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04-29-2009, 02:11 PM   #31
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QuoteOriginally posted by Alfisti Quote
Eh? It's a Tamron design not a Pentax design and I don't think SMC is written anywhere. My biggest gripe is colour and contrast which is why i feel it is not SMC.
of course its a Tamron design. are you using the Pentax version or the Tamron version? because the Pentax version is labled SMC.

04-29-2009, 04:39 PM   #32
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QuoteOriginally posted by farfisa Quote
Sounds like something's wrong with the lens to me--your methods all sound good. Maybe something misaligned in there?

If you're taking landscapes at infinity, maybe make sure your lens isn't going past infinity--that'd make your pics soft for sure. Some of my old screw-mount glass does that, but haven't seen it on a new lens.
...
Good point if your manually focusing or if your AF is adjusted wrong. My copy of this lens would focus past infinity when manually turned to the stop (if I remember correctly). Many AF lenses seem to do this.
04-29-2009, 06:27 PM   #33
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QuoteOriginally posted by séamuis Quote
thats odd because being able to go past infinity is a common trait of modern AF lenses, not manual lenses.
That's probably true--I just find it particularly annoying when it happens on a manual lens, because I expect infinity to be where they say it is! When on an AF lens, I probably just don't notice because I'm using AF!

QuoteOriginally posted by Alfisti Quote
Eh? It's a Tamron design not a Pentax design and I don't think SMC is written anywhere. My biggest gripe is colour and contrast which is why i feel it is not SMC.
On the front, it says SMC Pentax DA 18-250... I think Pentax uses their own glass and coatings, just uses the design.

QuoteOriginally posted by séamuis Quote
...considering Tamron has just developed its BBAR coating for the 60mm macro...
Is this a bad time to say I hope they bring that to K-Mount?
04-30-2009, 05:29 AM   #34
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QuoteQuote:
Is this a bad time to say I hope they bring that to K-Mount?
although I wouldn't buy it, im sure there are plenty of people who are hoping for a k mount version of this lens. it looks rather impressive.

04-30-2009, 09:58 PM   #35
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Thanks so much for all the feedback, erveryone. I posted a sample pic in the nature gallery at User Photo Gallery - Nature. I was only, like, 20 feet away from the subject and zoomed in at 250mm. I was really disappointed with the softness and the fringing. Thoughts? Thanks again, fello P-Shooters
04-30-2009, 11:07 PM   #36
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Cool Picture!

It doesn't look too bad to me considering. Here are my thoughts...
  • 250mm at 1/5 sec! - I'm assuming this was with a tripod (if not then it's really impressively sharp). What type of 'pod? This is (I believe) right in the range where mirror slap can cause vibrations which can really soften an image. These are best countered by a combination of a very solid tripod and good technique. Did you use the two second timer to lock the mirror up early to minimize vibration? (here's some more info from a quick google of mirror slap.)
  • How did you focus - I see in the comments that you are displeased with the softness of the eyes in particular, but using AF, it's hard to know exactly what point the camera is using - the red dot doesn't indicate the exact point of the AF sensor in most people's experience (there are many threads about this sort of thing). Have you adjusted the focus with this lens (using the K20D's focus adjustment feature) to rule out and front focus/back focus tendencies? That can help a lot.
  • I see you used f/16. It's been my experience that sharpness is visibly degraded by diffraction on most lenses past about f/11 (when pixel-peeped at 100%). I never checked my 18-250 for this but you'll almost certainly get more sharpness at the focus point using a more open aperture - somewhere in the f/8 to f/11 range probably, though I'd guess closer to f/8.
  • I'm one of the folks who differentiate Purple Fringing from Chromatic Abberations, and I can't see any PF in that photo - I do see some CA along the right edge of the bird where the transition to water happens. Have you tried to correct this using a CA correction tool like the one in Adobe Lightroom (you could use the demo - it's free for some time period). I bet that CA could be virtually eliminated with the right tool.
  • What file type are you using RAW or JPG? What sharpening settings? What sharpening was done in Post? RAW or JPG with a low sharpening level just won't look as sharp as after software sharpening has been applied.
  • Finally - yeah, the 18-250 really isn't that impressive at 250 - but it sure has some versatility.

All in all - I think you can milk some better performance out of that lens, but it'll never compete at the long end with a high end prime or a + $700 telezoom (say the Tamron or Sigma 70-200mm) There are trade offs in every lens choice, and the 18-250 favors convience over raw image quality. Many of the shortcomings of the 18-250 can be overcome with good post processing.

Here's a quick and dirty rework of a screen shot of your picture (I couldn't seem to download your version without putting in time and effort - I guess the site has copy protection - cool). This was about 10 minutes in Lightroom - it would be way better if I had the original (preferably RAW since that's the workflow I'm used to).

04-30-2009, 11:20 PM   #37
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I think Josh's comments address things well. I'd just add if you want to make a case that the 18-250 is not as good as the 18-55, it would be useful to post pictures from both lenses at the same focal length and aperture.

But as it is, I'd agree that shooting a superzoom at its maximum focal length and stopped down to the point of diffraction, yielding a shutter speed that may have resulted in some camera shake even mounted to a tripod - that's not a recipe for showing a lens at its best.
04-30-2009, 11:36 PM   #38
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Oops...

You provided more info than I read...
QuoteQuote:
Settings: f/16, 1/5, EV+1, ISO 200, AF Spot. Camera mounted on pro Manfrotto tripod & ball head with mirror lock, shutter release and Cokin polarizer.
And that sentence addresses a lot of my comments (I apologize ). I'll leave 'em up so that others may learn (and see me being a dumb@$$)

It really doesn't seem all that soft, but if it is, I'd still suspect diffraction (for sure), focus calibration (and just plain locking on the wrong point), and I'd still suspect camera shake even on a beefy tripod since you don't have a tripod collar on that lens, and the front element is now a weight cantilevered out on a long arm - I think it could still have adverse effects (though nothing like if you were using a cheapo tripod).

05-01-2009, 02:59 AM   #39
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I think heliphoto summed things up well. One thing I didn't see in your typical workflow was use of a hood. Won't help the sharpness much, but might help with some other issues you describe.
05-01-2009, 03:55 AM   #40
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I want to add two or three things to Josh's valuable comment:
  • at 1/5s exposure you certainly got slight motion blurr. That is not visible in this image as such, but may be a reason for a contrast loss
  • your white balance (set manually, according to the Exifs) is off and you have a green cast, probably from surrounding foliage. That colour cast adds to the impression of having a "dull" image.
  • the image is slightly underexposed, which takes out the real punge of the white feathers. Another 1/3 to 1/2 f-stop would have certainly improved the result.

Usually I would not nit pick that much - but I think, that overall the image is not really bad and could have been even better with just some slight improvements at the time of taking it. All in all, I do not think it testifies to any defficiency in the lens.

Ben
05-01-2009, 04:43 AM   #41
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I don't own the Tamron/ Pentax 18-250 for one simple reason: Compromise. With a super zoom, there are places where it will be softer, places where you miss having a bigger aperture, etc. If you shoot in the 100 - 300 range a lot, you would probably benefit a lot from looking at the DA 55-300 or the new DA* 60-250.

From what I have seen, your technique is good, you are just bumping up against the deficiencies of a super zoom.
05-01-2009, 05:53 AM   #42
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Wow, great shot! I like the slow shutter speed on the water.

I can see how you'd be disappointed at how it turned out though. 250mm is definitely the weak point of this lens.

Now that I see what kind of shots you're taking, I'd have to recommend a different lens. Something in like a Tamron 70-200 f/2.8 would cost a lot more and doesn't have quite the range, but you'd get much better results cropping a 200mm image from that lens, than from the 18-250 at 250mm.
05-01-2009, 09:24 AM   #43
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Thanks everyone for your help. I will do some tests based on all your feedback. I really hope it's me and not the lens. Y'all are a great group. Thanks again
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