SingAstro

kimo · Post by **kimo** » Fri May 27, 2011 11:24 am

New try on M13. I am trying to learn proper polar alignment.

18X20sec, stacked and processed.
Telescope 102mm F5 Refractor, Canon 300D non Mod.

timatworksg · Post by **timatworksg** » Fri May 27, 2011 4:15 pm

Good attempt Kimo! Though there is the apparent drift....the Globular is still well captured. Well done.

You could try CCD Drift alignment with the DSLR.
Here's a nice description on the subject FYI.
http://www.astrophotoinsight.com/node/568

The longer you can do the drift check (getting the 'V') the better the alignment would be for exposure in relation to the drift length used. I used to do anything from 30s to 2mins CCD drift alignment (depending on time I had..lol) and expose accordingly. Give it a shot and have fun!!

wucheeyiun · Post by **wucheeyiun** » Fri May 27, 2011 4:57 pm

It is very good effort... once you are able to do good drift alignment ... you will be very satisfied with the imaged captured.

cloud_cover · Post by **cloud_cover** » Fri May 27, 2011 5:06 pm

Erm, is that REALLY drift? After all, its a 500mm lens with 20sec exposures only. I remeber when I was doing M31 on Orly's GP which was about 10deg off axis, at 20secs, there was barely any trailing.
I'm wondering if that's uneven drive motors or maybe even wind/vibration

timatworksg · Post by **timatworksg** » Fri May 27, 2011 6:54 pm

Good observation cloud cover. Could be any or all...lol!
Improper alignment, payload balance (critical with AP...especially with a DSLR at the end of the scope. Make sure balance is obtained with DSLR coupled to scope and anything else needed for the session, and not without), motor errors, wind, etc etc.

@Kimo, take note of all that is mentioned here and prep for the next session. Make sure your AP set up is balanced all the way on the RA axis of the mount. Take note of any wind while shooting....(any of the subs streaked?). Keep at it and take notes....plan and try again. Takes awhile but such is AP....hence it takes so much effort to set up right, but once done, you sit back and let the equipment take over!

Post by **weixing** » Fri May 27, 2011 7:31 pm

Hi,

cloud_cover wrote:Erm, is that REALLY drift? After all, its a 500mm lens with 20sec exposures only. I remeber when I was doing M31 on Orly's GP which was about 10deg off axis, at 20secs, there was barely any trailing.
I'm wondering if that's uneven drive motors or maybe even wind/vibration

Did Orly's GP on GOTO or RA motors only?? If on GOTO, the drift usually don't look so bad.

Anyway, IMHO, I think it's mainly cause by not accurate polar alignment... also, I think he crop the image by a lot... that's why the drift look so bad or the polar alignment is really way off.

Just take your time to do a proper drift alignment and you are good to go.

Happy imaging and have a nice day.

kimo · Post by **kimo** » Sat May 28, 2011 8:37 am

Thanks for advice. Mount balancing with Telescope and DSLR is very hard. Here is the raw pic of AP. You can see the street light on top of the image. all are JPEG mode to learn how to do proper alignment and some techniques. Need lots of practice to get a nice pic, this is my first pic of M13.

RAW jpeg single 20sec PIC, only resize was done.

[left]http://i1181.photobucket.com/albums/x42 ... 93-new.jpg[/left]

timatworksg · Post by **timatworksg** » Sat May 28, 2011 9:55 am

Yeah balancing is tricky but not impossible..lol! Using a longer dovetail so the scope can move forward more, adding weight to the front of scope, are some things I have tried...till now I just use a longer dovetail.

Looking at your image again and if your orientation is as shown (East/West) the drift is up/down or North South drift. This would be due to polar alignment as any drift noticed on the East West axis is more to Error from motors/gears. Eliminate the North/South drift and you should have pretty good polar alignment. You have a fast scope so grabbing the brighter targets are easier with shorter exposures. Longer exposures will benefit from Autoguiding, which adds on weight and equipment.

Either use a reticle EP or CCD Drift alignment when aligning and spend some time setting this up before a session. Try not to use the bright stars like Canopus, Sirius instead use slightly lesser bright stars for drift alignment. To bright and you may notice hardly any movement and the 'V' will be hard to determine. I used to set up early and get the drift alignment sorted out for at least 3-4mins of no N/S drift. By then my target should be 30degrees or more above horizon and in a better part of the sky to image. I then keep exposures within what I drift aligned (1-2min subs) and fire away lots and lots...lol!

Shoot RAW and adjust all the RAW subs to taste,..then convert to TIFF and stack/register in DSS or whatever you use. Post in image programs like PS or Paint Shop, etc. Try not to work on JPEGS as they have a compressed pixel count and start to degrade (noise/pixelate) when adjustments are done. TIFF's can be huge...but the benefits are better.

My 2c....anyone can add/advise/correct where needed.

Post by **Airconvent** » Sun May 29, 2011 3:43 pm

I'm not into astrohphography so can't give advice but its amazing on the difference between the raw and stacked image. Just keep doing it and you can take on even more challenging objects! [smilie=crying2.gif]