Focus Set Point Questions


#1

So, I’ve been thoroughly enjoying SGP’s AutoFocus goodness, but you know, it isn’t fast when you’re using Narrow Band Filters. (That’s not SGP’s fault, of course.)

But, I’m thinking that I could increase the efficiency and speed of the whole business if I set up filter offsets.

Can I just use the data from FITS Headers captured in a recent set of light frames to populate the required information in the filter settings? Does that make sense as a scheme?

I’d appreciate any insight anyone is willing to share.

Karl


#2

Hi Karl,

There are surely better ways to do this but just working things out for my self I spent at least half a night to come up with the offsets that worked for me.

I let temperatures settle…both air temp and scope temp. I then did a focus run with Lum …noted the focus position, then did a focus run with the NB filter (much longer exposures as you well know)) and noted the focus position for the NB filter…then went & did the Lum again to make sure nothing had changed there. (Sometimes it had - as the NB focus run took a long time and things were not sufficiently settled - so did that one again all again).

Did the same for each NB filter. Thus I had a good offset for each individual NB filter from the Lum in the wheel.

Took quite a while simply because I started before things really settled…but in the end…if it takes half a night…it will be worth it in the end to have good offsets. Then you save a bunch of time for each imaging run.


#3

Thank you!


#4

I agree with Brendan, it took a good while for me to get my offsets sorted but worth it, surprisingly, my 3nm S11 is quite a bit different from my O111 filter despite claims of being par focal…

Ray


#5

Hi

I used a Bahtinov Mask + Bahtinov Grabber (software) and an artificial star to set my narrowband filter offset. It went quite easily.

John


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