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Old 15-07-2010, 12:54 PM
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Variable Star Image Capture Questions

Newbie questions here in regards to astrophotography. I'm posting these questions here as it is primarily based with the capture of images, but I only require a certain type of image. This is also expanding upon the "Astrophotography with a Dob" article here on IIS. There are a few questions so here goes.

Firstly the thinking behind the madness: I currently own a 10 inch dob and am interested in variable star work. This has been taken up previously by members of my society using the visual observation technique, with similar equipment (dobs and Eq. mounted Newtonians). None of their equipment was automated / motorised. I was hoping to continue some of their work.

With the advances in video capture technology and computer post processing, I was wondering if cameras could be used to capture star size on non motor driven scopes? I appreciate the benefit of motor drive scopes, but can't help but think there are people in the field doing this manually for near on 50 years now with non motorised equipment, and getting results through an eyepiece (and the variables (pardon the pun) that come with this opinion based assessment). That's question one.

Expanding on this to question two: The idea I'm toying with is to us a dob, but in place of the eyepiece, place a flip mirror box to enable myself to locate the object, then get several second of video footage to post computer process into a reference image. Does this sound reasonable?

This leads into the last question of flip mirror boxes. The only images I can seem to find are the ones where the eyepiece goes on top (at 90º to the path of the light entering the flip mirror box) and the camera is placed parallel, to enable light from the secondary mirror to go straight through to the image sensor. These don't seem to show the camera being mounted in the 90º position (I can understand why for long exposures, but for shorter exposures?). Are these flip mirrors flexible to allow the latter configuration?

The alternative to the flip mirror idea, is to utilise the newer features of 'Live View' that is appearing on more cameras; and mount a better finder scope for positional reference, and confirm the target star through the Live View feature.

So there are the ideas.

But before everyone answers with the obvious 'Why not go automated?' here is why I'm thinking along this path. Most obviously, automated scopes cost 3 times as much as a manual scope. I'm enjoying hunting around for items at the moment (learning the sky), so automatic searching while beneficial, is not a major hindrance to my enjoyment of this hobby. Secondly (and what I'm wondering), software development to compensate for distorted stars in captured images appears to have been getting better these past few years alone - combining this with higher video frame rates and higher quality video resolutions, is this enough of an advancement compensate for the Earths rotation in this short time of exposure / video capture?

Most importantly, (as strange as this sounds) I'm not wanting to use this set up for pictures of the sky. I want to collect the photons of light from a star to assess their size - not capture gases, or faint distance comets or other objects. it is purely for variable star capture and that is all. The enjoyment of this comes in the post processing and assessment of images, and the eventual graphing of possible variations - not the actual image itself.

So thanks for your patience reading this, and I look forward to hearing peoples responses. I can not find anyone, anywhere doing variable star work with a set up like this, making me wonder if the above thoughts are viable or not. Still, won't know until I ask.

Cheers.

NB. With reference to Live View mentioned above, I'm meaning more an image that is live on a screen of any sort (either camera back or camera tethered to a computer and screen)
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Old 18-07-2010, 08:05 AM
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bojan
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Hi Brett,
I was doing some novae, using lenses from 50mm to 1000mm mounted on my Canon 400D and IRIS (software, http://www.astrosurf.com/buil/us/iris/iris.htm).

The magnitude 12 was not a problem at all (with 1000mm MTO), even from Melbourne's light polluted skies.
However, equatorial mount and reasonable tracking (up to 30 sec) is essential here.
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