Baffling Question

[mick pinner]

for all design gurus out there a question, l would assume that baffling a reflector would have advantages as it does in a refractor but would this only be an advantage when viewing or imaging bright objects and not so much an influence on DSO's. thanks.

[jase]

The effectiveness of baffling is based on the reduction of scattered light and in turn increasing image contrast. Scattered light comes in numerous forms ranging from the object you are viewing/imaging through to light pollution and other environmental factors. It is still possible to have a bright star in the FOV of a DSO that can cause issues. A classic example of this is the witchhead nebula (ic2118) and the star Rigel - they are quite close to one another. Baffling is only part of the problem. You also need to consider internal reflections. A good example of this is in Scott's post - http://www.iceinspace.com.au/forum/showthread.php?t=17523
Filter reflections can be a big problem, though many manufacturers use anti-reflective coating today. This assists, but it does not remedy the issue. Typically, the rule of thumb I follow when mounting filters is if they have a shiny/reflective side (which many dedicated astro CCD filters do), position it towards the telescope, not the camera. You’re likely to experience greater issues with reflection between the filter and CCD glass window chamber.

[Starkler]

Something to bear in mind. With a refractor, reflections from any part of the tube could make it to the eyepiece so baffling is very important.

With a reflector, there isn't much of the tube that can be seen from the focuser. At the top end there is what can be directly seen, and at the bottom end only what gets reflected by the secondary. Light hitting any other part of the tube isn't going to make it to the eyepiece unless scattered off a dusty mirror etc and could be seen as inconsequential.

[mill]

Hi Mick.
I am using very dark felt opposite the focusser and in the bottom of the tube.
It makes the contrast better, you could also make all the mirror edges black with a feltpen so you won't have scattered light from the edges of the mirrors.
Last but not least, you can make up an lightschroud for the tube.
It has to be about 30-40 Cm high, this is to prevent stray light to hit the focusser because the focusser is high in the tube, i had that problem with my 10" dob.
After all these mods the view is a lot better and generally darker compared to the unmodded scope.

The felt is available from Spotlight on the canterbury road opposite Bunnings.
It is in the back, in the craft department.
I have some material here for free to make an lightschroud.

[gbeal]

Mick,
I reckon it works, as does a local ATM guru who I regularly observe with.
My humble 10" f5 gives such good images he often comments on it, and he has a 16".
My baffling essentially replicates the Intes Micro Maksutov Newtons. I can e mail you some pictures if you like, but seeing anything is difficult, it is that black, LOL.

[mick pinner]

thanks guys, l do understand the scattered light as such it was just the effect really on DSO's although l suppose being baffled can not detract from the scopes performance. Mill, the tube l'm making will actually be longer than normal from the end to the focuser to prevent stray light from having so much of an effect and l do have the flocking material already.