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Gary W. Graley
25th of November 2011 (Fri), 21:19
Just wondered how the mm numbers relate to 35mm lens focal lengths.
As an example, my SD1400 is 28mm with it's 5.0, while on the S100 at 24mm has a higher 5.2 mm listed
I would have guessed it would have been a lower #
G2

riverdog1
25th of November 2011 (Fri), 23:14
I was just wondering the same thing. Looking forward to the replies.

Scatterbrained
25th of November 2011 (Fri), 23:29
are the sensors the same size?

Gary W. Graley
25th of November 2011 (Fri), 23:40
That's what I was thinking, it must be the sensor sizes are different, which makes marking the mm on the lens kinda misleading when you check one camera from another, unless you just GO with the spec's they list and not pay any attention to the 5.0mm or 4.3mm or 5.2mm just adds to the confusion, since they seem to always relate back to the 35mm film lens sizes, why not just list THAT and be done with it?? but I'm a database kinda guy and having two things saying the same thing is redundant and I guess I don't like being confused, since I get confused pretty easily ;)
G2

c2thew
26th of November 2011 (Sat), 00:52
i'd like to know too! it's been bugging me since the zoom focal length doesn't match the perspective when comparing to my dslr. I get the full frame, 1.3x, 1.6x factors but how does it apply for point and shoots?

the jimmy
26th of November 2011 (Sat), 06:49
Here is a chart (http://www.jeffreysward.com/editorials/sensorsz.htm)giving the multiplier for different sensor sizes

Another useful site (http://sensor-size.com/)

sandpiper
26th of November 2011 (Sat), 09:31
That's what I was thinking, it must be the sensor sizes are different, which makes marking the mm on the lens kinda misleading when you check one camera from another, unless you just GO with the spec's they list and not pay any attention to the 5.0mm or 4.3mm or 5.2mm just adds to the confusion, since they seem to always relate back to the 35mm film lens sizes, why not just list THAT and be done with it?? but I'm a database kinda guy and having two things saying the same thing is redundant and I guess I don't like being confused, since I get confused pretty easily ;)
G2

Well, they use both because the shorter ones are the actual focal length, so are what you would expect to see on a tech specs sheet. However, because there are so many different sensor sizes in the P&S market, it is almost impossible to use the true figures for comparison between cameras. Therefore, the manufacturers also give the equivalent figure for the focal length that will give the same FoV on a 35mm frame. That allows a common reference point for all the cameras, but is not a true FL figure for the actual lens.

In reality, most people ignore the true figures and simply use the 35mm equivalent figures, for consistency between cameras. However, the more technical minded might need to know the true FL for DoF calculations etc.

It isn't redundant, because they are NOT saying the same thing. Actual FL is not the same as equivalent FL, which takes into account the crop factor. You can't list just one, because each is used for different purposes.

Gary W. Graley
26th of November 2011 (Sat), 09:53
Thanks for that chart, very helpful info.
and I guess for me the other info isn't as important as the relative 35mm focal length, but as you say, some folks really need that level of detail, appreciate your input on the reasoning behind the listings.
G2

mcluckie
26th of November 2011 (Sat), 12:11
Full frame sensors are the same angle of view as 35mm film cameras. For crop sensors, you need to multiply by the dinkiness of the sensor, 1.6 or 1.3. A small sensor takes just the center of the lens you're using, so it's like being pre-cropped and every lens gets longer (100mm is 160 on a 1.6 APS-C). the smaller the sensor, the longer the effective focal length.