Full Frame Lens and FF Sensors!

Started Oct 23, 2011 | Discussions thread
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jamesm007 Veteran Member • Posts: 5,641
Full Frame Lens and FF Sensors!

Pentax has been making cameras since 1919 and in 1952 Pentax made the first SLR camera! In 1971 Pentax came out with the first multi-coated lens; its now famous SMC (Super Multi Coat). Around 1975 Pentax came out with the K mount. Since that time until pentax stopped making film SLRs Pentax produced millions and millions of lens that are in peoples homes around the world.

Pentax kept its old K mount that let everyone use all those millions of lens just sitting around. Moreover they made those old lens easy to use with the “Green Button”. What this button did was meter for you even in manual mode!

Full frame is a bigger size than APS, and some photographers want Pentax to make full frame dSLRs again just as Canon and Nikon are making today. They feel Pentax is missing the boat or that it will make a more complete system. One reason is all of those millions of lens were designed for 35mm or full frame size film. So naturally why not make a full size sensor? Why does Pentax hold on to APS only for SLRs as of today?

Maybe this is one of the reasons -

It could be that 10 years ago Pentax tested and found what Klaus, owner (and tester) of the lens testing site Photozone found. Many, a good percentage of older film lens don’t work well with full frame sensors. The reason is film was forgiving of the angle light was hitting it (see examples below) film is a thick media compared to digital sensors. To help visualize the difference think of film as a piece of paper and a pixel of a sensor as a piece of paper down in a cup 3” round and a three inches deep with the paper at the bottom. Now imagine the light source a ceiling lamp but you your cup and paper are in the corner of the room. Which paper would receive the most light? Of course it would be the paper out in the open. Scientist have made bubble type lens that sit on top of the cup to help capture the light at the edges and corners but it still falls well short of film and there is a light loss.

Now what’s a good way to make all those millions of lens perform well in a digital sensor? Make a smaller room (in the analogy above) so the light hits the cup at less of an angle. And that’s what Pentax has been doing by staying with APS sensors that are 1.5X smaller than FF. It allows the best performance out of those older lens that are not made for the extreme demands of digital sensors. There is more to the benefits. Even if light did strike a FF digital sensor perfect, cropping out the edges leaves the best image quality produced from lens. That’s in the center then boarders, corner are worse but are cropped out with APS sensors. So it’s a double benefit by using APS sensors with older full frame lens. You eliminate the light loss in the corners and crop out the worse part of a lens image quality. For telephoto fans you also make it 1.5X longer e.g. 50mm is 75mm, but wide angle fans lose 1.5x!

Some reference and quotes for you to read and study. Look at all the older full frame lens tested at Photozone on full frame dSLRs. There is at times an extreme light loss in the corners.

“ The vignetting characteristic is somewhat critical. At max. aperture we're talking about an edge shading of about 2.9EV which is fairly extreme. Such a "key hole" effect is already difficult to correct without artifacts. The situation improves at f/5.6 ( about 1.8EV) but you should really stop down to f/8 to tame the problem to an acceptable level.”

“The Voigtlander gave us somewhat mixed feelings regarding its resolution potential. The center quality is very fine even at f/3.5 and the borders are quite good here but the corners are plain soft.”

Klaus of Photozone testing Voigtlander Color Skopar 20mm f/3.5 SL II on Canon FF


“Fast lenses tend to suffer from high vignetting on full frame cameras and the AF-S 35/1.4 is no exception to this rule. In fact, with almost 2.2 EV wide open the amount of vignetting is exceptional (in a negative sense) and higher than on any other lens we've measured so far on the D3x. Such a huge amount of corner darkening is of course clearly visible in the final image.”

Klaus of Photozone

Here is an article that I found to post reference and it’s a good read. Here is a quote then link.

Corners on wide-angle and open apertures. When examining a wide-angle picture shot with a Canon full-frame dSLR, Nikonians like to giggle and point at the corners.Indeed, often, there is something to giggle at. I do not know of any ultrawide (say, 20 mm and below) that will produce impeccable corners on full-frame digital at all or even most apertures. On the other hand, the reduced-circle ultrawide zooms from Canon, Tokina, Sigma, and Nikon (that 12-24 DX is absolutely gorgeous!) are more consistent than anything comparable for full-frame, even near-legendary glass like the Zeiss Distagon 21/2.8


Pentax did the right thing 10 years ago. They made it so you can use your FF lens and get superb Image quality. Now some want more. Which is natural. But think about what Pentax gave. Pentax has known for years full frame makes its older lens not so good anymore and will have to develop a lot of new FF lens! But people have begged for FF. Just know that a good percentage of those old lens won’t perform near as well or even poorly compared to the same lens on an APS sensor dSLR. Sometimes we don’t know what’s best for us. Or the truth.

 jamesm007's gear list:jamesm007's gear list
Pentax K20D Pentax K-5 Sigma 10-20mm F4-5.6 EX DC HSM Pentax smc DA 55-300mm F4.0-5.8 ED Sigma 17-70mm F2.8-4 DC Macro OS HSM +11 more
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