Upgrade from D300 for a poor college student?

Started Apr 7, 2013 | Discussions thread
Ray Ritchie
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Re: Upgrade from D300 for a poor college student?
In reply to ultimitsu, Apr 9, 2013

ultimitsu wrote:

Ray Ritchie wrote:

I believe DxO is the first to use the notion of "megapixels" as a measure of sharpness.

I am not sure why it is a difficult concept to wrap one's head around. If I could use the analogy of horsepower in automobiles. Generally there is a figure representing horsepower at engine. That is how much power the engine is capable of producing. Because no transmission is fraction-less, there is some powerless in the drivetrain, we then have another figure representing horsepower at the wheel. That is the amount of horsepower ended up available at the wheel. Two cars sharing the same engine may not have the same drivetrain therefore wouldhave different amount of horsepower at the wheel.

Same concept here. The sensor has a particular resolving capacity. that capacity would be fully utilised if there was a perfect lens. But since the perfect lens do no exist some resolution capability is lost.  The more imperfect the lens the more loss to the resolving capability of the sensor.

Yes, but as I said in my reply to your first post when you introduced the DxO pmp measure, I don't think the analogy holds as well once we start comparing different lenses on different bodies. I note on DxO's comparison tool, for example, that if I compare D300 and D700 with the same lens, the difference in pmp rating changes depending on what lens I select. And I don't think the pmp difference between D300 and D700 is the same as the difference between, say, a D7100 and a D600, even though in both cases we're comparing cameras with the same size sensors. There are a lot of factor at work determining the differences once we start changing both the lens and the camera, and I'm not yet confident that DxO's pmp metric is a consistent basis for these complex comparisons. Not to mention the fact that there are a number of other factors that go into IQ besides "simple" resolution (vignetting, distortion, chromatic aberration,...)

I also don't understand what DxO is really doing when they say they "correlate" the rating with human visual perception.

There are so many parameters other than pixel count that determine the IQ of a camera/ lens combination that I can't quite wrap my brain around what that specific number may mean.

Pmp does not attempt to represent other IQ metric - such as Dr or color depth, it only concerns with resolution.

I think it does take into account other factors than just sensor resolution, though - for example, the nature of the anti-aliasing filter used in each body. That is, two different bodies may have different maximum pmp ratings with ideal lenses, even though they are both 12 megapixel sensors. And DxO says differences of 10% or less are not significant, but how "significant" is a difference of, say, 20%?

Those are just some examples of things I have yet to understand about this metric.

But to return to my previous comment, I do believe you can see a distinct improvement in image quality going from a D300 to a D600 with the same lens. I even believe you can get significant improvement with the D600 using a less expensive lens than you use on the D300.

We are in agreement here.

Going from D300 to D700 with the same lens, however, the improvement may be noticeable under some shooting conditions, but up to ISO 800, I think it's pretty usually pretty hard to see.

From base ISO D700 has better colour depth, at ISO 800 it maintains over 11bit DR while D300 drops below 9.5.

I would be very interested if you can show me an image shot on a D700 with 24-85VR lens which is better in IQ than the same image shot with the D300 and 17-55. I've never seen that comparison, and doubt that it can be done.

I understand 17-55 is a better built lens with more exortic elements than 24-85. it has slightly less distortion and less CA. But I do not think these will be significant in real life. On the other hand 24-85 has a 2 stop VR, that is very significant when photographing static subjects in less than optimal light.

I have seen the advantages of the 24-85VR's stabilization in some shooting situations on my D800. But the 17-55 is more massive, and thus, less subject to vibration from things like mirror slap, and it is about a stop faster - so I don't think the 24-85 always realizes 2 stops of advantage vs. the more expensive lens on DX.

We're probably in as much agreement as we will get without the benefit of face-to-face discussion. Thanks for the interaction.

Ray
My blog: http://www.rritchie.com/wordpress

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