Got tilt in your images?

[Martin Pugh]

Well how about this.
I sent my STL11K off to SBIG for a mid-life service, so it went back in its original state i.e I took off the 8 position filter wheel.
When it returned, SBIG had shimmed the nosepiece on one corner, with a shim that was 0.006" thick.
In the instructions to the CFW8-L it tells you to be sure to carry over any shims when you relocate the nosepiece to the front of the CFW.

So, I put that camera on my FSQ just last weekend, and the tilt was shocking. So obviously, my first port of call was to remove that shim and the tilt is gone.

Now I had a fairly good understanding of CFZ and how important it is to square things off, but the result here was just amazing. So watch out for it.

cheers
Martin

[cventer]

Very interesting. I notice on my STX 16803 there are shims under the nose adaptor plate as well that manual says to use with FW. Guess these can't be trusted to be accurate.

[Poita]

Cfz?

[Dennis]

Critical Focus Zone maybe?

[Paul Haese]

I am yet to sort out the tilt on the STL11 that I have. That is coming up soon and wonder where I get the shims?

[bojan]

Cigarette paper, maybe?
Alu-foil (chocolate wrapper)?
Or plastic foil for printing on laser printers (exactly 0.2mm thick)

[cventer]

Model hobby shops also sell copper shim in little packets with varying size thickness. Hearns in Melbourne sell them. They are small sheets about 4 cm by 6cm and you just cut them with scissors to size or shape you want.

Good thing with copper as apposed to paper is that it wont change with pressure on it.

[bojan]

Well.. you would be amazed how sheet of paper is stable it terms of preserving the thickness under pressure.
It (pressure, N/mm^2) will be too low to deform either of those materials, though.

Some reading on the subject is here:
http://www.biltpaper.com/atoz2.asp#4
The variation in thickness will be mainly due to absorbed moisture - but if the paper is impregnated with silicon oil or wax for example, this issue will no longer be relevant.

[Paul Haese]

Thanks guys, I will think in those directions when the time comes.

[Martin Pugh]

I have used paper before to go effect. The shims I have of course are designed to go round a screw, so they would not be very useful if you wanted to shim up the entire side of a nosepiece.

CFZ is Critical Focus Zone - you simply have to know the smallest CFZ appropriate to your system (as it varies by filter), because if your focusser doesnt have the resolution, you will skip right past your CFZ and never be at optimum focus.

cheers
Martin

[Martin Pugh]

Paul

if you can determine what you need, I have a number of 0.005 and 0.002" shims. I can pop one or two in the post to you.

cheers
Martin

[Ken]

On a similar note I had a tilt problem that I was blaming on my focuser but turned out to be the qhy9 camera. The face plate sits on a O ring and any uneven pressure on the three holding screws tilts it enough to give odd stars.
clear skies Ken