Is ISO same across all formats?

[j.weegee]

Okay so lets say I'm in my studio. I got my subject lit and ready to go. I have my Canon AE-1 loaded up with a roll of Kodak 400 TMAX Black and White film. And then I decided to bust out my 4x5 view camera, set it up to achieve the exact same composition loaded it up with (you guessed it) a sheet of 4x5 400 TMAX Black and White film. Both cameras have the exact same settings amdist the exact same lighting setup. Will there be any change in exposure (other than the reduction in depth of field due to the larger format)? Will my image from the 4x5 film be darker or lighter than the image from the 35mm film? Are they the same for every company as well or is ISO 400 on Kodak film different from ISO 400 on Illford film?

 

[bhop]

Theoretically, it should be the same... that also goes for digital/film

 

[panblue]

I'd assume 400 TMAX is the same, regardless of format.

Certain films were rated at one speed but often as not, exposed at another speed.

I think the gamma of digital images on-screen changes with size adjustments.
Some digital cameras ISO ratings are a bit 'optimistic' as well.

Okay so lets say I'm in my studio. I got my subject lit and ready to go. I have my Canon AE-1 loaded up with a roll of Kodak 400 TMAX Black and White film. And then I decided to bust out my 4x5 view camera, set it up to achieve the exact same composition loaded it up with (you guessed it) a sheet of 4x5 400 TMAX Black and White film. Both cameras have the exact same settings amdist the exact same lighting setup. Will there be any change in exposure (other than the reduction in depth of field due to the larger format)? Will my image from the 4x5 film be darker or lighter than the image from the 35mm film? Are they the same for every company as well or is ISO 400 on Kodak film different from ISO 400 on Illford film?

 

[wsetser]

ASA, I'm sorry ISO (I'm showing my age) is the same across formats. ISO 400 is ISO 400. If you metered through your AE-1 the settings my not transfer to your 4x5 though. If you're shooting close you will have to factor in bellows extension.

 

[ann]

This is why we test film with various cameras and lenses.

Factory standards will be the same, individual EI will vary.

 

[mjhoward]

ISO - International Organization for Standardization

 

[j.weegee]

What effect could extended bellows have? Would the image be underexposed due to the light having to travel farther through the bellows to the film?

 

[j.weegee]

I understand what ISO means, but different manufacturers producing the same product can have tiny variations. I'm just trying to make sure that I wouldn't have to compensate 1/3 of a stop when switching from Illford to Kodak or vice versa.

 

[timor]

but different manufacturers producing the same product can have tiny variations.

It's a fact well known. The differences are also between different batches of the same film, you may notice on the boxes emulsion numbers and also on the edge of the film sometimes. Solution ? Use one type of film only in order to have same results all the time, buy in large quantities from the same batch and test each batch against your processing scheme.

 

[Helen B]

The ISO standard for B&W film does not specify which developer to use, and the choice of developer can affect the ISO, though usually by no more than a third of a stop (which is the step size in ISO speed values). Therefore the manufacturer's ISO may not be the true ISO in the developer you use. Very few people, however, do true ISO tests, not least because they aren't as important or useful as tests for effective EI - which take your equipment and technique into account.

 

[Derrel]

What effect could extended bellows have? Would the image be underexposed due to the light having to travel farther through the bellows to the film?

Well, when a camera's bellow is extended significantly beyond the "normal", as in close-range focusing, there is a decrease in the amount of light that each f/value transmits. In other words, there is a loss in effective aperture value. The formula for computing bellows factor that I used to use is image size divided by object size, squared, and then you take that and multiply it by your ISO, which yields an "effective ISO" or "adjusted ISO", and then you enter that number onto your light meter, and meter using the adjusted ISO. I used to do this using a pair of well-marked steel rulers that I had, and including one in the scene, and measuring the image size right on the back of the camera groundglass with the second ruler. THERE ARE however, some pretty nifty little calculator-type devices, which you can just plop right onto the shooting table. (Pardon me if my memory is in any way faulty on this formula, and of course,pardon my inability to do the proper mathematical notational form...)

 

[Helen B]

I think that your maths is a little rusty there Derrel. If the image size equals the object size, the ratio of the two is unity, and unity squared is unity, so no change in the ISO. It's probably better to think of it as it really is: the increase in effective f-number caused by the increasing distance between the lens and the film plane. Effective f-number equals lens-to-film* distance divided by the entrance pupil diameter.

Call it rear nodal point to film distance, though that isn't perfectly accurate.

 

[wsetser]

To compensate for bellows extension:

First, determine the magnification:

M = Image size / Object size

Then, find the Effective Aperture:

E = Aperture(M + 1)

 

[usayit]

btw... this is not true for DIGITAL. (Theoretically? maybe)

Digital sensors for the most part are "ISO-less" with signal gain. The gain is calibrated to mimic ISO to help photographers bridge the knowledge gap with the transition to digital. Even then, there are variances between "iso-settings" from one digital camera to the next. I do believe Dxomark measures and reports this variance in their results.

 

[rexbobcat]

btw... this is not true for DIGITAL. (Theoretically? maybe)

Digital sensors for the most part are "ISO-less" with signal gain. The gain is calibrated to mimic ISO to help photographers bridge the knowledge gap with the transition to digital. Even then, there are variances between "iso-settings" from one digital camera to the next. I do believe Dxomark measures and reports this variance in their results.

That is true. Nikon cameras typically have a Native ISO of 200 I believe (?) while With Canon it varies some... Some of their cameras has a native ISO of 100 but my 60D apparently has a native ISO of 160.

So basically any ISO that's not a multiple of the 160 is simulated in-camera by pushing and pulling the exposure