The 75-300 is reported to be soft on the long end; many XX-300 lenses
are that way (I have two that are, one that is not). The Kenko may add
more softness.

On a tripod, what "shake" can happen, unless you are next to RR tracks?

You may also have some focus errors -- not trivial to focus accurately
on the Moon.

First thing I would do is back off to 200 or 250 mm on the zoom and see
if photos get sharper. If so, I would say it is the lens. If not, I
would consider trying a bracket of (manual) focus.

Phil

rda wrote:

Hi guys, I am currently having a huge problem with camera shake.
I am using a canon 300D/DRebel with Kenko 300 pro 3x teleconverter on a
75-300mm lens.
I am trying to capture some lunar photos with more detail then the 75-300
was able to give me on its own (although I did get some good shots).
The image looks nice and sharp in the viewfinder (suggesting that the
problem is not with the 3x converter), but the final photos are always a
little blurry even when using high ISO settings and relatively short shutter
times.
The camera is mounted on a manfrotto tripod & I am using mirror lock up
(hacked firmware on the camera allows this).
Is 900mm just to long to expect sharp photos or is there anything else I
could try?

Thanks