|
|
Thread Tools | Display Modes |
#1
|
|||
|
|||
Alt-Az vs Equatorial mount
I will soon be taking delivery of a new Meade 16" LX200 GPS model and have
some fundamental decisions to make about its set-up. I want to get more involved in imaging and plan to buy a CCD imager after I have familiarised myself with the 16". I have one basic question: Alt-Az or equatorial mount? My understanding of the need for an equatorial mount is to assist with tracking accuracy and avoid the field rotation inherent in anything but short exposure imaging. But, these days, with stacked multiple-short-exposure CCD images, can the alt-az mount achieve the same results as an equatorial, especially if the telescope is fitted with a field de-rotator? This would also avoid the difficulties of equipment clearance/eyepiece position associated with aiming the scope towards the SCP which is the region of some of our richest sky objects. I am going to build the pier myself, so it makes no difference to me which one I build, but I would like to get the choice right before I starting cutting and welding. regards Colin James |
#2
|
|||
|
|||
"Anon" wrote in message ... I will soon be taking delivery of a new Meade 16" LX200 GPS model and have some fundamental decisions to make about its set-up. I want to get more involved in imaging and plan to buy a CCD imager after I have familiarised myself with the 16". I have one basic question: Alt-Az or equatorial mount? My understanding of the need for an equatorial mount is to assist with tracking accuracy and avoid the field rotation inherent in anything but short exposure imaging. But, these days, with stacked multiple-short-exposure CCD images, can the alt-az mount achieve the same results as an equatorial, especially if the telescope is fitted with a field de-rotator? Not really. To actually 'record' an image, exposures must be long enough, for some signal to be detected above the noise level. You can do amazing things with a sequence of relatively short exposures, possibly getting one or two magnitudes 'deeper' than would be achieved in single short exposures, but the longer the baseline exposures (within the limits imposed by the skyglow etc.), the deeper the 'set' will go. The problem with using a field derotator, is that the tracking accuracy of the final result, is dependant on three motors, all tracking together, and tripling the error sources. It is also nearly impossible to use with a guider, since the corrections that need to be applied are also rotating. It's advantage is that it is quicker to setup. To get good results, there is no substitute for multiple long exposures. This would also avoid the difficulties of equipment clearance/eyepiece position associated with aiming the scope towards the SCP which is the region of some of our richest sky objects. However the length of the derotator itself, adds other problems, and decreases the rigidity of the whole setup. It is perfectly possible to make a great setup using a derotator, but you need to be looking at seriously more solid units than the ones commonly sold, especially when using a reasonably large camera, and combining it with custom software, or a seperate guide scope, to handle tracking. Generally, the accuracy of the mounts sold on most scopes, are poor enough, that adding two more movement errors is not the way to go. I am going to build the pier myself, so it makes no difference to me which one I build, but I would like to get the choice right before I starting cutting and welding. regards Colin James You will get better results with the scope polar aligned. I'd have really asked this question beore buying the LX200!. You'd have none of the camera clearance problems, using a GEM, and something like an AP1200, with a C14, might well have been an easier permanent setup, than trying to mount the 16" Meade on a wedge. You should be talking quite heavy engineering for the wedge (1" plate), and remember that no matter how accurate you think the work will be, you will need adjustment, so welding all the joints is not an option. Best Wishes |
#3
|
|||
|
|||
"Anon" wrote in
: I will soon be taking delivery of a new Meade 16" LX200 GPS model and have some fundamental decisions to make about its set-up. I want to get more involved in imaging and plan to buy a CCD imager after I have familiarised myself with the 16". I have one basic question: Alt-Az or equatorial mount? That is one big and heavy scope. It really needs a permanent setup. Probably on a pier in an observatory. Putting a wedge on the pier to mount the scope in equatorial mode would be a good option. That way you don't need to worry about field rotation messing up your photography. My understanding of the need for an equatorial mount is to assist with tracking accuracy and avoid the field rotation inherent in anything but short exposure imaging. But, these days, with stacked multiple-short-exposure CCD images, can the alt-az mount achieve the same results as an equatorial, especially if the telescope is fitted with a field de-rotator? Large professional observatories successfully use field derotators but I haven't heard a lot of good words said about the Meade derotator. This would also avoid the difficulties of equipment clearance/eyepiece position associated with aiming the scope towards the SCP which is the region of some of our richest sky objects. I am going to build the pier myself, so it makes no difference to me which one I build, but I would like to get the choice right before I starting cutting and welding. Post your question again on sci.astro.amateur. You will probably get more feedback - there may even be some folks who own this particular scope who read that group. Klazmon. regards Colin James |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Equatorial Mount | Eric Johnson | Amateur Astronomy | 9 | November 23rd 04 09:01 AM |
replacing an equatorial mount | Andy Moore | UK Astronomy | 2 | October 3rd 04 06:38 AM |
Any suitable material to protect my equatorial mount? | Chotechai | Amateur Astronomy | 0 | December 30th 03 12:01 PM |
Can someone explain how an equatorial mount works please? | Malcolm Hewitt | UK Astronomy | 3 | November 11th 03 08:59 PM |
Making or Buying a Equatorial Mount | Ricardo | UK Astronomy | 11 | September 7th 03 10:55 AM |