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Thanks Bert;
50 minutes is about as long as I
can go with the Schmidt/W92 combo before the negative turns into a solar filter!
To think of it another way, 4 minutes with an f1.5 Schmidt is about the same
effective exposure as 1 hour at f6. The wratten 92 isn't as effective as the
Lumicon Ha filter, which in turn isn't as effective as the Custom Scientific
filters but you have little choice with Schmidts - they are focused for Wratten
filters only. If I could just get a Custom Scientific model in 8"
diameter........ :-)
John Mirtle
Calgary, Ab. Canada
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