Foto at top: Holland sept 2023 sun Grey Heron (Blauwe Reiger) catching lobster size 94cm distance 45m equivalent 1050mm Nikon Z50 Nikkor 500mm f/5.6E PF VR standard camouflage APERTURE Mode Birds Fast 1/2000 f/5.6 ISO 200 -1.5EV. Crop 1500 x 1000.

“Light, light and more light”: APERTURE, ISO and EXPOSURE TIME

The settings of APERTURE (diafragma lens in 1/f waarden), ISO (lichtgevoeligheid sensor in ISO waarden) and EXPOSURE TIME (sluitertijd in seconden) determine the exact amount of light that will create a digital picture. In photography these are sometimes called “Big Three“. Some call them “Holy Trinity”. They determine the amount of light that the image sensor will be exposed to.

When you use the camera in APERTURE Mode, values of APERTURE and ISO value will be set by you, however the value of EXPOSURE time in seconds will always be calculated by the camera which uses its automatic light measurement determining the amount of incoming light as described at Equipment & settings.

You can only indirectly adjust EXPOSURE TIME value by using the TIME Correction +/- button of the camera. This button is mostly used to apply more or less systematic permanent or an incidental last minute corrections of the standard EXPOSURE TIME calculated by the camera. You can explicitly assign this important function to the subdial of your Nikon camera as we will see. In APERTURE mode Birds REACH and APERTURE mode Birds ACTION, both derivatives od standard APERTURE Mode, this is important.

When actually photographing it helps to use some kind of “mental model” of the operation of Big Three. Particularly in bird photography a good understaning of the effects and essentially various side effects of each one of Big Three is key.

	APERTURE	“ISO”	EXPOSURE TIME
Amount of light sensor receives is determined by:	size lens opening (f/stops 1.4, 2.8, 4, 5.6, 8, 11, 18, …)	sensitivity to light of the image sensor (ISO values 64 .. 256000)	time duration image sensor is exposed to incoming light (seconds)
Side effect:	Large/small: large/small Depth Of Field (“DOF”)	Too high: noisy picture & low colour contrast	Too long: blurred picture

This may be a “mental model” of your camera’s operation:

“Photographing” is “writing with light”

Look at the picture of a lens-camera combination above: the (white) arrow represents the incoming light on its way to the image sensor (green) in the camera. What happens is this:

• 1 The size of the APERTURE (oppervlak lensopening) (red) as set by you will determine the amount of light that will be passed onto the image sensor.

• 2 The ISO value, also set by you, will control the ISO light sensitivity (regelbare gevoeligheid voor licht) of the image sensor (green) as represented by the sensitivity curve in the diagram below.

• 3 The duration in seconds, EXPOSURE TIME (belichtingstijd in seconden), that the shutter curtain (blue) in front of the image sensor is openend, will deterime how long the image sensor is being exposed to incoming light.

These three together will determine the voltage (strength) of the electronic signal that each individual pixel (beeldpunt) of the image sensor will output. This voltage is roughly linearly proportional to the amount of incoming light (within the limited range of light intensity: the “straight” part of the sensitivity curve of the image sensor).

The image sensor of the digital camera is – basically by you – set to a specific ISO sensitivity to light usually in the range of 64 – 512.000 ISO Sensitivity. (“ISO” is short for International Standard Organisation. They define things like “Kilogram”, “Meter”, “Second”, etcetera). For example Nikon D500 and Z50 both have a range of 100 – 512.000 ISO.

Every time you half press Release the camera will perform an automatic light measurement (lichtmeting) – details 5 EXPOSURE (A Mode) – and compute the optimal EXPOSURE TIME value, using the actual values of Big Three, and when you full press Release, “shoot” a picture (up to 11 times a second at D500, including opening and closing the mechanical shutter curtain) and write the *.NEF file containing the digital image into the data buffer of the camera (up to 11 times a second at D500). Nikon flagship Z9 can do all this up to 30 times per second. Some camera’s are even faster (and more expensive).

However: only you can observe and anticipate at everything happening out there in the field: the actal direction of the light like backlight or front light, speed and size of the bird(s) (expected), the type of action, required depth of field (scherptediepte), etcetera. So you have to inform the camera about al this by setting or adjusting camera parameters like APERTURE value, ISO value and possibly EXPOSURE TIME Correction +/- , according to your ideas and experience of required shutterspeed to get in-focus pictures, occasionally stopping down a lens to get some extra detail or setting under– or overexposure of the image sensor because of backlight/frontlight in this particular, unique situation.

So the camera all the time needs your input to calculate the required EXPOSURE TIME (shutterspeed in seconds).

More about APERTURE (diafragma)

APERTURE is an inverted (omgekeerde) measure (maat) in stops (stops) of the diameter of the lens opening through which all incoming light is passing to the image sensor: f/1.4, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32. In this definition of APERTURE a value f/2.8 represents a relatively large lens opening whereas APERTURE value f/22 represents a very small lens opening. More about stops down at this page.

APERTURE value determines overall correct exposure of the pictures but also the so called depth of field (scherptediepte) in the picture. The higher the APERTURE value, the more depth of field (scherptediepte). This is purely an optical feature of a lens but important in bird photography if you need good detail from head to tail when photographing large birds or when you want to isolate the subject bird(s) from the surrounding foreground and or background. Setting APERTURE value is one of the “creative” tools of a photographer.

“Stops” in photography

In photography the value of each one of “Big Three”, and generally the amount of light the image sensor is exposed to, is measured and reported back by the camera in so called “stops“, factors 2 or 1/2. Since they are powers (of number 2) and not factors (in multiplication), you can add and subtract those values. Some examples may illustrate this:

The overall effect on EXPOSURE TIME of increasing APERTURE by 2 (increasing size of lens opening by factor 4) is equal to the effect of increasing ISO by 2 stops (increasing sensor sensitivity by a factor 4).

The overall effect on EXPOSURE TIME in seconds of decreasing APERTURE by 2 stops, for example by decreasing the size of the lens opening one stop via adding a 1.4 converter and stopping down the lens one stop to protect Highlights detail, at the same time increasing ISO value by 2 stops, is zero.

Whenever you start photographing or the situation in the field changes: like distance to the bird(s), wheather condition, stationary bird, bird in action, direction or type of light, you should basically have to reset one or more of “Big Three” so the camera can compute the actually required optimal EXPOSURE TIME according to this particular situation, in bird photography often using the camera in “standard” APERTURE Mode.

Results of correctly setting Big Three

• Correct values of EXPOSURE TIME: Not blurred but correctly focussed pictures (assuming stabilisation and focussing of equipment are in order).

• Correct values of ISO: Minimal noise (ruis), sufficient detail, contrast and colour contrast in the Blacks (Lage Lichten) of the picture.

• Correct values of APERTURE: No too dark or too light pictures. and no clipping (“uitgebleekte Hoge Lichten”) but good detail in the Highlights (Hooglichten). Also no diffraction (onherstelbare optische vervorming) caused by APERTURE values like <= f/16.

• Optimal depth of field (scherptediepte) “DOF”: High APERTURE values like f/1.4, f/2.8, f/4, … result in large depth of field (scherptediepte) which is almost always welcome whereas low APERTURE values like f/16, f/22 … result in restricted depth of field (scherptediepte) which may cause problems in case of very large birds or birds moving towards or from the camera. In lightweight bird photography it is often difficult to acquire larger DOF when you are using super telelenses including converters and possibly stopping down lenses, alltogether resulting in small APERTURE values like f/8, f/11, f/13 or worse.

Possible negative side effects of setting, APERTURE, ISO, EXPOSURE TIME values

Generally the dilemma in lightweight bird photography is: avoid noise (ruis) but at the same time avoid worthless blurred pictures. You definitely should know by heart when and to which extent (re)setting one of Big Three may have significant or even disastrous and various (!) side effects. We will list those below:

• Too long EXPOSURE TIME may cause blurred pictures (bewegingsonscherpte).

• (Too) high ISO values may result in incorrectable noise (ruis) and some lack of detail and or colour contrast, progressively occurring at higher ISO values.

• (Too) high APERTURE values may cause overexposed pictures with insufficient detail and “clipping“of Highlights (“uitgebleekte Hooglichten”).

• Extremely low APERTURE values can cause diffraction (schadelijke optische vervorming met verlies in detail) progressively occurring at very low lens openings like 1/16, 1/22, etcetera, the amount of diffraction depending on the type of lens.

The next diagram summarises all this:

Some examples illustrating (side) effects APERTURE values

In the next picture only the Black Tern (Zwarte Stern) in the foreground is within depth of field. In this case it was what we wanted.

APERTURE and autofocus and “Nikons DSLR f/8 support”

Your setting of APERTURE value has two essentially different but quite important effects regarding autofocus:

• A small value of APERTURE (diafragma) may generally cause slower and or less accurate autofocus and tracking because the camera may not receive sufficient light. Repeatedly pressing or briefly touching manual focus ring often helps the camera to resume autofocus. So make sure, when working handheld, to support the lens in such a way that you can touch manual focus ring when photographing in difficult situations (and use the correct setting AF/M or M/AF or M as explained at Lenses. Repeatedly pressing AF-ON button (if using Back Button AF) or half pressing Release button (if not using Back Button AF) may often help also.

• Nikon DSLR’s only: At APERTURE openings smaller than f/8, some advanced autofocus functions of Nikon DSLR‘s are not supported. This is sometimes referred to as “Nikons “F/8 support“: Nikon DSLR’s, at APERTURE openings smaller than f/8, will not support the advanced AF functions 3 D, Group and Automatic choice AF area as explained at Focussing & tracking.

Be aware of these restrictions when photographing bird action. For example adding a converter may transform your Nikon, Sigma or Tamron D500-combination into an f/9-, f/11-, f/13-combination wich may not any more pass sufficient light into the camera to accurately autofocus and or support advanced AF functionality below lens opening f/8 (and or miss the bokeh you might have wanted). Using for example a Nikkor 300mm f/4E the amount of light that passes through APERTURE f/11 is but 1/8 part (3 stops down) of the incoming light, less than 12.5% compared to the full APERTURE f/4E. Stopping down this lens may also be disastrous with respect to autofocus fuctionality and reliability and or loss of bokeh.

Examples of not supported advanced autofocus functions:

• D500 Tamron 150-600mm f/5.0 – 6.3 + 1.4 converter: APERTURE f/9

• D500 Sigma 150-600 f/5.0 – 6.3 + 1.4 converter: APERTURE f/9.

• D500 Nikon 300mm f/4E + TC-20E III, 1 stop stopped down: APERTURE f/11.

However when adding a 2.0 converter to D500 Nikkor 300mm f/4E PF VR it will change APERTURE value to f/8 and the autofocus sensor will only receive 25% of the incoming light, when compared to f/4.0, but will still support all advanced AF functions D500. At Nikon mirroless camera’s (MLC’s) of System 1 and Z Series the situation of advanced AF fuctionality is essensially different.

So avoid stopping down lenses (lenzen afstoppen) particularly in situations with low availabe light.

Do practice all this, particularly setting and using advanced AF functions and setting APERTURE values and switches of lenses. It takes some time but is definitely worth it.

Having said all this, we nevertheless experienced that autofocus (not the advanced AF functionality 3D etcetera!) often still works quite well if one has good available light! For example using a D500 with Tamron 600mm G2 TC X14 or Sigma Sport 600mm TC 1401, by the way both being quite good combinations, the DSLR D500 will almost always focus reliably, except of course in classical difficult situations like low contrast-, vague, pale, non-structured objects, etcetera.

Effect of too large APERTURE values

Too high APERTURE values can cause incorrectably overexposed pictures with insuffcient detail in the Whites and Highlights (Hoge Lichten) (“uitgebleekte Hoge Lichten”) and low contrast.

Diffraction

Stopping down (afstoppen) a lens to extremely low APERTURE values like f/16, f/22 may cause diffraction (diffractie), a complex quamtum physical optical phenomenon that seriously deteriorates image quality and occurs when light is passing through extremely small openings. The amount of diffraction depends on the construction and type of the lens.

Some examples of bird action photography

The Woodpecker, an extremely fast starting and flying bird, was flying towards the camera at 3 meter/second and our Z50 managed to track it, albeit in good sunlght. Our time stamped pictures confirm this speed. And by the way the D500 is an even better subject tracker. Until recently (january 2023) Nikon Z mirrorless camera’s tend to be somewhat weaker in tracking than Nikon DSLR‘s, although this situation is improving graduallsy. MLC‘s don’t have a dedicated autofocus sensor. Image and autofocus tenchnique is integrated at the one and only sensor and it seems that it requires time to resolve this in firmware.

The beautiful Sandwich Tern was out fishing near its breeding colony at isle Texel in Holland. We expected that it would sooner or later scratch the water surface to catch insects or small fishes to feed its young and could track it using our lightweight Nikkor 300mm f/4E PF VR:

Effect “stopping down” (“afstoppen” of “diafragmeren”) of lenses.

Stopping down (“afstoppen” of “diafragmeren”), usually 0.5 – 1.5 stops, sometimes even up to -2.5 EV, affects the operation of the lens used. By using only the central part of the optical glass, which is less “curved” than the side parts, the lens suffers less from optical aberration so photographs will be slightly more detailed. The effect of this phenomenon varies per lens type. You better know the optimal amount of stopping down by heart:

• Nikkor 300mm f/4E PF VR: 1.0 – 1.5 stops stopped down clearly causes some effect.
• Nikkor 500mm f/5.6E PF VR: 1.0 or more stops stopped down causes hardly any effect (also some loss of AF speed). By the way Nikon claims no loss of detail using TC-14E III. In our experience this is correct.
• Nikkor 200mm-500mm f/5.6E: 1.0 stop stopped down causes some effect (also some loss of AF speed). +
• Sigma Sport 150-600mm f/5.0-6.3 1.0 stop stopped down clearly causes effect even with 1.4 converter, also some loss in AF speed.
• Tamron G2 150-600mm f/5.0-6.3: 1.0 stop stopped down clearly causes visible effect even with 1.4 converter, also some loss in AF speed.

When you add a 1.4 converter and stop down the lens one stop, for example a lens having APERTURE f/6.3, the lens will change into a lens with APERTURE f/13 and end up transmitting but 12.5% of the original light at f/6.3 and will loose its Nikon DSLR Advanced AF support and may suffer from decreased accuracy and or AF speed.

Anyway and nevertheless don’t ever sell your good old fast telelenses unless you have a beter alternative. For many years we are using our featherlight (770 gram) Nikkor 300mm f/4E PF VR handheld with or without converter if we want to be movable and versatile and hold our camera and lens pointed at fast moving bird(s) during longer periods and do have sufficient amount of light in difficult focus tracking situations. Look at the examples above of tracking a fast Great Spotted Woodpecker (Grote Bonte Specht) and tracking this Sandwich Tern (Grote Stern) at 45 meter away from us!

All this may sound quite alarming but nevertheless in reality in our experience autofocus (not the advanced AF functionality 3D, etcetera!) still works fine if you have good sunlight and high quality equipment! For example using a D500 with Tamron 600mm G2 TC X14 or Sigma Sport 600mm TC 1401, both being high optical quality combinations, our semi pro DSLR D500 will most of the time autofocus reliably, except of course in classically difficult situations like low contrast, unstructured objects, etcetera.

Positive side effect of using a large APERTURE: bokeh (onscherpe achtergrond en of voorgrond)

A large APERTURE (lensopening) will result in high bokeh.

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About our “APERTURE Mode Birds Reach” and “APERTURE Mode Birds Action”

In standard bird photography mostly tele or super tele lenses are used. This implies that usually APERTURE values have to be low and constant like f/4, f/5.6, f/8 or f/11, unless you stop down lenses, which we almost never do any more using our modern Nikon tele lenses. These exceptional APERTURE values are a disadvantage. So we tried to change the disadvantage into an advantage and we developed our rather succesful APERTURE Mode Birds Reach ( qqq ) and APERTURE Mode Birds Action ( qqq ).

These two variants of standard APERTURE mode enable us to photograph birds using Nikon equipment without this almost continuously checking and resetting of the camera during actual photography. And this works great! We are using these two modes for years using both Nikon DSLR’s and Nikon Z Series Mirrorless camera’s.

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