Sigma 24-70 f/2.8 for Nikon questions

[dallas75287]

Just received this bad boy. Wow! It's huge compare to 18-70 D70s kit len. Quick questions concerning setting the exposure mode. Here's a quote from the instruction manual,
When you use the Program exposure mode or Shutter speed priority auto mode, the Diaphragm control ring must be set to the smallest F-stop(i.e. largest number). All Nikon AF/MF and Minolta MF lenses have a safety button which should be moved to the lock position (fig2). When you use the Aperture priority auto mode or Manual exposure mode, unlock the button and set the Diaphragm value by turning the ring.
I use Aperture priority mode quite often. Why would I want to change the Diaphragm value? What is it for? Can I just keep it lock at the smallest F-stop? What would happen if I don't change it when in M or A mode?

Thanks.

[coldrain]

The diaphragm is the same as the aperture. Aperture is just the word used in English, we use the word 'diafragma' (nederlands).

The ring is for 35mm film DSLRs that do not have a dial on the camera to change the aperture. Since the lens is also usable on full frame 35mm film SLRs from Nikon, it offers that ring. A bit confusing of course, but now that you know it does not have to be confusing anymore. Just keep the ring at the smallest aperture value, and the lens will work fine with your camera.

[rawpaw18]

If you can lock the ring in place, then it should work like your 50mm does. Have you tried it yet?

[dallas75287]

I played with it last night. It's good so far! It didn't have any problem focusing. Thanks Coldrain for the information.

[Stoller]

A fixed aperture lens is the way to go. I am so happy with my Sigma 70-200mm F2.8, it performs awesome. It also must be locked in the smallest F stop position. I recently purchased the 17-70mm F2.8-4.5 and I am not real happy with it. In low light conditions, I have to adjust ISO, shutter speed or aperture when I change the focal length. Going from 17mm to 70mm is just like turning down the lights. You can see it through the view finder. I find myself taking pictures at 17mm to take advantage of the F2.8 and cropping them later. I might as well have got a fixed focal length lens. With my Nikon 18-55mm F3.5-5.6 you don't notice the variable aperture so much and I have never had to change ISO because I zoomed in or out. I guess I'm just bummed I did not get the lens you got. I will always try to stay to fixed aperture lenes in the future.

Share some samples when you get them. ;)