Minolta, ttartisan, AstrHori and Sigma cut-offs

[dabateman]

I scanned some recently purchased cheap lenses using a bright Hallogen bulb that goes to 350nm. I don't have the correct configuration to see the true transmission of the lenses. But I can get a reasonable estimate of the UV cut off. 

 

I was inspired with the AstrHori 28mm f13 probe lens, a recent purchase. The front Leds look like a great place to play with options, for illumination.  But the lens cuts off hard at 404nm. So you could do UV induced fluorescence, without needing a filter. But not UV reflectance.  Its a fun 2x lens on its own that covers the Gfx sensor from 2x to almost 1x. 

Also nothing from a 365nm flashlight passes through it. A great way to see dust on the inner elements though.

But then a quick test through my other recent lenses with the flashlight looked promising. 

So I looked at their UV cut-offs today.

 

Ttartisan 50mm f0.95 cutts off hard at 375nm. But most likely good for just the 380s and 390s. So possibility good enough for fast UVA imaging.

 

The Minolta 58mm f1.2 is similar, gental low slope to 375nm. 

 

The Minolta 58mm f1.4 is a little better with 370nm hard cutoff. But again mostly the upper 380s and 390s are passing.

 

The Minolta 55mm f1.7 lens was better with 365nm cutoff.  

But the Minolta 45mm f2 was best at 357nm cutoff.  The slope of these is hard to predict with my setup though. 

 

My Sigma 105mm F2.8 macro without OS in EF-mount cutts off at 370nm with a shallow slope. Possibly the shallowest. So maybe ok for UV.

 

 

[Stefano]

Thanks. Some lenses seem usable.

[enricosavazzi]

Perhaps spelled Astrhori?

[dabateman]

8 hours ago, enricosavazzi said:

Perhaps spelled Astrhori?

Yes corrected.  My phone wanted to spell it the other way.

[dabateman]

Well I tried to push UV through the Ttartisan 50mm f0.95 lens on my stock Fujifilm 50S camera.  I don't have a M-mount to m43rds adapter.  So couldn't test on my full spectrum cameras. 

But it wasn't very promising on the Fujifilm 50S. At ISO 12800, f0.95,  needed about 4 seconds with Baader venus u filter. Focusing was hard, but I could make out a Bullseye of the dandelion. You could kind of see something at 1 second shutter speed.

But I wouldn't buy this lens for UV photography with a stock camera.  Will have have to test the Fujifilm with sun light. Using UV lights, it was about 8 stops less sensitive than a full spectrum converted Em5mk2 camera inside with 370bp filter.

 

[nfoto]

A result quite in agreement with expectation. 'Speed' is frequently not a sufficient substitute for sensitivity.