focus errors

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donwaters201
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Joined: Mon Apr 19, 2021 2:09 pm

focus errors

#1

Post by donwaters201 »

Last night, I tried to use the Bahtinov mask and FWHM options unsuccessfully.

Using the mask on Altair, and a ZWO294MC Pro camera, I could never get good lines to analyze. I used the Goldfocus mask. I focused manually and then used Sharpcap to capture images of Altair and Goldfocus to analyze and Goldfocus showed near perfect focus. I went back to Sharpcap and the mask option still would not find good lines.

Then I went to FWHM on Sharpcap to see what would happen, and the rating was about 4.5 orange bars. Fine-tuning the focus moved toward 4 and got green bars. When I stopped and looked at the star image, it was clearly out of focus, so the green bars were actually opposite of what happened.

Seeing was average and there were high thin clouds.

I can't understand why the focus was an issue. Suggestions appreciated.

Don Waters
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Re: focus errors

#2

Post by admin »

Hi Don,

thanks for the feedback. In both cases, the most helpful thing to understand (and hopefully fix) any problems would be if you could share some sample images (snapshot to PNG).

1) Showing the bahtinov pattern that is not detected
2) Showing the stars at best focus as determined by your bahtinov focus
3) Showing the stars at 'best focus' as determined by SharpCap's FWHM score.

Screenshots showing the settings you have in each focus tool would also be helpful.

One more thing before trying any of that though... Can I check that you are using SharpCap 4.0 rather than 3.2? The FWHM calculations have been improved in 4.0.

cheers,

Robin
donwaters201
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Joined: Mon Apr 19, 2021 2:09 pm

Re: focus errors

#3

Post by donwaters201 »

Just an interim response:

1. I do have Sharpcap 4.0.
2. Next outing, I will get some screen shots.
3. Next outing, I will try mask from another supplier.
4. Next outing, I will try PHD2 focus assistant (with same camera) and see what FWHM number I get.

I assume that I am off on some setting or operation. Recently at a dark sky site, the focus assistants worked very well.

I am fairly new at this, but I really do like the layout and the way so many features are integrated into this program. (BTW, works very well with plate solve.)

Thanks,
Don
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Menno555
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Re: focus errors

#4

Post by Menno555 »

Hi Don

I don't know your knowledge, so maybe I am stating something obvious for you here. If so, sorry in advance :D
So question: did you use the GoldFocus mask for SharpCap measurement? If so, that will not work. SharpCap relies on a Bahtinov mask and the GoldFocus mask is actually a kind of Tri-Bahtinov mask. It creates another pattern than a Bahtinov.
I have both and did experiment with it a while ago.
Just in case, below the difference between the 2: left the Bahtinov pattern that SharpCap can use, right the pattern of the GoldFocus mask.

Menno

Untitled-1.jpg
Untitled-1.jpg (74.55 KiB) Viewed 635 times
donwaters201
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Joined: Mon Apr 19, 2021 2:09 pm

Re: focus errors

#5

Post by donwaters201 »

Yes, I did use the GoldFocus mask with SharpCap. As you point out, I should not.

I have used the correct mask and SharpCap works normally. I think my other issues were due to not being familiar with the settings, and I was not getting gain/exposure in the right range. It seems to be somewhat sensitive to these settings. (I have relatively poor skies.)

QUESTIONS:
1. When SharpCap starts, it always come up with "SER" and "RAW8" as settings. Is there a way to change the default, so it starts with RAW16 and FITS?
2. Sometimes the "RESET" button on focus assist does not reset and I have to restart the program. Any suggestions?
3. Is the scale for FWHM for single star the actual value, i.e., the same as programs like PHD2? Should I be getting the same reading for FWHM regardless of software used? (It appears that the multiple star focus is some other metric.)
4. For the "EXPOSURE" slider: If I set "auto", what does this do? I don't see it changing from manual.

Thanks,
Don
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Re: focus errors

#6

Post by admin »

Hi Don,

glad that you are making progress.

To set default camera settings that suit you, you need to set up a capture profile and make it the default profile for the camera (https://docs.sharpcap.co.uk/4.0/#Capture%20Profiles and https://docs.sharpcap.co.uk/4.0/#Captur ... Management). You may also need to adjust the settings in the 'Saving' section of the settings to turn off 'Auto output format'.

No idea on the reset button not working - if it happens again, please capture a screenshot and the log after pressing reset did nothing and I will investigate further.

The value of FWHM should be considered as something to help you adjust focus and/or seeing conditions when using a single set of equipement in SharpCap. Trying to compare it between SharpCap and other applications (or even between SharpCap values when using different cameras or telescopes) is dodgy - for instance DSS and PHD2 probably use different ways to calculate/estimate FWHM (and both different from SharpCap's way). They will all show an increase if the focus gets worse, but the values will not necessarily be the same.

Auto exposure for your ZWO camera is handled the ZWO code - SharpCap just sends a message to the camera SDK saying 'auto exposure please' and the camera will then do some sort of auto exposure. To be honest, I would tend to only use auto exposure for video imaging of daylight scenes and maybe all sky cameras. For lunar/solar/planetary and deep sky, I'd stick to manual exposure adjustments.

cheers,

Robin
donwaters201
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Re: focus errors

#7

Post by donwaters201 »

All is going well. I have played around with various combinations and I'm sure it is just my inexperience that as an issue.'

I am not looking at automatic focusing using a Starlight EFS system for the first time. Last night all connections worked smoothly and I did a preliminary trial.

QUESTION: How do I set steps and minimum and maximum focus? I do not see this in the excellent help provided. I am using a 9.25" Celestron with the Feathertouch focuser from Starlight.

Don
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Re: focus errors

#8

Post by admin »

Hi Don,

not quite sure what you are asking exactly... Normally ASCOM electronic focuser drivers have a range from zero to a certain maximum step value (maybe 50000). This range usually exceeds the physical range by which your focuser can move by some way, so you might find that you hit the inner end of focus at 15000 and the outer end at 42000 for instance. There isn't a way to program these end points into either ASCOM or SharpCap, but you tend to learn them for your hardware, and also the fact that good focus might be near about 27000...

cheers,

Robin
donwaters201
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Joined: Mon Apr 19, 2021 2:09 pm

Re: focus errors

#9

Post by donwaters201 »

Ok. I will check with Starlight.

What I am trying to do is understand the correlation between the number shown on the screen and the physical position of the focuser. Right now, the camera is in focus, and the screen seems to have arbitrary values, so I don't know where I am.

Is there a way to move the focus knob to one limit and set value and then repeat for the other end?

I understand I must "learn my equipment", but not sure how to do that and find how focus limits correspond to screen values.

Love the software, though,
Don
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Re: focus errors

#10

Post by admin »

Hi Don,

yes, in general the numbers for the focuser are pretty arbitrary and the numbers for a particular position may change over time (particularly if you hit the end stops or have anything in the focuser mechanism that might slip like a crayford focuser).

To get an idea of the end values, the only real way is to watch the hardware while moving the focuser through SharpCap until you get to the end points, sorry.

cheers,

Robin
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