I use a FSQ-106N and a SBIG STL-11K/FW-8 combo. Before I added
the FW-8, my images had nice round stars out to the corners of the
image. When I added the FW-8, I started getting elongation in my stars
on one side of the chip. This said to me that I probably now had a tilt
in the camera. However, when I rotated the camera (I also have a
Astrodon Takometer), the elongation got worse in certain PAs and better
in others. After much testing, I came to the conclusion that the
additional weight of the FW-8, plus the fact that the weight is offset
to the main optical path, was causing flex/sag in my optical train. I
started investigating where the flex/sag/elongation could be happening
and determined that there are 3 basic places this is most likely to
happen, 1. the focuser, 2. the CAA, 3. the guidescope. I addressed each
one and found "play, slop, looseness", in the focuser and CAA, and
eliminated the guidescope by installing an Astrodon MonsterMOAG. I now
have the imaging chip back square to the optical plane in all PAs and
the flex/sag is gone. I now guide with the MonsterMOAG (MMOAG) and
don't have to worry about flexure or focusing of the guidescope. The
addition of the MMOAG makes a very tight. compact, rigid imaging train
from the CAA to the main chip.

I put together a Word document that describes the adjustments I
made, and how I installed the MonsterMOAG on my FSQ. It is available
for download on my website here:

http://www.skyimager.com/FSQ-MMOAG/. The document is called
"Using an Astrodon MonsterMOAG with a Tak FSQ-106N".

Also, here is a link to the first image I took after these
modifications. It is a Ha image with the individual exposures (16 of
them, 30 min each), guided with the MMOAG.

http://www.skyimager.com/imagedata/IC405-IC410_12-18-07.html

If you are seeing any issues in your images similar to what I
did, this might be of some help. The MMOAG is an excellent alternative
to a separate guidescope.