andrew s

I am never clear what adding or subtracting backfocus means. I still believe the glass plate results in the focus being further from the objectve. I attach a sketch that show the effect. While not accurately to scale the key point is the light is refracted towards the normal as the light enters the plate and away when it leaves. This means the light converges less quickly when in the plate.

Regards Andrew

so its nothing to do with chip distance to flattner , just focus ??edit to last post , I am a few thu over not under 55mm

If the filter is between the flatner and the chip I would increase the flatner to chip distance to account for the filter as specified above in a previous post.

Regards Andrew

The filter acts to push the focus further away from the objective/mirror so to reach focus you need to move the CCD outwards

Regards Andrew

I don't think the length of a Chishire makes any difference as long as it fits well in the focuser. A sight tube is better to be long so there is some distance between the eye hole and the cross wire.

Andrew

Jasper - I think what you have is a bad pixel that continually generates charge. When you are reading the column out it is adding charge to the other pixels charge in the column as they pass through it (hence it only impacts one side of the pixel. If this was there when delivered then I feel it is a column fault not just a pixel fault. Andrew

Yes it looks that way to me. Contact Terry at Starlight Xpress and I am sure he will help you. Andrew

I am sure Epsilon Telescopes could make you one www.epsilon-telescopes.co.uk Andrew