gelatin filters for EtBr photography

FrohlichM frohlichm at STARBASE1.CALTECH.EDU
Thu Nov 17 23:23:40 EST 1994

>Paul Hengen wrote:
>This is nothing more than a Kodak Wratten Gelatin filter No. 15 yellow
>(catalog number 149 6648) that you can get for $6.95 US from your local
>camera shop.
>I wonder if filters for regular EtBr-UV photography are available at a 
>similarly low price from a camera shop.  Our camera rig has two filters
>in it - I'm not sure what they are - but they're so old scratched and
>smudged that image quality suffers.  Any suggestions?  Paul?
> Al McGraw
>	Univ. of Ga.

Many filters will effectively block the UV for photography of EtBr
fluorescence.  Unfortunatley, the filters typically also fluoresce, which
adds a diffuse glow to the picture.  You can avoid the problem by using two
filters; the bottom filter blocks UV but emitts a yellowish fluorescence,
while the top filter blocks the fluorescence from the filter below.  Gelatin
filters work well.  I recommend Kodak Wratten 8 (yellow) for the lower filter
and Wratten 25 (red) for the upper one.  Most good camera stores should stock
the Wratten 25, but the 8 will probably be a special order.  I find it works
significantly better than other yellow filters, so it's worth the wait to get
it.  Exposure times will be longer because the red filter blocks some EtBr
fluroescence, but contrast (the thing that matters) will be much improved.

Mike Frohich

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