Some thought about "sharpness"... (or rather "

[LucisPictor]

In a photo magazin from 2009 I have found a nice essay about "sharpness" and the problems to achieve it.

It's in German. Allow me to summarize the main aspects:

- The higher pixel count causes an increasingly dense pixel pitch. A 15 MPix APS-C-Sensor needs an optical modulation of the image which is twice as high as on (analogue) film.

- Not only the lens needs to have higher resolution power, also the precision of the whole focus mechanism and the bayonet need to be more precise to focus directly on the sensor level.

- Thus Curvature of Field, focus shift or variation of rendering within one lens copy are also more visible, since there is a displacement of the AF-calculated and the real focus level.

- Lenses that are controlled and focused by small motor rods have a normal free play which prevents the necessary exactness. That's one of the reasons why more and more manufacturers change to lenses with internal focus drive.

- Many photographers want a faster AF which can be achieved by lighter focus elements which moves faster but needs more play and by a steeper thread translation. Both methods cause a less precise focusing. The good old volution of highly precise manual lenses are not suitable for fast-focusing AF lenses. (Tell us about it! )

- Contrast-AF of compact cameras is more precise than the phase-AF of DSLRs but much slower so it is not used.

- The possible solution "manual focus" (hear, hear!) is often not usable, due to the super-bright matte screens inside the cams. In order to produce a bright viewfinder image with slow lenses (f/5.6 zooms), these superbright screens deflect the air image and thus do no longer base on a genuine matte screen*. The air image then does not have a defined position because the eye can re-focus on different levels estimating each one as "sharp".

- AF field indicators and other symbols that are casted on the screens distract the eye and impede the ability of the eye to focus correctly.

- APS and esp. 4/3 cams sport a smaller viewfinder and thus hamper precise focusing as well.

- Even LiveView does often not equal the image resolution (not even with the magnifying function) so that a mis-focus still is easily possible.

Conclusion: precise focusing is only possible when a lens with a not too steep focus translation and a suitable matte screen are used. (What a surprise! )

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*Some replacement screens can still do that (e.g. the EE-S for the 5D)

[Orio]

So you mean that we've been correct all the time?

[ludoo]

[visualopsins]

Thanks for summarizing the article LucisPictor! I am enjoying all of your recent informative posts.

This essay might have been about 'Focus' imho.

[bogolisk]

I believe: focusing, PD and CD, AF and MF, in the future will all move to the main sensor (a la Fuji).

[LucisPictor]

[Transit]