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UltravioletPhotography

Some lens transmission curves


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I found the following on another board. It is an old thread at http://global-infrar...th-repost-forum

 

""So here's today's data

Lens tested

1. 80mm f5.6 El-Nikkor enlarging lens (as recommenced by Dr Klaus Schmitt for UV photography)

2. An Early Shuttered Koni-Omega Hexanon 90mm f3.5 (hopefully an example of typical un-coated lenses)

3. Raynox 250 close up diopter

4. Fujain 35mm f1.4 c-mount

5. Olympus 17mm f2.8 (retested with extension tubes to allow better alignment)

6. Panasonic 14-42 kit lens (tested at 42mm)

7. A soft focus modified Pentax M50mm f1.7 (actually just the rear group removed, I'll test this separately later)

 

I'll post the actual measured transmission and leave any correction for bent/blocked beam for others to attempt.

(A repeat test of the Oly 17mm further from the detector showed significantly lower results - makes sense as the beam spreads more - however the ratio of the results generally increased with wavelength though not quite as a constant function. It may be a function of the refractive index of the lens)

 

http://uvroptics.com/images/Lens%20transmissionTable1.jpg

Most of the spectra were reasonably smooth, though one I think it was the 14-42 did show a strong narrow absorbance just short of 900nm."

 

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posted "2014-06-11 21:04:43",

"Time for another set of data http://storage.probo...iley/smiley.png

lenses

1 An Unbranded 25mm 1.7 c-mount

2 A Helios 44M (58mm f2)

3 A RJ focal reducer (EOS to µ4/3)

4 Tamron Adaptall2 SP90 macro

5 Tamron Adaptall2 200mm f3.5

6 Budget 0.42x wide angle adapter

 

Fresh Data

7 Sigma SA 28-200

8 Sigma SA 18-50

 

http://uvroptics.com/images/Lens%20transmissionTable2.jpg

 

Three of the lenses (1,4 & 6) had significant sharp dips in transmission around 920nm, loosing another 2-3% transmission over 20nm or so. Since most of these are among my cheapest lenses this may be down to trace internal muck."

 

 

http://uvroptics.com/images/LensTransmission1.jpg

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The Tamron 200 is mildly interesting--most refractive telephotos in that range do not fare so well. Otherwise, no big surprises in this lot. Zoom lenses have thick glass and tend to perform more poorly than primes--we see that here to some extent.

 

It might be advisable to normalize these spectra at some reference wavelength--perhaps 450 nm? That would give better comparisons.

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Reed, I can't access the link these came from as it requires registering to see it. Was there any more information on how the data was generated and the setup used?

 

I'm guessing that this was done without an integrating sphere though. In first set of data, the Olympus 17mm lens shows such a low degree of transmission even in the visible region, that looks like lots of light has been lost because of the wide exit angles from the lens. I've noticed this effect when just putting a lens between my collimated light source, and collimator on the fiber optic which goes to my spectrometer - the lens I want to assess distorts the light beam, even with a collimated light source and max transmission can drastically change.

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No, sorry, Jonathan, that is pretty much all the OP gave. No equipment or methods. :(

No problem and thanks for following up Reed. Lens transmission work is incredibly tricky, especially when you add in the complexity of trying to get meaningful numbers in UV.

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