Fahim,
I like the article you are mentioning below about focal reducers
This is how the review of optical component (including lenses) should be done: hard facts, no "poetic" language, clear conclusion.
Quote:
Originally Posted by netwolf
2. The scope you have is natively F10 so short exposures will not catch much light. But you could use a smaller sensor (DSI I or II or even III or cameras with similar size sensors) and use a Focal Reducer to get your scope down to F6.3/~F5 even, or F3.3.
http://www.isomedia.com/homes/cvedel...l_reducers.htm
Look at this page, there are good illustrations of the light cone, reducers, and chip size. A bigger chip will suffer Vigneting (dark areas around the edges where less light is getting in). |
However, you will not catch more light by reducing F number (as you are suggesting below), the amount of light will be exactly the same.
The difference between high and low F number is, the same amount of light from distributed objects (like nebulae or planets) is spread over the smaller area of the sensor (because it is FL that is reduced by reducer), so the illumination (amount of light per pixel) will be increased. The image of the object will be smaller but exposure time can be shorter for the same surface brightness.
This does not apply to stars, they are point-like sources, and their light will be focussed on 1-2 pixels in any case (unless the optical system is not ideal and/or resolution is decreased because of diffraction)
Quote:
Originally Posted by netwolf
3. By reducing to F2 you are catching more light in a shorter amount of time and hence can catch it before the "field rotation" kicks in. However I am not sure with a Single fork arm how sturdy your mount will be to support this method..
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Otherwise, ditto
