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08-17-2008, 10:32 PM   #16
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QuoteOriginally posted by Petermgr Quote
I have done some testing and starting to realize I really need to understand that a zoom lens needs to handled differently from the standard kit lens.
Of course, the kit lens is a zoom too. Any lens that does not have only a single focal length is a zoom. The difference is that the 18-250 is a "superzoom", and in particular, it is a telephoto zoom - it's maximum focal length is 250 instead of just 55. The more telephoto the lens, the faster the shutter speeds you need in order to avoid camera shake, even with SR.

QuoteQuote:
Perhaps the softer image I see in the K20D (compared to the *istDS) may not be a fault, but rather the way the image should look, more natural and allowing room for post sharpening by software.
Nah, it's just a matter of the DS not having enough resolution to expose the weaknesses of the lens.

QuoteQuote:
Exposure time - 1/125 s
...
Focal length - 250 mm
Note that even with SR, this is not really fast enough a shutter speed to ensure a sharp picture. It's not impossible, and it looks like you did OK in this particular case. But if yo're having problems getting sharp pictures at 250mm and 1/25 shutter speed, that shouldn't be even the slightest bit surprising.

08-17-2008, 10:43 PM   #17
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QuoteOriginally posted by Marc Sabatella Quote
. . . . The more telephoto the lens, the faster the shutter speeds you need in order to avoid camera shake, even with SR.

Nah, it's just a matter of the DS not having enough resolution to expose the weaknesses of the lens.

Note that even with SR, this is not really fast enough a shutter speed to ensure a sharp picture. It's not impossible, and it looks like you did OK in this particular case. But if yo're having problems getting sharp pictures at 250mm and 1/25 shutter speed, that shouldn't be even the slightest bit surprising.
Thanks Marc. Interesting comment, "DS not having enough resolution to expose the weaknesses of the lens", or the weakness of the photographer I suppose . . .

The speed btw was 1/125, not 1/25 . . .

Appreciate the feedback . . .

Peter
08-18-2008, 06:40 AM   #18
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QuoteOriginally posted by Petermgr Quote
The speed btw was 1/125, not 1/25 . . .
I assume Marc knew this and just made a typo. The rule of thumb is 1/(35mm equivalent focal length). For the 250mm shot posted, that would indicate 1/375s.

I suggest you try Program mode and Auto ISO (let it run up to 1600) to see how the system works when the camera is in control.

I have the 18-250. I find it a bit sharper and a bit brighter than my 18-55 at comparable focal lengths, but with more distortion at the wide end. The lens is known to be a bit soft above 135 mm, but still very useable. Mine is quite sharp up to 150 mm.
08-18-2008, 07:56 AM   #19
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QuoteOriginally posted by Petermgr Quote
I would like it to shot a friend's wedding at the end of the month . . .

Peter
Then I'd really suggest looking at Don Gale's site for some ideas on how to use this lens at a wedding. Keep in mind that he used an off camera flash, since this lens is pretty slow. On the K20D, you'll be able to bump up the ISO though, so it should work if you're careful.

Do you have the FA50 f/1.4? It's a very nice, inexpensive lens and would help you in a pinch if you couldn't use your flash for some of the shots.

08-18-2008, 09:32 AM   #20
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QuoteOriginally posted by Petermgr Quote
Thanks Marc. Interesting comment, "DS not having enough resolution to expose the weaknesses of the lens", or the weakness of the photographer I suppose . . .
No, I did mean the lens :-). That's why Pentax introduced version II of the 18-55 - because the K20D apparently exposed weaknesses in the original 18-55 that hadn't been as apparent previously.

QuoteQuote:
The speed btw was 1/125, not 1/25 . . .
As another poster guessed, I knew this - just a typo. 1/125 is not fast enough, either. You would need 1/350 just to match the old "1/ focal length " rule after adjusting for the crop factor. 1/125 is asking for a stop and a half of improvement from SR. Not by any means impossible of course - that's within its stated effectiveness. But still, we're talking about percentages here, not guarantees. Maybe you could expect 50% success here, and that's assuming the lens itself wasn't softer than you'd like at 250mm on the K20D.

Anyhow, since you are satisfied with this particular shot, it's kind of moot. But it might be interesting to see some of the shots you *don't* think came out well - also with EXIF info.
08-18-2008, 10:33 AM   #21
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I'd go along with the comment to do some focus testing.

I had over 7k photos with my K20D before I bothered using one of those focus test charts. It took an adjustment of -10 to get it right about spot-on. Suddenly I'm finding that all my AF lenses are consistently knocking out sharper photos than before - and here I was mostly blaming my Tamron 28-75mm F2.8. I was very happy with the camera before - now I really love it!

I'm actually planning on sending the camera in for service in a few weeks (one more event coming up soon I want it for), hopefully they can adjust it so 0 adjustment is correct and maybe check some inconsistent noise in the sensor.
08-18-2008, 11:13 AM   #22
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QuoteOriginally posted by audiobomber Quote
I assume Marc knew this and just made a typo. The rule of thumb is 1/(35mm equivalent focal length). For the 250mm shot posted, that would indicate 1/375s.

I suggest you try Program mode and Auto ISO (let it run up to 1600) to see how the system works when the camera is in control.

I have the 18-250. I find it a bit sharper and a bit brighter than my 18-55 at comparable focal lengths, but with more distortion at the wide end. The lens is known to be a bit soft above 135 mm, but still very useable. Mine is quite sharp up to 150 mm.
Thanks Dan,

See, that goes to show you that I need to learn more about using the zoom lens. I would have thought 1/125 would be sufficient. I never heard of the "1/35" rule of thumb. So I'm assuming the formula is 1.35 x 250 (or whatever focal length). Obviously I need to find this information, and other helpful information, in order for me to maximize the potential of the 18-250.

Appreciate the info

Peter
08-18-2008, 11:20 AM   #23
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QuoteOriginally posted by rfortson Quote
Then I'd really suggest looking at Don Gale's site for some ideas on how to use this lens at a wedding. Keep in mind that he used an off camera flash, since this lens is pretty slow. On the K20D, you'll be able to bump up the ISO though, so it should work if you're careful.

Do you have the FA50 f/1.4? It's a very nice, inexpensive lens and would help you in a pinch if you couldn't use your flash for some of the shots.
Thanks Russ,

I certainly did check out Don's site and the images looked good. Fortunately I just found out that the wedding is outdoors. For the indoor reception shots I have an older external flash (AF-330-FTZ). I read somewhere that this flash needs to be used manually since it does not go auto with the K20 like it did with my *istDS.

I don't have the FA50, but wish I did. I've heard a lot about it and may just get one if the price is right.

Peter

08-18-2008, 11:26 AM   #24
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QuoteOriginally posted by Marc Sabatella Quote
. . . As another poster guessed, I knew this - just a typo. 1/125 is not fast enough, either. You would need 1/350 just to match the old "1/ focal length " rule after adjusting for the crop factor. 1/125 is asking for a stop and a half of improvement from SR. Not by any means impossible of course - that's within its stated effectiveness. But still, we're talking about percentages here, not guarantees. Maybe you could expect 50% success here, and that's assuming the lens itself wasn't softer than you'd like at 250mm on the K20D.

Anyhow, since you are satisfied with this particular shot, it's kind of moot. But it might be interesting to see some of the shots you *don't* think came out well - also with EXIF info.
Thanks again Marc,

As you can tell, I'm learning here. The shot in question is acceptable, but it was one of the few that has been. However, now I know why my other shots were not acceptable. I was shooting at lower speeds and in some cases having the lens too far open. I did not take into account all the things I'm reading right now. Since I've posted, and have had so many great responses, I'm appreciating that I jumped too quickly in questioning the quality of the lens. The advice given here is already making a difference with some of my tests. I just have to understand the limitations and tricks of using the lens.

Peter
08-18-2008, 11:31 AM   #25
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QuoteOriginally posted by Petermgr Quote
Thanks Dan,

See, that goes to show you that I need to learn more about using the zoom lens. I would have thought 1/125 would be sufficient. I never heard of the "1/35" rule of thumb. So I'm assuming the formula is 1.35 x 250 (or whatever focal length). Obviously I need to find this information, and other helpful information, in order for me to maximize the potential of the 18-250.

Appreciate the info

Peter
The rule of thumb isn't just to do with zoom lenses. For reliable photography, the rule in the old days was "use a shutter speed equal to one over the focal length". Regardless of whether that's a prime lens with a 100 mm focal length, or an 18-250mm zoom set to 100mm focal length, you would use a minimum shutter speed of 1/100s.

When digital cameras came along, the rule didn't change, but the sensor size needs to be taken into account. A 100mm lens on a K20D has the same focal length as a 150mm lens on a full-frame camera. So that's why we said 1/350s (One / 250mm focal length x 1.5 crop factor). You can get away with less of course, depending on shake reduction and steadiness, but for reliable results, the shutter speeds should be kept up. I have to admit I'm pretty bad with this rule at the long focal lengths, so I do my best to hold carefully and take lots of shots. Or use a tripod when feasible.
08-18-2008, 01:07 PM   #26
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QuoteOriginally posted by Petermgr Quote
See, that goes to show you that I need to learn more about using the zoom lens. I would have thought 1/125 would be sufficient. I never heard of the "1/35" rule of thumb. So I'm assuming the formula is 1.35 x 250 (or whatever focal length).
Peter
I think you misinterpreted what was written. It is not "1/35" but rather, "1 / (35mm-equivalent-focal-length)". In other words, 1 / (focal length * 1.5), since you need to multiple focal length by 1.5 to get the 35mm equivalent due to the "crop factor" which I assume you've probably heard about by now (eg, a 50mm lens on a DSLR is more like a 75mm lens on 35mm film).
08-18-2008, 02:34 PM   #27
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My Tamron 18-250 was superior to the 18-55 I kit. It' actually a very good lens for a superzoom, and can be very sharp.
08-18-2008, 02:59 PM   #28
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QuoteOriginally posted by Groucho Quote
I'd go along with the comment to do some focus testing. ..
Thanks Groucho,

I'm thinking of playing with the focus adjustment. Could be that it is fine, and that I'm not . . . But I'd like to see how it works. . .

I found this link and it gives a chart and tips . . . Focus Testing - BobAtkins.com - I'll just play with it and see what it looks like
08-18-2008, 04:32 PM   #29
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QuoteOriginally posted by Petermgr Quote
Thanks Groucho,

I'm thinking of playing with the focus adjustment. Could be that it is fine, and that I'm not . . . But I'd like to see how it works. . .

I found this link and it gives a chart and tips . . . Focus Testing - BobAtkins.com - I'll just play with it and see what it looks like
There's a K20D-specific focus chart here - though I'm sure it'd work with any camera. I did my testing before finding that one, though - I think most any focus test will be at least enough to tell you if you're having legit focusing issues or not.

Having a couple AF lenses lets you know if it's the fault of the camera or the lens... hopefully you have more than just one single lens.
08-24-2008, 09:41 AM   #30
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Horrible lens, useless crap! The only 18-200/250 that ever delivered is the 18-200 VR from Nikon. All other Tamron/Sigma/Other creations in this extreme zoom range just plain suck. Get the Pentax 17-70mm, very sharp for a zoom. And yes, I tested all 18-200/250 lenses. -B
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