I've been doing some experimenting with interesting results.
A couple of nights ago I noticed I could see Sigma Octantis with live view and the 90mm refractor. Being that I'm not that good with the faint stars in that area visually, it got me thinking...
I've now got a *free* digital polar scope/reticle courtesy of the 40D, Eos Utility, Cartes du ciel, and a freeware app called "transparent window". How?
-Shoot an image of the polar region with the scope to establish a field of view. Theoretically this image could be of any sky region that you can find later on in CDC.
-In Eos Utility, find the size (x * y) of the live view preview. I used a screenshot and measured it in Photoshop, other apps would work for this as well.
-create an image with that resolution. Content not important, but CDC has to be able to open it, so a simple bmp is good.
-Import SCP image into Cartes Du Ciel, tinker with it till I figure out the exact field of view.
-Import live view sized image into CDC
-"Find" the SCP using CDC, using the field of view calculated above, and create and save a screen shot.
-Open the screen shot in any app, including the windows viewer.
-Start "transparent window".
-Start Eos Utility, launch live view
-Bring up the window displaying my finder chart, over top of the live view. Slide transparency to around 50%, position the image over top of the live view image. Slide transparency back to 100%
-Bring the live view image back in front, slide its transparency down to a usable level.
-Enjoy your software reticle!
For $95 USD you can get DSLR Remote Pro which handles the live view and overlay component, but, well, it isn't free
You'll still have to create suitable image files to use as your overlays. There are lots of potential applications here, including composing DSO shots.
I've currently got one image of the SCP to use prior to initialising goto on my mount, and one of Sigma Octantis at the centre for use in the polar alignment routine.
I'm also tinkering with the Canon SDK to see if I can come up with an app of my own to do this with selectable gain for live view, and alternate overlay techniques. We'll see where that ends up. I've noticed noise in the live view display in low light when using the PC mode, so it may not be very boostable.
Eric