focusmax

[multiweb (Marc)]

I'm learning how to use focusmax with Maxim DL through the various simulators. It does seem to take a while to make one run to generate a V curve. 10 to 15min on the night I'd estimate. Is that the time you guys spend doing your initial run?

[trent_julie]

Hi Marc,
I had the same sort of time with my rc8. Mind you I haven't read the instructions or anything of the like.

My ED-80 was a lot quicker.

Trent

[Paul Haese]

Marc, each v curve should take 3-5 minutes. I think I did the 15 I wanted for the TSA in a little over an hour and that was reviewing each run.

[RickS (Rick)]

Depends on the speed of your focuser and camera download speed and how many points you are doing, Marc. With an Atlas focuser (fairly slow) and Apogee U16M (without fast downloads) mine take around 5 minutes. 10 to 15 minutes seems awfully slow...

[multiweb (Marc)]

Understood. Got it down to 5min in average. I'll see on the first night how fast it goes with the real camera and focuser.

[stevous67 (Steve M)]

Rick is right, as there are a number of options that can increase V curve runs, also including focuser backlash compensation movements, averaging of position results, and repeating Rick, the number of samples entered. Some people I've seen with as few as twenty or so points, and others up to 50 or more points (looking for resolution).

On a slower system 5-10mins would be possible. You don't need fast generated curves, but quality curves generated under >good conditions. Poor seeing reduces V curve accuracy, which leads to inaccurate focus point predictions.

Good luck Marc, it's the way to go!

Steve

[Bart]

Three words for you , Marc.

Sequence Generator Pro.

Forget all the hassles with FocusMax and MaxIm DL, focus on the same star field as you are imaging in, no slewing to and fro etc. As long as you have some good darks for your autofocus routine all you will need to be is focused at the start of your sequence.

Works for me and I have forgotton what MaxIm is as I do all my processing in PI with some tiny tweaks in PS.

[multiweb (Marc)]

Originally Posted by stevous67

Rick is right, as there are a number of options that can increase V curve runs, also including focuser backlash compensation movements, averaging of position results, and repeating Rick, the number of samples entered. Some people I've seen with as few as twenty or so points, and others up to 50 or more points (looking for resolution).

On a slower system 5-10mins would be possible. You don't need fast generated curves, but quality curves generated under >good conditions. Poor seeing reduces V curve accuracy, which leads to inaccurate focus point predictions.

Good luck Marc, it's the way to go!

Steve

Thanks Steve. Will double check the steps I used.

Originally Posted by Bart

Three words for you , Marc.

Sequence Generator Pro.

Forget all the hassles with FocusMax and MaxIm DL, focus on the same star field as you are imaging in, no slewing to and fro etc. As long as you have some good darks for your autofocus routine all you will need to be is focused at the start of your sequence.

Works for me and I have forgotton what MaxIm is as I do all my processing in PI with some tiny tweaks in PS.

Thanks Bart. Another thing to look at. Will check it out too.

[Paul Haese]

Originally Posted by Bart

Three words for you , Marc.

Sequence Generator Pro.

Forget all the hassles with FocusMax and MaxIm DL, focus on the same star field as you are imaging in, no slewing to and fro etc. As long as you have some good darks for your autofocus routine all you will need to be is focused at the start of your sequence.

Works for me and I have forgotton what MaxIm is as I do all my processing in PI with some tiny tweaks in PS.

Something you might not have thought about though is that doing this can lead to soft focus nearer the horizon with it getting progressively better as the system reaches the meridian. If the object does not make it very high at all then you could have slightly defocused images. Focusmax if set to focus at the Zenith will produce sharp focus every time, it does take time to do this but worth collecting sharp data.

Out of interest though CCDautopilot also allows focus within the same field if you want that. I prefer to have the scope go to the meridian for the best focus I can get.

[Bart]

Never had a problem before and why would you really want to image that low anyway?

Each to his own, though, what works for some does not for others.

[alocky (Andrew lockwood)]

Originally Posted by Paul Haese

Something you might not have thought about though is that doing this can lead to soft focus nearer the horizon with it getting progressively better as the system reaches the meridian. If the object does not make it very high at all then you could have slightly defocused images. Focusmax if set to focus at the Zenith will produce sharp focus every time, it does take time to do this but worth collecting sharp data.

Out of interest though CCDautopilot also allows focus within the same field if you want that. I prefer to have the scope go to the meridian for the best focus I can get.

Interesting point here - but I find that the best focus position changes slightly due to flex and optics moving about in their cells from low altitude to zenith, which is why I prefer the SGpro method. Obviously going to be system dependent.
Cheers,
Andrew.

[multiweb (Marc)]

All good valid points. I think I will focus at the zenith before each imaging session and determine the best focus point on the night given the current conditions. 5 to 15min is not going to kill me.

I realise that focus might change depending on where the scope is pointing, how low it gets, seeing conditions, etc... but as Paul said if you manage to get a good run at the zenith and lock your absolute position in for the night the temperature compensation will do its bit and although all external conditions may compound to work against you, I reckon you'll still be better off than guessing anywhere else in the sky but right up ahead.

It's not an exact science. Lots you can't control, but a good start is just that.

[Poita (Peter)]

Originally Posted by Bart

Three words for you , Marc.

Sequence Generator Pro.

Forget all the hassles with FocusMax and MaxIm DL, focus on the same star field as you are imaging in, no slewing to and fro etc. As long as you have some good darks for your autofocus routine all you will need to be is focused at the start of your sequence.

Works for me and I have forgotton what MaxIm is as I do all my processing in PI with some tiny tweaks in PS.

I'll add another 3 words.

Buy It Now.

SGP is the best thing since sliced bread, so much less hassle, I haven't fired Maxim up in months.

[stevous67 (Steve M)]

The focus routine of Focusmax is very unique and comprehensive, predetermined measurement of predicted position based on a sequence of captures averaged to determine precise focus. There is a reason why leading observatories use it. Everyone to their own, but for longer focal lengths, it cannot be underestimated how difficult it is to automated a precise focus routine that has a very high success rate. For shorter focal lengths, the game is easier, and with refractors, it can be even easier, so other routines could be just as successful. For wide field systems, a 7 or so sampling routine would probably do okay (SGP).

But whats great is that you can try before you buy with a lot of these products.

[multiweb (Marc)]

Been using it for a couple of nights now and I'm sold. Works really well with MAXIM which I already had so will stay with it. 2-4min for a V-Curve now. No brainer.

[Paul Haese]

Yep, you will never go back to a bahtinov mask again. I wonder how I put up with doing that for years at a time now.