Quote:
Originally Posted by Startrek
Image scale or pixel scale of your imaging system ( camera and telescope ) is expressed in arc seconds per pixel and determines whether your system is oversampled or under sampled
Guiding error in PHD2 is normally expressed in arc seconds and determines how many pixels or fraction of a pixel your optical axis ( guide scope or OAG ) is from the centroid of the guide Star
My imaging system has a image scale of 0.88 arc sec per pixel which is oversampled ( usually between 1 and 2 arc sec per pixel is considered the norm but most folk are under sampled which is ok ) Undersampled imaging systems can end up with blocky stars
My guiding error changes night to night and ranges from 1.30 arc seconds to as low as 0.58 arc seconds
So image scale and guiding error don’t really directly relate to each other
Hope some other more learned folk than myself jump in and explain further
Cheers
Martin
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Here’s some more information I found in my iPhone files on Image Scale and Sampling
Image Scale and Sampling in Astrophotography
Image scale of your imaging system ( telescope and camera ) is measured in arc sec per pixel and is described as the amount of night sky that will cover one pixel of your cameras sensor
Generally your image scale should be between 1 and 2 arc sec per pixel but there are exceptions to this rule. It’s usually better to be slightly Over Sampled than Under Sampled with your image scale
The earths atmosphere limits the resolution we can achieve in our images and in most cases on a good still night the seeing will be around 2 arc seconds. That means objects that are smaller than 2 arc seconds in angular size will be blurred by the atmosphere
To calculate the image scale of a telescope and camera combination we use the following formula -
Camera Pixel Size uM / Focal Length of Telescope x 206.3 = angular resolution or image scale in arc sec per pixel
Under Sampling and Over Sampling
In the ideal world an image scale of 1 to 2 arc sec per pixel is a good guide
Under Sampling is generally above 1 arc sec per pixel
Over Sampling is generally below 1 arc sec per pixel
Under Sampling may cause stars to appear blocky or square formed which is caused by most of the light only falling on 1 or 2 pixels
Over Sampling may cause bloated stars due to the light falling on too many pixels
Longer focal length telescopes with medium to large pixel sizes on the sensor tend to work better with Sampling ( Oversampling ) and respond better during processing the image
Cheers
Martin