Mitutoyo QV objectives

[ChrisR]

Nope, not a clue! I've been looking for an answer to that one ever since I got a camera with the adjustment available. I've looked for but not seen the effect, but I don't have any really large aperture AF lenses.

[Charles Krebs]

Blame,

[rjlittlefield]

Charlie, dang, I was really hoping you'd know the answer to my autofocus question. That one's been nagging at me for years, and I've never run across anything that even hints at the answer. Nothing about open-loop, and if it's close-loop servo, nothing about why the stable point would be different for different lenses. Oh well...keep me in mind if you run across it.

I took a look at that Mitutoyo pamphlet. As I read page 26, the key point is that the objective cannot be too far away from the tube lens or you'll get some form of vignetting. The formulas compute maximum distance, as a function of diameters and focal length, but "A distance smaller than the specification does not affect an optical performance." This matches my understanding of how the system should work, not that that always means much.

Blame, regarding use of the 150, I don't know anything about Mitutoyos except that they're very expensive. But when I pushed a Nikon CFI 10X NA 0.25 to its limit last night, I was shocked to see how large the high quality circle was. See HERE for details. So I have high hopes for the Mitutoyos. I'm looking forward to the test report.

--Rik

[Blame]

rjlittlefield

Just checked out your thread, all I can say is wow!

Don't hold your breath for my report. Right now I am still puzzling out how to stick an objective on. They are very heavy so I am doubtful about using a lens cap kludge. After that comes the tricky problem of a microscope style mount for the subject. Then I have to find and understand the software.

Right now I am pushing my daughter through her GCSE exams, then comes summer holiday. I intend to enjoy the sunlight while it lasts. Could be Autumn before I even start. Sufficient time to assemble the parts from whatever turns up cheap.

I am sorry to say that I also don't understand why some lenses front focus.

Cyclops.

rjlittlefield's experiments show me to be wrong. It is well worth trying any infinite objectives you may have with a 100mm lens.

[DaveW]

Hi Chris,

No that was not the article, but it gave me the "Lens Rental" clue to search since I remembered it was on a Pentax forum. Anyway I have found it again here:-

http://www.pentaxbody.com/pentax-lenses/front-and-back-focusing

I found this on the Web Rik:-

"From the Canon document

<http://photoworkshop.com/canon/EOS_Digital.pdf> they state after
describing the AF system (camera) calibration:_

"Because each autofocus lens contains its own microcomputer and many
other internal devices such as focusing motors and diaphragm
actuators, lenses occasionally require calibration. If a focusing
error is detected, the circuitry of the lens itself can be adjusted to
ensure that it is operating according to design specs. Calibrating a
lens does not compromise its performance with other camera bodies
because the calibration standards for the lens are independent from
the calibration standards for the body. Please keep in mind that we do
not recommend sending equipment to the Factory Service Center unless
you are sure that the source of your image quality problems is not one
of the issues we have already discussed in this document".

If the focus motor would "drive away" variations, the lens calibration
would be unnecessary, wouldn't it?

The point is that the AF phase-detection sensor says how much the
image is OOF, and the camera tells the lens to move the right amount
to correct it. The right amount to move may differ from the intended
factory specs. Thus calibrating the camera (mirror) only adjusts for a
single lens (which may be out of tolerance for all I know), and it is
not necessarily valid for all lenses (which may also be out of tolerance but in the opposite direction). That's why Canon uses a lens with known (factory optimal) characteristics to calibrate the camera."

On autofocus methods:-

http://www.nikon.com/about/technology/core/software/caf/index.htm

DaveW

[Blame]

rjlittlefield


The interesting thing about mitutoyo objectives is that they are relatively cheap for apo's. There is a steady stream of them on Ebay. Admitedly most are set to a high "buy it now" price, but bidding is much lower.

They don't have particularly high numerical apertures but their working distance is second to none. I have high hopes that they will prove an economical alternative to the nikons, especially now you have proved that cheap camera lenses will work well as tube lenses. All that is lacking is a decent adapter.

[ChrisLilley]

Having been thoroughly converted to apo lenses for general and close-up photography, its slightly distressing to see how much extra apo lenses go for in low power microscopy. And that all the recent designs seem to be infinity lenses. And that some manufacturers skip apo for their lower power lenses and only use if for the higher powered ones.

[rjlittlefield]

[DaveW]

I found these additional ones on autofocus:-

http://www.fredmiranda.com/forum/topic/241524

http://www.digicaminfo.btinternet.co.uk/autofocus.htm

http://en.wikipedia.org/wiki/Autofocus

http://www.cambridgeincolour.com/tutorials/camera-autofocus.htm

DaveW

[ChrisR]

A thought - if they concentrate on predictive autofocus, that has to be open loop.
If the problemn were simply a positioning error, I'd expect missed focus of randon direction, depending which way the lens turned.

[Blame]

Open loop may be the problem with some lens.

Focus problems with sigma lens on canon cameras are common. Sometimes front focus, sometimes unreliable focus. Canon are not on friendly terms with Sigma. Story is that they would be happier if only canon lenses fit canon cameras. It is quite possible that they are not adverse to a little sabotage, at least to the point of making reverse engineering harder than it need be, and avoiding backward compatibility with 3'rd party lenses.

There is a focus shift when lenses are stopped down, and focusing happen with the iris fully open, but front focus seems to be independent of that.

I can only conclude that there is some small but fundamental difference of the light path for sensor and focusing sensor. It's effect must be lens dependent.

[DaveW]

All the major camera manufacturers don't like independent lenses on their cameras, so don't go out of their way to make it easier for them. They licence their autofocus coding to most for a price, but firms like Sigma chose not to buy it so have to reverse engineer a solution that works.

That is OK until the camera manufacturer tweaks (deliberately?) the coding on it's latest cameras to still be backwards compatible with it's own lenses, but upset Sigma's reverse engineered solution.

http://www.fredmiranda.com/forum/topic/369970

DaveW

[Craig Gerard]

Might be some information here?

http://www.mitutoyo.com/pdf/1785VisionMeasrSys.pdf


Craig
_________________
To use a classic quote from 'Antz' - "I almost know exactly what I'm doing!"

[lothman]

Sorry for digging out this old thread. Are the Mitutoyo QV lenses really the same as the M Plan ones?

Or are the QV telecentric since they are used in measurement microscopes.

And would telecentric lenses give better quality on "hairy" objects because of having smalle flare on out of focus objects?

[rjlittlefield]

I can't say about QV versus M Plan.

The question about telecentrics is subtle. The size of OOF blurs is the same for telecentrics as for any ordinary lens. That depends entirely on the aperture size (NA -- the angular width of the entrance cone). What changes with a telecentric is the exact alignment of features as focus changes. With a telecentric lens, you can turn off scaling adjustment in the stacking software. This removes one opportunity for small misalignment errors to creep in. If the stage or slide is very stable, you may be able to turn off X- and Y-adjustment also. Avoiding the need for these adjustments definitely can improve the quality of fine details at the pixel-peeping level. But if you're asking about the general "glowing" appearance that you get at high magnification, then I think that telecentrics do not have an advantage big enough to care about.

--Rik