What is the "crop factor" of a Pentax 645D? ...

[xpatUSA]

... or any medium format sensor for that matter?

Someone thinks it's about 1.5 here:

https://www.dpreview.com/forums/post/61354402

On the other hand, Wiki thinks it's about 0.8 here:

https://en.wikipedia.org/wiki/Image_...mats_and_sizes

I am referring to the commonly used "35mm crop factor" where the "35mm" is usually left out.

[george013]

... or any medium format sensor for that matter?

Someone thinks it's about 1.5 here:

https://www.dpreview.com/forums/post/61354402

On the other hand, Wiki thinks it's about 0.8 here:

https://en.wikipedia.org/wiki/Image_...mats_and_sizes

I am referring to the commonly used "35mm crop factor" where the "35mm" is usually left out.

The sensor is larger as the reference sensor so the crop factor must be less as 1: size reference/size sensor.
Don't believe everything you read.
Beside that I don't think cropfactor is the right word. It's the aov compared with equal focal length.

George

[xpatUSA]

The sensor is larger [than] the reference sensor so the crop factor must be less [than] 1: size reference/size sensor.

Thanks George, that's what I thought.

Don't believe everything you read.
Beside that I don't think cropfactor is the right word. It's the aov compared with equal focal length.

George

I've never liked the phrase myself. I prefer "focal length multiplier".

Actually, I tend not to think of focal length being anything other than what's marked on the lens itself ...

[george013]

Thanks George, that's what I thought.



I've never liked the phrase myself. I prefer "focal length multiplier".

Actually, I tend not to think of focal length being anything other than what's marked on the lens itself ...

The focal length is a property of the lens solely.

George

[Manfred M]

Actually, I tend not to think of focal length being anything other than what's marked on the lens itself ...

As long as that has been done correctly, I would agree with you. Lens manufacturers have been known to be a bit liberal in how they mark their lenses with respect to both the maximum aperture and the actual focal length.

However, especially on zoom lenses, the focal length markings refer the performance at "infinity" only. I know my Nikkor f/2.8 70-200mm was roundly criticized at some quarters of only being the equivalent of a 135mm focal length when at the closest in-fcous setting at the 200mm marking. Even fixed focal length lenses change their focus lengths between the closest and furthest distance settings; this is commonly referred to as "focus breathing".

[xpatUSA]

As long as that has been done correctly, I would agree with you. Lens manufacturers have been known to be a bit liberal in how they mark their lenses with respect to both the maximum aperture and the actual focal length.

However, especially on zoom lenses, the focal length markings refer the performance at "infinity" only. I know my Nikkor f/2.8 70-200mm was roundly criticized at some quarters of only being the equivalent of a 135mm focal length when at the closest in-fcous setting at the 200mm marking. Even fixed focal length lenses change their focus lengths between the closest and furthest distance settings; this is commonly referred to as "focus breathing".

Brings back memories of the Micro-Nikkor f/2.8 'G' macro lens on my Nikon D50 at 1:1 magnification ... the camera reported an f-number quite a bit bigger than 2.8, and truthfully so, I guess.

Bearing in mind the thread title, are we all agreed so far that the focal length multiplier for a Pentax 645D sensor (44mm x 33mm) is indeed 43.27/55 = about 0.79 and not some other number greater than 1?

[Manfred M]

we all agreed so far that the focal length multiplier for a Pentax 645D sensor (44mm x 33mm) is indeed 43.27/55 = about 0.79 and not some other number greater than 1?

I would agree as the standard Full Frame / 135 film is the base we measure on and any sensor that is physically smaller will have a numeric value that is greater than 1 and any sensor that is larger will have a value that is smaller than 1.

I believe that the Pentax 645Z, the Hasselblad X1D and the Fujifilm GFX all use the same Sony sensor that is 43.8 x 32.9mm. The Phase One XF uses a 53.4 x 40.1mm sensor and the Leica S uses a 30 x 45mm sensor. All medium format cameras have a slightly different take on how medium format is determined...

[george013]

Brings back memories of the Micro-Nikkor f/2.8 'G' macro lens on my Nikon D50 at 1:1 magnification ... the camera reported an f-number quite a bit bigger than 2.8, and truthfully so, I guess.
......

That's because Nikon is reporting back the f-number based on the "effective focal length" which is nothing else as the image distance. At M=1 the image distance is 2x focal length. Other brands don't I think.

The nominal values are based on focusing at infinity, the "effective" values are based on focusing at a shorter distance.

George

[DanK]

That's because Nikon is reporting back the f-number based on the "effective focal length" which is nothing else as the image distance. At M=1 the image distance is 2x focal length. Other brands don't I think.

The nominal values are based on focusing at infinity, the "effective" values are based on focusing at a shorter distance.

George

This site has a good explanation of effective f/stop values.

I can only speak for one brand. Canon cameras do not report effective f-stop values.