SharpCap 2.9 - Polar Alignment

[Andyb90]

Hi Everyone,

I've just downloaded 2.8 to have a go at video astronomy, but noticed version 2.9 (currently beta) has a Polar Alignment feature.

Has anyone tried this feature? If so how did you get on?

Andy.

[Iver]

I've tried it twice, it works very well! I only compared it to the accuracy of my Tak EM-200 polar scope. Set the mount down without using the polar scope, polar aligned with SharpCap and then checked the polar scope. Both times Polaris was right where it should be in the polar scope.

-Iver

[Andyb90]

That's incouraging. Will install 2.9 and give it a try next session. I have a finder guider, which should give a wide enough field of view.

Andy.

[Iver]

I gave the Polar align feature in SharpCap a real test tonight, I spent a little extra time getting the alignment as close as possible. This still took less then 5 min. I centered M13 and started guiding with Dec. corrections disabled.  I let this go for 25 min. and during that time the average error in Dec. remained at .06 pixel. No detectable drift in 25 min. Quite a nice PA tool.

[cardconvict]

This sounds very interesting indeed, I will have to give this a try.

[Andyb90]

There's a link on the Sharpcap website with info about the feature:

http://www.sharpcap.co.uk/sharpcap/polar-alignment

Andy.

[rwg]

Glad to hear that it's working well for you!

If you have any problems then please capture a pair of images (one in each orientation) and send them to me - I can use them to help improve the polar alignment and star detection routines.

cheers,

Robin

[saac]

I wonder if I could ask what is probably a few silly questions?

1.  What sort of camera would be necessary to use the align feature on Sharp Cap - would a mono imaging camera such as my DFK21 AU04 or say a modified web cam be any use?  I'm presently using a modified web cam attached to teh polar scope just to save the akward back bending during polar alignment. The web cam just about makes out Polaris.

2.  How would the camera be mounted - does it need to be fitted to the polar scope or can it be mounted to the telescope itself either on the focuser (as though doing planetary imaging) or on the finder as similar to a guide scope.

3. Would use of SharCap polar align effectively provide  a cheaper alternative to PoleMaster.

Sorry if these questions are a bit silly but I'm just trying to get my head around as to what a suitable setup would comprise.

 

Jim

 

[rwg]

@saac

The mono camera would likely be a good choice - you need to work out your FOV (there are several web based FOV calculators out there). As long as your FOV is between about 1 and 2.5 degrees in each direction you should be fine. Ideally you want to see about 10 or more stars, although you might get results with 5 or 6.

I haven't consiidered using this with a polarscope - it would be interesting to test - you would need a camera with a lens on it fixed over the eyepiece of the polarscope. No idea how the FOV would work out for this. I've generally considered using this with a finder scope to give the correct FOV, but you could use it with the main scope if the focal length is short enough or the sensor big enough.

I've not used a polemaster, so I don't know if it works in the same way as the SharpCap alignment - I guess that they both get you to the same end point.

cheers,

Robin

[saac]

Thanks for the reply Robin, I'll try setting up using my finder scope.  When I use the modified web cam through the polarscope I noticed that the fov is pretty limited.

 

Jim

[Andyb90]

Just to check should my mount be tracking at sidereal rate when doing the polar alignment routine?

Or does it not matter if the mount is tracking or not?

Andy.

[rwg]

Hi Andy,

really shouldn't matter, as you are pointing pretty much at the pole and you will be taking exposures of a few seconds. Nothing in view is going to move significantly in that time.

cheers,

Robin

[Dave_D]

Robin, have you been poking about in code again? just did a completely fresh install of ascom standards, ssag drivers (including ascom driver) and sharpcap 2.9 and lo and behold, my orion SSAG worked straight off the bat... happy is an understatement... will save me a fortune not getting a polemaster

[rwg]

Hi Dave,

I don't think I've tinkered with anything that would address problems with that particular camera, although I did make a couple of tweaks to ASCOM camera  support to get some old QHY cameras working. Maybe just the clean out and re-install did the trick? Anyway, glad to hear that you are up and running now!

Robin

[Crose01]

I did the Polar Alignment last night with 2.9 using an Altair Astro GPCAM Mono and their 60mm Finder Scope. managed to get my PA down from ~ 12 Arc Mins down to around 57 Arc Seconds. I must admit I'm impressed with this version. It took some tinkering with as I'm having issues focusing this setup but I found it works best with 8 second exposures

[rwg]

That's good to hear!

I'm working on a major update to the plate solving code which is the core of the polar alignment. The new code should be faster and more accurate too, and should also get a solution for the pole position in many cases where the current code fails. This should give some useful improvements and help to procedure work with a wider range of cameras and focal lengths.

One thing I've just discovered is that it doesn't work if your pixels aren't square - in other words it will fail if the camera image is squashed or stretched in the horizontal direction. For most digital USB cameras this won't be an issue, but if you are using a frame grabber with an analogue camera this could cause problems. It might be worth trying different resolutions in the frame grabber (ie 720x480, 720x504, etc) to get one that has an aspect ratio most closely matching that of the camera sensor.

cheers,

Robin

[Crose01]

I did notice when it got close to PA that the arrow disappeared and was replaced by two yellow lines reminded me of the artificial horizon cursor you see in aircraft. 

My PHD2 noticed the difference with a much flatter DEC line. RA was a bit chattery but the seeing was pretty awful last night.

Regards

 

Chris

 

[Gina]

Very useful addition to an already great program - currently my favourite for setting up for AP with ZWO ASI1600MM-Cool camera and with my all sky camera with ASI178MM   Now if only you did a Linux version to use with a Raspberry Pi I would be a very happy bunny

Edited August 24, 2016 by Gina

[rwg]

Chris,

yes, the artificial horizon thing replaces the arrow when the arrow becomes so short that it would be difficult to see clearly.

Gina,

glad you like SharpCap. No real chance of a Linux version I'm afraid - it's all too linked into Windows UI, camera SDKs, etc.

cheers,

Robin

[Gina]

I guessed that would be the case Robin since you're using a lot of Windows stuff.  Not to worry I'll find something

[ngwillym]

Another thumbs up for the polar alignment feature.

I'd struggled several times with PHD2 drift alignment, but with Sharpcap - including the time clouds got in the way - less than one hour to get the EQ8 aligned with areported (by shaprcap) accuracy of ~3 arcsec  - doubt if I could get any better - I'm thinking the imaging was seeing limited.

Achieved using my 70mm F5 Celestron Travelscope (piggyback on my C11 as finder/guider) and a QHY5L-II mono with 0.5 reducer.

lots of karma to Robin

Neil

[Vox45]

On 24/08/2016 at 11:41, rwg said:

Chris,

yes, the artificial horizon thing replaces the arrow when the arrow becomes so short that it would be difficult to see clearly.

Gina,

glad you like SharpCap. No real chance of a Linux version I'm afraid - it's all too linked into Windows UI, camera SDKs, etc.

cheers,

Robin

I really like Sharpcap and the PA feature you added is just brilliant !

There is a feature in Firecapture that I did not see in Sharpcap (maybe it's there) is the option to add a frame with information on the target (ephemerids I think) ... Sorry for not being more precise about how this is working as I never really used it, but I see a lot of picture posted with this information embeded and I was told that it was generated from Firecapture. Do you plan to add this to Sharpcap or is it there already ?

[rwg]

Hi,

currenly there is no framing feature - I don't see it as something I'm likely to add in the near future I'm afraid. I guess I imagine that sort of thing being done in post-processing.

cheers,

Robin

[Vox45]

16 hours ago, rwg said:

Hi,

currenly there is no framing feature - I don't see it as something I'm likely to add in the near future I'm afraid. I guess I imagine that sort of thing being done in post-processing.

cheers,

Robin

Yes I am doing the framing in post-processing. The feature I liked was that you could add to the frame some info taken directly from the session details. Apparently it is using "image magic" and to give you a batter idea of what I am talking about:

there is a short demo here

That would be a nice feature to be able to record all the session details and be able to embed them in the image in one click from inside Sharpcap

[rwg]

All of the camera settings are saved in a .CameraSettings.txt file next to the actual capture file, so the data is there if you want to use it.

cheers,

Robin