digital exposure experiments
This is a series of test exposures made on a Nikon D50 with a Sigma f/1.8 lens. Every file was shot as a Nikon RAW file and edited in Adobe Camera Raw.
The tests were done to learn just how far editing a RAW file can go in terms of digging up exposure information from the sensor. And hopefully allowing photography in low light.
The camera itself lets me choose between ISO 200, 400, 800 and 1600. Nothing in between..
Adobe Camera Raw has an 'exposure' slider, which is calibrated in 1 stop increments.. it goes up to +4 stops. With this in mind and a handheld ambient light meter in hand I decided to check how well this exposure slider worked.
I metered at and shot at ISO 25,000 and fiddled with the exposure slider and got an actual photo.. Tested in daytime bright light to dark with barely any light.
These photos were done in a 14x17x7 foot room with one household 75watt incandescent bulb in a desklamp shining off a white ceiling.
The ambient meter and d50 reflected meter both agreed on an exposure:
one third of a stop less than 1 second at F/1.8 ISO 200, or 0.8 seconds
here is what that looks like using my cameras automatic Aperture Priority setting:
Nikon D50, ISO 200 f/1.8 0.8 seconds
The rest of these images were done using fully manual operation based on the ambient meters readings.
iso200, 0.8sec iso400, 0.4sec, iso800, 1/5
iso1600, 1/10sec iso3200*, 1/20sec, iso6400*, 1/40sec
iso12500*, 1/80sec iso25000*, 1/160sec, iso50000*, 1/320
iso100000*,1/640
*ISO at which meter reading and exposure was made, actual camera ISO set to 1600
With results like these it is obvious something is happening in the blue channel.. Either way, for my purposes I am only considering this work applicable to black and white photography, as was my original intent.
This is a crop of the exposures above, with 0% saturation applied in adobe camera raw..
200,400
800,1600
3200,6400
12500,25000
50000,100000
As can be seen above, for black and white purposes the Nikon D50 and camera raw allow this camera to be quite a bit more capable than the cameras built in ISO 1600 speed.
Granted, a bit noisy at higher speeds but still quite a usable identifiable image..
Applied to photography at night or during the day this could really open up the ability to shoot at higher shutter speeds without blur hand held at night in a city or shooting at high shutter speed high aperture during the day allowing maximum depth of field and motion blur control.
Here is a 100% crop showing the gray card up close: (jpeg compression alters apparent noise)
200,400
800,1600
3200,6400
12500,25000
50000,100000
Something interesting I noted during these tests is that the ISO speed the camera is set at really doesnt matter.. The small amount of exposure information in the blue channel that is amped up in the '50,000ISO' exposure made at cameras 1600 is the same amount of info that can be had at iso 200 with the same shutter speed and fstop..
Simply put: this method of RAW editng isnt so dependant on the cameras claimed ISO speed.
Here is what I mean:
these 4 photos were all made at f/1.8 1/320th of a second, the equivalent of the ambient meters ISO 50,000 for this light level, but each of the 4 is set to a different camera ISO..
200,400
800,1600
When editing the above four, like all of the images in this test I used only the exposure, shadows, brightness and contrast settings in adobe camera raw.. It is obvious that iso 1600 is more sensitive than 200 but with the above 4 it is obvious that there isnt MUCH more sensitve than advertised when editing in adobe camera raw
Here is how all of this translated into actual use at night:
exposed at ISO 25,000 1/8th second f/1.8
exposed at ISO 25,000 1/60th second f/1.8
exposed at ISO 50,000 1/500th second f/1.8
So, wrapping up...
I'd just like to say that using RAW files I am able to do handheld photography at night at speeds above 1/60th all without too much trouble..