when do you need a better lens?

Started Oct 12, 2011 | Discussions thread
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james laubscher Senior Member • Posts: 1,224
when do you need a better lens?

I'm hoping that the well informed contributors to this forum can help me, and others, with the following question.

When does the camera's resolution outperform that of the lens?

I'm interested solely in lens resolution, not contrast, distortion, aberration or any other factor that determines total lens quality.

The method of testing lens resolution needs explanation in its own right.

On the photozone website, they use a product called IMATEST and quote resolution in line width per page height or lw/ph. All I can work out from that is the higher the ratio, the sharper the lens is. But others don't quote this number and instead talk about Nyquist, whatever that means.

So here are two areas already that need clarification - can someone please educate me?

Next, how do we know when a lens will out resolve a DSLR sensor? Or will modern DSLR sensors always be better than the very best lens available?

For example, the Pentax kit 18 - 55mm WR lens has a resolving power of around 2600 lw/ph, at its best - presumably since it is a kit lens, more expensive lenses will have a better resolution ? Well, the Pentax SMCP-DA 70mm f/2.4 ED Lens Limited Edition is tested to resolve to 2700 at its best - hardly a big difference, or is it in terms of what we will see?

Perhaps testing for sharpness will also call into play the software used to process the raw file? For example, playing around with the latest release of Raw Therapee shows that it has incredible sharpening ability if used knowledgebly and carefully. I find it sharpens better than the standard unsharp mask function in Light Room.

So. bottom line, since we can continue to expect sensors in APS-C cameras to improve, will the current crop of lenses simply look better and better as the sensor resolution improves or will we have to invest in sharper lenses to keep up?

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