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04-28-2009, 01:17 PM   #16
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WerTicus, you're right and I forgot to mention that. Kenko is the same filter in different package and much cheaper. I use Kenkos whenever they're available.

04-28-2009, 04:49 PM   #17
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QuoteOriginally posted by jesalonen Quote
WerTicus, you're right and I forgot to mention that. Kenko is the same filter in different package and much cheaper. I use Kenkos whenever they're available.
QuoteOriginally posted by WerTicus Quote
kenko being hoya but with half the price tag :P
Great tip guys - much appreciated. I was wondering about the AUD$100 + price tags on those Hoya filters!
04-29-2009, 06:14 PM   #18
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I believe its because the only real barrel distortion is at the edges where you see it corrected. The Sigma 10-20mm is very flat through out most of the frame. What you are trying to correct is perspective distortion, common to all wide angles. Look at my example with the brick wall it shows the only distortion the lens has by design. The way to correct that type of distortion you refer (perspective) is in the angle and focal length of the lens which you shoot.

Notice distortions of lens are measured on 'flat' test charts as the brick wall. The brick wall confirms what all measurements show, it has barrel at the edges but not the center.

Link to perspective distortion which you show,
http://en.wikipedia.org/wiki/Perspective_distortion_(photography)

This can not be corrected in design of the lens. If you use PTlens on say the Sigma 17-70mm or Pentax DA*16-50mm at 16mm/17mm you will see the whole frame change and become much flatter because these lens have high barrel distortion across the frame. The Sigma contrary to popular belief is very rectilinear across most of the frame.

I can completely control the type of distortion you show in 'how' I shoot.
One example I purposely made lines not straight.


In this pic I wanted it flat looking, and if you put a grid to it, it is fairly flat. Neither have any correction applied.
04-30-2009, 12:22 AM   #19
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Nice images James!

It really shows what this lens is capable of - and they look very sharp.

I'm quite impressed with the almost completely straight lines across the bulk of the 2nd image. The first image is also very visually interesting and shows how you can utilise the wide angle for effect.

Thanks for sharing that with us.

BTW, were both shots at 10mm? (I can't read the EXIF data)

I'm looking forward to getting this lens on my camera

Cheers

04-30-2009, 10:54 AM   #20
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QuoteOriginally posted by MoiVous Quote
Nice images James!

It really shows what this lens is capable of - and they look very sharp.

I'm quite impressed with the almost completely straight lines across the bulk of the 2nd image. The first image is also very visually interesting and shows how you can utilise the wide angle for effect.

Thanks for sharing that with us.

BTW, were both shots at 10mm? (I can't read the EXIF data)

I'm looking forward to getting this lens on my camera

Cheers
Thanks!
Yes both are at 10mm. The Sigma has some distortion at 10mm at the very edges but after (12-20mm) its flat as a board. The Sigma 10-20mm is very sharp corner to corner (F8) and looks even better than the 17-70mm with better contrast, better colors, and sharper with less distortion. Its really a very good lens. I enjoy it a lot and am still impressed with it IQ. I don't see any of the stuff dpreview got in its testing, more like Photozones testing.
05-01-2009, 05:45 PM   #21
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Jamesm007

Those are some very impressive shots...what do you mean by controlling the shots in how you shoot??...can you take the first shot, but with the lines more straight?....what did you do to make the lines all parallel in the second?...can you explain what your method is?....can you tell me what I could have done to avoid the tower leaning?

Thank you.
05-03-2009, 06:29 PM   #22
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I will give a more detailed answer to all your questions in a couple days (time). A quick answer for now is I have studied it a bit, know its common to wide angle lens; for example any 10mm lens will do as your pic did, to the same degree (lean the tower) as long as its a rectilinear (flat) type, as most are but fish-eyes. You *can see it in the OVF*. I know to look for it and just move the cameras angle, distance, and focal length until you achieve the results you want in the OVF. In my first pic there would be no way to fit in everything without perspective distortion, good/bad? More latter...
05-03-2009, 06:54 PM   #23
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Thanks...........

05-05-2009, 06:54 PM   #24
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QuoteOriginally posted by pcarfan Quote
Jamesm007

Those are some very impressive shots...what do you mean by controlling the shots in how you shoot??...can you take the first shot, but with the lines more straight?....what did you do to make the lines all parallel in the second?...can you explain what your method is?....can you tell me what I could have done to avoid the tower leaning?

Thank you.
OK some more shots to show the Sigma 10-20mm does not distort lines for most of the frame its flat at 10mm. Knowing this and knowing that this is different from perspective distortion takes the idea away that the Sigma 10-20mm has some type of optical problem. Its in how you shoot with this lens. I can't say for sure how I would have taken the shot with the rock and tower but 100% for sure I could have, and you can take it without any distortion. You would have to play with angle and focal length. Also remember you can see it in the OVF so you know before you click if its right or not. I think its best to let a PRO show you and here is a link to KenRockwell on how to shoot with wide angle lens.
How to Use Ultra-Wide Lenses

Ice Rink at 10mm, all I did was aim and shoot, this is straight out the camera no corrections applied.



Trial in my park at 10mm a complex scene but still not much distortions, no corrections
05-06-2009, 04:19 AM   #25
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Jamesm007

Thank you for the post, I really appreciate it very much. The second shot you posted is superb for 10mm with no PP, wow!
05-07-2009, 08:04 PM   #26
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James - you have me suffering severe lens lust with these images! I can't wait to get my hot little hands on that lens in a few days time.....

The second image looks really good, with the tree trunks and lamp posts quite straight and almost completely vertical (a small lean with the post on the left).

The first image looks like there is a small amount of horizontal stretching at the margins (the cars on the left looks a tad stretched and the wheel slightly elliptical) but its not significant.

Thanks for sharing, and the link as well - useful info!

Cheers
05-29-2009, 12:08 PM   #27
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This thread was instrumental in helping me make my ultra-wide angle selection, so I want to take a second and thank everyone who contributed--thank you, ALL!

I get happier with the lens the more I use it. The image quality from 10-11mm is great. It truly is about how you shoot the lens. The colors and contrast are also excellent, with plenty of sharpness.

Last edited by Jewelltrail; 09-25-2009 at 09:10 AM.
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