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Old 23-06-2015, 07:05 PM
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gregbradley
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Join Date: Feb 2006
Location: Sydney
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Yes good point Richard. Average QE would be a lower number.

Ray I think your system is of use I am not sure the multiplication factors of how much one system is faster than another are spot on. Perhaps it is and I haven't realised the differences as much as they are.

Certainly the Honders at 305 F3.8 with 16803 is plenty sensitive and with the Trius694 even more. I took an image of the Seagull Nebula with the Honders and the Trius and it showed the bubbly jellyfish part very clearly with little noise after only an hour of Ha. I was amazed as I have imaged that area with the CDK17 and the Trius and it was quite noisy still after an hour's exposure so yes there is a direct example. Of course the image scale was quite different with the Honders being more widefield and there is the rub I suppose - Image scale.

So aperture and QE still remain the 2 most important factors in the speed of the system and F ratio is more the wideness of the field.

Greg.
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