Swaggie
In film, my understanding of ASA was film sensitivity or how fast the film reacted to light.
In order to achieve a higher sensitivity or faster reaction speed the grains of photosensitive chemical were larger. A nice grainy effect could be achieved by using a faster film.
Now, with the new digital camera it doesn't use film but has a sensor instead. To me the equivalent in grains would be pixels. There is a fixed number of pixels. So why does the camera have an ASA setting? When I change this setting, what am I doing? What is it affecting?
AT REST
My understanding, when you increase the ISO (ASA) the camera sensor amplifies the signal created by the light on the image. However this amplification also amplifies the 'noise' created by the electronics etc and hence introduces random 'fuzziness' which is the film equivalent of grain.
(no doubt someone will have a better explanation later)
Martyn
1998 Defender
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2014 Centreing the Simpson
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Fossicker
SupporterHi Mick,
Bushies description is very accurate, it is very difficult to describe the impact that the ISO setting has on the image as every camera is different.
Many of today's high end DSLR's have unbelievable ISO performance, Nikon's D3s is a prime example, its performance at iso 6400 is fantastic.
The easiest way to understand the impact on the image is to go to a site like dpreview.com and see if they have a review of your camera. If they do, simply go to the ISO performance page.
Here is what the ISO page shows, this page is from my compact camera. At the bottom of the first image, you will see ISO settings of 50/64, 100, 200, 400, 800, Simply move your mouse to each ISO setting to see the impact of that setting..
Sigma DP2 Review: 10. Photographic tests (Noise): Digital Photography Review
Cheers
Steve
ForumSage
Yep. Bushie is 99% there.
Pixel (density or numbers) count equates to 'resolution', or the chances of a piece of image being seen...by a pixel, or two or three or...
Noise is the (usually) undesirable side-effect of increasing sensitivity, the ASA or ISO number. It won't reduce the 'resolution' but can mask it.
-Noise is not Grain. They are the results of totally differant phenomena, one electrical the other chemical/physical.
-Noise is sort of regular, whereas Grain is random in shape etc
-Noise is not nice to look at... well, for those of us familiar with grain, which can be aesthetically pleasing where appropriate.
-Grain cannot be easily/cheaply duplicated by software, though see the link for something that does. At a price.
A picture is worth a thousand words...
TrueGrain Overview
Hope that gives some, er, 'resolution'.
James the Luddite, still hand-developing his glass plates...
(not really)
Swaggie
I know a fellow who still has some glass plates and the camera that uses them.Originally Posted by superquag
Yep. Bushie is 99% there.
Pixel (density or numbers) count equates to 'resolution', or the chances of a piece of image being seen...by a pixel, or two or three or...
Noise is the (usually) undesirable side-effect of increasing sensitivity, the ASA or ISO number. It won't reduce the 'resolution' but can mask it.
-Noise is not Grain. They are the results of totally differant phenomena, one electrical the other chemical/physical.
-Noise is sort of regular, whereas Grain is random in shape etc
-Noise is not nice to look at... well, for those of us familiar with grain, which can be aesthetically pleasing where appropriate.
-Grain cannot be easily/cheaply duplicated by software, though see the link for something that does. At a price.
A picture is worth a thousand words...
TrueGrain Overview
Hope that gives some, er, 'resolution'.
James the Luddite, still hand-developing his glass plates...
(not really)
ForumSage
CALUMET 5x4 single rail,
Speed Graphic 5x4
(the one with focal plane shutter as well...)
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