2" filters on a 200mm f/5 skywatcher Newt.

[Kaptain Klevtsov]

I've been plagued by the vignetting that I get with 1 1/4" filters on this 'scope for too long and have now got round it, here's how.

The Skywatcher 200mm Newt. comes with two adapters. One is for 2" eyepieces and the other is for 1 1/4" eyepieces but unscrews to allow the use of a T thread closer to the focuser. There are good and bad points for both of these.

2" adapter - allows the use of a 2" nosepiece but doesn't allow enough in travel to actually focus a DSLR.

1 1/4" adapter will allow a T ring to be fitted and will allow focus to be acheived when using a DSLR, but then you can't use filters without a lot of pain. This caused vignetting with even the APS sized sensor.

The cure!

I had purchased a 2" to T thread adapter to get rid of the nasty vignetting only to realise that focusing is not possible ([removed word]!). This had a slight recess in the barrel to provide a step in the barrel to prevent the nosepiece from falling out, other types might not work. I found that the recessed diameter is a tight push fit into the back of the 1 1/4" adapter. This allowed me to saw off the T thread section and force the 2" sized end into the adapter. Now I can screw a 2" filter onto the threads of the nosepiece and fit the camera to the T ring. The indise diameter of the 1 1/4" adapter is as big as you can go with a T ring, so it's as good as it's going to get vignetting wise. It seems to work well (see M42 test post).

Thanks go to Gordon C who lent me the filter in the first place, the weather for giving me loads of time to mess with it and most of all to blind luck.

The fit is such that a vice was needed (not that kind of vice WH) and I used some high strength bearing retainer stuff just in case. please check that the fit is tight enough if you try this yourself, as the nosepiece could fall out, down the tube and onto the primary mirror.

HTH somebody.

Captain Chaos