Smart focus failed (too many range shifts)

Sequence Generator Auto Focus
1

I know there is something I haven’t set up properly here for autofocus to work consistently. I’ve researched several forum posts and made some changes to my configuration, but it still doesn’t nail it. Once in a while, I will get a good focus lock, but most of the time it fails with the message “Smart focus failed (too many range shifts)”.
My scope is an Astro-Tech 14" RC with a Starizona Apex ED L 0.65 reducer, which gives me a focal length of around 1849mm and a ratio of f/5.2. My focuser is a Moonlite Nightcrawler WR25. My cameras are ZWO ASI1600MM-Pro and ASI1600MC-Pro.

Here is a link to the logfile from my last imaging session: https://www.dropbox.com/s/l3k1jnyfxd6b94n/sg_logfile_20200821173150.log?dl=0

If I could resolve this issue, I think SGP will work well for me.

Clear Skies,

Dale

2

I’m using a Planewave reduced to 1677mm with ASI1600. F ratio is quite close. I also have a nightcrawler WR35. Using 900 steps and bin 2X2 and taking 2s frames has resulted in focusing working night after night. Not sure if that will help (WR35 and WR25 have slightly different number of steps).

3

Thanks drevonf,

Just to be clear, you are referring to the field circled in the screenshot where I have been using 300?

Step Size

4

Your step size looks pretty small. Over the entire focus run you’re only shifting about 0.5 HFR. You need to be moving a good deal more. Your low HFR is around 1.5 that means you need to move enough to put your high HFR around 3 - 4.5.

So you probably need to double (or more) your step size. On my Nitecrawler I use around 1500 steps as my step size. But your setting is likely different than mine…but don’t be afraid to increase this to high numbers with focusers like the NiteCrawler.

More info here:
https://www.mainsequencesoftware.com/Content/SGPHelp/UnderstandingAutoFocus.html

Jared

5

Thanks Jared,

It makes sense. My graphs were always looking like a partial “V”, probably because I was giving it too small of area to work with.

6

Checked again my profile:

  • Steps 950
  • Auto focus data points 7 (9 is not needed)
  • Min star diameter: 6

Good luck.

7

Thanks drevonf, I’ll give it a try next time the sky clears!

Dale

8

Couple things just glancing at the log

  • How are you calculating step size?
  • not very many stars found ~40 (i don’t image at these focal lengths so maybe this is normal??)
  • experiment focusing on a different location in the sky (far away from the horizon…)

What I do when I get a new focus motor is fire up CCDCiel and run through its focuser calibration tool and that gives me a good starting point on autofocus settings (this would be a great addition to SGP!!).

9

Last night was the first opportunity I had to try the new step size. I set it to 1000 and set data points to 7. Auto focus locked in 100% of the time during the night!

Thanks for your help. I think this is one more issue I can check off the list.

Dale

10

I am very interested in your setup with the PW reducer and mono camera. I just got a PW 12.5 and am struggling to meet the back focus requirement with a Starlight Xpress Maxi EFW and Trius camera. All the configurations put it over the recommended 2.35 inch limit.

Actually I also have the same problem with other scopes using the autofocuser. I always get a “failed” message. I just goes to the focus point which I had manually selected.

Peter

11

Well, all I can say is that if you find a way to meet the backfocus requirements, you will get flat field (as long as it si not a full frame camera). What is the optical backfocus for your camera and filter wheel ?
In terms of autofocus, it has worked flawlessly for me on all kinds of targets using my L filter (and offsets for the other ones). What is really important is following closely the advice SGPro provides on setting it up. Generally, larger steps work better than smaller steps. If you provide screen shorts of all your relevant settings, this should help understand the issues.

12

The autofocus problem is not a major issue for me at this point. I also will be switching from the Edge 1100 to a Planewave 12.5, with its own focuser.

I was using a QHY247C and a SX USB EFW with the SCT with a ZWO EAF on the primary mirror…not exactly sure what the added back focus is. I was able to manually achieve good focus with it. Until I get the PW set up, I will increase the focuser step size.

Peter

13

I just got a Planewave 12.5. With the PW focal reducer there is not enough back focus to keep it within specs using an EFW and mono camera. Can you tell me what your setup is?

Peter

14

Backfocus after the reducer is 47mm. You need an adapter for your filter wheel. Minimum size from preciseparts will be 6.25mm. You then need a filter wheel, which is typically 20mm. I have a FLI filter wheel but a ZWO filter wheel would be the same (remember to reduce by 1/3 of the thickness of your filters, so typically -1mm). That leaves you with about 21mm for a camera. I have used both a FLI16200 and ASI1600 that fit does requirement. In the case of ASI1600, I added 3mm of spacers. If you combination camera / filter wheel is more than 41mm you will need to consider changing one element if you want to use the reducer. There is really no alternative or you remove the reducer.