Perfect distance between Sigma LSA and microscope lenses=?

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lonepal
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Post by lonepal »

Lou Jost wrote:Adalbert, why not do some comparisons of different distances?
A very good idea Lou!

Ichty;

You gave some ranges about two objectives but what is the range for Mitutoyo 5X or 10X?

Where can we find it?
Regards.
Omer

RobertOToole
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Post by RobertOToole »

At some point I plan on running a tube lens comparison that I plan to share here on the forum, so this might help.

Also I plan to run a comparison with different extension tubes in front of the Sigma LSA and behind a Mitutoyo 5x. This part should be really quick and easy to run.

But it will be a couple of weeks at the earliest before I can make time, since I am traveling now for work.

Coincidentally over the last few days I have been giving live presentations of my images at professional photography trade show called 'imaging USA' :D

Robert

RobertOToole
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Post by RobertOToole »

lonepal wrote:
Lou Jost wrote:Adalbert, why not do some comparisons of different distances?
A very good idea Lou!

Ichty;

You gave some ranges about two objectives but what is the range for Mitutoyo 5X or 10X?

Where can we find it?
Once I am back in the office, it would be really easy for me to pop on 25mm, 50mm, 75mm, 100mm, 150mm, tubes and make an image with each.

The 50mm tube between the Sigma LSA and Mity 5X is a good place to start. That combination is sharp all the way to the corners with just a very slight, tiny amount of purple CAs in the far corners (compared to the CAs with a Raynox, its nothing).

All the best,

Robert

lonepal
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Post by lonepal »

RobertOToole wrote:At some point I plan on running a tube lens comparison that I plan to share here on the forum, so this might help.

Also I plan to run a comparison with different extension tubes in front of the Sigma LSA and behind a Mitutoyo 5x. This part should be really quick and easy to run.

But it will be a couple of weeks at the earliest before I can make time, since I am traveling now for work.

Coincidentally over the last few days I have been giving live presentations of my images at professional photography trade show called 'imaging USA' :D

Robert
Hi Robert!

Good luck with your presentations.
Looking forward to seeing your test results!
Regards.
Omer

Lou Jost
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Post by Lou Jost »

I also look forward to these tests. This is one of the least-explored parameters in our typical stacking arrangements.

Whatever the results, though, we should expect that they will depend very much on the types of aberrations that most limit resolution for the particular objective being tested. Some kinds of aberrations can increase and some can decrease with distance. We should be very careful about generalizing.

Adalbert
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Post by Adalbert »


Lou Jost
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Post by Lou Jost »

Adalbert, again, why not test at various tube lengths? As you have just done one length with each lens, we can't tell whether the defects are due to tube length or lens aberrations.

Adalbert
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Post by Adalbert »

Hi Lou,
I have just started with 50mm :-)
BR, ADi

Adalbert
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Post by Adalbert »

Hello everybody,

This time I have tested the LSA only with the NIKON LU Plan 20x / 0.40.

Tube-length=10mm
Image
https://farm5.staticflickr.com/4658/259 ... 50a3_o.jpg

Tube-length=100mm
Image
https://farm5.staticflickr.com/4741/259 ... 239f_o.jpg

Tube-length=200mm
Image
https://farm5.staticflickr.com/4718/259 ... 159a_o.jpg

BR, ADi

rjlittlefield
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Post by rjlittlefield »

I see no obvious difference between these, but it's impossible to compare closely when every test image has much different framing.

Comparative tests are most useful when the same framing is maintained for all tests.

When CA is an issue, and I assume it will be here, then every test should also use the same stack length and cover the same range of focus positions. This can be accomplished accurately and without much trouble by shooting all stacks longer than they need to be, then pruning all stacks to match. Be sure that all stacks are long enough to capture the whole target in focus, plus some extra on either end. Choose a frame in the middle of one stack as reference, and match that focus point to determine the middle of all the other stacks, before pruning off the ends of all stacks to make them be the same.

--Rik

Adalbert
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Post by Adalbert »

Hello Rik,
Actually I wanted to compare the ink in the corner of the images in order to determinate the best range of the length of the the tube.
As far as I can see the best quality is given between 10mm and 50mm.
Next time I will test only this range.
BR, ADi

rjlittlefield
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Post by rjlittlefield »

Adalbert wrote:Actually I wanted to compare the ink in the corner of the images
Then why, in one test, did you frame with no ink in any corners?? (I speak of the 100 mm test, 2nd image of the last set.

In any case, the point of using the same framing for every test is that it becomes much simpler and more accurate to compare quality. Take a look at Ray Parkhurst's tests HERE to see what subtle differences can be seen by using flash-to-compare, when the framing is exactly the same.

I know it takes a lot of time to run these tests. But it takes only a little more time to run a good test. I apologize for being blunt, but the tests that you have run here are not good. You have wasted some of your time because of the variable framing.
As far as I can see the best quality is given between 10mm and 50mm.
Next time I will test only this range.
This would not be surprising. Short separation will mean that the light goes through more central portions of the tube lens, and typical lenses have less aberration in those areas. But ultimately it's a matter for testing, because some lenses are different. To be sure that you have found the best separation, the test needs to show that the quality first improves and then falls off from one end of the range to the other. If the best quality occurs at one end or the other, then you don't know if moving even farther in that direction would have been better still.

--Rik

Adalbert
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Post by Adalbert »

Hello Rik,
Many thanks for the hints!
What kind of the test-picture would be good enough for the really good test?
BR, ADi

rjlittlefield
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Post by rjlittlefield »

In general, toner ink on paper makes a good subject.

But:

1) Every test should be framed identically (as close as possible) so that one can directly compare the same ink in the same corner.

2) It is best if there is some ink all over the frame so that one can evaluate coverage in case the corners go bad.

--Rik

Adalbert
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Post by Adalbert »

Hello Rik,
In the meantime I have stacked a test-slide (35 images) with the LU Plan 5x / 0.15

10mm
Image
https://farm5.staticflickr.com/4620/398 ... 5b2f_o.jpg

50mm
Image
https://farm5.staticflickr.com/4695/398 ... 5e46_o.jpg

BR, ADi

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