Lack of sharpness question

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Ingmire
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Lack of sharpness question

Post by Ingmire »

Hello

I am getting my first macro rig set up and running some test shots.
I've got a 24mm Nikon lens reversed on a Nikon bellows. I'm shooting with the bellows fully extended. My test shots were at f16 and lit with an elinchrom Dlite.

I think with the strobe my lack of sharpness is not do to any vibration (motion blur).

Could the image be soft due to the lens being used at too high of a magnification?

In the image I have a 100mm lens on. But my question is referring to my 24mm

Thanks!!

Image

Saul
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Re: Lack of sharpness question

Post by Saul »

Ingmire wrote:...I'm shooting with the bellows fully extended. My test shots were at f16...
Hi Jordan, diffraction kills your sharpness. Please try at 4~5.6 (not sure what is the "sweet" spot for this lens)
Saul

ChrisR
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Post by ChrisR »

As Saul says.

It's an "OK" lens, - for a retrofocus which is being used other than the way it was intended. Their best 28mm isn't great, reversed.

If your PB-4 is fully extended,
at a guess you have near 10x magnification, which means at a marked f/16 you have an effective aperture:
(10+1) x 16 = eff/ 176. :(
For an aps/DX sensor, you'd want lower than eff/20.

It may be best at about 3x to 4x at f/5.6.
Even there you could beat it, with for example a Canon MP35mm f/2.8, or a fairly cheap microscope objective ( ~ depending on your sensor size). You may not see an objectionable difference at say 1600 pixels wide after post processing.
So the method is to choose what magnification you need, find the best aperture , then stack pictures taken about 80µm apart with very diffuse lighting, and see what happens :)
Chris R

ohdeeremee
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24mm

Post by ohdeeremee »

I did some self tests on this lens a couple years back for "sweet spot". (Nikkor 24mm f/2.8 serial 463xxx) In my tests, I had a PB-4 bellows and an additional extension set (Nikon's PK-11A, K2, K4, K5, K3, which adds an additional 48.8mm). My charts are marked as follows:
Bellows at 141/190 (~6.3X) f/8 best
Bellows at 70/190 (~9.57X) f/5.6 or f/8 best
Bellows at 00/190 (~12.7X) f/5.6 best.
One stop + or - marked as OK
Others stops marked "fuzzy"
That puts all the effective F-Stops (for me) over 40... not good. Diffraction will kill you on this lens setup.
Hope that helps...
G

Ingmire
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Post by Ingmire »

I can't thank you guys enough for the solid info.
I'm looking to shoot between 5-10x magnification.
I'm using a full frame sensor (Nikon d750) on a pb-4 bellows.
Can someone recommend a lens or microscope objective I could / should try and what components I would need to attach the lens / objective to the bellows?

Thank you thank you!

ChrisR
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Post by ChrisR »

Have a look here:
http://photomacrography.net/forum/viewt ... 684#207684

Lots to read!
Sensor Coverage is something to watch out for, on FX.
Chris R

Lou Jost
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Post by Lou Jost »

Also you should consider coupled lenses instead of extension; for a given magnification there is less diffraction, especially for lower magnifications.

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