Imaging with a 70-300mm zoom lens

[PorkyB]

To compliment my 200p I bought a "Sigma AF 70-300mm f4-5.6 DG APO Macro Lens" currently available for around £140. I've been using it for a few months now so i thought i would let everyone know how I've been getting on. Just to be clear this is the "APO" version with the red band around the end, not to be confused with the cheaper non-apo version.

I have been pleasantly surprised with how well this lens has performed, considering the relatively low price. Focus seems a little soft when imaging the moon at 300mm but seems nice and crisp when imaging clusters and the like.

It does produce a set of (18, I think) diffraction spikes round very bright stars. I am guessing these are from the iris blades. I did experiment with masks to reduce this but this was unsuccessful.

The focus is very light so needs very careful handling. I did think of putting something round the base of the focus ring to stop it moving quite so easily (a ring of the loop part of velcro tape would probably do it) but in the meantime a blob of blue tac helps. Unfortunately the focus does change as the lens is zoomed, so if using a wide setting to find a target it is necessary to re-fosus after zooming-in.

I found that flocking the inside of the lens hood helps when working under the streetlights.

This is the best I've done with it so far and more results here http://www.flickr.com/photos/porkyb/sets/72157634353235461/

Double Cluster by porkyb, on Flickr

[Ouroboros]

Yes, I have the same lens. The focus can be tricky I agree. I find it's much easier if controlling the camera from my lap top in live view.

[Steve Ward]

You've done well there ...

I bought this lens a while back but found the zoom was so free/smooth/loose that as soon as I pointed it above 45 degrees it would creep to all the way back to 70mm , even from 80mm.

Took it back to Wex and went through the other ten they had in stock but all were identical so I swapped it for the Canon.

[Crunchard]

Nice work, as I only use my Astrotrac it is camera lenses all the way for me.

I'm a big fan of the older M42 prime lenses, and have a decent collection from 28mm up to 200mm (my 300mm just wouldn't cut the mustard so I am experimenting with using it for guiding).

[Kbramley]

I have the same lens too, picked up 2nd hand for £70, used it a few times on M45, M42 and M31 when at the darksite location. Appears to be reasonable for the price, and yes the focussing is tricky. I modded an old UV filter with some baader safety film so i can also now image sun spots on the move