Sharpcap for better Polar Alignment?

[smr]

Hi,

With a few clear skies coming up I thought it would be a good opportunity to try and get better alignment and guiding. I was looking into buying a polemaster, but then stumbled across a post about sharpcap being able to do the same thing, for a tenth of the price (£10 for the pro version per year)... I remember seeing something mentioned about sharpcap a while back, think it was bundled with a product I was looking at and someone mentioned being able to use it for PA.

So, is it relatively easy to set up and use? I understand I need to get reasonably accurate PA first manually, and then I should be able to use Sharpcap with my guiding camera for precise alignment and guiding. 

[Vixen4eva]

Its brilliant and very easy to use. The hardest part i find is the adjustments on the mount......the HEQ5 doesn`t have the best ones!!! As long you have a reasonably sensitive guide camera your good to go.... Can`t comment on the Polemaster as i`ve never used one so can`t compare...

Regards

Alan

[smr]

3 minutes ago, Vixen4eva said:

Its brilliant and very easy to use. The hardest part i find is the adjustments on the mount......the HEQ5 doesn`t have the best ones!!! As long you have a reasonably sensitive guide camera your good to go.... Can`t comment on the Polemaster as i`ve never used one so can`t compare...

Regards

Alan

Thanks very much Alan, you make it sound easy. I'm looking at it overly-complicatedly as usual !

[symmetal]

Yes, as the other Alan says it's very easy to use. The guidescope doesn't even have to have the NCP or Polaris in view though it needs to be reasonably close so that its plate solving and adjustment indicating can work. A wideish FOV is also needed on the guidescope again to enable platesolving. Your Starwave should be fine. You need your Sharpcap display screen next to the scope so you can see the results as you make adjustments. It will select a star (not necessarily Polaris) in your FOV and indicate on the display where the star needs to be moved to by altering the mount alt and azi bolts. That's it. 

Worth the small cost just for this feature alone. 

Alan

Edited April 11, 2020 by symmetal

[smr]

9 minutes ago, symmetal said:

Yes, as the other Alan says it's very easy to use. The guidescope doesn't even have to have the NCP or Polaris in view though it needs to be reasonably close so that its plate solving and adjustment indicating can work. A wideish FOV is also needed on the guidescope again to enable platesolving. Your Starwave should be fine. You need your Sharpcap display screen next to the scope so you can see the results as you make adjustments. It will select a star (not necessarily Polaris) in your FOV and indicate on the display where the star needs to be moved to by altering the mount alt and azi bolts. That's it. 

Worth the small cost just for this feature alone. 

Alan

Sounds great! And should give me much better guiding than before all going well? 

So if I understand it...

After I've roughly aligned Polaris in the HEQ5 reticule, I park the Mount in home position? 

When it asks me to rotate the RA through 90 degrees do I then lock the RA or just leave it unlocked? 

[Vixen4eva]

You just follow the instructions. Like i said the trickiest part is adjusting the mount. You obviously have to have the camera on loop and you`ll need to wait for it to refresh so you can see if your moving in the right direction...

Regards

Alan

[geeklee]

1 hour ago, smr said:

After I've roughly aligned Polaris in the HEQ5 reticule, I park the Mount in home position? 

When it asks me to rotate the RA through 90 degrees do I then lock the RA or just leave it unlocked? 

I wouldn't even roughly align in the reticule if that takes a while.  Just point it roughly North using a compass (or Compass app on phone).  Worst I've been off with a really ropey start in a new position was one and a bit degrees and it gives you 5 degrees leeway.  Of course if you're a way off you may need to move the whole unit a little - which depending on the size could be challenging...

Yes, lock it after the 90 degree move.

I found this on SharpCap's site really good - nice basic walk through

https://www.sharpcap.co.uk/sharpcap/features/polar-alignment

 

Edited April 11, 2020 by geeklee

[CaptainShiznit]

Here's my quick and dirty PA routine using SharpCap.

When placing tripod, try to aim the North leg at Polaris.

Run SharpCap and connect camera, set exposure to 2s then run polar alignment routine.

Let the first stage plate solve, hit next, release clutch and rotate RA 90° as instructed.

My Az is usually over a degree off so I tend to nudge one of the rear legs a few inches, otherwise I'll run out of Az adjustment. I do this till the Az is within 20 or 30 arc minutes.

I then adjust whichever has greater error between Alt and Az to within 30 arc seconds, then the other.

Then fine adjustments until both are managing to stay until 10 arc seconds error.

I've got this down to a few minutes at most now. I came straight from manual polar alignment and just can't believe I wasted all that time previously 😊

As a note, I used to use a second hand QHY5 mono and an unbranded 9x50 guide scope and found it difficult to plate solve with within SharpCap, which made the process frustrating. I upgraded to a ZWO 120mm and Skywatcher Evoguide 50ED and the improvement was massive.

Hope this helps you a bit.

Edited April 11, 2020 by CaptainShiznit

[smr]

Thanks guys. Only about 10 subs in at the moment on M101 as I had a right game trying to get the mount star aligned this evening for some reason. Just went way off when slewing to stars so I had to turn it off a few times until it started working properly.

Obviously took longer in that I was trying something new tonight as well with polar alignment. The graph did look better than this earlier on with a flatter line for both RA and Dec but the stars are round in 180 second subs. I think it's definitely an improvement but I've just got to get better at refining the process.

 

Edited April 11, 2020 by smr

[smr]

It's 1.20" total now as I'm writing... I thought it would be better given the 'Excellent' PA according to sharpcap. I'm wondering if the az and alt bolts are tight enough when locked but they seemed to be.

[symmetal]

Hi smr,

Having perfect polar alignment does not mean your guiding will necessarily be improved. Perfect PA is not actually necessary if you're guiding and depending on the mount performance can even be detrimental. If you are imaging unguided, then getting PA as close as possible is what you want. If guiding, small PA errors will be corrected by guiding, unless the PA is well out when you will end up getting the image rotating around the guide star during the exposure leading to elongated stars in a circular pattern, increasing the further the distance from the guide star.

For mounts with Dec backlash as most mid price mounts have, it can be beneficial for the Dec PA to be slightly out by a few arcminutes so that the Dec is always guiding in one direction to compensate and so the Dec gears stay meshed. With perfect PA, the Dec axis will end up sitting in the backlash area and Dec corrections may  seem to be ignored until the backlash is taken up, leading to the Dec cycling between fairly large +ve and -ve errors every 10 seconds or more due to the actual corrections being many seconds behind the command corrections.

Dithering in Dec can upset this beneficial constant Dec meshing if it dithers to the other side of the backlash area. The mount can then take a while before the Dec settles down again.

Getting a good guide star is important. I find at times the guiding is good and then half an hour later is all over the place and changing the guide star helps. The sudden changes in RA error you're seeing on your graph is due to the guide star shape changing between successive guide frames due to seeing, and PHD2 trying to correct for this. Getting the right guide exposure and star shape selection is a bit of a balancing act and will probably need changing throughout the session. I find stars below 100 SNR generally give worse guiding while those much higher are often clipped with flat tops. However, I find that clipped stars can sometimes give better guiding than the normally preferable sharp spike star profiles, as their overall profile remains more constant.

It may be worth running PHD2's 'Guiding Assistant' for a few minutes to see if that recommends any changes. It will also measure Dec backlash if you tick the box.

Alan

Edited April 12, 2020 by symmetal

[smr]

1 hour ago, symmetal said:

Hi smr,

Having perfect polar alignment does not mean your guiding will necessarily be improved. Perfect PA is not actually necessary if you're guiding and depending on the mount performance can even be detrimental. If you are imaging unguided, then getting PA as close as possible is what you want. If guiding, small PA errors will be corrected by guiding, unless the PA is well out when you will end up getting the image rotating around the guide star during the exposure leading to elongated stars in a circular pattern, increasing the further the distance from the guide star.

For mounts with Dec backlash as most mid price mounts have, it can be beneficial for the Dec PA to be slightly out by a few arcminutes so that the Dec is always guiding in one direction to compensate and so the Dec gears stay meshed. With perfect PA, the Dec axis will end up sitting in the backlash area and Dec corrections may  seem to be ignored until the backlash is taken up, leading to the Dec cycling between fairly large +ve and -ve errors every 10 seconds or more due to the actual corrections being many seconds behind the command corrections.

Dithering in Dec can upset this beneficial constant Dec meshing if it dithers to the other side of the backlash area. The mount can then take a while before the Dec settles down again.

Getting a good guide star is important. I find at times the guiding is good and then half an hour later is all over the place and changing the guide star helps. The sudden changes in RA error you're seeing on your graph is due to the guide star shape changing between successive guide frames due to seeing, and PHD2 trying to correct for this. Getting the right guide exposure and star shape selection is a bit of a balancing act and will probably need changing throughout the session. I find stars below 100 SNR generally give worse guiding while those much higher are often clipped with flat tops. However, I find that clipped stars can sometimes give better guiding than the normally preferable sharp spike star profiles, as their overall profile remains more constant.

It may be worth running PHD2's 'Guiding Assistant' for a few minutes to see if that recommends any changes. It will also measure Dec backlash if you tick the box.

Alan

Thanks very much for that detailed reply Alan. Explained very well.

[City9Town0]

+1 for this.

I set up HEQ5 Pro every time from fresh...

Roughly align mount by compass.

Sharpcap polar align (brilliant).

Launch EQMOD

I've Red dot finder/guidescope/ main scope all aligned....Carte du ciel for a few alignment stars.

Launch PHD and calibrate near celestial meridian and eqautor

Aim at target, run guiding assistant...

Fire up APT...

Start imaging

 

May not be the best/most efficient but takes 25 minutes and works for me...