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How To Use Diaphragm With Mitty Lenses

 
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lonepal



Joined: 28 Jan 2017
Posts: 188
Location: Turkey

PostPosted: Mon Jan 22, 2018 12:43 pm    Post subject: How To Use Diaphragm With Mitty Lenses Reply with quote

Hi;

I am currently using a Mitutoyo 5X with a Sigma LSA and also a diaphragm between them.
All of them mounted in front of a Pentax bellows.
Sensor-Sigma LSA=200mm
Mitty-Sigma LSA=76-77mm

Source for Mitty-Sigma distance;

http://www.photomacrography.net/forum/viewtopic.php?t=25321&postdays=0&postorder=asc&start=22

I made some trials but I think I lost details when I close the aperture a bit.
I think this is because I am so close to the diffraction limit.

Is it useful to use a diaphragm with Mitty lenses?
If so, how do you use it?

Please advice me about using it.
Thanks.
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Omer
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ChrisR
Site Admin


Joined: 14 Mar 2009
Posts: 7504
Location: Near London, UK

PostPosted: Mon Jan 22, 2018 5:25 pm    Post subject: Reply with quote

You will lose resolution when you close the aperture.

Two uses -
#1) when you only need a small picture, perhaps 1000 pixels wide, so you can use a smaller aperture for more DOF. You wouldn't see the finest detail anyway.

#2) more usefully, to add frame(s) at the end of the stack. This makes the transition from sharp to blurred much more gradual, and out of focus background features become recognizable. If you mark your aperture ring so you can reliably set, say, 4 stops smaller, then you can increase the exposure by that amount.
Align the extra frame but don't include it in the stack. Re-stack it with the output image, afterwards. The reason is that in-focus details will appear in strange places, which you don't want.
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lonepal



Joined: 28 Jan 2017
Posts: 188
Location: Turkey

PostPosted: Mon Jan 22, 2018 10:46 pm    Post subject: Reply with quote

Thanks Chris.

This is very useful information for me.
I will use the diaphragm as you told.
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Omer
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dolmadis



Joined: 07 Dec 2011
Posts: 391
Location: UK

PostPosted: Tue Jan 23, 2018 1:17 am    Post subject: Reply with quote

ChrisR wrote:
If you mark your aperture ring so you can reliably set, say, 4 stops smaller, then you can increase the exposure by that amount.


I am sorry but I am struggling to understand the procedure.

HELP !!

BR

John
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Adalbert



Joined: 30 Nov 2015
Posts: 317

PostPosted: Tue Jan 23, 2018 10:06 am    Post subject: Reply with quote

Hi Chris,
What do you think about that:
#3: to look for the interesting object/detail with the closed iris and to take the photographs with the open one
BR, ADi
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Lou Jost



Joined: 04 Sep 2015
Posts: 1973
Location: Ecuador

PostPosted: Tue Jan 23, 2018 10:33 am    Post subject: Reply with quote

Adalbert, if I may chime in, that is a very good use for an iris. There are often surprises in the construction of a stack, since not all elements of the subject are visible at the same time. An iris increases the odds that you'll see the whole composition correctly.
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