Spring 2012

Spring 2012
by ani

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I'm plannning to photograph negative film like this. And I would like to know what would be the sweet spot of my lens to achieve best sharpness possible, what f stop and at what mm I should be shooting, also I will be using extension tubes. Thank you.

enter image description here

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Note that adding extension tubes can pretty much change all of the results of tests with the lens mounted directly to the camera. Sharpness, distortion, vignetting, etc. because it is spreading the center of the light circle wider. – Michael Clark Jan 21 at 22:07
up vote 8 down vote accepted

35mm to 55mm at f/5.6 to f/8.0 will get you great results with the EF-S 18-55mm STM.

I really like SLR Gear's visual interactive graphs for checking out lens image quality at various focal lengths and aperture settings. SLR Gear Lab Test Results

This is what a GREAT lens looks like, and below is what a CRAP lens looks like:

enter image description here

enter image description here

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That "crap lens" is seriously decentered. As Roger Cicala of lensrentals. com will affirm, on average 1 out of 10 times a lens is shipped round trip via courier it arrives back at his business knocked out of alignment. – Michael Clark Jan 21 at 22:04
    
The results from any testing center that doesn't test at least three copies of a camera/lens to confirm that the results from at least two are in the same range probably isn't worth the time it takes to read them. – Michael Clark Jan 21 at 22:11
    
The question mentions extension tubes, which could make a significant difference to the results. – David Richerby Jan 22 at 3:34

Note the minimum focal distance of the 18-55mm STM is 0,25m so this is part of the limitation on what you can shoot. Photozone indicates the maximum magnification is at 55mm, which is probably what you should use regardless of "sweet spot". Distortion, CA and vignetting are best at f8 and above and resolution at f8 is as good as you'll get across the frame. So 55mm at f8.

Strictly speaking you should probably use a macro lens for this if possible.

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re: minimum focus distance & macro: the poster did mention that he will be using extension tubes, so he will be shooting closer with higher magnification. – scottbb Jan 21 at 19:33
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Hard to know if this may give vignetting bad enough to impact the resulting shot, but it can result is very strong vignetting effects. – StephenG Jan 21 at 20:34
    
indeed, it's possible. I digitized loads of slides with a Nikkor 55mm ƒ/3.5 and a bellows for 1:1 repro, and at ƒ/8 I had no noticeable vignetting. Of course, the Nik+bellows on full frame is a perfect setup for this type of work... – scottbb Jan 21 at 20:55

This is not an answer to your question, but a suggestion for your setup. In order to help minimize any extra glare or reflections off of the front of your negatives or slides, try to block out the rest of the light table.

Or, create some "gobos" (black absorption panels) out of dark construction paper, or black matte-painted foam board, and use them to surround the field of view to create a dark tunnel where your slides are exposed.

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Yes, I have already considered that, also I couldn't find the proper picture, but I will be shooting overhead and not like in the picture and I'm scratching my head as to how I'm gonna extend my tripod on to the light pad, I've seen many tripod extension arms, but damn, for a simple metal extension arm they charging almost $100. So yeah, still searching for a cheap way to photograph overhead with a regular tripod that I have. – Giancarlo Jan 21 at 19:50
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@Giancarlo is your tripod center column reversible? – user13451 Jan 21 at 21:56
    
@MichaelT It's this tripod: amazon.co.uk/Hama-00004161-Star-61-Tripod/dp/B0000WXD0W It has center column which is extendable, but not folding in any way. – Giancarlo Jan 22 at 6:38

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