SGP auto focus how does it work?

In layman’s terms please. I’m impressed by how it works… but I have my course steps to 200 and my fine at 10. Will it only fine tune in steps of 10? or will it try 1-2 steps to fine tune final focus. Still it does a better job than me using HFR. But curious about the fine steps? A video I saw said you could get a U shape. I don’t always - sometimes it’s just a one step down and one step up and says it’s happy. Also what goes the line mean that it draws at the end?
does it help if I set fine steps (boss II focuser) or does it over ride that and take over with it’s own step designations?

I’m pretty new to SGP but I have finally gotten my focus under control and now have a fully automated system. I finally sat down and figured out how to get my step size and it really does work.

10 might be a little low to start. I started with my coarse at 150 and my fine setting at 30.

But if you follow along with that way they tell you do it you can figure it out.

I’ll try to put it in laymen terms and I’m sure that others here will give you better ideas but try this.

Start with LUM and get it focused as best you can.

Once you have that do this.

  1. Shoot an image with the exact same settings you have set for your exposure in auto focus. Something like 10 seconds at 2x2.

  2. Write down the HFR Value and the IN Focus number that it is set at.

  3. Start looping at that same exposure and while it is looping start clicking on your fine or coarse focus buttons until the HFR number is 3 - 5 times higher than the number you wrote down. I split the difference and go for 4 times.

  4. Take your time here and let the images download before you click it a bunch of times because you might run right by it if you go to fast.

  5. Once the HFR is 4 times higher than the one you started with stop the looping and don’t click the buttons anymore.

  6. Now Take the new IN Focus number that is showing and subtract the original IN Focus number from it.

  7. Multiply that number by 2

  8. Divide that number by the number you have set as your “Auto Focus Data Points”
    (those data points can be found in the “Auto Focus Options” That’s where you go in the control panel and click on focus and then click on the word “set” next to the “use auto focus” tab. The number will be the 3rd from the top. You probably have it set to 9.)

  9. After you divide that number by your data points subtract 1 from that number and that will give you your step size number for that filter.

Put that in for your step number and run the auto focus. Remember that the number will be different depending on what filter you use. What I did was ran it on all of my filters one after another so the temp and conditions were the same for each filter.

That will at least give you a good starting ground for setting up your presets in the filter focus tabs.

Good luck I hope this works.

Sean

The course and fine steps in the focuser control panel do nothing for auto focus. They are only there for your convenience when manually moving the focuser.

The only values that have any affect on Auto Focus are found in the Auto Focus Options:

If you’re looking for a deeper understanding of how auto focus works and how to set it up, I’d recommend this:
http://mainsequencesoftware.com/Content/SGPHelp/UnderstandingAutoFocus.html

Thanks,
Jared

Hi Jared,

I might be misunderstanding you here but I thought using the steps outlined above was how I figured out the best step size for the filter I was using and then entering that step size in the auto focus box you posted here.

Okay I re-read the link you posted here and am editing this message again. I’m sort of confused. If I’m reading it right then what I posted above seems correct to determine the step size for the filter you are trying to auto focus. Where I’m getting confused is at the end it tells you to save all your hard work for your equipment, which is telling me that whatever step size you enter into that box would work no matter what filter it is trying to focus through correct?

I usually shoot 1 maybe 2 filters during a nights shoot, so what I have been doing is using that calculation to get the step size for the filters I would use and then entering that number into the step size box when I’m ready to auto focus for that filter.

Am I not understanding what it is trying to tell me to do here? hmmmm

Sorry for the confusion, my response was to Ron. You are correct in how to determine the auto focus numbers. I was just stating that the numbers in the Auto Focus area are the ones that actually control the auto focus algorithm.

Step size has little to do with the filter that is in front of your CCD. Step size is generally determined by the speed (F ratio) of your scope and pixel size (binning can also change your step size). The filter really only changes the amount of exposure time you need and not the step size. This is why we only allow one area for step size but allow you to specify different exposures per filter.

The steps that you’ve provided are correct and should work well :thumbsup: but I think where you may be getting confused is that the filter will no change the step size, only the exposure length. So do those calculations with lum and adjust your other filters accordingly. For Lum I typically use 5 seconds. RGB I use 10-15 seconds and I try to avoid focusing with my actual narrowband filters (I use the lum instead and have SGP apply the offset)

Hope that helps,
Jared

Thanks Jared. Okay that’s a relief.

Your last point is the piece that I’m unclear on. “Focus with the LUM and then apply presets”

Seems reasonable but I’m not sure how to get the presets. I’m using all Astrodon E series for both LRGB and Narrowband.

So what you are saying is SGP will focus with the LUM and then it will apply a certain number to either add or subtract based on the preset of the filter to achieve perfect focus for that filter. Correct?

So does that mean that if I have it set to auto focus during an imaging session that SGP will actually switch over to the LUM to re focus and then apply its preset and then move the needed filter back into place and keep on trucking?

That’s Nuts!!! But Cool if thats how it works.

If so how do I determine these presets?

Thanks again Jared.

Sean

Yes, that is how it works. More info can be found here:
http://www.mainsequencesoftware.com/Content/SGPHelp/AutoAdjustFocusPerFilter.html

Essentially in the AF area you tell SGP to use LUM. Or if you want to do it on a per filter basis you can set this up in the Filter Settings Dialog.

Red Highlight - Shows where to set the focus filter for that particular filter. This is useful if you want to focus with your RGB filters BUT use Lum for Narrowband.

Blue Highlight - Shows the “focus point” for each filter. These should be considered a “starting” point for focus but in when the “Auto Adjust Focus Per Filter” option is used these values are treated as offsets.

I would highly recommend checking out the Auto Focus section of our help docs:
http://www.mainsequencesoftware.com/Content/SGPHelp/Focusing.html
Particularly:

  • Auto Focus\Understanding Auto Focus
  • Auto Adjust Focus Per Filter

Some info here on determining offsets:

Thanks,
Jared

Thanks Jared,

It’s funny. Before I even started using SGP I read the manual twice. It was pretty much Greek.

But after time in the field I continue to go back to it and understand more and more.

I would encourage all newcomers to SGP to have that manual and go to it often. It constantly reveals more and more information to me as I use the system. It’s definitely not a one time read.

There’s a manual? I just started using it. :wink:

Yes there is a manual. I would suggest printing it and having it bound. That’s what I do for all my equipment and software. I pretty much have a library on everything. I cannot tell you how much they help.

The manual is a good reference but I don’t know if I would recommend reading it cover to cover…unless you like that kind of pain. It’s typically written to find answers to what things do rather than teach you how to use SGP. There are some exceptions to this.

There are lots of great resources for getting started with SGP. I’d recommend these as a good starting point (found on our Support page):
The First Week with SGP
SGP Tutorials by Harry’s Astro Shed
Getting Started: Mono CCD
Getting Started: OSC/DSLR
Some older YouTube videos

Hope that helps.

Jared

Yes I agree. The first two reads did me no good. It was not until I had several imaging nights that it became useful and helped me. It provided answers to things as I went along most of which would have been asked here on the forum I I did not have it. Consequently I only ask here after I have exhausted my abilities to find the answer on my own.

I finally made the move to autofocus with my new refractor setup…I found the manual really helpful…also the guys at the astro imaging channel made a really helpful video of autofocus with SGP that included a live demo: https://www.youtube.com/watch?time_continue=4&v=bB84JS5Uefo

I followed the manual’s suggestions…I got a perfect V on the very first run! I’m astonished and amazed at how good SGP is with autofocus!

one suggestion re: manual: the setting of “Default” for the “Focus with Filter” column within the filter setup is unclear…I thought default meant use that filter for autofocus rather than a specific filter with offsets. So as I moved from LUM to the RGB filters to determine the focus points for each, I realized it kept using LUM rather than switching to the new filter…so I changed the focus with filter setting for each filter.

jeff