Hey Fast Glass. No, having this lens won't make more spare time, but when you DON'T have a lens, then even on the rare cases where you find time and go out - you can't take pictures.
Hey Fast Glass. No, having this lens won't make more spare time, but when you DON'T have a lens, then even on the rare cases where you find time and go out - you can't take pictures.
Yeah I knowhat you mean. Fortunatly I can take my lens to work and on the lunch brakes or when knowbody is looking I can take a few pictures.[]Having the right lens is absolutely crucialfor bird photography. The Minolta 600mm is a great lens but there are other even better lenses such as the Canon FD 500mm f/4.5 L, Nikkor 600mm f/4 (the Canon 600mm is not as good as the old Nikon),r the Canon FD 800mm f/5.6 L, or Canon FD 400mm f/2.8 Lwith extenders (it does really well with extenders). All of these lenses are under $2000 and some times under a $1000.
John.
Good to know FG, I'll check it out when I have time. What about the conversion to EF mount? what should I know?
Originally Posted by Oren
But in going from 5.6 to 4, presumably, even if you don't gain access to the 'cross type' points, more light coming in means AF will work better, and in dimmer situations, right? I mean, an f1.2 would be faster than anything if its focal plane weren't the depth of rice paper run over by a steam-roller.
Or am I misunderstanding something?
Daniel Browning says that you are:
No. Let me illustrate. Imagine you're in a dark room with no windows. There is only a two-inch pipe that you can peer through to see a tiny circle of the outside world. Now, hold a cardboard tube up to your eye and look through the pipe. You can still only see a tiny bit of the outside world. If the two-inch pipe was replaced with a much bigger pipe, say, one foot in diameter, you would have a much bigger view. But if you are still holding the cardboard tube up to your eye, it wont help. You have to get a bigger pipe *and* a bigger cardboard tube in order to see anything more.
The lens is the pipe and the tube is the autofocus sensor. Canon cameras only have two types of autofocus sensors: f/5.6 (small cardboard tube) and f/2.8 (large cardboard tube). If your lens is f/4, then your pipe is bigger than your cardboard tube. If your lens is f/2.8, then you can finally switch up to the larger cardboard tube. But f/2 and f/1.4 do not help because you are limited by the cardboard tube, not the pipe.
The way autofocus works is that the AF sensor only sees light from one tiny part of the lens
"But in going from 5.6 to 4, presumably, even if you don't gain access to the 'cross type' points".
I'd like to add a correction here - 5.6 AF sensors doesn't mean that they aren't cross type. All the AF sensors in my 50D are cross type for instance.
The worst problem is with wider lenses because they usaully have the reflex mirror shaved a little in order to get itclose enough to focus to infinity. Usually longer lenses you don't have to do this because you can file down the lens where you put your new mount to instead of the reflex mirror, or file or mill the the new mount. I have a FD 35mm f/2 S.S.C that I will convert and will figure out exactaly how to do it for FD lenses. My Minolta 600mm does not need any fillingso it is way easier to convert. Google "how to convert FD lens to EF" and you will pull up quite a bit of information.
John.
<div style="clear: both;"]</div>No. Let me illustrate. Imagine you're in a dark room with no windows. There is only a two-inch pipe that you can peer through to see a tiny circle of the outside world. Now, hold a cardboard tube up to your eye and look through the pipe. You can still only see a tiny bit of the outside world. If the two-inch pipe was replaced with a much bigger pipe, say, one foot in diameter, you would have a much bigger view. But if you are still holding the cardboard tube up to your eye, it wont help. You have to get a bigger pipe *and* a bigger cardboard tube in order to see anything more.
The lens is the pipe and the tube is the autofocus sensor. Canon cameras only have two types of autofocus sensors: f/5.6 (small cardboard tube) and f/2.8 (large cardboard tube). If your lens is f/4, then your pipe is bigger than your cardboard tube. If your lens is f/2.8, then you can finally switch up to the larger cardboard tube. But f/2 and f/1.4 do not help because you are limited by the cardboard tube, not the pipe.
The way autofocus works is that the AF sensor only sees light from one tiny part of the lens
Okay. Well. You may be right about there being no AF speed/accuracy benefit, I really don't know, But if not, it's not for the reason you listed: that argument by analogy doesn't hold at all.
The 'tube' is its main failing point. Not the only one, but the important one.
Let's put ourselves back in that little box, with the tiny little hole we can see out of. We place our eye up to the hole. On the other side of the hole, on the world-side, let's put something less tube-like and more lens-like. Let's say: a lens. It is the function of a lens to project a focused scene onto smaller area (film, sensor). The reason you can fit a mountain range onto a 35mm sensor is because incoming light rays from many angles are focused onto it in an ordered pattern. Given two lenses mounted in front of our little hole, say, two 85mm lenses, they both show the same scene. But if one has a larger objective lens (and consequently a wider aperture) then MORE light will be gathered from an identical field of view, which will be concentrated into our little hole, giving us more information. The less light is available, the less contrast information is present, and contrast information is, I believe, what AF sensors use to determine focus. So, knowing that more light per unit space all normal situations provides more contrast information, knowing that the AF sensor is a static size, and knowing that a wider lens of identical focal length will increase light intake we must conclude that a faster lens would shed more light on an AF sensor.
It is still possible that faster glass wouldn't make a difference in AF speed because of:
Decreased DOF (harder to focus on)
Engineering specifics of AF sensors that make certain quanta of like less useful
Something else entirely
But more light has to be hitting those sensors. Lenses are not tubes.
Good call. I was stuck in my little 5DII world.
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