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Info On LMPLFL10X Objective
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rjlittlefield
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PostPosted: Thu May 23, 2019 7:55 pm    Post subject: Reply with quote

mjkzz wrote:
I guess shooting 100s of images of some random subject and then take the average (by taking 1/(n-1)th power) would not be a good measure for telecentricity?

Right. What happens then is that the alignment calculation is likely to get misled by how things change appearance as they go way out of focus, instead of accurately detecting the relative scale of two images that are essentially identical except for scale.

As an example of that difficulty, see the graphs shown by mawyatt at http://www.photomacrography.net/forum/viewtopic.php?p=243071#243071 just for different tiles of one of his angled chip stack-and-stitch projects. While you're there, revisit http://www.photomacrography.net/forum/viewtopic.php?p=243052#243052 for discussion that none of Mike's graphs are really exponential, despite the visual appearance of some of them.

--Rik
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mjkzz



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PostPosted: Thu May 23, 2019 10:11 pm    Post subject: Reply with quote

Quote:
Most important, you want a nearly planar subject with crisp fine detail all over the frame, that does not appear to "wiggle around" as you change focus. For that I use a piece of paper . . . "


That is what I am surprised with. I understand what it means, but I always thought it is better to "average".

It makes sense to have a planar object to test, maybe perform many of such tests. It also makes sense that it can go wild when using non-planar subjects (or part of it) due to things going out of focus, etc.

Thanks
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rjlittlefield
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PostPosted: Fri May 24, 2019 12:12 pm    Post subject: Reply with quote

mjkzz wrote:
I always thought it is better to "average".

Averaging is a good technique to reduce the effect of random noise, so yes, doing many tests with a planar subject imaged a short distance in front and behind perfect focus would give a more accurate measurement.

The problem with averaging across a single stack that has many frames is that the individual frame-to-frame measurements are likely to include systematic error that will not be removed by averaging.

--Rik
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Lou Jost



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PostPosted: Fri May 24, 2019 1:27 pm    Post subject: Reply with quote

I like to run the stack with scaling turned off and then with scaling turned on, and compare them. If they look equally good even after close inspection, then the objective is close enough to telecentric for the purpose at hand.
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ray_parkhurst



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PostPosted: Fri May 24, 2019 2:17 pm    Post subject: Reply with quote

Lou Jost wrote:
I like to run the stack with scaling turned off and then with scaling turned on, and compare them. If they look equally good even after close inspection, then the objective is close enough to telecentric for the purpose at hand.


I personally wouldn't judge by how good they look, since it could go either way from a subjective viewpoint. But indeed if you run the stack using both methods, then compare, if the two look identical in size, then you could conclude the objective is fairly telecentric, at least to the point that no scaling was required between frames.

Rik, what minimum % scale change causes Zerene to adjust scaling between frames?
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Lou Jost



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PostPosted: Fri May 24, 2019 7:52 pm    Post subject: Reply with quote

Ray, yes, that's what I meant.
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mjkzz



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PostPosted: Fri May 24, 2019 8:07 pm    Post subject: Reply with quote

rjlittlefield wrote:
mjkzz wrote:
I always thought it is better to "average".

Averaging is a good technique to reduce the effect of random noise, so yes, doing many tests with a planar subject imaged a short distance in front and behind perfect focus would give a more accurate measurement.

The problem with averaging across a single stack that has many frames is that the individual frame-to-frame measurements are likely to include systematic error that will not be removed by averaging.

--Rik


I see, thanks. I do not suppose we can control systematic error, as its name implies.
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rjlittlefield
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PostPosted: Fri May 24, 2019 11:34 pm    Post subject: Reply with quote

ray_parkhurst wrote:
Rik, what minimum % scale change causes Zerene to adjust scaling between frames?

See the new topic at http://www.photomacrography.net/forum/viewtopic.php?t=39677 .

--Rik
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