Position lens, filter, corrector

[Michael1971]

Hi,

On my DSLR I have a coma corrector directly attached.

I recently purchased a 2" GSO barlow and Baader neodymium filter.

All these accesoires are attachable to my DSLR.

At first I had, coma corrector, a barlow, and neo filter. I was unable to focus like this and even with a 50mm extension it did not work. (50mm was to much difference)

Then I changed it like this: DSLR, barlow, comma corrector, filter. Now I am able to focus. (barlow is now closer to CCD)

I red some paper that stated that the coma corrector has to be at a certain distance from the CCD to function properly , (I think its the same for the barlow)

What do you guys think? Should I try to find a 1 inch extender, or just use it like this?

Thanks for your thoughts.

Cheers,

Mike

[RikM]

The coma corrector is normally positioned at a set distance from the camera chip (the EOS 1100D has a CMOS sensor rather than a CCD). I wouldn't have though there would be a need to use both a coma corrector and a barlow together? The coma corrector is needed to stop the stars at the edge of a wide field of view from streaking out towards the corners. Using a barlow, you are increasing the effective focal length, so you don't have such a wide field of view, the stars visible in the remaining field might be sharp enough like that.

I wouldn't use a barlow with a DSLR on an f/5 Newtonian at all personally. It would make the focal ratio too slow for sensible deep sky images but a 2x is not enough focal length for planetary imaging (and a webcam would be better at that anyway).

[Michael1971]

Thanks, yes I didnt realise that. I will try the barlow without the coma corrector to see how that goes.

I wanted to try the barlow on DSO's to see how the effect would be.

Thanks for your explanation!