[RobG]

It is not strictly legal to derive a ratio with a higher precision than the numbers used to get it. Basically, given that the last significant digit in the focal lengths is entire millimeters we can assume it is rounded to the nearest millimeter. The ratio is then somewhere between 61.5/39.5 and 60.5 and 40.5, or between 1.494 and 1.557.

Legal? What laws are you referring to? Am I going to get arrested by the Maths Police?


If I divide 1 by 3 I'll get 0.3 repeater which has a lot more digits than the source numbers. Rounding it to 0.3 or zero wouldn't necessarily make sense. Anyway, you're over-thinking this. I don't know how the camera arrived at the numbers in the EXIF file. I don't know whether it rounded them, took the integer value or whatever. I simply worked with the numbers provided because I was surprised that the camera reported a different effective focal length than what was expected based on a 1.5 crop factor. I think what others have said is likely quite correct; that the sensor is a different size to the K3 sensor, so the crop factor is slightly different. I'm not getting hung up on the level of precision or anything like that.

---------- Post added 19-05-21 at 04:59 PM ----------

The camera does the calculation. ExifTool pulls the value from the standard EXIF.

Sure. I'm not sure that this contradicts the idea that the "effective focal length" reported by the camera is variable, though?

[xandos]

QuoteOriginally posted by xandos QuoteIt is not strictly legal to derive a ratio with a higher precision than the numbers used to get it. Basically, given that the last significant digit in the focal lengths is entire millimeters we can assume it is rounded to the nearest millimeter. The ratio is then somewhere between 61.5/39.5 and 60.5 and 40.5, or between 1.494 and 1.557.Legal? What laws are you referring to? Am I going to get arrested by the Maths Police?

Yes. Nobody expects the maths police.

If I divide 1 by 3 I'll get 0.3 repeater which has a lot more digits than the source numbers. Rounding it to 0.3 or zero wouldn't necessarily make sense.

Here we can assume from context that you are using the integers 1 and 3, which are defined with infinite precision. A vertical sensor size stated to be for example 15.5mm is not necessarily defined that precisely. Its likely not 15.50000000mm, but some value between 15.45 and 15.55mm. The pixel pitch stated earlier of 3.76um for example does not fit exactly in 15.5mm. But we have no way to know if that number is precise either.

Anyway, you're over-thinking this.

Definitely. Apologies for that, I can't help it.

I don't know how the camera arrived at the numbers in the EXIF file. I don't know whether it rounded them, took the integer value or whatever. I simply worked with the numbers provided because I was surprised that the camera reported a different effective focal length than what was expected based on a 1.5 crop factor. I think what others have said is likely quite correct; that the sensor is a different size to the K3 sensor, so the crop factor is slightly different. I'm not getting hung up on the level of precision or anything like that.

I agree with all of that. I was also one of those people stating that the sensor size is slightly different. Not 1.5 to 1.54 different though, the crop factor of the original K-3 was closer to 1.53.

However, I think my point is still valid, especially in cases where a lens has known focus breathing. To restate that point (at the risk of being somewhat obnoxious): you can apply a crop factor of 1.54, or maybe 1.5, but unless you know well how your lens behaves, and what its focal length is as a function of distance, its not that useful. The exact effective focal length will likely be different. But as long as you take the number with a grain of salt and don't expect your 100mm to become 'exactly' 154mm regardless of the circumstances, its fine.

[stevebrot]

Sure. I'm not sure that this contradicts the idea that the "effective focal length" reported by the camera is variable, though?

Did you mean "FocalLengthIn35mmFilm" (official name in the EXIF spec) or maybe "FocalLengthIn35mmFormat" (the slightly modified ExifTool tag name) or something else? My comment was in regard to the values as pulled from the EXIF. Since the same lens on other cameras is reported as FocalLengthIn35mmFormat = 60mm, I think it is reasonable to assume that the value of 61 was derived by a means other than that used on those other bodies.

Just where it got 61 from is a mystery. I would have expected 62.


Steve

[ulrich]

Lensfun is a database of cameras?

Of course not, but it helps (needs the camera mount and crop factor)

Quote from https://lensfun.github.io/faq/:

The camera entry in the database only holds crop factor and lens mount. As a workaround you can simply select any other camera with the same lens mount and sensor size or crop factor.

Adding a camera is here.

[wkraus]

And to make things even more complicated, you can use RawTherapee to get a frame size of 6216x4152 pixels instead of the nominal 6192x4128 pixels, with a different crop factor again that I am too incompetent to calculate. Apparently there is an unused border zone (a border value that can be set in RawTherapee) to accommodate the sensor movements in SR and so on.

[RobG]

Did you mean "FocalLengthIn35mmFilm" (official name in the EXIF spec) or maybe "FocalLengthIn35mmFormat" (the slightly modified ExifTool tag name) or something else?

Sorry, I didn't go back to Flickr which calls it "Focal Length (35mm format) - 695 mm" as opposed to the 450mm focal length shown next to the f-stop.

[xandos]

And to make things even more complicated, you can use RawTherapee to get a frame size of 6216x4152 pixels instead of the nominal 6192x4128 pixels, with a different crop factor again that I am too incompetent to calculate. Apparently there is an unused border zone (a border value that can be set in RawTherapee) to accommodate the sensor movements in SR and so on.

That is very interesting! I had no idea!

[wkraus]

That is very interesting! I had no idea!

We have several local RawTherapee specialists who probably can tell you much more – users heckflosse, The Squirrel Mafia, and possibly others.

[zapp]

I don’t care about crop factors, I care even less about a thousands of a crop factor. Equivalent focal length is an invention by monkeys hammering on typewriters. Understand the concept and life gets easy.