#1  
Old 07-11-2009, 10:00 AM
Allan_L's Avatar
Allan_L (Allan)
Member > 10year club

Allan_L is offline
 
Join Date: Mar 2008
Location: Central Coast NSW
Posts: 3,092
Imaging with Fork mount ???

I was looking at the DSI III for sale in the classifieds and wondered if it could be used on a fork mount (CPC1100).
I thought stacking multiple frames may overcome the obvious shortcoming of not having EQ Mount.

I am guessing no due probably to the length of exposure for Deep Sky Imaging and field rotation.

I have been advised the wedge for the CPC is, well, not well regarded.
(And Meade wedge is probably not compatible).

I have heard of Meade de-rotaters.
But not sure whether this would be practicle either.

The CPC has tracking, but it is not all that smooth.
And I dont have a guide scope.

Without being too ruthless, tell me if I am just dreaming at this stage.
Reply With Quote
  #2  
Old 07-11-2009, 10:16 AM
gbeal
Registered User

gbeal is offline
 
Join Date: Oct 2004
Location: New Zealand
Posts: 4,299
Allan,
dreaming? Get out of here. If there is a forum member who doesn't dream I'll eat my hat, and I have just had lunch too.
Go for it. Yep, it will be an uphill battle, but at least you know that before you start. Keeping the focal length as short as you can, so read "REDUCER" here, and the exposures short will mean you should get away with decent results.
I would try the wedge too, as having it polar aligned will make a world of difference to the alt/az method.
Plus, if and when you go from the fork to the GEM, the camera can stay and do further service with another scope/mount/whatever.
Gary
Reply With Quote
  #3  
Old 07-11-2009, 07:19 PM
mtodman's Avatar
mtodman (Matt)
Registered User

mtodman is offline
 
Join Date: Oct 2007
Location: Arcadia, NSW, Australia
Posts: 189
Hi Allan,
Imaging on a fork mounted SCT is indeed doable. Some people have managed some very fine results. Having said that, it's a lot of hard & frustrating work to get everything working well. I managed to get results with my 10" LX200GPS that I was reasonably happy with but there were many frustrating nights to get to that point. It the reason I have decided to change over to a GEM setup.
The list below is what steps I took to improve imaging (obvoiusly some of it doesn't apply to your C11).
  • Get a good polar wedge. I made my own which works very well. Needs to be very solid & have fine adjustments.
  • I replaced the standard plastic drive gears with stainless steel gears “Bucks Gears”.
  • Install a guide scope (ED80 with Meade LPI) piggybacked on main OTA using Orion tube rings.
  • Upgrade from Orion tube rings to home made piggyback system.
  • Train PEC using Andrew Johansen’s PEC utility.
  • Train PEC using Pempro.
  • Upgrade guide camera from Meade LPI to Meade DSI Pro II.
  • Balance setup with weight bias on the Eastern fork arm.
  • Use Bahtinov mask for focusing guidescope.
  • Achieve very precise polar alignment. This made a big difference as it meant that I could dissable DEC guiding and inly guide in RA.
As Gary said, I wouldn't bother with a field derotator. The main issue is that it relies on very accurate tracking in both Alt & Az so unless you have a very accurate mount with very little periodic error, you may be fighting a losing battle.
Definately get yourself a wedge. If you can't afford to get a solid one with fine adjustments, then at least try something that you can afford.
A DSI III should give you some pretty good results, especially is you use a Focal Reducer. I used a Meade F/6.3 reducer with my DSLR. You may even be able to go to a, F/3.3 with the small chip size of the DSI III. The short Focal Length would make tracking easier.

The main thing is to give it a go and see what you can achieve.

Cheers

Matt
Reply With Quote
  #4  
Old 07-11-2009, 09:52 PM
Merlin66's Avatar
Merlin66 (Ken)
Spectroscopy Wizard

Merlin66 is offline
 
Join Date: Oct 2005
Location: St Leonards, Vic
Posts: 6,967
The Meade de-rotator only works with the Lx series telescopes.
I'd start with short exposures in Alt-Az mode before working up to mounting it on a wedge.
I've used both set ups for spectroscope work. You can guide in Alt-Az but obviously the field rotation becomes an issue, also a reducer is almost mandatory; consider the x0.63 ( the x0.33 give a VERY small FOV!)
Reply With Quote
  #5  
Old 08-11-2009, 06:00 AM
mtodman's Avatar
mtodman (Matt)
Registered User

mtodman is offline
 
Join Date: Oct 2007
Location: Arcadia, NSW, Australia
Posts: 189
Quote:
Originally Posted by Merlin66 View Post
consider the x0.63 ( the x0.33 give a VERY small FOV!)
I would have thought that the F/3.3 gives a wider FOV?
Reply With Quote
  #6  
Old 08-11-2009, 07:35 AM
Merlin66's Avatar
Merlin66 (Ken)
Spectroscopy Wizard

Merlin66 is offline
 
Join Date: Oct 2005
Location: St Leonards, Vic
Posts: 6,967
You're correct!
What I was trying to say was the plate scale and un-vignetted field is very small. They were designed for first generatin CCD chips and are unsuitable for the larger chips available today.
Reply With Quote
  #7  
Old 08-11-2009, 08:13 AM
citivolus's Avatar
citivolus (Ric)
Refracted

citivolus is offline
 
Join Date: Sep 2007
Location: Carindale
Posts: 1,178
Another caution for imaging with fork mounts is that the length of your imaging train is limited. If you put it on a wedge, you may not be able to image at the pole as a result. A reducer + crayford focusser + DSLR will really be pushing it for space in some forks.
Reply With Quote
  #8  
Old 08-11-2009, 08:21 AM
jjjnettie's Avatar
jjjnettie (Jeanette)
Registered User

jjjnettie is offline
 
Join Date: Feb 2005
Location: Far Far Away
Posts: 16,726
Go for it!
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 02:19 AM.

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