f2.8 vs. f4

Possibly To get back to the original question:
f/2.8 Pros: Better AF, shallower DoF, brighter VF, 1 stop faster SS.
f/4 pros: price, weight.
The 'quick and dirty' answer would be: 'If you'ld need it you'ld know'

I was debating in another thread whether or not the 300 F2.8 L IS was worth 4 times as much as the 300 F4 L IS. For a pro shooter who can make it pay then yes. For a multi-millonaire then yes why not. For the rest of us NO F*@**@ WAY!!!

Similarly I don't think the 16-35 F2.8 L is worth twice as much as the 17-40 F4 L

but if shallower DOF,better AF,better to stop action with,are the pros of a f2.8 lens,how is it most 'wildlife lens'(eg.100-400,500 etc)start with at least f/4?
after all,you do want to stop motion(arent animals moving most of the time),shallower DOF(to put the creature in sharp focus with a very blur backgd)and faster AF,to capture the action asap?

I am very confused on this issue as well. f/2.8 is double the price of f/4, but is the difference in light worth THAT much of a difference?

On the kit lens, and this probably isn't even a fair comparison, f/3.5 and f/5.6 yield me only one quicker shutter stop. Even at the same shutter speed, the amount of light was noticeably brighter at f/3.5 but nothing to justify that sort of price, especially when it didn't even yield me a much higher shutter stop.

Would it not be better to just get a slower IS lens? The IS would take care of the light since you can have longer exposures.

Bah, now that I think about it, I think I see why. The quicker lenses will allow you to use faster shutter speeds to "freeze" the action while still sucking in sufficient light. IS would just allow you to lower the shutter speed to get your light which could easily end in a blurry subject.

Still though, I'd like to see a comparison of the same scene with an f/2.8 and a f/4 with the same shutter speed, just to see how much more light you are actually getting.

If you have the 50mm f/1.8 you can do that yourself. Not being smart...I don't know what you actually own....I'm just too lazy to set it up and do it.

cdi-ink.com wrote:
If you have the 50mm f/1.8 you can do that yourself. Not being smart...I don't know what you actually own....I'm just too lazy to set it up and do it.

Well would ya look at that, just put my "equipment" in my signature.
But like said, I tried the test with f/3.6 to f/5.6 with the stock lens. I certainly was not convinced. The amount of light was useless, only yielding me one quicker shutter stop which was hugely unnecessary at 18mm when I could easily shoot at 1/8.

Perhaps it's the focal length. Maybe at 200mm f/4 and f/2.8 make a huge difference, but at 18mm, bah!

My question, for the cognescenti here, is similar to one asked above, but more to the point.

Putting aside the difference in light gathering ability and its benefits, if you took the 300 f2.8 and the 300 f4 and used both at f8, would there be an appreciable difference in picture quality?

thanks
mark

1/8th shutter speed versus 1/15th or so isn't really going to change much. HOWEVER...if you're shooting sports, it can mean the difference between 1/250th (not really enough to freeze tennis) and 1/500th (enough to freeze at least most portions of tennis). Focal length has nothing to do with freezing action...although it can have an impact on camera shake.

At f/8...probably not. BUT these lenses aren't purchased with the intent to stop down anyway...they're built to use wide open and achieve superb results. You can take a fairly cheapo consumer zoom and stop down to f/8 and get good if not excellent results.

Your experience is not typical of high school indoors sports. I have found that f/2.8 is often not fast enough to freeze action. I tend to use f/2 or faster glass for high school indoor sports. There are a couple of gyms that I can push to 3200 ISO and shoot with my f/2.8 glass. I did some of that today and the results weren't as good as the faster glass. I think that f/2.8 is fine for college and above. I just shot a college game saturday and using a 70-200 IS wide open at f/2.8, I needed to go to ISO1600 to properly expose. And, there was full TV coverage by 4 networks at this game. So, I think the high school you refer to has an unusually bright gym.

All of that said, it really depends on what you intend to shoot. Often, around the house shooting candids, f/2.8 still isn't fast enough and I use flash. But, the f/2.8 will let you keep from getting the flashed out look you might get when your background isn't exposed properly.

I think you're prolly right. I was really quite amazed by how much i get out of the f/4 glass without flash.... BUT, f/4 was really at its limit... i was shooting iso1600 (without flash).
Perhaps if anyone's interested, please click on this link to check out the best ones i got from the game...
http://www.pbase.com/i​ncredirebelz/

overall, I managed to snap quite a few actions and was happy with what i got... (i m easy to impress tho)... so i think overall, the f4 lens for sport is NOT ideal, but nothing like mission impossible either...

That's because they're all long lenses.
You may have noticed Canon did produce a 50/1.0; 85/1.2 and even 200/1.8 once, but longer lenses get slower: 300/2.8; 400/2.8; 500/4.0.
That's because the aperture is the relation between focal length and width: The longer the FL, the larger the opening needs to be for the same f stop. That's why these fast lenses require massive pieces of glass.
Also it means that the bayonet on the camera becomes a limiting factor. I don't think it's possible to make a 50mm lens faster then 1.0 using this bayonet. Simply no room...
Also longer FL's give shallower DoF, so at 500mm you get pretty shallo DoF with f/4. With a 28 mm you might want too use f/2.8 to get any kind of shallow DoF.
And yes, in some cases the extra stopp is worth twice (or more) the price. It might make the difference between getting the shot, and getting a blurry mess. OTOH, you can always get a decent prime, which will probabely be half the price and twice the speed of a zoom.

so then,a quick summary,anything else that could be appended to the list?

Yes, that's a pretty good summary to generalize.