• Please use real names.

    Greetings to all who have registered to OPF and those guests taking a look around. Please use real names. Registrations with fictitious names will not be processed. REAL NAMES ONLY will be processed

    Firstname Lastname

    Register

    We are a courteous and supportive community. No need to hide behind an alia. If you have a genuine need for privacy/secrecy then let me know!
  • Welcome to the new site. Here's a thread about the update where you can post your feedback, ask questions or spot those nasty bugs!

The trouble with focal lengths

Doug Kerr

Well-known member
Hi, Michael,

For me the designation of 'full frame' is not very precise, it has entered common language as 36x24mm negative/sensor equivalent.

A lens designed for a 1/2.5" sensor and being used with this sensor is used full frame.
Same goes for a 4/3 lens used on this sensor, APS-C lens on the adequate sensor and so on up to a MF lens used on a MF sensor. In all cases the sensor fills the image circle in the best possible way.

Tilt/shift lenses and LF lenses are a different breed as these have an image circle considerably larger than the negative/sensor these are being designed for to permit for corrections (e.g. Scheimpflug).

A photographer being only used to 4/3 not having any other reference will refer to 20-25mm as his 'normal' focal length.

A photographer being only used to APS-C not having any other reference will refer to 30-35mm as his 'normal' focal length.

A photographer being only used to 36x24mm sensor/negative not having any other reference will refer to 40-50mm as his 'normal' focal length.

A photographer being only used to MF sensor/negative not having any other reference will refer to 75-90as his 'normal' focal length.

The 36x24mm sensor/negative is - being most common during the dominance of film - currently the best common ground for many people to establish a link between focal length (what is marked on the lens) and angle of view. The crop factor is just a mnemonic trick to get to this reference dimension.

Indeed. The "crop factor" is actually the inverse of the relative size of the format being discussed, compared to the size of the "reference" format, 36 × 34 mm

I wonder if future generations of photographers will still use it when sensor formats might use sizes other than in the list above and 36x24mm might have become just an obscure reference...

All very well said.

Thanks.

Best regards,

Doug
 
Top