Image sensor format
Three possible depth-of-field comparisons between formats are discussed, applying the formulae derived in the article on depth of field.
Considering a picture with the same subject distance and angle of view for two different formats: so the DOFs are in inverse proportion to the absolute aperture diameters
Using the same absolute aperture diameter for both formats with the "same picture" criterion (equal angle of view, magnified to same final size) yields the same depth of field.
But the aperture area is held constant, so sensors of all sizes receive the same total amount of light energy from the subject.
The smaller sensor is then operating at a lower ISO setting, by the square of the crop factor).
It is this result that gives rise to the common opinion that small sensors yield greater depth of field than large ones.
An alternative is to consider the depth of field given by the same lens in conjunction with different sized sensors (changing the angle of view).
The change in depth of field is brought about by the requirement for a different degree of enlargement to achieve the same final image size.
In this case the ratio of depths of field becomes In practice, if applying a lens with a fixed focal length and a fixed aperture and made for an image circle to meet the requirements for a large sensor is to be adapted, without changing its physical properties, to smaller sensor sizes neither the depth of field nor the light gathering
If the exposure is constrained by the need to achieve some required depth of field (with the same shutter speed) then the exposures will be in inverse relation to the sensor area, producing the interesting result that if depth of field is a constraint, image shot noise is not dependent on sensor area.
As typical f-numbers for lenses for cell phones and DSLR are in the same range f/1.5–2 it is interesting to compare performance of cameras with small and big sensors.
And even at short or medium exposure times, a few outliers in the dark-current distribution may show up as "hot pixels".
Typically, for astrophotography applications sensors are cooled to reduce dark current in situations where exposures may be measured in several hundreds of seconds.
One way of considering the effect that diffraction has on cameras using different sized sensors is to consider the modulation transfer function (MTF).
Other factors are typically the MTFs of the lens, anti-aliasing filter and sensor sampling window.
Considering the three cases above: For the 'same picture' conditions, same angle of view, subject distance and depth of field, then the f-numbers are in the ratio
It might be expected that lenses appropriate for a range of sensor sizes could be produced by simply scaling the same designs in proportion to the crop factor.
[9] Such an exercise would in theory produce a lens with the same f-number and angle of view, with a size proportional to the sensor crop factor.
Moreover, to maintain the same absolute amount of information in an image (which can be measured as the space-bandwidth product[10]) the lens for a smaller sensor requires a greater resolving power.
[13] Semiconductor image sensors can suffer from shading effects at large apertures and at the periphery of the image field, due to the geometry of the light cone projected from the exit pupil of the lens to a point, or pixel, on the sensor surface.
To combat the effect discussed above, smaller format pixels include engineering design features to allow the reduction in f-number of their microlenses.
These may include simplified pixel designs which require less metallisation, 'light pipes' built within the pixel to bring its apparent surface closer to the microlens and 'back side illumination' in which the wafer is thinned to expose the rear of the photodetectors and the microlens layer is placed directly on that surface, rather than the front side with its wiring layers.
[b] Some professional DSLRs, SLTs and mirrorless cameras use full-frame sensors, equivalent to the size of a frame of 35 mm film.
Most consumer-level DSLRs, SLTs and mirrorless cameras use relatively large sensors, either somewhat under the size of a frame of APS-C film, with a crop factor of 1.5–1.6; or 30% smaller than that, with a crop factor of 2.0 (this is the Four Thirds System, adopted by OM System (formerly Olympus) and Panasonic).
Canon selected the intermediate APS-H size, since it was at the time the largest that could be patterned with a single mask, helping to control production costs and manage yields.
[18] Newer photolithography equipment now allows single-pass exposures for full-frame sensors, although other size-related production constraints remain much the same.
Some older digital cameras (mostly from 2005–2010) used even smaller 1/2.5" sensors: these include Panasonic Lumix DMC-FS62, Canon PowerShot SX120 IS, Sony Cyber-shot DSC-S700, and Casio Exilim EX-Z80.
Finally, Sony has the DSC-RX1 and DSC-RX1R cameras in their lineup, which have a full-frame sensor usually only used in professional DSLRs, SLTs and MILCs.
Due to inch-based sensor formats not being standardized, their exact dimensions may vary, but those listed are typical.
[29] The listed sensor areas span more than a factor of 1000 and are proportional to the maximum possible collection of light and image resolution (same lens speed, i.e., minimum f-number), but in practice are not directly proportional to image noise or resolution due to other limitations.
