Best position for a screw-in filter?

[Stargazer33]

Hi, I was hoping someone could answer a question that has just popped into my head?

I am thinking about getting an imagemate or powermate barlow for my planetary imaging using a webcam and for nebulae like M57 using my DSLR and suddenly thought, "where is the best place to put a filter in this stack?"

Would it be best on the nose piece of the barlow or would it be better to keep it closer to the image plane and fit it to the nose piece of the camera? Or does it not matter.

My thinking was that if you have any problems with the filter scattering light it would be worse fitted to the barlow, but then if you had dust on the filter it would be so blurred by the time it reached the image plane it probably wouldn't notice. These problems being reversed if the filter was screwed to the nose piece of the camera. Or am I way off base again?!?

[Leveye]

If your using a Canon EOS camera Astronomik makes clip in filters that fit inside the camera body but you cannot use EF-S lenses with them they make contact with the filter

[laser_jock99]

I think the idea of keeping filters as far away from the CCD is soundest- any dust on the filter will have less effect.