Reducer-Flattener?

[BEYOND EARTH]

Could some one explain what a reducer-flattener does and why it's needed for DSLR imaging.

Thank You!

[Merlin66]

They may be one optical element - or in two parts...

A reducer - the opposite of a barlow...it reduces the focal length and ratio of your scope - making it "faster". ie a f8 with a x0.6 reducer becomes effectively a f4.8.

This improves the imaging of nebulae and DSO's.

A flattener - basically corrects the curvature in the field of view and provides a "flatter" image to match the CCD sensor. All telescopes suffer (some more than others) from the curvature where the stars at the edge of the field appear elongated.

There can also be "coma" which causes the edge stars to look like seagulls...a good flattener will correct for both these aberrations.

HTH

[E621Keith]

I don't know much about imaging, so I may be wrong but from what I know, a reducer reduces the magnification / shortening the effective focal length of the scope. In practice, it increases FOV and reduces exposure time.

A flattener turns a curved focal plane into a plane. Most telescope's focal plane isn't flat but a curve, so stars near the edges of the field will go out of focus. The problem become more pronounced as chip size increased. DSLR has a large chip, so it will need a flattener on most scopes to ensure all the stars are in focus on a chip.

[BEYOND EARTH]

Nice thank you for your help guys!

[cgarry]

There some images in this thread showing the correction a flattener can make.

http://stargazerslounge.com/member-equipment-reviews/160015-ts-2-field-flattener-tsflat2-review.html

[ollypenrice]

...and since DSLRs have large chips they reach out into the edges of the light cone of the scope and into the distortions therein. Image with a tiny webcam chip and this won't happen because you are using only the inner part of the light cone.

Olly