Nikon CF Plan 50X 0.55 inf/- EPI ELWD, initial impressions

[morfa]

This objective was recently discussed in this thread.

I got one of these in the mailbox yesterday and thought I'd share some initial impressions.

First of all, here it is:


It's a regular RMS thread (and there is no hollow chamber in the barrel which the "EPI" designation might lead you to believe).

The first I did was to attach it to a Nikkor 200/4 (AI) mounted on a Canon 5DmkII. This is my first infinity objective and I have to say that looking at the tiny (5mm) exit pupil of the objective and then at the ten times bigger front element of the 200/4 I expected to get a black viewfinder with a pathetically small image circle in the middle.

I was equally surprised and puzzled by the fact that there was no vingetting at all. I'm hoping someone on this forum can help me understand: how on earth this can be the case?

I then tried mounting it on a Leitz Summar 12cm f4.5 since that one easily gives infinity focus on the bellows on my vertical stand. Again – no visible vingetting. I added a 1.4X in order to get closer to 200mm which I presume is the intended focal length for these objectives (?).

Then I shot a test stack: 92 exposures using flash with 1um increments and stacked using PMAX (1% X/Y alignment, 0 scaling and rotation.)



Original 21MP version available for download HERE

100% crops

CENTER:



UPPER LEFT:


EXTREME CORNER UPPER LEFT:


EXTREME CORNER LOWER RIGHT:


Summary: Considering the NA and the fact that it's used with a ≈170mm FL lens rather than a 200mm, on a fairly wobbly setup I think the performance looks promising. The 8.7mm WD is very manageable.

Thoughts?

(BTW: the seller still has 3 left @175$, eBay#170572870030)

[rjlittlefield]

Thoughts?

I think this is a strikingly good result, and I just bought one of the remaining lenses. Many thanks for the pointer!

This is my first infinity objective and I have to say that looking at the tiny (5mm) exit pupil of the objective and then at the ten times bigger front element of the 200/4 I expected to get a black viewfinder with a pathetically small image circle in the middle.

I was equally surprised and puzzled by the fact that there was no vingetting at all. I'm hoping someone on this forum can help me understand: how on earth this can be the case?

I sympathize with your surprise and puzzlement. I once spent two weeks trying to make sense of confusing results about apertures. The resulting article HERE may provide background information that helps you to understand.

In brief, you will get no vignetting if every point in the field of view has an unobstructed path through to the sensor. Obviously light from any point in the field can get through that small aperture at the rear of the objective. The question then is, can it finish getting to the sensor? This depends on the aperture in the rear lens. If the aperture in the rear lens is large enough and far enough forward, then it will not block any of the light and you will get no vignetting. But if the rear aperture is too far back, or is too small, then light headed for the corners will be blocked.

One way to think about this is to consider the rear lens by itself. Position your eye in front of the lens at a place that corresponds to a corner of the field of view, and look into the lens to see where the aperture is. Is the aperture large enough and far enough forward that it covers a small circle at the front center of the lens? If it does, then you will get no vignetting, because that's where the aperture of the objective will be.

... to get closer to 200mm which I presume is the intended focal length for these objectives (?)

Yes. As far as I know all Nikon infinity objectives are designed to be used with a 200 mm tube lens. If you use them with a shorter tube lens, then the magnification will be less and the image circle will be correspondingly smaller.

--Rik

[AndrewC]

I see that triggered the normal feeding frenzy - hopefully they went to people who will use them rather than treat them as investments

[RogelioMoreno]

John,

Thank you for the report, I went for mine and all are gone!

Rogelio

[Pau]

Sorry Rogelio, Rick and myself (and another one) were faster

Some sellers would be grateful to the skilled forum testers!

Thanks John for your test (and number...) The image looks impressive for this magnification. With a bit of correction of the lateral CA (PT lens) and a bit of USM it's near perfect!
21Mpx... Up to the border in a 5D MKII?

[morfa]

In brief, you will get no vignetting if every point in the field of view has an unobstructed path through to the sensor.

Rik, many thanks for your clues to understanding this – I will take a careful look at that article! I realize a large portion of my puzzlement is due to some very basic misconceptions with regards to optics and how an image is formed. Even though, from an intellectual standpoint, I am aware of these, it hasn't quite made it through to "the core" yet. If I just keep pounding my brain with correct notions I'm convinced some of it will rub off eventually.

I'm glad that a couple of these objectives ended up in the hands of active users of this forum and I look forward to seeing the results!

21Mpx... Up to the border in a 5D MKII

Yes. I did try on a 105/f4 Micro-nikkor as well. I didn't get any dark corners but magnified live view inspection revealed clearly reduced corner performance.

--

I'm curious as to why this objective is called "EPI" – any theories?

[rjlittlefield]

I'm curious as to why this objective is called "EPI" – any theories?

I notice that the objective is corrected for no cover glass. That normally implies dealing with an opaque subject, which implies front illumination. With 8.7 mm WD, it is possible to illuminate around the objective as you have done. But I'll bet that this objective is intended to be used with scopes that send illumination light down through the objective itself, using a beamsplitter arrangement. That would be a "brightfield episcopic" mode, hence the label EPI would make sense. It's just a theory, however. Aside from the description HERE, I've never read anything from Nikon about their labeling conventions.

--Rik

[larrynicks]

This objective is apparently for the Epiphoto inverted metallurgical scopes. With a slew of changeable beamsplitters/filters, they are capable of brightfield, darkfield, DIC, epi-fluorescence, and polarization. Brochures are available at the Nikon site:

http://www.nikon.com/products/instrumen ... /index.htm

[Joaquim F.]

The first I did was to attach it to a Nikkor 200/4 (AI) mounted on a Canon 5DmkII. This is my first infinity objective and I have to say that looking at the tiny (5mm) exit pupil of the objective and then at the ten times bigger front element of the 200/4 I expected to get a black viewfinder with a pathetically small image circle in the middle.

I was equally surprised and puzzled by the fact that there was no vingetting at all. I'm hoping someone on this forum can help me understand: how on earth this can be the case?

I then tried mounting it on a Leitz Summar 12cm f4.5 since that one easily gives infinity focus on the bellows on my vertical stand. Again – no visible vingetting. I added a 1.4X in order to get closer to 200mm which I presume is the intended focal length for these objectives (?).

Is a very good picture, you have tried the nikkor 200/4?
Given that you have used a 1.4X multiplier in this may be a prime 200mm lens can give better quality!
With a 20X/0.35 in the same 200/4 AI objective mounted in a DX sensor camera can add some cms between objectives without vignetting, can be very interesting to see how well it perform in a full frame camera!

best regards

Joaquim

[morfa]

Thanks for the "EPI info" Rik and Larry!

With Nikkor 200/4 AI on top of a Olympus CHK frame with the 50x in the turret:


Full size HERE

The turret and adapter increased the distance between the lens and the objecitve from 0.5cm to 5cm. This introduced dark corners when focused to infinity. Changing focus to the near limit of the Nikkor got rid of the dark corners and from magnified live view inspection I wasn't able to detect any significant drop in quality.

With this combo the performance seem more even across the frame but overall definition seem a little lower to me (I'm guessing this is because diffraction softening becomes more pronounced as magnification go up).

[Joaquim F.]

John, I think it's a very good image considering the file size and coverage.
In a DX camera you can frame just a couple of that scales!

Some adddional information about Infinity 45 CF Plans and Nikon Optiphot system found here:

http://www.capraoptical.com/products/ni ... tives.html

Best regards

Joaquim

[morfa]

Thanks for the link Joaquim! It indicates a DOF of 0.91um – so the 1um increments I used are perhaps a bit coarse.

/John

John, I think it's a very good image considering the file size and coverage.
In a DX camera you can frame just a couple of that scales!

Some adddional information about Infinity 45 CF Plans and Nikon Optiphot system found here:

http://www.capraoptical.com/products/ni ... tives.html

Best regards

Joaquim

[Pau]

Thanks Joaquim and John. In the CapraOptical site I think there is a mistake: Focal length (micrometers)

[Craig Gerard]

John,

Watching your adventures with interest.


Craig

[rjlittlefield]

Thanks for the link Joaquim! It indicates a DOF of 0.91um – so the 1um increments I used are perhaps a bit coarse.

That number seems a bit small.

Formulas at the microscopyu calculator HERE indicate a DOF of minimally 1.8 µm, using e=0.

Add to that, I'm not seeing any evidence of focus banding in your images. Are you?

--Rik

Added 10/11/2012: I just ran across this old issue for which I now know the answer. The capraoptical.com link is quoting single-sided DOF -- the maximum distance from perfect focus at which the objective will still be close to diffraction limited (less than 1/4-wavelength error across the aperture). This is exactly half the value computed by microscopyu for e=0, which gives double-sided DOF counting both in front and in back of the focus plane.