[g__day (Matthew)]

I have had several goes with my off axis guider - that has a built in focal reducer (f6.3 I think) and I must say I like the results generally.

I presume it brightens the field of view especially in the centre - because if I take a 20 minute guided shot of a star near the centre of the frame then the centre is a large wash out - in a fat capital L shape.

1) Does the L shape rather than a central blob suggest the collimination is out - or is it more likely a tracking related error?

2) With a focal reducer what is the best way to calculate your maximum length exposure for a DSLR (before you flood your pixel well due to either sky glow or a bright star swamping everything)?

3) I see stars all around the edge of my shots (C9.25 -> OAG -> Canon 400D) tend to be slightly streaked in toward the centre of the shot. Is this normal - and can it be corrected by hardware (is this what a field flattener is used for?) - or do you just trim it out of the shot?

Lastly what advice or links might folk point me to as a first time user of focal reducers who know needs to know what must be done to process shots with them correctly?


Many thanks,

Matt