200p Prime Focus Photography With a Filter

Having tried prime focus photography with my Skywatcher 200p and my Canon EOS 1100d, I've decided that for my location, a light pollution filter is a must. Other filters will come in handy, too, depending on my target. The challenge was to figure out how to place a filter in the light path between the telescope and the camera, without moving the camera too far out from the sweet spot for focussing.

It turns out there's a neat method to do this, and I'll illustrate it here with photos.

The 200p focusser has a choice of 1.25” and 2” eyepiece adaptors. Take the 1.25” adaptor, and unscrew the barrel from the ring:

Screw it back in on the other side of the ring, so that it would be poking into the telescope if you were to put it back in the focusser. Take the two knurled screws out of the 1.25” barrel, and replace them with M3.5 grub screws. I used stainless steel ones that are 4mm long (easily available on ebay).

Unscrew the barrel from an eyepiece, and hold it in place with the grub screws:

Now you're set. Add your t-ring and filter:

And you can put the whole assembly onto the camera:

And finally, mount the whole lot onto the telescope:

I hope this was helpful. Now all we need is clear skies.