Astroimage processing

Re: Explanation needed!

TeleTaurus7 — Fri, 27 Feb 2009 03:30:15 GMT

chipdatajeffB:

TeleTaurus7:

Who said you could take Afocal with a DOB?

Lots of us do that. The trick is you are limited to brighter targets, like the Moon and Venus, Mars (at or near opposition), Jupiter, and Saturn ... and once in a great while a very bright comet (Holmes was brigfht enough).

What I thought. Thanks

Re: Explanation needed!

chipdatajeffB — Fri, 27 Feb 2009 03:17:02 GMT

TeleTaurus7:

Who said you could take Afocal with a DOB?

Lots of us do that. The trick is you are limited to brighter targets, like the Moon and Venus, Mars (at or near opposition), Jupiter, and Saturn ... and once in a great while a very bright comet (Holmes was brigfht enough).

Re: Explanation needed!

chipdatajeffB — Fri, 27 Feb 2009 03:15:37 GMT

Most DSOs are too faint to record in exposures of a fraction of a second, the telescope must track them and the camera must make a lnog exposure (minutes to hours).

With the Moon and the brighter planets, you have enough light that even a simple digital snapshot camera or webcam can make an adequate exposure in a fraction of a second. Hence, since they don't move faster than about 1/4 of a degree per minute, they don't blur.

You can remount a dobsonian (it's a newtonian telescope on a dobsonian mount) on an EQ and track with it. You can also track with what's called an EQ platform or Poncet platform, but with exposures longer than about 1 minute you will get star trails in the image due to what's called field rotation.

In summary, for bright objects like the Moon and some planets, you can do short-exposure astrophotography with a typical dob. But for DSOs you need longer exposures than the mount can accommodate with blurring or trailing.

Re: Explanation needed!

TeleTaurus7 — Fri, 27 Feb 2009 03:13:19 GMT

Who said you could take Afocal with a DOB?

Explanation needed!

Alfred Sagan — Fri, 27 Feb 2009 02:50:30 GMT

Hi, there's one thing I don't understand when it comes to astrophotography... You can't do AP with a dobsonian mount because of lack of tracking...but still pictures of the moon and planets are possible...however these drift out of the FOV quickly, dont they?(rhetorical) Deep sky objects don't drift as fast though cuz of low power mag, or do they? I'll just assume they don't so that I can ask my question...Why can't a dobson take pics of deep sky objects if they stay in the field of view for a long time? I mean if you just move it a bit every 5 minutes and start taking pictures again you can allign them when you stack them can't you?

Sorry I'm a complete rookie, pardon my ignorance...

cheers