40mm Pancake

Started Jun 24, 2013 | Discussions thread
audiobomber
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Re: 40mm Pancake
In reply to Ivan Gordeli, Jun 27, 2013

Ivan Gordeli wrote:

What is clear to me is that there does exist some kind of problem, not just the "down-rating" the Pentax lenses but also "inconsistencies" between some reviews which the reviewers do acknowledge themselves in fact. I don't know what is the core of the problem and I don't have time to investigate. However maybe someone else has already thought about this (after reading a bit on the topic I see that I am not the first to notice the problem).

I have noticed that PopPhoto's Subjective Quality Factor (SQF) results match shooter's perceptions of "sharpness" much better than MTF numbers. SQF considers contrast, while MTF doesn't. If you view a DA 40mm image beside an FA 35mm image, many people will describe the DA 40 image as sharper because of the punchiness of the photo (the colours pop). If you check MTF figures, the FA 35mm has significantly higher MTF scores. PopPhoto says of the DA 40:

Standout Spec: SQF test showed unusually sharp results even with the lens wide open.

This is a trend I've noticed over and over. Pentax fans rave about a lens, Photozone MTF figures are lukewarm, PopPhoto praises it for SQF. The DA 55-300mm was the first lens where I noticed this dichotomy.

"SQF was developed by Grainger et al in the 1970s to provide a more easily understandable measure of image quality which takes into account not only the intrinsic quality of a lens, but also the nature of how we see things." (quote from Bob Atkins website)

Here's a detailed explanation:

http://www.imatest.com/docs/sqf/

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Dan

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