The lens for the camera All of us are accustomed to the lens on the camera, and there are few who think about the fact that this is, at first glance, a simple device actually so difficult.And, the truth, in the first place by the lens depends on the quality of the image.Therefore, when choosing a camera should not only pay attention to the number of megapixels and cherished number of functions.As the theater begins with a hanger, so the camera starts with the lens.And no wonder the cost of serious models of up to 60% of the cost of the entire apparatus.
course to a responsible approach to the selection, you must be why you need the lens, how it works, what are the types and how to determine what is needed for you.That's what will be discussed.The journal will begin, as usual, with the theory.

lens apparatus includes a lens optical system in the form of one or more lenses (including lens components - the lens glued together), and sometimes mirror, made in the general frame.
Socket - it is nothing like the lens barrel.It serve
s not only to hold all the components, but also for proper adjustment (adjustment of their relative position).IeAll items should be located with sufficient accuracy, especially the notorious optical axis.And what is it, and why is it notorious?
optical axis - is the center of symmetry of the optical body, ie,imaginary element.And to put it simply - the diametric center of the lens.
Socket performed for a specific type of apparatus that defines an object is compatible machines.The simplest frame comprises: blackened inside and usually outside the tube, inside which there are lenses or lens components which multi-part devices are divided into two groups - the front (inside the machine) and back, between the iris feature.Objective optical system
- projected on the film surface or matrix image of the desired size.And it has done so.
light source in the theory is regarded as a point of light-emitting unrestricted flow (beam) radiation.If the path of the beam aperture supply, ie,lightproof screen with a hole inside the light beam is limited, thus reducing the amount of light (luminance decrease).The lens maximum amount of light able to pass through its optical system, an inner diameter of the rim is limited.The larger diameter of the rim and, consequently, the lens, the more light will pass and is better illuminated screen.The lens becomes a large aperture.Looking ahead, I will say that the larger the diameter, the better in many ways.This, for example, can reduce the effect of the "vignetting" and expand the latitude.But the details about this MirSovetov tell hereafter.
small apertures can be achieved even more narrow beam of light, which further reduce the light in the image and increase the depth of field.But allocate a separate beam from the beam, reducing the aperture to the maximum, you can not, because the phenomenon of light diffraction begins.At the same time losing the straightness of rays and begin to bend around the edge of the diaphragm.And what that means?
As is known, the use of the maximum aperture of the lens decreases the depth of field and the emergence of this "vignetting".To increase the depth of field and to avoid this effect, it is necessary zadiafragmirovat lens.But sharp (sharp) objects in the scene will be only for a time.When will the diffraction image becomes fuzzy, blurry.It is therefore advantageous to choose lenses with a larger diameter.This increases the breadth of its possibilities.But the phenomenon of diffraction of the shortcomings of the optical system does not end there.
refraction of light - this change in the direction of light as it passes through the transparent polished (smooth) surface, for example, through the surface of the glass lens.
Refraction of light - a change in direction of light passing through the transparent polished ( smooth ) surface such as glass surface through the lens
Part of the light is refracted at the boundary of "air - optical body" (hereinafter - the lens) goes into it, changing the angle (refraction phenomenon leads to aberrations (image distortion). To reduce themin optical systems use a variety of techniques usually require increasing the number of lenses.
But the problems do not end there. The fact that the refractive index, and hence the angle depend on the composition of the light passing through the lens. It's simple,if the light monochromaticity example, yellow, for which are provided in the tables and refractive indices. Then a light changes its direction. When a beam of white light passes, it starts here, "tricks." And it was. The white light consists of a set of colors thathave different refractive indices. This results in a "bundle" of the beam.
Stratification of the light beam
biggest angle in purple, and the smallest - in red.This phenomenon is called dispersion or chromaticism .
Perhaps you saw a rainbow after the rain, when the sun peeps out - this is the chromaticism of sunlight into tiny droplets (aerosols) after rain.This feature greatly complicates the task of developers optics for color photography.And in this regard, color photography is essentially different from black and white where the chromaticism almost no role.
There is also a fun moment.If you enter into the lens light can at any angle, it's come out of it can not happen.
Choosing a lens for the camera
This is due to the fact that the phenomenon of refraction occurs at each transition boundary (air-to-lens and lens-to-air).So when exceeding the angle of incidence of light entering the lens (first border) light at the second interface (output) is refracted so that falls back into the lens and fixate there, creating some noise.Just listen useless becausethe noise of the light rather than acoustic.But the result is that the light in this case is out of the lens at all.Which leads, naturally, to limit the angle of view (field of view).
Now, with regards to that reflection.Reflected light from the surface is almost no effect on image quality, except that the reflection on the inner lenses.But this greatly reduces the flow of light.To reduce the loss of light lenses that are used.Without going into much detail, MirSovetov say that this is achieved by applying to the surface of the lens of the film special composition.The thickness of this film is clearly defined and consistent with the middle of the visible spectrum - from the green.Thusthe best light transmission, so to speak, is obtained for rays of green.As, however, and the human eye.
should also be noted that the lens with a large diameter lens is much better than the "midgets".Why is that?And this is connected not only with the above advantages, but with a reduction in aberrations caused by the curvature of the lens.The fact that the amount of aberrations increases with the curvature of the lens.The more the lens diameter, the smaller the curvature, i.e.they become more flat.
Now that we have at least a small idea of ​​the device, we can proceed to the choice of lens.Or rather, it is likely you will buy a camera as a unit.But not to make a mistake and do not choose the wrong option, here are a few recommendations.

How to choose the lens?

So, you have come to the store, and your eyes on the shelves fled windows.How to determine which yours?You've got to just decide what you want for the device and what (we talked about in the previous article "How to choose a digital camera").There is an important point - is the lens mount to the unit.And this type of attachment is only two: zhestkovstroenny and detachable (removable).Most devices have a first type and only "SLR" have removable lenses.
And why all this is necessary?Zhestkovstroenny lens, as you probably guessed, is an integral part of the device, and you can not remove it.It would not need to.And in fact, there is no need, if you are completely satisfied with the quality and performance standard lens or, as it is called, Kit-lens.And if not?If not, then in this case you have nothing to be done becausethere is no way to change the lens.
And now let's see, why change it.There are a variety of reasons.
Firstly, it is quality.You filmed material and quality you extremely satisfied.Here then we have to think about the possibility to change the lens.
technical quality of the lens is determined mainly by the technology (including the speed of the process) melting glass lens and quality of polishing including manual finishing.The fact that the glass, as well as any amorphous solid, melting point is unpredictable.If the temperature rises rapidly, the glass may not only melt, but also to boil, leading to the appearance of air bubbles, which then zastynut lens in perpetuity.To avoid this, it is necessary to heat the glass slowly and to stop further increase in temperature, as soon as the glass "melts".Naturally, this is much more slow and expensive process.
And what terrible bubbles?Not difficult to guess that this is an obstacle to the bubbles of light and the transition boundary, which will again take place above mentioned processes.The more bubbles, the worse will be the image.Try to look through a fluted glass.What do you see ?!And
plays an important role not only the number of bubbles and their size.In the domestic lens "Helios", for example, allows up to four bubbles visible size.In foreign optics, usually you will not see them.No !?You still notice?Then it is very cheap optics.Even in simple inoobektivah I've never met bubbles.Stop!And how do they look like?To see them best, you need to remove the lens (if possible) and see-through lens.The bubbles look like extraneous blotches.If the diameter is very small, as the black point resembling debris.If the lens is not removable, it is much more difficult to detect bubbles.We need a good source of light directed into the lens.On examination, we must also pay attention to the purity of the first lens.It should be clean, free of scratches and stains.
But to determine the correct geometry of the lens you will not succeed, becauseit requires sophisticated equipment.
Secondly, the use of interchangeable lenses is associated with the need to change the focal length.But let there also zoom !?Yes, it is, but if your requirements will be proposed wider zoom range, you will need to extend it by another lens.Most full-range of the optical zoom lens is very small.The more that can be done (for technical reasons) lens with a very large spread of focal lengths.There are times when the need ultrashort focal lengths, then you need the lenses of the "fish-eye» («fish eye»).
Fish eye
Or, conversely, you may want to take on the extra-long distances, and then you need a telephoto lens has an equivalent focal length of 500 or even 1000.
For shooting on super-long distances need a telephoto lens with a focal length equivalent to 500 or even 1000
Here in these cases, interchangeable lenses - something irreplaceable.But such biases is very unprofitable, becauserequire an expensive SLR camera and very expensive lenses in stock.Therefore, this option is suitable either for professionals or for the fans of photography.But if you are neither the one nor the other, then it is necessary to consider whether you need a machine with the ability to change the lens.
For a simple change of the lens is hidden a lot of difficulties.The fact that a machine will not fit what you want lenses, and, as a rule, only original and only certain models.Under the original, it is understood that the same manufacturer (system).For example, the machine will not work Canon Lens Nikkor, which is designed for machines Nikon.
course there is the ubiquitous third-party vendors such as Sigma, Tamron, etc., Which produce a wide range of products for different vehicles.But here is not so smooth.For example, the Nikon device can "make friends" with any Nikkor lens, or its analogues (bayonet type F).But do not think that everything ends with mechanical compatibility.If you're on a modern machine jammed, "the old man", it does not mean that you get all the features claimed in the machine.Also can not "to" any of the functions on the lenses from other manufacturers.
Why?It's simple!But before you learn about the relationship between the unit and the lens MirSovetov tell how, in fact, made a removable lens mount.
There are two types of mounting : threaded and bayonet.
threaded applied for a long time, in a fully mechanical devices, and foreign - for a long time.
Screw mount lens
not difficult to guess that in this case the lens is screwed to the machine on the thread, which is necessary to get first in the thread advance (and it can be difficult, as fine threads), and then turn the lens a few turns.
Probably the only plus - a low cost structure.But a lot of minuses.The longest - is the process of changing the lens.It is very, very slow.This makes it inapplicable for this type of shooting, requiring frequent changes of lenses.In addition, you run the risk of blurred images due to incomplete or tightening samootvorachivaniya lens;the inability to make an electronic lens;potentially the worst alignment.
second type - bayonet .There must be aligned for fixing the dots on the lens and the device, drown the lens until it stops, and turn it clockwise (when viewed from the front of the unit) until it clicks.Elementary and fast!
Lens with bayonet mount
Now this type of attachment is completely replaced the first, becauseIt does not have those disadvantages.And it has such advantages as speed and accuracy of connection and disconnection, high reliability with a stable mounting and precise alignment, the ability to give objective "intelligence", iemake it electronically.Cons: higher price, the large number of different and incompatible type bayonets, which leads to complication selection optics.
So, talk about the last detail.
Now almost every company is trying to "excel" and produce a camera of his own design, explaining that his know-how or creed.And this leads to the fact that a particular device is suitable only a limited number of interchangeable lenses.And it would seem that in this special.And that's what!You say you picked the right of the subject and it is very like you, and even the price of it is much more tempting than navyalivaemogo original.But there it was!It does not fit.In this situation the two solutions.Or struggling to save for a suitable original.But there is a possibility that when you accumulate, it will not be true for one reason or another.Either try to make friends "fell out" a couple.And then, unfortunately, a lot of difficulties.
And the first - whether the bayonet.If appropriate, it is already good.And if not?That's okay too!Achievements "Kulibin" high and has adapters from one type to another bayonet.Here it is only necessary to choose the desired adapter.But we must remember that the majority of firms with access to the new model change the type of mount and the focus should be not on the name of the company and the type of device.By the way, this is done specifically to older lenses do not fit, and vice versa.
And what threatens to use an adapter?Virtually painless could use them only in a fully mechanical camera.Whereas in modern devices in this case, you lose all the "goodies" including AF.Why is that?And the loss of the connection between the unit and the lens.And it may happen that the device will refuse to work at all, because"Thinks" that it does not have the established objective.If
remove the lens and look at it from the mount, you'll see a lot of contacts.
If you remove the lens and look at him from the mount, you
Yes!Through these contacts the camera "talks" to the lens.Naturally, the adapter would deprive completely this possibility.
But even if you did without the adapter, you do not flatter yourself.Though suitable for mounting the lens may not be suitable for interface protocols, for example.Then it will be as in the saying - "Your my understanding is not present."At least, in the best case, you can simply forego any functions.What to do?It would be a shame, and the savings would be unjustified.And it is really so!Therefore, if you are burning desire to experiment with alternative (non-original) optics, then get ready for surprises.Here before you buy, and we should all learn to weigh carefully.And suddenly, those functions that are not "gone", you to anything!Then it will be the best for the price of an option.What is the problem?That's right!Why is that?Ie