The format factor comes from the diagonal length ratio between the frames resulting in 1,5-fold and 2,5-fold factors for full-frame and medium-format compared to Fuji X (APS-C).
Also, why do you insist on referring to aperture stops as "speeds"?
Your question must be re-addressed to a native speaker. who introduced the term "fast lens":
"A faster lens means the maximum aperture is larger, and more light will hit the sensor compared to a “slower” lens. This is usually expressed in an “f-number.” The smaller this number is (like F2. 8), the “faster” the lens is, and vice-versa."
speed (f-stop wide open)
> speed (f-stop wide open)You said:
That's the crop factor. Sensor size is distinct from focal length. My observations with the etup aren't restricted to the image size, although it is generally considered to be a good indicator.
I think you may also be making the mistake that effective focal length is based on a full-frame comparison as a baseline, not on the sensor or film size for which the lens was originally designed..
> speed (f-stop wide open)
It has the same meaning:
"Lens speed is the maximum aperture diameter, or minimum f-number, of a photographic lens. A lens with a larger than average maximum aperture (that is, a smaller minimum f-number) is called a "fast lens" because it can achieve the same exposure as an average lens with a faster shutter speed."
I spent about eight years actively participating in the projects to adapt medium-format lenses for digital mirrorless cameras. In all those years, you are the first person to tell me that I am wrong.
Moderator hat on:
Gentlemen - please!
Hat off.
Be cautious about any such analysis where the sensor/frame sizes being compared have different aspect ratios.
When those aspect ratios differ, there are actually four different equivalencies:
1) short dimension of the frame;
2) long dimension of the frame;
3) diagonal of the frame; and
4) area of the frame.
So you can have four different answers, all of which are right, even though their appropriateness depends on the use being made of them.
Moderator hat on:
Gentlemen - please!
Hat off.
Be cautious about any such analysis where the sensor/frame sizes being compared have different aspect ratios.
When those aspect ratios differ, there are actually four different equivalencies:
1) short dimension of the frame;
2) long dimension of the frame;
3) diagonal of the frame; and
4) area of the frame.
So you can have four different answers, all of which are right, even though their appropriateness depends on the use being made of them.
The angle of view of a lens is the only parameter that makes it possible to determine the equivalent focal length of the system with different sensor or frame sizes.
I would also recommend you the Calejnar (or Arsat or Hartblei) 150mm/2.8. This lens is smaller than the CZJ Sonnar 180mm and creates excellent images with a very pleasant bokeh. The Vega-28 120mm/2.8 was my favorite lens for a long time.I've done a lot of testing of the Carl Zeiss Jena Sonnar 180mm f/2.8. It would be a good candidate to adapt to digital of any sensor size.
Through testing it on 35mm film I found that the central portion, even with a teleconverter, out-resolves my ability to digitize the film at 36 megapixels with pixel shift, as long as you stop down the lens to f/5.6. Without a teleconverter, it out-resolves wide open.
Then I shot a 6x6 film frame and digitized it with stitching at around 120 megapixels. This was the first time I noticed any aberrations from the lens, it only happens towards the corners of a big MF frame.
Not bad at all for a 5 element lens you can buy for a few hundred dollars.
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