Scope guiding, platesolving and polar alignment

[George Gearless]

I figured this was the most appropriate place to post, since I need to get some pretty basic stuff sorted out.

If I've understood platesolving correctly, it is an automated function in my Stellarmate that automaticaly aligns your scope, based on what it 'sees' through the guidescope. If this is correct, does it mean that the whole 2-3 star alignment process is no longer necessary? Or have I misunderstood what platesolving is?

If I am using a guidescope, do I still need to polar align?

Can I use my guidescope to track a planet for planet photography?

 

I've been 'dry-training' a bit during the light evenings of the summer. So I haven't been able to actualy test my equipment in practice. Now that winter is approcahing I've realized how far behind I am in the training I had planned to do this summer. So if you can help me with the above questions, you'll grant me a head start for the season.

 

 

[Davey-T]

No idea about Stellarmate but plate solving uses the main imaging camera, you need to polar align. Unless you're planning on hopping around the sky using GoTo there's no need to star align you can just sync on a star where you're going to image.

Some software can plate solve an image to see where it's aimed then align your scope on the target by plate solving another image to centre it.

You don't need to guide to take planetary videos, you may be able to use it to capture planetary videos depending on which camera it is by fitting it to your main scope.

Dave

Edited August 15, 2019 by Davey-T

[michael8554]

Polar Alignment gets the mount's RA axis accurately pointing at the North Celestial Pole, so that the mount tracks stars as they move across the sky.

At this point the mount has a rough idea where it's pointing at any moment, based on date, time, location.

So the Star Alignment gives it two or three accurate star positions to fine-tune its sky map.

Plate Solving tells you the RA and Dec of an image from your imaging camera, and as Dave said some software will then slew the scope to where you intended the scope to point.

But again as Dave said, if you're just going to image one target, skip the Star Alignment and Plate Solving.  Goto and sync on a star near the target, that will fine-tune the mount's sky map to an area around the star, so a subsequent goto your target should be in the camera's frame.

Normally planets are imaged by shooting a very high frame-rate movie. Then software discards blurred frames and aligns and stacks the rest into a single still, so guiding isn't necessary.

Michael

[George Gearless]

@Davey-T Thanks for the reply.

Ok, so I still need to polar align. Got it.

Admitedly, I have not done enough 'research' into platesolving (particularly on Stellarmate) to ask qualified questions. But wether I use platesolving or the regular alignment procedure, I do need the go-to function on occasion when photographing a particularly faint object. I just figured platesolving would be a short cut to just that.

I know that I don't have to guide the scope for planetary photography. But once again I was just looking for a shortcut :). I figured that I could dispense with the polar alignment of the scope, if I let my guidescope correct the drift that would occur on a non-polar aligned setup. If it could keep the planet I'm photographing 'mostly' centered, I'd let Registax handle the rest in post production. Keep in mind that I will be using a 180mm Maksutov for planetray and lunar photographing. So it'll drift quickly out of sight if I don't set up proper polar alignment.

[George Gearless]

@michael8554 Thanks Michael.

Ok, so platesolving is not just a nifty way of aligning your scope. It's a procedure to make sure the observed stars correctly correlate to the map? Think I got it now.

As for the planetary photography, read my response to Davey. I was just wondering if my guidescope could handle the corrections needed to keep, say, Jupiter in the frame on a non-polar aligned scope.

[Davey-T]

Average PA is good enough for planetary videos, shouldn't need guiding, does your mount have a tracking mode for planets.

Dave

[George Gearless]

34 minutes ago, Davey-T said:

Average PA is good enough for planetary videos, shouldn't need guiding, does your mount have a tracking mode for planets.

Dave

I believe it does. Skywatcher Mount EQM-35 PRO SynScan GoTo. If i remember correctly, there's a setting in one of the initial menus where you can set the tracking rate. Siderial has been enough for me so far and found no reason to change it. Planetary and lunar  photographing is usualy not more than a few minutes of recording anyway.

 

[wimvb]

Platesolving on a Stellarmate replaces any star alignment, except polar alignment. You just point the scope in your planetarium program (the Stellarmate "client" app) at the dso you want to image. The scope will then slew to what it thinks is the correct position. Depending on how you've set it up it will be close or a mile and a half off. Stellarmate will take images and correct the scope's position until the star field in the images matches the star field in the planetarium program, within a certain accuracy. For Stellarmate, the default accuracy is 30 arcseconds. Depending on your scope focal length, mount pointing accuracy, and sensor size, you may want to adjust that value. For widefield you increase the tolerance, and for long focal length on an accurate mount, you decrease it somewhat.

The first time you tell Stellarmate to point at a target, it may take a few corrections to center it. But the more points/targets you add to the Stellarmate pointing model, the more accurate it becomes.

[George Gearless]

51 minutes ago, wimvb said:

Platesolving on a Stellarmate replaces any star alignment, except polar alignment. You just point the scope in your planetarium program (the Stellarmate "client" app) at the dso you want to image. The scope will then slew to what it thinks is the correct position. Depending on how you've set it up it will be close or a mile and a half off. Stellarmate will take images and correct the scope's position until the star field in the images matches the star field in the planetarium program, within a certain accuracy. For Stellarmate, the default accuracy is 30 arcseconds. Depending on your scope focal length, mount pointing accuracy, and sensor size, you may want to adjust that value. For widefield you increase the tolerance, and for long focal length on an accurate mount, you decrease it somewhat.

The first time you tell Stellarmate to point at a target, it may take a few corrections to center it. But the more points/targets you add to the Stellarmate pointing model, the more accurate it becomes.

Excellent news. Thanks Wim.

I have been neglecting my studies into the Stellarmate. I had some problems getting the app to work when I got it, but I finally got it solved with the help of Stellarmates excellent support. And once I got it working, I couldn't realy test the darned thing because of the summertime light nights. Now we're approaching the star-hunting season and I'm behind on my homework.