Halos when using Mitutoyo 10x - how to solve?

[Ron_S]

Hi all,

I’m new here, thanks a lot for letting me join! Not a very technical guy, so apologies in advance for stupid questions. I basically just love to photograph slime molds, the necessary equipment is more or less a result of their size.

Recently got the Mitu 10x with ITL200 and use it with a full frame camera (Canon 5D Mark IV) in the ‘Thorlabs-setup’ as described by Robert o’Toole (https://www.closeuphotography.com/mitut ... m-plan-apo - he recommends a slightly different setup, but nonetheless).

But, whatever I do, I get extremely ugly halos in the image, see example (slightly exaggerated in Lightroom by turning up contrast, blacks and whites). Basically, they start almost from the center of the image, alternating lighter and darker rings. They occur in single shots and in stacks (no difference in intensity).

So, in order to exclude internal or external reflections, I covered the back of the objective (inside) and the shiny exterior of the objective with dark paper, a bit like Alan Walls recommends. That makes no difference at all.

I checked with a ‘colleague’, who uses the same setup. He has no halo-ing or vignetting at all.

I checked several threads and sites (viewtopic.php?t=38314 - https://www.closeuphotography.com/mitut ... m-plan-apo - https://makrodunyasi.com/en/mitutoyo-microscope-lenses/ - etc.) and in general, I read that the Mitu 10x should work quite well on a full frame sensor.

I looked down the bore as Rik Littlefield recommends (viewtopic.php?p=83897). It seems like the first thing that interferes with the light is the objective itself.

In short, I have no clue as to what might cause this halo-ing. Might it have to do with something faulty in this particular copy of the lens?

If you have suggestions on what I might try to improve the image quality, I’d be very happy to hear it.

Thanks in advance!

Ron

[rjlittlefield]

Fuzzy rings that appear in an empty field strongly suggest reflections from something inside the optical assembly.

See the discussion at viewtopic.php?t=35350 .

Again this involves looking down the barrel, but this time searching for bright reflections rather than obstructions.

--Rik

[Ron_S]

Oh wow, thanks very much Rik! So maybe it could be easily resolved. That's a huge relief! Just to be sure I'll flock the entire inside of the tubes in the setup. Will come back here with the results when I finished that.

Thanks so much for this!

Ron

[aphi]

Is that long middle tube an SM2E60? If so, because the inside isn't fully threaded it has a fairly large amount of reflections, as it is just smooth, anodized aluminium. On the standard tubes the threads act as AR baffles, in fact various old lenses use the same approach, as it is relatively easy to machine on a lathe.
I used black paper tape (Kip #911) on mine and that works splendid. Real flocking probably works better, but it seems to be fine, really.

I also recall Robert re-testing tube lenses on full-frame and finding that the Raynox performs better overall than the ITL200, while the ITL200 performed slightly better on APS-C.

[FotoChris]

Fuzzy rings that appear in an empty field strongly suggest reflections from something inside the optical assembly.

See the discussion at viewtopic.php?t=35350 .

Again this involves looking down the barrel, but this time searching for bright reflections rather than obstructions.

--Rik

Interesting!

I "only" have the 5x Mitu and according to most sources the best Raynox orientation is forward (49mm label facing towards subject) - is the 10x Nikon a better performer with the Raynox reversed?

[rjlittlefield]

according to most sources the best Raynox orientation is forward (49mm label facing towards subject)

I think this depends on exactly what you test and what you care about.

https://www.closeuphotography.com/tube-lens-test tested his mostly in normal orientation, noting that "Reverse mounting results in better corners but worse in the center."

That was tested only on APS-C, so "corners" were only 14 mm from image center.

At viewtopic.php?t=23898 , I found the Raynox DCR-150 covering full-frame D800E, with clean corners (21 mm from image center), and center sharpness that compared well with the ITL-200. That was with the Raynox reversed, and on slightly shortened extension so as to match magnification with the standard 200mm tube lenses.

The intended use for the system described at viewtopic.php?t=35350 was for full frame, so I went with the known-good reversed orientation.

--Rik

[FotoChris]

At viewtopic.php?t=23898 , I found the Raynox DCR-150 covering full-frame D800E, with clean corners (21 mm from image center), and center sharpness that compared well with the ITL-200. That was with the Raynox reversed, and on slightly shortened extension so as to match magnification with the standard 200mm tube lenses.

The intended use for the system described at viewtopic.php?t=35350 was for full frame, so I went with the known-good reversed orientation.

--Rik

Thanks for sharing!

Looks like I still have a few tests to run hehe

Good thing I now have a few perfectly flat microscope slides which makes it easier to determine the performance over the whole frame.

[rjlittlefield]

Good thing I now have a few perfectly flat microscope slides which makes it easier to determine the performance over the whole frame.

If you're planning to use for focus-stacking, then be sure to evaluate each area at its own best focus.

Sometimes image quality at best focus improves if you allow more curvature.

It is one of those tradeoffs that makes "best" so hard to nail down.

Even better, evaluate after stacking around best focus so as to catch troublesome aberrations like astigmatism.

--Rik

[FotoChris]

If you're planning to use for focus-stacking, then be sure to evaluate each area at its own best focus.

Sometimes image quality at best focus improves if you allow more curvature.

It is one of those tradeoffs that makes "best" so hard to nail down.

Even better, evaluate after stacking around best focus so as to catch troublesome aberrations like astigmatism.

--Rik

Of course - after all I intent to shoot mostly insects so curvature/flatness is a low priority.

But it's still great to check for sharpness and aberrations, especially since I don't have any silicon wafers to test with ;-)

[Chris S.]

But it's still great to check for sharpness and aberrations, especially since I don't have any silicon wafers to test with ;-)

I do have silicon wafers, but at low magnifications such as 5x, I prefer to test on laser-printed paper glued onto a microscope slide. I illuminate the paper frontally with two small light sources at about 2:00 o'clock and 10 o'clock positions. Add a little bit of diffusion, but not too much. The carbon grains, and particularly the specular highlights on them, are very revealing.

--Chris S.

[FotoChris]

But it's still great to check for sharpness and aberrations, especially since I don't have any silicon wafers to test with ;-)

I do have silicon wafers, but at low magnifications such as 5x, I prefer to test on laser-printed paper glued onto a microscope slide. I illuminate the paper frontally with two small light sources at about 2:00 o'clock and 10 o'clock positions. Add a little bit of diffusion, but not too much. The carbon grains, and particularly the specular highlights on them, are very revealing.

--Chris S.

That sounds even better! Do you use a special target or "just" text?

[Chris S.]

That sounds even better! Do you use a special target or "just" text?

Just text, but here are some things I've picked up through trial and error:

• In Microsoft Word, it's possible to enter a very small font size. For some fonts, this number can be much smaller than the lowest number listed in the drop-down menu. Smaller fonts are better at squeezing maximal information in your field of view.

• It's helpful to specify "leading"--the amount of blank space between lines of text--that is also very small. This way, you have more type in your frame and less white space.

• Just how small you can go with font and leading (without getting mush) may depend on your printer--there are definitely limits with mine.

• If you choose for your text a long poem or song you know, it's easy to figure out where you're looking on the target. (My go-to is "Rime of the Ancient Mariner"--color me weird, but it's quite long.)

• Eliminate unnecessary line breaks and extra spaces between sentences to get denser text.

• I have at times made particular targets for specific magnifications, with a box drawn just inside where the sensor would be--but this extra effort produces little additional value.

--Chris S.