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08-11-2007, 03:36 AM   #1
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Help on blurry pictures.

Here's my problem: I have a Sigma 18-200, which I use on my K10D and when using the lens at 200mm, I very often have blurry pictures. What troubles me is that I don't know exactly what I'm doing wrong. Some of the reason I have in mind are:
- SR is unable to compensate my shaking hands when the lens set to 200mm.
- no good focus ( the auto-focus was not usable for several weeks because of a bad contact in the MF/AFc/AFs switch, so I've had to use MF a lot during my holidays)
- The sigma just isn't sharp enough at 200mm

It cannot be only the SR, since I've tried shooting at 1/1000sec and still have problems.
I doubt it's only the focussing, since I rely on the 'in-focus' beep when manually focussing.
I can't just put the blame on the sigma, since I _do_ have some pictures which are sharp at 200mm.
So I guess it's just a combination off all of the above ???

What are your tricks to have sharp pictures at such focus lengths ?

Here's an example of a really bad one: it's the impact hole in the center of the "Meteor Crater" in Arizona. It's was taken at a distance of about 800 meter on a very windy day, ISO 400, 1/1000sec, 200mm, F1/6.7.

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Thanks,
Erik.

08-11-2007, 04:10 AM   #2
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At this kind of focal length I will always use a tripod and if this is not available try and find a railing or something to steady myself on. SR isn't really able to compensate much at this kind of focal length in my experience. I also don't have very steady hands and dont mind taking a tripod with me.

There looks to be a slight motion blur on the photo but its really hard to tell because there is very little contrast in the shot. but there does seem to be some diagonal movement. having said that, looking at the shot and that you say its not sharp at very fast shutter speeds, you probably have a focussing problem.

If you have had issues with contacts take the lens back. I find MF difficult through the k10d at these kind of distances.
08-11-2007, 04:16 AM   #3
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Just to extend on PixelPruner's comments.

That Sigma is a wide range zoom - perhaps it is often not giving you satisfactory sharpness at the longer range esp at certain apertures. When you put the speed up to 1/1000 the aperture has to open out to compensate and then you are aggravating the problem as open wider apertures have greatly reduced dof and or reduced general sharpness in many lenses. Try to stay at f8 if possible by upping the ISO when necessary.

The infocus beep isn't always reliable I find. In some subjects there is other things being focussed on that aren't always clear to me in the view finder.Other issues that could cause oof images is heat haze (how hot is the bottom of a meteor crater in the Arizona desert?) or even dust in the wind.

Issues like this can be fun experiments as you work through a range of variables and try to seek an elegant solution - afterall the film isn't costing very much...

Cheers, Arjay

Last edited by Arjay Bee; 08-11-2007 at 04:21 AM. Reason: clarification
08-11-2007, 05:14 AM   #4
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why not set apature priority and allow it to set the shutter time, maybe us the apature at f/16 and allow it to take the picture at 1/180 maybe. then see what the result is in the camera.

08-11-2007, 02:43 PM   #5
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Have you tried all the different focus modes? I just tried with my DA 50-200mm lense, on low contrast subject, the auto focus seems to pick something other than the center of the viewfinder and on focus length of 200mm the hand held images taken are always blurry on max LCD zoom, even at 1/1000 shutter speed with SR on. It was less blurry with center auto focus, but not as sharp as with a tripod!
08-11-2007, 03:33 PM   #6
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Mostly I'm using center focus (including the pictures above), but as mentioned my AF switch was stuck at that time and I had to use MF.


Let me explain my theory why SR can never be perfect on the K10D.

Cameras get the focus length from the lens via a few contacts on the lens mount. That information however is not very accurate since the numbers increase in large steps. To be more specific: I set the camera to wide angle and zoom in very slowly, while frequently pressing the info button to read the focus length on the LCD.
So it starts at 18mm. It remains the same number while zooming in untill suddenly the camera reports 22mm.
Again in other words: the information which the camera has on the focus length increases in discrete steps. For my Sigma these are: 18, 22, 26, 30, 34, 40, 45, 53, 63, 75, 93, 113, 133, 155, 170, 200.

This info is critical for the SR: when you tilt the camera up by 1 degree at 18mm the sensor needs to shift down by a small amount. When you tilt it by 1 degree at 200mm, the sensor must shift by much more.

Based on these two facts, I conclude that SR can never compensate your movement (even if it knows exactly how much you moved) exactly because it doesn't know whether the actual focus length was 177 or 199 mm.

Let's say that a 1 degree shift needs to be compensated by a 1mm movement of the sensor at 200mm. But maybe the actual length was 171mm. Now the sensor moves by 1mm, whereas it should have moved by something in the range of 0.85mm. The result is a significant amount of blur remains.

Does anyone see any holes in this theory ?

Note: maybe this limitation doesn't exist on in-lens stabilization systems: they might have more accurate focus length info.

Erik.
08-11-2007, 04:11 PM   #7
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I think your theory does make sense, but there is a maximum design limitations to how much the SR can shift to adjust for the shaking, that limitation is easily breached on longer focal length than at wide angles. In the 200mm focal length case, it really is pushing the SR's limitation, maybe an in lense SR is marginally better, but really should use a tripod or at least a monopod.
08-11-2007, 05:42 PM   #8
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???

re: shake reduction.

I shoot at 300mm, and often with the 1.7x TC, at speeds of 1/30th, and SR seems to handle this flawlessly. I never use a tripod, and focus is no problem.

Maybe I'm rock steady?

08-11-2007, 06:29 PM   #9
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Hay Lipsistraat,

Hope you are enjoying yourself, I know I am. This is one of the better ones I've seen.
Thanks,
ken
08-11-2007, 06:36 PM   #10
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I'm wondering if it isn't partly due to manual focus error; the beep is a false friend, as can be the focus indicator light. Focusing at that sort of distance, on a scene with little in the way of helpfully contrasting elements, with a matte screen....sort of a tall order. Plus, as you intimated, one mustn't discount the "shaking hands" element. Tripod, monopod, brace against a wall, kneel and brace against your knee, anything at all would have helped to one degree or another.
08-11-2007, 08:25 PM   #11
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I'll just sit here on the sidelines and see where this goes.......
08-12-2007, 03:06 AM   #12
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QuoteOriginally posted by Mike Cash Quote
I'm wondering if it isn't partly due to manual focus error; the beep is a false friend, as can be the focus indicator light. Focusing at that sort of distance, on a scene with little in the way of helpfully contrasting elements, with a matte screen....sort of a tall order. Plus, as you intimated, one mustn't discount the "shaking hands" element. Tripod, monopod, brace against a wall, kneel and brace against your knee, anything at all would have helped to one degree or another.
If it's a focus error, it must be a pretty big one, since you can see that neither the background nor the foreground is in better focus then the center.

QuoteOriginally posted by Tom Lusk Quote
re: shake reduction.

I shoot at 300mm, and often with the 1.7x TC, at speeds of 1/30th, and SR seems to handle this flawlessly. I never use a tripod, and focus is no problem.

Maybe I'm rock steady?
Interesting... Can you give some more info how you use the camera ? What focus method (AF.c or AF.c, focus selection: center/auto/manual, ISOs ? etc...) Clearly you have a different lens. Which one ? Have you ever tried the Sigma 18-200 ?


Now about the Sigma: I have some doubts about the indicated 200mm focal length. When the lens is turned to 135mm on the zoom ring, the LCD dispays 133mm (that's not far off). The if you turn the zoom ring till then end, I notice that the lens barely extends any further, and also the framing of the picture changes very little. The difference 200mm/135mm should give me roughly a 1.5 magnification right ? That's not what I see in the viewer: that looks more like 1.1 factor of zoom.

Oh one more thing: the picture shown above was taken with a circular polarizer on the lens. I guess this shouldn't have a big impact since I focussed manually. I remember also checking the focus ring, and it was set to 'infinity'. That should have been a good approximation for 800m.


Thanks for your feedback,
Erik.
08-12-2007, 03:33 AM   #13
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QuoteOriginally posted by lipsestraat Quote
If it's a focus error, it must be a pretty big one, since you can see that neither the background nor the foreground is in better focus then the center.
At 800 meters, and with a shot that blurry, I wouldn't really expect to be able to spot the difference. Depth of field at 200mm @f6.7 runs from about 215m to infinity, according to what I could come up with from an online calculator. How much background to foreground variation could we expect on that shot, even with perfect focus and no shake?

I still suspect a combination of manual focus error and camera shake.
08-12-2007, 04:30 AM   #14
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Maybe a good thing to focus on something closer.

looks like a hot dessert to me, hot air gives often some kind off blur.

Good thing for testing is sticking a newspaper to a garden fence and make picture off that its an ideal test chart. Make sure your sensor is paralel to the paper.

Guido
08-12-2007, 08:00 AM   #15
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I think the lens has a loose element.... and may have been affected by the heat.
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