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06-29-2018, 11:05 PM   #1
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Grand lens Test 12: 645 A 80-160 f/4.5

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The 645 A 80-160 zoom lens has a reputation for being very good, particularly at the short end of the zoom range. Given no change in optical design between the A version and the FA version, and the probability that this would be a secondary lens to primes, I opted for the A version. And it was cheap at $75 on ebay.

Like the 45-85, reasonable sharpness from this lens is available, but only by f/8. I would not, however, heitate to use this lens if I needed flexibility in this range and could bring only one lens. It might limit print size a bit, though.

As with the 45-85, I looked at three focal lengths: 80, 120, and 160. I only show the performance wide open and at f/8, but I explore a couple of other aspects, too. And I'll compare it to primes.

80mm

Here's the full image at 80mm:


And the 1:1 center crop, at f/4.5:


This is pretty soft. The bokeh is decent, but at f/4.5, it's hard to really paint the background with a wide, smooth brush.

Let's compare it to the 75 leaf shutter lens at f/5.6:


At maximum aperture for the zoom, the prime wins handily. What about the 45-85 at 85, wide open? Here it is:


So, the 80-160 is better wide open on the short end than is the 45-85 wide open at the long end. Buf if you want a wide aperture, use a prime.

As with the shorter zoom, the 80-160 sharpens up very well at f/8:


It's still not as good as primes, or as the FA 45-85 at f/8, but this is a snip from the middle of what would be a seven-foot print at the usual monitor resolution of 100 pixels/inch. This is quite usable.


120mm

Full image at f/8:


1:1 center crop at f/4.5:


Not too sharp. But let's look at it at f/8:


At 120mm, it's still getting sharper at f/8, but let's compare it to the 645 A 120 Macro, at f/8:



Again, the prime is better.

160mm

Full image at f/8:


1:1 Center crop at f/4.5:


A little soft, but no worse than at shorter focal lengths. In fact, I think it's rather better than the short focal lengths. So much for the conventional wisdom.

1:1 center crop at f/8:


As with 120mm, it takes until f/8 to get all the way sharp, and that's the only weakness at the long end that I can see. Wide open, it has a soft-focus effect and reasonable bokeh, with a similar effect to the 165/2.8 Pentax 67 lens.

So, how does it play at the edges, wide open? Here's the lower right corner at 1:1 and f/4.5, and 160mm. The grasses are near the focal plane, so a severe curvature would show them softer than they are. The field is pretty flat. I see some coma, where the safittal performance is perhaps not quite as good as the tangential performance. This would sharpen up pretty nicely with some unsharp masking.


I don't see any lateral color, either, or longitudinal color, though the contrast might not be high enough here to reveal it.

Now, let's explore a different application. Usually, lenses of this length are thought of as portrait lenses, where we will often use selective focus to bring attention to the subject. But let's say our real objective is a landscape, where we want everything sharp. We are often most afraid of diffraction, but this is an unreasonable fear. Diffraction takes the edge off the stuff right in the focus plane, but it adds sharpness to the foreground and background, and can therefore often make an image look sharper.

Here's that center crop again at f/22:


The center is fractionally less sharp than at f/8, but everything else in the photo is sharper. Nothing is ever fully sharp if it isn't in the focal plane, but make a big print (let alone a small print) of the above and those background leaves will seem sharp.

Continuing the examination of f/22, let's look at the upper left corner, which shows foreground material, and the upper right corner, which reveals background material.

Upper left corner at 1:1 and f/22:


The leaves, which are close to the focal plane, are sharp. The bark isn't sharp at this magnification, but in a moderate print at normal viewing distance it will seem sharp enough, perhaps, and some judicious sharpening will also help.

Here's the upper right corner, with pine trees in the distant background:


Out of focus is out of focus, even at f/22, but this magnification is pretty unforgiving. Of couse 160mm is long--too long for f/22. But it illustrates the point that being out of focus is a LOT worse than diffraction.

So, when people say a zoom is as sharp as a prime, well, no. In this focal range, I'll stick with primes, though this lens will serve if I have room for only one that has to cover this range.

Rick "it probably looked pretty good on film for those who didn't own a microscope or an enlarger with a drop bed" Denney


Last edited by rdenney; 06-30-2018 at 12:20 AM.
07-02-2018, 11:08 PM   #2
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mauvais exemplaire
07-03-2018, 10:03 AM   #3
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Original Poster
QuoteOriginally posted by french Quote
mauvais exemplaire


That is always a possibility. But when I get a bad example, I tend to keep it because I feel guilty selling it, yet I’m rarely motivated to buy a second one on the mere chance of getting a better example.

Rick “who has two P67 200mm lenses for that reason” Denney
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