field flattener or field corrector. are they the same

[philip57]

Hi ,

I have a celestron focal reducer/correctorf6.3 for my sct c9.25 but i still get trailing stars nearer the edges of my astroimages. Do i now need a field flattener or does a field flattener do the same as my existing focal reducer/corrector. If not then how does it fit in combination with the focal reducer/corrector to my c9.25.

Thanks

Philip

[JimStan]

Focal reducers and field flatteners are the same device with different names. The Celestron F/6.3 reducer/corrector does two functions, it reduces the focal length of an F/10 telescope to F/6.3, and reduces coma near the edges of the image as it actually flattens the curvature of the focal plane.

Unless you are really stretching out to get a larger scale on a very small deep sky object, you are probably much better off trying to photograph the object with the reducer/corrector. What you lose in image scale, you will make up in increased brightness, resulting in less exposure time needed to obtain the same data, and the stars will be pinpoint sharp ( or reasonably so ) out to the edges of the frame.

I assume you are using an equatorial mount. Trailing stars near the edge of the picture are probably a result of errors in your polar alignment.

Jim S.