Is guiding required for short sub exposures?

I currently have a native 420mm refractor on an AM5 mount working well. I'd like to add a 6 or even 8 inch RC for planetary. If I use the new scope for DSOs, I will need to upgrade my guide scope. My refractor would be a good fit for that purpose. Not sure if I'd want to re-configure things all the time. However, I'm in a Bortle 7-8 area with lots of light coming from the neighbors. I would need to keep the subs to 60 seconds or less. For that amount of time,  is guiding going to help me at all?

Thanks,

Mike

It depends on your image scale and how much PE or tracking error you have in your mount. The math I have seen on the AM5 is as I recall around 0.5" per second ( I looked this up just yesterday for another post). This will vary depending on your mount and how steep the curve is.

If your image scale is 1.5"/px you can take an image of around 3" before that starts to show in the subs. 

You do not need a large guide scope. Any 30mm to 50mm cheap one will do. These are the wrong type of mounts to do unguided imaging. Arguably probably one of the worst. 

I currently have a native 420mm refractor on an AM5 mount working well. I'd like to add a 6 or even 8 inch RC for planetary. If I use the new scope for DSOs, I will need to upgrade my guide scope. My refractor would be a good fit for that purpose. Not sure if I'd want to re-configure things all the time. However, I'm in a Bortle 7-8 area with lots of light coming from the neighbors. I would need to keep the subs to 60 seconds or less. For that amount of time,  is guiding going to help me at all?

 

Thanks,

 

Mike

Short answer yes ALWAYS guide no if ands or buts.

Thing to know about tracking error many people dont understand.

The tracking error is sharp spikes like tectonic plates shifting (dramatic comparison i know) not quite the slow drift of error many would suspect (that is still possible though)

The reason short subs are primarily favored unguided is because you have a higher chance of getting subs with minimal noticeable error. So you can toss the bad and keep the good. If you do longer exposures sub all that tracking error across the 60 seconds is all blurred onto one sub.

With harmonic mounts the tracking is more rigid compared to EQ mounts. I would say 10-15 seconds with an average EQ mount unguided (at your imagescale). Harmonic you'll probably want to be around the 5 second area.

If you currently have a guiding setup go ahead and run a short tracking session but disable guiding inputs and watch the amount of error you'll get.

Edited by Andros246, 14 May 2024 - 01:56 PM.

Are you not guiding at the moment?  At similar focal lengths to what you mention (420mm refractor) I cannot go longer than 30s with my AM5 without guiding.  Honestly, I have never seen imaging with that mount with anything other than a wide angle camera lens as even possible or desirable without guiding...  But then you mention having a guide scope so I am a bit confused....  

Are you not guiding at the moment?  At similar focal lengths to what you mention (420mm refractor) I cannot go longer than 30s with my AM5 without guiding.  Honestly, I have never seen imaging with that mount with anything other than a wide angle camera lens as even possible or desirable without guiding...  But then you mention having a guide scope so I am a bit confused....  

Yes, guiding well now with a camera and scope appropriate to the refractor focal length https://astronomy.to...ope_suitability. Should I go up into the 1300-1800 focal length range, it suggests I need something in the 400 range (with ASI120MM Mini guide camera).

Yes, guiding well now with a camera and scope appropriate to the refractor focal length https://astronomy.to...ope_suitability. Should I go up into the 1300-1800 focal length range, it suggests I need something in the 400 range (with ASI120MM Mini guide camera).

1300-1800 calls for a RC or newt? I'd go OAG with a 220mm or 178mm

and leave the current guiding setup on the refractor

Edited by Andros246, 15 May 2024 - 09:12 AM.

"Required" is not a useful term without clarifying what you want out of the image. 

After all, "Tracking" is not even necessary. There are more than a few images posted in this forum where the imager used an undriven Dobsonian telescope. 

Can you get better pictures with good tracking and guiding.......most assuredly so. But the pics that can be gotten without either can be very good. 

Alex