what you mean with strain free? You mean the KPL "pol" eyepieces? These eyepieces just have a "cross" inside and a "pin" at the barrel to match exact position into the fitting notch/slot at the tube of the tube head. But optically they are the same.

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Re: Strain free eyepiece

#6 Post by 75RR » Sun Jul 12, 2020 12:11 pm

ImperatorRex wrote:
Sun Jul 12, 2020 11:52 am
Hi 57RR,
not sure actually what you mean with strain free? You mean the KPL "pol" eyepieces? These eyepieces just have a "cross" inside and a "pin" at the barrel to match exact position into the fitting notch/slot at the tube of the tube head. But optically they are the same.
Had assumed they were strain free as they are designated pol. Good to know. Thanks :)
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Re: Strain free eyepiece

#7 Post by MichaelG. » Sun Jul 12, 2020 5:07 pm

Probably already widely known ... but this seems a good place to quote Zeiss:
.
As is the general practice today, the magnification of the eyepieces is indicated by a figure followed by " x ". Letters before the magnification mark the type of eyepiece. Since we manufacture only compensating eyepieces, such an identification would normally be superfluous. However, our eyepieces of higher power are so designed that they produce a flat field, which is not necessary for the low-power systems. The latter are therefore marked C (compensating eyepieces) to distinguish them from the former marked Kpl (compensating flat-field eyepieces).
.

Ref. http://www.science-info.net/docs/zeiss/ ... ystems.pdf __ [p40]

MichaelG.

.
Edit: There are some useful numbers on [p74]
Too many 'projects'

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Re: Strain free eyepiece

#8 Post by 75RR » Wed Jul 15, 2020 10:52 am

MichaelG. wrote:
Sun Jul 12, 2020 5:07 pm
Probably already widely known ... but this seems a good place to quote Zeiss:
.
As is the general practice today, the magnification of the eyepieces is indicated by a figure followed by " x ". Letters before the magnification mark the type of eyepiece. Since we manufacture only compensating eyepieces, such an identification would normally be superfluous. However, our eyepieces of higher power are so designed that they produce a flat field, which is not necessary for the low-power systems. The latter are therefore marked C (compensating eyepieces) to distinguish them from the former marked Kpl (compensating flat-field eyepieces).
.

Ref. http://www.science-info.net/docs/zeiss/ ... ystems.pdf __ [p40]

MichaelG.

.
Edit: There are some useful numbers on [p74]
The blurb on page 72 is more in line with what I had gathered about the difference between C and Kpl eyepieces:

"C-type eyepieces may be used in conjunction with simple types of objective. Objectives of higher correction should, if possible,
always be combined with Kpl eyepieces. This applies above all to the Planachromats and Planapochromats."
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Re: Strain free eyepiece

#9 Post by 75RR » Wed Jul 15, 2020 11:00 am

ImperatorRex wrote:
Sun Jul 12, 2020 11:07 am
Actually I wonder what is the camera length / distance with your photo adaption? With a 125mm distance the magnification factor of a 10x Objective will be 5x. So still a lot of the intermediate image will be cropped on a APS-C DSLR chip?
Remembered to measure the distance from the top of the eyepiece to the camera sensor. It is 52mm

Note that the the eyepiece is raised from its normal position in order to project a real image on to the sensor.

I found with the 12.5x Kpl eyepiece that 10mm gave a satisfactory magnification.

Sensor size is 17.3mm x 13mm
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Re: Strain free eyepiece

#10 Post by ImperatorRex » Wed Jul 15, 2020 4:04 pm

Hello 75RR,
75RR wrote:
Wed Jul 15, 2020 11:00 am
Remembered to measure the distance from the top of the eyepiece to the camera sensor. It is 52mm
I personally do not have any experience with lifting up the ocular for direct projection to the camera sensor. I only have read the following advise (tried to translate from german):
"(Optical camera length = Distance between „exit pupil“ above the ocular to the Camera sensor). Distance shall be at least 125mm or even more because otherwise the sphaerical aberation errors may get larger."

I understand that you keep the distance shorter because to reduce the magnification to fit better to the camer sensor.
I guess even with Ocular 8x and optical camera length of 125mm the magnification will be quite large for the sensor size.
(mangification is 4x with camera length of 125mm but the optimal fit for the sensor would be 1,2x if I calculated correctly).

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Re: Strain free eyepiece

#11 Post by 75RR » Wed Jul 15, 2020 5:12 pm

ImperatorRex wrote:
Wed Jul 15, 2020 4:04 pm
Hello 75RR,
75RR wrote:
Wed Jul 15, 2020 11:00 am
Remembered to measure the distance from the top of the eyepiece to the camera sensor. It is 52mm
I personally do not have any experience with lifting up the ocular for direct projection to the camera sensor. I only have read the following advise (tried to translate from german):
"(Optical camera length = Distance between „exit pupil“ above the ocular to the Camera sensor). Distance shall be at least 125mm or even more because otherwise the sphaerical aberation errors may get larger."

I understand that you keep the distance shorter because to reduce the magnification to fit better to the camer sensor.
I guess even with Ocular 8x and optical camera length of 125mm the magnification will be quite large for the sensor size.
(mangification is 4x with camera length of 125mm but the optimal fit for the sensor would be 1,2x if I calculated correctly).
See step 1-B of Charles Krebs pdf: http://krebsmicro.com/parfocal/index.html
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Re: Strain free eyepiece

#12 Post by ImperatorRex » Wed Jul 15, 2020 5:49 pm

Procedure is very intuitive and well described by Charles.
And since the result of your camera setup seems to work very well, the shorter camera distance seems not really to be an issue obviously.
It is funny...if you like it difficult and complex you could calculate the lift-off distance for the oculares.
Formula is provided on page 149 (with reference to the sketch d) page 146) in the following document: https://www.mikroskopie-forum.de/pdf/mikrofibel.pdf (sorry it is in german language)

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Re: Strain free eyepiece

#13 Post by 75RR » Wed Jul 15, 2020 6:19 pm

Thanks.

I think this is the relevant part:
The necessary extensions for a camera length of 125 mm are: for an eyepiece 6.3 x → 12.6 mm; 8 x → 8 mm; 10 x → 5 mm; 12.5 x → 3.2 mm; 16 x → 2 mm.
For other camera lengths, the necessary extension of the mechanical tube length (amount of eyepiece lift) is calculated as follows:
∆ t m = f 2 ok: k.
Dtm = f2Ok: k.
f is the focal length of the eyepiece. It is calculated by dividing the reference field of view of 250 mm by the eyepiece magnification. A 12.5x eyepiece therefore has a focal length of 20 mm.
k is the optical camera length that is measured, as explained under 2.1.
The lifting rings I have go up in 2.5mm increments but will try to approximate 3.2mm to see at what height the camera is in focus.
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Re: Strain free eyepiece

#14 Post by Voyager-1 » Mon Mar 29, 2021 10:21 am

Just in case anyone else wants to know!
I just wanted to know what was meant by "Strain Free Eyepieces". Strain Free kept being mentioned.
Could not find the answer in the thread of the discussion...
So did a search and found out that:

It is not a strain of bacteria or fungus found on glass! But stress induced on the glass from
incorrect annealing temperature cooling down time, inducing chromatic aberration, what a revelation!!

http://www.public.asu.edu/~aomdw/GSI/Glass_Strain.html

Also learned what KPL eyepieces are. Also, an assortment of other abbreviations for eyepieces.

http://microscopy.berkeley.edu/courses/ ... ieces.html

Love the discussion, just got lost in the lingo!

V

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Re: Strain free eyepiece

#15 Post by Placozoa » Tue Mar 30, 2021 10:40 am

If you stretch a piece of plastic it puts strain in the plastic. This piece of plastic then operates as a (very cheap) polarising lens. Thats how movie 3D glasses work. By the same token, if you are not careful manufacturing your lenses you can introduce strain. This doesnt matter, since you cant see polarisation, until you are using polarised light or DIC (need strain free objectives). Then it does matter.

Presumably camera sensors can see polarization, Im guessing..

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Re: Strain free eyepiece

#16 Post by Greg Howald » Tue Mar 30, 2021 12:28 pm

I can notice a dimming effect and a change in focal length when using a single polarizer. And yes, there are cameras sensitive enough to tell you it is there. Cameras are generally much more sensitive than the human eye making them worthy of the science behind them.
Greg

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