Mitutoyo 50x Sharpness Problems?

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Adalbert
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Re: Mitutoyo 50x Sharpness Problems?

Post by Adalbert »

Hi Zack,
do not want to damage the objective
in the worst case you can saw through it :D
viewtopic.php?p=229291#p229291
Best, ADi

rjlittlefield
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Re: Mitutoyo 50x Sharpness Problems?

Post by rjlittlefield »

As far as I know, all BD outer barrels are "just" threaded on, but then the manufacturer applies some sort of threadlocker so that taking them off can range from simple to almost impossible.

On one of my Nikon BD's, the outer barrel became removable when I applied a few microliters of ethyl acetate to the thread area and let it soak in for a while. But for another, I never was able to unthread the outer barrel and finally resorted to cutting it off with a rotary abrasive wheel.

I have no experience with Olympus objectives. I hope somebody who knows Olympus can chime in.

--Rik

Zack
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Re: Mitutoyo 50x Sharpness Problems?

Post by Zack »

Oh boy... it seems like I am literally and metaphorically opening a can of worms here. Now I have another thing to worry about! As the objective is returnable and I want to test it before deciding to keep it, I think that a permanent removal solution may have to wait. I might just have to find a way to work around the barrel at least to shoot a few test stacks and make sure the objective stands up to my needs. Then I’ll pull out the metal saws :shock:

rjlittlefield
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Re: Mitutoyo 50x Sharpness Problems?

Post by rjlittlefield »

Zack wrote:
Thu Mar 24, 2022 3:20 pm
I might just have to find a way to work around the barrel at least to shoot a few test stacks and make sure the objective stands up to my needs.
That sounds familiar.

I stuck a piece of double-stick tape to a glass slide, used that to peel some scales off a moth wing, then looked at those using transmitted illumination.

A short stack with the 40X NA 0.80 showed no interesting aberrations and was quite a lot sharper than my previous 40X NA 0.50, so I decided it was worth keeping.

Only then did I discover that the barrel was stuck on tight so I hauled out the Dremel.

--Rik

Scarodactyl
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Re: Mitutoyo 50x Sharpness Problems?

Post by Scarodactyl »

Some fluorites are better than others. The olympus 50x/0.8 is very apoesque, with some axial CA that generally stacks out and relatively minor lateral CA. Note rhat the mitutoyo 50x/0.55 'apo' shows axial CA as well, probably a comparable amount or more. I recently did a test comparing my olympus mplanfl 50/0.8 (this is a slightly older model too, not the newer umplanfl n 50x) with a current Nikon TU plan fluor 50/0.8 and cf plan apo 50/0.95, and it held its own quite well.
viewtopic.php?f=25&t=44722

Zack
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Re: Mitutoyo 50x Sharpness Problems?

Post by Zack »

I have received the BD lens, but as you all said, the photos are nearly pure white and just lens flare because I have not properly blocked the outer channel. Should I block it from both the front and the back? I was planning to do so with a bit of black felt. I see no feasible way to actually remove the collar short of using a saw, as some of you suggested, but I am afraid to damage the objective and it would obviously then be unreturnable. Thank you!

rjlittlefield
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Re: Mitutoyo 50x Sharpness Problems?

Post by rjlittlefield »

Blocking from the back will work fine, as long as you do get all the light blocked.

I use mine with a BD-to-RMS thread adapter, which serves the dual purpose of adapting the threads and blocking the channel.

--Rik

Zack
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Re: Mitutoyo 50x Sharpness Problems?

Post by Zack »

This objective has 26mm threads and I have a 26mm stepdown ring already. Would you suggest getting a 26-RMS adapter and then another adapter the other way just to block light? In that case, maybe just felt is a better alternative.

As an edit, I managed to stick a felt disk in there and it blocked the flaring, although with the .66mm WD I do not see any way to sneak enough light in there, even firing two diffused flashes at 1/2 power from inches away. I will continue to try different lighting setups, but I am realizing more and more how important at least some wiggle room in working distance is in order to get usable images.

rjlittlefield
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Re: Mitutoyo 50x Sharpness Problems?

Post by rjlittlefield »

Sorry, I did not mean to suggest an extra adapter. My point was only that blocking the back works fine for me.

Regarding your illumination for testing, I suggest to do something like what I described above:
I stuck a piece of double-stick tape to a glass slide, used that to peel some scales off a moth wing, then looked at those using transmitted illumination.
Any old piece of glass would work for this, since it is behind the specimen and not in the optical path. A piece of window glass with a couple of layers of matte transparent tape on the back for a diffuser would work OK.

If you decide to keep the objective, then after you cut off the barrel you should be a lot more comfortable with getting light in. Remember that the objective is intended to work with light coming from around the imaging lens, reflected in by the outer barrel. By cutting off the outer barrel you will essentially just be exposing the normal BD illumination range of angles, plus a little, and with the potential to have asymmetric illumination.

The biggest challenge then will be managing to frame and focus without running the objective into your specimen. For that, I suggest calibrating the difference in focus distance between your high power objective and a lower power one with longer working distance. Then you can frame and focus safely, using the lower power objective, before mounting the higher power objective and adjusting for whatever the known difference in focus distance is. In my own case, I happen to know that a particular 10X objective focuses 6.30 mm different from my 40X NA 0.80 in its RMS adapter with bellows adjusted to be ideal for the 40X NA 0.80. So then I frame and focus with the 10X, back off by 6.30 mm, set a hard stop in my focusing mechanics, then back way off to change objectives, advance again to the hard stop, and voila, the 40X is close enough that all I have to do is tweak framing and focus before starting to shoot.

--Rik

Zack
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Re: Mitutoyo 50x Sharpness Problems?

Post by Zack »

Just as an update for those interested - I spent hours with the 50x/.8 over the past few days, but whether due to my setup or incompetence, I just could not manage to take photos that I was happy with. I think I may pause my higher magnification attempts for a while, at least until I can afford a similar objective but with greater working distance. I am also considering trying a 300mm tube lens with the Nikon 20x that I already have, although I understand that would just be giving me "empty magnification" and not resolving any additional detail. Hopefully this saga will continue in the future, but for the time being, so much appreciation to all who so patiently answered my questions and offered advice!

Nurz
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Re: Mitutoyo 50x Sharpness Problems?

Post by Nurz »

Guys, does anyone have an idea about the image quality of Motic L Plan achromatic 50x 0.55? If the apochromatic version has CA, as I read, then the achromatic must be even worse?
Vasilis

Scarodactyl
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Re: Mitutoyo 50x Sharpness Problems?

Post by Scarodactyl »

I don't think this specific one has been tested. 'Motic' is just branding, and these objectives are likely made in a different factory by different people than the mitutoyo clones they also sell under the brand. So it may be better or worse. Definitely cheaper in this case.

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