"Real" ISO values of sheet film.

[Stephen Benskin]

AA also found that same thing with + & - development as I remember.

I'd like to be clear that that the latitude of a film that I speak of isn't based on shooting to "a" speed point, it's simply a limit at one end of the range.

I think this happens a lot. People are simply discussing different topics. In this case, film speed and exposure latitude. Add exposure preference to the mix and it's a trifecta of confusion.

 

[markbarendt]

I think this happens a lot. People are simply discussing different topics. In this case, film speed and exposure latitude. Add exposure preference to the mix and it's a trifecta of confusion.

Absolutely!

Good Photography is almost always a compromise between competing priorities.

 

[MattKing]

Absolutely!

Good Photography is almost always a compromise between competing priorities.

I refer you to the quote in my signature

 

[removed account4]

I refer you to the quote in my signature

there you go

-john

 

[ic-racer]

Ok here is an an analogy. ISO film test is like brake performance testing of trucks and automobiles. ISO film speed is derived from the MINIMUM exposure to produce the good print. Likewise the brake performance test is the MINIMUM distance. In actual driving, though, If you auto comes out to have a 0-60 stopping distance of 135feet, and you are traveling 60mph, it would be safer to start braking sooner than 135 feet from a stop sign (though you are not required by law do do so).

 

[Diapositivo]

The analogy I propose is: a person buys a Ferrari. Its engine is quoted at let's say 300 HP DIN. Then someone drives it mainly on city roads, fraught with perils (e.g. the ones with lights over the top), at no more than 50 Km/h.

So, this person says: "when I drive my Ferrari in town, I rate it at 50 HP DIN". We understand what he means, but it ain't proper technical lingo, you know.

The point somebody made is that the "real" (DIN) power of your engine is the one, and only the one, measured on the test bench, according to DIN specification. This measurement is made regardless of any road, and drive style. It is made "logically before driving".

By the same token, the "real" (DIN, ASA, ISO) sensitivity of the film if the one measured at the "bench". You can use your film at a slower speed, just like your Ferrari. But the "rate" of the film is measured abstractly and independently from any possible print, it is made "logically before printing", just like the HP of an engine is measured independently and abstractly from the way one drives.

That is why saying that one is using an "exposure index" is proper, and saying that a film has a "real" speed, that is different from the "nominal" (theoretical, laboratory, bench) speed, is IMV improper.

But it all is becoming just a discussion about the proper use of words. It is clear to everybody that people to overexpose their negative do it for a very sensible, legitimate, technically sound reason .

It's just that they fail to express properly what they do

By the same token, if a light meter is 1 EV off, and forces to set a different ISO speed on it, one might say:

"I rate this film at half its speed because it works with my lightmeter. YMMV" and one might say "I have a lightmetre 1 EV off so I trick it by telling it I have a film half the speed it actually has". The second is correct

Fabrizio

 

[JBrunner]

The analogy I propose is: a person buys a Ferrari. Its engine is quoted at let's say 300 HP DIN. Then someone drives it mainly on city roads, fraught with perils (e.g. the ones with lights over the top), at no more than 50 Km/h.

So, this person says: "when I drive my Ferrari in town, I rate it at 50 HP DIN". We understand what he means, but it ain't proper technical lingo, you know.

The point somebody made is that the "real" (DIN) power of your engine is the one, and only the one, measured on the test bench, according to DIN specification. This measurement is made regardless of any road, and drive style. It is made "logically before driving".

By the same token, the "real" (DIN, ASA, ISO) sensitivity of the film if the one measured at the "bench". You can use your film at a slower speed, just like your Ferrari. But the "rate" of the film is measured abstractly and independently from any possible print, it is made "logically before printing", just like the HP of an engine is measured independently and abstractly from the way one drives.

That is why saying that one is using an "exposure index" is proper, and saying that a film has a "real" speed, that is different from the "nominal" (theoretical, laboratory, bench) speed, is IMV improper.

But it all is becoming just a discussion about the proper use of words. It is clear to everybody that people to overexpose their negative do it for a very sensible, legitimate, technically sound reason .

It's just that they fail to express properly what they do

By the same token, if a light meter is 1 EV off, and forces to set a different ISO speed on it, one might say:

"I rate this film at half its speed because it works with my lightmeter. YMMV" and one might say "I have a lightmetre 1 EV off so I trick it by telling it I have a film half the speed it actually has". The second is correct

Fabrizio

Not quite. In a different developer the engine could have say 200 HP DIN and would measure that on the test bench, no matter how or where you drive. Different petrol. Lower octane perhaps.

 

[markbarendt]

I refer you to the quote in my signature

'Tis a good one.