Quote:
Originally Posted by acarleton
So in case any one is interested for posterity's sake, i have talked with the guys from Bintel and they have informed me that putting a barlow or a powemate in a F4 scope does not make it act as a F8 scope. the coma is an artifact of the mirror and magnification will only zoom in on the issue, not correct it. therefore if you want to have a flat FOV you need to attach the barlow/powermate to a coma corrector. this is what i will be doing, hoping for some good results.
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Yep sorry Aidan I was a bit slack in my explanation. It will change the field of view, and as you know the coma is worse toward the edges of the fov than the centre. so not as much zoom in on the issue but 'crop' the fov toward the centre where its not as bad. will it suffice? hard to know, depending on your optics and how well you have centred the subject. the pictures I have seen where people have photographed with a barlow are usually planetary nebs which I suppose have again been cropped in processing as they are generally small. it would be interesting to test out on a star field.
edit - I know with an f5 it would be ok - f4 I couldn't say, it is exponential ..