Characterizing the Transmittance of 7 Lenses using a Simple Method

[Andrea B.]

Omegabob on Ebay often sells filter over-runs or "seconds" there, so it is a great way to eventually pick up small narrow bandpass filters for a Sparticle board. Of course, what you also need to do is make sure the Sparticle filters have similar transmission rates. In a single Sparticle shot it would not do to compare a UV-pass filter which can pass 90% at its peak to one which can pass only 40% at its peak. You could, of course, photograph each such filter at an appropriate exposure length for that filter's transmission rate. It all gets very tricky very quickly. :D

 

Then too, in sunlight we have ever decreasing amounts of UV with shortening of UV wavelength. So in either the Pinhole Test or the Sparticle Test it's not like sunlight is really all that much better for in informal determination of a lens's UV-capability than is a 365nm peaked UV-Led output. Running a Sparticle test might very well need to include several exposures at increasing exposure lengths in order to better determine where a lens transmission bandwidth begins to drop as wavelength decreases.

 

So anyway, I think the Pinhole Test in good sunlight would tell a similar tale as you have shown here. And the Sparticle Test would further narrow down the approximate transmission range. That's been the case with other results from such informal lens UV transmission tests.

 

All these informal tests are good in the sense that they do give us an indication of approximate UV transmission for a lens.

 

Someday we need to delve further into other factors which make a lens good for UV. B) :rolleyes: :rolleyes:

[Andrea B.]

P.S. Different conversion apps can give different false colours depending on the algorithms and samplers of a particular white balance tool. So, I would suggest not using Photoshop false colour as any indication of UV capability? I'm thinking you should look at the amounts of raw, demosaiced colour recorded by a particular camera + lens + filter combination before white balance is applied? The Raw Digger* app might be very useful to you for this.

 

 

*Neither I nor Bjørn nor UVP is associated in any with Raw Digger or its developers. I have simply found this app to be quite useful for UV/IR experiments.

[Andy Perrin]

Then too, in sunlight we have ever decreasing amounts of UV with shortening of UV wavelength. So in either the Pinhole Test or the Sparticle Test it's not like sunlight is really all that much better for in informal determination of a lens's UV-capability than is a 365nm peaked UV-Led output. Running a Sparticle test might very well need to include several exposures at increasing exposure lengths in order to better determine where a lens transmission bandwidth begins to drop as wavelength decreases.

 

I don't entirely agree with that, because sunshine is often what we use to shoot with (unless you are fortunate enough to have a UV modified flash -- I am not! -- in which case pictures with the flash would be more helpful). So the performance in sun is what I am really interested in, speaking for myself here only. Then, too, we all have a good feel for how the sun behaves with the lenses we own, so as an informal reference I think it's kind of helpful?

[Andrea B.]

Yes, you have made a good case that lens evaluation in sunlight (via Sparticle or Pinhole Test) is more useful for evaluating lens UV capability than is 365 nm UV-Led peaked light. ;)

For most of us, most of the time anyway. :D

 

I just got to thinking about that decreasing UV sunlight slope....

[Andy Perrin]

Heh, Andrea, I am going on a bit, I guess. I will go back in my cave and stop barking now. :)