Narrowband imaging with Astrotrac?

[roarke80]

Would it be possible to have a beginner's astrophotography narrowband setup with just the Astrotrac, a normal tripod, and a CCD camera with perhaps a long lens or a small telescope? I've been trying to really get into astrophotography but am constrained by lack of technical knowledge and a lack of space, no car or access to dark sites, and being stuck in Central London with extreme light pollution. So I'm after something really light and easy to setup and use. Any advice or tips would be really welcome. Many thanks!

[andrewluck]

No problem at all. I find the Astrotrac ideally suited to short focal length imaging (up to say 300mm. Shorter is easier when you're starting out). There are some nice extended Ha objects in the Milky Way over the summer and autumn months.

To attach a lens to a CCD camera you'll need an adapter. I use the Geoptik with my Canon lenses but there's a Nikon version as well. There's space in the adapter to fit a 1.25" filter. Back focus can be critical so you'll probably need to experiment with M42 spacer rings to get the correct spacing from the lens to CCD. You can also attach a red dot finder to the adapter to make pointing easier.

Cheers

Andrew

[roarke80]

Thanks very much for the reply Andrew! Would you say that the pier that Astrotrac sells, or a good Manfrotto tripod would be good enough as a mount for the setup? Sorry for the newbie questions, I've only just started researching narrowband imaging, but just as a guide, if I wanted to put a 300mm lens onto the camera, how many spacer rings would I need? 

Many thanks! Jess

[andrewluck]

Hi Jess

I use a Manfrotto tripod with the Astrotrac wedge and head on top. This is a nice stable combination and I haven't found the pier to be necessary. Relatively easy to get 5 minute exposures at 150mm, longer exposures and focal lengths become progressively more difficult so start at the short end of both scales until you get the hang of it. This is possible: https://cosmicbug.files.wordpress.com/2008/11/tak-fs-152-tt320-glee1.jpg but not when you're just starting out .

The spacers required depends upon the camera you use. A Canon lens requires 45mm from the mounting face to the sensor. The Geoptik is 19mm thick. Add that to the distance the camera sensor is from the front face of the camera and subtract from 45. With my QHY9 I need about 8mm.

Cheers

Andrew

[roarke80]

That is a stunning picture, I'll be happy if I got anything close to that...ever. Thanks so much for the tips, glad to know Manfrotto would work just fine as I would be able to use it for photography as well. Are 5 min exposures good enough to achieve good images in narrowband? My rudimentary research seems to show the narrowband imaging requires longer exposures than RGB. Would this setup eventually allow me to get longer exposures or would it need to be guided? 

Sorry for the million questions, I'm just trying get a better understanding so I know what to expect. Thanks so much for your thoughts!

[andrewluck]

Like all things, there are no real hard and fast answers here. It all depends upon your focal length and accuracy of polar alignment. Master drift alignment and you can go for longer.

Andrew

[roarke80]

Thanks very much for your help Andrew.