Getting to grips with SC

Using SharpCap's Polar Alignment feature
woldsweather
Posts: 7
Joined: Thu Dec 31, 2020 5:07 pm

PA Grief.

Post by woldsweather »

After spending then end of last winter enjoying a dslr camera and a 200mm lens I invested in an EQM-35 PRO mount, Altair 72EDF and an Altair 60mm RACI finder/guide scope. Some 4 months on and still no success with the new technology. After having difficulty seeing the reticule in normal polar aligning (bad neck and colourblindness) I thought I'd try sharpcap - it came free with the Altair gear. After 17 hours over 4 evenings I eventually got an excellent in Sharpcap. This took 4 hours last night.

I am having to push gain to max and exposure to 30 s to stand any chance of getting a plate solved but then only about 1 in 4 come up as solved hence taking hours to home in.

There must be a better way??
Attachments
20210121_181231.jpg
20210121_181231.jpg (266.33 KiB) Viewed 234 times
User avatar
oopfan
Posts: 828
Joined: Sat Jul 08, 2017 2:37 pm
Location: New York
Contact:

Re: PA Grief.

Post by oopfan »

Hi,

ALTAIRGP130M. Is this it?
https://www.altairastro.com/altair-gpca ... a-33-p.asp

Altair 72EDF. Is this it?
https://www.altairastro.com/altair-72-e ... -451-p.asp

Altair 60mm RACl finder/guider. Is this it?
https://www.altairastro.com/altair-10x6 ... 2504-p.asp

Which scope do you have the camera plugged into?

Do you have the illuminated reticule turned on or off?

I calculated your Field Of View from this website:
https://astronomy.tools/calculators/field_of_view/

Scenario #1: Camera plugged into Altair 60mm RACl finder/guider:
1.22 degrees x 0.92 degrees

Scenario #2: Camera plugged into Altair 72EDF:
0.64 degrees x 0.48 degrees

My Analysis:

* Polar Alignment will not work with Scenario #2. The Field Of View (FOV) is too narrow.
* Scenario #1 is your best bet, but the FOV may be too narrow. I'll leave that decision up to Robin.

My Kit:

I do Polar Alignment with a 50mm f/3.2 finder/guider, 162mm focal length. I use an Altair GPCAM2 290M having 2.9um pixels at 1920x1080. The FOV is 1.92 degrees x 1.11 degrees.

Good luck,
Brian
User avatar
oopfan
Posts: 828
Joined: Sat Jul 08, 2017 2:37 pm
Location: New York
Contact:

Re: PA Grief.

Post by oopfan »

Hi,

You have posted before with similar problems: not seeing any stars.

Have you tried taking your scope out during the day? Can you see distant objects?

I see that the finder scope has a "helical focuser". Mine has one too, and I despise the thing. Perhaps your problem is related to focus.

The Moon is out now. You can try it. Don't worry about polar alignment until you solve this issue.

Brian
User avatar
oopfan
Posts: 828
Joined: Sat Jul 08, 2017 2:37 pm
Location: New York
Contact:

Re: PA Grief.

Post by oopfan »

Also, please note that finding focus using an eyepiece is not the same as using a camera. What I mean is, if you replace the camera with an eyepiece in order to find focus, that is true for only the eyepiece. You shouldn't expect that it should remain in focus after swapping the eyepiece with the camera.

Back in the old days, when photographic film was used, I did more visual astronomy than photographic. Today, it is the other way around. In fact, I think that visual observers are in the definite minority. Now I do everything by camera. My old eyes aren't what they used to be.

Each eyepiece has a different focus point as does your camera. What complicates the matter is a helical focuser. A better focuser would be Crayford. My main scope has a Crayford focuser with a graduated scale that reads down to the millimeter. I keep a document for the scale reading for each combination of filter wheel (manual vs electronic) and camera (Altair 290M vs Atik 314E). If you also want to do visual observing then your table becomes even longer. Like I mentioned it is best to do this during daylight on a distant object. Those will be your first best guesses. Next, choose a bright, large object like the Moon to further refine the focus points. All of this should be done before attempting anything like polar alignment or astrophotography.

Brian
User avatar
admin
Site Admin
Posts: 5732
Joined: Sat Feb 11, 2017 3:52 pm
Location: Vale of the White Horse, UK
Contact:

Re: PA Grief.

Post by admin »

Hi,

I can see from your screenshot that you have tinkered quite a bit with the star detection settings - probably best to put them back to default by pressing 'reset all'. There's also no need to be in MONO12 mode for polar aligning - MONO8 will do fine.

The GPCAM in the 60mm finder/guider should be fine in terms of field of view. In the 72EDF you will be right on the limit - if you are using the 72EDF, change to the finder/guider. I use the 50mm non right-angle version with great success.

As Brian points out, check your focus - poor focus will hide most of the smaller stars.

Finally, if you get to the point that you are finding lots of stars and it still isn't working, the check the plug step is to be sure you are within 5 degrees of the pole.

Robin

more help here : https://www.sharpcap.co.uk/sharpcap/fea ... leshooting
User avatar
oopfan
Posts: 828
Joined: Sat Jul 08, 2017 2:37 pm
Location: New York
Contact:

Re: PA Grief.

Post by oopfan »

One last thought:

I never change the focus on my finder/guider since I use it for two purposes: polar alignment and guiding. In both cases I use the same camera: Altair 290M. But sometimes I use the 290M in my main imaging scope. Focusing is easy with the main scope since I have the Crayford focuser with graduated scale. But when I am done and I put the camera back into the finder scope, then I have the problem of finding focus again. This is what I do to eliminate that problem:

https://www.amazon.com/parfocal-ring/s?k=parfocal+ring

It is called a parfocal ring. It slips over the business end of the camera. When the ring butts up against the tube then I know I have perfect focus. But to make that work, I first decided on a convenient spot to place the ring and then clamped it down with the Allen wrench, then I adjusted the helical focuser to find perfect focus using SharpCap. Now that I have the ring in place, and never touch the helical focuser, I am guaranteed to return to focus whenever I need to remove the camera.

Brian
User avatar
oopfan
Posts: 828
Joined: Sat Jul 08, 2017 2:37 pm
Location: New York
Contact:

Re: PA Grief.

Post by oopfan »

Sorry, but I need to finish my thoughts on the differences between visual astronomy and astrophotography...

In my opinion, you are opening a "can of worms" if you want to do both types, and much of the problem has to do with finding focus. Honestly, there is no need to look through the scope. You will achieve much better views by looking at the SharpCap screen because the camera is far more sensitive than your eyes.

Having said that, there is one problem that you haven't encountered yet, but you will soon. That is, how do you find an object and center it in the scope? The answer is "plate solving". Perhaps you were thinking that you should use an eyepiece in the finder scope, but that is not necessary. It is best to not mess with the finder's helical focuser.

In my case, I have a completely manual mount so I completely rely on plate solving built into SharpCap. All that is required is for your image to be in focus. Then from the Tools menu, click "Plate Solve". That will do something called a "Blind Plate Solve". SharpCap will take a single frame given your current exposure settings, and then start a process that compares the stars that it sees in the image with a large database of stars in the sky for all seasons of the year. Yes, it can take a while to run but you only need to do it once. Once complete then you can click a button on the right-hand panel that runs a much faster process which looks within a 20 degree radius of your last plate solve. (I think it is 20 degrees but it might be 30 degrees.) I have mine set up to send the coordinates to C2A planetarium software which visually shows me where the telescope is pointing. Of course, if you have a computerized mount then things become easier. The point I am making is that there isn't a need to look through your scope.

Brian

PS: In your screenshot in the original post, I see that you have "Black level" set to "3" in the right-hand panel. That is another can of worms. Please take my word for it and set it to the midpoint on the slider control.
woldsweather
Posts: 7
Joined: Thu Dec 31, 2020 5:07 pm

Getting to grips with SC

Post by woldsweather »

Tonight my 5th evening having spent around 20 hours trying to polar align with SC. Last night I thought I'd cracked it. Tonight it won't pixck up a single star with 30s exposure 4x digital, full gain.

Where am I going wrong?

Using Altair GPCAM2.
chongo228
Posts: 173
Joined: Fri Nov 24, 2017 3:34 am

Re: Getting to grips with SC

Post by chongo228 »

I've only used cooled cameras but a few things jumped out in your post....

30s is waaayyyy too long. You are almost certainly blowing out stars and probably putting them over the maximum pixel width so SC is ignoring them. Go down to around 4 to 7 second exposures and leave it around there. Adjust your other settings like black level and noise reduction until you see the star count go up. Don't look at the yellow boxes as an indication of star count. That can be subjective and changes with each frame so rapidly you can't count them. Look at the stars detected value in the bottom and only pay attention to that. Adjust one thing at a time and see how it changes the star count. When star count starts to go up keep adjusting.

Full gain with a non-cooled camera is probably creating a lot of noise that will make picking up stars harder. Go down to medium to low gain.

And the most important one is be perfectly in focus....not eyeballed focus. Get a Bahtinov mask and focus perfectly. When I'm going through my autofocus routing 50 steps can increase my star count by 50 to 75%. When I eyeball focus I'm usually more than 50 steps off from perfect focus. What looks good to your eyes is not good enough.

Next clear night I'll try to plate solve with my guide scope and non-cooled 1290 mini and see what settings work. Perhaps that will get you in the right ballpark.
User avatar
admin
Site Admin
Posts: 5732
Joined: Sat Feb 11, 2017 3:52 pm
Location: Vale of the White Horse, UK
Contact:

Re: Getting to grips with SC

Post by admin »

Hi,

I've merged the two threads you started together - that way we can have an ongoing conversation as we track down whatever the issue is. Creating lots of separate threads with one or two posts in ends up hiding information from people who may only see one of them.

cheers,

Robin
Post Reply