UAT 85/4.5 Focus Shift Test

[Andrea B.]

I first focused the UAT in visible light at f/4.5, then stopped down to f/11 to shoot the tree trunk covered in vines and aerial rootlets. I focused (I hope!) on the frontmost diagonal branch and not on the tree bark. Without refocusing, I then made a UV version and an IR (830nm) version. I'd say I was about 12 feet from the tree trunk.

 

Let me know what you think about this test. The Visible and UV shots look pretty close to me. However I think there might have been a small amount of focus shift between the Visible and the IR shot? Sometimes it is hard to say because the eye can be tricked by differences in contrast or tone. Also, lenses promoted as "corrected" throughout a particular ultraviolet, visible and infrared range may still exhibit minor amounts of focus shift depending on aperture setting, subject distance and lighting.

Added: I didn't think to add filters to the cause of focus shift.

 

The UAT is sharp and captures huges amounts of detail. It provides stellar performance on the 36MP Sony a7R-broadband.

 

My UV light meter was reading 3.8 mW/cm2 during these shots made between 14:24 - 14:28 UTC-5. The light was behind me, slightly to my right as I faced the tree trunk.

 

Equipment [sony a7R-Broadband + Asahi Ultra-Achromatic-Takumar 85mm f/4.5 + M42-Nex Adapter + Sunlight]

The images were converted in Sony Image Data Converter V4.

The only edit to each was an adjustment on the right side of the histogram (white point reset).

 

Visible [f/11 for 1/640" @ ISO-800 with Baader UV/IR-Cut Filter]

Unresized crop. Focus on frontmost diagonal, not on tree bark.

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Ultraviolet [f/11 for 1/3" @ ISO-800 with BaaderU UV-Pass Filter]

Unresized crop. Focus on frontmost diagonal, not on tree bark.

 

Infrared [f/11 for 1/400" @ ISO-800 with B+W 093 IR-Pass Filter]

Unresized crop. Focus on frontmost diagonal, not on tree bark.

 

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In the following resized, uncropped views, we cannot really see any differences in focus. (I can't anyway.......)

 

Visible [Resized, uncropped]

Resized to 1200 pixel width and re-sharpened in Photo Mechanic.

 

Ultraviolet [Resized, uncropped]

Resized to 1200 pixel width and re-sharpened in Photo Mechanic.

Ultraviolet is such a dark art!! I might have opened up the shadows a bit for artistic purposes, but not in this focus shift test.

 

Infrared [Resized, uncropped]

Resized to 1200 pixel width and re-sharpened in Photo Mechanic.

Typically the longer Infrared wavelengths make for slightly softened surfaces, but that doesn't seem to be the case with this lens at f/11. Of course, downsizing does promote sharpness, but still this IR looks very detailed to me. A slightly decreased DoF can be noted if you look at the background on the left and right sides of the image.

[colinbm]

You could lean a yard or meter rule against the tree at a 45deg angle & focus on the middle, then you can see the shifts ?

Col

[Alex H]

Adding any glass (=filter) to the optical system will cause focus shift even in super-achromatic lenses.

[Andrea B.]

I'd better go back and add that to my little list. :D It was rather late when I wrote this.

 

Col, I'll check to see if any of our yardsticks or rulers have markings which will show up across UV/Vis/IR.