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Old 26-09-2014, 03:05 PM
glend (Glen)
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Imaging a DSO you can't see?

I am sure there is a simple answer to this question but I can't find it:

When setup to image a fairly faint DSO that I can't actually see through my Canon 450D Liveview screen, how do you tell if your actually on target?

I use a ASI130MM guide camera on a 60mm ZWO guidescope mounted on the top rail of my 8" imaging newt (with Baader Coma Corrector attached to the Canon).

Guiding works fine - using Metaguide with this guide camera.

My approach has been to go to my target object with the scope setup for visual and check the seeing and that it is visable in the scope and centre it. (Obviously the scope has been carefully polar aligned in advance and in some cases is 0 0 on the SCP - using the Syncscan polar alignment routine).

Then I go to a nearby star and setup the camera and use the mask to focus it. Punch in my target and slew back to its location - but of course I can't actually see it. So I take a few test subs and sometimes it's there but sometimes its not and I can't really tell how far out of field of view it actually is. My finder scope can't see it as it's too faint, nor will it appear in my guide camera field.

So what's the practice for centering a DSO in the DSLR field of view?
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Old 26-09-2014, 03:22 PM
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killswitch (Edison)
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Quote:
Originally Posted by glend View Post
So I take a few test subs and sometimes it's there but sometimes its not and I can't really tell how far out of field of view it actually is. My finder scope can't see it as it's too faint, nor will it appear in my guide camera field.

So what's the practice for centering a DSO in the DSLR field of view?
Hey Glen

I do this as well. I take a test subs at ISO 6400 and/or longer exposure time then bring it back down to something more decent once its in the FOV.
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Old 26-09-2014, 03:40 PM
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pluto (Hugh)
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I don't know about Metaguide but I used to find it useful to take 5 or 10 second exposures in PHD with my guide camera and its wider FOV.

Now I use AstroTortilla to plate solve and I've never looked back.
Even if you're not controlling your mount through your computer I would recommend getting AstroTortilla set up and then take a quick highish ISO image and solve it. Then find that location in Stellarium, or whatever planetarium you use, and you should be able to see how far off you are.
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Old 26-09-2014, 06:25 PM
PeterEde (Peter)
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Test shot at high ISO is the way to go.
But focus on a bright star first up
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Old 26-09-2014, 07:15 PM
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White Rabbit
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Plate solving, one you've tried it you will never go back. What software are you using?
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Old 26-09-2014, 07:21 PM
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Yep, plate solving is insanely useful and worth the grey hair to get it going well. You'll probably still need to adjust your FOV for some objects however unless your mount is high end. So once you use plate solving to get in the ball-park, then you can worry about a few high iso 30sec to 1min shots to get the field composed the way you want it.

Plate solving is SO useful for multiple night runs too. Once you do get centred, record your co-ordinates and subsequent imaging runs or pier-flips so much less time consuming.
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Old 27-09-2014, 05:50 AM
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lazjen (Chris)
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Further on Rob's details, with plate solving, you can re-use an existing image from a previous night to plate solve and slew to that location.

Plate solving plus something like Stellarium seems the most sane way to go for me!
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Old 27-09-2014, 08:33 AM
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codemonkey (Lee)
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Parroting the rest here, but plate-solving is the way to go. I've just discovered it and haven't fully utilise it but it's pretty awesome.

The other thing I used to do was set binning to 8x and push the display white point right down to about 2-4k... I've always been able to see the thing I'm looking for with <= 5 sec subs that way. Having said that, probably the dimmest thing I've looked for is NGC 55.
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