K25 against digital imaging questions.

[tybrad]

They've been in the back of my head for a while.

1. In a 35mm format, what digital pixel density is equivalent to what K25 used to have? I know that it's likely a poor translation, but roughly?
Wasn't there an ISO 16 B&W film at some point? Cannot recall. But what would it's equivalency have been?

2. Diffraction-limiting apertures. Is it just that digital sensing at 3+ stops down from wide open allows us to see the de-sharpening? I don't think that I ever saw it on K25, at even f/22.

[Manfred M]

I have no idea what a K25 is; I assume some model of film camera?

The film and digital technologies are not easy to compare because the whole technology is so completely different. In film, randomly distributed silver salts (halides) in a gelatin emulsion. The actual silver halide plus the size of the crystals determined film sensitivity (i.e. ISO rating). Colour films work in a similar fashion to B&W except that photo-chemical reactions activate dyes in three different colour layers in the emulsion. The silver halide crystals were never exactly the same size.

Camera sensors work quite differently; the vast majority of sensors are based on the Bayer array (RGGB), so there is a non-random pattern in how the colours are recorded and unlike the film, the different colours are located adjacent to each other. Slight variants, like FujiFilm's Trans-X sensor do exist. The Foveon sensor, used by Sigma, is more akin to how film worked, but it has issues as well and has never seen wide-spread adoption. The other "strange" sensor out there is the one used in the Leica Monochrom camera, where the Bayer array is completely missing and every pixel represents a distinct gray value.

I've never seen a convincing argument for comparing the two types of photography. It's a little like comparing a Tesla car and a Mack truck; they are both vehicles, but that's where the similarity and comparisons end.


In terms of diffraction limits; that is and has always been there. It has nothing to do with the 3+ stops down, but rather the size of the iris opening. On the same camera body (pixel size is important) a 50mm f/1 lens will be the same as an f/2.8 50mm lens. There will be other issues, but pure diffraction limit is depending on how small the hole that the light passes through is.

I expect the reason we did not notice it in the film days is that with our digital tools, pixel peeping has become a lot easier. The laws of physics have not changed.

[tybrad]

[QUOTE=Manfred M;772180]I have no idea what a K25 is; I assume some model of film camera?

Kodachrome 25

[Manfred M]

[QUOTE=tybrad;772183]

I have no idea what a K25 is; I assume some model of film camera?

Kodachrome 25

Oh. I used to shoot a lot of that film some 40 years ago and was not happy with Kodak for discontinuing it. That being said, one had to like punchy reds that came with it and a tripod was pretty well mandatory to shoot with it. Kodachrome 64 became my slide film mainstay, but it was not as punchy. I still have a few rolls in the freezer that I never threw out...

I think the slowest B&W film I shot was AgfaPan 25; lovely fine grain structure but again, a tripod was important to get good Golden Hour shots with it.

[tybrad]

Yep- I remember Kodachrome fondly. I recently found a roll of developed 120 that I ran through my Ciroflex TLR (which I still have) in the 80s.

Thank you for the great information in your first reply- very helpful!

[Martin A]

Here's a link to an article about the subject: https://www.kenrockwell.com/tech/film-resolution.htm Scroll down to the heading "The Digital Resolution of Film". It does not specifically mention Kodachrome, but still is informative concerning the film vs digital resolution issue.

[tybrad]

Here's a link to an article about the subject: https://www.kenrockwell.com/tech/film-resolution.htm Scroll down to the heading "The Digital Resolution of Film". It does not specifically mention Kodachrome, but still is informative concerning the film vs digital resolution issue.

Yikes!! Velvia 50 = 175MP on 35mm? That's insane.

[DanK]

I have no expertise in this area, but I note that Rockwell's calculations are not uniformly accepted. E.g., this is from Wikipedia:

A 36 mm × 24 mm frame of ISO 100-speed film was initially estimated to contain the equivalent of 20 million pixels,[6]: 99 

https://en.wikipedia.org/wiki/Compar...lm_photography

[Manfred M]

I have no expertise in this area, but I note that Rockwell's calculations are not uniformly accepted. E.g., this is from Wikipedia:



https://en.wikipedia.org/wiki/Compar...lm_photography

I agree Dan, numbers I have seen in the past seem to suggest 17MP - 20MP for a full frame sensor. I have never found Rockwell to be a particularly reliable source and his assumptions could be suspect. My own wet darkroom experience was that I could never print an image that is as large and sharp as I have been able to over the past decade.

[Acorn]

They've been in the back of my head for a while.

1. In a 35mm format, what digital pixel density is equivalent to what K25 used to have? I know that it's likely a poor translation, but roughly?
Wasn't there an ISO 16 B&W film at some point? Cannot recall. But what would it's equivalency have been?

2. Diffraction-limiting apertures. Is it just that digital sensing at 3+ stops down from wide open allows us to see the de-sharpening? I don't think that I ever saw it on K25, at even f/22.

I certainly don't remember K25 film [Kodak?]. I do remember film stock with low ASA ratings produced under the brand name, ADOX.

[BobGilbody]

Thirty years ago I used Velvia. 5x4 with a Sinar and 645 with a Pentax. I was just playing with stuff. At that time to get the best quality prints was very expensive. I never did it. The only place that did the 'process' was in Brisbane. The 'slide' was scanned on a drum [ from memory different colours and b and w ] Then somehow an 'interneg' was made [ not to be confused with taking a photo of a transparency ]. The image was then printed on plastic. Cost thirty years ago was Aus $300 and up. I had enough sense not to pretend I had images worth the cost. I did see some prints of images taken in Antarctica of penguins. Amazing quality.

Tried to find the process on the internet. Failed. Might have it a bit mixed up. I have lost a lot of brain cells since 1993.

These are the people that used to do the process: https://www.prolab.com.au/

I ph'd then and was told these days they just scan the tranny. I would be interested to know if that gives a similar quality.