frankie c Loc: Lake Havasu CIty, AZ

This started out as a quick reply that took on a life of its own. Anyway decided to post it as a new topic.
The exposure triangle and why ISO is a part of it:
Back in the day of film there were several organizations that set standards for everything (time, viscosity of fluids, intensity of a light bulb) they mostly did this with a thing called measuring. They did this with very sophisticated methods to establish standards by which all like things were rated. One of the things they measured was a given films sensitivity to light. We had things like ASA values (American Standards Association) and DIN numbers (which was the German version) and a few more I think. Well there were some differences in opinion and measuring techniques. Someone brilliant said lets come up with an International Standard and we can call it the International Standards Organization, hmm (ISO). Anyways for us photographers our ASA and DIN numbers went away and we all gots a new bunch of numbers called ISO.
http://en.wikipedia.org/wiki/Film_speed
the above link splains it good.
So, why was a films sensitivity to light so important? After all we only set our aperture and shutter speeds on our camera…… (WRONG). You have to either know intuitively or measure using a meter to know how much light you can let your film emulsion see to produce a properly exposed print. Now films in time came in a great number of flavors. We gots ISO 25, ISO 32, ISO 64, ISO 80, ISO 100, ISO 125, ISO 200, ISO 400, ISO 800, ISO 1000 and up and up it went. Adding into that mix we gots Black and White, Color, also negatives or positives (Slides) not even touching yes on inferred films or orthochromatic. Anyway the only way to get a proper exposure was to know that ISO value. Even if you wanted to divert from that formal proper exposure you still had to know what the films sensitivity to light was. So what’s the big deal pick one and set it and continue to go with your aperture and shutter speed. Picking the ISO speed was usually relative to what you were shooting (moving stuff, still stuff, family fun pics, portraits of fine art). The higher the ISO speed the faster you could shoot. What are the results and consequences of ISO speed. The lower the ISO the finer the film grain (small grains of silver halide distributed throughout the films emulsion). The higher the ISO speed the larger the grain size of silver halide distributed throughout the films emulsion). The smaller the grain the more detail you get however requires longer exposure times and larger aperture were helpful. The higher the ISO with larger chunks of silver halide produced more noise/GRAIN thus less detail in the picture. By now I think you can start to see the relationship you get with you Digital sensor. Now your camera shutter speeds and aperture are in values of 2x or -2x. That’s twice the light or half the light for every full stop or shutter speed up and down. This 2x is also what your ISO does. So changing any one of the three will allow you to control your exposure. So even if you do not want to think about ISO it is still part of the exposure triangle and if you do think about it you can greatly improve your creativity get the right exposure for your picture project.
So if you had a set of exposure priorities (shutter speed and aperture) you needed to pick the right film to handle those priorities. Your film choice needed to be based on what you shoot. Now if you had more than one set of requirements you needed to pack a camera for each or plan it out to make a film change at the appropriate time. You just couldn’t change the films ISO as you shot. You could if needed shoot a film at a higher ISO then push process the film (basically longer development time or higher concentration of developer) to over process to develop silver halide that was not exposed correctly (under exposed) and force it to build exposure where there was little to none. Today with digital we can accomplish this with a single click with our software. With film when we had a faster film and wanted to resolve the grain to look more like a slower film we could process the film in a 3:1 solution and get a less grainy result. Today we call this smoothing (adding pixels where there were no pixels in a very smart way). Anyway my point is that ISO (film speed). Maybe the key component of the exposure triangle to get the picture we want. You can have the best easel and paint and brushes but if you don’t have the canvas to put it on, or know how they work together, you won’t wind up with a very good picture. With the switch to digital photography, we have changed a lot of terminology, even changed some of the methods and expanded our horizons and our film is now a sensor. The process is still the process. You gottsa do the process right.
Some additional thoughts on film ISO:
Film ISO was a really good guide to the light sensitivity of film. However, the competition to achieve the next level of film speed was seen as a marketing advantage by film manufacturer’s and stretching the data to achieve the next bench mark in film speed was not unheard of. I am pretty sure there was a lot of politics that went into getting that ISO approved rating. So maybe the rating on some films was stretched to highest end to meet the spec. Photographers kinda figured this out and most did not shoot at the published ISO rating. It was pretty common to shoot Kodacolor VR 100 at ISO 80 instead of 100. This fudge factor was true with many films. Anyways, manipulations were possible as were processing variations. OK so in today’s digital world we can’t take a 3rd stop out of are ISO each value is a twice or half the light sensitivity choice but we can use exposure compensation to accomplish what we did by manipulating ISO. So now we are gonna use a different element of the triangle to adjust our exposure (pretty cool stuff). It all kinda winds up as same stuff different day.
Like I said this started out as a quick replay to one of our fellow members or the UHH forum. It got totally out of control. Whether you agree or not It keeps me thinking and one day less without Alzheimer’s :). It’s kinda a gigantic brain fart. I apologize I wasted your time but after all this I just hasta postit.

RWR Loc: La Mesa, CA

What are ISO 50, 64, 80, 100, 125, etc., etc., if not 1/3 stop increments?

frankie c Loc: Lake Havasu CIty, AZ

that was a relationship I was making on films and film cameras (SLR's) but yes looks like your right and I am wrong. Yippee ki yo for you :) have a great day.

boberic Loc: Quiet Corner, Connecticut. Ex long Islander

I don't think that your post was a waste of time at all. It brought back a lot of memories of many pleasent huors in my (long gone) darkroom. I actually liked the smell of the chemistry. BTW is used to push Panatomic X to 500. Souped in Diafine. I still hve the photos hanging on my B&W wall.

RWR Loc: La Mesa, CA

Don't know about Yippee ki yo, but at least no newcomer will be mislead! And yes, as someone also wrote in another thread, ISO must be considered when exposing on film or a sensor. :)

SharpShooter Loc: NorCal

Frankie, not sure I understood your question but maybe that's because I only read the first paragraph of your rant before I fell asleep! :lol:
Seriously, the ASA values have not changed one bit, only the names of the players have changed.
You can set any one of the three values of the triangle and either change the other two automatically or manually, your choice, so what has changed?? It's alway been that way!!
A triangle only has three corners, no matter WHAT anybody else says! :lol:
SS

frankie c Loc: Lake Havasu CIty, AZ

Thanks for the thumbs up. I use to I use to 3 to 1 process Tri X to cut the grain. Did you ever process Ektachrome when you had to use a flood lamp to do the reversal. My first dark room was wooden frames with card board walls and my first print box was home made of wood a 40 watt light bulb and piece of frosted glass. I was about 12. LOL you could get high on sniffing fixer. Have a great day.

frankie c Loc: Lake Havasu CIty, AZ

Sorry you fell asleep. What you said is exactly what I said. The thing I was responding to was someone who was trying to say that ISO was not a part of the exposure and exposure only involved aperture and shutter speed. Did not want to be a prick about it so I focused on the importance of ISO as part of the exposure triangle. Plus I took a little side trip down memory lane. I guess you need to have some memories to appreciate that. So just go back to sleep.

frankie c Loc: Lake Havasu CIty, AZ

I should have thunk about this more before I responded. The guy that pointed out that third steps were available on a DSLR and in my writing I talked about taking film rated at any given ISO and shooting it at a ISO setting different that the film. Yes I guess there are ISO settings on a DSLR that would in fact be third stop increments, I don’t think it’s the same dynamic as if you had a film at a given ISO and shoot it at a different ISO. In a film camera you are saying take this film at that has a light sensitivity at a given value and change the exposure to match a different value (so effectively changing the way my meter response which would be more like under or over exposing). If you change your ISO on a digital camera the sensor becomes that value for light sensitivity. Your meter still processes the exposure as normal (as applied to a theoretical 18% grey). You can’t tell the sensor to maintain the sensitivity of ISO 100 but calculate my exposure as if it were at a sensitivity of ISO 80. You can’t lie to the meter cause the meter knows cause it’s smart. The meters in our SLR’s were not so smart so we could lie to it . To change the exposure to sensor relationship you need to do something else, not change the ISO. I am not too bright by me thinks me gots this right. I’m right Yippee Ki Yay for me. I hope ya’ll don’t mind me having some fun with this.

jerryc41 Loc: Catskill Mts of NY

Thanks for that. Good refresher.

Bob Grove

My take on this "exposure triangle" thread is that it's all a question semantics. There's no question that the three elements of the triangle interrelate, but but only shutter speed and aperture adjust the amount of light that's coming in (exposure time and brightness). The ISO setting is a matter of adjsusting the sensitivity to that light, and not matter what ISO setting is selected, the same exposure occurs if the shutter speed and aperture remain unchanged.

Okay, your turn :-)

WessoJPEG Loc: Cincinnati, Ohio

Ty

I love your comments and haven't heard Yippee I O Ki yay for a long time. Also brought back Dark Room memories. Thanks 😂

Screamin Scott Loc: Marshfield Wi, Baltimore Md, now Dallas Ga

Liked working in the darkroom but not having to set it up & take it down. (I lived in apartments way back then & had no space to set up a darkroom that stayed up)

Apaflo Loc: Anchorage, Alaska

You'll have to come to grips with the fact "someone" was exactly right! Exposure is defined as the number of photons captured, and it is purely and exclusively a function of light intensity over a time interval. Aperture and shutter speed, but not sensitivity.

ISO is sensitivity, which is not part of exposure. But the "Exposure Triangle" is not just exposure. It is much more, because it is what a photograph needs to be useful. ISO adjusts sensitivity to make the chosen exposure the "correct exposure".


This is a good point that can be describe, hopefully, in a way that helps more.

With a film camera sensitivity is set by the film and development used, not by the "ISO selector". The ISO selector is essentially the same as an Exposure Compensation selector on a digital camera.
With any given film and development used, changing the ISO selection merely biases the light metering system for a higher or a lower match. The ISO isn't actually changed unless either the film or standard development is changed (which is exactly what happens when ISO on a digital camera is adjusted).

zigipha Loc: north nj

I do agree...the three vertices are not the same

ISO tells you how much light you SHOULD put in

aperture/speed is how much you DO put it.

In old days you pretty much fixed the iso when you put the film in, so i guess it was more of an exposure line back then.

But with digital it can be changed in a pic by pci, so i guess its more of a triangle. But i would asterisk the iso point