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56

The effect's name is parfocality, we are speaking of parfocal lenses. Lenses that change their focus when zooming are called varifocal lenses. Like reducing focus-breathing (change in focus also changes the focal length), parfocality is a premium-feature. Since photographers usually work with autofocus and since photographers tend to not recompose the image ...


52

How to zoom with Canon 77D with Canon 50mm 1.4 lens To zoom in, step forward. To zoom out, step back. It's often called zooming with your feet.


51

Who in the world buys large primes? Wildlife and sports photographers, mostly. I'm struggling to see how one would find use in a long focal length prime, 300mm and above for example: without zoom, isn't your shot composition always at the mercy of how close or far away your subject is, meaning heavy cropping is almost always necessary in post? It's the ...


44

Angenieux (for one) makes some f/2 zooms. They're used primarily for movie making. The Optimo 17-80, for example, is an f/2 (T2.2) lens, covering, obviously enough, the 17-80mm range. As for why these aren't common, consider that this particular lens weighs 11 pounds and costs about $50,000US. Going even more extreme would be the Optimo 24-290, which is f/...


40

You can’t. The 50mm f/1.4 is a prime lens, which means it has a fixed focal length, or fixed field of view. This is what some people call a “sneaker zoom” lens, where you as the photographer have to physically move to change what you see in the viewfinder. See mattdm’s great response in this question.


36

There is no simple relationship between the physical length of the lens and its focal length. For example, a retrofocus wide angle is generally longer than its focal length, while a telephoto lens is shorter than its focal length. Inside a zoom, you have several lens groups that move independently. The focal length of the zoom depends on the relative ...


36

You can't. I don't care what you've seen on CSI, this just isn't possible in the real world. Even taking Canon's ridiculously big (and now discontinued. Oh, and $100,000) 1200mm lens, The Digital Picture say: faces were recognizable at distances up to a mile or more However, you're talking about six times that distance. You could think about mounting a ...


31

These letters refers to zooming depth as follows, W = Wide angle T = Telephoto Read more about wideangle and telephoto in the tags.


31

You are not required to purchase any lenses at all. It all depends on your photography needs and what you're willing to spend your money on. Regarding range, the superzoom 18-200 mm covers the same range as the other four lenses you mentioned. All of the other lenses focal ranges are parts of the large range of the 18-200 mm lens. The 18-200 can surely ...


29

The answer to this question revolves around explaining how zoom lenses function because you are correct in your observation: As you zoom to higher and higher magnifications the image dims unless somehow compensation is applied. Suppose you zoom from 25mm to 50mm, should the working diameter of the aperture remain unchanged, image brightness would suffer a 4x ...


27

At 50mm on your 18-55, the max aperture is f/5.6. On the 50mm f/1.8, the max aperture is - obviously - f/1.8. It is perhaps not immediately obvious, but f/1.8 lets in 10-12 times more light than f/5.6. That is the difference between shooting at 1/10 second shutter speed (which is absolutely a no-go for moving subjects) and shooting at 1/100 (which is a ...


26

do most photographers avoid using zoom No. If "most photographers" avoided zoom lenses with variable aperture, there'd be fewer zoom lenses with variable aperture on the market. Furthermore, there are plenty of fixed aperture zoom lenses available at a range of focal lengths, so it's safe to say that photographers don't have to avoid zooms just to have ...


25

By specifying that you want to do your surveillance photography in "good sun light", you have already shot yourself in the foot. The best time to do this kind of photography is at night or in the very early morning before the heat from the sun has time to create the "thermals" that make extreme telephoto photography almost impossible, even with the very best ...


24

The 24-70 is an incredibly good lens - it's as sharp wide-open as just about any prime at every focal length across just about its entire field. But it's only 24-70. As you're talking about a full-frame Canon, that's as wide (16mm * crop factor of 1.5 = 24mm), but you'll be losing a lot of length at the telephoto end - your 90mm on APS-C is equivalent to ...


23

Presumably because the people who buy their first DSLRs mostly come from the point-and-shoot world and care about the versatility afforded by the zoom more than about image quality. Also, a 50mm is way too long to be a good "default" lens with an APS-C camera, and good-quality ~30mm lenses are, due to certain quirks of optics, much more complex (and thus ...


22

The short answer is because it is cheaper to manufacture such lenses. The longer the lens and the wider the aperture, the larger the optical elements in the lens - thus larger the expense to produce them. A lens like 70-200/2.8 must have a front optical element of 200mm/2.8=72mm, which is quite a chunk of glass. On the other hand, the 70-300/4-5.6 needs to ...


20

The entrance pupil is limited by the diameter of the front element, and that is what usually restricts the maximum aperture of telephoto zoom lenses - not the physical size of the aperture diaphragm. The physical size of the diaphragm is only part of what determines the maximum aperture, expressed as an f-number, of a lens. Magnification between the front ...


19

Image quality. The wider the range of focal lengths on one lens, the more design compromises are made and the more correction must be applied deal with things like geometric distortion, chromatic aberration, and light fall off in the corners. Aperture. Even though the EF-S 18-200mm f/3.5-5.6 has the same maximum aperture of f/5.6 as the EF-S 55-250mm f/4-5.6 ...


19

Provided your lens isn't a power zoom (fairly rare, these lenses have motors that drive the zoom mechanism), then no you will not damage either camera or lens.


19

The general consensus in this thread is that detailed photography of a subject at a range of 10km is exceedingly difficult, and probably impossible using commercially available equipment — and there's plenty of evidence to support that in the other answers. However, there is a way to photograph extremely distant targets in extreme detail — it's just not ...


18

The two generally control two different aspects of the image projected by the lens. Focusing sometimes has the effect of changing "zoom" a little as well, however its purpose is different. To keep it simple: Focus adjusts the Focal Plane The focal plane is the thin plane of reality that is focused clearly on the imaging medium Focusing moves this plane ...


17

A prime likely still has several advantages over a zoom at a given focal length. (Well, depending upon your needs and habits.) A less complex optical design. All else being equal, a less complex design is likely to have fewer compromises, which means the prime is more likely to have less distortion of any sort -- pincushion, barrel, coma, and chromatic ...


17

The only ethical ways to get closer is to either use a lens with a longer focal length ("more reach"), or to view them in captivity, such as in a zoo. Trying to get closer to wildlife will only stress them (which you have observed their reaction — to run away). Without stalking the deer, you can use the approach favored by hunters: be in places they are ...


16

Constant-Aperture Zoom Lens.


15

No, the lens does not zoom automatically. Almost all SLR zoom lenses are zoomed using the zoom ring, very few have a motorized zoom mechanism.


15

Provided you keep focus distance, ISO, aperture & shutter speed the same, and you zoom your 18-55mm lens to exactly the same focal length as the 50mm prime (which wont be exactly 50mm) then the images will very extremely similar when viewed as a whole. On closer inspection you will see differences in the level of distortion, sharpness, contrast and ...


15

The lens is not parfocal in either direction. What you have discovered is the difference between narrow Depth of Field (DoF) at longer focal lengths and deeper Depth of Field at wider focal lengths. The focusing error you introduce when you focus at 18mm and then zoom to 105mm is greater than the shallow DoF at 105mm even at f/8, so you notice how out of ...


15

It just means you push / pull the front of the lens to zoom, rather than twisting a zoom ring. The mechanism is simpler to design/manufacturer but is less precise and has a reputation for sucking dust into the lens due to the large change in volume when zooming.


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