Zoom lenses - Why pay more ?

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Anthony
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Im just starting off at home with some studio flash and there's room in my budget for a 70-200 zoom.

Most of my flash shooting is done at f8-f16. Given that do i need to spend a fortune on a fast lens of f2.8 ? If i were to how would i see that extra money in the images i took, over a lens that was f5.6 ?

Obviously with flash i won't struggle with available light, so are the optics that much better ?
 
It's agreed that at small apertures most lenses look sharp.

The primary reason for the expense, size and weight of the f/2.8 zooms is to give the option of f/2.8, for available light shooting and shallow depth of field.

If you want neither of these features and want to save some money, go for a variable-aperture.

Although... if you're shooting flash in a studio I'm guessing you're shooting portraits? If so, the option of shooting with shallow depth of focus is surely an attractive one?
 
Your right, it's for portraits and full length. Is there any noticeable difference in sharpness and detail due to the better quality of the optics. I can see why you might want a shallow dof, but that aside ?

So given two identical shots at the same f stop, say f8 would one look sharper and more detailed than the other ?
 
Don't forget when you look through the lens you see the brightness of the fundemental f stop. So if you have a low light situation then F1.8 is good 'cos you can see more due to the brighter viewfinder. If you have modeling lights then this may not be a problem. The benefit of shooting portraits at low F stops is the out of focus areas are rendered in a much smoother way, ie can smooth wrinkles etc.. which saves PP work. Uber sharpness in portraits may not be the most flattering thing for your subject and may adversely affect sales!
 
Beagletorque said:
The benefit of shooting portraits at low F stops is the out of focus areas are rendered in a much smoother way, ie can smooth wrinkles etc.. which saves PP work. Uber sharpness in portraits may not be the most flattering thing for your subject and may adversely affect sales!
Click to expand...

I feel it's much better to get sharp portraits then use an OOF layer in PP to selectively reduce wrinkles etc.

That way you have full control over the finished portrait.
 
At screen size and 6x4 prints, you're unlikely to see too much difference between a 1/2 decent kit zoom and an f/2.8 at the same apertures. Start zooming in a bit or printing larger sizes and it'll become more and more obvious. That's all before looking at the possibilities of shallow DoF etc that the wider apertures available with the f/2.8 offer and even those are eclipsed by the even greater effects when using wider primes.
 
Thanks for all that, the Ken Rockwell site was an interesting read.
I think i'll go halfway and get a Sigma 70-200 f2.8, they seem to have a good write up and are about half the price of the Nikon equivalent.
 
At higher f/numbers, the overwhelming influence on sharpness is diffraction. This is an optical effect, and happens regardless of the design or manufacture of the lens.

With crop format cameras, lenses reach their peak at around f/5.6, full frame is a bit higher at f/8. After that, they are all limited by diffraction. There is a bit more to it than that, but nothing significant in practise.

I think that for the comparison you are making there will be no noticeable difference between a medium quality lens and a premium grade lens at f/11-f/16. Both will be way past their best and essentially identical in terms of sharpness.
 
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