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

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ChrisR
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Post by ChrisR »

The blur circle on the subject is smaller with increasing NA
It looks bigger on the sensor with increasing M

So the BLOB looks M/NA size:

Image

Yes, No?

Annoying, isn't it? :shock:
Chris R

nielsgeode
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Post by nielsgeode »

ChrisR wrote:The blur circle on the subject is smaller with increasing NA
It looks bigger on the sensor with increasing M

So the BLOB looks M/NA size:

Image

Yes, No?

Annoying, isn't it? :shock:
I see where you're going :)

This weekend I hope to have time to do a more thorough direct comparison between my Mitu 20x and 50x. In addition, I also have an Olympus 80x NA 0.75 with a small working distance of 3 - 4 mm (don't remember exactly and I'm also not entirely sure about the NA). I'll try to include it as well, but for many mineral specimens it is hard to use because of the very small working distance and crystals are very often in cavities.

I hope it gives more information for a (better) conclusion.

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Post by rjlittlefield »

Saying the same thing as ChrisR, but in a different way:
nielsgeode wrote: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.
Have you run a calculation like I described earlier? For example
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.
At low magnification, NA tends to increase in proportion to magnification, for example from 5X NA 0.14 to 10X NA 0.28, both magnification and NA increase by a factor of 2 so the images look equally sharp.

But at high magnification, NA tends to increase only slightly as magnification continues to rise a lot. From 20X NA 0.42 to 50X NA 0.55, the NA increases only 1.3X while the magnification increases by 2.5X. The result is that the 50X looks only half as sharp as the 20X.

Within the Mitutoyo line, for magnifications 5X, 7.5X, 10X, 20X, 50X, 100X, with NA 0.14, 0.21, 0.28, 0.42, 0.55, 0.70, the relative sharpness (NA/magnification) goes as 1, 1, 1, 0.75, 0.39, 0.25 .

--Rik

nielsgeode
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Post by nielsgeode »

rjlittlefield wrote:Saying the same thing as ChrisR, but in a different way:
nielsgeode wrote: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.
Have you run a calculation like I described earlier? For example
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.
At low magnification, NA tends to increase in proportion to magnification, for example from 5X NA 0.14 to 10X NA 0.28, both magnification and NA increase by a factor of 2 so the images look equally sharp.

But at high magnification, NA tends to increase only slightly as magnification continues to rise a lot. From 20X NA 0.42 to 50X NA 0.55, the NA increases only 1.3X while the magnification increases by 2.5X. The result is that the 50X looks only half as sharp as the 20X.

Within the Mitutoyo line, for magnifications 5X, 7.5X, 10X, 20X, 50X, 100X, with NA 0.14, 0.21, 0.28, 0.42, 0.55, 0.70, the relative sharpness (NA/magnification) goes as 1, 1, 1, 0.75, 0.39, 0.25 .

--Rik
Very clearly explained, thank you! :D
It makes me wonder how these objectives would perform in terms of the perception of the image sharpness when viewed at 100%:

- Mitu 50x NA 0.75 WD 5.2
- Mitu 10x NA 0.42 WD 15
- Mitu 5x NA 0.21 WD 25.5

In particular the 5x and 10x: Would you be able to get (almost) identical results when the 7.5x 0.21 is used at 5x instead of the 5x? And when the 20x 0.42 is used at 10x instead of the 10x?

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Post by rjlittlefield »

nielsgeode wrote:Would you be able to get (almost) identical results when the 7.5x 0.21 is used at 5x instead of the 5x? And when the 20x 0.42 is used at 10x instead of the 10x?
When you push down the magnification, the resolution on subject remains the same, but the image gets sharper because you've packed the same amount of detail into less area.

Using the 20X objective with a 100 mm tube lens ends up giving you a 10X NA 0.42 image, substantially sharper than 10X NA 0.28 using the 10X objective.

It turns out that on my APS-C camera, the sharpest 10X setup I have is exactly that: 20X NA 0.42 on 100 mm tube lens. But I don't use it very much because I get more annoyed by the reduced DOF than I get pleased by the increased sharpness.

--Rik

nielsgeode
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Post by nielsgeode »

rjlittlefield wrote:
nielsgeode wrote:Would you be able to get (almost) identical results when the 7.5x 0.21 is used at 5x instead of the 5x? And when the 20x 0.42 is used at 10x instead of the 10x?
When you push down the magnification, the resolution on subject remains the same, but the image gets sharper because you've packed the same amount of detail into less area.

Using the 20X objective with a 100 mm tube lens ends up giving you a 10X NA 0.42 image, substantially sharper than 10X NA 0.28 using the 10X objective.

It turns out that on my APS-C camera, the sharpest 10X setup I have is exactly that: 20X NA 0.42 on 100 mm tube lens. But I don't use it very much because I get more annoyed by the reduced DOF than I get pleased by the increased sharpness.

--Rik
Correct me if I'm wrong, but if you're using a Mitu 20x at 10x magnifiction, effectively you are projecting an image circle with 2 times the diameter. I wonder how it effects corner sharpness and how it compares between Mitu 20x 0.42 at 10x, at 20x, the Mitu 10x 0.42 and the Mitu 10x 0.28.

There must be a reason why Mitu makes a very expensive 10x 0.42...

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Post by rjlittlefield »

nielsgeode wrote:Correct me if I'm wrong, but if you're using a Mitu 20x at 10x magnifiction, effectively you are projecting an image circle with 2 times the diameter. I wonder how it effects corner sharpness and how it compares between Mitu 20x 0.42 at 10x, at 20x, the Mitu 10x 0.42 and the Mitu 10x 0.28.
You have it correct. I worried about corner sharpness also, but the one time I specifically checked that, I was surprised to see that the 20X NA 0.42, operated at 10X on APS-C, was sharper everywhere than the 10X NA 0.28.

In other tests, discussed at http://www.photomacrography.net/forum/v ... 243#208243 and surrounding, nathanm determined that the Mitutoyo 7.5X and 20X are somehow special, having much wider fields than the other magnifications in that line.

As for the 10X NA 0.42, I don't know anything about that beast.

--Rik

nielsgeode
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Post by nielsgeode »

rjlittlefield wrote:
nielsgeode wrote:Correct me if I'm wrong, but if you're using a Mitu 20x at 10x magnifiction, effectively you are projecting an image circle with 2 times the diameter. I wonder how it effects corner sharpness and how it compares between Mitu 20x 0.42 at 10x, at 20x, the Mitu 10x 0.42 and the Mitu 10x 0.28.
You have it correct. I worried about corner sharpness also, but the one time I specifically checked that, I was surprised to see that the 20X NA 0.42, operated at 10X on APS-C, was sharper everywhere than the 10X NA 0.28.

In other tests, discussed at http://www.photomacrography.net/forum/v ... 243#208243 and surrounding, nathanm determined that the Mitutoyo 7.5X and 20X are somehow special, having much wider fields than the other magnifications in that line.

As for the 10X NA 0.42, I don't know anything about that beast.

--Rik
That's good to hear :) I have both the 7.5x and the 20x and will see what they do as soon as I have time.

How useful would it be to compare the 50x 0.55 at less than 50x (somewhere between 20-30x) with the 20x 0.42 at the same magnification?

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Post by ChrisR »

I tried a Nikon ELWD 100x NA 0.8, with 2mm WD.
I found it so difficult to light the subject, that I got sharper resuts with a 50x NA 0.55 Mitutoyo.
It still sounds unlikely, but I spent a good amount of time trying.
Chris R

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Post by Beatsy »

nielsgeode wrote: How useful would it be to compare the 50x 0.55 at less than 50x (somewhere between 20-30x) with the 20x 0.42 at the same magnification?
I regularly use the 50x at ~33.5x onto APS-C with a 135mm tube lens. It's still not as sharp as the 20x on APS-C and I'm pretty sure the corners of the 50x wouldn't hold up on a 100mm tube lens for 25x (though I've never actually tried it).

Oh, and please stop mentioning the 7.5x in such glowing terms everyone - I'd managed to convince myself I didn't need any more Mitties - I thought! :roll:

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Post by Lou Jost »

Beatsy, I love my 7.5x, which I bought after reading nathanm's analysis.

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Post by Beatsy »

Lou Jost wrote:Beatsy, I love my 7.5x, which I bought after reading nathanm's analysis.
Noooooo! Stop it!

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