Future of Pentax?

Started Mar 29, 2013 | Discussions thread
Richard B.
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Re: Future of Pentax?
In reply to Andrew53, Mar 31, 2013

Andrew53 wrote:

EFL as you noted. This is generally negative for APS-C at the wide angle end where fast wide angle lenses are rare. I like the Sigma 8-16 but it is no replacement for my 16-35 f2.8.

These lenses produce very different fields of view.  The Sigma is significantly wider. A more appropriate comparison for the Sigma would be to a FF lens that covered 12-24mm.

Noise is about 1 stop better for a given framing and ISO. The K-5 is pretty good but one stop is one stop and it makes a difference if you like shooting a night.

As a landscape shooter, I find DR is a more useful metric. i.e. I care about the highlights as much as noise in the shadows. In DR, the K-5's gives little away to FF. At base ISO, the Pentax K-5IIs measures at 14.1EV - the D800 only manages 14.3EV. Hardly a significant difference and new Canon FF 6D only measured 12EV.

DOF is not the same for a given f-stop. You need about a 1 stop wider aperture on APS-C to get the equivalent DOF of FF. So the f2.8 zooms of APS-C are more like the f4.0 zoom on full-frame. It is harder to get good background blur with APS-C than with FF for equivalent framing.

There are times when shallow DOF is useful, but landscapes more typically require a deep DOF. APS-C is at an advantage here. I often need have some near foreground object and the background sharp.

Here is a theoretical example: On APS-C, using 16mm at f11 focused to 4 feet, I have a DOF from 2 feet to infinity. On a FF to achieve the same FOV, I would need to use 24mm. On FF, a 24mm lens at f11 focused to 4 feet gives me a a DOF from just over 2 feet to 13.5 feet. Keeping all other settings the same, I don't get infinity back in focus until f18. If you are considering maximum resolutions, that is well on the way to diffraction territory.

(BTW, I don't do these calculations in the field. I used one of the online DOF calculators to illustrate the DOF differences between APS-C and FF.)

The lower enlargement requirement of larger sensors means the lens "defects" are also not enlarged as much. This is partially offset by the APS-C being able to use the "sweet" spot of a lens.

I don't know what you mean by this. The proportion of the frame a defect occupies is not changed due to enlargement. As you enlarge a picture, the defect becomes bigger, but so do the good parts of the picture i.e. everything remains in proportion. The number and size of defects in the original capture would depend on the lenses in question.

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