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> ISO limitations for film cameras |
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#1
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ISO limitations for film cameras
When looking at a lot of tutorials they often talk about opting for a higher ISO film when light is scarce. As far as I understand the higher the ISO the more sensitive the film is to light.
That is all great with a digital SLR when you can switch the ISO however on film you can't do the switch that easily. So my question is rather than selecting a higher ISO in darker scenes would changing the aperture/shutter speed have the same effect to selecting film of a higher ISO? If so what would be the need in opting for a higher ISO film in the first place? Would it not just be easier to select a ISO film of say 100 and then as you move into darker settings just change the aperture/shutter speed instead of having multiple films of different ISO's? |
#2
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Yes that's right, however under some low light situations your lens may not have large enough apertures (low f stop number) or you want to use a relatively fast shutter speed to avoid blur if handholding the camera or "freezing" movement within the frame.
Ben |
#3
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In a sense we're almost back to the manual metering mode. The camera's meter takes readings which depend on the film's ISO. It does this because it assumes that whatever you have set the film ISO at is the genuine film speed. So if you have a ISO 400 in the camera then the meter assumes, rightly in most cases, that the film is capable of taking good pictures at that speed.
You can of course re-set the ISO speed on the camera from the speed of the film so if the shutter speed of the camera with a 400 film isn't fast enough for the nature of the photo then 800 or 1600 might resolve that problem. However as I think you have inferred from your readings this doesn't really change the true speed of the film. It is still a 400 film and even with push processing you will lose some shadow detail at a higher speed. This may or may not matter greatly if the shot is a night shot where shadows tend to disappear anyway. The only real way to get a higher ISO speed is to remove the 400 film and replace with say a 3200 film. The latter will give you a higher genuine speed but not the full 3200. It is generally thought that the Ilford D3200 may have a maximum true speed of 1250. On a brighter note there are many users who believe that the likes of HP5+ can be uprated to 1600 or even 3200 when required for night shots. However you need to be aware that 1600 and 3200 requires push processing and if you have 400, 1600 and 3200 shots all on the same film then the required push processing for the 1600 and 3200 shots will over-develop the 400 shots so acceptance of some compromise in the negs is required. I hope this makes sense to you Mike |
#4
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You can see how this works by trying different film speed settings on your camera, without loading film. Indoors at night should give typical low light readings. An ISO of 1600, for example, will give you better shutter speeds for hand-holding than one of 100. If using a tripod, on the other hand, the shutter speed can be much slower, and a lower film speed would be ok. The slower film should give better quality negatives, but its not always practical to use a tripod. Recently I have been using B&W film rated at 1600 or 3200 ISO to avoid the need for a tripod. I have found short rolls of 24 exposures useful to avoid being stuck with a high speed film in the camera when subject matter changes and a lower speed would be preferable.
Alex. |
#5
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In engineering terms a film with an ISO speed of 100 requires about 0.1 Lux.seconds of light to hit the film in order to deliver a well exposed picture. And this remains true no matter how bright or dim the subject matter external to the camera is. It doesn't matter how you get your 0.1 Lux.seconds. Lots of Lux and few seconds or few Lux and many seconds gets you the same exposure as long as the Lux multiplied by seconds product is the same.
The equation looks like this: E = I x T where E is exposure (Lux.seconds), I is intensity (Lux), T is time (seconds). The usual challenge posed by dimly lit subject matter is that the maximum aperture of the lens sometimes delivers so little intensity (Lux) to the film that the exposure needs to be made up by increasing the exposure time (seconds). Long exposures can lead to blurring of moving subject matter or blurring of the entire picture if the camera is held in an unsteady hand. The only way around this problem is to use a more sensitive film (higher ISO speed) that requires a lesser quantity of light for a satisfactory exposure. Higher sensitivity films tend to deliver pictures with lower image quality due to increased graininess and reduced sharpness. The digital world offers variable ISO values that vaguely mimic what different film ISOs do. Going for a high digital ISO value generates pictures with nasty speckles of electronic "noise". It may be a matter of opinion but I think the grain pattern of high ISO film has a beauty that the speckles of digital electronic noise don't match.
__________________
The word Photography first uttered and defined by its author Sir John Herschel at Somerset House, London on the evening of March 14, 1839: quote "Photography or the application of the Chemical rays of light to the purpose of pictorial representation" unquote. |
#6
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My theory was that you could stick with a particular ISO film such as 100 and be able to manipulate the shutter and aperture to get the right level of exposure in any giving setting. However, I think the problem with this is the shutter speed. If I wanted to take shots in darker scenes I could lower the shutter speed however lower shutter speeds means more potential for motion blur. The only way therefore to prevent motion blur AND get the right exposure level in darker settings would be to switch to a higher ISO film.
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#7
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The other problem you run into at long shutter speeds (typically shorter than 1/2 sec) is the issue of reciprocity failure. This can be quite significant with some films (Ilford, Foma,) and insignificant with others (Fuji Acros).
The downside of reciprocity failure is that for longer exposures you need to add additional exposure to get the same result from the film. For FP4+ for example you have the following: 0.5 - 1 sec 1.5x 1 - 2.5 secs 2x 3 - 6 secs 2.5x 7 - 12 secs 3x 13 - 18 secs 3.5x 20 - 22 secs 4x 24 -26 secs 4.5x 28 -32 secs 5x So if you take a low light reading that suggests a 30 second exposure you actually have to give an exposure of circa 2.5 minutes. In my opinion there are only two benefits where using a higher end Digital Camera over a similarly specified Film Camera these are for high ISO work and teaching (due to the instant feedback available). With sheet film each sheet can be developed individually so there is no issue with having to use a specific ISO for every image so the fact that you can do this with digital is slightly negated when using sheet film. |
#8
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Quote:
Steve. |
#9
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You're definitely getting it gsingh , you can manipulate settings and film but there are limits, you can't just dial in iso 128000 like you would with a digital camera, film just doesn't stretch that far easily. |
#10
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