Bintel Diagonal - on rotation star moves significantly off centre?

[g__day (Matthew)]

Is this normal? I noticed when I took my DSLR off and put a Bintel 2" diagonal on - that my SCT and Megrez where badly out of alignment with each other - and they are not when used without diagonals at all!

Further when I rotate the diagonal say 180 degrees at the back of the SCT and then lock it the star moves considerably. Is this common and is it a sign of a bad diagonal whose mirror doesn't sit at 45 degrees to the tube or some other factor?

Many thanks,

Matthew

[citivolus (Ric)]

That sounds like bad collimation of the mirror in the diagonal. I just tested my Bintel GSO 2" dielectric diagonal and it didn't show noticeable shift with a 17mm eyepiece on the Megrez, but I didn't test it at very high power.

[gary]

Originally Posted by g__day

Is this normal? I noticed when I took my DSLR off and put a Bintel 2" diagonal on - that my SCT and Megrez where badly out of alignment with each other - and they are not when used without diagonals at all!

Further when I rotate the diagonal say 180 degrees at the back of the SCT and then lock it the star moves considerably. Is this common and is it a sign of a bad diagonal whose mirror doesn't sit at 45 degrees to the tube or some other factor?

Hi Mathew,

As the earlier respondent noted, indeed it could well be the diagonal
is out of collimation.

Also note that in some setups, the weight of the camera itself can cause the
diagonal to shift downward within the mating collar of the OTA or the camera
sags downwards within the eyepiece end of the diagonal if the couplings aren't
nicely toleranced. In this later case, the star will be offset always in the direction
opposite gravity, something that can determined with a little experimentation.

The above effects will also degrade the scope's pointing performance if
you are using computerized positioning.

Best Regards

Gary

[g__day (Matthew)]

Gary,

Thanks - but my description was unclear. The Camera mounts directly via a 2" Canon connector to a Meade Motor focuser at the rear of the SCT. So its static and I use the Camera DSLR eye pieces central focus dot as the true image centre. This point happens to align well with two other scopes centre spots where I using illuminated retcles in them and no diagonals.

Now take out the camera and insert a Bintel brand 2" diagonal and put a Vixen LVW eye piece in that. A star that was centred in the DSLR is no longer centred in the eye piece like. Worse still, if I rotate the diagonal anwhere significantly through 180 degrees the star moves considerably off centre.

So yes collimination of the diagonal could be bad. Not sure if there is any other way to check for this - or fix it.

Matthew