Hi out there,
an often asked question brings up a thought I have for a long time and I'm not sure if I answered it to myself correctly. So I'd like to ask for some explanations to help me understand this better.
There is always this recommendation, that the pixel scale of the camera/telescope combination should be between 1 and 2 arcseonds. I understand, that those numbers depend on the seeing and the observing conditions and should be adopted a bit. But lets say, I have the "standard" seeing of germanys darker regions (2 arcsec). For a long time, I dreamed of a scope with a long focal length and it was hard for me not to buy one. This pixel scale explanation finally helped me understand, that this may not be a good choice.
So if I summarize my knowledge, I know that focal length and pixel size depend on each other because of the seeing and finally this limits the possibilities of the equipment. If I want to use a longer focal length, I need to choose a camera with larger pixels to compensate for the seeing. That means, the amount of detail I can image is always limited by the seeing. Larger pixels usually means larger sensors and that leads to a wider FOV in the final image. So far, so good…
But there are some huge scopes out there one can buy. For example the 14" Edge HD or even a 14" RC or some more fancy stuff. If I adopt the mentioned rules, I have to buy a camera with larger pixels as well to use these scopes under the same seeing conditions. One benefit of these scopes is the aperture, that allows you to see more details, because this is only dependent on the aperture, isn't it?. But lets say, I want to image a tiny galaxy. Then I will never be able to get a better resolution with those larger scopes because of the seeing.
So I am at the point, that a shorter focal length with smaller pixel sensors should be comparable to a longer focal length with larger pixels, right? (noise not included in the thoughts) The difference is, that the latter will have maybe a larger aperture which lets me image fainter details but the light will be spread on a few pixels only. So I can't resolve those details. So why are so many people buying larger scopes if there is not much benefit from doing so? (Planetary imaging not taken into account, I concentrate on deep sky imaging.)
Thinking about this, I am wondering if I miss something here. What is wrong with my thoughts?
Thanks for your help.
CS
Christian
an often asked question brings up a thought I have for a long time and I'm not sure if I answered it to myself correctly. So I'd like to ask for some explanations to help me understand this better.
There is always this recommendation, that the pixel scale of the camera/telescope combination should be between 1 and 2 arcseonds. I understand, that those numbers depend on the seeing and the observing conditions and should be adopted a bit. But lets say, I have the "standard" seeing of germanys darker regions (2 arcsec). For a long time, I dreamed of a scope with a long focal length and it was hard for me not to buy one. This pixel scale explanation finally helped me understand, that this may not be a good choice.
So if I summarize my knowledge, I know that focal length and pixel size depend on each other because of the seeing and finally this limits the possibilities of the equipment. If I want to use a longer focal length, I need to choose a camera with larger pixels to compensate for the seeing. That means, the amount of detail I can image is always limited by the seeing. Larger pixels usually means larger sensors and that leads to a wider FOV in the final image. So far, so good…
But there are some huge scopes out there one can buy. For example the 14" Edge HD or even a 14" RC or some more fancy stuff. If I adopt the mentioned rules, I have to buy a camera with larger pixels as well to use these scopes under the same seeing conditions. One benefit of these scopes is the aperture, that allows you to see more details, because this is only dependent on the aperture, isn't it?. But lets say, I want to image a tiny galaxy. Then I will never be able to get a better resolution with those larger scopes because of the seeing.
So I am at the point, that a shorter focal length with smaller pixel sensors should be comparable to a longer focal length with larger pixels, right? (noise not included in the thoughts) The difference is, that the latter will have maybe a larger aperture which lets me image fainter details but the light will be spread on a few pixels only. So I can't resolve those details. So why are so many people buying larger scopes if there is not much benefit from doing so? (Planetary imaging not taken into account, I concentrate on deep sky imaging.)
Thinking about this, I am wondering if I miss something here. What is wrong with my thoughts?
Thanks for your help.
CS
Christian