SharpCap Forums

hi,
I have recently had success with auto focusing using multiple stars and my Sesto Senso / ASCOM set up.

My focus scan is very flat, with not much difference around the "Best Position" point.

Question is this shallow graph OK, or should it be steeper?

any feedback would be greatly appreciated.

Colin

How many steps are you moving between stops? Few steps will result in a flat curve. Your gear will also make a difference. A higher focal length will result in a larger focus zone so you will have a different shaped curve. Focusers can also make a difference, different move the draw tube at different rations to turns of the knob.

Add steps between stops until you get a nice curve. This will cover more area making the starting point not as important.


Can you post a screen shot?

Hi chongo228,
Thanks for your reply. Here is some data that might throw some light on the issue. (I should have included this in my original post.)

I didn't take any screen shots but I will next time (whenever that will be!). My settings are (SharpCap 4): Scan Step Size 50; Max Step count 16; Samples at each Step 3

I was imaging with the AA 183C Pro TEC camera, the PrimaluceLab 65F 420mm FL telescope and the PrimaluceLab Sesto Senso focus motor @ 0.7 microns per motor step.

And thanks again for your help.

Colin

Hi,

I guess to give a sense of scale to this, how many steps does it take for your focuser to go from clearly out of focus one side, through focus to clearly out of focus the other side? Your scan will do a total of 800 steps (50 x 16). If running through focus from one side to the other is 5000 steps then it would make sense that with an 800 step range you wouldn't see much change.

cheers,

Robin

Robin,

Thanks for that. If I have understood you correctly then with my current settings a shallow plot is to be expected and not necessarily a problem?
However, I will experiment with the "out of focus - in focus - out of focus" range and settings to try and minimize the uncertainty of the estimated best focus position.

Colin

Hi,

The plot should be a U shaped curve, and could be quite deep - say dropping from 10+ on one side down to low single figures, then rising to 10+. My worry is that you may not be looking at the full range, meaning that you only see a small fraction of the bigger U shape.

I would suggest having another go, making sure you have an idea of the range you want to cover. If you still have problems, post a screenshot so we can see what is going on.

cheers,

Robin

Thanks again Robin,

I will experiment with this and send a screenshot if I cannot get a decent U shape.

Colin