Re: NGC5371 and surrounding galaxies

Roland Christen

I'm not into pixels, I'm more looking at allowable arc seconds. The skies some nights allow you to capture 3 arc sec FWHM, but on good nights you can get perhaps 1.5 arc sec FWHM. With a shorter scope you might only be able to get 4 arc sec FWHM on even the best of nights. So, the amount of allowable drift changes with the resolution capabilities of the scope and your local seeing conditions.


-----Original Message-----
From: Seb@stro <sebastiendore1@...>
To: <>
Sent: Sat, Jun 6, 2020 10:30 am
Subject: Re: [ap-gto] NGC5371 and surrounding galaxies

Focal length has nothing to do with how long to do unguided. Unguided depends on how well your model is made and how much drift you are willing to accept in your image. 

Rolando, I'm not sure I'm getting this right. I'm probably missing something about the modeling part here... Please enlighten me.

I thought the "amount of drift I'm willing to accept" was the amount of recorded signal (pixels) that is "offset" in the frame due to the mount's (in)ability to accurately track an object,(isn't it why we usually guide ?) which is also related to the image scale, which in turn relates to the focal length of the telescope...

So I'm not sure how two scopes with different focal lengths would lead to the same amount of drift in an unguided sub of the same exposure time (all other parameters being equal). Seems to me that the more focal length, the more drift (pixel offsets over time) I get, wether it's caused by PE (which I understand is not an issue with AE) or bad PA.

Sorry if my question seems silly, I'm a kind of "advanced newbie in astrophotography" as I like to call myself... 😉



Join to automatically receive all group messages.