Introduction

[DKoch]

Hello everyone, just wanted to introduce myself; thanks for accepting me! I am a Toronto Canada based cinematographer; I love experimenting and UV imaging is a newer target of mine.I have done a bit of UVA photography with photochemical films in the past but of course that is much trickier with CMOS sensors etc...I have begun some experiments with high end digital cinema cameras, particularly the RED camera family as they allow the OLPF / IR cutoff filter to be easily removed. There are " Full Spectrum ( essentially clear) " OLPFs made by other parties for these cameras. Usually they are expecting IR imaging by doing this; I have done a bunch of this, but I wish to explore the UVA/ deep violet region.

  I am also exploring vintage lenses with higher UVA transmission characteristics.

I used to do electronics as a hobbyist, so years ago I made a UVA photodiode "light meter cell" that can plug into my Kenko Incident Light meter ( so I didn't have to make an entire light meter; I can use all the electronics of the meter...I only have to provide the spectrally modified sensor)see attached photo.It works really well for UVA measurements in "arbitrary" units so far. We sometimes use various UVA 365nm light sources to excite fluorescent paints etc, so I'm trying to create a measurement system for that too, as newer LED based UVA sources are sometimes added to the market.

 

doug

 

[OlDoinyo]

Welcome. UV cinematography is largely an unexplored frontier; it will be interesting to see results from that direction (you may find it easier to do with film, however.)

 

[lukaszgryglicki]

Hi, nice to have you with us!

 

[Fandyus]

Can't wait to see UV videos taken with s high end cinematic camera.

I might sound like a broken record because I say this to almost every newbie, but look into the Industar 50-2. It's an exceptionally cheap lens with decent sharpness and full frame coverage that transmits UV well. It also has a long flange as it's been made for SLRs.

[colinbm]

Welcome aboard Doug
UV photography & electronics can be fun.

[Andy Perrin]

Hi Doug, I'm looking forward to some experiments with that RED camera! Gee whiz that thing is fancy.

[DKoch]

I shall keep you all informed! I'll try and get at the experiments with the RED cameras in January. My long range plan is to actually have a custom filter to use in place for the OLPF that will leave the green and red channels unaffected , but essentially create a UV/deep violet channel in blue channel... that filter will take a few months to figure out and get made...there are locally available "full Spectrum" OLPFs for the RED cameras that apparently do have reasonable UVA / deep violet transmission.The camera's UV sensitivity is a big unknown at this point.

 

[DKoch]

Fandyus: I must search out this lens you suggest!

[DKoch]

Quote

Welcome. UV cinematography is largely an unexplored frontier; it will be interesting to see results from that direction (you may find it easier to do with film, however.)

 

certainly true...it used to be easy for us to get Plus-X ( ISO 80) and Double-X (ISO 250) Kodak B&W negative films in 16 and 35mm... they had very good UV sensitivity.Focus was a serious issue though, especially in 16mm where the flange depth accuracy is more critical. The corrections in our lenses just didn't take UV into consideration! I remember once in 16mm using my trusty 18A filter on a favourite 16mm film lens.We were near wide open in overcast light T2 ( f2); when we got the film back the image was completely out of focus! 10mm @ f2...yikes

[Andy Perrin]

1 hour ago, DKoch said:

I shall keep you all informed! I'll try and get at the experiments with the RED cameras in January. My long range plan is to actually have a custom filter to use in place for the OLPF that will leave the green and red channels unaffected , but essentially create a UV/deep violet channel in blue channel... that filter will take a few months to figure out and get made...there are locally available "full Spectrum" OLPFs for the RED cameras that apparently do have reasonable UVA / deep violet transmission.The camera's UV sensitivity is a big unknown at this point.

 

 

We have plenty of people who have experimented with "BUG" stacks which have Blue Ultraviolet and Green (BUG). It's going to be hard to reduce the red and green light to levels where the visible does not overwhelm the UV, but you also don't get IR contamination. On the plus side, most of the UV does go into the blue channel naturally. 

 

Many of us have taken photos where we combined a visible and a UV photo into a composite like this in a photo editor, but we don't usually do it in realtime video with a single filter!

 

This is literally the opposite of the IRchrome filter, in which the red channel is replaced with IR.

[nfoto]

The camera's UV sensitivity is a big unknown at this point.

 

I'd be even more concerned about the UV transmission properties of the used lens(es).

[Andy Perrin]

Well the lens transmission issue can be fixed by getting a different lens, although the choices may be limited for a sensor that large. If there is coated sensor glass or other weirdness he may have a point about the sensitivity. It is a very odd camera. 

[Nate]

Welcome Doug, lots of great people here to help with any questions you have. 

[Doug A]

Welcome to the forum. Your hand built UV A detecting module is a very interesting piece of electronics. Looking forward to your posts.

 

Another inexpensive UV lens is the Igoriginal Kyoei 35mm F3.5 clone on eBay. $129 with UV filter stack.

 

Thanks for sharing,

Doug A

[DKoch]

dumb question: if I see a specific comment I want to reply to , but there are other comments below it, how do I reply to that specific comment? By using the "quote " from that comment? I see that I can't just click on a "reply" tab for a specific comment...

[nfoto]

You are correct. Click on the "+quote" field and the required quote appears in a reply box.

[DKoch]

On 12/14/2021 at 6:36 AM, nfoto said:

The camera's UV sensitivity is a big unknown at this point.

 

I'd be even more concerned about the UV transmission properties of the used lens(es).

yes, both are big issues, unlike with IR which is pretty simple by comparison. My last big testing in IR with RED camera with modified " Flash Color IR" OLPF ( Optical Low Pass Filter) was really simple as we could monitor our results on a high quality monitor in real time! Hot spots in certain lens/f stops, focus offsets due to wavelength and exposure differences were all simply to monitor and take note of...back in photochemical days with Kodak  IR B&W 2481 film, it was "cross your fingers and hope for the best!"

 

[nfoto]

Indeed. However, the pesky hot spots apparently were less ubiquitous if memory serves (a long time ago since I used that wonderful film 2482).

[DKoch]

On 12/14/2021 at 12:16 PM, Doug A said:

Welcome to the forum. Your hand built UV A detecting module is a very interesting piece of electronics. Looking forward to your posts.

 

Another inexpensive UV lens is the Igoriginal Kyoei 35mm F3.5 clone on eBay. $129 with UV filter stack.

 

Thanks for sharing,

Doug A

I was thinking that I might make another module that detects from about 250 -400 nm as a " safety tester"... just to know what any UV source is putting out in wavelengths that could be dangerous to our eyes... UV LEDs don't have a malfunction mode I am aware of whereby they could suddenly start producing , say, 300nm UVB and we are not aware of it...older  mercury vapour based UV sources could potentially leak UVB (C?) and you'd not know it...I bet by now I can find a photodiode with that kind of sensitivity range!

[DKoch]

1 minute ago, nfoto said:

Indeed. However, the pesky hot spots apparently were less ubiquitous if memory serves (a long time ago since I used that wonderful film 2482).

there were so many things to worry about back then. Starting with film loading in our changing bags: I'd make the assistants load the IR film inside their black bags inside a darker truck or film loading room ; you couldn't bet that the black fabric of their changing bags was IR opaque! 

  The next thing was that all our cinema cameras had pressure plates that would press the film against the gate to keep it perfectly flat; all of them were polished smooth chrome.The problem with the Kodak B&W IR film was it had no antihalation coating ( hence the dreamy ,smeary look, especially in overexposed areas of the frame!)...so you would frequently get pressure plate " images" exposed into your image if you were unlucky from the light going right through the films emulsion and substrate, then coming back again and exposing the film... eventually, we used a very high end camera , the  Arriflex 435; it could film at up to 130 frames per second, was rock steady and , paradoxically, could do all this with it's chrome pressure plate removed! You would think it was an essential part, especially as the IR film was 50% thinner than the colour film the cameras were designed for! odd, a tribute to the precision of the machining of the camera's parts I guess...fine German engineering.

Finally, this newer slick camera used an IR LED to detect the film run out at the end of a roll and shut down the camera! So we had to tape over that to disable it.. 

Once we had discovered all these weird details, B&W IR cinematography became much more consistently better...

[DKoch]

On 12/13/2021 at 9:25 PM, Andy Perrin said:

 

We have plenty of people who have experimented with "BUG" stacks which have Blue Ultraviolet and Green (BUG). It's going to be hard to reduce the red and green light to levels where the visible does not overwhelm the UV, but you also don't get IR contamination. On the plus side, most of the UV does go into the blue channel naturally. 

 

Many of us have taken photos where we combined a visible and a UV photo into a composite like this in a photo editor, but we don't usually do it in realtime video with a single filter!

 

This is literally the opposite of the IRchrome filter, in which the red channel is replaced with IR.

I had been anticipating this problem: the UV sensitivity will be very low compared to the green and red channels; my solution is to use a simple filter on the lens that is effectively and blue/UV transmitting filter that attenuates the red and green channels appropriately.This should bring the 3 channels into a closer " white balance" as it were, but of course the whole system's sensitivity will be fairly low! I think it's going to be difficult to find "fast" high speed lenses with good UV sensitivity! Some of our higher end digital cinema cameras have very low noise  and can shoot beautifully at ISO 3200 and look great...   also, for pure monochrome UV shooting, there are some true monochrome digital cinema cameras for rent; they have no Bayer RGB filters on them... the question would be if one can remove whatever IR cutoff/cover glass that would be potentially attenuating the UV reaching the sensor...I think the sensors are Back Illuminated now, so they might have better UV response than one would think..

[Andy Perrin]

We have plenty of examples of F/2.8 or F/3.5 35mm lenses here that do well in UV. Also ISO3200 is no problem for my Sony A7S, which does indeed have a BSI sensor. I’ve taken UV video here and it’s not a big deal. If you can bring the visible red and green down enough, I think it will be ok. 
 

By the way, you must block the blue very well or the UV won’t stand a chance of overcoming it. 

[Doug A]

@DKoch a new module would be a worthwhile addition to the kit. Can't be too safe. 

 

 

Amazing the Arri worked without a pressure plate. 

 

Thanks for sharing behind the scenes stories,

Doug A

[dabateman]

The Old Sigma art 19mm f2.8 and 30mm f2.8 in m43rds or Sony E-mount are great, as is the Canon 40mm STM f2.8 lens.  For video I would work with those.

Then you can use a camera like Andy's Sony A7S mk1 for high ISO video.

[Andy Perrin]

He has better cameras than mine, Dabateman. I just meant if it works on mine it will definitely work with one of those Red cameras.