How to measure if my Mitu50x performs as it should do?

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nielsgeode
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How to measure if my Mitu50x performs as it should do?

Post by nielsgeode »

Since I purchased this second hand Mitutoyo 50x NA 0.55, I have the feeling the images are so soft. The difference in sharpness between the 50x/0.55 and my 20x/0.42 is huge.

The seller said: 'someone clumsy removed the objective with pliers'. There are marks on the barrel and of course it is very well possible it has been subjected to shock or impact, without visual evidence.

How do I now with reasonable certainty whether or not my copy of the Mitu50/0.55 performs as it should do?

Thanks!
Niels

concon
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Post by concon »

Is yours an M or BD version? If it's a BD they were most likely removing the outer barrel (I recommend doing so- but with rubber strap wrenches, not pliers). Also, if you have a BD and haven't covered the gap of the outer-barrel, this is contributing to your soft imagery.

I also bought a Mitty 50x recently. I chanced a 'minor ding on front element' and was hoping it was referring to the barrel and not the lens...no dice; however, it performs totally fine.

Beyond 20x, images will generally appear softer and can require submicron steps. Apologies if you already knew all that! I just finished upgrading my own rig as I am now shooting with 50x and 80x objectives.

I'm actually interested in what the others have to say in regards to testing and such, but you may just need to realign your expectations (this was the initial advice I was given).

rjlittlefield
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Re: How to measure if my Mitu50x performs as it should do?

Post by rjlittlefield »

nielsgeode wrote:How do I now with reasonable certainty whether or not my copy of the Mitu50/0.55 performs as it should do?
By far the best method is head-to-head comparison with a known good objective of the same model, imaging the same subject in the same setup.

If that's not practical, then you can use your 20X as the known good comparison, by resizing the 20X image to be 2.5X bigger and comparing the result with what you get from the 50X in the same setup.

If all is working properly, then in this test the 50X image should be slightly sharper (OK, slightly less blurred), due to its NA 0.55 versus NA 0.42 for the 20X. But notice that this ratio of NA is only about 1.3:1, versus the 2.5:1 ratio of magnification. That why the image shot at 50X will only look about half as sharp as the image shot at 20X, even though it will be resolving slightly more detail on subject.

Another way to look at it is that at rated magnification, the 20X NA 0.42 objective has effective aperture about f/23.8, while the 50X NA 0.55 is about f/45.5. Pixel-peeping with any modern DSLR, both of them will be significantly blurred from diffraction, and the 50X will be about twice as bad.

--Rik

nielsgeode
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Post by nielsgeode »

concon wrote:Is yours an M or BD version? If it's a BD they were most likely removing the outer barrel (I recommend doing so- but with rubber strap wrenches, not pliers). Also, if you have a BD and haven't covered the gap of the outer-barrel, this is contributing to your soft imagery.

I also bought a Mitty 50x recently. I chanced a 'minor ding on front element' and was hoping it was referring to the barrel and not the lens...no dice; however, it performs totally fine.

Beyond 20x, images will generally appear softer and can require submicron steps. Apologies if you already knew all that! I just finished upgrading my own rig as I am now shooting with 50x and 80x objectives.

I'm actually interested in what the others have to say in regards to testing and such, but you may just need to realign your expectations (this was the initial advice I was given).
Image
I have the M version and I do know that one should expect softer images at larger magnifications.

Here's an example of a stack shot with this objective using the stackshot macro rail at 1um step size. I used mirror lockup and second-curtain sync flash with an exposure time of 0.8 seconds.

100% pixel crop:
Image
Here's a link to the full-size image

rjlittlefield
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Post by rjlittlefield »

In the full-size image, I see indications of another factor that may be messing up your results. Here is a section of the image a little above your sample. Note the "stuttering" pattern marked by arrows.

Image

That stuttering pattern is typical of what happens when the illumination is not diffused broadly enough. Directional illumination bounces off shiny surfaces in a way that causes it to mostly enter only a small part of the lens aperture. This "utilized aperture" issue causes a number of problems, including increased diffraction, reduced resolution, "squirming" of the subject (localized lateral shifts that change with focus), and increased DOF. As an example of squirming, see http://www.photomacrography.net/forum/v ... 187#149187 . Another example is shown at http://www.photomacrography.net/forum/v ... 498#123498 , and the rest of that thread has a lot of related discussion.

You might wonder why I've listed increased DOF as a problem, not a nice feature. That's because a) it makes the squirming worse, especially in a stacked image, and b) the increased DOF goes along with increased diffraction and correspondingly reduced resolution.

To get the cleanest images at 50X NA 0.55, you need heavily diffused, very uniform illumination, striking the subject from as wide a range of angles as you possibly can. Yes, this unfortunately conflicts with the desire to use directional illumination for modeling, but that's an unavoidable tradeoff.

It looks to me like your subject consists of a collection of clear crystalline spikes organized into clusters. For what it's worth, you have my sympathy. That's a very difficult type of subject to capture at high magnification.

--Rik

Chris S.
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Post by Chris S. »

Niels,

You might check out a comparison of two 50x Mitutoyos I posted a while back. The fourth image might serve as something you can compare directly with, if you have or obtain a specimen of the sunset moth.

The black wingscales on this moth (and other species) have interstices sized around the resolution limits of this lens.

Like Rik, the only way I trust a lens is to test it against a known specimen on a the same test target under identical conditions. This said, I've also hoped that someone would make a slide like mine, light it the way I did, test a 50x Mitty with it and post their results. There is some hope in the back of my head that interstices of this moth might be potentially compared by different photographers.

--Chris S.

nielsgeode
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Post by nielsgeode »

Chris S. wrote:Niels,

You might check out a comparison of two 50x Mitutoyos I posted a while back. The fourth image might serve as something you can compare directly with, if you have or obtain a specimen of the sunset moth.

The black wingscales on this moth (and other species) have interstices sized around the resolution limits of this lens.

Like Rik, the only way I trust a lens is to test it against a known specimen on a the same test target under identical conditions. This said, I've also hoped that someone would make a slide like mine, light it the way I did, test a 50x Mitty with it and post their results. There is some hope in the back of my head that interstices of this moth might be potentially compared by different photographers.

--Chris S.
Thanks! No, I don't have that one. In fact, I almost never shoot insects and 99% of my stacks are mineral specimens.

Unfortunately, I don't have time before coming weekend to make actual photographs.

For what it's worth: I've recently shot (with flash) a sulfur crystal. It seems here's les "squirming", but sharpness is still terrible in my opinion.

Can you make any tentative conclusion on this picture?

rjlittlefield
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Post by rjlittlefield »

Code: Select all

For what it's worth: I've recently shot (with flash) a [url=https://nl.imgbb.com/]sulfur crystal[/url]. It seems here's les "squirming", but sharpness is still terrible in my opinion.

Can you make any tentative conclusion on this picture?
Can't even see the picture. The link that you've provided is to imgbb in general, not to any one image in particular.

--Rik

nielsgeode
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Post by nielsgeode »

rjlittlefield wrote:

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For what it's worth: I've recently shot (with flash) a [url=https://nl.imgbb.com/]sulfur crystal[/url]. It seems here's les "squirming", but sharpness is still terrible in my opinion.

Can you make any tentative conclusion on this picture?
Can't even see the picture. The link that you've provided is to imgbb in general, not to any one image in particular.

--Rik
I was struggling to get full-res posted and updated the link. It should work now. Can you see it?

Pau
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Post by Pau »

The link to your sulfur crystal doesn't show any image, just the https://nl.imgbb.com/ start page
Pau

nielsgeode
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Post by nielsgeode »

Pau wrote:The link to your sulfur crystal doesn't show any image, just the https://nl.imgbb.com/ start page
I updated the link and now it should point to. Maybe refresh the page?

https://prodibimedia1we.blob.core.windo ... 3A40Z&sp=r

For what it's worth: I found raw files of the same specimen shot with the Canon 70-200 f/2.8 and the Canon 1.4x teleconverter with a mitu7.5x. I borrowed the teleconverter to see how useful it would be in gaining some extra 'reach'. I'll quickly process them and post the result for comparison.

Here's a link to the same crystal, shot with 70-200L II f/2.8 + 1.4 TC III + Mitutoyo M-Plan Apo 7.5x NA 0.21 WD 34:

https://prodibimedia1we.blob.core.windo ... 3A37Z&sp=r

ChrisR
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Post by ChrisR »

No Luck, I get

Code: Select all

<Error><Code>AuthenticationFailed</Code><Message>Server failed to authenticate the request. Make sure the value of Authorization header is formed correctly including the signature.
RequestId&#58;c47c0e35-001e-0022-1d0c-41a0ff000000
Time&#58;2017-10-09T14&#58;36&#58;48.5996424Z</Message><AuthenticationErrorDetail>Signature not valid in the specified time frame&#58; Start &#91;Sun, 08 Oct 2017 08&#58;14&#58;37 GMT&#93; - Expiry &#91;Mon, 09 Oct 2017 09&#58;14&#58;37 GMT&#93; - Current &#91;Mon, 09 Oct 2017 14&#58;36&#58;48 GMT&#93;</AuthenticationErrorDetail></Error>
Chris R

nielsgeode
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Post by nielsgeode »

ChrisR wrote:No Luck, I get

Code: Select all

<Error><Code>AuthenticationFailed</Code><Message>Server failed to authenticate the request. Make sure the value of Authorization header is formed correctly including the signature.
RequestId&#58;c47c0e35-001e-0022-1d0c-41a0ff000000
Time&#58;2017-10-09T14&#58;36&#58;48.5996424Z</Message><AuthenticationErrorDetail>Signature not valid in the specified time frame&#58; Start &#91;Sun, 08 Oct 2017 08&#58;14&#58;37 GMT&#93; - Expiry &#91;Mon, 09 Oct 2017 09&#58;14&#58;37 GMT&#93; - Current &#91;Mon, 09 Oct 2017 14&#58;36&#58;48 GMT&#93;</AuthenticationErrorDetail></Error>
I suspect that one should be logged in to access that link :(

Hope this works:
https://www.dropbox.com/s/rvuarf278qcprxy/mitu50.jpg
https://www.dropbox.com/s/u7nnrblwqe8j2 ... C.jpg?dl=0

rjlittlefield
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Post by rjlittlefield »

nielsgeode wrote:For what it's worth: I found raw files of the same specimen shot with the Canon 70-200 f/2.8 and the Canon 1.4x teleconverter with a mitu7.5x. I borrowed the teleconverter to see how useful it would be in gaining some extra 'reach'. I'll quickly process them and post the result for comparison.
I downloaded the images from DropBox and displayed them with IrfanView. With display scale adjusted to make the crystal be the same size on screen, the 50X image appears significantly sharper. In this test, I don't see problems with the lens.

--Rik

nielsgeode
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Location: Groningen, Netherlands

Post by nielsgeode »

rjlittlefield wrote:
nielsgeode wrote:For what it's worth: I found raw files of the same specimen shot with the Canon 70-200 f/2.8 and the Canon 1.4x teleconverter with a mitu7.5x. I borrowed the teleconverter to see how useful it would be in gaining some extra 'reach'. I'll quickly process them and post the result for comparison.
I downloaded the images from DropBox and displayed them with IrfanView. With display scale adjusted to make the crystal be the same size on screen, the 50X image appears significantly sharper. In this test, I don't see problems with the lens.

--Rik
Why does it look so much softer than my 20x 0.42? My 20x is slightly softer than my 10x, but the difference between 20x and 50x is much much bigger than the difference between any other pair of microscope lenses that I have.

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