What is lens aper­ture? This is a para­me­ter that char­ac­ter­izes the trans­mis­sion of light by an opti­cal sys­tem (cam­era lens). It is nec­es­sary to pay atten­tion to it when buy­ing pho­to­graph­ic equip­ment. In this mate­r­i­al, we talked in detail about what lens aper­ture is and what it affects.

Such equip­ment is need­ed when shoot­ing in low light con­di­tions. For exam­ple, if you want to beau­ti­ful­ly shoot a star­ry sky, a dark grot­to or a cave. Pho­to: sway.office.com

About opti­cal aper­ture in sim­ple words
What is lumi­nos­i­ty mea­sured in
Effec­tive and geo­met­ric lumi­nos­i­ty
What is a fast lens
When high cam­era aper­ture mat­ters
Aper­ture and lens choice

About optical aperture in simple words

All lens­es allow light to pass through the lens­es. The amount of trans­mit­ted light depends on var­i­ous para­me­ters. For exam­ple, on the degree of trans­paren­cy of the lens­es.

But the main para­me­ter that affects the beam of trans­mit­ted light is the degree of aper­ture open­ing. This is a plas­tic rotary disk, which con­sists of plates, “petals”. When turned, the petals open (a round hole appears between them) or close. The more the plates are opened, the more light they let in. The more the aper­ture of the lens can be opened, the high­er its aper­ture ratio.

How to find out the aper­ture ratio of the lens, where to see the desired para­me­ter? The val­ue is writ­ten on the hard­ware itself. The num­ber writ­ten on a par­tic­u­lar mod­el is the max­i­mum. Aper­ture opens up to this val­ue. Less is pos­si­ble, more is not.

The small­er the num­ber, the high­er the val­ue. For exam­ple, there are three lens­es with dif­fer­ent aper­tures: F4, F2.8, F1.2. The last one has the largest one (the diaphragm can open as much as pos­si­ble), the first one has the low­est one. The sec­ond option is the aver­age.

Aper­ture is not light sen­si­tiv­i­ty. The first is the char­ac­ter­is­tics of the lens. The sec­ond is ISO, a para­me­ter that char­ac­ter­izes the lev­el of sen­si­tiv­i­ty of the matrix (the detail that “turns” light into a pic­ture) to light. This term refers to expo­sure. It has already been dis­cussed in detail in the blog.

Aper­ture is a para­me­ter that is not always con­stant. For exam­ple, there are lens­es for which this val­ue changes with dif­fer­ent zooms. For exam­ple, NIKKOR Z DX 16–50mm f/3.5–6.3 VR. It was men­tioned in one of the reviews.

The NIKKOR Z DX 16–50mm f/3.5–6.3 VR is a fold­ing, com­pact wide-angle lens. Pho­to: millenniumoptiks.in

At the min­i­mum focal length of this mod­el, the indi­ca­tor is F3.5 (max­i­mum aper­ture), at the max­i­mum it drops to F6.3. This fea­ture is more com­mon in bud­get equip­ment. For more expen­sive mod­els, the indi­ca­tor is unchanged. This means that they have the same aper­ture at any focal length.

What is luminosity measured in

The let­ter “F” is writ­ten next to the num­ber on the equip­ment. This is the “F‑number”. It is deter­mined by a sim­ple for­mu­la: Divide the focal length of the lens by the aper­ture diam­e­ter. The result is the num­ber we need. For exam­ple, the focal length is 50 mm. And the max­i­mum open­ing is 25 mm. Divide 50 by 25. It turns out that the aper­ture ratio is 1: 2 (F2.0).

It is impor­tant to under­stand that the aper­ture is only a mech­a­nism that reduces and increas­es the diam­e­ter of the hole (light enters through it). Its max­i­mum size is lim­it­ed by the design of the lens.

But the diaphragm may not be at all. In this case, the shoot­ing always takes place at the “max­i­mum open aper­ture”. It is this mech­a­nism that is used in smart­phones.

What is the dif­fer­ence between F32, F1.4 and F5.6 lens­es and oth­ers? In the degree of aper­ture open­ing and in the amount of light trans­mit­ted. The avail­able dif­fer­ence is shown in the pic­ture below.

diaphragm row. Pho­to: assets.prophotos.ru

With a small­er aper­ture, there is more depth of field (the area in which objects are in focus), and less light enters the matrix.

If the aper­ture blades are wider open, the oppo­site hap­pens. The depth of field decreas­es, and a larg­er beam of light enters the matrix.

What is the max­i­mum aper­ture open­ing? Usu­al­ly it is not more than 1. But there are fast mod­els with F0.95 and more. How is this pos­si­ble? Every­thing is sim­ple. The focal length of the lens must be less than the hole diam­e­ter. As a result, when divid­ing a small­er num­ber by a larg­er one, the result is less than 1. Exam­ples of such mod­els:

– Laowa 33mm f/0.95 Argus CF APO;

– Han­de­vi­sion IBELUX 40mm f/0.85;

– Han­de­vi­sion IBELUX 40mm f/0.85;

– Canon 65mm F/0.75;

– Carl Zeiss Pla­nar f/0.7.

The Carl Zeiss Super Q Gigan­tar 40mm f/0.33 is a joke mod­el that has nev­er been pho­tographed. Pho­to: cameralabs.org

Effective and geometric luminosity

Every­thing we talked about above refers to geo­met­ric para­me­ters. Since the size, diam­e­ter is tak­en into account. But no lens trans­mits light 100%. For exam­ple, part of the light is reflect­ed from the glass sur­face. The qual­i­ty of lens­es and anti-reflec­tive coat­ings can affect this.

And if the lens is dirty, then light loss can reach up to 50%. There­fore, it is bet­ter not to for­get to clean it from time to time.

Out­come: due to many fac­tors (the qual­i­ty of the lens­es, the com­plex­i­ty of the design, etc.), the actu­al aper­ture ratio of the equip­ment will always be slight­ly less. How much? There is no uni­ver­sal indi­ca­tor. It is nec­es­sary to con­duct research on a spe­cif­ic lens.

If the geo­met­ric indi­ca­tor indi­cat­ed by the man­u­fac­tur­er is marked with the let­ter “F”, then the effec­tive one is indi­cat­ed with the let­ter “T”. You can find it on the web­sites of var­i­ous lab­o­ra­to­ries that are engaged in such research. For exam­ple, DXO­mark.

In the graph table with the desired para­me­ter — Trans­mis­sion. Pho­to: dxomark.com

Impor­tant: for lens­es with the same “F”, but dif­fer­ent “T”, the pic­ture will be dif­fer­ent. The bright­est will be the one that is shot on the “T” with a large indi­ca­tor. Some­times it is very impor­tant. For exam­ple, when film­ing. That’s why cin­e­ma lens­es are marked not “F”, but “T”.

What is a fast lens

This cat­e­go­ry includes options that have an indi­ca­tor of F2.8 and above (F2, F1.4, etc.).

If we are talk­ing about zoom lens­es, then such mod­els have the high­est aper­ture val­ue of F2.8. Equip­ment with this indi­ca­tor is usu­al­ly large in size and has fast aut­o­fo­cus.

There are also fast fixed lens­es. They do not have the abil­i­ty to change the view­ing angle. But at the same time, they are usu­al­ly small in size, allow­ing you to get a clear image even in dim light. Their aper­ture can be from F2 and above.

The fastest lens­es can be used by own­ers of full-frame cam­eras. There are bud­get and expen­sive mod­els from dif­fer­ent man­u­fac­tur­ers.

For medi­um for­mat cam­eras (matrix larg­er than 36x24 mm) there are no such super­mod­els any­more. The max­i­mum that man­u­fac­tur­ers offer is F2.8. Why is that? The larg­er the sen­sor, the larg­er the lens that can let in enough light to cov­er a larg­er area of ​​the sen­sor. As a result, the equip­ment is very large, expen­sive and incon­ve­nient.

When high camera aperture matters

With insuf­fi­cient light. For exam­ple, when shoot­ing in a dark room, in the evening on the street. Such a lens will give the matrix a max­i­mum of light. This is bet­ter than rais­ing the ISO and end up with a lot of noise in the pic­ture.

With a fast lens, you can shoot in places where arti­fi­cial light and insuf­fi­cient nat­ur­al light can­not be placed. For exam­ple, a tem­ple, a the­ater, a spe­cif­ic muse­um where you can not change the light­ing of the com­po­si­tion.

In such lens­es, as we men­tioned above, an improved aut­o­fo­cus sys­tem. And even in dif­fi­cult light­ing con­di­tions, the cam­era will still work quick­ly and con­fi­dent­ly. And if you arm your­self with a tri­pod, you can take fas­ci­nat­ing pho­tos of the star­ry sky.

With this lens, you can take beau­ti­ful pic­tures even at night. Pho­to: wall.alphacoders.com

A styl­ish and beau­ti­ful blurred back­ground is an artis­tic tech­nique that is avail­able with such lens­es. Depth of field decreas­es as the aper­ture is opened wider. There­fore, a fast lens allows you to make a blur­ry back­ground, and make one object clear. This allows you to focus on the object, make it more volu­mi­nous and hide unwant­ed details from the back­ground.

Aperture and lens choice

Such lens­es help to take beau­ti­ful and unusu­al pho­tos. But there are gen­res in which they are not need­ed. For exam­ple, shoot­ing:

- for a cloth­ing cat­a­log;
- Items: fur­ni­ture, acces­sories, dec­o­ra­tive items;
- land­scapes, nature;
- mon­u­ments, archi­tec­tur­al ensem­bles.

In these cas­es, aper­ture is not impor­tant. Because you usu­al­ly have to take pic­tures in a loca­tion with good light­ing, from a tri­pod, on a closed aper­ture.

But to buy such a lens for the cam­era is when shoot­ing:

- Events (e.g. wed­dings, grad­u­a­tions);
- por­traits;
- reportage;
- cre­ative (star­ry sky, unusu­al effects in the stu­dio or out­doors, etc.).

Such equip­ment will help you cre­ate beau­ti­ful cre­ative images that will become a wor­thy addi­tion to your port­fo­lio. We hope that our mate­r­i­al has helped you under­stand what aper­ture is and what it affects.