Originally posted by stevebrot That is pretty bold.
@MadMathMind, I do believe it is time to stand and deliver. A good place to start would be the list of lenses that were out-resolved by the K-7 sensor.
Seemingly most of them, actually. The K-7 is 14MPix and no Pentax lens has pulled a resolution that high on any camera.
The only place who really measure this stuff is DxO. Let's just pick a lens, say the DA*55. Let's look at its sharpness ratings on various bodies:
K-3: 11 MPix
K-5 IIs: 8 MPix
K-10D: 8 MPix
Now let's look at something else. We'll look at the Canon 35mm f/1.4L II. Here it is on various camera bodies:
5DS R: 37 MPix
6D: 17 MPix
1D Mark III: 9 MPix
70D: 15 MPix
The MP of those Canon bodies are 50MP, 20MP, 10MP, and 20MP. How about another
really expensive Canon lens? The 85mm f/1.2L:
5DS R: 30 MPix
6D: 18 MPix
1D Mark III: 9 MPix
70D: 14 MPix
So what are we seeing here? We never get the entire resolution of the sensor from a lens but on the 1D Mark III, we get 90% of it. On the 6D, we also get ~90% from both of these lenses. One thing that is true is that the full frame cameras see higher effective resolution than the APS-C ones--look at the 6D (FF) vs. the 70D. That makes sense: resolution is a pixel-level measure. The lens needs to be able to resolve the individual pixels to have them count; 20MP on an FF camera are a lot bigger than the ones on an APS-C camera with the same number. But still, what we see from these two lenses is that they are capable of delivering most of the MP the camera offers, with exception of the 5DS R (because that thing is absurd).
On the Pentax side....not so much. The DA*55 pulls half the available pixels on the K-5 II, less than that on the K-3. But on the K10D, it's 80%--that's good! So what this tells us is that the DA*55 is not keeping up with better sensors. There was little improvement in resolution when the number of sensor MP increased. This lens is being out resolved by the sensor.
Of course, this is if you want to put high stock in these tests. Given how lenses are used and how artificial these tests are, they're not gospel. But they do tell us something.
The bigger thing is, though, is it reasonable? The two Canon lenses cost $2200 and $1600, respectively. The DA*55 can be found for $569 now. Let's pick a Canon lens comparable in price, the 50mm f/1.4 ($385):
5DS R: 22 MPix
6D: 15 MPix
1D Mark III: 8 MPix
70D: 12 MPix
This lens can't keep up with the cameras either, with exception of the 6D. It fares no better than the DA*55. Moral of the story: you do get what you pay for. There's a point to those expensive lenses. Whether those prices are worth it...well, I don't think they are necessarily, since most of what most of us do is keep for ourselves and post on the web--Facebook sure makes all that resolution good for nothing.
On another forum, a guy suggested that perhaps a 20MP sensor would have been better for Pentax, that the current crop of lenses would have done better with that than with the 36MP. I didn't understand him and thought he was nuts. He may be right. Unfortunately, Canon doesn't have a ~36MP camera--everything was 20MP or 22MP until the 50MP monster that is the 5Ds. Let's do a quick check with an inexpensive Nikon lens: the 50mm f/1.4G. Here it is on a few bodies:
D810 (36MP FF): 21MP, 58%
D750 (24MP FF): 18MP, 75%
D4 (16MP FF): 12 MP, 75%
D7100 (24MP APS-C): 13 MP, 54%
D7000 (16MP APS-C): 10 MP, 62.5%
The D810 and D7000 have about the same pixel pitch (like K-5 and K-1). We see that the resolution as a percentage of available pixels is about the same! The lens cannot resolve objects to an area below 2.4 micrometers^2. Now, it doesn't quite work exactly linearly like that (because the sensor is more than just its pixel counts) so we do see slight increases in resolution as we increase the number of MP but there are costs: frame rate, file size, etc.
I guess we should expect the DA*55 to get about 16MP on the K-1. The equivalent pitch to a K-10D in FF is 22MP. We'd could see 17.6MP with that--a higher number! At 20MP, we may actually have gotten
more from our lenses than we do at 36MP simply because most of what the 36MP is giving us is lost on our old lenses.
End thought: it's not all about pixels. But it is a bit annoying to pay a high file size and processing speed price for pixels that are ultimately going to waste. I may start downsizing my TIFFs simply because there isn't 36MP of resolution in there and the HDD space is fantastic. 22MP seems to be a good number for me so far--that's what I'm exporting my JPEGs at because there's no point to going any higher. I'm not seeing better quality than at 22MP.