Prime focus on Skywatcher 200P

[Andy Milner]

Hi, I've just purchased a 200p, and I'm about to purchase a DSLR camera and I was wondering what is the best way to get Prime focus. I see there are prime focus adapters which are closer than using a t ring? And what about bhatinov masks and coma correctors?

I've heard it's possible to move the primary mirror in further on its own screws, however not giving enough.

Any advice from existing owners of a 200P and how you do it will be much appreciated.

Thanks!

Andy

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[LouisJB]

You may need to try it out. It might just work, depends on the exact camera etc. Normally a T-ring adapter into the focuser is how you get prime-focus. With a CC it again depends what one and if it changes the focal position. The Baader MPCC is 1.0x and does not move the focus position.

Bhatinov mask, yes - you'd normally get one to match the scopes spec (speed, size, focal length) - you should be able to find a universal one matching a 200P as it's a pretty standard OTA.

If you really can't get prime focus with your combination then longer screws that hold the primary mirror cell in place will allow you to shift the mirror up the tube to help gain focus. How much would depend, on my 130P I did it and had to move the mirror quite a lot.

By the way, the Skywatcher PDS range is designed to deal with this as optimised for prime focus astrophotography - but they are a bit more (but you get a dual-speed crayford focuser).

[Pyrodave]

I have a 200P and Sony A350 with T-ring and achieve focus with no problems 

[WaveSoarer]

I have the same set up. You need to be careful with the T-ring sizes as one size will fit a coma corrector while the other will screw directly on to the supplied 2" adaptor to achieve prime focus. Steve at FLO can put you right on this. I have the coma corrector and it has an additional advantage of keeping dust out of the camera. There are various videos on youtube showing how to attach a DSLR to a skywatcher telescope (which is actually easier than with other manufacturers). Incidentally, the supplied 2x Barlow also screws into the T-ring (the size that also fits the 2" adapter) and this also allows the camera to be brought to focus - though not now at prime focus - and effectively increases the magnification for smaller objects. I use a Bahtinov mask for focusing. This is essential as it's very imprtant that you nail the focus otherwise you end up with blurry images. Even a tiny tweak on the focuser (and I do mean tiny) can make an appreciable difference.

You absolutely don't need to fiddle with the position of the primary. This can have serious consequencies for the match in size between the primary and the secondary.

[SnakeyJ]

My black diamond 200p works great with or without the SW CC. Though I did fit a low profile m57 to 2" compression fitting - available via teleskop service or Modern Astronomy.

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[WaveSoarer]

Here is the tutorial. You'll see the trick with the 2" adapter about 3:50 in.

http://www.youtube.com/watch?v=cYTmsfpL0M4

[Andy Milner]

Thanks guys. I'm a lot clearer on this now. Hope this thread helps other beginners like myself. snakeyJ I saw this on modern astronomy... Is this the item you mean "m54"?

-2" Adapter with Compression Ring - for SkyWatcher Newtonians with M54 thread - £37-

Thanks!

Andy

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[Tiny Small]

Incidentally, the supplied 2x Barlow also screws into the T-ring (the size that also fits the 2" adapter) and this also allows the camera to be brought to focus - though not now at prime focus - and effectively increases the magnification for smaller objects.

You can unscrew the glass from the barlow and just use it as a nosepiece.

[SnakeyJ]

Thanks guys. I'm a lot clearer on this now. Hope this thread helps other beginners like myself. snakeyJ I saw this on modern astronomy... Is this the item you mean "m54"?

-2" Adapter with Compression Ring - for SkyWatcher Newtonians with M54 thread - £37-

Thanks!

Andy

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Andy, spot on - sorry for the bum steer, but was writing from memory - no so sharp now at 46!

I would definitely recommend this for imaging as it is much firmer, more concentric and gives you about 30mm extra in focus in comparison to the standard SW M54 fitting and standard 2" extension.    Not only this but won't mark you coma corrector or nice lenses.   However the rub is you will probably need some extension for visual with both 2" and 1.25" EPs.       There are some small differences with the focuser and extension fittings on the older blue tube Explorer 200Ps, though at first glance it is not easily noticed - on my first explorer the 1.25" and 2" extension pieces had a steeper taper with a 2" external diameter, which I can clamp in the TS M54-2" adaptor.   However the extensions from my more recent black diamond Explorer 200P are a shallower taper, but larger OD and do not fit.     As with all things astro you can usually find a suitable adaptor/extension somewhere, but always shocking how much these little bits can add up   TS is a good source for odd adaptors and most of these can be sourced via Bern @ MA, usually slightly cheaper and more convenient than the TS web price.