The diaphragm is simple. In a nutshell, aperture is a device in the lens that measures the amount of light.
Aperture device in the lens Nikon Nikkor 105mm 1: 1.8 (AI-S)
For a better understanding of the operation of such a device, I will give an example from life. When people look at the sun, they squint their eyes, that is, they reduce the gap through which light passes. If people did not squint, the sun would burn the retina with its strong light. At night, you need to do the opposite - open your eyes wider to capture more light, while the pupils also dilate. Eyes with large pupils have many animals that need to see well at night.
Often the diaphragm is also called 'luminous efficiency ' or 'aperture' or 'relative hole' or 'number F'. These concepts are strongly related to each other and are synonymous for many photographers. But among them there are small differences, described below.
Lens aperture Is the ratio of the effective aperture of the lens to the focal length of the lens. The reciprocal of the relative aperture is called f-number or aperture number.
The relative aperture of the lens is expressed numerically by ratio or fraction. For example, take a lens that has a relative aperture 16 times smaller than its focal length; as a result, the relative aperture can be numerically written in the following ways: 1:16 or f1 / 16 or f = 1: 16 or F 1:16, etc. d. There is no particular difference in the recording, and every photographer will always understand what is at stake.
If we take the number opposite to the relative aperture, then we get the number of aperture. Usually it is by this number that photographers directly understand the general term 'aperture'... If we take the same lens, which has a relative aperture 16 times smaller than its focal length, then its aperture number will be equal to 16. And numerically it can be written in the following ways: F16, F / 16, 16 (such a 'bare' number aperture is indicated on the lens barrel). There is no particular difference in recording.
Some lenses have an aperture ring on their body. There is usually a marking on the ring, consisting solely of aperture numbers (shown in the figure below). Almost all modern lenses do not have such a ring, and the diaphragm is controlled by the electronics and camera controls.
Lens aperture control Nikon ED AF Nikkor 80-200mm 1: 2.8D (MKII). Using the ring you can set the values F / 2.8, F / 4, F / 5.6, F / 8, F / 11, F / 16, F / 22.
Usually the concept of 'aperture' and 'aperture' are synonymous, but in fact there is a certain sacristy between them. So, the diaphragm is only responsible for geometric aperture (the ratio of linear geometric indicators). And not only the aperture is responsible for the overall 'real aperture' of the lens, but also many other factors: the optical design of the lens, the percentage of light reflection and transmission by the lens, the drop in the aperture number when focusing at different distances, the percentage of light absorption by the photo filter, etc. More details about the difference between the concepts of 'aperture' and 'aperture' can be found in the section about 'T-feet'.
The aperture is sometimes also called the 'Lens Aperture' (Latin 'Apertura' - 'Hole'). Therefore, on many cameras, the metering mode exposure с aperture priority called 'A' or 'AV'-'Aperture Value '-' Aperture Value '. Details about this mode are described in the section 'P, A (AV), S (TV), M'.
Please note that the magnitude of the front lens of the lens and, in fact, the magnitude of the front light filter have no direct relation to the aperture ratio of the lens. Different lenses with the same focal length and the same maximum aperture can have completely different diameters for their front lenses. For example, take two class 50 mm F / 1.4 lenses: Nikon AF Nikkor 50mm 1: 1.4D и Sigma 50mm 1: 1.4 DG HSM EX... The first has a tiny filter diameter - 52 mm, the second has a huge one - 77 mm. But their aperture (practically - maximum aperture) will be the same.
What is the diaphragm?
By the mechanical part of the diaphragm device is understood a changing circular hole in the lens. Typically, the hole opens and closes with the petals. In this case, the petals are called diaphragm blades, and the diaphragm itself is 'iris' (from the English 'iris' - 'iris'). The number and roundness of the aperture blades determines how much the hole will be formed round. The stronger the rounding of the diaphragm opening, the better. Professionals often refer to the diaphragm simply as'hole'since it is real, a kind of hole that changes its size and doses the amount of light.
What the diaphragm affects:
- The amount of light that the lens can let through over time.
- To control the depth of sharply depicted space (GRIP)
- The brightness of the image in the optical viewfinder
- On image quality, especially on its sharpness, aberration, vignetting, bokeh and various visual effects.
IMF impact
As it turned out, the aperture affects not only the amount of light, but also the depth of field. The smaller the number F, the smaller the depth of field. The larger the F number, the greater the depth of field. This is one of the main techniques in photography to control the point of attention in the photo. It is very important to be able to manage GRIP for portraits where you need to focus on a person. Macro photographers are well aware what is DOF, they have to shoot on very tightly closed apertures to increase the depth of field. In general, where write about DOFwrite about blurred background. You can read the best way to take pictures with a blurry background in my article - Taking Pictures with Blurred Background.
Blurring the background at different apertures
Depth of field preview
Typically, modern cameras have the ability to focus with a fully open aperture. When a picture is taken, the camera’s automation closes the iris to the set value. To see how the images will look when the aperture is closed, you can sometimes use the aperture repeater. This allows you to look into the viewfinder (optical or electronic) without a picture how the picture will look when the camera closes the iris. You can read more about depth of field preview.
Aperture for picture enhancement
Aperture is understood to mean simply changing the aperture value. Using aperture control, you can achieve a sharper image from the lens. Basically, the sharpest image is achieved somewhere at the average aperture of a lens. At their largest aperture, lenses suffer from chromatic aberrations and vignetting. When closing the diaphragm HA and vignetting practically disappears. At very small apertures, lenses suffer from diffraction loss of sharpness. Also, when you close (decrease the aperture), not only the sharpness increases, but also the contrast of the picture. A large aperture allows sighting through the optical viewfinder without any problems, since the lens gives a lot of light and the entire frame is clearly visible through the peephole. You can only view with an aperture below F5.6 through the optical viewfinder in good lighting conditions. Also, pictures with a larger aperture can appear brighter and more saturated - this effect is associated with smoother transitions in pictures from dark to light areas.
Bokeh and aperture connected forever
Aperture greatly affects the bokeh pattern. Usually the best bokeh for the lens is achieved at the maximum open aperture. In this case, the physical hole itself is as round as possible. When closing the diaphragm, the diaphragm petals instead of a circle form different polyhedrons. These polyhedra are clearly visible in the blur zone. Very often such polyhedra are called nuts, washers and circular saws.
Since in cheap lenses there is a small number of aperture blades, usually no more than 5-6, then in the blur zone figures appear exactly like “nuts”. Those lenses that on closed apertures give the correct round luminous spots in the blur zone, for example, can be attributed to them. Nikon AF DC-Nikkor 105mm 1: 2 D Defocus Image Control or Tair-11A 2,8 / 135. In new lenses, it is very rare to find a large number of aperture blades, but now they make more rounded blades, which, even with a small number of them, give a round hole.
Below are my photographs taken with different cameras and lenses and taken at different values of the number F. Shooting options (EXIF) for each photo are indicated in the bottom line.
Aperture in phone cameras and other small devices
The diaphragm is a mechanical part of the lens, it cannot be done programmatically. Almost all phones lack a physical diaphragm device. Many 'soap dishes' also lack a diaphragm. How to be? Usually the camera in such devices doses the amount of light only shutter speed and a variation of the ISO value, and the aperture value itself is constantly fixed at the maximum value. For example, on my Nokia 7610 it is indicated that F2.8, because the camera always shoots at F2.8.
How to adjust the aperture in the camera?
In cameras, it is responsible for the diaphragm F number (aperture number)... It shows how many times the diameter of the relative aperture is less than the focal length of the lens, on the lens it is written as f1 / 1.4 or f1 / 5.6, sometimes you can find the spelling f = 1: 6.3 or 1: 5.6, or f / 16, f / 3.2. Often, lenses or cameras only have one f-number, such as' 1.4 'or '16.0 .8.0'. Usually, the aperture number is written with a large letter 'F' without fractions, for example, F 1, and the relative aperture is more often written through a small letter 'f', for example f 11:XNUMX (there can be any spellings). The easiest way to adjust the aperture is by putting the camera in aperture priority mode. On the main control wheel of the camera, or in the menu of the camera, this mode is indicated by 'A' or 'AV'. To make it easy to remember, you can simply say: Aperture means you need to turn on the 'A' mode. Details about the creative aperture priority mode are written here.
'Light' and 'dark', 'fast' and 'slow' lenses
The maximum aperture value determines how much the lens can be used in poor lighting conditions. Lenses with a large aperture are called 'bright' or 'bright', usually an F value should be below 2.8. That is, lenses with maximum apertures F1.4, F1.8, F2.0, F2.2, F2.5, F2.8 are called fast or just bright. Everything below F1.4 is called super fast. Super fast lenses include Nikon 50mm f / 1.2 AI-S Nikkor or Canon Lens FD 55mm f / 1.2 SSC. Lenses that have an aperture value of F / 2.8 to F / 5.6 are called ordinary. medium-aperture lenses, these lenses can be attributed Nikon 24-85mm f / 2.8-4DAFIF Nikkor or Nikon 300mm f / 4.5 Nikkor-H Nippon Kogaku Japan Auto Non-AI. Lenses with a maximum aperture less than F / 5.6 are called low-aperture or 'dark'. These lenses include MS MTO-11 1000mm F10.0. By the way, it is very difficult to make a fast zoom, in more detail here.
Different holes for different values of the number F
Since aperture affects speed excerpts, then the lenses are still divided into fast and slow. A fast lens means that you can use it to shoot an image with a short shutter speed (with 'fast' shutter speed). And under slow, that it can be used to take a photo with a long ('slow' shutter speed). If you fix the ISO value, it depends on the aperture excerpt, and the brighter the lens, the faster it is. And the darker the lens, the slower it is.
The difference in aperture ratio
The difference in aperture and other photographic variables is usually measured in feet. When changing the aperture by one stop excerpt will change in twice... Also, if you change the aperture by one stop, you can change the ISO by two instead of the shutter speed. It is very important to note that the difference in aperture values is not linear, but quadratic. Take two apertures F / 5.6 and F / 2.8, it would seem that the difference in geometric aperture is 5.6 / 2.8 = 2 times, but this is not true. On aperture affects the area of the circle formed by the diaphragm, and not its diameter. The number F is associated only with the diameter. To calculate the difference in area you need to take the squares of the diameters. Therefore, it turns out that the difference in aperture ratio between F / 5.6 and F / 2.8 is (5,6 * 5,6) / (2,8 * 2,8) = 4 times. Here is such a trick. How to remember this? There are two ways out, either by dividing the squares of the F numbers, or by first dividing the F numbers and then squaring the result. Why am I bored with calculations - but because often amateur photographers have no idea how many times one lens is 'lighter' or 'darker' than another lens.
Also, experienced photographers know about the so-called aperture series of numbers, in which every two adjacent numbers F differ by one stop.
A number of numbers F: 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32, 46, etc.
Golden Rule:
Aperture and shutter speed are bound by the golden rule. To keep correct exposure with the same ISO, you must either close the aperture and increase the shutter speed, or, conversely, open the aperture and reduce the shutter speed.
Close, open, increase decrease - no need to be confused
Everything is very simple. Closing or decreasing the aperture means increasing the F number. The aperture was F2.8, when it was closed, it became F5.6, it was closed even stronger, it became F16.0, etc. For example, there is the phrase 'covered the hole by two stops', it is deciphered as follows: 'made the number F large and reduced the area of the hole by 4 times'. The main thing is not to get confused, when the aperture opens, the F number decreases. And when the diaphragm closes, the F-number increases. For example, the aperture was F32.0, when it was opened, it became F8.0, when it was opened even stronger, it became F5.6.
What to do - nothing is clear
If you have a DSLR, turn the camera backwards so that you are looking into the lens, press the shutter button (take a picture) and you will see the hole in the lens close and open - this is how the aperture works. If you peered into your lens and did not see anything, then below is a slow-motion video, where you can clearly see how the aperture works during shooting. In the video, the petals close to F / 16 and form a very 'small hole':
- The method of operation of the device aperture on Nikon digital SLR cameras and its effect on video recording
- Nikon 'E' Lenses with Electromagnetic Iris Control
- An interesting aperture on Nikon digital SLR cameras
- G-type and Non-G type lenses (with aperture ring and without aperture ring)
- Work with old Nikon lenses such as AI, AI-S, NON-AI, PRE-AI, AI-Converted, which transmit or do not transmit aperture value to the camera
Comments on this post do not require registration. Anyone can leave a comment. Many different photographic equipment can be found on AliExpress.
Conclusions
Diaphragm Is a luminous flux dispenser that affects exposure, GRIP, brightness of the optical viewfinder and image quality. In general, if you don’t shoot at different values of the number F, you don’t really know what it is :)
Material prepared Arkady Shapoval. Training/Consultations | Youtube | Facebook | Instagram | Twitter | Telegram
This site is simply awesome. Arkady, thank you very much for your work. The material is presented in an accessible way, so much useful.
Tell me, what could be the problem if the aperture value does not appear on the camera screen at all ?, there is a blank dash. I have a PENTACON auto 1.8 / 50 lens
This is a manual lens, modern cameras do not have the ability to control the aperture with lenses under M42, for more details here - https://radojuva.com.ua/2011/04/optika-na-nikon/
Sorry, apparently I'm an ignoramus in this matter, because not very clear:
"Macro photographers know very well what depth of field is, they have to shoot at very closed apertures to increase the depth of field."
the photo of a cat with aperture of 16 has no depth of field (if I understood correctly), but 16 is “closed” 1.2 ...
maybe I didn’t understand something, please explain.
In the example with F / 16, the sharpness zone is much larger than at 1.2, that is, the depth of field is thicker.
Arkady, how was the photo taken at the beginning of the article, with a bottle ??? and the like, with nuts ?? very interesting.
The photo was taken very simply, in the background of the bottle there is a garland, which is laid out in the shape of a stream of champagne. Lens https://radojuva.com.ua/2013/01/obzor-mc-biometar-2-8-80-carl-zeiss-jena-ddr/ focused on the bottle, the bottle is highlighted with a flashlight from a tripod. The shooting parameters are imprinted in the photograph at the bottom of it, there you will find ISO, shutter speed, aperture, etc.
I have been using Arkady's articles for a long time. Many thanks to him for his availability, patience and ... the desire to share experience, professional secrets!
Arkady - respect !!!
Thank you :)
I use a 50mm F1.8 lens. It has a constant focal length and a maximum aperture of 1.8. And what is the minimum aperture? Is this not marked anywhere in the lens marking?
Usually it is F / 22 or F / 16, if you specify the exact name, I would also suggest, more accurately.
Thank you for a very wonderful site, the materials are "chewed and put in your mouth."
I will try to leave my thought as well - I recently bought a NIKON 5100 as a gift to my wife and I myself “got hooked” on this business on a new one, in childhood there was a “change of 8M”, my father's Zenith ET ... I used the camera for the first time at a New Year's corporate party, naturally programmed modes , more or less studied before ...) and a lot of photos turned out as Eric wrote. It turned out that I had not turned on the VR mode on the lens. Eric just in case it might.
Hello Arkady. I bought a Fujifilm S4200, surprised that only two values can be set in aperture priority mode - 3.1 and 8.0. Does this limit the camera's capabilities? It is not possible to make incremental changes.
Very strange, I can not precisely indicate such a reason.
Hello Arkady! Thank you very much for the article! I read this “Juicy” material with great pleasure! Everything is beautiful, understandable and intelligible! And, most importantly, useful and instructive! Indeed, everything is chewed and put in the mouth. Clearly. Happy for the youth! About twenty years ago, such information was not so easy to find. And now “on a silver platter” you only have to ask in a search engine. All the best! Good luck, Arkady!
:) I'm glad you liked it.
Thank you for this article, very detailed and clear. As for the golden rule: “close the aperture and increase the shutter speed, or, conversely, open the aperture and decrease the shutter speed,” you can remember from the same example from life, namely, when we look at the sun, we blink faster, i.e. the shutter speed is shorter, and in the dark it is slower, the shutter speed is longer, so it turns out?
Yes something like that :)
you are all bitches
I tried to change the aperture value, it turned out that the larger the aperture value, the photo was darker, and with a lower value, the photo was lighter, i.e. if there is not enough light, then it is necessary to open the diaphragm, and if there is a lot of light, then to cover, is this the rule? Or sometimes there are exceptions? Thank you for the site, you can learn a lot from it.
Yes, that's exactly it.
Arkady, I'm confused: “As it turned out, the aperture affects not only the amount of light, but also the depth of field. The larger the aperture value, the shallower the depth of field. The smaller the aperture value, the deeper the depth of field. …. Macro photographers know very well what depth of field is, they have to shoot at very closed apertures in order to increase the depth of field. ” ????? and then the photo with two bears on top f.3,5 is blurred, bottom f.40 sharply ?????? maybe the larger the aperture value (the number of the aperture is larger, the hole is smaller), the greater the depth of field, and vice versa, the smaller the value of the aperture (the number of the aperture is smaller, the hole is larger) the shallower the depth of field? ????
DOF is the depth of the sharply rendered space.
Arkady, and here's another confusion: "At the highest aperture value, the lenses suffer from chromatic aberrations and vignetting." ... I understand that a large aperture value is a large aperture number, for example 22, a small hole ... but then it says "When the aperture is closed, the CA and vignetting practically disappear." ... I understand that when closing, this is again a large aperture number, a small hole ... that is. contradiction between 1 and 2 sentences? in the first, maybe at small aperture numbers 2,8, for example, when the hole is large, HA and vignettes appear? ????? Or did I confuse everything myself in concepts?
Not understood correctly. A large aperture value is an open aperture, and a large aperture value is a closed aperture.
thank you) now unraveled, everything converges)
Arkady, I have long been interested in one question, open the topic, if possible.
Let's say there are two lenses (I do not specifically cite specific models as an example - we are considering the issue “in theory”): both, for example, fixes with the same focal lengths, but one of them, for example, will have the maximum aperture opening of 1,2 (hereinafter - lens A), and the other has 1,8 (hereinafter - lens B).
It is generally accepted that the first lens is "faster" than the second (as a rule, it is also noticeably more expensive).
Let’s say in practice, I don’t need to use aperture greater than 2,5 for my tasks, because a very narrow depth of field does not correct me.
Attention, question :))
Is it obligatory that lens A will continue to be "faster" at aperture of 2,5?
than lens B? That is, I set the same shutter speed and the same aperture on both lenses - do I get the same amount of light at the output that hit the matrix?
I guess that most likely there is no direct physical dependence here - the more the lens has the maximum open hole, the more light gets into the middle hole. Rather, the dependence here is mediated - in the manufacture of more expensive glass A, more enlightened lenses are used and the design of lens A is more advanced than that of a more budgetary lens B.
Or here's another, more obvious example:
there is a cheap universal zoom of 18-200 (3.5-6.3), and there is a fifty fifty.
I put a focal length of 50 on the zoom and open the aperture by 2,5, on the fix I also put 2,5. The question is the same: at the same shutter speed, the same amount of light will fall on the matrix?
Intuition suggests that it is different (I myself did not compare the histograms).
In other words, I have an assumption that it is necessary to give the correct definition of a "high-aperture" lens: one lens is "faster" in relation to another, NOT SO SOLY BECAUSE it can provide a larger aperture at the maximum open hole, but because on the same values of the average apertures, it will be able to let in more light.
I even have a conspiracy thesis that, for marketing reasons, optics manufacturers have specially agreed to artificially limit the maximum possible appetruction on cheap glasses so that expensive glasses sell better. In other words, constructively making an inexpensive fifty kopeck 1,4 in production at prime cost will not be more expensive than fifty fifty 1,8. However, this is not done on purpose so that there are three separate price niches: 1,2 (“Premium” segment), 1,4 (“Profi”), 1,8 (“mass” segment).
What do you think, Arkady?
Objective A will always be a faster prime. Closing the diaphragm is another matter entirely. With the same values of the number F, the same amount of light will fall in the same period of time. Please note - 18-200 (3.5-6.3) will in no way allow you to use F / 2.5.
In my article it is clearly stated that aperture is not only aperture. The aperture ratio depends on the luminous flux loss in the lens glasses, due to different optical schemes of the lenses - these losses will be different, but in general this can be neglected and only talk about the aperture-dependent aperture ratio. It is really difficult to make a high-aperture lens, it is even more difficult to teach the autofocus system to work with it.
I am also interested in the question of the need for a faster aperture lens, if I do not need fully open apertures (due to the small value of the depth of field).
I took a 50 mm 1,4g AF-S from a friend to play with, so the child on the F2 has one eye in focus, and the other is not. (I shoot close-ups at 5100, so that the face fills the frame as much as possible). So the question is - what kind of portrait is it?
Still interested in the dependence of the depth of field on focusing (I suspect that with the same F, the depth of field will be greater than the focus on 1 m). And also the dependence of the depth of field on the mm lens, although it may be the same as I wrote above. I will look for an answer further.
The site is super!
Yes, you are right, I made a mistake at the expense of F / 2.5, I hurried.
I wonder if some kind of objective, purely physical laboratory test is practiced for the amount of light transmitted by the lens to the matrix under the same conditions. After all, it is this key characteristic that could be a cornerstone when comparing the parameters of different lenses. It's just that now when they say “high-aperture” - this inference is made exclusively from the numbers on the marking of the lens itself (F / 1.2, F2.8, etc.), although this, you see, is not the most objective parameter. And so, we would make a summary table: when shooting test chart A at a distance of B meters, at focal C with aperture D on camera E, lens X did not give N lux of light, and lens Y gave N + 10% of lux of light. It would immediately become clearer what we pay money for :)))
Although I understand that in addition to the notorious aperture ratio, there are other quality characteristics of the lens. On the forums, they often operate with words such as "drawing", "color rendering", but it is impossible to measure them.
As I already wrote, the aperture is just one of the most objective parameters in terms of the general concept of “aperture”.
Hello, help me figure it out I got a lens CANON 28-80 3.5-5.6 III ultrasonic I have a photo camera CANON 1000D I can’t open for some reason the diaphragm i.e. it is in the near and far focus 5.6 I can close it it knocks it out to 32 but make less to 3.5 not get-what can it be and what can be done
Please tell me as accessible as possible! I was given a Pentax k-30 trying to figure it out! I read your review, very cool! BUT! I can’t understand how I can change the aperture and does the shutter speed change manually? F / number from 5.0 to 7.1, can I change these numbers somehow ??? For example, up to 11 or 3.5 ?? Thanks in advance!
Everything changes, read the instructions!
Well, thank you!! Very good advice !!)))
I want to say a clever idea: The relative aperture of the lens is the ratio of the actual aperture of the lens to the focal length. The reciprocal of the relative aperture is called the aperture value or aperture of the lens. The following series of relative apertures 1: 0,7 1: 1 1: 1,4 1: 2 1: 2,8 1: 5,6 1: 8 etc.
Hello Arkady, the best question for me is the question: "Where to start studying the art of photography?" To be honest, my brain is boiling with information. Something is clear, something is not at all clear. I have a Nikon D90 camera and an AF-S Nikkor 17-55 mm 1: 2.8 G ED lens.
I'm trying to take a photo according to your notes, there are obvious improvements. But for example, I can't find a common language with the diaphragm. I put the wheel on “A” - to change the aperture values and nothing happens: (But when I start changing the shutter speed to “S”, then naturally the aperture changes. To be honest, I am completely desperate. I want to try all the options :)
And again I repeat, where to start an overnight study, what is the priority ???
Thank you!!!!
Everything is very simple, first you need to read the instructions for your camera, find out which twists are responsible for what. And then twist, read, shoot, etc.
Thanks Arkady! I went to read the instructions and thanks for the review of the lens https://radojuva.com.ua/2013/01/nikon-17-55-f-2-8-g-ed-af-s-dx/
After reading the instructions, what should be studied further ?????
And another question, I was asked to take a photo of the child in the room, according to my observations, the light in the room is catastrophically small and the artificial light is yellow. What do you advise??? What parameters will be more or less optimal ???
Thanks in advance!
Arkady, I have one more NIKON AF-S NIKKOR 12-24mm 1: 4G ED lens, but you can get a go at it to review it. THANK!!!!
Yes, no problem, send it to me for a review.
I would love to send it, but I’m afraid from Canada it will go to you for a very long time, and the transfer will be ROAD)))) But, upon arrival in Ukraine I will contact you and give my lens for TEST DRIVE.
If it is possible to describe this lens, please describe (NIKON AF-S NIKKOR 12-24mm 1: 4G ED lens). He got to me in pursuit that I wouldn’t know what to do with him.
Arkady, it may be a stupid question, but it turns out that the aperture hole at a value of say 2,8 on Fix 50 mm will be smaller in geometry than the aperture hole at 2,8 on a 85 mm fix?
This is a relative hole. The word "relative" is often omitted. Relative aperture is the ratio of the effective aperture of the lens to the focal length of the lens. 2,8 is the reciprocal of the relative aperture, that is, the f-number. It is the very physical aperture of the lenses that may differ, but the ratio of this nat. apertures to the focal length of the lens for 2 lenses will be the same.