tonight’s images are part of an ISO test, first comparing the different ISO settings on the nikon d70 and nikon d700, and then comparing those same settings across cameras.
for this test, i had a guitar in a lit hallway against a door. i used the same 50mm lens on both cameras, moving the tripod back a bit on the d70 to account for the crop factor of the sensor. in hindsight, i should have adjusted the shutter speed instead of the aperture to balance out the change in ISO, but i think the results still achieved what i was looking for, and that’s to compare the grain in the images at the different ISO settings.
in basic terms, ISO is the term thrown around to describe the sensitivity of film (or in the case of the digital cameras, the sensor) to light. the lower the ISO number, the less sensitive the film is to light. this means that more light (either in terms of how much light or how long the light has to hit the film) is necessary to complete an exposure compared to a higher ISO rating, where the film is more sensitive to light and, therefore, less light is necessary to complete the exposure.
so why not just set that ISO number really high to make the film very sensitive? well, a few reasons.ISO is the third leg of the exposure stool; you need to balance all three elements to get the final image you want. sometimes you want to make the film less sensitive to light so that you can use a slower shutter speed or a wider aperture. but the real reason that gets kicked around when most folks talk about ISO is grain, or noise. when they say they make the film or sensor more sensitive, its kind of cheating. basically, instead of each sensor being individually responsible for deciding how much light is sees, sensors are clumped together. the higher the ISO, the larger the clumps. so instead of each sensor seeing light, they’re like “hey, my buddy next store saw some so i probably saw some too”.  what you wind up with, though, is noise. certain cameras are better with noise than others, and let the photographer shoot at higher ISO settings without producing so much noise as to negatively impact the final image. others, it’s pretty noticeable right away, forcing the photographer to make different decisions. for example, if your aperture is super wide open, and your shutter speed is as low as it can go or you need it to be a certain speed to capture some sort of action, the only variable you have to mess with is ISO, so upping the ISO to make the sensor more sensitive will allow you to capture that image at the shutter speed you need in exchange for a bit of noise.
anyway, there is a lot of information on the internet talking more about ISO and the technical aspects of what it means. tonight was about comparing my cameras and their ISO levels, so to the images we go!
the original image looked something like this. to check the level of noise, i zoomed in 100% cropped an area of the guitar to show some detail.
first, the nikon d70.
d70 – iso 200
d70 – iso 400
d70 – iso 800
d70 – iso 1600
as you can see, the is0 1600 on the d70 is less than desirable (which is why i upgraded to the d700!)
now, the d700
d700 – iso 200
d700 – iso 400
d700 – iso 800
d700 – iso 1600
d700 – iso 3200
d700 – iso 6400
d700 – iso 12800
lastly for tonight, here are the images with the same ISO side by side.
d70 – iso 200
d70 – iso 400
so, keep in mind that these are zoomed in 100%, so obviously the noise is exaggerated. but the larger the print from the underlying image, the more noticeable the noise will be.
on the d70, i was able to do prints at iso 400, iso 800 was fine with smaller prints, although it was better when i ran a noise reducer on the file.
on the d700, ISO 1600 is still great, iso 3200 would likely be fine for most situations, although i’ll do some prints at some point in the future for final determination.
