About aperture

In their everyday life, many photographers often mean the same thing under the words 'Aperture', 'Aperture', 'Relative aperture'.

About aperture

About aperture

If everything is greatly simplified, then the F number (aperture number) is responsible only for the ratio of the geometric aperture of the lens to its focal length - therefore you can still find the definition that the F number is called geometric aperture. In fact, aperture Is the ability of the lens to transmit light, and this ability is influenced not only by the ratio of the focal length of the lens to its diameter (i.e., geometric indicators). A huge role in the ability to transmit light is played by the optical design of the lens, which tends to transmit not all of the incident light.

An ideal lens would let in all the light that falls on it, but due to reflection, reflection and absorption by the optical elements of a real lens, only a part of the light flux reaches the photosensitive element, which forms the final image. Therefore, different lenses with different optical schemes, but with the same relative aperture, can create different exposures in photographs, all other things being equal. This is very often encountered in a movie where you need to mount a lot of short videos, for example, shot from different angles, into one big one. At the same time, if the scene is shot from different angles with different optics with the same F value, then in the final gluing you can get different brightnesses, which will look very bad when viewing. This is the most primitive example that videographers often cite.

To make it more convenient to work with photo and video equipment, there is a so-called T number (from the English 'Transmission' - transmission, transmission). The T-number is the F-number corrected for the light transmission efficiency of the lens. The T number indicates the equivalent of a lens with a specific F number that allows 100% of the light to pass through. For example, if a 50mm, f / 1.4 lens only transmits 50% of the light, then an ideal T 2.0 lens would match. The number T can be used in the same way as the number F.

Example. If we have a 100mm T 4.0 lens, it doesn’t matter which geometrical hole it actually is and what its F number is, it will still transmit as much light as any other lens with the same T number, for example, some 50mm T 4.0 At the same time, 100mm T 4.0 and 50m T 4.0 can have completely different values ​​of the number F. If you put a neutral filter on such lenses, you can say that their values ​​of the numbers F will be preserved, and the numbers T will change to the degree of dimming by the filter. Thus T-stop (an analogue of the step of the number F) is in many ways more convenient to use.

On the network, I met information that photographers cheatedindicating on the lens barrel is not the real aperture value. In fact, no one is deceiving anyone, just between the concept of "aperture" and "relative aperture" there are certain differences that an experienced photographer knows about. On the lens, the usual value of the relative aperture is indicated (it is also called the maximum aperture, or F number), but how much light such a lens actually lets through can sometimes only be found in the instructions for the lens.

When I wrote the text for this article, I found instructions for a modern lens Nikon Nikkor AF-S 35mm 1: 1.8G DX, re-read it from cover to cover, but did not find information about the light transmission of the lens. Therefore, you can still slander the manufacturer for incomplete information about the lenses.

Due to the different light transmittance, even small paradoxes with the f-number can occur. For example, let's take two lenses - Nikon 35mm 1: 1.8G DX Nikkor (lens for cropped cameras) and Nikon 35mm 1: 2D Nikkor (full-format lens). It would seem that the first lens has a slightly higher aperture than the second. But if you try to shoot using these lenses using a cropped camera, it may turn out that the amount of light projected onto the camera’s matrix with the first lens will be less than the second. This is due to the fact that the cropped lens has stronger vignetting at F / 1.8 and with different luminous flux losses in optical circuits.

Photo for paragraph separation :)

Photo for paragraph separation :)

Many aspiring photographers tend to use high-aperture optics for the common reasons - excerpts, more flexible control of depth of field, beautiful drawing and excellent image quality. But high-aperture optics give some more very pleasant (and maybe not pleasant?) Nuances.

The first of them I want to note the brightness of the optical viewfinder. High-aperture optics give a nice bright picture in JVI. With such lenses it is much more convenient to aim manually, you do not need to peer very much at JVI and squint your right eye. The human eye adjusts very well to the light intensity, and therefore you can’t always notice the difference with different lenses, but there is one. Personally, I tried to determine my personal sense of brightness. JVI with a fast manual aperture lens - Porst Color Reflex MC Auto 1: 1.2 / 55mm. Here's what I noticed:

  • The difference between F / 1.2 and F / 1.4 is not felt at all
  • The difference between F / 1.4 and F / 2.0 is almost elusive
  • The difference between F / 2.0 and F / 2.8 can already be easily caught, but on F / 2.8 in JVI everything is clearly visible and does not cause any discomfort
  • The difference between F / 2.8 and F / 4.0 is enormous, you immediately notice it. Visually working on F / 2.8 is much nicer
  • The difference between F / 4 and F / 5.6 is not very noticeable, but at F / 5.6 after F / 2.0 there remains a feeling of extreme limitation.
  • With further closure of the diaphragm, everything becomes faded.

Based on the experience (and some others), I came to the conclusion that the most comfortable values ​​of the maximum relative aperture for sighting are F / 2.8 and lower.

You can conduct your own experiment on brightness JVI your camera. This is easiest to do if the camera supports depth of field preview via JVI. If there is no such function, then you need to use a lens with manual iris control. The electronic viewfinder is not suitable for such a test.

Helios 44 bokeh with 8 petals

Helios 44 bokeh with 8 petals. Photo separator

Aperture optics not only gives a brighter and brighter picture in JVIbut also allows in many cases where more accurately and quickly handle the autofocus system.

Roughly speaking, the stronger the light flux from the lens to the mirror, the easier it is for the phase focusing sensor to focus. The first time I felt the difference was shooting in the studio for a long time, where I had a weak modeling light from the fixtures at hand. The high-aperture lens that I used for a half-length portrait easily clung to the subject, but when I had to shoot a group of people and use the standard zoom with an average aperture, it simply refused to focus in such light.

I suppose that high-aperture optics should improve the quality of focusing also in the Live View mode.

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In addition to improvements in the focusing system, the camera, with fast lenses under certain conditions, much more accurately produces and measures exposure. I can’t say for sure how and for what reasons this or that camera improves the operation of the exposure meter, but, based on my experience, for some reason I’m sure that there are errors in exposure with aperture optics much less.

In my practice, errors in exposure most often occur when using medium-aperture optics and when shooting on covered apertures. When using high-aperture optics at the same values ​​of the number F, errors are much less. Of course, small errors in exposure not critical if you shoot in RAW, but still this is a good plus of such lenses.

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Also, I notice that fast aperture optics give less rejection due to focusing errors when used on covered apertures. I assume that if a slight error was made when focusing on a fast lens, then during shooting, when the aperture is closed, a noticeable expansion depth of field zones just make up for this mistake.

Who does not know, then modern SLR cameras always perform focusing with the aperture fully open and close it to the set value only during shutter release.

For an example we will take a fast fifty dollars with F / 1.4 and a usual regular zoom with F / 3.5-5.6. We will shoot at 50mm and F / 6.3. If the focusing error was initially made at fifty dollars, then due to the closure of the aperture to F / 6.3, the depth of field will greatly expand and will most likely capture our subject. At the same time, if there was a focus error at the zoom, then a small change in the depth of field during the transition from F / 5.6 to F / 6.3 will not be able to compensate for inaccurate focusing.

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True, high-aperture optics have obvious drawbacks. One of them I want to highlight the diffraction threshold, which sometimes starts from F / 8. Super-fast lenses with f / 1.4 and f / 1.2 and below suffer especially from diffraction at very closed apertures. Usually the minimum F number they can use is F / 16. Low-aperture optics are less prone to diffraction because they need to perform less aperture maneuver. So the stock "dark" zooms at F / 8 only come to life and show excellent photo quality. This can be critical only for certain types of shooting, and the threshold is different for different lenses. The features and subtleties I have described cannot always be clearly shown, but over time they begin to be felt in practice and affect the work :)

↓↓↓ like :) ↓↓↓ Thank you for your attention. Arkady Shapoval.

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Comments: 132, on the topic: About the aperture

  • Maksim

    Good day! New Riq Vi, Arkadiy, we thought it was better With the upcoming new rock !!!

  • Serg

    Well done Arkady! Three days, three articles! Keep it up all of 2014! And what is the bandwidth indicated as a percentage?

    • Arkady Shapoval

      If the lens transmits all the light, then it is 100%, if not all the light, then only a certain percentage, for example 80%, 90%, and the remaining 20% ​​or 10% are scattered, reflected before reaching the matrix or film.

  • Serg

    Is this the same as transmittance ???

    • Arkady Shapoval

      In fact, yes, that q = 0.8, that 80% is the same :)

  • Igor

    Putting on after Nikon 35 f / 1.8G - 50 f / 1.8G, it immediately felt that the OVI became brighter, although both F 1.8.

  • Sergey

    Interesting article, thanks for the info!

  • Volodimir

    Good day, Arkadiy. I don’t know, I’m writing more beautifully here. I want to buy an asset, I'm vibrating my Tamron 17-50. What is more beautiful to take for Kenon 650D, what’s more about sacrifice in price? Tsіkavit tіlki yakіst vihіdnih photos.

  • Mark

    One of the most interesting articles! Very clear and very interesting. Thanks!

  • Ivan

    My guesses were confirmed. Often observed that for different lenses with the same value of F, the exposure is different. Thanks for the interesting topic.

  • Sergei

    great article. can add:
    - some lenses are noticeably “darker” than you might expect (the same Kenon 24-105 / 4 )
    - hanging any filters reduces the aperture (polaric and gradient - greatly reduce)

  • Vasily Artamonov

    Arkady, Zeiss in the names of many of his lenses in front of the aperture number writes the letter T, what is it? Just a letter or these lenses have a 100% light transmission, because the characteristics indicate F is the same?

    • Valentin

      T. is a new type of multi-illumination. There is no connection with light transmission.

      • Vasily Artamonov

        Thanks for the educational program.

      • Oleg Muravitsky

        and there is not T, but T * (exactly so, with an asterisk)

    • AlekK

      Index T is the type of enlightenment used by Zeiss from the thirties, after the war, this marking migrated to the German Democratic Karl Zeiss Yen. T * multi-enlightenment on West German and Japanese Zeiss.

  • Valentin

    Interesting article, thanks Arkady.

  • Roman D

    Diffraction does not depend on the "light output" of the lens. This is a subjective feeling. For example, 50 / 1.4 is very sharp at f / 4, but at f / 8 there is already a noticeable drop in sharpness. At 18-70 / 3.5-4.5 at 50 / 4.2, the sharpness is STILL insufficient, and at 50/8 it is pulled up to the sharpness of the band at f / 8.
    Why do apertures have a minimum aperture of about f / 16? Everything is very simple. The discreteness of the stroke of the pusher moving the diaphragm blades is always fixed. Therefore, for example, fast aperture 50 / 1.4 reaches only f / 16.

  • Kirill

    and yet T has a direct dependence on F - according to the dxomark tests, the larger the maximum hole of the lens, the more T, but a number of lenses with the same F may have different T

    • Alexey

      And where to get this number T? What sources?

      • Novel

        If the manufacturer didn't bother to indicate it in the manual or on the website - nowhere. This is a factory defined value.
        At the moment there are only 2 serial lines of optics that indicate honest T and at the same time that are available in Ukraine:
        1 - Canon Cinema Lenses - fixes and zooms for filming, very expensive (they require about $ 5000 for a fix)
        2 - Samyang VDSLR - inexpensive fixes with no autofocus and built-in FollowFocus rings (cost $ 300-700)

        • AlekK

          All line of film optics with honest T, otherwise they will be unclaimed.

  • stiob

    Yes, the first three days of the year and three equally wonderful articles! great start!

  • Neofot

    Hello everyone. I have long had the question: why, with a difference in aperture of 1-2 steps, the price of the lens rises sharply (an example of fifty-fifty 1,4 and 1,8G from Nikon). is it marketing or does manufacturing cost really skyrocket?

  • Artyom

    Thank you, Arkady, for an interesting article!
    For a long time I wondered why Wave 9 at aperture 2.8 has the same exposure time as the 50 mm 1.8 Kenon.
    Tell me, does the aperture affect the depth of field or only the relative aperture?

    • anonym

      believe that only a relative hole!
      Question to Arkady, please explain to a dark man, what does the diameter of the front lens affect?

      • Arkady Shapoval

        If you mean whether the front lens affects the aperture ratio, then its magnitude on the straight line is not connected with this. The diameter of the front lens only affects the weight of the lens and the diameter of the filters.

        • kiev_poznyaki

          still strongly affects the "prestige" and the price of the lens - the larger the diameter, the steeper the type

        • Alexander

          “If you mean whether the front lens affects the aperture ratio, then its magnitude on the straight line is not related to this. The diameter of the front lens only affects the weight of the lens and the diameter of the filters. ”

          Well, for some reason I can't believe it. After all, the diaphragm actually reduces (cuts off) the light flux from the edges of the lenses. And this, as I understand it, is the drop in the luminosity - you need to increase the shutter speed.
          Or am I mistaken in something?

          • Arkady Shapoval

            The diaphragm is almost always not behind the front lens, therefore it has nothing to do with it.

          • Alexander

            It doesn’t matter where the diaphragm is.
            She cuts the luminous flux around the edges? So ?
            And the amount of light delivered to the light receiver, if ideally it is not lost on the lenses, directly depends on how much the very first lens collects it.
            For example: mirrored solar power plants - a highly exaggerated mirrored lens. This is the aperture ratio !!!
            Or am I misunderstanding the term aperture in this article?

            • Arkady Shapoval

              Just climb into the wilds.

          • Alexander

            PS all of the above for a light detector of the same size.

            • Arkady Shapoval

              Think about why different lenses with the same relative aperture have different sizes of the front lens, this will help to reach the conclusion I indicated above.

          • Lynx

            for industar 50-2 the aperture is 3,5 .. for jupiter 37 it is also 3,5, however, the diameters of their front lenses differ several times.

        • Sergei

          But what about the theory (from Wikipedia) The relative aperture of the lens is the ratio of the diameter of the entrance pupil of the lens D to its rear focal length f. Its value is expressed as a fraction: D \ f = 1 \ k when the numerator is reduced to unity. The denominator of the relative aperture k is called “aperture value” or “aperture number”. That is, a direct dependence on the diameter of the front lens (in the sense of a theoretical minimum diameter should be provided for a certain aperture, for example, for 50 1.8 is something about 27 mm) or I'm wrong.

          • Arkady Shapoval

            Explain what a pupil is and do not confuse it with a front lens.

        • Sergei

          Yes, the pupil and the front lens are not the same thing, I agree. And I completely agree with your article, I just wanted to convey the idea that the aperture ratio is in any case proportional to the geometric aperture, taking into account the focal length, corrected for various kinds of losses, which you write about. Simply, in a hypothetical tube in a vacuum)) without lenses, only the hole size will affect the aperture ratio.

    • Vadim

      I would even supplement the question: does the degree of background blur at the same focal length and the same 1 / f value depend more on the f-stop or t-stop lens?

      • Arkady Shapoval

        It depends only on the geometry, that is, on the focal length, F number, and focus distance. If we put a neutral filter on the lens, its T number will decrease, but this will only affect the exposure.

        • Novel

          If we put on a neutral filter, the T-number decreases (or light transmission, to be more precise), while the degree of blurring, which depends on the relative aperture, remains the same.

    • AlekK

      Modern manufacturers on household photo optics lines, for marketing purposes, indicate a geometric relative aperture, rather than a real aperture.

      • Arkady Shapoval

        Actually, this article is written about this.

  • Konstantin

    Arkady, good afternoon! Happy New Year, I wish you more creative success in the new year, interesting staff and efforts to educate less experienced colleagues :)
    Thank you for a very interesting series of articles - they clarified some points.

    P.S. a small typo crept in:
    "If we have a 100mm lens" - probably "we have"

    • Arkady Shapoval

      Fixed

  • Dmitriy

    Tell me, is the information about the luminosity in the file of Nikon files (I did not find such information in the Canon files) honest? Or is it just some kind of software calculation and not "honest" information?

    • Arkady Shapoval

      in EXIF, the most honest aperture value is indicated at which the picture was taken :) But what to mean by aperture is described in this article.

      • Dmitriy

        Windows axis 7. Right-click on the image-properties-tab “details” -scroll down. There are items aperture, shutter speed and aperture. Where did this aperture come from? did the lens transfer it to properties or did the camera somehow calculate it programmatically?

        • Arkady Shapoval

          You should ask the software developers what exactly they mean by the word “aperture” in their tab. This is definitely not a T number, because sometimes it is less than the minimum F number of the lens used for shooting (for example, if you take a Nikon 85 1.8G lens and look at this field, the “aperture” value will be equal to 1.6).

        • Michael

          The “Aperture” item shows the F value set for this picture (ie taken from the camera settings), and the “Aperture” item shows the minimum F number of the lens (the camera takes from the lens). Sometimes the latter is indicated incorrectly in the lens firmware.

  • Maksim

    Arkady Happy New Year and thanks for an interesting and intelligible review. I returned to the photo 30 years later and got to this site, reading about my former Zenith ET with Helios 44. Now I go here almost every day and constantly draw the necessary info. It is also striking that if Arkady was given a test railroad tie or scrap with an adhered piece of glass, he would be able to take pictures of decent quality  for this. Thanks again and look forward to new reviews ...

    • Vladimir

      I agree with you, Maxim. Also "hooked" on the articles of Arkady. Thanks to his website, he gave a second life to Helios 44-2 / ​​58 from Zenit E, which had been idle for 10 years (when he bought the first digital camera).

  • Ivan

    Is it logical to assume that the real aperture of the lens depends not only on the quality of the design and lenses of the lens, but also has a direct dependence on the diameter of the lenses. After all, the larger the diameter of the lenses, the more light beams will fall on them and be refracted when entering the matrix? If so, then the most aperture would have been nicor 14-24 f2.8 ..

    • Arkady Shapoval

      The diameter of the lenses, as discussed here, only the cossveno affects the aperture ratio. The diameter of the lenses is associated with the optical scheme, which then decides the issue of the lens aperture. For that matter, take a look at Nikon 8mm f / 2.8, etc. To close the question, a counter-example - the Sigma 50mm f / 1.4 EX DG HSM sigma lens has a 77mm front filter diameter, and the Nikon 50mm f / 1.4 AF-D lens has a 52mm diameter, which is 2,2 times smaller than the sigma one in terms of circle area. But in fact, the T feet of the lenses do not differ 2 times, but are approximately the same. We conclude that the aperture ratio directly depends on the optical scheme, and which lenses and their sizes this scheme requires is a completely different question.

      • leshka

        The aperture ratio certainly depends on the size of the front lens, and the larger the focal length, the larger the optical design of the lens requires an increase in the size of the front lens. The law of conservation of energy has not yet been canceled. You compared 2 lenses with a similar aperture but different focal lengths, which is what caused your seemingly paradoxical conclusion.

        • Arkady Shapoval

          I compared the Sigma 50mm f / 1.4 EX DG HSM with a focal length of 50 mm and the Nikon 50mm f / 1.4 AF-D with a focal length of 50 mm and wrote their difference in the diameter of the front lens (77mm versus 52mm). Now explain the difference in the size of the front lens of these two lenses.
          Nikon 8mm f / 2.8 was cited as another example.

          • leshka

            Yes, I agree about the second part of the phrase, I looked badly at what you compared, but about the first part of the phrase - if you can prove otherwise, feel free to submit an application to the Nobel Committee :).

          • leshka

            And the difference in the diameter of the lenses is easy to explain: at a distance of 50 mm, a diameter of 52 mm is enough to obtain this aperture ratio.

  • Ivan

    And here's a question to break your head)) When we put a fast FX lens on a cropped camera, don't we almost double the aperture? Since the light passing through the fx lens is designed to hit the full matrix and probably from that data its aperture was calculated, and here we put it on the matrix half as much ... well, the head moves out)) admit it was much easier to live when I thought that the aperture ratio is the maximum open hole.

    • Artist

      Well, they made fun)) But seriously, I think that Arkady is right, the aperture depends on the optical scheme ... For example, on the D7000 I have a Nikon 85mm F1.8 filter diameter of 52mm.

    • Arkady Shapoval

      Each pixel of the matrix receives the same amount of light. On a crop with the same lens, the same exposure parameters will be, just the image will be cropped around the edges, that's the whole focus.

  • Lancet

    Chic article. Thank you very much.

  • Ivan

    Arkady, did you think about the level, to test the levels on the cameras?

  • Schoolboy

    Wouldn't it be better and more accurate instead:
    "The F number (aperture number) is only responsible for the ratio of the geometric aperture of the lens to its focal length"
    write:
    "F-number is the ratio of the focal length of the lens to the diameter of its pupil"

  • anonym

    There is a small problem on such glasses, called shift focus. This means the focus area shifts slightly depending on the aperture (in fact, the focus point does not move anywhere, it is just that the DOF spreads unevenly). Focusing occurs at 1,4 aperture, and during shooting it closes and the depth of field floats beyond the focusing point. But in any case, the point where you were aiming should remain at least on the border of the DOF. If the focal point floats out of the depth of field, then to the service, for adjustment. 50 / 1,4 is done in China in very large quantities - a lot of frank marriage.

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