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09-29-2008, 02:05 PM   #16
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Thanks.

Distortion is severe but only at the widest end. Like I said, if you can help it use it from about 25mm rather than 18mm. You can't always do that but where possible you'll like the results.

04-24-2009, 08:35 AM   #17
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Just got one, as I am often having to change lenses in windy, dusty conditions between the kit 18-55 II, and the Sigma 28-200.

Right away I am finding blue fringing. Horrible towards the sun, and on bright white mayflowers which are blooming now, at any angle, even present at 120 degrees from the sun.

Do I have a bad copy? I did not have this problem with the Sigma.

I do think it is sharper than the sigma.
04-24-2009, 09:06 AM   #18
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Tamron or Pentax version? I *never* had fringing problems with my DA copy.
04-24-2009, 09:06 AM   #19
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Post some pictures to give us examples. I have a Tamron 18-250 and I have not seen the issues you are describing. Do you have a filter on the lens while shooting? Are you using the hood? The more details the better.

04-24-2009, 10:27 AM   #20
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QuoteOriginally posted by Jasvox Quote
My Tamron version does the same thing. It is the weight of the lens elements and gravity, who can fight that? Think of it, its an 18 to 250mm lens in a barrel about the same size as the kit lens, I can live with the occasional zoom creep when its pointing down. Once you get used to "locking" it when not shooting, it's not an issue at all.

As for the vignetting, just learn to find the lens' sweet spot with the aperture setting and vignetting usually isn't such a bother or issue.

Jason
You can ask the camera to use the lens' sweet spot by setting your program line to MTF. Shoot for a day in this program line, and then check the aperture settings the camera used. My 50-135 uses f/4-f/5.6 when it can, for example.
04-24-2009, 09:24 PM   #21
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Samples of the blue halo or fringe

Pentax. Hood. No filter. I'll see if I can upload the samples. Um, how do I do that?[ATTACH][ATTACH]Name:  IMGP2669-1.jpg
Views: 138
Size:  29.8 KB[/ATTACH][/ATTACH]
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04-24-2009, 10:24 PM   #22
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These look like crops. Can you post the originals?
04-25-2009, 07:03 AM   #23
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If you can't post the originals I will definitely say that my lens does not do that to highlights. Can you post the shot deatils? ISO, Shutter Speed and Aperture?

04-25-2009, 08:29 AM   #24
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Those are 100% crops. You want the original PEFs? Can I upload files that big here?

I will try. . .
04-25-2009, 08:37 AM   #25
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Just convert them to jpg. But it seems like the very high contrast areas are the problem but it would still be helpful to see the whole picture to see what is happening elsewhere on the frame.
04-25-2009, 09:35 AM   #26
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won't allow uploading of PEFs or any large image

So, now what?

Here is the exif for the branches:

DA 18-250
50 mm
1/60
F 4.5
Program Auto
Spot metering
Automatic white balance
ISO 100
Ex Dyn No
RAW
Ex Comp 0.0
Single AF
AF Select
Color space sRGB
Image Tone Landscape
Saturation 0
Hue 0
Sharpness 1
Fine Sharpness Yes
Drive mode Continuous
Flash Off
Bracket off
Multi off
Shake enabled
K200D Ver 1.0
04-25-2009, 10:27 AM   #27
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Here is the exif for the flowers:
250mm
1/180
F6.3
P
spot
Auto WB
ISO 100
No ED
RAW
EC -0.5
Single AF
Select
sRGB
Landscape
Sat 0
Hue 0
Sharpness 1
Fine Yes

The majority of the flower images do not seem to have this problem. However in them I had given a negative exposure compensation because the flowers are so brilliantly white compared to the foliage that they burn out otherwise.

It always seems to show up to some extent with branches against the sky, though the sample I uploaded is by far the worst.

I really hope that this is user error and that I can learn how to avoid this. I don't want to have to wait for sending it back and getting a replacement from Adorama, because now are the very few days of the best of spring around here.
04-25-2009, 10:32 AM   #28
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For comparison here is the exif info of an image from that same walk, also of a mayflower, that does not have the blue halo:

250mm
1/350
F8
Spot
Auto WB
ISO 100
ED No
High-Iso noise reduction Yes
ED 0.5
Single AF
Select AF
sRGB
Landscape
Sat 0
Hue 0
Sharpness 0
Fine Yes
Contrast 2
04-25-2009, 11:30 AM   #29
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Regarding your branches shot: That was shot close to or actually wide-open. Most lenses have a tendency to produce purple fringing unless stopped down. (although some Canon owners will zealously deny it)
04-25-2009, 11:34 AM   #30
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You are using spot metering. Depending on what you were metering on I can see you blowing out your highlights as you see here. You meter off of a dark portion of the frame and you will lower your shutter speed accordingly as showing in the first set of numbers 1/60 shutter speed is pretty slow for a bright sunny day IMHO. Instead of spot metering try center-weight average. This is why I asked for the whole picture. If you metered on a darker portion of the frame I can see the results as you have posted here happening. You may have told the camera to properly expose the darker portion of the frame resulting in the blown highlights.
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