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02-08-2011, 05:16 PM   #16
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Thanks for all of the replies.

Had a chance to go head-to-head with the A* 200 f2.8 + A series doubler vs, the 120-400 Sigma.

Unfortunately the store didn't have a Pentax mount so I had to use a Nikon D7000 for the Sigma. That threw a curve into my plans, but I think the results are still relevant.

The sharpest indoor shot with a monopod was scored with the Pentax. The sharpest outdoor shot using the monopod, by a smidgen, was the Sigma at 400.

The big problem however was colour. Frankly the shots using the Sigma sucked. It could've been the Nikon sensor, but somehow I doubt it. Reds went orange, whites went to cream, yellows lost their pizzazz, only blues held in there. Blacks were better on the Sigma, but a small boost in contrast for the Pentax brought the blacks into the same range. Working with hue, tint, saturation and other controls didn't save the reds and the whites on the Sigma shots. If I was willing to pull out all of the software stops in Aperture, I could've dragged the Sigma shots into the same colour range as the Pentax, but that's not the point.

So, the big question for Sigma users. Were my results an aberration or typical?

02-08-2011, 05:38 PM   #17
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Here's a tight crop on the Canon box on the wall rack that illustrates the colour difference. I did not make any PP corrections.

Doesn't look like the EXIF data came across, but the top image is the Sigma at 400mm at 400 ISO at f8 and 1/15th of a second. The bottom image was Pentax 200mm + doubler at 400 ISO, f4 (effective f8) and 1/5th of a second.

Interesting exposure differences. Both were shot aperture priority and 0 EV exposure bias. The Katz Eye screen in the K20D does lead to slight over exposure with long lenses.
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Last edited by Rusty Rat; 02-08-2011 at 05:52 PM.
02-08-2011, 05:49 PM   #18
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are you sure it isn't just that the two cameras have used a different white balance?
02-08-2011, 06:24 PM   #19
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Quite possible, but I didn't get that impression when looking at a range of indoor and outdoor shots. The outdoors shots showed the same problem with Sigma reds gong orange, but blues were virtually identical, indoors and out. Colour balance should affect both. Both cameras were on AWB.

I am willing to accept that using two different cameras has made a total hash of this, but I need convincing.

Here's a very tight crop, top photo is the Sigma at f8, the middle is Pentax at 2.8 (f5.6 effective) and then at 5.6 (f11 effective).

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Last edited by Rusty Rat; 02-08-2011 at 06:29 PM.
02-08-2011, 06:29 PM   #20
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QuoteOriginally posted by Rusty Rat Quote

Top photo is the Sigma at f8, the middle is Pentax at 2.8 (f5.6 effective) and then at 5.6 (f11 effective).
Looks like the Sigma came out on top on this one - no pun intended.
02-08-2011, 06:32 PM   #21
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QuoteOriginally posted by SpecialK Quote
Looks like the Sigma came out on top on this one - no pun intended.
Agreed. The Sigma did better here, but we're talking blues which the Sigma managed OK indoors and out. I should've done a third batch on a tripod as I think a bit of camera shake or focus inaccuracy got me here. I've had sharper shots with the 200 + doubler before. It was friggin' freezing and I didn't have the coat done up.
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