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Old 08-02-2019, 03:32 PM
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Stonius (Markus)
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Dumb question re field flatteners and barlow/powermates

So far I've used my powermates just for planetary where I don't bother with a field flattener because the curvature over the width of a planet is likely to be negligible.

But say I want to try for a smaller DSO - planetary for example, or a galaxy, whatever...

Do you then need to put the field flattener back in there, or does the magnification flatten things enough since you're just seeing the centre of the field on your sensor?

And if you *do need your flattener, does the imaging train go Flattener - Powermate - OAG or Powermate - Flattener - OAG?

I feel like I *should know the answer, but I don't. Guess I could spend a couple of hours faffing and find out, but I'd rather not waste precious imaging time if someone here knows the answer straight up. Otherwise, a-faffing I will go.

Thanks

Markus
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Old 08-02-2019, 07:24 PM
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Ukastronomer (Jeremy)
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Can I add a dumber question please, do you need a field flattener for visual for any reason

thanks Stonius
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Old 08-02-2019, 09:16 PM
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Camelopardalis (Dunk)
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If you’re putting a powermate in-line, then you’re effectively increasing the focal length of the scope, and thus increasing the radius of curvature of the scope, resulting in less severe field curvature than before.

Just remember that any field curvature is going to be at maximum on the field edge, not near the centre.

Field flatteners are important for imaging where the camera sensor is flat, whereas the focal plane (especially so in small refractors) is curved. Without correction, the stars would be out of focus towards the edges/corners.

The eye generally accommodates field curvature, but eyepiece design can influence how it appears, and some eyepieces are more suitable to some types of scope than others.
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Old 08-02-2019, 09:41 PM
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Ukastronomer (Jeremy)
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Old 08-02-2019, 10:23 PM
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Stonius (Markus)
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Thanks Dunk.

And Jeremy, +1 to what Dunk said about visual. :-)
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