A variety of lenses for the T2i

TheOpusFuller

TheOpusFuller

I know zilch about lenses. Wondering if some lens techies can fill me in on the following lenses.

Canon EF 35-105mm f/4.5-5.6 Zoom Lens
Canon EF 75-300mm f/4-5.6 Ultrasonic (USM)
Canon EF 100-300mm f/4.5-5.6 Ultrasonic
Canon EF 100-300mm f/5.6 Macro zoom lens
Canon EF 20-35mm f/3.5-4.5 Ultrasonic
Canon EF 22-55mm f/4-5.6 Ultrasonic

Wondering if they are beneficial? What the price range for each of these is going for. How much would you pay for them, etc.

Any and all help is appreciated.

Thanks guys!
 
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Ernest Worthing said:
Was ur answer that a slower lens like 2.8 fully open will not have the same shallow dof as a 1.4 fully open?
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Indeed! The key portion is:

The aperture determines how collimated the admitted rays are, which is of great importance for the appearance at the image plane. If an aperture is narrow, then highly collimated rays are admitted, resulting in a sharp focus at the image plane. If an aperture is wide, then uncollimated rays are admitted, resulting in a sharp focus only for rays with a certain focal length. This means that a wide aperture results in an image that is sharp around what the lens is focusing on and blurred otherwise.
WiKi
Click to expand...

So, it means I can MANUALLY control how wide the aperture is open using T2i menu, can I?
 
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There is one unclear moment I find strange.
Wide aperture (say f/1.4) = shallow DoF.
Long focal length (even with standard kit lens) = shallow DoF.

Zoom lens (even with slow one like 55-250mm f/4-5.6) at its extreme focal length actually reduces the aperture. Why then DoF is there?
 
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Re-Maker said:
There is one unclear moment I find strange.
Wide aperture (say f/1.4) = shallow DoF.
Long focal length (even with standard kit lens) = shallow DoF.

Zoom lens (even with slow one like 55-250mm f/4-5.6) at its extreme focal length actually reduces the aperture. Why then DoF is there?
Click to expand...

There's a range in which objects are in focus. If you position your subject far enough from the background and/or stand far enough from the subject as well, you will get a blurry background once again.
 
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Re-Maker said:
There is one unclear moment I find strange.
Wide aperture (say f/1.4) = shallow DoF.
Long focal length (even with standard kit lens) = shallow DoF.

Zoom lens (even with slow one like 55-250mm f/4-5.6) at its extreme focal length actually reduces the aperture. Why then DoF is there?
Click to expand...

Because the aperture number is a ratio of lens opening diameter to lens focal length. On the zoom you referenced, f4 at 55mm is a certain size opening. When you take that lens to 250, the widest the hole can physically open is only f5.6 relative to the focal length of the lens. This causes rays to hit the image plane at a straighter angle, meaning more of them fall within the CoC, and thus in focus. If you were using a 50mm f.28 prime, and a 250mm f2.8 prime, you would notice a very strong change in DoF between the two lenses.

That's an oversimplification. DoF changes are non-linear.

Given the same parameters except for the ones changed, DoF changes occur most rapidly at the top of this list, and least rapidly at the bottom:

Distance to subject. Changing this variable will widen or shorten your DoF the fastest - or rather the most change on the output side of the equation. This creates the illusion of wider field with longer lenses because of the tendency to move back when using them.

Focal length is in the middle, changing this will change DoF characteristics rapidly but not as rapidly as subject distancel. If you leave camera in the same place, the subject in the same place, and all other variables stay the same.

Aperture changes have the smallest effect on DoF, from a mathematical perspective.

A great way to demonstrate this is to have an actor walk into the lens, any lens. You'll note that as s/he approaches the CF distance (near focus on the lens) the DoF becomes very shallow, even at a wide focal length like 25 or 18mm. Do this test at a couple of different apertures to really see the difference that subject distance can make.
 
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David.rhsc said:
Because the aperture number is a ratio of lens opening diameter to lens focal length. On the zoom you referenced, f4 at 55mm is a certain size opening. When you take that lens to 250, the widest the hole can physically open is only f5.6 relative to the focal length of the lens. This causes rays to hit the image plane at a straighter angle, meaning more of them fall within the CoC, and thus in focus. If you were using a 50mm f.28 prime, and a 250mm f2.8 prime, you would notice a very strong change in DoF between the two lenses.

That's an oversimplification. DoF changes are non-linear.

Given the same parameters except for the ones changed, DoF changes occur most rapidly at the top of this list, and least rapidly at the bottom:

Distance to subject. Changing this variable will widen or shorten your DoF the fastest - or rather the most change on the output side of the equation. This creates the illusion of wider field with longer lenses because of the tendency to move back when using them.

Focal length is in the middle, changing this will change DoF characteristics rapidly but not as rapidly as subject distancel. If you leave camera in the same place, the subject in the same place, and all other variables stay the same.

Aperture changes have the smallest effect on DoF, from a mathematical perspective.

A great way to demonstrate this is to have an actor walk into the lens, any lens. You'll note that as s/he approaches the CF distance (near focus on the lens) the DoF becomes very shallow, even at a wide focal length like 25 or 18mm. Do this test at a couple of different apertures to really see the difference that subject distance can make.
Click to expand...

Or that. :lol:
 
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sonnyboo said:
The lower the number, means the "faster" the lens, which means it takes less light to get a good exposure with those lenses.

F4.5 and higher are light hungry, and even with this great camera, might be a little too slow for video. I'd be leery of anything that slow for video.
Click to expand...

Sometimes you want slow. Greater depth of field. Lots of people choose to shoot at f8 and above, for this very purpose. My outside daytime shots have been almost exclusively on f13.

The following clip was shot with a low f-stop, because I wanted relatively shallow DOF:

http://www.youtube.com/watch?v=2-T4NFBiu4A

However, the vast majority of my shots at this location, with this light setup (a single 400W bulb) have been shot on f8, and they look EXACTLY like this, but with a wider DOF.
 
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