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Miketmbt
2006-Nov-27, 08:56 PM
Astrophoto question for you all.

I have an EQ mount and I have been carefully working on getting god polar alignment w an illuminated eyepiece for some time now. I have been using a webcam to shoot Saturn and the moon. I notice in the video making process my subject moving back and forth across the screen. It never leaves my view it just moves back and forth. I imagine that when I finally have a long exposure camera this will be a problem. Is my polar alignment off or is there something else I am doing wrong. Thanks for your help

Here is my first Saturn. I cant wait to try a barlow lense on it next.

Melusine
2006-Nov-27, 09:28 PM
It's so cute! :razz:

Nice going there.

AutoClub
2006-Nov-27, 10:51 PM
Hi Miketmbt - I don't think you are doing anything wrong. If your mount is a tracking mount, with a motor drive, I suspect what you are seeing is something called Periodic Error, which is basically the small amount of error induced into the mount by small imperfections in the drive gears. I've heard or read that all mounts have some of this. On some mounts, there is a way to at least partially correct this, with a feature called periodic error correction; this feature lets you compensate for the play or wear in the gears. Some mounts have more periodic error than others. I believe, if you have very accurate polar alignment to minimize field rotation, that either using an autoguider or manually guiding your scope (very tedious) will allow you to correct for this. Programs like RegiStax or others will help in aligning your individual single images, but I'm not sure if RegiStax will work with video images. Since I don't have a video camera that would work well for astrophotography, I'm not sure. Periodic Error Correction is much more critical for longer exposures.

Hope this helps :)

Miketmbt
2006-Nov-27, 11:00 PM
Yeah, Registax works great with AVI's im just concerned that when I get a digital camera and try to take a 5-10min exposure that my stars will be little lines. Ill researsh Periodic Error. Thank you

Bokmakierie
2006-Nov-28, 04:53 AM
Quite a nice image of Saturn!! Thanks.
Could this have been a seeing problem? I have noticed this on my AVI's taken of the moon. Looked as if the craters are wiggling around like belly dancers!

Phil

tegwilym
2006-Nov-30, 05:47 PM
Few questions:
What kind of scope did you use for that Saturn image?
If the back and forth thing is over a period of about ~8 minutes, that is probably periodic error. I think 8 minutes is pretty common for most scopes.

Could also be the atmosphere. Not sure what time that saturn shot was taken, but I'm guessing it was possibly still pretty low in the sky - therefore, going through a lot of thick atmosphere.

Yeah, try a barlow on that next. Have you tried image stacking? Take maybe a minute .avi video and record it on the computer, then try a nifty little program called Regsitax to stack the frames. You'll be amazed at the detail you can pull out after doing that! Good fun, frustrating, difficult, but rewarding once you get the hang of it. :surprised

Tom
Highlands Astro-shack observatory (http://www.eastsideastro.org/observatory)


Astrophoto question for you all.

It never leaves my view it just moves back and forth. I imagine that when I finally have a long exposure camera this will be a problem. Is my polar alignment off or is there something else I am doing wrong. Thanks for your help

Here is my first Saturn. I cant wait to try a barlow lense on it next.

Miketmbt
2006-Nov-30, 05:52 PM
I am using an Orion 130mm refector. I used a webcam to make an avi and registax to align. I wish I could upload the avi so you could see what im talking about. Im pretty sure its periodic error. My whole setup only cost me $240 new.

Bokmakierie
2006-Nov-30, 07:23 PM
I am using an Orion 130mm refector. I used a webcam to make an avi and registax to align. I wish I could upload the avi so you could see what im talking about. Im pretty sure its periodic error. My whole setup only cost me $240 new.

Hi Mike,
What is the size of the AVI file? If it is not too big, say less than 20Mb, you can send it to my e-mail addy to have a look at it. Better yet, if you have Skype, I can give you my Skype handle and you can then send it by that route.
Would love to see it.

Clear skies

Phil

Miketmbt
2006-Nov-30, 07:31 PM
I dont have skype. Ill have to waint untill I get home to see the size. I dont think its over 20mb

Miketmbt
2006-Dec-01, 05:12 PM
I was wrong. The file is like 600mb. Ill just keep practicing. Thanks for your input

tegwilym
2006-Dec-01, 05:28 PM
I was wrong. The file is like 600mb. Ill just keep practicing. Thanks for your input

Keep posting your stuff here. We can lead you through a lot of mistakes that we have done and probably flatten out your learning curve! This stuff isn't easy as you have probably figured out already. Hehe! :)

What kind of webcam are you using? My favorite webcam for this stuff is the Philips Vesta Pro. The ToUCam Pro is also great also, but I don't have one of those.

Tom
Highlands Astro-Shack (http://www.eastsideastro.org/observatory)

andyschlei
2006-Dec-01, 09:47 PM
I was wrong. The file is like 600mb. Ill just keep practicing. Thanks for your input

FWIW, AVIs compress quite well with Zip...

And I have noticable periodic error on my CGE mount (much improved by PE correction) - Even the Paramount ME ($13k) has software to reduce periodic error. It needs to be corrected and / or guided around.