constant f2.8 - why is it important?

[snapper27]

Sorry, but I have to ask a beginner question-

I see that everyone likes and reccomends the zooms that are a constant f2.8., and all the expensive zooms have this ability.

Why? How does is affect picutres taken outdoors or with a flash if you are going the use a smaller aperture anyway?

I want to but a good starter lens for my 20d, maybe the tamron 28-75 but I want a little more zoom, so I am considering the canon 28-135, but this does not have constant 2.8. - what capabilty will I loose with the canon?

[Jarrad]

It lets you shoot at lower ISO, Faster Shutter speeds, more possible handheld shots, more control of depth of field, build bigger biceps and makes you feel like more of a man (or woman). :)

It can be the difference between whether or not you have to bring a tripod with you (depending on the lens and situation).

It's all about options and convenience.
You May or may not need the options at this time.... but you may in the future.

[Sean-Mcr]

Many people like shooting in available light (no flash), they may well need 2.8 for a certain condition (overcast day, low light in doors) and if they can't get that when they zoom out then they may well miss a shot because the aperture becomes too small. Flash is not going to light up a landscape, apertures going to do that

For that reason i'd never have a zoom lens that does not have a constant aperture.

well actually i have the kit lens (always forget about that) so i should say i'd never buy another lens that never had it

[lostdoggy]

Sorry, but I have to ask a beginner question-

I see that everyone likes and reccomends the zooms that are a constant f2.8., and all the expensive zooms have this ability.

Why? How does is affect picutres taken outdoors or with a flash if you are going the use a smaller aperture anyway?

I want to but a good starter lens for my 20d, maybe the tamron 28-75 but I want a little more zoom, so I am considering the canon 28-135, but this does not have constant 2.8. - what capabilty will I loose with the canon?

Zoom lenses that have variable aperature (non-constant) will change with change in focal length. Eg, 35-135 f/4.0-5.6, at 35mm the aperature will be f/4.0 and at 135mm the aperature will be f/5.6. Because of the change in the aperature, more light is needed or slower shutter speed for correct exposure.

[lostdoggy]

Many people like shooting in available light (no flash), they may well need 2.8 for a certain condition (overcast day, low light in doors) and if they can't get that when they zoom out then they may well miss a shot because the aperture becomes too small. Flash is not going to light up a landscape, apertures going to do that

For that reason i'd never have a zoom lens that does not have a constant aperture.

well actually i have the kit lens (always forget about that) so i should say i'd never buy another lens that never had it

That is not accurate. Some of us like our Bokeh and the larger aperature provides that. The other situation is when flash is not possible,eg church weddings.

[SkipD]

One good reason for the constant aperture lens is so that when you zoom you don't have to change (or concern yourself with changes to) the exposure settings on the camera. For somebody who's under pressure to produce with the camera - such as at weddings, news events, or sports - this is definitely a plus.

[grego]

Including what they said above, it also helps you blur the background and get rid of the distractions.

http://img99.echo.cx/img99/3999/crw2549rj3fj.jpg

Of course, the more you fill the frame with the subject, the more it'll blur out the bg.

[snapper27]

grego - is this photo shot at 2.8?

Compare the image if you took it with 2 lenses, a 28-70 2.8 shot at 70mm, f5.6 and the same scene shot with a 28-135 f4-5.6 shot at 70mm f5.6 - will the picutre look the same?

[drisley]

You will also get a brighter viewfinder image, and usually better AF, especially in low light with lenses that have a smaller f-stop.
So a constant F2.8 will give these benefits, as opposed to a lens with a variable aperture, or a constant, slower aperture.

[ron chappel]

Fixed aperture designs are kind of traditional for professional lenses.The main reason they started making them like that is so studio photographers could set the aperture and not have to worry about resetting the (complicated) lighting when they zoomed in and out.

They could design professional lenses to have a variable aperture but it doesn't cost a whole lot more to make them with constant aperture instead.Or to put it another way--adding this design feature to an allready expensive lens doesn't change the apparent price much.If they did the same to cheap consumer lenses the difference in price WOULD be noticable

[tim]

I might be nice to have a 70-200 F1.4-F2.8L IS.

(I guessed the wide open aperture).

[grego]

grego - is this photo shot at 2.8?

Compare the image if you took it with 2 lenses, a 28-70 2.8 shot at 70mm, f5.6 and the same scene shot with a 28-135 f4-5.6 shot at 70mm f5.6 - will the picutre look the same?

Yes, and I was pretty far away. That was my first time covering baseball for the newspaper. As I got more comfy(during the season), i moved in closer. But that was from the entrace(where the fence is, which is considerably far, considering the wide foul lines).

At the same distance, you wouldn't have the same amount of blur with a smaller aperture.

[DocFrankenstein]

I might be nice to have a 70-200 F1.4-F2.8L IS.

(I guessed the wide open aperture).
I can only imagine the chromatic aberrations at the wide end. :p

The constant aperture lenses are professional glass. They are *(supprosed to be)* shart wide open as well as stopped down and that's usually the case with the L glass. To get sharp, consumer lenses have to be stopped down to f/8

f/2.8 will let in 8 times more light than the f/8... it will also blur the background MUCH better.

And you also feel like da man, having that big heavy lens hang off your neck all day :lol:

[grego]

And you also feel like da man, having that big heavy lens hang off your neck all day :lol:

You do get a lot of questions and comments from people, I must say. So if you like attention, the lens is defintely an attention getter.

[tim]

If you want attention, try using a flash bracket and a LightSphere II. Everyone's a comedian when that thing comes out. Use it at the same time as the 70-200 F2.8 and you want have to say "look at me for the photo", everyone'll be looking already.

[Rob612]

I can only imagine the chromatic aberrations at the wide end. :p

What about the price ???? Somehow CA can be handled, but the price ? :(

[lostdoggy]

Fixed aperture designs are kind of traditional for professional lenses.The main reason they started making them like that is so studio photographers could set the aperture and not have to worry about resetting the (complicated) lighting when they zoomed in and out.

They could design professional lenses to have a variable aperture but it doesn't cost a whole lot more to make them with constant aperture instead.Or to put it another way--adding this design feature to an allready expensive lens doesn't change the apparent price much.If they did the same to cheap consumer lenses the difference in price WOULD be noticable

It took a long time after zoom lens was introduce before studio photographer accept them because of image quality not because of the variable aperature.

As far as cost I can't argue on the point of R&D and Manufacturing, but market cost is a different story.
1. A EF 75-300 f/4-5.6 IS USM goes for $400
2. A EF 70-200L f/4 USM goes for $600
3. A EF 70-200L f/2.8 USM goes for $1200
4. A EF 70-200L f/2.8 IS USM goes for $1600

If #1 is an inexpensive lens and #2 is a relatively expensive lens and #4 is very expensive lens. Can you explain how the cost increase by $1200??? and how is it not noticable???

[DocFrankenstein]

If #1 is an inexpensive lens and #2 is a relatively expensive lens and #4 is very expensive lens. Can you explain how the cost increase by $1200??? and how is it not noticable???
I think what's meant is that you'd notice the increase in price of the consumer zooms...

The problem is that physics has it's laws and R&D guys have their specs and limitations.

Imagine building a 70-200 and you're constrained by:

Maximum diameter of the back element - EF mount constraint
Mirror box - can't be too close to the film
Weight - it has to be handholable
Front element can't move, can't rotate
Has to be internal focusing
For focusing, you can't have lots of glass moving inside, it'll slow down the AF speed
You have to fit in a motor somewhere
The lens has to be sharp
The cost should not be astronomical
The manufacturing process should be as simple as possible...

I'm sure there are tons more limitations. I'm surprised 70-200 work as good as they do.

And you can't really make the lenses go any faster than they can. IE if you have 200/2.8 at the long end... you theoretically have enough light entering the lens to make it 70/1.0

And that's just not happening... not if we want to cover full frame sensors.

Minolta or whatever, managed to make an f/2.0 zoom recently and there was some fuss about that. But what's the point?

When your system is to cut out "four thirds" and leave only a quarter of the chip, you can come up with something... but you're gonna have tradeoffs.

[BearSummer]

Hi snapper27

Sorry, but I have to ask a beginner question-

I see that everyone likes and reccomends the zooms that are a constant f2.8., and all the expensive zooms have this ability.

Not all expensive zooms have this ability, just have a look at the EF100-400 F4.5-5.6 IS L, most people who have used it will rave about it. yet it has a variable aperture depending on the zoom level and its not the cheapest of lenses :)

Why? How does is affect picutres taken outdoors or with a flash if you are going the use a smaller aperture anyway?

Smaller apertures will cause the depth of field to decrease making objects close to you subject to get blurrier quicker.

I want to but a good starter lens for my 20d, maybe the tamron 28-75 but I want a little more zoom, so I am considering the canon 28-135, but this does not have constant 2.8. - what capabilty will I loose with the canon?

The 28-135 f3.5-5.6 IS L is a very good lens, it also has image stabilistaion which allows you to hand hold the lens at slower shutter speeds (you should have your shutter speed be at least 1/zoom level of the lens (eg a 200mm lens shouldn't use a shutter speed slower than 1/200 or you might get camera shake)) so instead of having 1/30 as your slowest shutter speed with this lens you get two extra stops with the IS and can hand hold it at (28/(2*2)=7 which is roughly 1/8 of a second).

All the best

BearSummer

[Sean-Mcr]

That is not accurate. Some of us like our Bokeh and the larger aperature provides that. The other situation is when flash is not possible,eg church weddings.


I never spoke of Bokeh that is correct, but i did mention where a
constant aperture when zooming may well be needed, like indoors in low light (i spoke of available light) and over cast days. Reasons just as valid as Bokeh i have to say, so i'd not say incorrect just yet another reasons why constant aperture is a good idea

[ron chappel]

I might be nice to have a 70-200 F1.4-F2.8L IS.

(I guessed the wide open aperture).



It does sounds like a GREAT lens doesn't it?!;) ;) :D
Unfortunately i don't think it works quite like that but i can't explain why at the moment .I vaguely remember it's something to do with the constant aperture pro lenses allready using the front element to it's maximum potential... so that if the design was changed to be a variable zoom of (about) f1.4 at 70mm to f2.8 at 200mm then the front element size (at least) would have to be scaled up.
...Or i could be talking utter rubbish:) .I'm abit off tonight so i can't think very well:oops:

It would be facinating to ask someone that knows about these things

[AXENA]

It does sounds like a GREAT lens doesn't it?!;) ;) :D
Unfortunately i don't think it works quite like that but i can't explain why at the moment .I vaguely remember it's something to do with the constant aperture pro lenses allready using the front element to it's maximum potential... so that if the design was changed to be a variable zoom of (about) f1.4 at 70mm to f2.8 at 200mm then the front element size (at least) would have to be scaled up.
...Or i could be talking utter rubbish:) .I'm abit off tonight so i can't think very well:oops:

It would be facinating to ask someone that knows about these things

I asked this very same question to a pro-photog who has been shooting over 40 years. His response was very similar to yours. In order to obtain that type of setup in a lens, the front and middle elements would need to be SUBSTANTIALLLY larger, and of the highest quality. Therefore, one would end up with a lens that looks like a large telescope and would weigh in at around 8 pounds with glass that would rival a NASA Observatory Telescope tracking asteroids. That would put the price somewhere in the range of $8-10,000 for that lens. Ummm... personally, I think it would be easier to buy the primes with the large aperatures and deal with swapping lenses. But hey, that's just me. I could use the extra 10-grand to buy the rest of the L-glass in the lineup and have enough for a second 20D body as a backup. Of course, this is all in theory, and includes Canon's mail-in rebates!

Would be a neat lens though!
-GSL

[AXENA]

Oh.... BTW..... a STOBOFRAME with a 580EX on it causes INSTANT attention.... no need for white lenses. At almost every ball-game I shoot, I get the same questions from players and fans alike.... "what paper are you from?" or "are you the league photographer?"

I've gotten more jobs this way, with the flash being in the OFF position! Just have it mounted.... people do get awestruck from silly frames and bulky flashes. I also notice a lot of fans looking at their P&S or DRebels and thinking... "hey... howecome my camera doesn't look like that?" If they only knew that $70 gets them that "pro-look".... but that's why they all use their built-in flashes and get "snapshots" and not professionally done photos. But that's our secret..... unless they find this forum that is... :-)
-GSL

[MarkH]

Sorry, but I have to ask a beginner question-

I see that everyone likes and reccomends the zooms that are a constant f2.8., and all the expensive zooms have this ability.

I want to but a good starter lens for my 20d, maybe the tamron 28-75 but I want a little more zoom, so I am considering the canon 28-135, but this does not have constant 2.8. - what capabilty will I loose with the canon?

The 20D has a full cross-type AF (for apertures down to f5.6) at the centre which has a high precision mode available, but only when using a lens with a max aperture of 2.8 or better. So a lens like the 28-135 will give good focusing performance, but not as good as a f2.8 lens.

If you want to use the high precision mode of the centre sensor on the 20D then you need the f2.8 lenses, but the AF works pretty well even when not in high precision mode.