6.3 Celestron Focal Reducer Question

[lune lupine]

Have been pondering getting a 6.3 Focal Reducer for my Evolution 8" SCT. One thing I've seen references to is that it reduces exposure times for astro imaging? On the FLO site for example it says by a factor of 3 I think. Is this right? I'm currently getting 25-30s imaging no blurring so would the above focal reducer provide the equivilent of 75-90s exposures? Seems to good to be true!

[MartinB]

It will reduce the exposure time required to achieve a the same signal to noise ratio.  Given that this is determined by the increased area of sky that falls on the chip a factor of 3 seems about right.  However the time to star trailing is inversely proportional to the focal length, so, if you can currently manage 30 seconds you should be good for around 47 seconds.

From memory it needs a spacing of around 110mm between back surface of the reducer and the camera chip, which is a lot and an cause issues with flex if you are using a heavy camera.  You can have less spacing although you won't get as much reduction in focal length or as much field flattening.

 

[Owmuchonomy]

Just be aware that the 0.63 reducer used on SCT scopes causes significant vignetting, certainly on an APS-C sensor, so the end result depends a lot on the chip you are using and the clever use of fat frames.  Martin is correct about the spacing certainly for a 9.25" SCT so I imagine it will be similar for yours.

[lune lupine]

Thanks guys. That's really helpful. I know reducer won't help with planetary imaging but getting into shooting at nebula so every extra second sounds good to me

[RayD]

The spacing on my C8 with Celestron FF is noted in the instructions at 105mm, but I'm not sure how critical this would be.  Worth having as it does make quite a bit of difference.