Camera lens aperture question?

Question

Hello, i have a question about camera lens' aperture.

I recently got a job and am thinking about getting the Canon 70-200L F/2.8 IS USM or Canon 100-400L F4.5-5.6 IS USM...both have different apertures of course...however, I was on flickr the other day and was looking at the EXIF info and some say the pictures taken with the first one (i mentioned) has an aperture of more than F/2.8, and some say the aperture of a certain pictures taken with the Canon 100-400mm L lens are larger than 5.6. My question is, shouldn't the aperture of the pictures taken with the 70-200mm remain F/2.8 at all times and the aperture of the 100-400mm remains within the F/4.5-5.6 range? Some appears to have F/8 aperture...I'm confused...

Thanks for reading and answering this question, much appreciated.

Answer 1

Have you ever used an interchangeable lens?

Clearly, your budget exceeds your experience, so congratulations on making it through the interview and securing employment that allows on the job training.

Answer 2

Hold on a minute ... You got a job as a photographer?  Or am I miss reading your question?

First of all the maximum aperture has nothing to do with the aperture needed to expose the film or sensor properly at a given lighting situation or ISO or at a certain shutter speed.  This is what reciprocity is all about.  And the f/stop listed on the lens just tells us what the maximum aperture of the lens is, nothing else.

The reason to buy a 100-400 mm is not at all the same as the one to buy a 70-200 mm lens.

Here is a breakdown of the lenses I use most:

* 12-24 mm ... for landscapes, architectural and confined spaces (like sailing on a 45 foot yacht) photography

* 24-70 mm or 24-85 mm macro ... for general photography including editorial, fashion and some scientific work

* 18-200 mm VR ... for editorial shots indoors without flash.

* 105 mm macro VR.   For shooting subjects at predetermined subject to image ratios  ... 1:1, 1:2, etc.

* 400 mm f/2.8 and 600mm f/4 ... for shooting sports and other action shots or shooting wildlife at dawn or dusk when they are out and about.

I have many more specialty lenses and cameras that I use from time to time based upon the requirements of the assignments my photo rep finds for me.

Answer 3

The problem you are having is a misunderstanding about zoom lenses. Aperture marked on a lens only applies at ONE specific, fixed, focal length, not over the whole range of the zoom. Think about what happens as you zoom in from wide angle to narrow angle. The total area you have in view is decreasing and since the reflected light is about uniform over the area, as you zoom in, you effectively decrease the total amount of light entering the lens, effectively decreasing the aperture, i.e., stopping down the lens. This is only a concern if you are also manually adjusting the exposure time, i.e., shutter speed. If you leave the shutter in automatic, which virtually all digital cameras do, then the effective change in the amount of light is compensated for by the exposure time, possibly combined with the flash. In this case, the aperture setting marked on the lens now becomes more of a depth-of-field indicator, with the further down the lens is stopped, the larger the depth of field. The thing is, as with standard film, you are combining both aperture and exposure time to achieve a correct exposure  If you decrease aperture, you increase time. If you need a large depth of field, you stop down. If taking a portrait, you want the shortest depth of field so the background is blurred so you go with the widest you can, likewise if you want to stop motion. Short depth-of-field or fast motion both require shorter shutter times but for different reasons. Generally, lenses are rated by the best "cutting" point. This is where the lens has the best overall performance and least distortion. In most lenses this is at or near the middle of the range of aperture, usually either f5.6 or f8, So, with a zoom lens, you really can not compare things easily since there are variables you have no way of determining accurately. Most digital cameras also do NOT have an actual mechanical shutter, but rather electrically control the light sensing elements which is why it is advisable to let the automatic exposure control take charge. Light always falls on the light sensing parts, which is why digital cameras have a screen which shows you what the lens is "seeing" in real-time. With the automatic control in charge, you get a continuously variable shutter/exposure time which means it can control the amount of time like you can smoothly control the volume on a radio, without click-stops at fixed points, which will always give a perfect exposure. Exposure settings you see on digital video are there, but serve NO purpose other than to be a general indicator that you can compare with another video from the same camera under different conditions. It has no relation to any other camera than as a generaal guideline.

Answer 4

The aperture you listed is the widest possible for that lense.

70-200L F/2.8 refers to the fact that the widest it can open is 2.8 throughout the whole focal range (70-200) but still retains the whole aperture range.

100-400L F/4.5-5.6.

At 100mm the widest aperture is 4.5 and at the longest end 400mm the widest aperture is 5.6

The range in between also have their own widest aperture possible.

But they all can go the smallest aperture.

Answer 5

The aperture stated on the lens is the maximum aperture. You will have a wide range to choose from. I think the 70-200 can go all the way to f/32 but dont quote me on that.

You really need to take a course in photography. This information is really key to getting what you want out of your pictures. Your local community college will have something that will cover this. I am not trying to be condiscending but if you dont know the difference between a shot taken at f/2.8 and a shot taken at f/8 then you really need to do some reading at least.

Go here http://www.photonhead.com/simcam/shutter... play around a bit. You should see eventually what I am talking about. Every setting on the camera is relavent.

Answer 6

Hi. With regards to your question, here goes:

1. Aperture ratings that appear on lenses specify the largest aperture the lens is capable of. For lenses with constant aperture, like the 70-200mm F2.8 it means that it can keep the F2.8 aperture all through the focal range.

2. The 100-400L F4.5-5.6 means that at 100mm the maximum aperture is F4.5 while at 400mm the maximum aperture is F5.6. The aperture size changes with the focal range. Thus it is not a constant aperture lens.

3. All lenses are capable of getting aperture values that are smaller than their specified maximum value. i.e. the F2.8 lens can be set to an aperture of F4 or F6.3 or even F11 when taking shots. The thing with aperture is that the lower the number, the bigger the opening. Thus F2.8 has a bigger opening than F5.6. Logically all lenses can be set to have an opening that is less than its maximum value. The minimum aperture value usually range from F22 to F36

Hope that helps

Answer 7

man sounds like some people are jealous of people who are able to afford L series glass...hey if you can afford the best why not get the best?