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 ...


21

There have been stories for years of mail order (and now online) retailers that pull a scam that goes something like this: You respond to an ad for an insanely low price on a lens. They accept your order and bill your credit card. A few days later they contact you to say the exact lens is out of stock, but they will sell you the upgraded version for only $$ ...


21

The twisting motions you apply to focus and zoom rings are converted to forward and backward movement by helical threads and tracks cut into the barrels inside the lens. This photo shows an example of the threads that do the focusing duties in a partially-disassembled Nikkor prime: Note the tracks cut into the inner barrel and the metal rails in the outer ...


19

The focal length/speed is only one factor in the retail price of the lens. Other goodies like construction (metal vs. plastic), image stabilization (and other automation in general) and vintage can easily add (or remove) a zero. The two lenses in the question are very different products. The 2.8G is a newer product and lacks an aperture ring - the diaphragm ...


13

A lens that maintains the same distance of focus as it is zoomed is said to be parfocal. This is a highly desirable quality in a lens if one is shooting film or video and wishes to maintain focus while zooming in or out during a continuous shot. Some zoom lenses that are not really parfocal, particularly those with smaller maximum apertures, can appear to ...


12

A simple lens (like the lens in a pair of glasses) forms an image at a distance of f behind the lens for an object at infinity (where f is the focal length). The same lens will form an image at 2f behind the lens for an object 2f in front of the lens. This will achieve 1:1 magnification, i.e. the definition of macro. Thus any single element lens is a macro ...


7

The "elements" and the "blades" are two completely different things. An "element" is a single piece of glass in the lens. Most of what's shown on the diagram are the lens elements. Some elements are colored pink, to indicate that their shape is aspherical. Other elements are colored blue, to indicate that they are made of a special type of glass. Others are ...


7

Sadly, you can't, without taking them apart to find out. Unfortunately, it's not reliable to assume anything about the construction of photographic equipment. Even if two instances of what is marketed as the same lens contain optically identical elements, which isn't always guaranteed, you may find that a bevel on the edge of a particular element (or ...


6

For the most part, there is no way to predetermine the quality of a lens's bokeh simply by looking at its construction, and even if you look at sample images you may be flummoxed, because the quality of the bokeh can change with the aperture setting as well as with the subject and background distances. For example, the whole "number of blades" thing where ...


6

Never heard of that. While disproving it 100% is impossible, I would be extremely doubtful if Canon make lesser L-lenses. Most likely you are dealing with a shady vendor and you should avoid them. The difference between local and imported versions is usually in the scope of the warranty and documentation language. Know that an import version is local ...


6

According to a related discussion on dpreview: A lens can be made physically shorter than its focal length by the use of additional lens elements called a telephoto group. According to the Wikipedia page for Telephoto lens: The basic construction of a telephoto lens consists of front lens elements that, as a group, have a positive focus. The focal ...


6

Almost every piece of every modern lens from the major manufacturers has a part number. If you can access the service manuals for the two lenses in question you can compare the part numbers. If the numbers are not identical, they're not the same part. Perhaps one lens uses part # 123xyz and the other lens uses part # 123xyz-a. This would indicate that a ...


5

AFAIK the 28-70 isn't being produced anymore since 2008-ish? So if you are buying a new one today chances are it's been in somebody's warehouse for at least 6 years burning a hole in their pocket. The new version also allegedly boasts a better nano-coating on the front element. Not sure what else might be making up for the price difference.


5

It is not just the barrels of high quality lenses. The light boxes of the top tier cameras from both Canon and Nikon are now made of engineering grade composites (i.e. plastic). This includes models such as the 1D X and D4. Why? Because those materials can be engineered to be stronger, lighter, and less sensitive to expansion/contraction with changes in ...


5

The AF-S 28-70/2.8D f/2.8 has been out of production since 2007. It's an older version of the lens that's more or less be replaced by the newer 24-70. Nearly every lens that's been superseded tends to cost less than newer replacement models, especially if found used (when it was brand new in 2002, the 28-70/2.8 cost $1400, which if you cost adjust, comes in ...


4

Typically, the constant aperture zoom would be sharper. The vast majority of lenses get sharper when stopped down, this includes constant aperture zooms and prime lenses too. So when you stop down an F/2.8 lens to F/4.5, let's say, you get would get an image which is very sharp. The variable aperture lens though would be wide-open at some focal-length and so ...


4

All other things being equal, yes — mostly. In terms of exposure and depth of field, they would be as close to functionally equivalent as things get in the real world. The shape of the aperture blades will have some impact, so in some cases you could probably tell by looking closely, even if that were the only difference. But in the real world, those lenses ...


4

The edge of the blade may reflect light. Such internal reflection is certainly to small to produce visible flare but may introduce some kind of blur. Rounding the blades will reduces this parasit reflection. As these reflection may possibly show-up in the bockeh it may be slightly improved. Diffraction will be not be directly affected. I don't know if ...


4

It would basically be impossible for anyone other than the manufacturer to answer that question about any given pair of lenses. Two very similar lenses might have some of the same outer elements (particularly the front lens, which is the most commonly damaged part), but they could also be subtly different. For example, the Canon 16-35 L, L II, and L III ...


3

Nikon made two versions of the old 70-300. One had a plastic mount, the other metal. However these were not produced at the same time - one version replaced the other at some point. I have never, ever heard of a manufacturer offering a metal mount as an upgradeable option. Definitely smells like scam.


3

With respect to color, better is often a matter of opinion. Different wavelengths may be transmitted differently depending on lens element materials and coatings. This is most noticeable when comparing very old lenses with modern lenses. They are usually most noticeable as warmer or cooler colors when white balance is set to auto (on some cameras). However, ...


3

There's not really any standard for what "better" or "not better' color is. There are only more saturated or less saturated colors, and colors with a cast or tint in one direction or another around the color wheel. What one considers "better" or not is strictly an individual opinion. There are standards for capturing and displaying accurate color, but that ...


2

Part of it is due to the grease on the moving parts, yes. On my Canon 70-200mm f/2.8L, I can feel the notches in the gearing. I think plastic parts have more "give" and also wear down slightly to give a smoother feel.


2

Arrangement of optical elements, level of correction for abberations such as Secondary Color / Chromatic Abberation and Spherical Abberation, shape of the aperture diaphram, a narrower-than-ideal lens barrel which partially occludes the exit pupil, as inkista says your chosen aperture and shooting distance. There are any number of factors which determine the ...


1

Lenses have to be specially designed in order to keep the same focus point when zooming. Making lenses this way is more complex and costs more, so such lenses are more expensive. This feature is usually not important to photographers, so lenses intended for photographic use typically don't do this. But video lenses typically do have this feature as it ...


1

Short answer is that it is indeed a bi-concave lens element. When two lenses are attached, they are called a doublet. The most common type of doublet you'll find is used to reduce chromatic aberration (and frequently spherical aberration as well) by using two elements made of materials with different refractive indexes. The beveling of the lens does not ...


1

I think it's folly to select a lens based on sharpness rather than focal length. First pick a focal length that works for you. Then find a lens with that focal length. The other way is just putting the cart in a different field from the horse, never mind in front of it. Likewise even after you select a focal length sharpness is not even the second ...


1

Generally, if you're talking about across-the-frame, has the higher line on MTF charts, test-chart type sharpness, then telephotos and primes will tend to beat out wider lenses and zooms--particularly in the corners. That doesn't mean you can't find individual cases where that doesn't hold true (e.g., Canon's EF 70-200 f/2.8L IS USM II can pretty much hold ...


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