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Discussion Starter · #1 ·
Hi Guys

Thanks for all the info i've lurked on and absorbed. The forum is outstanding.

I'm looking for some suggestions/insight into my issue. I have DIY'd an exposure unit. Neoprene vac top (works great) with a signle point 400 watt Metal Halide. Just got a new bulb in the right nm spectrum. around 400.

My previous bulb took 20 minutes but was still slimy (not fully exposed), but getting decent images. But I upgraded to save exposure time. Takes the Same time with the new bulb. And still not fully exposed. Could it be my Ballast that's not allowing a full 400 watts from the bulb? 20-25 minutes with a metal halide seems a bit lengthy no?

I'm stumped. Thanks for any help.
 

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What glass did you use? How thick is it?

I didn't go all-out and get the ultra clear glass, but I did use low iron glass. My 1000w unit exposes Saati PHU in 24 seconds. Mine is a light intended for use in stadiums, and the like.

Are you absolutely sure that the bulb is unfiltered? There are two types of MH bulbs. Ones that have a coating that filters out UV light and ones that do not have such a coating. That latter type of bulb is for use in light fixtures that themselves filter out UV light. My guess is that either you have a filtered bulb or that the glass in your unit is blocking the UV.

Unless you have a compelling reason to use a Diazo emulsion, I would use a fast poly-type like emulsion, like Saati PHU. Also, a thicker coat of emulsion is not always better (unneeded for water base).
 

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Discussion Starter · #3 ·
Thanks for your help, I didn't get a low iron glass, which definately would help for sure I just didn't think it would affect it that amount.

I am using a dual cure. Poly plus s. I know that affects exposure time significantly too, but I'm using laser vellum, and my past photopolymer screens were hard to
Blow out, (I'm assuming because of opacity issues from the laser printer) but edges were still chipping during washout.

The bulb I have is a 10,000 k grow bulb I found in the right light spectrum, I can't see there being a uv filter for growth purposes but I have no way of telling.

Maybe I'll start with the glass.

I just figured a 400 watt would at least get me around the 3-5 minute mark. 20-25 minutes seems a bit nuts to me.
 

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Discussion Starter · #5 ·
In case anyone is having the same problem, I somewhat fixed the issue. I added the halide reflector back in the mix and I raised the bulb to glass height to 18 inches (from 24 inches). Got a decent exposure with dual cure at 5 minutes. Thanks for the help.
 
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