20d Weird Pattern

[drisley]

Hi guys.
I took my 20D out tonite for some long exposure, wide angle shots with the Tokina 17mm ATX PRO.
When I got home, I "developed" this 25 second Raw exposure with DPP software. I noticed when I blew the image up 200% in photoshop, there was a weird pattern on the vertical bars on the railing of a bridge.
I then tried Photoshop CS to convert the Raw image, and the pattern was even more visible. I remember seeing this problem in a review for another camera once. This is the first time I've seen such a thing.

200%
http://www.fotop.net/albums/sharpnsmart/miscellaneous/pattern.jpg

[drisley]

I should also add that the temperature was 4C, and the aperture was F11.

[Seamless]

Not considering results of optics or light source, the time exposure may be long enough (depending on wind strength and gusts, bridge structure design) for the bridge or portions to move during exposure. I would not be surprised that oscillations not normally observable to the eye can cause a pattern. It looks as the camera on a tripod was not set on the same surface as the bridge, thus immobile as compared to the bridge railing.

(Unless you were in Tokyo last week, in which case the perspective would be reversed.)

Jay Giusti

[Jim_T]

I think it's mainly a bokeh issue.. (The way out of focus areas appear).

The railing is slightly out of focus and the tight pattern of the railing combined with the bokeh of the lens has caused it to appear strange..

FWIW, You were standing too close to that particular bridge... :wink: ... It looks nicer if you get a lot farther away.. (Like on the docks of the Prominade across the river in St. Boniface. Then you don't have to worry about distortion in the railing :) :) :) )

http://www.mts.net/~jwt/bridge.jpg

.

[tannoy]

Looks like maybe Moire, I saw something similar on the Nikon D70 in a review.

http://www.outbackphoto.com/reviews/equipment/nikon_d70/Nikon_d70.html


Cheers,

Darrin

[drisley]

Tannoy, you hit the nail on the head.
That is a demosaicing artifact caused by Photoshop CS Raw conversion.
This doesn't happen nearly as badly with the DPP software.

JimT, nice picture! I was actually just making a demo photo to compare 17mm and 50mm for someone in the Share Photos forujm.
Plus, I was freezing and my bladder was about to explode if you know what I mean :lol:

That's a very photogenic bridge.
http://www.fotop.net/albums/sharpnsmart/072004/CRW_2111.jpg

[Radtech1]

Where is the bridge? I really like the look of it.

Rad

[tannoy]

Drisley,

You say that the DPP is not as bad? If it is not too much trouble could you post one of each to see how much different they are?

I am very curious to see how C1 will handle this once support is available...

Thanks for the info.

Cheers,

Darrin

[drisley]

Here is the DPP result.
There is still some slight wierdness, but definately better than the obvious pattern produced by PS CS.

DPP
http://www.fotop.net/albums/sharpnsmart/miscellaneous/pattern_dpp.jpg

[tannoy]

Thank you Drisley, that is very interesting indeed, appreciate the information.

Best,

Darrin