Greetings,
I recently purchased a new QHY 16200A CFW7 camera that with the supplied OAG and adapter is 2.4 mm longer than the required back focus for my reducer/flattener. I might be forced to ditch the OAG and use a finder scope. I currently use a ZWO 30F4 with a ZWO ASI 120MC-S for polar alignment and it sees lots of stars to a fair degree. I was considering getting a longer focal length finder scope such as the ZWO 60280 which gives a rather narrow Field of View of 0.98 x 0.74 (from Astronomy Tools). I do polar alignment with SharpCap because I am in the southern hemisphere in a Bortle 5/6 area and can't see Octans for most of the month. Would such a narrow field of view muck about with my ability to see enough stars for good polar alignment. Even with the 30F4, SharpCap gets a bit upset if I am not looking in roughly the right direction.
Regards
Stephen
Field of View 0.98 x 0.74
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Re: Field of View 0.98 x 0.74
Hi,
I've had reports of people getting it to work down to about 0.75 by 0.5° or even a bit below, but as you noted it can become less reliable as you get less stars in the field-of-view. If your current camera has the ability to select a smaller resolution ROI mode then you could pick an ROI that gives a similar field-of-view to the setup you are proposing and see how well that works before you invest in new hardware. For instance if your camera is 1280 x 960 at full resolution and you pick a resolution of 800 x 600 then you will be getting a mauler field-of-view. You should be able to calculate the resolution that will give you the field-of-view you are interested in without too much trouble on one of the FOV calculator websites.
Cheers, Robin
I've had reports of people getting it to work down to about 0.75 by 0.5° or even a bit below, but as you noted it can become less reliable as you get less stars in the field-of-view. If your current camera has the ability to select a smaller resolution ROI mode then you could pick an ROI that gives a similar field-of-view to the setup you are proposing and see how well that works before you invest in new hardware. For instance if your camera is 1280 x 960 at full resolution and you pick a resolution of 800 x 600 then you will be getting a mauler field-of-view. You should be able to calculate the resolution that will give you the field-of-view you are interested in without too much trouble on one of the FOV calculator websites.
Cheers, Robin
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stephen2615
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Re: Field of View 0.98 x 0.74
Hi Robin,
Thanks for the response. I tried to see the difference in the various calculators online and they didn't produce anything of value. Changing the resolution settings did change the field of view but the same image was used at the end just a bit smaller but still showing exactly the same stars.
I will try using the camera tonight and take pics to see the real difference.
Regards
Stephen
Thanks for the response. I tried to see the difference in the various calculators online and they didn't produce anything of value. Changing the resolution settings did change the field of view but the same image was used at the end just a bit smaller but still showing exactly the same stars.
I will try using the camera tonight and take pics to see the real difference.
Regards
Stephen