Canon 70-300mm Zoom lens

[valleyman]

Can somebody give me the benefits of using this type of lens on a Canon 1000d for astrophotograph. What are the advantages and disadvantages, assuming it was piggybacked onto my OTA, (not the dob)

[Psychobilly]

Advantages...

Range of focal lenghts so plenty of choice of FOV...

Cheaper than a bag full of primes

Disdvantages...

Zooms (unless you go upmarket) will generally perform worse than primes... I had the 70-300 but bit the bullet and went for the 70-200 f4L which is a completely different animal but significantly more expensive... The 70-300 was OK on the 1000D but didnt "cut it" on the higher MP 500D

Need to make sure that the zoom is locked during exposure (focal length doesnt change) - bit of tape or blutack sorts thius out...

Zooms tend to be a stop or more slower than the equivalent FL primes...

Billy...

[StevieDvd]

I have a Sigma zoom up to 300mm and wondered what sort of images that would give - just clouds at the moment. Though not as good quality as the Canon lens I'd guess.

I intend to try it out when the skies clear up a bit.

[TJSnapper]

Are you talking about the DO version or the normal one? My GF had a copy of the normal one and I didn't rate it for contrast or sharpness but I am quite fussy about such thinks

[valleyman]

Was thinking something along these lines

Cannon Ef lens 90-300mm 1:4.5-5.6 on eBay (end time 12-Feb-11 19:44:47 GMT)