Guiding in asiair. Importance of FL

[powerlord]

New ota, everything else the same, but stuck a sw50mm finder I'd converted to use as a guidescope on there. The Internet told me it was 180mm.

After guiding setup the graph was WEIRD. totally symmetrical :

I couldn't understand what was wrong. In an effort to eliminate anything I could think of, I told asiair to use the 120mm as main camera with FL 0, and plate solved. It told me FL was 162mm.

I recalibrate guiding, and now I'm getting what I expect, and 0.4rms.

 

So just a tip really - make sure that FL you enter is accurate. Why it doesn't just plate solve it anyway I've no idea...

Edited December 16, 2021 by powerlord

[Richard_]

Hah! A similar thing happened to me a month ago when I was trying my new telescope out. I forgot to change the focal length value to the new scope so it was unable to plate solve during polar alignment. 

Kinda related, but there are other options in the software which allow the ASI Air to work out what the value should be if you enter "0". One which comes to mind is the backlash setting for the auto focuser. 

[powerlord]

yeh, but you can't enter 0 for the guide camera. doesn't let you. who knows why.

so you have to faff about like i did and pretend it's the main camera, set it to 0, take a preview and plate solve, remember the value, flip the camera back to be the guide camera and then enter it.

why in the love of all that is good do I need to do that ? why can't it just plate solve the guide camera pic ? i can't believe its not been suggested as a feature enhancement.

[iantaylor2uk]

I think if you put zero in the focal length box it will work out the right value for you

 

[powerlord]

no the text underneath says 'accurate value required'. for main camera it says enter 0 if unknown and it will be calculated after platesolve.

it does not platesolve guide camera images.

[iantaylor2uk]

Just swap over the guide camera to be the main camera temporarily and then you can get the value u need.

[powerlord]

yes I know. That is what I was advising people to do.

regards

 

stu

 

Edited December 16, 2021 by powerlord

[Clarkey]

The top graph looks more like a software glitch or a calibration issue. 180mm or 162 it should still guide, it will just under-compensate. The more accurate FL will just give you better guide accuracy.