Polar alignment through finder with QHY5v

[badgerchap]

Does anyone know any reason this wouldn't work? I propose using the QHY through the finder with a crosshair on the screen.

[russellhq]

Are you suggesting drift aligning through the finder scope? Otherwise, just centring polaris on the finder scope isn't going to work.

[kirkster501]

PA is about aligning the mount so it tracks around the NCP precisely. The scope you decide to put onto the mount has nothing to do with it. Or do I not understand your question?

[badgerchap]

Are you suggesting drift aligning through the finder scope? Otherwise, just centring polaris on the finder scope isn't going to work.

Yes, I mean aligning! Centrong polaris would be faitly pointless!

Yes I just thought it would be easier than using my rubbish illuminated reticle but thought also I should check to make sure I wasn't missing anything. But as far as I can tell it's not too bad an idea. The only thing I can think of that using drift alignment is best with high mag, and I may not get that through the finder.

But yes, I should have specified that I mean drift-alignment.

[chrisshillito]

If you're planning on imaging through the main scope then that is what you should drift align with. Drift aligning the finder will not guarentee sufficiently accurate alignment to remove drift from images taken through the main scope.

Chris

[badgerchap]

Thanks Chris! Why is this?

[Freddie]

No reason why you can't use the finder as it is the mount you are aligning not any of the scopes you have on it.

May be easier to use your imaging cam and give this a go though.

CCD to Align Your Scope.pdf

[badgerchap]

Excellent PDF there Freddie, cheers for that, I will give that a pop next time I'm out. I suppose, thinking out loud, that if you were to measure the angle, and if you knew how many turns per cm your azimuth and altidude screws had, you could work out an almost exact number of turns needed to correct the deviation. If one were to make a table of degrees against turns needed, one could reduce PA time even further. I now have a job to do tomorrow!

[badgerchap]

Right so the calculation would be (360*t)/pi*d where t is the distance between 2 teeth of the alt or az screw and d is the diameter of the appropriate axis at the point at which the screw operates. This will give the number of degrees per turn. So then divide the angle of error over this number and you'll get the number of turns needed to correct the error.

I guess to get the angle you could a)put a protractor on the dslr screen or trace the lines in PS and get a precise ish measurement. So past an initial bit of fiddling around, I reckon one could get accurate PA within a couple of minutes?

[badgerchap]

Haha that smiley was meant to be a 'b' and an ')'

[astrosathya]

Someone here good with programming can perhaps write a code to display a protractor on screen with opaqueness control. This way we can then use the image from the dslr without a physical hand held protractor and things may be a little bit easier.

Regards,

Sathya

[Freddie]

Unless your PA is initially MILES out, you will find the adjustments are a tiny tiny fraction of a turn so what you suggest may be a bit overly complex.

[badgerchap]

Good point. May well be a case of overthinking a simple problem!

[RikM]

I use PHD on the finderguider to refine my polar alignment. I have the finder and main scopes very well aligned using cross hairs on the display.

Select a bright star close to 0° Dec in the South.

Calibrate PHD and start guiding.

Open the graph tool and set it to display dx/dy.

Turn off guiding in DEC and watch the drift on the graph. (Unless you are very lucky, the line will start to drift off either up or down.)

Adjust the azimuth until the graph is flat all the way across. (you may need to stop guiding, recenter the star and start guiding again)

Slew to a star near the east or west horizon and recalibrate. (Click on 'force calibrate' under the brain icon)

Turn off guiding in DEC again and watch the drift on the graph.

This time, adjust the altitude until the graph is flat all the way across.

If your tripod is not completely level you may have to go back and do them both a second time to get it spot on.

[chrisshillito]

Thanks Chris! Why is this?

Your finder scope has, I presume, less resolution than your main imaging scope and so will be much less sensitive to drift effects. Yes, you can use your finder scope but to get the same precision of alignment you're going to have to wait much much longer to detect and therefore correct the alignment error. Also whilst perfect alignment isn't essential you do need a level of alignment that prevents compromise of your image subs. Using your imaging train to measure/correct drift will give you some confidence that you have achieved this - using your finder scope won't.

Chris.

[badgerchap]

Thanks Chris. Think I will try Freddie's method above - looks fairly easy to do with my current setup!

[RikM]

Yes, you can use your finder scope but to get the same precision of alignment you're going to have to wait much much longer to detect and therefore correct the alignment error.

Chris.

The beauty of using PHD or using the DARV method is there is no lengthy wait. Using the camera you can see and correct for drift much more rapidly.

[Sunset Observatory]

Polar alignment can be tricky at best. There are several software programs that will aid in this set up. PHD is a decent program, however there is one out there that beats them all. It is a short download, and works extremely well. It will even give you the option of your present longitude and latitude and works off your computers internal clock. By default it will show you 4 windows, however you can set it up to show 6. Each window can be set to whatever time frame separation you want, I find a difference of 10 minutes per winder works well. The name of this program is Polar finder. Bring it up in your browser and click the download according to your operating system. Best of luck. Clear skies brother