Focus Issues?

[Rod M]

Hello all, 

I've been using PHD2 for over a year now with multiple mounts and recently on the .11 version the GA is recommending better focus. I've run an ASI290MM with an Orion 60mm guide scope (240mm fl) for the last 6 months on this Redcat 71 (350mm fl) and it's never given me that message even when the focus was not perfect. 

After I got the message I've refocused several times using both visual, a b-mask, as well as the focusing tools in Sharpcap and I still get the message when I run the GA. I also adjusted focus by watching the HDR and FWHM values to get them as low as possible and also rebuilt my dark library, recalibrated, and lowered the gain values but almost every time the GA recommends a better focus even though the focus is fine. I went outside today and pointed at a wall to make sure it looks good during the day even though I can see clear stars through the guide scope at night and Sharpcap is showing a ton of stars when I run the focusing tools. 

Attached is a screenshot from last nights session as well as the capture from outside today where I did a rough focus against a wall. 

I know there were changes in .11 to the GA and it mentions HDR so I'm looking for ideas on what to check. I was wondering if the HDR is big and that is triggering the error message because Im basically running a 1:1 imaging/guide setup and there is something in the new version that doesn't like it. 

Appreciate any ideas or recommendations.

[Bruce Waddington]

If you're confident the camera is well-focused, you're getting good SNR values on the guide stars and few lost-star events, you should ignore the recommendation.  PHD2 can't know whether the camera is well-focused, so the GA is using a heuristic based only on the image scale of your guiding setup and the apparent size of the guide stars.  It looks like your image scale is around 2.5 arc-sec/px, so star HFD values above 5 seem unusual.  But there could be many reasons for that, I suppose, and if you're happy with the star-finding and star-tracking performance, you should just forget about the recommendation.  However, nothing is different in this area in release 2.6.11.

Regards,

Bruce

[Rod M]

Thank you Bruce. 

For my education, is the HDR value of 5.85 because I’m running such a large guide scope? If I was running a guide scope with a shorter focal length and the same camera would the HDR value be lower?

 Ive used the product a lot but don’t quite understand all the numbers. I assume most people are not running a 1:1 imaging to guide scope ratio.

[Mike Jerry]

Rod,

I run the same guide cam and scope as you and regularly get HDR values below 4, and even 3 on nights of good seeing. So this issue is not your scope focal length.

Mike

[Rod M]

Thanks Mike. 3-4 is what I usually get on my SCT so I guess I will try to figure out why that is so high. It was suggested to run an IR Cut filter on the guide camera although I'm not sure why I would need one now after 6 months. I'll probably clean the optics and maybe even swap with my other guide camera to see if the problem changes. 

[Chris. S]

Rod, Bruce,

Sorry for the interruption. I also have had notice, having never before had a message, I also recently installed the latest updated driver for PHD, I use a ZWO 120MC-S on a Skywatcher 9*50 Finderscope, I originally focused with Mk 1 eyeball, the last time was with a Bahtinov Mask, never had a problem with Focus Errors, however since the Update, I have also had noticed that I have been advised to carry out a focus, whilst using GA, I did and the focus was ok...

Regards

Chris S.

 

From: Rod M
Sent: 27 May 2022 23:12
To: Open PHD Guiding
Subject: [open-phd-guiding] Re: Focus Issues?

 

Thanks Mike. 3-4 is what I usually get on my SCT so I guess I will try to figure out why that is so high. It was suggested to run an IR Cut filter on the guide camera although I'm not sure why I would need one now after 6 months. I'll probably clean the optics and maybe even swap with my other guide camera to see if the problem changes. 

On Friday, May 27, 2022 at 2:57:48 PM UTC-7 mjtransc...@gmail.com wrote:

Rod,

 

I run the same guide cam and scope as you and regularly get HDR values below 4, and even 3 on nights of good seeing. So this issue is not your scope focal length.

 

Mike

 

On Friday, May 27, 2022 at 2:07:00 PM UTC-7 Rod M wrote:

Thank you Bruce. 

 

For my education, is the HDR value of 5.85 because I’m running such a large guide scope? If I was running a guide scope with a shorter focal length and the same camera would the HDR value be lower?

 

 Ive used the product a lot but don’t quite understand all the numbers I assume most people are not running a 1:1 imaging to guide scope ratio.

 

 

On Friday, May 27, 2022 at 1:08:33 PM UTC-7 bw_m...@earthlink.net wrote:

If you're confident the camera is well-focused, you're getting good SNR values on the guide stars and few lost-star events, you should ignore the recommendation.  PHD2 can't know whether the camera is well-focused, so the GA is using a heuristic based only on the image scale of your guiding setup and the apparent size of the guide stars.  It looks like your image scale is around 2.5 arc-sec/px, so star HFD values above 5 seem unusual.  But there could be many reasons for that, I suppose, and if you're happy with the star-finding and star-tracking performance, you should just forget about the recommendation.  However, nothing is different in this area in release 2.6.11.

 

Regards,

Bruce

 

On Friday, May 27, 2022 at 11:06:42 AM UTC-7 Rod M wrote:

Hello all, 

 

I've been using PHD2 for over a year now with multiple mounts and recently on the .11 version the GA is recommending better focus. I've run an ASI290MM with an Orion 60mm guide scope (240mm fl) for the last 6 months on this Redcat 71 (350mm fl) and it's never given me that message even when the focus was not perfect. 

 

After I got the message I've refocused several times using both visual, a b-mask, as well as the focusing tools in Sharpcap and I still get the message when I run the GA. I also adjusted focus by watching the HDR and FWHM values to get them as low as possible and also rebuilt my dark library, recalibrated, and lowered the gain values but almost every time the GA recommends a better focus even though the focus is fine. I went outside today and pointed at a wall to make sure it looks good during the day even though I can see clear stars through the guide scope at night and Sharpcap is showing a ton of stars when I run the focusing tools. 

 

Attached is a screenshot from last nights session as well as the capture from outside today where I did a rough focus against a wall. 

 

I know there were changes in .11 to the GA and it mentions HDR so I'm looking for ideas on what to check. I was wondering if the HDR is big and that is triggering the error message because Im basically running a 1:1 imaging/guide setup and there is something in the new version that doesn't like it. 

 

Appreciate any ideas or recommendations.

 

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[Patrick Chevalley]

Hi,

Some remark about the Star profile from Rod screenshot:

We can see the top part of the curve is typical of a well focused star, with a sharp top and the width at half maximum (FWHM) is only 1.8 which is a good value.

But the lower half of the curve is much flatter and wider, making the half flux diameter (HFD) to be much bigger at 5.85.  This represent some bright halo around the star image.

This is the kind of image we get with an achromatic lens because of the dispersion of the infrared light.

I also guide with an achromatic lens and for a time I added an IR-cut filter to get better shaped images.

But this is not really necessary because the important point is PHD2 can reliably find the star centroid, we not look for pretty image here.

So now I guide without filter to get some more photon and not care about the HFD value as long the top of the curve is sharp.

Patrick

[Rods Cox Account]

Thanks Patrick.

As a test, last night I swapped my ASI290MM for my ASI174MM with a new profile and that HDF number was 3-4 and the GA did not suggest better focus. So … I then swapped back the 290 and created a new profile for it and it gave me HDF values of 3.5-4.5 even with clouds in the sky which should have increased those values.

No other changes and did not do any fine focusing just a visual focus tweaking while watching the HDR.

My conclusion is that something must have happened to the old profile or some parameter did not properly get set when I changed profiles a few days ago.

Unfortunately testing was cut by clouds prior to any imaging so I’ll see if it’s back to normal tonight.

Rod Malone

On May 28, 2022, at 8:42 AM, Patrick Chevalley <p...@ap-i.net> wrote:



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[Bruce Waddington]

There is nothing in the PHD2 configuration profile or in "settings" that has anything to do with this other than the choice of camera.  The HFD measurement is blindingly simple - take a picture, measure the width of the star profile where 50% of the total energy is above that line, 50% below.  Rinse and repeat.  If you really want to spend time chasing this, you need to think about the various things that can cause the ADU values in the Airy disk to be dispersed into the "wings" of the profile which is what Patrick is pointing out.  What comes to mind just off the top are these things:

1.  Focus

2.  Seeing - usually the biggest factor after focus

3.  Moisture on the optics

4.  Moisture in the air

5.  Thin clouds

6.  Chromatic aberration, particularly if there are blue halos around the stars

7.   Higher sky background brightness

8.   Star saturation (a "square top" in the profile)

Regards,

Bruce

[George Shoup]

Make sure your binning is set where you want it.

Sent from my iPad

On May 28, 2022, at 10:44 AM, Rods Cox Account <rmal...@cox.net> wrote:

Thanks Patrick.

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[Rods Cox Account]

I’ll check tonight. I would think if binning changed in the original profile it would have told me I needed a new dark library but I’ll see.

Rod Malone

On May 28, 2022, at 12:07 PM, George Shoup <gjs...@gmail.com> wrote:

Make sure your binning is set where you want it.

To view this discussion on the web visit https://groups.google.com/d/msgid/open-phd-guiding/2A2F6DBF-0E87-4F89-8962-C37FF99E6EB8%40gmail.com.

[Rod M]

Got it Bruce. 

No clue why the numbers were better with the same camera on the new profile especially when it was so cloudy last night I could barely find a visible bright star to use. 

If it's back to normal tonight I'll just assume it was a hickup and move on. Appreciate the information though. 

Rod

[mau...@gmail.com]

Very informative comment, Patrick, thanks for that!