Thread: F-ratio myth
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Old 20-02-2018, 08:09 PM
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RickS (Rick)
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Quote:
Originally Posted by Slawomir View Post
However, if I put a reducer on my modest 4" f/6 scope and make it work at f/4.5, while keeping the same camera, I should be capturing data more quickly. Or I do misunderstand something fundamental here?
That's correct. You have kept the aperture the same but increased the image scale. You're stuffing more photons into each pixel. Thanks for illustrating my point perfectly, Suavi

Quote:
Originally Posted by Slawomir View Post
Some other factors that come to my mind that might be worthwhile consideration are refractor vs reflector with similar apertures (loss of light at mirrors), and working at really fast f-ratios with 3nm filters (wavelength shift).
Optical efficiency does matter (light loss through reflection vs lenses) but it's not a large effect. Central obstruction in some reflecting designs is a bigger consideration.

Really fast scopes and NB filters can be an issue, but a different one.

Cheers,
Rick.
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