Originally posted by luftfluss
In the US, the DA 18-135 is consistently available for $400 or less. Currently, I see it for $349 (maybe w/o hood)
The current pre-order price for the DA 16-85 is currently ~ $750 USD.
Naturally, the price of the DA 16-85 will eventually drop.
Do not, I repeat, do not
ever compare MSRPs and street prices.
DA 16-85 and DA 18-135 were launched at similar MSRPs, even identical in the UK: £599,99. In the Euro zone, the launch price of DA 18-135 was a bit (€50) higher than that of DA 16-85.
Pre-order prices are almost always equal to MSRP. As you recognise yourself, the price of the DA 16-85 will drop, as the one of DA 18-135 has done. Your previous statement
Quote: Since it appears the DA 16-85 will cost roughly twice as much as the DA 18-135, and the DA 18-135 already does a nice job with image quality attributes unrelated to sharpness, the DA 16-85 needs to be sharper.
is therefore void of any legitimacy other than an extemporaneous and erroneous perception.
---------- Post added 11-23-2014 at 12:35 AM ----------
Originally posted by luftfluss (...) the relationship of the edge sharpness to center sharpness won't change based on the sensor's MP count. So, for example, if the lens's borders are 75% as sharp as the lens's center on a 10MP sensor, the same 75% should apply on a 16MP sensor.
(...)
Do not imagine I am picking on you but I am afraid this isn't valid either.
The more MP in the sensor, the higher the ratio between the centre sharpness, which fully benefits from the increase in MP count, and the edge sharpness, which, weaker, only partly benefits from this increase.
In the extreme, when the lens becomes the limiting factor, a further increase in MP count doesn't increase the resolution in the edges (whilst it still does in the centre): when the resolving power of the lens becomes the limit, you can add MPs and increase the sensor's sampling power, you won't get any more detailed data.
As an illustration of the above, I suggest your having a look at the two tests of the FA 43mm f/1.9 Limited made by Photozone, the first one on K10D (10 MP)
Pentax SMC-FA 43mm f/1.9 Limited - Review / Test Report
and the second one on K-5 (16 MP)
http://www.photozone.de/pentax/736-pentax43f19k5
As you can see from the tables above, the relationship of the edge sharpness to centre sharpness at f/1.9 is equal to 0.63 with the 10 MP sensor and 0.50 with the 16 MP sensor. The centre resolution takes full advantage of the increase in MP count (from 1,774.5 to 2,351 i.e. +32.5%) whilst the edge resolution is only marginally improved (from 1,119 to 1,179 i.e. +5.4%).