Focal Length VS Photo distance

[Littlebike]

I had a rep from Sigma tell me that when using a lens of a given focal length I should not expect to get stallar results unless I am approxiamtely 50 times the focal length from the subject.

Focal length x 50 = sweet spot

70mm x 50 = 3500mm = 3.5m = 11.5 feet

So to get best results from my 70mm setting on my zoom I should be 11.5 feet or furhter from my subject.

Has anybody ever heard of such a thing? I am being a bit disgruntled about the quality of photo I am getting from my Sigma 24-70 2.8 ex.

At first i thought it may be my body but now I am thinking it may be my lens, I borrowed a Canon 50 1.4 and the focus is incredible! I have never seen an image come from my camera that looked so good!

[Roger_Cavanagh]

I've never heard that. Doesn't mean it's not true, of course, :D but it does sound like salesman's flummery to bamboozle a somewhat dissatisfied customer. I used to own the previous version of this lens - the 28-70 - but I didn't like the results when I first got the D30. Pictures were very soft. It sounds like your lens performs the same. Of course, zooms are always a some disadvantage compared to primes, and the 50/1.4 is, by all acounts, a very fine lens.

It comes down to how much you want to pay for your lenses.

Regards,