Aperture Question

[SZLiao214]

Why do so many camera lenses i see have a fixed an aperture of 2.8?

 

[996GT2]

Originally posted by: SZLiao214
Why do so many camera lenses i see have a fixed an aperture of 2.8?

It's not a fixed aperture, but rather a constant maximum aperture throughout the zoom range of a lens. You can still change the aperture; most large aperture lenses have an aperture range of f/2.8-f/22.

This trait is especially desirable because it means that the exposure will not change as the lens is zoomed in/out. It also means that the lens will have the same light gathering ability at any point in the zoom range, which is a great attribute for sports/low light shooting.

Also, even though the aperture is constant, the actual opening in the lens is changing as the lens zooms. Aperture is defined as f/D, where f is the focal length and D is the diameter of the diaphragm opening. As the lens zooms outward, f increases, so D must also increase to maintain the same aperture. This is why long telephoto lenses with large apertures have extremely large front elements: the diameter of the aperture opening in a 400mm f/2.8 lens needs to be 143mm in diameter!

Less expensive lenses usually do not have a constant aperture because making a lens with a constant large aperture results in a larger, heavier, and more expensive lens (larger glass elements/more elements to correct for chromatic/spherical aberrations). Case in point: the Canon 18-55mm f/3.5-5.6 IS kit lens weighs a paltry 200 grams or so, but the 17-55mm f/2.8 IS weighs over 600 grams.

 

[Demo24]

slightly related, can someone explain why on most DSLR's these days you can't manually set the aperture on the lens? I'm aware you can do it in the camera settings, just curious why it gives me that error when I change it on the lens.

 

[996GT2]

Originally posted by: DEMO24
slightly related, can someone explain why on most DSLR's these days you can't manually set the aperture on the lens? I'm aware you can do it in the camera settings, just curious why it gives me that error when I change it on the lens.

Part of this is due to cost-cutting. Nikon, for example, removed the aperture rings in their "G" lenses to cut costs; this basically removed compatibility with older film cameras.

Another part of this is due to the automatic modes found in many newer cameras. For example, in Program Auto mode, the camera selects an appropriate aperture and shutter speed. Let's say that for a certain condition, Program Auto determines that 1/250 sec at f/11 will provide the ideal exposure. If you had a lens with the aperture ring set to f/5.6, for example, then it becomes a tricky point as to whether the lens setting of f/5.6 should override the camera's automatically selected aperture of f/11. This is why Nikon's older AF lenses with aperture rings had to be locked to their smallest apertures for the auto modes in the camera to work.

However, on any lens that has an aperture ring, you CAN set the aperture manually by putting the camera into manual mode and setting aperture/shutter manually. You have to do this with many older lenses; for example, old Zeiss glass mounted on a Canon EOS body.

Some higher-end cameras do give you the ability to set the aperture through the lens and not the camera in shooting modes besides manual. On the Nikon D200 I used to have, for example, you could set it so that the aperture was selected by rotating the aperture ring on lenses which had one (the camera would show the correct aperture in the LCD when you did this).

 

[SZLiao214]

Thank you very much for the thorough answer!

 

[fuzzybabybunny]

I've always wondered this about Nikon: how do you lock in the aperture on the lens when you take it off the camera? Like you stop the lens down to f/8 with the camera, you unmount the lens, and the lens stays at f/8 (instead of snapping back to minimum aperture), so that you can then reverse mount it or something for macro shots.

 

[troytime]

Originally posted by: fuzzybabybunny
I've always wondered this about Nikon: how do you lock in the aperture on the lens when you take it off the camera? Like you stop the lens down to f/8 with the camera, you unmount the lens, and the lens stays at f/8 (instead of snapping back to minimum aperture), so that you can then reverse mount it or something for macro shots.

i think you set the aperture, hit and hold the DOF preview button, then remove the lens while holding the DOF button.

regarding using the aperture ring, with my d80 in manual mode, i can't seem to change the aperture on my 1.8 50mm using the aperture ring. the camera will flash some error on the top lcd where the fnum is.

but on my other manual lenses, using the aperture ring is the only way. Its the 50mm that doesn't play nice. (unless reversed or extended)

 

[fuzzybabybunny]

Originally posted by: troytime

Originally posted by: fuzzybabybunny
I've always wondered this about Nikon: how do you lock in the aperture on the lens when you take it off the camera? Like you stop the lens down to f/8 with the camera, you unmount the lens, and the lens stays at f/8 (instead of snapping back to minimum aperture), so that you can then reverse mount it or something for macro shots.

i think you set the aperture, hit and hold the DOF preview button, then remove the lens while holding the DOF button.

regarding using the aperture ring, with my d80 in manual mode, i can't seem to change the aperture on my 1.8 50mm using the aperture ring. the camera will flash some error on the top lcd where the fnum is.

but on my other manual lenses, using the aperture ring is the only way. Its the 50mm that doesn't play nice. (unless reversed or extended)

This works on Canon, but it doesn't seem to work with Nikon...

 

[ElFenix]

you press the aperture pin/lever on the nikon g lens.

 

[Demo24]

Originally posted by: 996GT2

Originally posted by: DEMO24
slightly related, can someone explain why on most DSLR's these days you can't manually set the aperture on the lens? I'm aware you can do it in the camera settings, just curious why it gives me that error when I change it on the lens.

Part of this is due to cost-cutting. Nikon, for example, removed the aperture rings in their "G" lenses to cut costs; this basically removed compatibility with older film cameras.

Another part of this is due to the automatic modes found in many newer cameras. For example, in Program Auto mode, the camera selects an appropriate aperture and shutter speed. Let's say that for a certain condition, Program Auto determines that 1/250 sec at f/11 will provide the ideal exposure. If you had a lens with the aperture ring set to f/5.6, for example, then it becomes a tricky point as to whether the lens setting of f/5.6 should override the camera's automatically selected aperture of f/11. This is why Nikon's older AF lenses with aperture rings had to be locked to their smallest apertures for the auto modes in the camera to work.

However, on any lens that has an aperture ring, you CAN set the aperture manually by putting the camera into manual mode and setting aperture/shutter manually. You have to do this with many older lenses; for example, old Zeiss glass mounted on a Canon EOS body.

Some higher-end cameras do give you the ability to set the aperture through the lens and not the camera in shooting modes besides manual. On the Nikon D200 I used to have, for example, you could set it so that the aperture was selected by rotating the aperture ring on lenses which had one (the camera would show the correct aperture in the LCD when you did this).

I assumed it would cut costs, and thus why I am confused on those with the rings. I realize in any automatic modes it would cause problems but it won't let me set it via the ring even in full manual mode. This is what has always confused me.

I do have a Nikon btw.

 

[996GT2]

Originally posted by: DEMO24

Originally posted by: 996GT2

Originally posted by: DEMO24
slightly related, can someone explain why on most DSLR's these days you can't manually set the aperture on the lens? I'm aware you can do it in the camera settings, just curious why it gives me that error when I change it on the lens.

Part of this is due to cost-cutting. Nikon, for example, removed the aperture rings in their "G" lenses to cut costs; this basically removed compatibility with older film cameras.

Another part of this is due to the automatic modes found in many newer cameras. For example, in Program Auto mode, the camera selects an appropriate aperture and shutter speed. Let's say that for a certain condition, Program Auto determines that 1/250 sec at f/11 will provide the ideal exposure. If you had a lens with the aperture ring set to f/5.6, for example, then it becomes a tricky point as to whether the lens setting of f/5.6 should override the camera's automatically selected aperture of f/11. This is why Nikon's older AF lenses with aperture rings had to be locked to their smallest apertures for the auto modes in the camera to work.

However, on any lens that has an aperture ring, you CAN set the aperture manually by putting the camera into manual mode and setting aperture/shutter manually. You have to do this with many older lenses; for example, old Zeiss glass mounted on a Canon EOS body.

Some higher-end cameras do give you the ability to set the aperture through the lens and not the camera in shooting modes besides manual. On the Nikon D200 I used to have, for example, you could set it so that the aperture was selected by rotating the aperture ring on lenses which had one (the camera would show the correct aperture in the LCD when you did this).

I assumed it would cut costs, and thus why I am confused on those with the rings. I realize in any automatic modes it would cause problems but it won't let me set it via the ring even in full manual mode. This is what has always confused me.

I do have a Nikon btw.

Which Nikon do you have?

I don't know whether you can do this on the lower-end Nikon DSLRs, but I know that it was possible with my D200 and Sigma 24-60mm f/2.8 EX DG lens (which had an aperture ring, although it was quite small...almost an afterthought).

In the D200, there is a setting in the menu that will allow you to use the lens's aperture ring to set aperture instead of using the command wheel. I found this a hassle and always used the command wheel, but it was possible to have the lens's aperture ring do essentially the same thing (provided that you were using a lens with electrical contacts, of course) You should dig through the menu on your camera to see if the same setting is there.

If you're using a fully manual lens without electrical contacts, then you HAVE to use the aperture ring, but the camera will not display the selected aperture on the LCD screen because there is no way for the camera to know what lens is attached to it. In this case, you should open up the lens to max aperture for composing the shot, and then stop it down to the desired aperture before taking the shot.

 

[Demo24]

A D50, and I don't recall any such option. I doubt I would ever use it anyway as it's kind of a pain to do when I can just turn a dial.

 

[996GT2]

Originally posted by: DEMO24
A D50, and I don't recall any such option. I doubt I would ever use it anyway as it's kind of a pain to do when I can just turn a dial.

Nope, the D50 can't do this. It's kind of a moot point though, since most of the lenses that have aperture rings nowadays are old manual focus lenses, none of which will meter on any entry-level Nikon DSLR...so it's kind of a pain to use manual lenses unless you have a D200 or above.

 

[soydios]

You can't set the aperture on a Nikon G-type lens. The camera body mechanically controls the aperture.

FBB, you need a Nikon D-type lens. A D-type lens is compatible or can be made compatible with every Nikon F-mount SLR ever made.