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03-07-2010, 08:58 AM   #1
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Pentax DA 18-55mm WR stops down to F40!

Like so many, when I bought my K-7 with this kit lens, I had no idea why this lens was, well to put it plainly, pretty craptacular.

If you go read the review at photozone, the results at "wide open" are fairly abysimal: photozone test report

I of course didn't know that at 5.6 on the "long end" this lens was really only useful for outdoor photography in broad daylight. Fortunately due to the $100 rebate Pentax was running at the time it was practically free.

This lens was quickly replaced by the DA* 16-50mm.

However I've discovered a nifty feature of this lens that keeps it in my (secondary) bag. At 55mm this lens can stop down to a whopping F40.

I've got no other lenses in my bag of tricks that I can stop down to this pinhole of light, and so it makes this lens an interesting option for shooting water with associated scenery and nighttime light motion. As pointed out in the photozone.de article, it's resolution is decent and the other problems tend to go away once stopped down.

Of course, you'll need a tripod for that 15" water exposure at F40.

Conclusion: before you go selling that kit lens for $40, consider that it might be able to do something no other lens in your collection can do.

03-07-2010, 09:49 AM   #2
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Stopping down to F40 will ruin the performance of any lens (diffraction effects), use a ND filter if you want a longer exposure time and do not go further than F11 or maybe F16.
03-07-2010, 10:18 AM   #3
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QuoteOriginally posted by glasbak Quote
Stopping down to F40 will ruin the performance of any lens (diffraction effects), use a ND filter if you want a longer exposure time and do not go further than F11 or maybe F16.
So that lens can go in the 'glasbak'
03-07-2010, 11:02 AM   #4
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QuoteOriginally posted by glasbak Quote
Stopping down to F40 will ruin the performance of any lens (diffraction effects), use a ND filter if you want a longer exposure time and do not go further than F11 or maybe F16.
I suppose this goes back to one of the points of my post, or at least one that I should have made more clearly. If I want a unique look, this is something I try out. If I want a top quality high resolution shot, this lens really doesn't enter into my thoughts.

03-07-2010, 04:38 PM   #5
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QuoteOriginally posted by cgoudie Quote
Like so many, when I bought my K-7 with this kit lens, I had no idea why this lens was, well to put it plainly, pretty craptacular.

If you go read the review at photozone, the results at "wide open" are fairly abysimal: photozone test report
FYI: this is not a review of the lens your K-7 came with. The review is of Mark I, and the last model to ship with that was the K100D Super. The WR version is a weather sealed version of Mark II, which is a different, higher resolution optical design.
03-07-2010, 04:44 PM   #6
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Ok, so ignore the review entirely. It's F5.6 at 55mm. No more review needed
08-10-2011, 01:46 PM   #7
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F/40 with this lens, I just discovered it recently

I know about "diffraction", but it's not a big deal. Sometimes we shoot for depth of field, sometimes for optimum sharpness, sometimes to freeze motion, etc.

Here are two samples of f/40 I just made the other day :





I find the sharpness acceptable. I shoot in RAW and end in a half strength unsharp mask.

And here is Bryan Petersen talking about shooting at smaller than f/11 apertures :


f/40, it's what's for dinner
08-10-2011, 02:46 PM   #8
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Diffraction is a concern if you're shooting for maximum resolution and will display the image LARGE. Rule of sharpness: Almost any image looks good if it's shown small enough. Print that f/40 shot at 4x6in / 10x15cm and you just won't notice.

Here are my few small-aperture Pentax zooms and their tiniest holes:

f/32 DA 10-17
f/32 F 35-70
f/32 Takumar-A 70-200
f/38 FA 100-300
f/40 DA 18-55
f/45 DA 18-250

Among other brands for small-format cameras, I have a few zooms but very very few primes that go to f/32. (Medium-format is another story, of course.)


Last edited by RioRico; 08-10-2011 at 04:52 PM.
08-10-2011, 04:14 PM   #9
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QuoteOriginally posted by glasbak Quote
Stopping down to F40 will ruin the performance of any lens (diffraction effects), use a ND filter if you want a longer exposure time and do not go further than F11 or maybe F16.
I guess you can also use stacking these days if you want DOF, but if you want to take an image in one shot, small apertures don't produce results as bad as one might think.

Here's an example using f/32:
08-10-2011, 06:28 PM   #10
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One advantage of shooting at really small apertures is the star effect from the aperture blades when shooting point light sources.
08-10-2011, 06:55 PM   #11
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RioRico posted

QuoteQuote:
Diffraction is a concern if you're shooting for maximum resolution and will display the image LARGE. Rule of sharpness: Almost any image looks good if it's shown small enough. Print that f/40 shot at 4x6in / 10x15cm and you just won't notice.
I beg to differ. There are images where a narrow depth of field just looks bad because more than 90% of the image is out of focus. By pulling more of the image in focus, even though it might not be as sharp in one little spot in the middle of the image but over all, the part of the image you want sharp is sharper and F-16-22 image looks better. I shoot many macro images from 5.6 to 22, and often enough, the F-16 or F22 image is the best image. Blown up or small, doesn't matter in those cases. This diffraction thingy is way overblown sometimes. You still need to shoot f-16 or f-22 to get the best image in every situation. Sharpness doesn't matter if lack of DoF ruins the shot.
08-10-2011, 07:31 PM   #12
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I've heard lot's of talk about diffraction, but in all honesty, I don't think I've ever seen one clear cut example of it.
08-10-2011, 09:34 PM   #13
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QuoteOriginally posted by Jodokast96 Quote
I've heard lot's of talk about diffraction, but in all honesty, I don't think I've ever seen one clear cut example of it.
Its there if you are using MATLAB to measure pixel blur.

Its invisible as far as art is concerned.
08-11-2011, 03:50 AM   #14
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QuoteOriginally posted by Jodokast96 Quote
I've heard lot's of talk about diffraction, but in all honesty, I don't think I've ever seen one clear cut example of it.
Well, some people act like diffraction is a cliff you just fall off of at f11, but what you notice is that your photos are just softer at 100 percent. Just try shooting a series of shots starting at f8 and going to f22 and look at them and you will find a gradual softening.

There are still times that you need to stop down, either to try to increase your focal range, or to slow your shutter speed (shooting waterfalls in the middle of the day).
08-11-2011, 05:04 AM   #15
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QuoteOriginally posted by Clinton Quote
pretty craptacular
Given that you almost only own STAR lenses, I'd say in comparison with your kit that statement is true. Taken by itself the lens is the best kit on the market (any brand), and it's a reliable tool, capable of sharp enough results, ok contrast (a bit too harsh) and surprising saturation. You could by a wagon full of 18-55 by selling ONE of your other lenses, so the comparison isn't very fair.

Just get yourself a 38-70 F lens and you'll see what crap is really about. Or better yet, get a Rebel with a 18-55 from Canon

QuoteOriginally posted by Clinton Quote
This lens was quickly replaced by the DA* 16-50mm
Apples to oranges, again. For a hiker, the kit would be a better choice than the ultra-heavy 16-50.

QuoteOriginally posted by glasbak Quote
Stopping down to F40 will ruin the performance of any lens (diffraction effects)
Yep. They're all bad at that aperture (when available).
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