Foto at top: Holland Sanderling (Drieteenstrandloper) 10 meter windy dark cloudy wheather handheld V3 Nikkor 300mm f/4E PF VR equivalent 810mm (2.7 x 300) standard camouflage. This picture has been “soft cropped”, cut out off the RAW original file (shown below), thereafter image edited using software Adobe Lightroom.

This is Workshop Light page 5: Soft cropping, hard cropping, crop factor Light

Soft cropping using software like Adobe Lightroom

See the picture of the the Sanderling at top of this page. We have cut a piece out of the original digital file using appication Adobe Lightroom. We call this operation “soft cropping” to emphasize the difference with “hard cropping” whic always is performed by hardware. By the way: “to crop” in dutch means: “afsnijden, oogsten”.

The original unedited RAW picture of the Sanderling is shown here:

You can see more examples of soft cropping at: 13 Post production

“Hard cropping” and “soft cropping”, sensor formats, image area modes and crop factors in camera’s

In digital photography two essentially different methods of “cropping” exist. It is quite important to understand this difference if you want to buy the right digital camera or want to understand into which image area mode you should switch this camera:

Soft cropping (“kaderen”) is done by the photographer when “cutting” a part out off a digital picture using image editing software like in the example above. The more you crop the less resolution (pixels per square millimeter) the cropped picture will contain.

Hard cropping (by the way this is not an official expression but we use this terminology here to stress the difference between soft and hard cropping) is accomplished in one of two ways:

• When the photographer uses a full frame lens on an APS-C type digital camera sensor. The camera automaatically and irreversably “cuts” a piece out of the full frame lightbeam and stores this in the data buffer of the camera and displays it on the image screen of the camera, whether you like it or not.

• The photographer intentionally switches his/her digital camera into one of a camera’s secondary image area modes (beeldformaten) and as a result the camera will “cut”, again irreversably, a smaller piece out of the sensor area and transfer this smaller amount of pixels into the data buffer of the camera and display it on the image screen of the camera.

A hard crop happens for example when using:

• Nikon D800[E] 46 Mpixels standard full frame DX mode (36 x 24mm) (7360 x 49120 pixels) used in DX Mode (24 x 16mm) (4800 x 3200 pixels): crop factor 1.5.

• Nikon D500 21 Mpixels standard DX mode (24 x 16mm) (5568 x 3712 pixels) crop factor 1.5 in 1.3 mode (18 x 16mm) ( 4272 x 2848): crop factor 2.0.

• Panasonic 16 Mpixels G3: (standard crop factor 2.0) in 8Mb mode (crop factor 4) or 4Mb mode (crop factor 8).

Hard cropping a full frame lens lightbeam by an APS-C type camera

When you use a full frame lens at a digital camera with an APS-C type image sensor of size (rounded) 24 x 16 mm, for example a Nikon D300, D7200, D500 or Z50, this camera will only “see” and subsequently “hard crop” a part out of the full frame lightbeam projected by the full frame lens into the camera. It just happens that way.

Bird photographers do welcome hard dropping because it looks like the lens used has a larger focus distance. Marketeers like to call this phenomenon “focus enlargement” or something lik that. A 300mm lens used on a D300 “miraculously” behaves like a 450mm lens! This was of course good news especially for bird photographers. This confusion started when the first semi professional digital camera’s like Nikon D100 appeared on the market featuring a rather small image sensor still using lenses that projected an oldfashioned full frame (kleinbeeld film) 36 x 24mm image lightbeam on the smaller 24 x 16 mm image sensor of the camera. This type of sensor was originally called “APS-C type sensor“, whatever that means.

By the way: Nikon structurally calls its 36 x 24mm-sensor-formats “FX” (full frame) and its 24 x 16mm- sensor-formats “DX” (APS-C type).

The so called crop factor and 35mm equivalent of a combination camera-converter-lens

The crop factor of a camera has been officially defined as follows:

crop factor = (length diagonal full frame sensor) / (diagonal image sensor actual camera.

For a full frame sensor (36 x 24 mm) the length of the diagonalis 43 millimeter, for an APS-C sensor (24 x 16 mm) this is 29 millimeter. The crop factor of an APS-C type sensor is 43/29 = 1.5, the well known crop factor of DX camera’s like Nikon D300, D7200, D500 or Z50.

The “35mm equivalent” of a combination camera-lens-converter has been officially defined as follows:

35mm equivalent (millimeters) = focus distance lens (millimeters) x converter factor (if converter used) x crop factor camera.

More about the special meaning and value of this 35mm equivalent, oftn called “equivalent”

Generally the optical magnification of a lens is linearly proportional to its focus distance in millimeters, so the optical magnification of a camera-lens-converter-combination will be linearly proportional to the 35mm equivalent. The amount of detail of the surface in the digital picture of a bird at a certain distance, will therefore be squarely proportional to the 35mm equivalent because length and width of the bird (surface) will both be magnifed to the same extent. So the reach (bereik) of a combination camera-lens-converter will be squarely proportional to the 35-mm equivalent of this camera-lens-converter combination.

This “equivalent” can be regarded as the total focus distance of a combination of a digital camera-lens-converter. A lens, like a loupe, produces a magnified image of an object. The amount of magnification is linearly proportional to the focus distance of this loupe. In classical small film photography, wich uses 35 millimeter film negatives, the focus distance of (tele)lenses used, has always determined the magnification of these lenses.

In digital photography this happens to be a bit more complex because the surface of the image sensor of a digital camera, for instance an APS-C type camera like a Nikon DSLR D500, is substantially smaller than a classical 35 mm small film negative or positive.

So, on top of the real magnification of the lens used, the digital camera “crops” this “full frame” image, it cuts a piece out of the full frame-light bundle”produced by the full frame lens. See the illustration above. This results in an “artificial” magnification factor 1.5 in case of a D500 or any other APS-C type digital camera like a D7200 or a Z50. The size of this “extra magnification” is the so called “crop factor“. This crop effect is interpreted, if you like marketed, as “enlargement of focus distance” of the lens used. Anyhow this focus distance-comparison of sensor-based digital camera’s versus classical smallfilm camera’s is confusing if not meaningless but this discussion has been years fuelled by marketing nonsens in past years.

Nikon full frame camera’s like D800, D750, Z5, Z6 and Z7 can operate either in so called FX mode (full frame mode, 36 x 24mm) or DX mode (APS-C mode, 24 x 16mm) and often in some extra “image area modes” all of them implemented as extra hard crop modes. Particularly video modes may be hard cropped to accomplish higher FPS rates.

Only if the image sensor of the camera has sufficient resolution (a large number of pixels per square millimeter) the “extra magnification” caused by this hard cropping can be “realised” preserving considerable high image quality regardless of the implied lower resolution caused by the “stretching” process of hard cropping. In reality however the portion of the image “cut out” of the full frame image sensor is, within the camera, technically transformed and projected in lower than the original full frame resolution onto the camera’s display and written as an image file on the memory card of the camera.

So when the camera sensor has ample resolution your eyes will not notice any degradation of resolution and consider this “lesser detailed” image displayed on your screen or printed on paper as a genuine orifinal high quality full frame image. Precisely that is what for example a high quality high resolution image sensor of a modern D500 or Z50 can accomplish. And this, by the way, is also the reason why many bird and sport photographers asked Nikon to develop an APS-C type Z camera like the Z50. The combination of high image quality and crop factor 1.5 makes these APS-C sensor type camera’s ideal for sports, wildlife and bird photographers because soccer players, tennis players, athletes, lions, elephant, birds and the like are often far away and are moving fast (video!) and this type of photographer often works while carrying lots of stuff like tripods, camouflage, binoculars, camera’s, lenses, bird guides, cell phones, laptops, coffee, sandwiches, tents, backpacks, etcetera.

It is worthwhile knowing by heart that an APS-C Type camera cuts, “hard crops”, a portion of the full frame light beam that produces a hard cropped image with a surface being 1/1.5 part = 4/9 of a full frame image (because (16 x 24) / (24 x 36) = 4/9). For example a Z7 II of about 46Mp wil have about 5/9 x 46 Mp, APS-C normalised, and will have about the same reach (bereik), in fact ia bit more, than an APS-C tyoe Z50 of rounded 21 Mp.

Nikon DSLR full fame sensor D800	1.0
Nikon DSLR APS-C sensor D300 D7200 D500	1.5
Panasonic four thirds sensor MLC LX3 G1 G3	2.0
Nikon System 1 CX sensor MLC V1 V3 J5	2.7
Nikon MLC full frame sensor Z7	1.0
Nikon Z Series MLC APS-C sensor Z50	1.5

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35mm equivalent D500 Nikkor 500mm f/5.6E PF VR TC-14E=500 x 1.4 x 1.5=1050mm	APS-C sensor
35mm equivalent D500 Sigma Sport 150-600mm f/5.0-6.3 TC 1401=600 x 1.4 x 1.5=1260mm	APS-C sensor
35mm equivalent D500 G2 Tamron 150-600mm f/5.0-6.3 TC X14=600 x 1.4 x 1.5=1260mm	APS-C sensor
35mm equivalent Z50 Nikkor 500mm f/5.6E PF VR TC-20E III=500 x 2.0 x 1.5=1500mm (!)	APS-C sensor
35mm equivalent D7200 Nikkor 300mm f/4E PF VR TC-14E=300 x 1.4 x 1.5=630mm	APS-C sensor
35mm equivalent V3 Nikkor 300mm f/4E PF VR TC-14E=300 x 1.4 x 2.7=1350mm	CX sensor
35mm equivalent Swarovski 50X + V1 1 Nikkor 18.5mm f/1.7=925 x 2.7=2700mm (!)	CX sensor
35mm equivalent Nikon ED82 30X + Panasonic G3 Lumix 20mm f/1.7=600 x 2.0 = 1200mm	Four Thirds sensor

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Next page of workshop: 6 Reach