[Nick Rocco]

I know the DIY exposure unit is an old topic with lots of posts. This is more of a survey.

I am building a 1000 watt metal halide exposure unit with a vacuum lid.

My question is... Should I use a reflector behind the metal halide bulb or not?

Please let me know if you are using a reflector or not and how it works if you are.

Thanks!

 

[PositiveDave]

Professional ones have a reflector, really you are wasting a lot of energy without one.

 

[BroJames]

Wasting as much as 94% energy?

For an A3 size image/transparency, the diagonal distance would be 19" or so. This would make the ideal distance of the bulb at 27-1/2" below the glass. Without a reflector, the UV lost is quite great.

I am not sure what or how much the effect of reflected UVs have on the overall quality of the exposure but it seems that commercial exposure units claiming to offer the sharpest possible exposures have reflectors and/or are painted white inside.

[media]http://i7.photobucket.com/albums/y295/BroJames/silkscreen/exposureUVangles2.jpg[/media]The illustration is only an estimate but shows that at a distance of 27.5" or 1.5x the diagonal measurement of an image/transparency about the size of an A3 or 11x16inches more or less, without any reflectors and depending from which side you measure, only 6-9% of the UVs from the lamp reaches the entire film/image.