Nikon CF N 10/0.30 Plan Achromat. Phase vs BF version

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Charles Krebs
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Nikon CF N 10/0.30 Plan Achromat. Phase vs BF version

Post by Charles Krebs »

Eric F was wondering how the phase contrast version of the Nikon CF N 10/0.30 would compare with the non-phase version when used on a bellows. I really didn’t know, but he asked the question at exactly the right time… I was just about to do a few “tests” on some other lenses and I do have both objectives he was asking about.

So I took a look and here’s what I saw comparing a phase version of the CF N 10/0.30 Nikon with a brightfield version. The brightfield Nikon CF N 10/0.30 Plan Achromat produced a slightly better stack. Not by a huge amount, but it was noticeable, especially toward the edges. I’m always leery to judge by the stacked images so I compared similar individual frames and the conclusion was the same. I can’t say if this is simply a lens “sample” variation or whether it is due to the presence of the phase ring.

One thing I did notice, that was obviously due to the phase ring, was the appearance of out-of-focus areas. Now I realize that “bokeh” is not a concept used too often by us stackers :wink: , and since the software will select the sharp sections most of these OOF section will be ignored. (There will be some pictures with large OOF areas where this could be an issue). But it does make me wonder if the phase ring is also having a subtle effect on the “in-focus” areas as well.

If I already owned only the phase I would certainly use it. Both are capable of producing great looking images. But if I were looking for an objective with the primary purpose of putting it on a camera bellows I would probably skip the phase version and keep looking until I found the brightfield.

This subject was chosen only as a “test” (not intended to be a pretty picture!). Both images treated exactly the same. Slight sharpening after resizing, and that’s all.


brightfield objective
Image


phase objective
Image


part of single image from stack. Phase (top), brightfield (bottom)
Image

Eric F
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Nikon CF N 10/0.30 Plan Achromat. Phase vs BF version

Post by Eric F »

Thanks Charles. Your comparison of the CF N 10/.30 versions is very interesting. I am a little puzzled by the single image shots though...
I think for a CF N 10/.30 I will wait for BF only. I do have several other objectives in this magnification -- including an Olympus 10/.30 S Plan (which I'm disappointed in, as it seems to be outperformed by some Leitz 0.25 Achros I have).

Cheers, Eric

Charles Krebs
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Post by Charles Krebs »

Eric,

The single images are sections taken from one of the frames used for the stack. I chose the frames that had the same focus point for each objective for comparison. You can see the section used here:

Image

The subject was very "wavy". The high point was the left side of the indicated section, the low point was the right side. (Sometimes you can learn quite a bit about an optic by looking at OOF parts). So when I chose the frame that was in focus on the right side, the left potion was greatly out of focus.

In these sections the small, bright points where the scales attach to the wing are grossly OOF. In the upper image you can see clearly how the phase ring is clearly echoed in each of these OOF "points". (This is exactly the type of thing that is seen with "mirror" telephoto lenses where OOF points turn in "doughnuts" of light). In the lower section these points are images as overlapping solid white circles.

Eric F
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Nikon CF N 10/0.30 Plan Achromat. Phase vs BF version

Post by Eric F »

Ah, yes, now I see; amazing! Charles -- thanks very much for explaining that to me, as I was completely misinterpreting it (even thinking that perhaps the legends for the two shots had been switched...).

Eric

bvalente
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Post by bvalente »

Hi Charles

i've seen several mentions (including your website) of mounting the microscope objectives directly to the dslr body via bellows.

Can you elaborate on your setup? From your previous setup pictures I assume you have it in a vertical orientation on your copy stands, and I would guess you have some sort of RSM-to-nikon f-mount type of adapter.

Also When you take the images for stacking, how do adjust focus without too much disruption? I would love to be able to work without my labophot 2 as well, but haven't really figured out a good reliable approach to adjusting focus for stacking

Cheers

Brian

rjlittlefield
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Post by rjlittlefield »

Brian, see the FAQ: What's the best way to focus when stacking?. Look at the setup by NikonUser, and follow the links to the setups by rjlittlefield and AndrewC.

The common theme in all these setups is that either the camera or the subject is mounted on a screw-driven table, linear stage, or microscope focus block capable of making small movements.

Horizontal versus vertical is not very important, except that it is often simpler to make a setup rigid if it is horizontal. Some rigs can be tipped to operate horizontal, oblique, or vertical (as HERE), which aids a little in positioning some specimens if you don't want to glue or pin them.

Yes, you need an RMS adapter to fit whatever bellows you have. These are commercially available for many mounts, or they can be made fairly easily from a body cap if you have access to machining tools.

--Rik

Charles Krebs
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Post by Charles Krebs »

Brian,

I'm a big fan of using coaxial (coarse/fine focus) microscope focus blocks. I also like the lighting access to the subject that a horizontal set-up provides. There's a huge amount of info on this forum... probably more than any other spot on the web.

My set-up is considerably different now, but you can see the Olympus focus block that I still I use here:
http://www.photomacrography.net/forum/v ... php?t=2825

Also take a look here:
http://www.photomacrography.net/forum/v ... php?t=6070

rjlittlefield
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Post by rjlittlefield »

Thanks for the links, Charlie. I added those to the FAQ as well.

--Rik

enricosavazzi
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Post by enricosavazzi »

It would seem that the bokeh of a phase objective is partly comparable with the "nisen bokeh" produced by catadioptric telephoto lenses, in which the secondary mirror is equivalent to a centre stop (the phase ring is clearly visible in the bokeh of OOF highlights).

I should expect that diffraction in a phase objective is slightly higher - the edges of the phase ring more than double the total length of the objective aperture edge, and it is near opaque edges that light is diffracted instead of refracted. In addition, the phase ring should also slightly lower the effective lens aperture.

If I remember correctly, Nikon partly solved this problem of increased diffraction by using a gradual transition (a partial mirror) between transparent and opaque areas along one or both edges of the phase ring, matched by a corresponding phase condenser. I don't have any reference to this.
--ES

bvalente
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Post by bvalente »

Thanks all - sharing of your setups is extremely helpful.

I have all the parts including the RMS adapter, so it's good to see the path ahead is clear.

I have had some moderate success with my micro/bellows setup (peach blossom):


Image

I am looking to go a little more micro, and the only last missing part seems to be the ability to finely adjust focus without disturbing the whole setup.

It seems the microscope focus block is really the key here and I'd be interested in folks' thoughts on this. I have looked at linear stages, but none seem to offer the same ergonomics, markings, and precision combination the focusing blocks do. They are just hard to find!

Cheers

Brian

Charles Krebs
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Post by Charles Krebs »

Brian,

A key thing to keep in mind is that ideally you really want at least two ranges of focus movement. The very fine movement needed for the individual steps, and a coarser movement to get things set up.

There are many ways to do this, but the beauty of the right microscope focus mechanism is that you have, in the same unit, two ranges that are coaxial, smooth and accurate. Also, due to the nature of the fine focus mechanism (on many, but not all microscope "blocks") you never have to "back off" the fine focus many turns to get back to the starting position, as is necessary with micrometer drives.

A linear stage, like those made by Newport and others, works well for the fine adjustment (if set-up with the right micrometer drive) but will require a coarse method as well. The overall focus on a good camera bellows can usually handle this job OK. (You can see a simple implementation of such an arrangement here:
http://www.photomacrography.net/forum/v ... php?t=6290

bvalente
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Post by bvalente »

Hi Charles

yes I agree - it's only that finding a microscope focus block isn't that easy :)

I opted short term for a couple of Newport linear stages to experiment with for the fine focus (hoping they will be fine enough for the stacking I expect to do) and the PB-6 bellows will have to be my coarse for now.


Thanks again for all the input.


Cheers

Brian

mgoodm3
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Post by mgoodm3 »

I recently tested a 4/0.13 Phase objective and was a little disappointed in the results. Did not perform quite a well as other 4x objectives I have. Performed on par with an Oly 38/2.8 bellows lens which it should outperform.

lothman
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Re: Nikon CF N 10/0.30 Plan Achromat. Phase vs BF version

Post by lothman »

Charles Krebs wrote:Eric F was wondering how the phase contrast version of the Nikon CF N 10/0.30 would compare with the non-phase version when used on a bellows.
Currently there is a phase contrast version on ebay.

bklein
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Post by bklein »

I've never personally seen/used a phase objective. Does this phase ring interfere with the normal overall image? Some things I've read make it seem like it is visible (around the periphery?). Funny how the phase ring artifacts become so apparent once you pointed them out but I was ok with them at first.

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