AF motor focusing with a microscope objective

[rjlittlefield]

excellent test, thanks for posting it. I will try it some day with my 70-200.

I will be interested in the results. One of the tradeoffs is that the 100 mm macro gives away some magnification, but it will focus much closer than the 70-200 mm. I rechecked, and the stack I shot first in this thread ended up with the 100 mm macro focused only about 2 feet beyond the end of the lens. This was well within the range where the 10X NA 0.25 objective was still sharp. So, I think that the 70-200 will not have enough focus range to fully exploit the capabilities of that objective, but for subjects where it does have enough range, the extra magnification will probably give a better image.

--Rik

[Joaquim F.]

It's a very interesting setting for Studio and stack outside.
I tried it with the Nikon D300, micro-nikkor 105/2.8 D AF and Nikon Camera Control Pro ... and the Canon system is much better.
To access to focus adjustment control is necessary enter in LiveView mode and there the problems begin. I can not shoot while in LiveView mode and mirror-lockup, error message appears saying that it needed a standard S, C or "Quiet" mode and my camera don't have the last.
The focus adjustment has 5 different settings and the minimum "jump" is enough to stack correctly at aprox. 5X f/10.5 with this combination.
My lens has more than 10 years of use and has lost accuracy in focus mechanism. They are lateral movements of the image by changing from one direction to another which I imagine is something like the Backlash of microscope stands.
The AF control with this objective is entirely mechanical through the bayonet AF screw, probably the Nikon AF-S and Canon Eos lens work better.
I have to try the 70-300 VR to see that it works. Like the canon 55-200 in this Rik post: http://www.photomacrography.net/forum/v ... php?t=9664 vignetting appear if the lens is set to less than 200mm focal length in a DX sensor camera.
The vignetting seen with the Canon 100 L at 0.5 meters focus must be produced in part by focal reduction at close distances like in Micro-Nikkors and others IF lens?

Regards

[rjlittlefield]

The vignetting seen with the Canon 100 L at 0.5 meters focus must be produced in part by focal reduction at close distances like in Micro-Nikkors and others IF lens?

I guess. I'm not sure how to think about this. Looking into the front of the lens, I see the entrance pupil move backward and get bigger at closer focus. Obviously it doesn't get enough bigger to compensate for moving backward, in terms of playing nicely with the objective's aperture. But I have no idea whether this would be true for all IF lenses. Maybe it's very specific to the lens design and works the other way for some other lens.

--Rik

[Charles Krebs]

Rik,

Great conversation.

Your experience with the 50X is similar to something occasionally encountered on the microscope.

Essentially, the right side of the focused region was shot with a lot better optics than the left side was.

You can see the same thing on a microscope with a very thick rounded subject (such as an amoeba test or certain radiolarians) when using a high NA 20X or 40X. When you start the stack, the top of the subject (right up against the cover slip) is very sharp. As you run the stack down deeper to parts that are away from the cover slip, it is possible to see a degradation of image quality as the amount of water between the cover slip and the subject increases. (Due primarily to the increase in spherical aberration).

[malpertuis]

Hi everybody,

Very interesting post ! I want to try such method using a Sigma 105 mm macro on Eos70D body (APS-C sensor) in the aim to overload X2 magnification reached by DCR250. But what kind of microcope lens to use ? Plan Apo X5 or X10 finite or infinite lens ? Directly on 105 lens or mounted after 105+DCR250.
I want to reach higher magnification range than here :
https://www.flickr.com/photos/worldwide ... Bir-nvHvN9
But using USM focusing to avoid mechanical vibrations.
Thanks for your attention.

[ChrisR]

You can't use an objective on a macro lens with a Raynox (type) as well.
The thread which gives you almost all the information you seek is
How do I hook up a microscope objective to my camera?

You will find that you can only push the focus "so far" using the camera lens with an infinite objective. It may or may not be enough for your purposes.
Best objectives are still arguably the Mitutoyo plan apos, 5x and 10x, for your needs.
You can't do in-camera focusing at all, with finite objectives.
There have been many threads since the one to which you are replying; some searching should find more results.

[malpertuis]

Thanks for this reply. So I understand I have to choice an infinite plan apo objective directly mounted on my 105 macro.
So a Mitu X10 should give something like X5 enlargment ratio ?
But what about internal focusing ? I thinked the rear objective should be imperatively set on infinity for good working of the infinitive lens. Wrong ?

[rjlittlefield]

I thinked the rear objective should be imperatively set on infinity for good working of the infinitive lens. Wrong ?

Yes, wrong.

As the rear lens is focused away from infinity, some amount of aberration is introduced by dragging the objective away from its design point.

However, for low power objectives with NA below 0.30 or so, the added aberrations are small enough to have little effect on image quality. Meanwhile the internal focusing may be very convenient, so it's a good tradeoff.

The added aberrations become more important with larger NA objectives. At NA 0.55, as shown earlier in this same thread, there are clear limitations to how far you can push focus of the rear lens and still get a good image.

--Rik

[malpertuis]

Thanks a lot Rik for this reply.
Did you try your USM Stacking method not olny with telephoto or zoom lenses but on a specific USM macro lens ?

[malpertuis]

Is anybody else tried USM staking with infinite APO Plan microscope lens mounted directly on a USM macro lens ?