Last question on equivilent digital focal plane to 35mm?

Question

I am usually very, very good at numbers. This will be the LAST time I ask this question (unless my next toy is a DSLR). I got the equivilent number yesterday for my Fuji. Can I please ask you geniuses Dr. Sam, Pigoros and antonio m same question for Sony DSC-H2? 2.8/3.7 6-72 (12Xoptical). Sensor size 1/2.5 I'd like to give each of you 10 pts but can't. Should I not vote at all?

Answer 1

For ANY 1/2.5" sensor the crop factor is 6.03X.

6 mm x 6 = 36 mm equiv.
72 mm x 6 = 432 mm equiv.

For ANY 1/1.8" sensor, the crop factor is 4.83X.
For ANY 1/1.7" sensor, the crop factor is 4.50X.
For ANY 1/1.6" sensor, the crop factor is 4.44X.
For the Olympus 4/3 system, the crop factor is 2.0X
For many Canon DSLR's, the crop factor is 1.6X.
For most Nikon DSLR's, the crop factor is 1.5X.

If it rains tomorrow, I'll see if I can figure out a formula for this stuff. I guess I'd have to figure out what the heck 1/1.8" means first, though. Maybe I can find it on the internet.

Answer 2

The 35mm equivalent ratio for this sensor is 6 (calculated on the diagonal ratio to 35mm film it is 6.0243, which is close enough to 6 for practical purposes).

The lens focal length equivalent will be 36-432mm. This might just be counted as a wide angle at the shorter focal lengths. At the longer focal lengths, it would be a long telephoto, giving about x10 magnification.

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Added after reading Dr Sam's response.
The 1/2.5in etc seems to be an archaic reference to TV camera tubes, and is the outer diameter of the sensor tube. The usable sensor area is then about 2/3 of the diagonal of the tube, but this is not governed by some exact relationship that can be calculated. So a 1/2.5in sensor has a 'tube dia' of 25.4mm/2.5 or about 10mm. Typical sensor diagonals are then around 7mm.

I hope Dr Sam has fun working on this. The key issue is not the sensor type (1/2.5in, 1/1.8in etc) but the sensor diagonal and aspect ratio.

------------------- Added
The rough sum for equivalent ratio (ER) is

ER = 43 * TR / (25.4 * 0.7) where TR is the denominator of the sensor size (1/2.5 sensor - TR = 2.5). Simplified, this gives

ER = TR * 2.4.

This seems to be okay to about one decimal place.

(I know, it's a sad, sad person who does this when they could be outside on a lovely Saturday morning taking photographs!)