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11-18-2013, 09:17 AM   #1
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Zoom length IQ falloff?

Hi guys,
My question is for any experienced photogs who can confidently say when zoom lens length passes that mark which typically results in visible IQ loss. I called it falloff here.
See I was doing fine with me lens collection until I got my first (and likely last) superzoom, a tamron 18-250. I used it heavily on two summer trips a few months ago and have decided its gotta go.
In its place I'll now likely use my tamron 17-50, da*50-135, skipping 135mm+. I do have a fa80-320 available.
I now started looking at a 20ish - 90 zoom. The 24-90 appears to lack the IQ I want and well thinking about that led me to wonder in general sense: generally, with non-*/limited/pro-lenses, where does noticeable IQ falloff occur?
I realize there might be no clear answer due to such great variation in lens IQ.
I'm basically looking for a great IQ 24-90, although a 17-70 might do but not sure. Thanks in advance!

11-18-2013, 10:02 AM   #2
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QuoteOriginally posted by Iksobarg Quote
generally, with non-*/limited/pro-lenses, where does noticeable IQ falloff occur?
With the older film zoom lenses, the general trend is to have resolution issues toward the edges at the wide end, and an over-all loss of resolution toward the long end, with better performance toward the middle. There are exceptions to this rule. In terms of consistency of performance from one end to the other, two of the best performing not star Pentax film era zooms are the A 35-105 and the F 35-70. There's very little change throughout the zoom range of both lenses (except at the very far end of the 35-105). While neither lens can match the peak performance of the FA 24-90, they are each more consistent throughout their range than the FA zoom.

I actually regard the FA 24-90, despite its resolution inconsistencies, as a very nice lens capable of producing stunning images. At it's best (in the 30 to 75 range), it is better than any Pentax non-star FF zoom lens (with the possible exception the FA 20-35). At all focal lengths, it has the microcontrast, rendering, and color rendition of pro glass. It's merely lacking in the resolution department at the wide end and at the long end (it also suffers from mediocre build quality).
11-18-2013, 10:27 AM   #3
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It's hard to generalize with lenses. There are some really good zooms. I own a F 35-70 and can vouch for it's IQ although the build is kind of cheap and it isn't a fast lens. The DA 12-24 is close to a prime in IQ from most reviews. There are plenty of photos and examples along with good info on most lenses right here in the forum. The best course is to look at each lens individually. The F 35-70 isn't wide enough for me to use as an everyday walk around which is too bad because it's compact and light, inexpensive, focuses fast and has very decent close up capability. I think the DA 18-135 holds it's own very well.
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