Lenses and exposure

[jeffydan]

I have a beginner question :headslap:. Will all lenses set at the same settings shoot the same? If the camera is set at 35mm, f5.6, 1/80 sec, ISO 100 will the histogram be the same? Will my 18-55mm kit lens have the same exposure as a $2000 Carl Zeiss lens 24-70mm f2.8 at 35mm? Does the CZ lens let much more light in just like wide binoculars?

[Iguanasan]

I am by no means an expert considering I only own 3 lenses but I'll give it a stab based on what I Know.

Yes, those settings will generally get you the same exposure regardless of the lens, however, there are many other factors than the lens. For instance, if the camera is a 1.6 crop or a 1.7 crop, or a full frame camera, the image size will be slightly different. There may be a minor differences due to the clarity and sharpness of the lens but I would expect it to be negligible. Someone who knows better should let me know if I'm wrong.

The more expensive lenses are really more about resolving power. It's the level of detail that you get out of higher priced lens, not the amount of light.

One other thing to note is that the histogram is based on a JPG version of the RAW image as processed by the camera and it not 100% representative of the original scene.

[Andrew]

Stab 2.

35 mm is 35 mm no matter the lens. (note there is a difference in camera formats. FX, DX, 4/3 etc but that is due to what the camera does with the light after it gets there..)

f5.6 is f5.6 no matter the lens. It's a ratio of diameter to length and indicates how much light is getting to the film/sensor.
At the same f-stop the amount of light hitting the film/sensor from a kit lens comparable to an expensive lens is the same. If someone tells you he got a photo at 500th of a second at f8 then that setting on your lens will let in the same amount of light.

The differences in the lenses between the high and low cost are typically caused by the chemistry and purity, of the glass and the glass coatings used on them. Refraction of light causes blur whether by the inability of a lens, or arrangement of lenses, to keep it confined or on purpose as in DOF adjustments

Take a look at this and Google others. You can find as much detail as you can handle.


Camera lens - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Camera_lens)

[Marko]

Good answers here.
Exposures across different lenses will be identical. Sharpness, contrast and other factors related to individual lens resolution will differ but not exposure; which is simply the relationship between sensor sensitivity/film speed the size of the hole the light passes through in a lens (aperture), and how fast it passes through that hole by way of a shutter (shutter-speed) to get to the camera's sensor or film for any given quantity of light.

[thoughton]

In addition to the answers above (that the exposures will be the same, given the same settings), the expensive lens will also give you a brighter image in the viewfinder due to the larger aperture (don't forget that unless you are using some ancient fully manual lens the aperture is held wide open until you press the shutter). This can make a significant difference if you are shooting in gloomy conditions.

It may also allow your camera to autofocus faster and more accurately, again due to the larger wide-open aperture letting more light in.

[jeffydan]

Thanks for the reply guys. Makes sense now. I have an old Tamron 35-135 manual lens with the manual aperature. It's kinda fun to play with but I can't get my shots crisp.

[Marko]

Unless your lens is defective....it's probably user error in my experience
Keep in mind that if you are handholding your camera (regardless of subject) your minimum shutterspeed should usually be at least 1/60 for a shorter lens and perhaps 1/250 or more for a longer lens. This is because humans aren't still like a tripod and we can introduce our own movement into the exposure if the shutterspeed is too slow.

IF on a tripod and you are shooting a rock, any shutterspeed will do, since rocks don't move.
If you are shooting a person or animal though, then unlike the rock, it has a natural movement. Choose too slow a shutterspeed and shots won't be crisp. Choose a high enough shutterspeed and the shot WILL be crisp. For birds, which have very fast jaggedy movements you may well need shutterspeeds in the 1/500 to 1/1000 range and the shots should be sharp in the spot you focused on.......so long as the lens is not defective. Hope that helps - Marko

To make sure it's not the lens....tape some newsprint to the wall, put the camera on the tripod and test the various shuterspeed/aperture combinations assuring tack sharp focus on the newsprint....if the shots are sharp, it's not the lens.

[jeffydan]

Thanks Marko. I'm sure its user error but I figured more that I wasn't focused just right instead of shutter speed. I'll have to look at some of my shots and see if I had a lower than desired shutter speed.

[Marko]

No prob JD. If you wanted to post a coupla shots, we can be even more precise. If no zone in your image is sharp, this further supports my theory of too slow a shutterspeed.