DSLR spherical resolution
Intro
In general photography megapixels are more or less synonymous to resulting image resolution. Panorama photography is a bit different. Here the sensor pixel density is more important than the sensor pixel count.
Cameras
Digital Single Lens Reflex (DSLR) cameras exist in four major groups:
- With FourThirds sensor (crop factor 2.0)
- With an APS-C type sensor (crop factor 1.5 or 1.6)
- With APS-H type sensor (crop factor 1.3)
- With a sensor of the full 35mm film size (crop factor 1.0)
In each size category there are several cameras with different sensor resolutions. And there are several lenses that can be attached to cameras with different sensor sizes.
Pixel density
To deduce the pixel resolution obtainable by a certain sensor/lens combination we should know the density in pixels/mm of the respective sensor. The pixel density can be calculated roughly from the Megapixels and the sensor size.
You get the exact pixel density by dividing the sensor size in pixels by the corresponding size in mm.
For the four major groups and some typical Megapixel sizes:
FourThirds
with 13.5mm short side
Megapixel 6 8 10 12 16 20 Short side px 2121 2450 2739 3024 3460 3900 px/mm 157 181 203 232 260 290
APS-C
with 16mm short side
Megapixel 6 8 10 12 15 20 24 28 Short side px 2000 2309 2582 2828 3160 3650 4000 4320 px/mm 125 144 161 177 197 228 250 273
APS-H
with 19mm short side
Megapixel 8 10 16 Short side px 2336 2592 3264 px/mm 123 137 172
Full size
with 24mm short side
Megapixel 6 8 10 12 16 21 24 28 36 42 46 Short side px 2000 2309 2582 2828 3266 3742 4032 4320 4900 5300 5500 px/mm 83 96 108 118 136 156 168 180 204 220 229
Lenses
To determine the angular resolution we need the ratio between the angular distance as seen by the camera and the physical distance on the sensor. This ratio depends on the angular distance from the optical axis for all projections but the equidistant fisheye. Luckily at the optical axis all projection formulas converge to the equidistant projection The angle is expressed in radians, which gives an angular mapping of
In simple words: The angular mapping in mm/radians equals the focal length in mm in the image center. The actual mapping is not relevant, the formula applies equally to all kinds of fisheyes as well as to normal (rectilinear) lenses.
Pano sizes
From the above values we can easily calculate some sample panorama resolutions. The table gives some rounded values for the maximum pixel width of an equirectangular (f
= focal length, MP
= Megapixel):
FourThirds MP - - - - 6 7 8 10 12 - 16 20 APS-C MP - - 6 8 10 11 12 15 20 - 24 28 APS-H MP - - 8 10 - 16 - - - - - - Full size MP 6 8 12 16 21 24 28 36 42 - - - pixel/mm 80 100 120 140 160 170 180 200 220 240 260 280 f=5.6mm width 2820 3520 4220 4920 5280 5980 6340 7040 7740 8440 9140 9860 f=8mm width 4020 5020 6040 7040 7540 8540 9040 10100 11100 12100 13100 14100 f=10.5mm width 5280 6600 7920 9240 9900 11200 11900 13200 14500 15800 17200 18500 f=12mm width 6040 7540 9040 10560 11300 12800 13600 15100 16600 18100 19600 21100 f=16mm width 8040 10060 12100 14100 15100 17100 18100 20100 22100 24100 26100 28100
The formula for an exact calculation is
with = focal length, = pixel density, = full circle. This is the exact same formula f.e. PTGui uses.