Field Flattener Lens to Chip distance

[Roy Challen]

I am thinking of buying a flattener as my images have distorted stars. The problem I have is that it seems that the distance from the camera sensor to the flattener lens is important, but how does one calculate or find this out? How important is this? Can it be adjusted - ie if I buy brand X flattener and the distance isn't correct, how can it be made correct?

Any help much appreciated.

Roy

[DaveS]

The manufacturer will specify the distance in their literature, from that you subtract the chip-mount distance (44 mm for Canon) this gives you the distance you must set any spacers to. You'll have to buy the correct ones from an astro dealer, though some have adjustable spacers so you can set the exact distance. You will normally have to get this right within +- 1 mm.

[Tinker1947]

On a DSLR the sensor to T-ring (lens edge) is 55mm, different flatteners have different distances..the Celestron 6.3f is 105mm from the camera side to the sensor....that's the only one i know....

[Roy Challen]

Thanks Dave and Tinker,

I have ordered a Sky Watcher flattener from FLO. Apparently that puts the chip at the correct distance for my camera.