stefang said:
What's this obsession with constant aperture? I love my 24-70 F/4, but would love it even more if it was a 24-70 F/2.8-4.0, even if quality dropped a bit at 2.8.
If you want to shoot at F/4, you can simply set the camera to do so. (Heck: it could even be a programmable option to not use a lens below it's highest maximum aperture)
? I'm not sure what you are saying about why people are obsessed with constant aperture.
A constant aperture lens like the EF 24-70 f/2.8L II can be set from f/2.8 all the way up to f/22. Constant aperture means the lens can maintain the set aperture throughout its zoom range. The aperture does not change as one zooms.
If at 24mm I set aperture at f/2.8 and then I zoom to 70mm because the scene has changed or I wish to adjust composition, the lens maintains the f/2.8 aperture. In this way the lens acts like a prime lens except that it zooms.
I like this because the light gathering ability of the lens doesn't degrade the more I zoom. For a person who shoots in manual mode 99.999% of the time... this is wonderful. I don't have to raise the ISO or shorten the exposure time just because I zoom. When I was obsessed with shooting birds, this was a fantastic thing.
However, one can still set the aperture anywhere one wants on the scale. It's just that the zoom with a constant aperture is like having a bag full of prime lenses.
Now, my dream is for Canon to come out with zooms that have a constant aperture beginning at f/1.4. Wow! The lenses would be huge, but wow! No more need for primes at all except for weight.
The constant aperture lenses cost more, but I think they are worth every penny.
Isn't your 24-70 f/4 a constant aperture zoom lens? Yes, but you can stop it down. What you are really saying is that you want an f/2.8 so that you can stop down to f/4. That is already available, at a higher cost... that may be your point. That you would give up the constant aperture for lower cost. F/2.8 costs money. There is no way around that unless you go 3rd party.
Tamron SP 24-70mm f/2.8 DI VC USD Lens is available for $1,199 at B&H with the $100 rebate. It has image stabilization (VC) that the Canon doesn't have. Dustin Abbott liked it in his review. He's a trustworthy reviewer.
The Sigma 24-70mm f/2.8 IF EX DG HSM Autofocus Lens is available for $749.00 when including the $150.00 instant savings. I have no idea how good it is. If any good at all it seems like a real bargain to me.
The Canon is spectacular.
Your post confuses me.
Your lens can do exactly what you are wishing for, except it cannot get wider than f/4. Get an f/2.8.