RobertC

Sorry, shouldn't use abbreviations - Optical Tube Assembly.  You have the 200P, so it would be a ring of cardboard to go round the end that points at the sky.  If the bahtinov is on your 'list to buy' I would strongly recommend you make up a Y-mask first and try it.  People tend to fall into either the 'Y-mask' camp (there's more gap so the image is brighter and so easier to focus) or the 'bahtinov' camp (the spikes are more pronounced and so easier to focus). Like most of these divisions, the only way you can decide which you are in is by trying them, but as the Y is so easy and cheap (actually, you don't even need to make a ring to go round the scope, just three lengths of card, cellotaped/stapled/whatever into the right shape, with the ends turned down so it doesn't fall off) I would say it has to be worth a try.

If you have live-view on the 60d(?) you can get approximate focus before you start taking short images to refine it.

HTH

Just went ahead and built one, made it so it will stay on the scope no matter where it is pointed. Covered it in duct tape to weatherproof it better Had a very close call with the tip of the craft knife, it snapped off and off places bounced off my eyelid. So close !

A 

Hi Robert

What (if anything) do you already use?

A bahtinov mask is the common answser, but a really good (and cheap/easy to make) alternative is the Y mask.  Simply make a ring of card that goes round your OTA, then cut three thin strips of card and make them into a 'Y' shape over one end.  There are formulae for working out the exact ratio of width to OTA size, but i have never bothered and it works really well without bothering.

In case this is new (feel free to ignore this paragraph): go to a bright star and take a picture with the mask in place.  This will produce 'X' spikes across the star with another bar cutting through the X.  Adjust the focus until this extra bar exactly bisects the 'X', You now have perfect focus. GOTO the object you want to image and enjoy!

Most importantly - remember to remove the mask before taking your proper photos (been there, done that, got the T-shirt!).

HTH

A bahtinov mask is on my list to buy. At the moment i am using a canon 60d with t-ring simply fitted to the standard focuser that is on a 200P. I have it connected to the laptop so i can see the view on a larger scale for ease of focus ( or not ).  

Can i ask what OTA is ? I'm not yet familiar with the terms used by the advanced astronomers.

-Rob

Really struggled tonight to get any focus tonight. Has anyone got any tips for prime focus ?

Just about managed to focus enough to get M31, only 6 minutes of exposure.

fantastic effort Robert, i'd have [removed word] my pants when that came up on the screen knowing it was me who took it.....well done!

Neil.

I've been desperately trying to get a nebula shot for a few days, i've been working my way around the sky and now know some constellations from sight now so it will help in the future. Thankyou

My first DSO, m42.