Jump to content

740427863_Terminatorchallenge.jpg.2f4cb93182b2ce715fac5aa75b0503c8.jpg

Checking PA with PHD - This is madness


swag72
 Share

Recommended Posts

OK, I am sitting in the cold and so far in 1 hour I have achieved very little while I am checking my PA in PHD. Admittedly, my graph isn't swinging quite as wildly as it was (Still on 1st star) but I just can't level it out - Anyone help with their tips?

Can you also confirm that I would have to carry this out prior to any imaging session?

Maybe I'm turning the wrong bolts? Black twist ones for the meridian star and metal ones for the other?

Edited by swag72
Link to comment
Share on other sites

  • Replies 46
  • Created
  • Last Reply

Top Posters In This Topic

Top Posters In This Topic

Why do you want to check it? What are you going to do when you have a measure of PA? Maybe I don't understand your question here.

I would just calibrate your autoguider and give it a try. If it over corrects, adjust the guide parameters accordingly by making it less aggressive. If it is too slow to correct, make it more aggressive. If you seem to have backlash (clusters of guide hits in two slightly displaced locations) put a weight bias on the east side of the mount for a problem in RA. If you have backlash in Dec make the camera end a bit heavier and alter the dec backlash parameter slightly by trial and error.

I don't use PhD but the principles are pretty universal, I would have thought. Sorry I can't help specifically with your programme.

Olly

Edited by ollypenrice
Link to comment
Share on other sites

The reason I am checking it is because my PA has been suggested as needing to be better as I am struggling with my guiding. In a couple of threads of mine, it has been suggested that this would be a good thing to do.

Well, it has left me feeling like crying as after 4 hours I have acheived NOTHING. I am ready to throw the lot in the bin.

Are you suggesting that the way to correct my guiding is just adjusting my weights? Sorry Olly, but I'm just not sure what you're saying. I have evidence of field rotation im my 3 min guided image of M31. So, how do I know what to adjust and how?

Edited by swag72
Link to comment
Share on other sites

Sara, you're having a night of pain... we all do... The bin is not the way to go ;)...

I've not had a chance to even look at doing the drift alignment using PHD and the guidecamera myself yet, if you want to see if you can blow away the clouds for me, I'll have a go... I've been trying but they just won't shift. I do wonder, if the finder scope isn't possibly a little short on focal length to make it easy... hmm... perhaps put the QHY5 in the 120ED... and drift align that way... the longer focal length of the main scope is gonna show the effect far more.

Olly is suggesting that when you balance, you put a slight bias to the balance so that the lowest part of the axis (scope of counterweight) is ever so slightly heavier. This causes the gears to always be pushing against something, meaning you can't get the gears bouncing a little.

I'd suggest, just set up and go, and capture something, even if there are some oddities along one edge... you can always crop them out :p... you'll feel better confirming that the kit is actually working...

Link to comment
Share on other sites

I was using the QHY5 in the 120ED - I guess it's not helped by not knowing what I am doing, essentially why or how to improve it. All I want to do is be able to get a nice 5 mins guided, but instead I am left feeling utterly ****, useless and stupid.

How can I hope to get a 5 min exposure? What can I do to achieve that?

Lat time I guided I did a 1 star alignment. Will it help the guiding if I do a 2 or 3 star?

Edited by swag72
Link to comment
Share on other sites

From the other threads, with my take on what it means... I still get muddled over which axis is which, I probably ought to label them on my mount ;)...Ok... looking at definitions, if I've got this right... RA is the axis aligned to Polaris, and DEC is the axis aligned with the counterweights. Someone please correct me if I've muddled it...

1. Turn on the guiding program (PHD) , select the mount and camera and run thru your calibration a usually.

2. To Check the RA select a star near the Meridian at 0° elevation. Aim for something South

3. Start Guiding on the selected star.

4. Turn on the GRAPH and select DX/DY instead of RA/DEC. (tools, view graph)

5. Turn off the DEC guiding - Do this by clicking the brain button, and there's a drop down for the DEC guiding

6. If your mount is perfectly aligned the DY ( red line) should track across the graph near the center line. If it drift up or down you need to make a very small adjustment to your AZIMUTH screws to compensate for that. You will see the change immediately. No need to wait 5 or 10 minutes for the visual drift.

Watch the direction the red line moves and adjust as described

7. Now set up the elevation.

8. Stop the guiding and look for a star near the western or eastern horizon at whatever elevation allows you to clear any obstruction. The lower the better.

9. Recalibrate the guiding on the new star.

10. As in step 3,4 & 5 above start guiding and make sure that the DEC guiding is off.

11. Once again if your alignment is on then the DY trace should not drift from the horizontal graph line. If it does, carefully make small adjusts to the ELEVATION screws to compensate. Again you should see an immediate change in the graph.

Hopefully that'll help with the techniques involved... I hope...

Link to comment
Share on other sites

Cheers John - That was the guide I was following. I was aligned to Rigel in the South and turning the black Azimuth knobs and for the East I was using Regalus.

All in all, a disaster. If the graph was showing me that my PA was poor, it did a good job. Try as I might I could not flatten out the graph and it just seemed like a waste of 4 hours. Also, correct me if I'm wrong, but I'd have to do this before each imaging session? Mmm, I don't think that is the way forward for me - I'll have no time left to do anything.

Here is the best I managed to get my PHD graph - I think you'll agree, not exactly a fruitful evening.

swag72-albums-dso-s-picture8736-phd-graph.jpg

Edited by swag72
Link to comment
Share on other sites

Using Johns method and your descriptions - when doing the south bit, move the BLACK knobs, when doing the east/west bit use the SILVER bolts. And yes you will need to do this every time you set up.....BUT after you have done it a couple of times it doesnt take long to do....I start at twilight, as long as the camera can see a couple of stars thats all you need.

Link to comment
Share on other sites

Using Johns method and your descriptions - when doing the south bit, move the BLACK knobs, when doing the east/west bit use the SILVER bolts. And yes you will need to do this every time you set up.....BUT after you have done it a couple of times it doesnt take long to do....I start at twilight, as long as the camera can see a couple of stars thats all you need.

So I was using the right bolts! But as you can see from the graph Martin, I didn't achieve anything. Nothing I did seemed to flatten it. All I could do was basically move it up and down the graph, none of the settings seemed to make anything any better.

Link to comment
Share on other sites

You wont get a FLAT line on the graph, what you are looking for is the spikes to be centred about the central horizontal line, not drifting up or down.

Look at the 3rd section on your graph, can you see the genral drift upwards? thats what you are aiming to get rid off.

Link to comment
Share on other sites

So, it's OK up to that point? I thought that I was aiming to get the line as flat as possible. Perhaps all is not lost?

If I combat the drift up or down, will that mean I will get better guiding then?

Edited by swag72
Link to comment
Share on other sites

Did you turn off the tracking in DEC ? I'm thinking probably not, as you're showing wavy lines in both, which I think means PHD is correcting both axes... Having said that the OSC-index doesn't look too bad..

Thankfully it looks like PHD MAC (and the MAC is awesome for screengrabs :p) is the same ;).. and you know what they say :D

Click the Brain

Screenshot2011-01-29at2229191.png

You'll get

Screenshot2011-01-29at223013.png

Change the DEC guide mode to

Screenshot2011-01-29at223027.png

Don't forget when you enable guiding properly again, and for calibration (not sure on this, but it can't hurt... to set PHD back to

Screenshot2011-01-29at223013.png

Edited by jgs001
Link to comment
Share on other sites

I did have the DEC tracking turned off. I didn't have the 'force calibration' checked at the bottom. Not sure what that will affect.

When you say that it looks like it was coeecting both axis - Is that the blue line? I ask as that one was always pretty much mirroring the direction in which the red line was going.

Edited by swag72
Link to comment
Share on other sites

That forces PHD to redo the calibration... so if you calibrate in one part of the sky, PHD works out how to move the mount... but if you change and go to another part of the sky, it's worth forcing the calibration again so that PHD again knows how to correctly move the mount (the camera orientation inverts when the scopes change sides of the mount, so for PHD up is down etc...)

It sounds like you were doing everything right as I understand it... Sorry... I've still yet to try it myself, I'll have to let someone else answer the specifics on this stuff.

Link to comment
Share on other sites

I'd be fairly happy with that graph ;)

Each horizontal line represents 1 pixel...

Ant

Yep I'd go with that too.

And yes its best to re-calibrate when you move to a different part of the sky so that PHD can workout the star movement for that area.

Link to comment
Share on other sites

Sara, when you get the alignment to be where it should, you wont need to run the corrections, the star will stay centred. So if you just turn on CAPTURE and click a box round the star, or use the bullseye overlay, just let PHD run and loop, you'll soon get the hang of it.

Are you setting up fresh each night? If you use a tripod, try marking the point where the legs should stand on the floor, that way you can get close right away next time.

We all know what we mean, but its hard to explain ;)

I usually use this guide to remind me

Classic Astrophotography - Photographing the Cosmos with ordinary film

cheers

Tim

Link to comment
Share on other sites

One thing, from your graph, you could turn the aggression down a little bit. Take a look at the red lines for instance, when PHD brings the line back towards the centre, it is overshooting the mark a little. The buttons there at the bottom will help you.

Link to comment
Share on other sites

Hi Sara,

I don't know if you've seen this video before. It's the best description I've seen of doing PA. Even if you use another method it's good to get your head round what's going on.

http://www.andysshotglass.com/DriftAlignment.html

I've not used PHD for doing this but those who have say it's quicker than using an eyepiece.

Dave.

Edited by davew
Link to comment
Share on other sites

Thanks for all this folks - I may pluck up the courage to go out again some time. Just to confirm though, I need to recalibrate after each adjustment to the scope while I am using PHD, yes? So I find the star, get PHD guiding, then once I make my first adjustment of the screw to stop the graph from drifting, I have to recalibrate again, I can't just click on the star again and tell it to carry on tracking - Even if the move is minute?

Link to comment
Share on other sites

If you find yourself needing to perform polar drift alignment each night i.e. if normal polar alignment through the polar scope is not allowing you to get the length of subs you want without trailing.... I would invest in an application to assist you. I use WCS Polar Alignment - WCS - Fast and accurate polaralignment for astronomical mounts, using a CCD / webcam and drift alignment I dont think it supports the QHY5 though so thats a non starter, sorry.

I think you should work on your initial polar alignment and see if you can get that better, as you have found out, to do a full drift align each night is going to take ages.

So.... How are you doing your normal polar alignment?

Link to comment
Share on other sites

This question keeps coming up, I answer it, but no one comes back to say that what I am doing is right or wrong. The way I do my polar alignment is how I followed it via a site suggested here - Idiots guide to PA.

Here's what I do - If you spot a flaw, I'de be really grateful for you to point it out.

1) Set up the HEQ5, facing North. It's on a level surface.

2) Attach and balance the scope

3) Set the time and date using the RA axis on the polar scope.

4) Get Polaris in the middle of the small circle in the polar scope, using the Azimuth and altitude screw and bolts.

5) Just moving the DEC, get Polaris in the eyepiece of the scope.

6) Move the mount to the home position - weights down.

7) Star align.

I live in Spain, so am running on CET - I always use GMT for the time on the polar scope and handset. I live at 0.5 degrees latitude - Forum members suggested that there was no need to adjust the latitude scale on the polar scope for that.

I check against the Polar app that the circle where I am putting Polaris is in the same place on the PC as in the reticule. Again, using GMT for all of it.

So, if anyone reads this and sees that I am missing something, or that I am going something wrong - Please do tell me!

Thanks for all your help though - Invaluable as ever. Not sure I'd have made it this far (Albeit not very far!!) without your help.

Edited by swag72
Link to comment
Share on other sites

Here's what I do...

1. Set up, face North (use a compass that can do magnetic off set if you can)

2. Attach and balance

3. USE THIS PROGRAM Free Polar Alignment Software Download Polar FinderScope by Dr. Dale Jason Version 2.04 to show where Polaris should be

4. Move scope using bolts to put Polaris in the little circle

5. Unlock clutches and move scope to Home

6. Align

This should put you close enough to get the guding going.

I don't use PHD so can't offer any further advice, but unless you are swinging from one side of the meridian to the other, you shouldn't need to recalibrate I think..

Give the program a go and let us know how you go - and trust me - all of us imagers have been EXACTLY where you are now, don't feel you are alone!! ;)

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.