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40X and ApsC Sony a6100: how calculate step size?

 
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anto74



Joined: 06 Feb 2020
Posts: 66
Location: Italy

PostPosted: Thu Mar 12, 2020 9:32 am    Post subject: 40X and ApsC Sony a6100: how calculate step size? Reply with quote

Hello,
i would buy a good 40x ( Nikon M Plan Elwd i think...) but i have one question: i have Wemacro rail and i can set step size to 0,001mm. With 40x how can i calculate right step size?
Thanks
Antonio
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rjlittlefield
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Joined: 01 Aug 2006
Posts: 20649
Location: Richland, Washington State, USA

PostPosted: Thu Mar 12, 2020 10:01 am    Post subject: Reply with quote

With microscope objectives, a good estimate of DOF can be calculated as DOF = 0.00055/(NA*NA) .

So for example, a 40X NA 0.5 objective would have calculated DOF = 0.00055/(0.5*0.5) = 0.0022 mm.

You definitely will not be able to use a step size that is much larger than this, or you will get focus banding.

Depending on the subject and illumination, you may get cleaner results with a smaller step size.

I suggest trying both 0.001 and 0.002 mm and see which you are happier with.

--Rik
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anto74



Joined: 06 Feb 2020
Posts: 66
Location: Italy

PostPosted: Fri Mar 13, 2020 12:42 am    Post subject: Reply with quote

Thanks Rik!
Antonio

rjlittlefield wrote:
With microscope objectives, a good estimate of DOF can be calculated as DOF = 0.00055/(NA*NA) .

So for example, a 40X NA 0.5 objective would have calculated DOF = 0.00055/(0.5*0.5) = 0.0022 mm.

You definitely will not be able to use a step size that is much larger than this, or you will get focus banding.

Depending on the subject and illumination, you may get cleaner results with a smaller step size.

I suggest trying both 0.001 and 0.002 mm and see which you are happier with.

--Rik
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Macro_Cosmos



Joined: 15 Jan 2018
Posts: 632
Location: Sydney

PostPosted: Fri Mar 13, 2020 3:33 am    Post subject: Reply with quote

I suggest 1um/0.001mm.
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Miljenko



Joined: 01 Jun 2013
Posts: 170
Location: Zagreb, Croatia

PostPosted: Mon Mar 16, 2020 6:41 am    Post subject: Reply with quote

Antonio,
I'm using Nikon MPlan 40x 0.50 ELWD and setting my DIY rail at 1.25 um for this objective since that is default full step for my rail. It seems just about right.
However, Kurt from Switzerland used 0.5 um step with his wonderful Odysseus butterfly wing scales stack using the very same objective.
Maybe he can comment on reasons for using such small step.
Best,
Miljenko
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