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06-22-2010, 02:06 PM   #1
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At the crossroads

I started with the K100D with the standard kit lens. I then moved up to a Sigma 18-200 F/3.5-6.3. I started out modestly with simple snapshots. After getting decent feedback, I decided to upgrade to a K20D and a Pentax 50mm F/2.8 Macro. I have started to get serious real serious about photography.
I used the Sigma early last night for a nice landscape pic of the backside of a sunlit thunderstorm with a wheat field and corn field in the foreground. I ran home to see the images and found that the lens at 18mm was very soft. Very soft. The wheat in the foreground lost all of it's detail. The same setting with the 50mm was tack sharp.

So hear we are; do I go with the primes or find a great tele zoom? I think I am leaning towards a fast zoom. I would like a travel lens so I don't have to carry around 2-3 primes.

Your opinions please.

Thanks

06-22-2010, 03:02 PM   #2
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QuoteOriginally posted by bluebronco Quote
I started with the K100D with the standard kit lens. I then moved up to a Sigma 18-200 F/3.5-6.3. I started out modestly with simple snapshots. After getting decent feedback, I decided to upgrade to a K20D and a Pentax 50mm F/2.8 Macro. I have started to get serious real serious about photography.
I used the Sigma early last night for a nice landscape pic of the backside of a sunlit thunderstorm with a wheat field and corn field in the foreground. I ran home to see the images and found that the lens at 18mm was very soft. Very soft. The wheat in the foreground lost all of it's detail. The same setting with the 50mm was tack sharp.

So hear we are; do I go with the primes or find a great tele zoom? I think I am leaning towards a fast zoom. I would like a travel lens so I don't have to carry around 2-3 primes.

Your opinions please.

Thanks
First thing to check is the aperture used with your Sigma. If it is wide open, then the depth of field will be very narrow, and part of the scene will be out of focus more than desired.

If that is not the problem, then the Sigma is giving soft images. I personally do not use wide range zooms because of the optical compromises the designers have to make to keep the image quality acceptable throughout the range. My zooms, as in my signature, are 3:1 or less, with the sole exception of the 24-90 which is a bit outside the range.

If I were going to print 24x36 inch prints consistently, I would shift to prime lenses, not just any primes, but those that cost a lot of money, Limited, FA* DA* etc. Only top quality lenses will give you the image quality that you need for large prints.
06-22-2010, 03:06 PM   #3
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There's a reason people use primes, and reasons they're still made.

All things being equal, they're better.

But carrying 2 or 3 primes with you is nothing. I have a tiny bag, and although my camera is never in there and lives on my shoulder, that bag can carry 8 to 10 primes, up to 200mm.
06-22-2010, 03:10 PM   #4
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You have to weigh the pros and cons. It is generally agreed upon that primes have better overall IQ but there is no doubt that zooms are more convenient but there is one lens that I believe will suit your needs very well and that is the DA 12-24. This lens is very sharp (close to any pentax prime (maybe not the limiteds though)) and is a zoom, but not a long zoom by any means. The 12-24 is an F4 constant, which is not that fast so if you shoot in low light you will have to use a tri-pod with a long exposure. So if carrying 3 limited primes is not an option for you then I would buy the 12-24.

06-22-2010, 04:07 PM   #5
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As pointed out by a previous poster, 'super-zooms' have real compromises in IQ to produce the focal length range they can achieve. With almost all zooms, they will not perform at their best at either extreme of the zoom range. Often the wide end is the weakest. Top zooms can usually come close to matching the good primes, but for real top IQ primes will win out, not just in sharpness, but in rendition and bokeh, although you might stuggle to tell a good zoom in the middle of it's zoom range and stopped down, to a prime.
06-22-2010, 04:52 PM   #6
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QuoteOriginally posted by bluebronco Quote
The wheat in the foreground lost all of it's detail. The same setting with the 50mm was tack sharp.
Where were you focusing with your Sigma? Are you aware of what hyperfocal distance is? Was your camera on a tripod? Although I’m no fan of the superzooms, I wouldn’t be so quick to blame your equipment until you’ve ruled out incorrect technique.
06-22-2010, 05:10 PM   #7
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Without seeing the picture (and take that as a request to post it!) - I agree with Albert and twitch that it's entirely likely the problem is DOF not being enough - in other words, not a lens issue at all. Shooting a landscape at 18mm, the foreground is *much* closer to you than the background, and it's normally unreasonable to expect both in focus. Sure, the 18-200 lens - like most lenses - is *slightly* softer in the edges than the center at 18mm even when the edges *are* in focus (eg, shooting brick walls that curve toward in just the right way). but what you're describing - "lost all detail" - sounds like a simple matter of being out of focus

In any case, this discussion is not about cameras but about lenses and perhaps also about shooting technique. It's not obvious where to move this to so I'll leave it alone, but do try to be more careful in the future to choose appropriate forums for new threads.
06-22-2010, 06:56 PM   #8
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I'd stick with prime.
In fact, that's what I did.
Except where I didn't.
But even then, I kinda did.
It's all very confusing.
But I own a heck of a lot more primes than zooms.
Though one could say that I have to.

06-22-2010, 08:51 PM   #9
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QuoteOriginally posted by KxBlaze Quote
You have to weigh the pros and cons. It is generally agreed upon that primes have better overall IQ but there is no doubt that zooms are more convenient but there is one lens that I believe will suit your needs very well and that is the DA 12-24. This lens is very sharp (close to any pentax prime (maybe not the limiteds though)) and is a zoom, but not a long zoom by any means. The 12-24 is an F4 constant, which is not that fast so if you shoot in low light you will have to use a tri-pod with a long exposure. So if carrying 3 limited primes is not an option for you then I would buy the 12-24.
I have the 12-24 myself, and agree with you that it is a superb quality lens. At these super wide angle ranges, I can see why Pentax and Nikon left them at 2x zooms.
06-23-2010, 12:25 AM   #10
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The earlier posts already gave you some sound suggestions. Let me add another perspective.

If you like an all-around lens, to walk with your camera and a single lens (and avoid swapping lenses), it is worth to consider a newer, more performant zoom lens. The Sigma 18-200mm is an older lens. The Pentax DA18-250mm, and its sibling Tamron 18-250mm, is a much improved telezom with better image quality (eg review of Tamron 18-250mm at www.slrgear.com). Another alternative is the newer Sigma 18-250mm OS HSM. It is more expansive, and the OS is un-needed since your camera has IS. Both the DA18-250mm/Tamron18-250mm and Sigma 18-250mm OS HSM have excellent reputation as all-rounder lenses.

Alternately, if you are prepared/willing to swap lenses, I agree strongly that the prime lenses should be a definite choice. There are a wide range of excellent prime lenses for K-mount, both Pentax and 3rd party lenses. Among the Pentax primes, the pancakes are really unique for their very small size. A fast prime (f1.4) is another alternative for some low-light shooting..

Hope that the comment will help...
06-23-2010, 07:42 AM   #11
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I don't think it is techniqe. I had the lens stopped down to around 11. The camera was on a tripod. Like I said in the original post, under the same conditions, the 50mm was great. I think I have a bad copy of the Sigma. I think I am going to go with the primes.

I would post the pics, but I trashed them in disgust. :-/
06-23-2010, 09:14 AM   #12
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Then take another. If the problem is the lens, it will behave the same next time, so it should be easy enough to produce another example of the same problem.

I still say, even stopped down to f/11, at 18mm the foreground is just *much* closer to you than the background in a way that isn't true when shoting at 50mm. So it's just not reasonable to expect the foreground to be in focus at 18mm unless you actually focused on the foreground.
06-23-2010, 01:57 PM   #13
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18mm is reasonably wide, f/11 is pretty stopped down, that should actually give you a lot of depth of field to play with, unless you focus super close.

This might be useful: Online Depth of Field Calculator
Although the image would be useful to look at.
06-23-2010, 04:18 PM   #14
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OP, moving up from the 6.1 megapixel sensor of the K100D you will quickly discover that lenses that performed adequately with the old camera suddenly are found wanting in terms of sharpness with the higher resolution of the K20D's 14.6 megapixel sensor. This is something that I have experienced firsthand especially with some cheap lenses. You can stop down to increase dof but if your existing lens just doesn't resolve enough detail, no amount of dof or post processing will improve on what isn't there. Time to carefully consider lenses of higher optical performance.
06-24-2010, 04:21 PM   #15
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QuoteOriginally posted by creampuff Quote
OP, moving up from the 6.1 megapixel sensor of the K100D you will quickly discover that lenses that performed adequately with the old camera suddenly are found wanting in terms of sharpness with the higher resolution of the K20D's 14.6 megapixel sensor. This is something that I have experienced firsthand especially with some cheap lenses.
I've experienced the same thing. The 18-55 seemed like an adequate lens on an *istDL, but on the K200D it just wasn't up to snuff.

Incidentally, it's not quite true that primes are always sharper than zooms. Zooms have come a long ways in recent years; and with sophisticated computer designs, there are now zoom lenses that can hold their own with all but the very best primes. The 12-24, which has already been mentioned, holds it's own pretty well against the primes offered in its range. As do the DA* zooms. But those are all rather expensive lenses.
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