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Film ISO


16 May 2012 11:30PM
If you have a film rated at 100 iso and you altered the exposure on the camera to iso 50 ( like on the OM 10). Would there be a degradation of the image? I understand increasing the iso would result in more grain, but I've taken some shots at various iso on FP4 (iso 125) and they are distinctly 'noisy' and not sharp. Whether the shot has been taken at iso 125, 400, 800 or 50, they all look the same. I'm wondering whether they maybe a problem with the way the film has been developed or scanned. FP4 is supposed to be quite a good film to work with, having a good latitude and fine grain. Or am I just a wally? When I get a chance I'll upload some shots.
Nick

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Paul Morgan e2
13 16.1k 6 England
16 May 2012 11:32PM
Are you processing your own films.
Pete e2
13 18.7k 96 England
16 May 2012 11:33PM
When you adjust the ISO you have to do it for the whole film and then you normally also adjust processing time to compensate. Most film developers show the ISO range that a film can be adjusted along with the necessary development time.
jembo e2
11 104 United Kingdom
17 May 2012 12:15AM
This is useful (if you don't already have it).
17 May 2012 12:16AM
I'm not processing my own films. Snappy snaps did it for me.

Quote:-When you adjust the ISO you have to do it for the whole film and then you normally also adjust processing time to compensate. Most film developers show the ISO range that a film can be adjusted along with the necessary development time.

Does this mean I should leave the iso as is or if I've adjusted it then leave it for the whole film.
Thanks
Nick
Paul Morgan e2
13 16.1k 6 England
17 May 2012 12:38AM
If you change the ISO, leave it like that for the whole film.

Then use a decent lab like ilford and tell them you adjusted the ISO, and tell them what ISO you set so they can process to compensate.
NEWDIGIT 3 401 United Kingdom
17 May 2012 8:07AM
Sounds as if the lab has processed at the original ISO for the particular film, adjusting ISO for individual shots on film is not the way to go if you need to adjust do it for the whole film and then advise your chosen processor of what you have done.
Before I get shot down calling Snappy Snaps a lab is trying to be PC.
lemmy e2
7 2.1k United Kingdom
17 May 2012 10:10AM
If you rate a 100iso film at 50iso, all you are doing is over-exposing it by one stop. That will be within the exposure latitude of a colour neg or black and white film and nothing to worry about, just give you a denser than ideal neg but easily enough coped with in printing.

If you are scanning the negs, the scanner will compensate for too dense or too light negs (up to a point, of course) which could be the cause of all your exposures loking the same.

If you have exposed the film at iso's 50 through 800 and the negatives all look the same, there is something wrong with your camera. FP4 film is anything but unsharp and 'noisy' (actually, noisy doesn't apply to film, it is 'grainy', since it is the light sensitive chemicals clumping together that causes it.)

In my Fleet Street days, the two films we mainly used were Kodak TriX and Ilford FP4. My regular print size for show biz stuff was 20x16in. The 400asa Tri X was capable of pin sharpness and hardly noticeable grain at that size. FP4 could be razor sharp and at 20x16 if properly exposed no grain would show.

I don't think uploading scans would tell anyone much - it is the negs that are the problem. They should have a full deep black on the lightest parts of the image and be transparent on the darkest parts. Any veiling in the transparent parts would show overexposure. 'Greenness' as we called it, or a kind of greyness in the blacks would show underexposure.

By the way, at one stage FP4 film WAS rated at nearer 50 officially. There was a change in standards by the ASA (as it was then) and a slightly 'thinner' neg became preferred by the standards authorities, who deemed it to show less grain when printed.

All this stuff was part of the art of photography. Much as I prefer digital cameras, they have tended to make everyone's work look similar and to a general blandness. In the film days, you could often tell one photographer from another by their style of print alone - witness David Bailey or Terry O'Neill. It's nice to know someone is still fascinated by and learning about film. I have many fond (and not so fond!) memories of developing colour film in hotel rooms in far flung places. Try developing C41 colour neg film which requires a controlled temperature of 30c in a hotel room with an ambient temperature 40c Tongue
thewilliam e2
6 4.9k
17 May 2012 4:14PM
If you listen to a "zone system" fan, you'll hear that the "real" ISO of many mono films is about a stop less than the box speed. We used to expose Kodak TCN at 160 ISO instead of 400 ISO because it was then the same speed as our colour neg film and it also gave slightly less granularity.

Chromogenic films give smoother tonality when slightly over-exposed and increased "grain" when under-exposed. I've found that the "ordinary" mono films like Tri X give their best with correct exposure as measured using the zone system.

A decade ago, I had an assistant who was a good artist but incapable of getting exposures right. Colour and chromagenic film could be over-exposed by 5 stops and still give an artistically pleasing print. Much more than 1 stop under and it was sometimes quite tricky to rescue.
17 May 2012 7:09PM
Thanks for your comments. I'm hoping the fault lies with me where I've been using the iso for exposure change. I'll put some film in the camera over the week-end and keep it at the film's iso and see how I get on. I'll use it in manual and alter the exposure using the aperture and shutter speed. I would have thought that some of them would have come out o.k. as some shots were shot at iso 125. However as lemmy says, the scanner may be compensating for the negs. If the problem is with the camera or lens, what would be the cause. Thanks again, another lesson learned!
Nick
lemmy e2
7 2.1k United Kingdom
17 May 2012 7:50PM

Quote:If the problem is with the camera or lens, what would be the cause.


Probably that the shutter speed or lens iris is faulty but I doubt that is the cause. From what you say, I think you may misunderstand the nature of film a little. No surprise in that if it is new to you.

With film, the sensitivity of the film is fixed. If you have 125 ISO film in the camera, that is what you have, ISO125. If you want ISO 400 you have to put an ISO 400 film in there. So, if you have an exposure of 125th at f8 in a given lighting with IOS125 film and you want to shoot at 250th, you must change the shutter speed to 250th and open the lens up to f5.6 to feed the film the light level it requires.

With digital, if you have the same 125th at f8 with ISO set to 125 you could do the same as film and set the shutter to 250th and the lens to f5.6 - or, as I think you are used to doing, you could up the shutter to 250th, keep the lens at f8 and raise the ISO to 250 on the dial.

I think, reading your post that this is your problem.

To recap, film speed is not negotiable. If you have slow ISO64 film in a camera and you want to shoot in a dimly lit cathedral, you have a problem. You will simply have to use wide apertures and slow shutter speeds and do the best you can. Whereas with a digital sensor, you can just up the sensitivity to to1600 and shot away at hand holdable speeds at the cost of a little more noise on your images.

Luxury! In my day, the cameras weighed 600kilos and film cost 500 a roll and 600 to process. If you wasted one single frame, the chief photographer would have you beaten up and thrown in a coal cellar for six months while you held the camera up above your head. You don't know you're born these days Wink
17 May 2012 8:02PM
Thanks Lemmy. I think you're right with me using film like digital. As I said earlier I'll get some film and use it on it's native iso and see how I get on.
Thanks again.
Nick
Snapper e2
9 3.8k 3 United States Outlying Islands
17 May 2012 8:41PM
As mentioned above, the Zone System is pretty much based on finding a personal speed for any film+developer combination with the camera and meter that you are using, and this could be a different speed for each camera depending on whether the meter read a bit high or low and the shutter was accurate or slightly slow. I remember doing a 1 day course on this at the local college complete with all of the processing and printing only to find out that my gear gave box speed with FP4+ and that developer, but at least I then knew I was accurate. Wink
lemmy e2
7 2.1k United Kingdom
17 May 2012 8:54PM

Quote:different speed for each camera depending on whether the meter read a bit high or low and the shutter was accurate or slightly slow


I know Anselm Adam's zone system but I do think it is unnecessarily complicated for someone starting out with film, snapper Wink


Quote:use it on it's native iso and see how I get on


Le us know, Nick.
Snapper e2
9 3.8k 3 United States Outlying Islands
17 May 2012 10:52PM

Quote:I know Anselm Adam's zone system but I do think it is unnecessarily complicated for someone starting out with film, snapper Wink



I wasn't actually recommending he tried it, more trying to point out that you can get all caught up with an idea and still find that the box speed is the best place to start! Grin

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