The Digital Sensor: A Guide to Understanding Digital Cameras
by Wesley Fink on April 21, 2008 1:00 AM EST- Posted in
- Digital Camera
Lens Equivalence
It is important to understand that a 50mm lens is always a 50mm lens, as that is the focal length. That 50mm specification affects depth-of-field and other image characteristics tied to the lens focal length. However, we can calculate focal lengths for each multiplier that will give the same field of view in the finished image.
With a closer look at field of view and the impact of the changes in field of view, it is easier to understand recent DSLR lens developments. Early DSLR lenses were generally 35mm lenses mounted on the new smaller sensor cameras, except for complete new systems such as the 4/3 digital-only system championed by Olympus.
Using 35mm or full frame lenses was great if your primary interest was telephoto and bird photography, as that 35mm 70-300mm lens that was the second lens for most film buyers now had a field of view like a 112mm-480mm zoom on the new Canon Digital Rebel. Unfortunately interiors, architectural photography, scenes, and fans of the extreme wide angle point of view were left in the cold in the early transition to small digital sensors.
That has been corrected in recent years with lenses designed for smaller sensors, lenses like the Canon 10-22mm, the Nikon 12-24mm, and similar APS C zooms from Sigma, Tamron, and Tokina. Today, whatever your mount and lens multiplier, there are lens choices that can cover the full range of choices for field of view.
A few lenses by Sigma are actually available in every mount and multiplier listed above. Obviously, these few lenses were originally full-frame 35mm that have been carried over with new coatings for improved performance and reduced flare on digital sensor SLRs. One such lens is the Sigma 24mm f1.8. The field of view on the different mounts and sensors this lens will fit illustrates just how the digital sensor size can influence the use of any lens. On the full-frame Canon5D, IDs III, and Nikon D3 this lens is a fast super wide 24mm. On the Canon 1.3X pro models it is still a fast f1.8, but with the FOV of a 31mm moderate wide angle.
On the Nikon D300/D60, the Sony A700/A350, and the Pentax K20D/K200D this fast lens is now a moderate wide angle to near normal lens that shoots images with a 36mm angle of view. On the Canon XSi and 40D we are at 38mm, which most would consider near normal. The Sigma SD14 FOV of 41mm has definitely crept into the normal range. Finally the 4/3 mount version of this lens is one of the "normal" lens choices on the Olympus E3/E510/E410 and Panasonic and Leica 4/3 digital SLR cameras. The 24mm on a 4/3 camera looks at the world as though it is a 48mm f1.8 lens, and competes with the Leica 25mm f1.4 as a much lower cost normal lens.
Similar comparisons could be made in other focal length ranges, but you get the point. Olympus makes a 70-300mm telephoto lens for 4/3, and it is much sought after by "birders", because the view on a 4/3 camera with this lens extends from 140mm to 600mm.
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andrewln - Monday, April 21, 2008 - link
This was followed in about 6 months by the introduction of the Samsung 14.6MP CMOS sensor in the Pentax D20.should be Pentax K20D
Wesley Fink - Monday, April 21, 2008 - link
Typo corrected. Unfortunately spell check can't catch model numbers that are misstated.araczynski - Monday, April 21, 2008 - link
now i know what pc tech illiterate people feel like :)its a good thing i don't care about photography, interesting read none the less.
finbarqs - Monday, April 21, 2008 - link
the thing is, I've read the reviews and saw the comparisons between the 5D and the D200 (I believe that was the last CCD sensor that Nikon used). The 5D has way better per-pixel sharpness than the D200. Perhaps the technology of the CMOS made it so it finally "looks" better than the CCD. Or at least on the Canon side of things. I'm not biased towards any camera. I've own an XTi, 5D, Panasonic DMC-L1, and now a D300. I'm hoping to own the next 5D MKII (or whatever they call it).Even the D2X used a CMOS sensor, and I thought Nikon made the D300 sensor, as well as the D3 sensor (FF). What I also find "funny" is that Sony doesn't have a FF sensor yet, but nikon does, thus leaving me to believe that Nikon came up with their own FF sensor.
melgross - Monday, April 21, 2008 - link
It's Nikon's own design, though I don't remember who makes it.haplo602 - Monday, April 21, 2008 - link
Nice article Wesley, finaly one Anandtech photo related article I enjoyed reading.On note on the growing megapixel count. Sooner more than later, DSLR in APS-C (and later full frame ones) will hit the same technology wall P&S are facing (too small photosite).
This is one factor that makes me a happy film shooter :-) I know that my limit is the scanner up to around 10MP and I have less flexibility in shooting conditions (either 2 bodies or limited by ISO and film type), in every other situation I am equal or better off.
I am waiting for an affordable Nikon full frame body and then I will make my switch to digital (but that is yet years to come).
wally626 - Monday, April 21, 2008 - link
A sensor technology improves APS-C will be able to go to high enough pixel counts and have very good quality. For most consumers some where around 12 MP is enough, if the sensors improve to where this can hit 3200 ISO with low noise 99 percent of the market would be satisfied.The full frame bodies will replace the medium formats of the film world. There have been some really good medium format cameras that take much better images than 35mm but very few are sold. I think the article is correct in saying the full-frame DSLR will be the PRO cameras and priced as such.
melgross - Monday, April 21, 2008 - link
The number ofpixels is directly related to the print size.If you go by the oft quoted 300 dpi on the final print for maximum quality, you will need a sensor with 2400 x 3600 resolution for a full frame 8 x 12 print, or 8.64 MP. For an 8 x 10, it would be 7.2 MP (4/3 sensor).
For a larger 11 x 17, it would be 3300 x 5100, or 16.83 MP, or 13.86 for the 11 x 14 4/3 sensor print.
You can figure the rest of the sizes my multiplying the inch size of the print edges L x W by 300 to come up with a number.
But the truth is that 240 dpi is going to be good enough fot most prints, and youcan do the numbers that way.
When you know the numbers, you can figure out what size sensor you will need for the highest quality work.
But for most people, even 180 dpi will be enough for their prints. Going to that gives more flexibility, as the sensor pixel count is much smaller.
It's better to get a camera with a longer OPTICAL zoom rather than to go for the biggest number of sensor pixels.
haplo602 - Tuesday, April 22, 2008 - link
^ this ^It's all a matter of print size. I am an amateur/hobbyist, and anything past A4 is large for me. I have printed reasonable quality 8x12 prints from a consumer slide film and home film scanner.
I can hang them up on the wall in a nice frame and they will serve their purpose :-)
Idealy I'd need a 12-14MP full frame Nikon with goot ISO/Noise characteristics (f.e. D3) and it will satisfy my needs for years to come.
Heidfirst - Monday, April 21, 2008 - link
especially as I was wondering the other day what smaller process technology would do for digital sensors?Normally of course smaller process means cooler & more importantly smaller>cheaper to make but of course with sensors you are talking a fixed size so not any cheaper.
But would the potential increased precision of circuitry mean any better image quality?
& a little nitpicking:
Sony didn't buy Konica Minolta (which continues in business) but certain assets from the Photo Imaging division of KM. As to what that actually means there is little hard knowledge outside the 2 companies as it seems that KM still retain some IP & indeed a shareholding in some of the production facilities.
Also, current thinking seems to be that the "A900" may not be called that but something else to differentiate it from the APS-C models.