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UltravioletPhotography

Monobloc studio flash as a UV light source?


dunksargent

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dunksargent

I'm considering various possible UV flashlight sources and wondering about the feasibility of modifying a small monobloc studio flash. These are frequently listed secondhand at £reasonable cost and offer:

 

User changeable / replaceable flash tubes

Modelling light

Variable power

Low trigger voltage (on most modern types)

Large efficient reflector

 

Because the flash tubes can be easily pulled out, polishing off the UV coating should be relatively easy using e.g. Polywatch or metal polish.

 

I would intend using a monobloc flash manually - adjusting flash intensity via the unit's variable power and by altering the flash to subject distance.

 

The main advantages of such a unit(s) compared to a regular speedlight would be that:

 

1) The monobloc's light output quality should be much better by virtue of its efficient reflector.

2) The UV output should be greater by virtue of its relatively higher power

3) The modelling light would be an aid to lighting composition / shadow control.

 

However, before I decide to buy a secondhand example and attempt to modify it, can anyone think of any reasons why the proposal might not be feasible?

 

And is the UV coating only on the outside of the flash tube?

 

Best wishes

 

dunk

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Get an uncoated Xenon flash tube and you're halfway to UV light bliss. The protecting dome of many studio heads is often coated for UV reduction. These are easily spotted by their golden-yellow tinge. Replace with a non-coated version if possible. Using a naked flash tube is not recommended as there is great power involved and an exploding Xenon tube is no joke.

 

Do note that studio flash reflectors tend to be very inefficient for close-ups since they are calculated for use with umbrella reflectors or soft boxes. Removing the reflector entirely only makes the situation worse. Do experiment to learn where the focused distance of the flash unit resides.

 

I'm using Broncolor studio flash heads (Minicom) and they are really powerful. I have two of them with uncoated Xenon tubes and a third for fill-in and portrait work (visible and IR). No problem doing UV shooting at f/16-f/22 @100 ISO.

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dunksargent

Thank you for the advice. I've ordered a secondhand Interfit 150 monobloc which is a relatively low power unit (150 watts) and has a user changeable flash tube. The 'price was right' and I'll try some regular close-up photography experiments with it first. If it's a viable close-up light source then I'll attempt polishing/removing the flash tube's UV coating. I do not plan to use the light at ultra close distance - I'll be using a M4/3 camera with an 80mm lens so there should be a reasonable lens to subject distance within which the lamp can be aimed. Unlikely that will be able to use 100 ISO but 400 to 800 ISO might be possible. My camera is still away being full spectrum converted and the UV light source is the last of the initially required apparatus.

 

Best wishes

 

dunk

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Dunk - Looking forward to seeing how your Interfit will work as a UV light. Be sure to show us a photo of the set up.

And OK to post a Visible experiment photo here in this thread too. "-)

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dunksargent

Polishing the UV coating off the flash tube will be a little more difficult than anticipated. The flash tube spring retainer unhooks and the tube then pulls out of the unit - but the tube has wire safety harness threaded around it which will require removal before the UV coating can be polished off … and then I will need to make a new safety harness by wrapping/coiling fuse wire or similar around the tube via a series of half-hitches. The wire harness prevents tube glass fragments flying out of the monobloc in the event of the flash tube exploding. The polished tube could be used 'bare' but for H&S reasons I prefer to make a new wire harness. The unit's slave cell works fine so can be activated by the G1's built-in flash - but the camera is still away being modified with a 'full spectrum' sensor filter.

 

 

Best wishes

 

dunk

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Dunk,

I think perhaps the thin wire harness as you call it is part of the electrical triggering circuit.

If removed the tube may not flash, don't ask me why, I am sure to get that confused.

There is a thread from last year over on PhotoZones you might find a helpful review.

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I can confirm the 'harness' is an integral part of the flash tube itself. It is required for the firing of the tube.

 

The tube may be uncoated if it looks clear (without any yellow or brownish tinge) against a white background. Usually the UV correction is implemented by the protective dome of the flash unit.

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dunksargent

Dunk,

I think perhaps the thin wire harness as you call it is part of the electrical triggering circuit.

If removed the tube may not flash, don't ask me why, I am sure to get that confused.

There is a thread from last year over on PhotoZones you might find a helpful review.

I can confirm the 'harness' is an integral part of the flash tube itself. It is required for the firing of the tube.

 

The tube may be uncoated if it looks clear (without any yellow or brownish tinge) against a white background. Usually the UV correction is implemented by the protective dome of the flash unit.

 

Thank you for preventing me ruining my new s/h studio flash! There is no coating visible on the Interfit Venus 150 flash tube. By 'dome' do you mean a glass dome with a UV voting? If so, there is none - just has the standard metal reflector with silver interior. But if no UV filter present, how can the unit be safe to use for portraiture 'as it is' i.e. without, e.g., a softbox or an umbrella? Surely there would also be UV light spill/reflections when using the unit with just the metal reflector or without it in bare bulb mode - which cumulatively could be dangerous for the photographer - as well as being dangerous for the model?

 

Best wishes

 

dunk

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Another point to consider is that the tube may be constructed from a UV blocking glass rather than coated. It seems logical that fragile external UV coating, which might be inadvertently removed via handling, would not be preferable for user replaceable flashtubes.
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dunksargent

A picture or two of your flash unit would be helpful at this stage.

Another point to consider is that the tube may be constructed from a UV blocking glass rather than coated. It seems logical that fragile external UV coating, which might be inadvertently removed via handling, would not be preferable for user replaceable flashtubes.

 

Unfortunately the studio flash unit was dropped accidentally (it fell out of its box) and has ceased functioning - and unlikely to be an economical repair if internally damaged. I will try and post some photos of the unit but initial attempts at adding images to my posts have not been successful - but I will persevere - I post images on other fora without problems.

 

Best wishes

 

dunk

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Dunk, sorry to hear about the studio flash's demise.

 

I'm not sure why you would be having problems posting photos.

What is the error message you are getting?

 

The advanced uploader requires Flash 9.

The basic uploader does not.

Try them both.

 

On occasion I've had an upload fail because the browser needed to be refreshed for some reason. Probably because I left the post I was working open for so long, something timed out.

 

Anyway, please let me know of the error message you got so I can try to help.

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