Changing ASA on camera to gain extra stops ??

BADGER.BRAD · Aug 1, 2017

A theoretical question at the moment but how many stops would I gain by setting ASA on the camera to double or half of the actual film speed, I am talking exposure time here. Can I change this mid film ? I have a couple of cameras that seem to suffer from not having quite enough of a range of exposure times to cope with either poor or too much light plus a couple of point and press cameras that will just be unusable in British winter.

Thanks all

Chan Tran · Aug 1, 2017

Basically you can't change it. Using color negative film you can change the ISO downward a stop or two but not upward. If you do it for the entire roll you can push a couple of stops but I wouldn't do that. For me choosing the ISO to set for a particular film in order to get the best exposure is OK but not because you lighting is too much or not enough. I rather not take the pictures.

Paul Manuell · Aug 1, 2017

Unlike digital, you can't change the iso mid film; whatever you've set it to when starting the film, that's what it has to stay at for the whole film.

BADGER.BRAD · Aug 1, 2017

Thanks to both of you ,much appreciated. As Paul will know in the UK the light can go from blinding to near darkness and back again in a very short space of time My Cosmic will over expose in very bright light even at it's fastest setting ( only slightly) and under expose in poor light then my point and presses will under expose in anything less than bright light. As I like the challenge of trying to get the best out of limited equipment I was looking for a cheat ! I guess I will have to stick to carrying multiple cameras.

Thanks again.

Saganich · Aug 1, 2017

Choose film with high ISO like 400 or 1600. If its B&W you can push it more if necessary with longer development times. You can use the ISO and light meter to figure out what film speed is suitable for your environment and equipment.

Saganich · Aug 1, 2017

There is no magic bullet for such varying light conditions. In B&W I've managed by using a f/1.4 - 16 lens, triX, careful exposure (letting detail-less areas go black or white and medium to low contrast developing. I can go from a darkish pub to full sunshine without too much trouble. Not for color.

Kino · Aug 1, 2017

Use a higher ASA/ISO film and carry a few ND filters for bright situations...

.30 ND is 1 stop subtracted from the scene
.60 is 2 stops.
.90 is 3 stops and so on...

To maintain exposure on a camera that is Non TTL, or if you are using a hand-held light meter, simply subtract HALF of the film speed per .30 of ND.

For example: if you start with 400 ASA and put on a .30ND, change your ASA to 200, .60 would be 100 ASA and .90 would be 50.

Don't forget to change the ISO/ASA setting back when you remove or change the filters!

The film can be processed normally and all exposures should be correct, if your through the lens metering system works properly.

TTL cameras will automatically compensate for the ND filters.

Remember: ASA/ISO - F stops - .30 ND are all equal gains or losses of light by Half or double.

(Edit: thanks for catching that E. von Hoegh)

zanxion72 · Aug 1, 2017

It depends on the film. Films with wide exposure latitude, like Portra 160, you can shoot it anywhere +-1 stop from the metered exposure and get good results. There had been other films that have been marketed as films that could be shot over a variable ASA range, such as Agfapan Vario XL supposedly from 125 to 1000, but that was not really true. It had been mostly a marketing trick relying on the exposure latitude of the film and on what you could get away with it.

Gerald C Koch · Aug 1, 2017

Paul Manuell said:
Unlike digital, you can't change the iso mid film; whatever you've set it to when starting the film, that's what it has to stay at for the whole film.

Even with digital cameras when you change the 'ISO' the noise level of the image increases. Essentially you increase the gain on the sensor array. The higher the gain the more noise. This is analogous to an increase in grain with film. Remember the principle of TANSTAAFL.

jim10219 · Aug 1, 2017

If you want a cheat, bring some neutral density filters and use a high ISO film. Either that, or shoot sheet film.

I will agree that Portra is a good choice if you need some latitude from shot to shot. I once shot half a roll of Portra 160 metered at 1600, unaware of what I did. I corrected hit half way through and finished off the roll at 160. I had it developed normally, and I got a few usable shots from the 1600 side. It took some manipulation to get them to work, and none of them looked amazing, but some were decent enough to post on my FB page. So that film certainly has a decent bit of leeway should you ever need it.

Sirius Glass · Aug 1, 2017

For black & white and color print film the light latitude is so wide that the ISO does not to need to be changed.

Craig75 · Aug 1, 2017

you can change your iso for b/w - you can go a stop under exposed and 2 or 3 over and develop the roll the same. They will print differently and you may have to learn how to drag what you want out of them but yes you can do it.

Find a shot with some shadow and highlights and bracket from one stop under to say 3 over and see what you get!

Paul Manuell · Aug 1, 2017

jim10219 said:
If you want a cheat, bring some neutral density filters and use a high ISO film. Either that, or shoot sheet film.

I will agree that Portra is a good choice if you need some latitude from shot to shot. I once shot half a roll of Portra 160 metered at 1600, unaware of what I did. I corrected hit half way through and finished off the roll at 160. I had it developed normally, and I got a few usable shots from the 1600 side. It took some manipulation to get them to work, and none of them looked amazing, but some were decent enough to post on my FB page. So that film certainly has a decent bit of leeway should you ever need it.

I did something similar once, put Portra 400 in the camera instead of what I thought was 160 (foolishly kept both in the same side pocket of my camera bag). I always set the ISO to 100 for the 160 (320 for the 400), so basically exposed the whole of a 400 film at 100. It was only when taking the finished film out that I got that heart sinking feeling of realising what I'd done.
Amazingly though, after explaining to the shop what I'd done and them making the necessary adjustments in processing, the results were absolutely perfect. So I can concur with what others have said here about Portra's exposure latitude.

E. von Hoegh · Aug 1, 2017

Kino said:
Use a higher ASA/ISO film and carry a few ND filters for bright situations...

.30 ND is 1 stop subtracted from the scene
.60 is 2 stops.
.90 is 3 stops and so on...

To maintain an automatic exposure on a camera that you can vary the ISO upon, simply subtract HALF of the film speed per .30 of ND.

For example: if you start with 400 ASA and put on a .30ND, change your ASA to 200, .60 would be 100 ASA and .90 would be 50.

Don't forget to change it back when you remove or change the filters!

The film can be processed normally and all exposures should be correct, if your through the lens metering system works properly.

Remember: ASA/ISO - F stops - .30 nd are all equal gains or losses of light by Half or double.

If you use an ND filter on a camera with TTL metering you do not change the ISO setting.

Paul Howell · Aug 1, 2017

As noted a film's emulsion speed is determined by the manufactures. Consumer grade film has more latitude as a safety factor than pro levels like Porta or Ektar. A given ISO can be pushed or pulled by adjusting the development time. So if you push Porta 160 to 400 that is one stop, development time is extended which for negative films sacrifice shadow detail. Some old timers pull color films from say 160 to 80 in the belief that pulling color film improves color satiation. To decision push or pull film speed must be made at the beginning of the roll. I recommend loading your different cameras with different films to cover varying shooting situations. I keep Koda or Fuji 400 in my point and shoots and either Porta 160 or Kodacolor 200 in my SLRS. Sometimes the only viable option is flash.

Theo Sulphate · Aug 1, 2017

With digital, when you change the ISO you're effectively changing the sensitivity of the sensor. You can do this individually on a frame-by-frame basis. Also, with digital, you want to avoid overexposure because once you blow the highlights you have nothing there. That's why many will shoot at high ISO and high shutter speeds: less chance of overexposure. In postprocessing you can get the underexposed image to look right.

Film --negative film, not positive/reversal/transparency film-- is like the opposite of digital. The sensitivity is for the whole roll because you're developing the whole roll the same way. Negative film can tolerate a fair bit of overexposure (one web site had an experiment showing color film overexposed up to 8 stops and still being usable). You don't want underexposure because if the shadow detail didn't make it onto the negative then it's just not there. So, with negative film it's common to choose a slightly lower ISO than the film's actual speed in order to gain that +1 stop or so of overexposure (or just choose your camera settings for overexposure).

So: both dark and bright? You can use Ilford HP5+ at 400 for the dark scenes and still have reasonable (hand holdable) shutter speeds and maybe apertures of f/4 or f/2.8 at the worst. Then, having the same roll in the camera when it brightens up, just use faster shutter speeds and narrower apertures - I'll bet you won't overexpose by much and, if you do, it's not really a big problem when that negative gets printed.

Bill Burk · Aug 2, 2017

So you've got a Soviet camera with something like f/4 to f/16 and maybe one shutter speed around 1/60? Keep shooting the 200 black and white film.

Set that Weston II to 100 and if you can hit one of the f/stops it tells you to use, go for it. Do not worry about overexposing in bright light, just set it to f/16 and shoot away. When it gets dark and the meter is telling you f/4 is barely enough... Don't worry you have a little extra play. Not much though. If it gets much darker turn on more lights, light some fires or just put the camera away until it gets brighter.

You can't change the ASA of the film mid-roll but you can overexpose, properly expose and barely expose enough all on the same roll... each shot you'll have to see what you can do with it. But with black and white, you don't have to expose it just right to get a picture. You'll have worse luck with the underexposed shots, maybe not even be able to see anything. But you should be able to pull something out of everything else.

RalphLambrecht · Aug 2, 2017

Paul Manuell said:
Unlike digital, you can't change the iso mid film; whatever you've set it to when starting the film, that's what it has to stay at for the whole film.

Oh, I didn't know you could change the film speed on digital cameras mid -roll.lol

RalphLambrecht · Aug 2, 2017

BADGER.BRAD said:
A theoretical question at the moment but how many stops would I gain by setting ASA on the camera to double or half of the actual film speed, I am talking exposure time here. Can I change this mid film ? I have a couple of cameras that seem to suffer from not having quite enough of a range of exposure times to cope with either poor or too much light plus a couple of point and press cameras that will just be unusable in British winter.

Thanks all

Sure you can but, it will not change the fact of over or underexposure. You are just kidding yourself; might as well just change the exposure time to what you need; same effect.

markbarendt · Aug 2, 2017

BADGER.BRAD said:
Thanks to both of you ,much appreciated. As Paul will know in the UK the light can go from blinding to near darkness and back again in a very short space of time My Cosmic will over expose in very bright light even at it's fastest setting ( only slightly) and under expose in poor light then my point and presses will under expose in anything less than bright light. As I like the challenge of trying to get the best out of limited equipment I was looking for a cheat ! I guess I will have to stick to carrying multiple cameras.

Thanks again.

I'm not familiar with the "Cosmic" so the specifics you gotta figure.

First, each film has a given box speed, say 200. That's a fixed value. Nothing you can do with the camera can change that baseline. Once the film is in the camera there are only two variables, time and aperture.

Changing the iso/asa on any meter simply changes the base line the meter uses to determine shutter speed and aperture. A change from 200 to 100 can "trick" the meter into thinking the film needs another stop of exposure but that only matters if the meter is coupled to the shutter speed and/or aperture. If the camera is manual adjust you gotta do the work.

Paul Manuell · Aug 2, 2017

Theo Sulphate said:
With digital, when you change the ISO you're effectively changing the sensitivity of the sensor. You can do this individually on a frame-by-frame basis. Also, with digital, you want to avoid overexposure because once you blow the highlights you have nothing there. That's why many will shoot at high ISO and high shutter speeds: less chance of overexposure. In postprocessing you can get the underexposed image to look right.

Film --negative film, not positive/reversal/transparency film-- is like the opposite of digital. The sensitivity is for the whole roll because you're developing the whole roll the same way. Negative film can tolerate a fair bit of overexposure (one web site had an experiment showing color film overexposed up to 8 stops and still being usable). You don't want underexposure because if the shadow detail didn't make it onto the negative then it's just not there. So, with negative film it's common to choose a slightly lower ISO than the film's actual speed in order to gain that +1 stop or so of overexposure (or just choose your camera settings for overexposure).

So: both dark and bright? You can use Ilford HP5+ at 400 for the dark scenes and still have reasonable (hand holdable) shutter speeds and maybe apertures of f/4 or f/2.8 at the worst. Then, having the same roll in the camera when it brightens up, just use faster shutter speeds and narrower apertures - I'll bet you won't overexpose by much and, if you do, it's not really a big problem when that negative gets printed.

With regards to using narrower apertures and/or faster shutter speeds. This might not be desirable by the photographer if he/she wants either shallow depth of field, therefore needing wider apertures, or movement in a photo, therefore needing slower shutter speeds.
I think the best solution for the OP of this thread is to use a 400 film to address his problem of sometimes not being able to get fast enough speeds when the light starts to fade (though obviously even 400 has its limits once it gets too dark), and carry a selection of ND filters to take care of 400 being too fast in bright light.

Paul Manuell · Aug 2, 2017

RalphLambrecht said:
Oh, I didn't know you could change the film speed on digital cameras mid -roll.lol

I didn't say you could, I said unlike digital you can't change the ISO mid film, ie., with digital you can change the ISO any time you want, but with film, once the film's in the camera and the ISO's set, that's the ISO you're stuck with for the whole film. lol

Bud Hamblen · Aug 2, 2017

BADGER.BRAD said:
A theoretical question at the moment but how many stops would I gain by setting ASA on the camera to double or half of the actual film speed, I am talking exposure time here. Can I change this mid film ? I have a couple of cameras that seem to suffer from not having quite enough of a range of exposure times to cope with either poor or too much light plus a couple of point and press cameras that will just be unusable in British winter.

Thanks all

The speed of your film depends on what you load the camera with and how the film is developed. Likewise, the range of shutter speeds and apertures on the camera are all you get. I would load a roll of 800 speed film in a point-and-shoot for pictures on a dull day.

You might be able to change the ISO setting on the meter of the camera for exposure compensation. Halving the film speed setting on the meter increases the exposure by one stop. Doubling the film speed setting on the meter reduces the exposure by one stop. I use this trick on a couple of old automatic exposure cameras that I have.

Kino · Aug 2, 2017

E. von Hoegh said:
If you use an ND filter on a camera with TTL metering you do not change the ISO setting.

True. I got a bit mixed-up there when I edited the posting. The original would be for a camera without TTL. I will edit it yet again!

BADGER.BRAD · Aug 2, 2017

The Cosmic has no meter and aperture is auto set by setting the ASA so you only have exposure time as a variable.I will have to try using 400ASA in winter and 100 or 50 ASA in summer. As it has a fixed smallish lens I think ND filters would have to be held in place.I will just have to accept the limitations of the camera. It does take really nice photos in the right conditions at least equaling my SLRs. I have no idea what the point and press camera photos are like as have yet to process them. I have a suspicion that there is really no ASA setting on the Cosmic and it is just relying on the Aperture setting to expose photos correctly with exposure times for each light condition if that makes sense.

Changing ASA on camera to gain extra stops ??

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