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UltravioletPhotography

JML test - does this mean anything?


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One of the icons of the extreme macro world is the JML 21mm f/3.5. It can deliver really nice photos, and you can

get a good 5:1-8:1 out of it or so before diffraction sets in. This is a shot of mine with it a couple of weeks

back, a pretty Jewel Wasp.

 

Anyhow I've always wondered why people were landing on my JML page looking for some JML 50 and it turns out

that is a nice UV performer. So I thought I'd see what happens with JML 21mm.

 

I don't have a spectrometer or anything to test UV but I did learn from this thread that sensors don't like excess

UV much (the red shot). So I'm hoping red indicates UV transmission, and then I also added a UVIR cut filter

to compare.

 

The only remotely UV capable optic I have is El-Nikkor 80 f/5.6, the chrome version, so I also used that as

a reference. This is just a cotton bud lit with 365nm torches, one of which is venus filtered.

 

I don't know if this means anything but I'd appreciate it if someone more knowledgable than me might comment

on this, or suggest a DIY UV transmission test that would be better. To me this reads like JML21 might be UV

capable to some degree, which would not be all that surprising as we know the 50 isn't too shabby. But if so

that would be rather nice, as it would make one of the nicest extreme macro lenses even nicer!

 

Thank you

 

14172109305_865ee5f6a7_o.jpg

 

 

As another note of interest, a focus shift that I alluded to in my other thread above is actually pretty visible in

the bottom shot, it obviously changes when I cut the UV...

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The Jewel Wasp is beautiful!

 

Did you use a filter for the left-hand shot ? I'm not sure what that shot represents ??

 

Do-It-Yourself UV Transmission Tests:

  • Shoot a known UV-bullseye flower (Dandelion, Sunflower, Rudbeckia). If none are growing wild, you can usually purchase a Sunflower in a grocery store or florist shop.

  • Aim a UV torch through the lens and aim it at a piece of ordinary white printer paper. This kind of paper fluoresces under UV light due to optical whiteners. Look for the round (usually blue) fluorescing spot on the paper. (This is also a good check to ensure there is no internal fluorescence or strong reflectivity from the lens which might contaminate a UV photograph.)

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Thank you Andrea & Bjorn, I will try the second of those tests tonight!

The left hand shots Andrea are just a Nichia torch onto the cotton with no barrier filter.

 

One thing Bjorn I'm unclear about. If the red is excess IR, why does a Wratten 2b block it as per the pics

on this thread. The curves of that Wratten filter would indicate it passes IR or am I reading that chart wrong :(

 

Anyhow I have a hot mirror on the way, let's see what difference that makes!

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Fwiw, the second of these tests didn't reveal much. Every lens I shone it through shows the

blue spot :D

 

I think my understanding (or imagination) is a bit limited here, something I'm not grokking.

When we see infrared as red, is it because the thing is hot? I always thought IR meant heat :(

Can someone point me to a link that might explain this in layman's terms?

 

Thanks!!

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The Wikipedia article is as good as any: http://en.wikipedia.org/wiki/Infrared

 

Thermal Infrared is "way out there" at 8000nm or so. We photograph in the non-thermal, near-Infrared wavelengths -- typically between 700-1000nm.

 

The photos above are not fully labeled for easy reference, so it is hard to say why you recorded red. For the bottom left photo above, *IF* you used a 365nm UV-Led with no filtration and a lens with no filtration, then likely you recorded some Visible light leakage from the torch IF you were shooting in a totally dark room. Those torches are not perfect. IF, instead, you were shooting filterless in ambient light, then you likely recorded some IR contamination also.

 

I don't recall what camera you are using, but your blue spot is likely some kind of light leakage. Be sure to cover the viewfinder while photographing in IR or UV. Light can also leak through open ports or through aperture windows (on such lenses as have them). Sometimes there are internal reflections from a lens which causes flare or hot spots when used outside the Visible range.

 

Continue the experiments and soon you will sort out the various variables !! :D

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Thanks Andrea - yes there's a lot to discover, it's interesting stuff and I hope people will put up with my newbie mistakes :D.

 

I have a cap on the viewfinder, the first thing I did because of my ND110 days!

 

The red photos were with 2 365nm torches, the left one had baader u on it. No barrier though.

 

Hohum, onwards and upwards

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Rubbing salt in the wound :D. I also read that link - late last night half a day after ordering one!!! Stellar :(
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