I find the Av value can be set between 3.19 and 16. How can I extend the range beyond 16 to say 32 or more?
Also, to record star tracks on a moonless clear night, can anyone give a set of values for the above 3 parameters that I can use as a starting point to my experiments?
On the SX230hs the aperture is a physical hole so you cannot make it any smaller.
Thanks for your response. Will certainly follow the links.
Quote from: Microfunguy on 27 / October / 2013, 06:12:39On the SX230hs the aperture is a physical hole so you cannot make it any smaller.In that case, how is it that the aperture is adjustable between 3.19 and 16?!!
The values you see in the CHDK menu going outside this range are just generic CHDK values that CHDK will try to let you use. Sometimes you can actually get an f-stop smaller than the official ones given in the Canon manual.
However I don't know of any way to actually find out how much its able to achieve although its set at Av 16.
If you want to roughly calibrate this, manually override the Tv, Av & Sv settings to 1/60, f8 and ISO 100, and take a reference shot. Then set the Av at f16 and take several shots using different Tv values until the resulting image appears to have the same exposure as your reference shot.
.....Well, that is what f16 on the SX230hs is equivalent to as far as depth-of-field is concerned.Image sharpness will be VERY poor.
Quote from: Microfunguy on 28 / October / 2013, 11:10:59.....Well, that is what f16 on the SX230hs is equivalent to as far as depth-of-field is concerned.Image sharpness will be VERY poor.Actually, I was a bit intrigued that a night scene I shot using f/8 turned out better than the same shot taken using f/16 ( of course with appropriate Tv setting, ISO maintained at 100). I expected the f/16 to be better with greater depth. Could it be that, extending the f stop beyond an optimum (and adjusting Tv appropriately) could be counter productive?Raja.
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