2.8f vs 400 iso

[mediyoga]

Is there a diff in quality given a particular scene when we use 2.8 ( say on a tamron lens) and for those canon lenses which dont have this luxury we up the iso to 400? I have the 17-85 (max is 5.6) and the new 70-300 is ( max here again is 5.6).

I ask this because Tamron has released a new lens here is the link

http://www.photographyblog.com/index.php/weblog/comments/tamron_17_50mm_di_lens/

I was then analyzing the comparison between 2.8 and iso 400. Can some kind soul post a snap taken at F 2.8 and also the same at iso 400 with f 5.6 for comparison? thanks a lot
cheers:)

[cdifoto]

You can't really compare ISOs and apertures. There are upsides and downsides to each function. Higher ISO means more noise and wider apertures mean less depth of field. Sometimes even if you have a 2.8 lens you need a deeper depth of field because you might be shooting a group or something larger and you need the entire thing in focus...so you increase your ISO anyway.

Sometimes you're so desperate for light you up your ISO AND open your aperture.


That said, your camera is perfectly capable of producing quite clean ISO400 images.

[timmciglobal]

I really don't personally belive in F 2.8 being of that much value. If I want to shoot in low light it's going to be with a 1.8 or 1.4 prime.

The one issue which F2.8 is of course superior is high boken or blured background which most F 2.8 lenses will produce more of due to apature then say F4.

Keep in mind, F2.8 to F 5.6 is a wide change. Thats ISO 400 vs ISO 1600.

Tim

[mediyoga]

Thanks to all of you. Is it not then an advantage to have a 2.8 and the option of noise free 400 iso images? We can use any one or both when needed?
Krishna Raman

[timmciglobal]

Of course, just hard to find both :p

For example, I bought the 24-105 F4 IS because they don't make a 24-70 F2.8 IS and sometimes IS outweighs the extra stop, depends on what you shoot.

Tim