Bike Tourist
Well-known
Well, this resulted in a good discussion wherein I learned a lot about the sensor. I have much early Leica experience but no lenses lying around so, again, while tempting, I think I'll stay with my Fujis and pretend they're Leicas. Thanks!
Godfrey
somewhat colored
This makes no sense to me.
Sensors are arrays of photo sites. Photo sites are electron counters. The sensitivity of a photo site is set by its chemistry and the electrical bias applied to it. Given a particular photo site chemistry (fixed) and set electrical bias, when you expose a photo site to light, it responds by building up a charge in the range from minimum activation energy to saturation, depending on the strength of the light and the amount of time that it is exposed. This analog charge, or voltage (the integral of how intense the light that the photo site was exposed to over how much time, given its chemistry and electrical bias), is converted to a digital number representation when the charge states of the sensor's photo sites are read out after the exposure.
When you underexpose you are either a) attenuating the amount of light falling on the sensor by closing down the lens' aperture, or b) reducing the amount of time light is falling on the sensor; usually a combination of both. This reduces the charge state at the end of the exposure.
Nothing about underexposure changes the sensitivity (what you mean by "ISO") of the sensor. The International Standards Organization (ISO) sensitivity is a rating of a sensor's response to strength of light over time, given a fixed chemistry and electrical bias. In other words, given a particular sensor with a set electrical bias, and given an input light source of X intensity over Time t, the charge state N results after the exposure. If N is a value that is in the expected bracket for ISO 100 materials/devices, the ISO rating is said to be 100. This is the base ISO of a sensor, or its 'native setting'. If you change the sensor's electrical bias, the ISO setting changes as a result of the electrical bias interacting with the chemistry. If you change the values produced by the readout after exposure by amplification or numerical means, the ISO setting changes as a consequence as well. The ISO setting is used in combination with other standards to calibrate the camera's meter, in order to produce predictable exposure results.
Underexposure is a term used to describe "reducing exposure from the metered standard". Underexposure is used to minimize photo site saturation, because photo site saturation is the point at which no additional amount of light falling on the photo site changes (raises) the accumulated charge value. Widespread saturation in an exposure, resulting from an averaged exposure setting that includes a range of light values outside the sensor's range from activation to saturation, leads to areas of 100% white values with no tones even though the subject area in reality might have tones. The result of proper use of underexposure is to reduce values at or beyond saturation and allow those tones to be expressed while letting tones under the saturation value be displaced a linear amount lower in the dynamic range.
If ISO sensitivity was raised when you underexposed, the result would not solve the issue of exposure saturation.
Along with the ISO sensitivity rating, a sensor also has a dynamic range—that range mentioned earlier as its post-exposure range from activation value to saturation. The sensitivity rating and dynamic range are coupled; the reason that sensors with high sensitivity are desirable is that they also tend to have a broad dynamic range. When sensitivity is changed from the base rating, for any sensor, the dynamic range is reduced. With a sensor that has a high sensitivity rating, this means you use a high sensitivity setting (obtained by some combination of changes to the sensor's operating electrical bias, post-capture amplification, and post-capture numerical manipulation) and still have enough dynamic range after doing so to be useful to capture a continuous toned image.
The problem with using underexposure to bias-offset saturation values into the usable range is that you inevitably also bias-offset lower values down into the activation threshold range. It's basically a dynamic range violation issue; it is what causes noise ... attempting to use values below the activation level as real data where it is difficult if not impossible to separate what is real signal vs what is just an ambient electrical charge. This is why sensors with high sensitivity ratings do well .. you have more space in the dynamic range window to detect and utilize real signal when you underexpose.
Again, if underexposure caused ISO setting to be elevated, this would not achieve the goal of underexposing. Saturated values would stay saturated, and normal values would be raised, producing in effect signal compression (a limited range of values) rather than proper exposure.
G
Bike Tourist
Well-known
Still thinking about the M-E. I would mate it with a 35mm Summicron, Ver. 2. Would this lens require coding? This is something I picked up in various conversations. I'm not sure what lenses require coding and why.
Duane Pandorf
Well-known
You don't need to code an uncoded lens. In the camera menus setup you would manually set to this lens. You could then save it as a preset. I shot with this same lens on my M-E for a few months.
However if using Lightroom with this specific lens you will need to use the plugin lenstagger as Lightroom does not understand the v2 35 Cron code that the camera saves to the Exif info.
I wish I hadn't sold that lens.
Hsg
who dares wins
Sorry I did not see your reply until today.
A simple way to find out if underexposure causes the sensor to up the ISO (light sensitivity) is to try it out.
Underexpose by as many stops as you like and then in the RAW software disable noise reduction.
As you increase the exposure in the raw software, you'll see noise even though the image was shot at ISO 100.
Noise is the result of high ISO.
Bike Tourist
Well-known
Thanks for all your interesting comments. I was considering an M-E+35 Summicron or a Leica Q. Both were finally ruled out for many reasons or, possibly, my faulty reasoning. Anyway, I'm ready to slink back into the loving arms of the Fuji crowd and concentrate on photography.
hepcat
Former PH, USN
Dick, no need to slink anywhere.
FWIW, the Fuji bodies and M lenses are all quite complementary as a system. I have an X-T1 as a back up body to my M9-P (same camera essentially as the M-E.) Each has strengths where the other has weaknesses and I find them a delightful setup that covers just about any contingency.
Roger