What are the FX, DX and APS-C sensor size dimensions and crop factors for 35 mm DSLRs?

APS-C” is the acronym for “Advanced Photo System – Classic“.

Remember Kodak 35mm film?

35mm film had two sets of sprocket holes and was often packaged in the “135 film cartridge”…

One set of sprocket holes ran along the top edge of the film strip and one set ran along the bottom edge, horizontally along the length of the entire strip.

Standard 35mm film’s exposure area was landscape format.

  • 36 mm along the film strip
  • 24 mm across the film strip
  • in between these two sets of sprocket holes

So, why is a 36 mm x 24 mm film called 35 mm?  It is the same film format that Hollywood was using when making 35 mm film movies…  The same sprocket spacing… Made on the same manufacturing equipment…  And, most importantly … 35mm film is 35 mm from top of strip to bottom of strip.  Ha!

There was even old movie color film stock sold to 35mm camera buffs for cheap…

Kodak again took this same 35mm film, without any changes to the film itself, turned the exposure area side ways into a portrait formal along the strip.

  • an vertical exposure area of 25.1 mm × 16.7 mm was created

Some of us called this format “half-frame.”  You may have seen these also referred as 24 mm x 18 mm … I never measured.

For those of us who had cameras for this film, often range finder models, we got 72 shots on a 36 exposure roll.  72 shots on a roll of film was pretty cool back in the day taking snaps.  And, it saved a ton of money on film …  Quality was pretty good for vacations and family outings.

This half frame film format was essentially a “re-cropping” of the standard 35mm film roll

… which Kodak officially dubbed with the frame name “APS-C.”

Canon, when it came out with its DSLR sensors, adopted this APS-C nomenclature for its “cropped sensor” sized format.   And, so the fun began with “crop sensor” cameras…

To keep it a bit more confusing, no one actually uses the exact APS-C film format size in their DSLR sensor sizes.

If this were not confusing enough, there are model to model variations within each vendor …

  • Olympus Four-Thirds:  17.4 mm x 13.1 mm
  • Canon APS-C:  22.5 mm x 15.0 mm
  • Nikon DX:  23.6 x 15.8mm (D3000), 23.6 mm x 15.6mm (D7000) 23.6 x 15.8mm (D90), …
  • Nikon FX:  35.9 mm × 24.0 mm (D3X), 36.0 mm x 23.9 mm (D700), …
  • Canon FF: 36.0 mm x 24.0 mm
  • Sony APS-C:  21.5 mm x 14.4 mm
  • Sony Alpha 900:   35.8 mm × 23.9 mm

The Nikon crop sensors give you about a 1.52 “crop factor” vs the standard FX full frame format lenses.  Crop Factor can also be thought of as a “Magnification Factor”.

What does this mean?

A 200mm lens on a DX format camera gives you about 6 power magnification.

On a 35mm film camera, this same 200mm lens provides about a 4 power magnification.

The 35mm film camera is much like an FX sensor format.  So, the full frame FX sensor DSLR will also provide about a 4 power magnification with this 200 mm lens.

So, why is the magnification 6x on a DX DSLR and 4x on a FX DSLR?

The 1.52 crop factor times 4 power on full frame for a 200 mm equals about 6 power on the DX DSLR.

On DX sensors this is a great magnficiation advantage…

For Wide Angle Lenses, you get correspondingly less width for any given lens, as these too are “magnified”.

Think of being magnified as the same as being less wide or more telephoto.

Thus on a DX DSLR using wide angle lenses:

  • 35 mm lens ( slightly wide on FX ) becomes a “normal lens” on DX
  • 20 mm lens  ( very wide on DX ) becomes only slightly wide on DX  and, so on

Why does this work this way?

MATH:

Well, it’s a rule of thumb that magnification factor is the lens focal length divided by the diagonal of the film frame…

The film diagonal length on 35mm film is about 43.3 mm, or about 50 mm … So, it is about 1 power, or like “normal vision” magnification.  Thus, the 50 mm lens was considered the “normal lens” for 35 mm film…

For a DX sensor, the diagonal is about 28.4 mm …

Crop Factor for Nikon DX format is 1.52

  • ( 43.3 mm diagonal divided by 28.4 mm diagonal = 1.52 )

You can figure out the APS-C crop factors accordingly, here they are roughly:

  • Canon –  1.6
  • Nikon – 1.52
  • Sony –  1.7

Then there are the Canon EOS cameras … which are another bird entirely…

  • Sensor:  27.9mm × 18.6mm
  • Crop Factor:  1.3

Get it .. ?

Got it … ??

Good …. !!!

Now to confuse you further, while the crop factor is about 1.52 for a DX sensor, the sensor area itself is of a DX is less than 50% the size of an FX sensor.

So, these DX sensors gotta work a lot harder to get their information … but, this is a topic for yet another day…


 

 

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