Quote:
Originally Posted by Zuts
Hi,
Someone please correct me if i am wrong but with guiding while aperture is good its not that necesary as with a smaller guide scope you can just increase the shot time on the guider to find more stars.
What is important is matching the FL of the imaging scope with the FL of the guidescope. For example if you tried to guide a Celestron C11 at 2700 ml with an ED80 at 600 ml you would get very poor photos because the guide scope would not see the movement being seen by the C11. In this case you would need to Barlow the ED80 significantly to at least get closer to the C11 FL and increase the shot time on the ED80.
Paul
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This is true and the focal length has to be taken into consideration. With modern guiding programmes able to compute a centroid to sub pixel size the old need for the guide scope to have a longer focal length than the imaging scope is no longer valid.
You can increase the the exposure time of the guider to find more stars but there is a limit to this. I find going over about 5 sec exposure reduces my guiding accuracy. Having said this I am yet to find an area of sky that I couldn't find a guidestar with a 3 sec exposure using my current set up with a QHY guider and 120mm scope.