M57 by manual tracking piggybacked

[Sam Bo]

Hi all

Whilst having issues with firmware on my recently purchased CG5 mount, I decided to attempt a manual track of M57. Nikon dSLR was piggybacked to 70mm scope with a 200mm lens. Manually tracked the scope using an illuminated reticle to take 10 x 1 min subs, with 4 x darks and 4 x bias. Stacked in DSS.

Quite pleased with what I got considering the method but am a bit bugged as to the quality of the stars which look like blobs. My first thought is obviously because of my manual tracking but could it also be slightly out of focus?

Interested in thoughts on this. Silly question but are stars in focus slightly back from infinity?

Cheers

Sam

[rfdesigner]

Well done!.. manual tracking is not for the faint hearted.

Been there, done that, got the backache (1 hour shots on film)

yes you could be a little out of focus, lenses don't hit perfect focus at their endstop, try a bahtinov mask, or a FWHM computer readout (harder on DSLR).. I'd go for the mask in your position.. home made will do.

stop your lens down by 1~1.5 stops (prevents little comets in the corners)

polar align... you need to drift align. even if you were shooting at 18mm flocal length you need to drift align, the three factors that increase the requirement for good alignment are:

Field of view

Length of shot

Distance from guide star to furthest edge of image.

note how focal length isn't in the list.

good luck and thanks for sharing

Derek

EDIT: I re-read your post and realised you'd taken 10x1min shots, not 10min shots.. so polar alignment is 10x less problematic, you just need to make sure you've allowed your stacking program to rotate the images, not just move them in x and y to align.

[Catanonia]

Never tried manual guiding and would hate to.

Awesome work, something I would never try myself, like computers too much.

[Sam Bo]

Many thanks for your comments!