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Guiding issue using PHD2 and ZWO ASI 120 mini

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#1 Scoutmaster Jim

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Posted 22 May 2019 - 08:16 AM

I'm hoping someone can help me with a situation I am having using a guide scope and camera. I recently purchased the ZWO miniscope as the guide scope (120mm focal length) and the ZWO ASI120 mini as the camera (3.75 pixel size). After downloading the drivers and configuring PHD2 for the specs of the guidescope and camera, I connected both the camera and mount and it started looping through pics. My issue is as shown in the attached photo, that the screen is noisy. If I move the scroll bar for the gain all the way to the left, I get a completely white screen. If I move it all the way right, I get roughly what is shown in the photo. 

 

I am using a Windows 10 machine and not sure if that is an issue or not, but I do not know what my configuration settings I should change to clean this up. The second photo shows the settings for the camera....hopefully they can be seen.

 

Thanks in advance

 

Scoutmaster

Attached Thumbnails

  • IMG_20190521_230900165.jpg
  • IMG_20190521_230944376.jpg


#2 rgsalinger

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Posted 22 May 2019 - 08:28 AM

The most likely reason for this is that you are very very far from being focused. You should try focusing during the day - use low gain on the camera - at a object as far away as you can. That way you will have rough focus for the night. If you bought this as a package, it may have come with spacers and it is very common to have to use these with a guide camera. I know that I did and many others have posted the same thing. Then, at night, turn up the gain and slew the scope to the moon (easy to find and very bright). That will allow you to get excellent focus easily.

 

The only two things you can really change are the gain of the camera and the gamma of your screen. Hopefully someone else who has this exact system can give you more specific advice. The points above are generic and apply to most any camera.

 

Rgrds-Ross


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#3 Scoutmaster Jim

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Posted 22 May 2019 - 08:34 AM

The most likely reason for this is that you are very very far from being focused. You should try focusing during the day - use low gain on the camera - at a object as far away as you can. That way you will have rough focus for the night. If you bought this as a package, it may have come with spacers and it is very common to have to use these with a guide camera. I know that I did and many others have posted the same thing. Then, at night, turn up the gain and slew the scope to the moon (easy to find and very bright). That will allow you to get excellent focus easily.

 

The only two things you can really change are the gain of the camera and the gamma of your screen. Hopefully someone else who has this exact system can give you more specific advice. The points above are generic and apply to most any camera.

 

Rgrds-Ross

Thanks Ross. I need to look at the guidescope further since I do not see how to focus it. Only thing I can think of is moving the guiding camera out of the scope a little to see if that is how to "focus". I am new to guiding and its all a mystery to me. 



#4 StephenW

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Posted 22 May 2019 - 08:40 AM

+1 for not being in focus.

 

From the ZWO product page (https://astronomy-im...minguider-scope) it looks like you can adjust focus by turning the front section of the guide scope (scroll down on the page I linked)


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#5 Scoutmaster Jim

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Posted 22 May 2019 - 08:49 AM

+1 for not being in focus.

 

From the ZWO product page (https://astronomy-im...minguider-scope) it looks like you can adjust focus by turning the front section of the guide scope (scroll down on the page I linked)

Thanks StephenW. I was getting frustrated with issues last night since this was my first attempt. By the time I got to image (without guiding) it was after 10pm so I did not think of trying to see if the scope actually had any type of focusing. NEwbie mistake. I will check when I get home to see HOW to focus it. 

 

Jim



#6 Scoutmaster Jim

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Posted 22 May 2019 - 08:53 AM

+1 for not being in focus.

 

From the ZWO product page (https://astronomy-im...minguider-scope) it looks like you can adjust focus by turning the front section of the guide scope (scroll down on the page I linked)

cripes! It even show a picture of the focuser out.....LOL! The 5 P's come into play here.....Proper Planning Prevents Poor Performance!


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#7 bobzeq25

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Posted 22 May 2019 - 09:14 AM

Tip.  Getting focus can be difficult.  It's easier if you use something bright.  The Moon is ideal.  A very bright star can work.  Or focusing on something far away in daylight.


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#8 Scoutmaster Jim

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Posted 22 May 2019 - 09:41 AM

Tip.  Getting focus can be difficult.  It's easier if you use something bright.  The Moon is ideal.  A very bright star can work.  Or focusing on something far away in daylight.

Will do. Thanks bobzeq25!



#9 BetaDraconis

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Posted 22 May 2019 - 09:45 AM

Your gain is also way too high. When using the 120 I'm usually around 50 - 55.



#10 Scoutmaster Jim

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Posted 22 May 2019 - 10:01 AM

Your gain is also way too high. When using the 120 I'm usually around 50 - 55.

Thanks. I was trying out different settings to see if I could clean it up but nothing worked. Possibly as others mentioned that my focus was off. Now I need another clear night just to test, or partially clear anyway.



#11 bobzeq25

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Posted 22 May 2019 - 10:12 AM

Thanks. I was trying out different settings to see if I could clean it up but nothing worked. Possibly as others mentioned that my focus was off. Now I need another clear night just to test, or partially clear anyway.

The reason we're all saying focus is that we've all had the same problem, and seen exactly what you're seeing.  PhD just goes haywire in exactly that way when the focus is off.  It is a bit strange.


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#12 rgsalinger

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Posted 22 May 2019 - 10:42 AM

I think that with these guide scopes you're running at something like F4 and so the critical focus zone is really small. That just ads to the problem of getting it right. Sometimes I wonder if these are really easier to set up than an OAG. Sometimes. 

Rgrds-Ross


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#13 Scoutmaster Jim

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Posted 22 May 2019 - 11:16 AM

I appreciate the help from all! Now I have things to check when trying again.

 

Thanks!

 

Jim



#14 Stelios

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Posted 22 May 2019 - 11:33 AM

Suggestion: Focus using Sharpcap, not PhD2. 

 

Sharpcap (free--for the part you need) produces a significantly sharper image and you don't need to fudge the gain slider. Just make sure you set the exposure *very* low for daytime focusing (milliseconds, perhaps under a millisecond). 

 

Sharpcap (in case you've not used it) works very simply--you connect the camera from the dropdown, and it *immediately* starts taking images. Your initial screen will likely be white, so just keep lowering the exposure till you see details (an easy slide control). 

 

When you're focused with Sharpcap, you will be also focused with PhD2. Manipulating the gamma slider then will get you where you want to be.

 

And a Windows 10 tip: Rather than photographing the screen, use the Snip icon to take a snapshot of any rectangular area of your screen. You can then save and email or post it.


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#15 Scoutmaster Jim

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Posted 22 May 2019 - 02:21 PM

Suggestion: Focus using Sharpcap, not PhD2. 

 

Sharpcap (free--for the part you need) produces a significantly sharper image and you don't need to fudge the gain slider. Just make sure you set the exposure *very* low for daytime focusing (milliseconds, perhaps under a millisecond). 

 

Sharpcap (in case you've not used it) works very simply--you connect the camera from the dropdown, and it *immediately* starts taking images. Your initial screen will likely be white, so just keep lowering the exposure till you see details (an easy slide control). 

 

When you're focused with Sharpcap, you will be also focused with PhD2. Manipulating the gamma slider then will get you where you want to be.

 

And a Windows 10 tip: Rather than photographing the screen, use the Snip icon to take a snapshot of any rectangular area of your screen. You can then save and email or post it.

Stelios

 

I will give Sharpcap a try. I assume just use it to focus the guiding scope/camera and then switch over to PHD2 to do the actual guiding?



#16 bmhjr

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Posted 22 May 2019 - 02:28 PM

Stelios

 

I will give Sharpcap a try. I assume just use it to focus the guiding scope/camera and then switch over to PHD2 to do the actual guiding?

That is what I do.  With Sharpcap you can either eyeball it on the frame screen or use their various focus aids.  Much simpler, then close it and switch to PHD2.


Edited by bmhjr, 22 May 2019 - 02:28 PM.

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#17 Dan Finnerty

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Posted 22 May 2019 - 05:47 PM

I find it handy to check guide scope focus when I first set up the scope/mount before polar alignment. Unless you are waaaay off in polar alignment, the guide scope should have Polaris in the FOV when you are pointed at 90 degrees declination/counter weights down, the usual initial position for scope set up.

 

Polaris is a bright mag 2nd star, very bright and there is nothing else near as bright anywhere near it. Even if you are way out of focus, you can see the out of focus disk. As you come into focus, dimmer stars in the field will appear. They are better for fine focus. Then you guide scope is ready for action. Not a bad place to start focusing your main camera either.

 

Once you get your guide camera focused, carefully note (or mark with a piece of tape) where the focus position is for future reference.

 

For your guide scope that rotates the objective lens for focus, note that that has a limited range of motion. You may need to move your camera in or out for rough focus. Again, mark its final position for future reference.

 

After focusing, if your astro camera is connected, it is a good time to tweak alignment of your guide cam to your main telescope. Polaris is there to help you.

 

Once your guide scope and camera are set up, there will be little change needed in the future except for checking and occasionally tweaking fine focus or alignment when you start a new imaging session. And Polaris is a great place to do that at the beginning of the night. You will become quite familiar with Polaris and surrounding stars in a while, you will have no problem knowing that you are in fact looking at Polaris and not some other field star, and it will be a comforting and confidence building start to your nights imagine ops.


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#18 Scoutmaster Jim

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Posted 26 May 2019 - 04:35 PM

Update for everyone...

 

I was able to get out Friday night and as Dan Finnerty said (before I even saw his reply...lol) I had the scope in the zero position pointing at Polaris. I saw this huge "ball" and realized that must be it and kept turning the lens out until it got more into focus and more stars began to appear. It would seem I may need to try to adjust the amount that the guide camera is in the guide scope to get pinpoint stars since they were always not sharp, but I was able to run through calibration on one of them and then began guiding. 

I slewed to M101 and started guiding again and tried a 5 minute exposure and saw the graph in PHD2 was showing total RMS error of 0.71 (4.56") which I think was out of whack a little. Also when I saw the first photo I had the main stars and next to almost each one was a smaller clone of it...like a ministar. Took another shot, same thing. Thought...okay lets take a look at polar alignment to see if that was correct, which it was and then it hit me.....I balanced the scope with a different alignment scope that with the guiding scope/camera so my balance was slightly off. Balanced with guide camera on and tried another 5 minute exposure....bingo! The total error now was coming up at 0.17. Tried some more shots of M101 but it did a meridian flip and my camera was hitting the leg now so I slewed to the Iris Nebula and shot 15 5min exposures of this object. Unfortunately my camera is an unmodified DSLR so I cannot get the full details of this object but at least my tracking was perfect. Attached are two pics. one showing the bad, unbalanced guiding (M101) and the second shows the better guiding (Iris Nebula) these are just single shots, not stacked and mildly PS.

Attached Thumbnails

  • M101 ps processed bad guiding.jpg
  • Iris Nebula PS good guiding.jpg

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