School me on ISO.

[KerrKid]

What can you tell me about ISO? For example, why shoot at a different ISO than box speed? Thanks!

 

[Bill Burk]

Kodak took a bunch of pictures at Willow Pond in Rochester and made a bunch of prints and asked volunteers which ones look best. Then Kodak reverse-engineered the pictures they liked and related meter setting to the film ability so amateurs could make the best pictures. That was ASA. Later when cameras got better light meters they took out about a stop of safety factor they originally built in. That stuck and became ISO. (All true but storytelling mode).

 

[KerrKid]

Kodak took a bunch of pictures at Willow Pond in Rochester and made a bunch of prints and asked volunteers which ones look best. Then Kodak reverse-engineered the pictures they liked and related meter setting to the film ability so amateurs could make the best pictures. That was ASA. Later when cameras got better light meters they took out about a stop of safety factor they originally built in. That stuck and became ISO. (All true but storytelling mode).

Very interesting backstory. Let's say I'm shooting Delta 400 in my SRT-101 and I have the camera set to box speed. What would be achieved by changing the camera setting to a lower or higher ISO than 400?

 

[jnamia]

Hi KerrKid
This is a tricky subject. Box Speed is figured out in a lab. It is made in a very controlled environment ..

good luck!

 

[Dali]

Overexposing and underexposing, assuming that you meter is OK and your shutter accurate.

 

[madNbad]

If you are using filters with B&W film, it’s much easier to adjust the ISO when figuring filter factor. Divide the box speed of the film by the factor on the filter and use that as the ISO.

 

[pbromaghin]

Wow, Too Much Information from the Wizards of Oz. As a poor amateur, I always shoot box speed - setting to higher ISO means I get lousy, under-exposed shots and setting to a lower ISO means I get lousy, over-exposed shots. At box speed I get lousy, properly exposed shots.

 

[jimjm]

What you're doing by changing the ISO setting is you're fooling your camera meter into thinking you're using a slower or faster film than you actually are. This will then result in overexposure or underexposure of your film in general. The manufacturer rates the film ISO depending on the sensitivity of the emulsion. Most print film (not slides) has a pretty wide latitude for over- or underexposure, so you can usually get acceptable prints if you vary by one or two stops either way.
Many cameras have an exposure compensation dial, which allows you to do this for selected shots, rather than the entire roll.
I routinely shoot 400 speed B/W film at 200, which is one stop overexposed. For what I like to shoot, this gives me more detail in the shadows without sacrificing any highlights. I realized years ago that I preferred printing negatives that were denser than normal, i.e., overexposed. This suits the look of the prints I like to make.
If you underexpose (push) film, this may allow you to shoot in lower light conditions, or with faster shutter speeds and smaller apertures than you normally might. The trade-off might be increased grain or contrast, but some folks are looking to get that effect.
These changes will also impact your film development times, so you need to consider that or tell the lab that is processing your film.
It's generally best to start by shooting films at box speed, then try experimenting over time as you become familiar with the films in the situations/subjects that you shoot.

 

[KerrKid]

What you're doing by changing the ISO setting is you're fooling your camera meter into thinking you're using a slower or faster film than you actually are. This will then result in overexposure or underexposure of your film in general. The manufacturer rates the film ISO depending on the sensitivity of the emulsion. Most print film (not slides) has a pretty wide latitude for over- or underexposure, so you can usually get acceptable prints if you vary by one or two stops either way.
Many cameras have an exposure compensation dial, which allows you to do this for selected shots, rather than the entire roll.
I routinely shoot 400 speed B/W film at 200, which is one stop overexposed. For what I like to shoot, this gives me more detail in the shadows without sacrificing any highlights. I realized years ago that I preferred printing negatives that were denser than normal, i.e., overexposed. This suits the look of the prints I like to make.
If you underexpose (push) film, this may allow you to shoot in lower light conditions, or with faster shutter speeds and smaller apertures than you normally might. The trade-off might be increased grain or contrast, but some folks are looking to get that effect.
These changes will also impact your film development times, so you need to consider that or tell the lab that is processing your film.
It's generally best to start by shooting films at box speed, then try experimenting over time as you become familiar with the films in the situations/subjects that you shoot.

Wow. Terrific response. Thank you!

When I was using my SRT-101 many moons ago, I remember often taking 3 shots of the same subject matter; One with the meter lollipop centered on the meter needle and then one stop higher and lower. How does this compare with changing the ISO? (I do know it changes depth of field).

 

[Paul Howell]

ASA was the American Standard Association, it morphed into the International Standards Association which uses a somewhat modified scale from the older ASA scale, in my experience the 2 are close enough for government work. Film manufacture's test their film in a laboratory setting and assign a box speed based on a number of factors. Looking at the manufacture's data sheet you see that most films exhibit different film speeds depending on the developer.

When I taught photography at the local community college in the 90s I would have the class meter the same scene and records their camera's meter reading to compare with a tested and calibrated Gossan hand held meter. The older cameras with mechanical shutters, Cds meters were sometimes 1, 2 or even 3 stops off. Newer bodies with matrix metering and electronic shutters were usually within a 1/2 stop. I then taught the class how to shoot a ring around followed by using the school's densitometer to find their E.I or what I called a personal ISO for their camera and developer.

So the 2 reason to use a different ISO from the maker's "box speed" is compensate for metering or other camera issues, second if you use developer that does not produce box speed.

here is a link the Foma 400 data sheet, you will see that Foma 400 does not reach box speed of 400 in most developers, comes close, but shooting at 400 when developed in D76 you might see some loss of shadow detail. Foma on the other hand 100 shoots pretty well at 100.

https://www.foma.cz/en/fomapan-400

 

[Andrew O'Neill]

I just did a push test with HP5 (sheet film is more practical for tests such as this) over the weekend. Pushing is something I never do (well sort of do...like when I have a low contrast scene, and I give maybe a third stop less exposure, and give longer dev time). I shot at my usual EI of 200, and worked my way up to 25,600. Seven stops less than my normal. I was pretty surprised at my results.

 

[Alex Benjamin]

When I was using my SRT-101 many moons ago, I remember often taking 3 shots of the same subject matter; One with the meter lollipop centered on the meter needle and then one stop higher and lower. How does this compare with changing the ISO? (I do know it changes depth of field).

It's called "bracketing". It does nothing to the ISO. You are under-exposing and over-exposing one stop. Your film ISO doesn't change. Think about it this way: speed limit on the highway is 60 m/h. You're going 60 m/h, then 2 minutes at 70 m/h, then 2 minutes at 50 m/h. You temporarily changed your speed, but did nothing to change the speed limit.

And no, bracketing 1 stop higher / 1 stop lower does not necessarily change the depth of field. It only does so if you bracket by changing the aperture — shooting an f/11 scene at f/11, f/16 and f/8, for example. If you bracket by changing the shutter speed and keep things at the same aperture, the depth of field will be the same for all three shots.

 

[Paul Howell]

I just did a push test with HP5 (sheet film is more practical for tests such as this) over the weekend. Pushing is something I never do (well sort of do...like when I have a low contrast scene, and I give maybe a third stop less exposure, and give longer dev time). I shot at my usual EI of 200, and worked my way up to 25,600. Seven stops less than my normal. I was pretty surprised at my results.

Which were?

 

[Andrew O'Neill]

Which were?

You'll have to wait for the video which I'll post this weekend...

 

[pentaxuser]

When I was using my SRT-101 many moons ago, I remember often taking 3 shots of the same subject matter; One with the meter lollipop centered on the meter needle and then one stop higher and lower. How does this compare with changing the ISO? (I do know it changes depth of field).

Changing the ISO should have no effect on DoF. Your DoF is decided by several factors such as lenses( a 28mm wide angle will give a larger DoF than say a 200mm telephoto) format of film( a camera using 35mm film gives a bigger depth of field than say a 6x6 MF camera) but these are not related to film ISO

If you saw a change in DoF when changing ISO then I feel something else was changed as well

pentaxuser

 

[KerrKid]

ASA was the American Standard Association, it morphed into the International Standards Association which uses a somewhat modified scale from the older ASA scale, in my experience the 2 are close enough for government work. Film manufacture's test their film in a laboratory setting and assign a box speed based on a number of factors. Looking at the manufacture's data sheet you see that most films exhibit different film speeds depending on the developer.

When I taught photography at the local community college in the 90s I would have the class meter the same scene and records their camera's meter reading to compare with a tested and calibrated Gossan hand held meter. The older cameras with mechanical shutters, Cds meters were sometimes 1, 2 or even 3 stops off. Newer bodies with matrix metering and electronic shutters were usually within a 1/2 stop. I then taught the class how to shoot a ring around followed by using the school's densitometer to find their E.I or what I called a personal ISO for their camera and developer.

So the 2 reason to use a different ISO from the maker's "box speed" is compensate for metering or other camera issues, second if you use developer that does not produce box speed.

here is a link the Foma 400 data sheet, you will see that Foma 400 does not reach box speed of 400 in most developers, comes close, but shooting at 400 when developed in D76 you might see some loss of shadow detail. Foma on the other hand 100 shoots pretty well at 100.

https://www.foma.cz/en/fomapan-400

Thank you! Excellent information. jimjm also mentioned that developer choices and times would affect the exposure. I don't develop my own film, yet, and when I used to do that in college I don't remember much of what we used - 40 years ago.

I never knew that mechanical shutters and Cds meters could be off until I joined this forum. My SRT's were all serviced by John Titterington who said they were off and he fixed them. I have a Pentax KM that I haven't checked. Would I need to get a calibrated light meter to check that? What do you mean by "shoot a ring around"? I'm without a densitometer so that part is out of the question.

Rabbit hole alert...You mentioned Foma. I'm not married to one film over another, yet, and welcome suggestions. 40-45 years ago my "go-to" was Tri-X. I bought some Delta 400 when I got back into shooting film recently and, though I'm happy with the results, don't really know how that compares with anything else. I'm thinking of getting some HP5+, but I also hear decent things about Kentmere. What do you like about Foma?

 

[mshchem]

Problem solved.

 

[KerrKid]

Changing the ISO should have no effect on DoF. Your DoF is decided by several factors such as lenses( a 28mm wide angle will give a larger DoF than say a 200mm telephoto) format of film( a camera using 35mm film gives a bigger depth of field than say a 6x6 MF camera) but these are not related to film ISO

If you saw a change in DoF when changing ISO then I feel something else was changed as well

pentaxuser

In my example, I was keeping the shutter speed and ISO the same and changing the aperture to increase or decrease the light coming in to the camera. I realize this is somewhat of a kludge.

 

[MattKing]

In my example, I was keeping the shutter speed and ISO the same and changing the aperture to increase or decrease the light coming in to the camera. I realize this is somewhat of a kludge.

That is not a kludge - that is one excellent way to bracket exposure. When you do, the depth of field will change.
The other excellent way to bracket exposure is to keep the aperture the same and change the shutter speed. In that case, the depth of field will stay constant, but the motion stopping ability of the camera will change. That can be important with moving subjects, and when you are trying to get sharp photos that aren't blurred by camera movement.
Technically speaking, the setting you set on your meter is the Exposure Index you are using - "EI". If you use an EI that is different from the manufacturer's ISO speed rating, it can help clarify these discussions.
Something like: "The ISO rating for the film is 400, but with my meter, my metering technique and my favourite developer I prefer the results I obtain if I use an EI of 250 when setting my meter".
But at your stage of returning to film, I'd suggest staying with the meter set to the ISO or "box" speed. You can experiment more as time goes on.

 

[KerrKid]

That is not a kludge - that is one excellent way to bracket exposure. When you do, the depth of field will change.
The other excellent way to bracket exposure is to keep the aperture the same and change the shutter speed. In that case, the depth of field will stay constant, but the motion stopping ability of the camera will change. That can be important with moving subjects, and when you are trying to get sharp photos that aren't blurred by camera movement.
Technically speaking, the setting you set on your meter is the Exposure Index you are using - "EI". If you use an EI that is different from the manufacturer's ISO speed rating, it can help clarify these discussions.
Something like: "The ISO rating for the film is 400, but with my meter, my metering technique and my favourite developer I prefer the results I obtain if I use an EI of 250 when setting my meter".
But at your stage of returning to film, I'd suggest staying with the meter set to the ISO or "box" speed. You can experiment more as time goes on.

Thanks for the explanation, Matt. Yes, at this stage I do need to keep things simple. Am I to assume that the one setting that remains fixed is referred to as the "priority" setting? I have never kept the aperture setting static and changed the shutter speed to bracket, but I can see how useful that would be.

Thanks!

 

[MattKing]

Thanks for the explanation, Matt. Yes, at this stage I do need to keep things simple. Am I to assume that the one setting that remains fixed is referred to as the "priority" setting? I have never kept the aperture setting static and changed the shutter speed to bracket, but I can see how useful that would be.

Thanks!

Usually I decide on an EI based on the film and developer usually, and the meter setting remains unchanged through the roll.
I do, however, sometimes increase or decrease the exposure for a particular shot. Sometimes I even bracket for a particular shot. The EI doesn't change. Instead I intentionally add or subtract exposure - say 2/3 of a stop or 1 stop or whatever - from the exposure recommended by the meter. I use the controls on the camera to make that intentional over-riding change and think of it that way. Something like "metered exposure plus 2/3 of a stop". That way it doesn't matter if the light changes, because rather than recording or remembering the exact settings, I just record or remember the adjustment.
Sometimes I'll be photographing in constant conditions that require the same adjustment for all shots. Situations like that include situations where filters are employed. Another example is where the light is particularly high or low in contrast, and I intend to adjust development to take that into account. In those circumstances I'll use and record a different EI as well as any required change in development.
This shot was taken in conditions where the light was filtered by fog - very low contrast. I intentionally increased the development to deal with that. I could have also reduced the exposure (used a higher EI) as well, but made the decision not to based on the subject.

 

[Moose22]

I just did a push test with HP5 (sheet film is more practical for tests such as this) over the weekend. Pushing is something I never do (well sort of do...like when I have a low contrast scene, and I give maybe a third stop less exposure, and give longer dev time). I shot at my usual EI of 200, and worked my way up to 25,600. Seven stops less than my normal. I was pretty surprised at my results.

That's a fun sort of test.

I started pushing Hp5 around, just to see. I think of it s an 800 speed film now. Not that it is 800, it's 400 like Ilford says, I just really like how it looks pushed a stop and that extra stop helps in some situations I like to photograph. I also like it pulled and at box, but I was quite surprised at how it looked good to me at 800 and 1600, the extra contrast was nice for my aesthetic sensibilities and the noise from the grain not distracting.

Should be a nice video. Hope it comes out great.

 

[Moose22]

Rabbit hole alert...You mentioned Foma. I'm not married to one film over another, yet, and welcome suggestions. 40-45 years ago my "go-to" was Tri-X. I bought some Delta 400 when I got back into shooting film recently and, though I'm happy with the results, don't really know how that compares with anything else. I'm thinking of getting some HP5+, but I also hear decent things about Kentmere. What do you like about Foma?

HP5 is versatile. It's lower contrast than tri-x, and pushes nicely. I dev in xtol and use it at 800 for shooting musicians on stage and it's... well, it's worth your trying a roll or two for yourself.

I haven't shot the kentmere or foma brands, but I have used Arista. It's bargain film, but certainly worked fine for me and have seen quite a few decent photos taken with it. I think that's made by Foma. I have no problems working with it myself and would not discourage you from trying it at all.

 

[Andrew O'Neill]

That's a fun sort of test.

I started pushing Hp5 around, just to see. I think of it s an 800 speed film now. Not that it is 800, it's 400 like Ilford says, I just really like how it looks pushed a stop and that extra stop helps in some situations I like to photograph. I also like it pulled and at box, but I was quite surprised at how it looked good to me at 800 and 1600, the extra contrast was nice for my aesthetic sensibilities and the noise from the grain not distracting.

Should be a nice video. Hope it comes out great.

It was a real eye opener for me!

 

[Alan Edward Klein]

In my example, I was keeping the shutter speed and ISO the same and changing the aperture to increase or decrease the light coming in to the camera. I realize this is somewhat of a kludge.

If you want to bracket less than a full stop, many camera only allow you to do that by changing the aperture. That's because shutters only operate in full stops. You can;t, for example, set the shutter between 1/30 and 1/60 of a second. You can set 1/30t or 1/60 only. So if you want to bracket in a half stop, you would set the aperture in the middle between two full stops. Some lens have a "click" stop at halfway between the two stops. Other lenses may have 1/3 stop clicks. Once you change the aperture, the DOF will be different for the three shots with the smallest aperture having the most DOF.