In astro photography we look at things differently. When it comes to small objects where you crop the image and present it at full scale the parameter we use is scale in arcsec/pixel. Anyone a bit above noob level should say that a mount is capable of tracking within <any number> of arc seconds. Then you can check how many pixels that is in your scale.
All that crop stuff does not matter in AP. It is meant to give people aged 50+ (my generation) an idea about the field of view because the field of view a particular focal length yields on 24x26mm film is so deeply burned into our minds. A better way is simply to state how much field in degree you have. If you image a large object (filling the full field of view) and present it on screen or a small print you cannot zoom to pixel scale not even on a 4k display.
The thing to worry about is picking up plenty of signal. You use the reducer to make the scope faster. The math tells you that you loose resolution but that is not quite true. As the noise eats up the fine detail first you can often see more detail when you use a reducer due to the stronger signal than you can see at a higher resolution with less signal. This is totally counter intuitive to a daylight photographer.
Edited by the Elf, 20 January 2021 - 03:37 PM.