#1  
Old 16-01-2009, 12:53 PM
prova's Avatar
prova
Registered User

prova is offline
 
Join Date: Aug 2007
Location: Canberra
Posts: 490
Do I need to guide to produce good images?

Wondering if the need for guiding is an absolute must for deep-space astrophotography? I want to start imaging galaxies but wondering if I get my polar alignment and drift "bang-on" upto around 4-5mins (unguided) will this exposure time suffice if there are 2+ hours of data?
Reply With Quote
  #2  
Old 16-01-2009, 02:02 PM
Octane's Avatar
Octane (Humayun)
IIS Member #671

Octane is offline
 
Join Date: Dec 2005
Location: Canberra
Posts: 11,158
prova,

Depends on what you define as "good". Have a look in the deep space forum, and the best images are the ones that have been guided. Even if you capture two hours (plus) of data, having guiding errors will introduce artifacts in your final image.

For open star clusters, you might be alright, but, for getting intricate details out of galaxies, I think guiding would be fundamental in producing a good image.

Regards,
Humayun
Reply With Quote
  #3  
Old 16-01-2009, 02:13 PM
Zuts
Registered User

Zuts is offline
 
Join Date: Mar 2007
Location: sydney
Posts: 1,431
Quote:
Originally Posted by prova View Post
Wondering if the need for guiding is an absolute must for deep-space astrophotography? I want to start imaging galaxies but wondering if I get my polar alignment and drift "bang-on" upto around 4-5mins (unguided) will this exposure time suffice if there are 2+ hours of data?
Hi,

Unfortunately I wouldnt think a HEQ5 pro could go for more than a minute unguided. The reason is PE. No matter how well polar aligned you are the machining errors in your gears will give you around 30 to 50 arcseconds error.

Try it and see, basically though you will get sick of egg shaped stars and eventually fork out for a guide scope and camera.

Cheers
Paul
Reply With Quote
  #4  
Old 16-01-2009, 03:21 PM
leon's Avatar
leon
Registered User

leon is offline
 
Join Date: Apr 2006
Location: ballarat
Posts: 10,825
No mate it is not an absolute must, if you are pretty well aligned, and you are going reasonably wide you will get away with fine images of up to 30-40 seconds, no problem.

Leon
Reply With Quote
  #5  
Old 16-01-2009, 03:57 PM
prova's Avatar
prova
Registered User

prova is offline
 
Join Date: Aug 2007
Location: Canberra
Posts: 490
I have another interesting question then as I am currently able to perform 60sec exposures with zero drift, if I take 3 hours or so of 60sec exposures for example, with this still render a nice image?

I know it depends on what I'm imaging but in general?

I'd be more than keen to stack 8 hours worth of 60sec exposures if the image came up!?
Reply With Quote
  #6  
Old 16-01-2009, 04:17 PM
montewilson's Avatar
montewilson (Monte)
Registered User

montewilson is offline
 
Join Date: Apr 2007
Location: Sydney
Posts: 374
What is the focal length? What you are talking about might be possible up to about 200 - 300mm but you can forget it for anything higher. Guiding is cheap these days and this is why so many guys with modest equipment produce results that rival observatory images from not so long ago.
Reply With Quote
  #7  
Old 16-01-2009, 04:27 PM
Zuts
Registered User

Zuts is offline
 
Join Date: Mar 2007
Location: sydney
Posts: 1,431
Quote:
Originally Posted by prova View Post
I have another interesting question then as I am currently able to perform 60sec exposures with zero drift, if I take 3 hours or so of 60sec exposures for example, with this still render a nice image?

I know it depends on what I'm imaging but in general?

I'd be more than keen to stack 8 hours worth of 60sec exposures if the image came up!?
In general, you image will be less noisy but no deeper than 60 seconds. When you say no drift you also mean no drift at your focal length.

In your original post you said you wished to image galaxies. Except for a few examples most galaxies are better at longer focal lengths.

Basically if you wish to go deep, you must guide. As Monte says, guiding is cheap and easy these days.

Cheers
Paul
Reply With Quote
  #8  
Old 16-01-2009, 05:12 PM
AlexN's Avatar
AlexN
Tunnel Vision

AlexN is offline
 
Join Date: Mar 2008
Location: Brisbane, Australia
Posts: 6,708
Yes indeedie... Guiding is really a requirement of great images... You can polar align your mount within arc sec of the pole, and still not obtain 5~10 minute exposures without tracking errors.. Why? Because there is more at play than just the earths rotation and your RA drive. the atmosphere is unpredictable, and refractive. meaning that it can bend and shift light around, potentially ruining images.. Guiding can definitely help here... Also, depending on your mount, you RA drive is not going to be perfect. PE is a problem also...

With nearly 4 hours of time spent drift aligning one night I was able to capture 4 minute unguided images at a focal length of 714mm, and the result wasnt BAD, but it could have been better... With the same mount, and guiding, I have managed 10 minute exposures at 1764mm focal length... and up to 30 minutes at the 714mm that I could only get 4 minutes with unguided.

Guiding is good, cheap and easy... Theres really no need to avoid it... Lets face it, after you've spent all that money on a mount, camera and imaging scope, whats another $400? (can be done cheaper, and more expensive depending on the components you choose to use.)

No, its not needed to image, but to image well... It is very much preferred..
Reply With Quote
Reply

Bookmarks

Thread Tools
Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +10. The time is now 07:40 PM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
Advertisement
SkyWatcher Australia
Advertisement
Lunatico Astronomical
Advertisement
Meade Australia
Advertisement
NexDome Observatories
Advertisement
OzScopes Authorised Dealer
Advertisement
Bintel
Advertisement
Celestron Australia
Advertisement
Astronomy and Electronics Centre
Advertisement