Regarding "What magnification are you taking your pictures in? Is it 125x except for the cameras extra 10x ?"
Yes. 8" F/8, 26mm EP, 2x Barlow, yup 125x (actually around 127x with my focal length of ~65". The extra 10x camera optical probably pushes me above the ~400x maximum usable, but because of the inherent small scale I get using this method, I push it as far as it can go (and which could be corrected with software by reducing the image size, but I don't need to with Saturn, but with Jupiter it's a different issue); another factor might be the camera chip is 8 megapixel scaled down by the camera's software to 640 x 480 pixels, so I need to push the scale as much as I can; I'd rather be over than under.
"I've been experimenting with everything from 125 to 333 (8 inch reflector, f/5). In the smaller magnifications the picture is stable but Saturn is small, too bright, and lacking detail. In the larger magnification Saturn is showing some detail but is pretty fuzzy and the picture is jumping areound a lot more."
In my case, Saturn being too bright means I'm not applying enough magnification (I don't need a filter for Saturn, especially now that it's at its lowest in brightness).
If the image jumps around at higher magnifications, either your seeing is bad or you might have a large temperature differential between your mirror and the outside temperature, you also could have tube currents (heat again) or heat rising from a nearby source (sidewalk cooling, observatory shelter etc.)
The atmosphere is obviously the other 'seeing' factor. Before going out, a lot of people check the clear sky clock at http://www.cleardarksky.com/csk/
. I personally prefer to check the weather satellite loops at http://www.goes.noaa.gov/
; when the Water Vapor satellite is black over your location and the IR is clear, your chances of good seeing are very high. If you can see high speed movement on either the IR or Water Vapor, the seeing will be bad (i.e. it's a cloudynights.com night :^)
MOST IMPORTANTLY regarding seeing, wait until Saturn is at least within 1.5 hours of crossing your local meridian (at Meridian is best as there will be less atmosphere to look through.)
"Your picture is pretty large compared to what I get even in 333x... I suppose you magnify it somewhere in the process?"
As mentioned above, once the 10x camera optical zoom is factored in, my magnification is higher than 333x, so no, the 2 images of Saturn I posted on this thread are not re-sampled/scaled upward. Assuming that you are factoring in that you are using an F/5 scope (versus F/8.13), another thing to watch is the distance between the EP and the camera, there is a significant impact on scale for it to be a few millimeters further away.
Another thing is, not all Meade 26mm Super Plossls are created equal!!! I'm using a older one, probably older than 15 years old. I have brand new ones that give a much darker image, not as crisp, and do not show the same scale as my older one (i.e. I never use the new ones!)
"Oh, and what sliders are you refering to? I've got Registax5 as well but I didn't quite grasp what you meant."
Once you have run your video file through the process (click the automatic processing button before clicking the align button) after it completes stacking your image, you will see 6 sliders on the left-hand side of the screen, move them one at a time and you will see a considerable improvement in your image (it will sharpen it) with one or two sliders pushed to the right.
Regards, Jason H.