M51 - My Second Attempt, and my Second Attempt at Drift

[CKemu]

Ahh the Meade LX90 8", if I ever wanted to give myself a series of challenges, then this scope would be the ideal choice!

I am still learning how exactly to align my scope, but I can honestly say that I am seeing progress, which at this point is spurring me on.

Several Weeks Ago:

ISO 3200 | 5 Minutes (300s) Sub

Last Night:

ISO 3200 | 8 Minutes (480s) Sub

A VERY Forced Stack in DSS:

17 x 480s Lights | 7 x 480s Darks

I have done a few 14 minute exposures to, and noticed the hook streak turns into a "Z" shaped streak, and the galaxy / streaks travel in the same direction. So still a bad alignment issue, that and I think I am now seeing periodic error (the hooks).

My worry is that even with me perfecting alignment, the light pollution, regardless of filter is going to make me loose contrast, and DSS gave me an exceptionally noisy image to work with.

[Looking Up]

It's coming along, the difference from the first image is giant, a little more work and you're there!

[lukebl]

If you're not guiding, then attempting 8 and 14 minute exposures is ambitious and impressive indeed!

Seriously, though, I wouldn't consider attempting anything over a couple of minutes unless you're autoguiding, even if your polar alignment is good. No-one would attempt exposures of 8 or 14 minutes unguided!

[peter shah]

i would say that the Z shaped stars are due to poor alignment combined with Periodic Error, there will be a certain amount of movement in the optics but that would be more noticable over a longer period....best thing to do is use an off axis guider it wil sort out any flex, mirror flop which is well known in these sort of SCT's and will guide out the PE.....the down side of the OAG is the long focal length gives a narrow field and slower optics of the SCT reduces the amount of suitable guide stars