Quote:
Originally Posted by gary
Indeed, it is a result of the FOV.
As you would have read, the focal ratio is the focal length divided by the aperture.
Longer focal length instruments have smaller FOV's. So a scope with a long focal
length and large (slow) f/ratio works fine for photographing bright objects such as
the Moon and Jupiter as exposure times can be kept short. For extended objects,
the better choice is a scope with a smaller f/ratio (faster) as the imaging time
for these types of objects becomes smaller.
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Hi,
does the size of an object vary with focal ratio when the prime focus
method is used? for example, would a planet vary in size between an F/4 and F/8 when viewed through a camera at prime focus?
Is there any information that details how the exposure time can be calculated from an F4 to F6, eg, if a 30 min exposure is considered minimal to achieve reasonable detail for a DSO with an F/4, is there a way to calculate how much longer the exposure time would be with an F/6? I'm just trying to understand the difference and then invest in a shorter focal length mirror as I'm using an F/6.
on the topic of polar aligning, how important is it to get the alignment accurate for tracking, and what is the best way of aligning, would a digital compass be more accurate than a conventional compass?
are gyroscopes used for alignments ? reason I ask is because there are several semiconductors with gyroscopes built in and it would be an interesting application if adapted.
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