Kit lens test + reply to Bojan

[raymo]

I decided to try my kit 55-250. 600D, 55-250 @ 70mm, f/4, 5 x 15 secs
@ ISO 6400. 6400 was used as I had a strange tailing of stars, but not
caused by poor tracking, so something had to be moving during the exposure,
leaving me with a 15 sec max exposure. Lots more subs would have reduced the noise, but got clouded out.
Bojan, the Yongnuo 100MM f/2 lens is faulty, the right hand third of the field from top to bottom does not focus quite as sharply as the rest of the field, resulting in slightly larger stars. Fine for for normal photography, but naff
for astro.
raymo

[Mickoid (Michael)]

Raymo,, that's still a reasonable result. You must tell everyone you're using a Nano Tracker on a tripod now and we will be even more impressed!

The movement may be the camera connection at the ballhead. I have found if I'm shooting an object to the west of the meridian, the weight of the heavier longer focal length lens will actually loosen the screw connection as it is weighted anti clockwise on the thread.

You must make sure that connection is tight because if not, the camera will move during the exposure and cause star trailing.

[raymo]

I hear what your'e saying Michael, but the camera was tight on the upper ball joint, and the upper ball joint was tight on the lower ball joint,and the lower ball joint was tight on the tracker. more importantly the target was way east of the meridian. If it stays clear I will try and sort it out tonight. Thanks for the comments.
raymo

[xelasnave]

I would be happy with that Raymo.
Alex

[raymo]

Thanks Alex, yes it is o.k. for what it is; I'm currently having trouble with the
P.A. on my tracker, so am limited to very short subs.
raymo

[bojan]

Originally Posted by raymo

...
Bojan, the Yongnuo 100MM f/2 lens is faulty, the right hand third of the field from top to bottom does not focus quite as sharply as the rest of the field, resulting in slightly larger stars. Fine for for normal photography, but naff
for astro.
raymo

The lens is not necessarily faulty, maybe just tilted. Perhaps you shoud try first if you can achieve fosul at all in that particular corner.... if yes than perhaps a piece od cirarette paper (or thin alu foil) on flange could help bringing the whole FOV into focus at the same time.