All of the online calculators for exposure, I have seen, factor in time, film speed, and aperture (which is a function of the iris diameter and the focal length of the lens).   However I would have thought a lens with a larger diameter (with the same focal length and aperture) would collect more light and therefore be faster!  For example lets say I have a scene of a candle 10 meters (32 ft) away, with a black back drop. I have a 10 mm diameter lens, with lets say a focal length of 80 mm, an aperture of f/8 and 100 iso film.  This takes say 10,000 seconds of exposure. Now what if we get four 10 mm lens. Use some fancy arrangements of mirrors/prisms to have them focus on the one piece of film. That should take 1/4 of the time (2,500 seconds). Lets just ignore any image distortion for now.  Ok so lets say, rather than four 10 mm lenses we use one 20 mm lens (which would be the same area) I would expect that to take 1/4 the time as well.  However this doesn't seem to be take into account with any calculators I have seen.  Am I just looking at rubbish exposure calculators, or am I missing something?  Edit: This question specifically asks about lens diameter and Exposure. The duplicate linked questions, deal with exposure (not taking lens diameter into account or look at image quality and diameter. Neither of which deal with my question at all!
122952
I have tested two different 50mm lenses in my camera. One was a Nikkor 50mm ∅52mm. The other one was a Sigma 50mm ∅72mm. I took some pictures with both lenses using the same setup for aperture and shutter speed, but couldn't notice significant differences in the quality of the pictures.   So, how does the diameter affects the photo quality, if it does? What advantages would the ∅72mm lens have over the ∅52mm one?
73703
What settings of my DSLR camera will emulate the scene exactly as I can see through my naked eyes?  I think it's not possible to get the contrast and colors exactly as my eyes can see, and it may vary from person to person. So, I am more interested in focal length of the lens. If anyone can give more insight beyond focal length, I will be glad to know.  For example, if I am standing on the seashore and want to capture the sunrise, what should be the focal length so that I can cover the angle of view which my eyes can see, and so the size of the objects in the photo will be precisely like my eyes perceive it?  My camera is an APS-C Canon EOS 1000D. I have 50mm 1.8 and 70-300mm Sigma , Can it be achieved through this equipment lens? Till now, I have not achieved or been satisfied with what I see and what I get.
120374
I can understand that a zoom lens with a maximum aperture wider than f/2.8 would be difficult and costly, but it seems like something pros would kill for.  Surely it can't be more expensive (if its possible) than some of the $10k+ lenses and they exist to sell in limited quantities.  Is it just near impossible or is there another reason we don't see zoom lenses faster than f/2.8?
91451
This is a follow-up to a .  I've been comparing cycle times (or shot to shot times in single shot mode) of mirrorless cameras with interchangeable lenses with traditional DSLRs and all of them, even the highest end ones (like the Olympus OM-D EM-5 or Panasonic GH3) are slower than even entry level DSLRs.  How's that possible? The electronics should be the same and they don't have the burden of a mirror going up and down between each shot. I think that there must be a technical reason for that (maybe some cpu time is going to feed the live-view before the image is encoded?), because from a commercial point of view it does not make sense.  I've seen the cycle times under the performance tab in the reviews pages of .  The average CSC has cycle times around 0.7~1.2s, the flagship ones around 0.5s. The average DSLR has cycle times around 0.4s and the flagships around 0.25s.
19067
I just picked up photography a few months ago as a hobby (not planning to go professional at all), but will be getting good gear and glass over time. Right now I have a T3i, which I'm considering upgrading to a 7D or probably a used 5d Mk II next year.  For my next lens purchase, I'm considering a 70-200 L lens, I'm just not sure which one to go for.  I'm deciding between the 70-200 2.8 L with no IS, or the 70-200 f4 L with IS.  My thinking is the following:   While I do not plan to photograph weddings or anything like that, I do plan to use the lens to take pictures of my kid on school plays over the years, so I'm guessing the 2.8 would be useful there? He's not on school yet, but I hear flash is not allowed there? How would the f4 fare in such situations? I have the 18-135 kit lens with IS...I turned off the Image Stabilization on the lens, and was able to take decent pictures handheld with not-so-fast shutter speeds (1/15, 1/20's), although I do NOT have a good pulse. Would being able to do this translate well to using the 2.8 with no IS? Most of the shooting with the 70-200 will probably be done outside..just that case of shooting plays or a concert or too.   So..what should I do? Anything I'm not considering?
102372
I am trying to understand something that is really confusing me.  If I want to make a captured image brighter I can do this in many ways.  I can   Leave the shutter open for longer Make the aperture wider Increase the ISO Use a flash Do something else I have not considered   Which of these options is the right one?  How do I decide which of these things to do in which circumstances?
30242
Zoom lenses and cameras with superzooms are often sold with a times ("×") zoom number — like a 12x zoom or 30x zoom. The question  explains how this relates to focal length numbers, like 70-200mm or 18-55mm. But how does ×-zoom relate to magnification, when used for macro or just to make something far away look bigger?  How can two 70-200mm lenses have different magnification?
35825
I just bought a Canon 2X extender and I always believed that it would only result in 2 stops' loss of light and not change the aperture.    However, when I tested this extender on a Canon 135mm f/2 lens, the maximum aperture I could set went down to F/4.  So it kind of confused me, because if I step down the aperture to f/5.6, is it actually setting the aperture to f/5.6 or f/2.8 (i.e., 1 stop below f/2)?
109189
My  wasn't specific enough. I'll try to be more specific.  Let's imagine we have a hot body let's say 6000K hot that emits lots of thermal radiation. Let's assume 1kW of radiative power falls on on a m². Now if we use a lens with 1m² area, we can focus this 1kW into a smaller area which heats up until it radiates back the incoming power.   Now by using a lens with a smaller focal length, the image of the hot body can be smaller. So we can concentrate the radiation into a smaller area. The smaller the area you concentrate the power, the hotter that area becomes isn't it?   But I read in lot of places that this hot spot cannot be hotter than the body that that provides the energy, so in our example it cannot be hotter than 6000K, because it would violate the laws of thermodynamics. So what happens if you keep decreasing the focal length and size of the image? Maybe you cannot shrink the hot spot smaller than some size due to the wave interference and diffraction, thus ensuring this constraint?
5077
I'm reading that a 50mm lens is recommended as a first prime lens for DSLR owners as it's supposed to give a 'natural' perspective, but when used on (most) DSLRs, the view is cropped, as if you were zoomed in by 1.5-1.6x, so it's more of a telephoto lens when used on a DSLR. I've also read however that the 50mm lens gives the same perspective on a DSLR and a 35mm, and shouldn't really be considered to be 'equivalent' to an 80mm lens as the crop factor isn't really a magic focal length changer.  Can someone explain how the image is different from (for example) a 50mm lens on a DSLR and an 80mm lens (assuming 1.6x crop factor) on a 35mm camera?
6011
I wanted to get some cheap old lenses to use on my Nikon DX DSLR (D3100).  However, Nikon has one of the greatest flange distances of all manufacturers, which means that most lenses I can buy (M42 mount, etc) will not focus to infinity. I saw some adapters with correction lens to allow infinity focus, but also read they worsen picture quality.  Has anyone here used this kind of setup? (M42 cheapo old lens + adapter to Nikon with/without infinity focus correction lens)  If so, what can I be expecting, quality-wise? I read M42 lenses are not that bad, and I only have DX lenses, so I would not be expecting heavenly performance. Basically, I'd like a nice big tele lens (300mm+) and the ability to focus it to infinity.  Example pictures would be awesome, and particularly I'd like to hear some interesting opinions complemented by example photos of the setup I'm talking about — a picture is worth a thousand words.
6015
This week I've read two news stories about two different camera lenses that can magnify things that are very far away.  The first is the , which is a point-and-shoot camera that costs $600, has an 83x optical superzoom lens ("the same field of view as a 2,000mm lens on a full-frame camera"), and lets you see the craters of the moon.  The second is the , which weighs 36 pounds, costs $180,000, and can take portraits of people a half mile away.  A non-photographer might ask, "Why would somebody spend their life savings on a gigantic telescope of a lens when you could take far away pictures with a handheld camera for 1/300th the price?"  Well, I am basically a non-photographer, and I would like to ask that question. What does the big one give you that the little one doesn't provide? I understand that small changes in lenses can make a big difference in size and price, but this seems to be of a different scale entirely.   What is going on with the optics of the lenses that makes the small one able to be so small and the big one have to be so...big?   I'm trying to get a basic intuition for what makes lenses different, and I realize I don't understand enough about how lenses work to even know how to compare these apples and watermelons.
114801
Now that I am finally getting a fast zoom (Tamron 17-50mm 2.8) I've been considering a fast prime to go with it, specifically a Sigma 50mm 1.4. Despite its shortcomings, it still does really nice subject isolation past f/2, which is important to me. I was wondering if it might be redundant since my zoom is already a pretty fast fixed aperture. Of course, 1.4 is two stops faster than 2.8, but as with all primes you have to stop it down to get sharp results.   The main thing I am worried about is that if I drop $500 on a Sigma, it won't get used because there is already something O.K. in that range. Basically, is two stops difference enough to make you want to switch lenses?  EDIT: Perhaps I should add and as may have already been mentioned, these $500 could go to a nice speedlight which could sove the low-light 'issue' you get with f/2.8 vs f/1.4.
68019
How do lenses produce 2-dimensional images, if a lens bends all incoming rays of light to intersect at the focal point? Shouldn't this produce a single dot of light on a screen placed at the focal length?  This is basically the standard diagram that always shows up in textbooks:    I know this doesn't happen in real life--I used to use telescopes pretty frequently for work. The most in-focus image would be the one with the smallest diameters for the stars, which, of course, we think of point sources at infinity. But--the light from all stars (despite being at infinity) is not all focused at a single point. Instead, each star's light is focused at its own $(x,y)$ point on a 2D image.  I can't reconcile the theory as I understand it with any of my real-life experience with optics. What am I missing?
20546
I am looking for a prime lens to pick up, and I'm wondering if there is any difference between 35mm and 50mm in terms of the end product if I just stand back more with the 50mm. I use the Sony a6000 and am looking at the SEL50F18 and SEL35F18.  I understand that something like a fish eye lens will give a different effect, but is that what is going on in 35 vs 50mm? Or is 50mm effectively just taking a 35mm and cropping the center out (but with increased quality)?
31555
To take a good self-portrait, I'd look in the mirror, see the expression/angle/light I like, and... fail to capture it.  Any tips on exposure, positioning of the camera (e.g. relative to the eyes), focal length/lens to use.  What it boils down to:   What is the digital (optics, settings) equivalent of an eye? How do you position the camera in such a way, so that the image resembles what you would have seen? (elevation, angle, distance, focal length)   I am not talking about photographing through the mirror. The mirror is only a tool here.
5082
When should I use exposure compensation, rather than ISO, shutter speed or aperture?