Camera lens and maths

[ericmark]

I have a Casio EX-Z600 camera and I wanted to work out how it compared with my D-SLR but clearly the sensor is much smaller so needed to work out how the focal length compared. The focal length is given 6.2 mm to 18.6 mm however the sensor dimensions are not only the area which is given as 1/2.5 inches well would have to be square inches.

The aspect ratio can be worked out from the pixels given as 2816 x 2112, but try as I could I got really silly results got it to 11 mm to 34 mm and quite clearly from the pictures wide angle was no where near 11 mm.

thinking I had made some silly error I used Java Script so I could feed in know information from other cameras to as much as possible test the method of calculation I have put it here I feel sure it is 1/25 inches rather than 1/2.5 inches as it would be strange to mix imperial and decimal but a sensor 5.8 x 4.4 mm is rather small I would have expected it for a phone, but not a camera. My D-SLR is 23.5 x 15.7 so having a sensor 18.5 x 14 is not impossible but unlikely.

So question which is most likely correct 1/2.5 or 1/25.

 

[Sam Gangee]

Sensor size: 1/2.5" (~ 5.75 x 4.32 mm)
See http://www.digicamdb.com/compare/casio_exilim-ex-z600-vs-casio_exilim-ex-s600/

 

[ericmark]

Thanks I clearly made a mistake with post this is correct link to the program I was trying to run.

I have since found what the 1/2.5 inch means it seems it's an antiquated measurement from the days of cathode ray tubes where the whole tube would not receive so it refers to the centre bit.

My maths has stumped me I can't work out given area and aspect how to convert to width and hight must be a way but can't think how to do it.

So as it stands I have to work backwards from real focal length and equivalent 35mm focal length plus the pixels the latter gives the aspect I can work out sensor size in mm.

But even if I could work out dimensions from area and aspect the 1/2.5 inch measurement it seems varies from manufacturer to manufacturer and is designed for a round sensor so is based on a square and sensors are rectangular not square so the size found would be so approximate as to be next to useless to compare cameras.

It would seem manufacturers don't want to say how small the sensor is with compacts and this allows them to hide the real size. The Casio EX-Z600 it would seems has approx 5.5mm x 4.1mm sensor compared with 23.7 x 15.7 for a cropped sensor on a D-SLR. So in real terms likely many phones are better than the compact camera.

It would seem with sensor sizes there are 16 mm to the inch not 25.4 as with any other system. Using that conversion did give reasonable results but with the two cameras I have the details for I can't get both to work it would seem Casio and Fugifilm do not sing from the same sheet so likely neither do the other camera manufactures.

As a result I have given up using the Optical Format.