View Full Version here: : 8" GoTo Dob on a Wedge to stop Field rotation Can it be done?
15-06-2012, 06:52 PM
Hi Guys, I'm new to Iceinspace. I have a DIY question for any one that can help me. I have a 8" GoTo Skywatcher Dob, And I have just got into Astrophotography which I am enjoying greatly. I am building a home observatory with a roll off roof so I can do some imaging at home as I have limited time and I would like to permanently mount my Dob to a pier I have made inside my Observatory so I can leave it set up. And I don't particularly want to spend a $1000+ on a EQ mount so I can stop field rotation. (call me frugal but my funds are limited) .
My scope as you know already has GoTo drive so I was wondering if there is any way I can change the set-up to think it is an EQ drive instead of an AZ? I think that's right
I can easily make a wedge to mount the Dob this in no problem at all The thing that is puzzling me is, My friend has a LX200 on a fork mount and when he puts it on a wedge he just changes the setting in the hand controller to the other mode( as far as i'm aware) But mine doesn't have this function.
I hope this all makes sense
Any ideas would be great thanks. Ps I have also posted this in the Diy forum please forgive me if I am not supposed to.
16-06-2012, 08:13 AM
I was at a Kilcoy dark sky weekend and saw an Aqua-torial setup that used controlled water release from a bladder to allow for longer exposure photos. It was constructed for a very small amount of money. The owner of this rig is a member on IIS but is more of a reader than a poster.
Any chance of some photos and information H?
16-06-2012, 08:38 AM
You would need to build an equatorial tracking platform. Needs to be fairly precision build - for an 8 inch you would be better off buying an Heq5 and have all the computer control features. Astronomy is not the best hobby to be in if you do not want to spend money :)
Theer is plenty of information on the wenb onb how to build them but they are best just for visual observing . It would be cheaper and easier to experiment with some kind of field derotation device to rotate your camera.
16-06-2012, 08:57 AM
The goto dobs are designed for alt azimuth and unless incorporated in the firmware, can't work in equatorial
But try a google search I see if anyone has reverse engineered them
Both are very different
Some make dual mounts like Ioptron and Meade
By lot easier would be to get yourself a field de-rotator
I'm not sure how much they cost but are a lot simpler than mounting a dob on a wedge as the azimuth is not designed for radial loading unless you can reinforce it
You could end up reducing the life of the motor drive depending on how it's designed
There's also balance issues to consider
But that's if your controller supported eq mode
16-06-2012, 09:01 AM
As mark mentioned, an eq tracking platform is another option but needs to be quite precisely built
You would turn your dobs tracking off and just let the platform track
16-06-2012, 10:07 AM
Try the Yahoo Group eqplatforms (http://groups.yahoo.com/group/eqplatforms)
16-06-2012, 10:44 AM
Thanks very much for your comments guys, I might look into a field de-rotator, It sounds like a good option.
16-06-2012, 10:59 AM
I tried a wedge about 3 months ago, in most it worked but with one major flaw. The strain was too high for the motor when trying to use the standard DOB base.
I will eventually when I get time try to complete the wedge project using a modified drive mechanism that will hold more load. My only concern is the proportionally the load is a bit excessive and may just end up building an EQ mount instead.
16-06-2012, 06:06 PM
Clive, I thought I'd replied earlier so if similar comments show up from me sorry. I've got a 10" Skywatcher Dob and my experience so far does not leave me thinking that the tracking is clean enough to do long exposure regardless of field rotation.
Others might have different experience but my impression is that even with good alignment the object wavers in the field of view. I've not done much testing yet to see if I can improve that behaviour.
Id suggest some thorough testing of how well the mount keeps an object centered over time before chasing field rotation if thats not already done.
Others might be able to suggest how long an exposure is required before field rotation is an issue but you should be able to get a feel for the stability of the tracking with a long exposure as is.
16-06-2012, 06:39 PM
I have had the same expierence as Bob. When an object is under high magnification the tracking is fine for visual but it does waver as the the goto system keeps the target in the field of view.
I have just rigged up a webcam so I will be able to test how much of an impact this makes on the stacked images. I am taking my first steps away from a-focal photography, so it will be interesting.
17-06-2012, 01:23 AM
Thanks for your input guys I really appreciate it. Its good to see that other people have considered doing this to, I thought you might think What is this crazy guy doing.
So far I have been able to get very good images up to 30 sec with the standard base on the ground, but after that field rotation starts to come in. So for now I'll just have to stack lots of short exposures.
I'm using a Canon 350d EOS prime focus and I'm very happy with the results I'm getting but I would like to try A Cmos Or ccd imager in the future.
So for now I might just mount it flat on the pier as I can always change it later.
mswhin63 I would be very interested to see your set up with the modified drive when you get it going. Good on you for giving it a go. also how did you go with the alt-as operating as EQ as far as the controller goes? Clive:)
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