The time has come for a bit deeper follow-up on performance of this cheap mount..
Last night I did some imaging with 200mm lens and Canon 400D.
The series of 20 45-sec shots every minute was used for the analisys below..
Here it is:
PE (p-p) was found to be 132 arcsec.
The fastest change was about 79" in one minute, pretty bad.
The pixel sizes for various lens FL:
200mm = 5.88"
50mm = 23.51"
From the above, the conclusion is: this mount is good for 50mm lens and exposure times up to 1 minute, if we want 90% of the images in series to be good (that means, elongation of star image size smaller or equal to pixel size).
However, due to the shape of the PE curve, 4-5 minutes exposures are feasible, with perhaps 50% of them un-usable.. Still pretty much OK.
For 200m lens (with pixel size 5.88") it is not so good - max exposure will be 30" ) for 90% good frames), but this may be quite enough for some (serious) purposes (photometry, spectroscopy etc).
So, all in all, not too bad for the price ($50 plus a bit of tinkering). Especially because the mount itself is very light weight (11kg, with lens, camera and counterweight).
But, definitely not for the perfectionists
