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09-20-2014, 11:03 PM - 1 Like   #46

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QuoteOriginally posted by harklee Quote
Guys, here is an update.

So the corner degradation at the wide end (28mm) turns out to be caused by some degree of field curvature, meaning that you can only focus either on the perimeter or on the center of the frame. This is only noticeable at the wide end and is still far better than that of the D-FA 25mm or the FA 35mm. The field curvature can be easily seen by focusing (try manual focus with focus peak on) on different parts of the frame during live view and monitoring the distance meter on the side of the lens. It will change as the focus moves from the center to a corner. However, the live view keeps the aperture wide open, so you are really looking at the field curvature when wide open rather than when stopped down. Regardless, I think the lens is well designed since no wide angle lens is free from some degree of field curvature. I will update the original text accordingly.

The black tapes on the camera are just to prevent it from scratching. I am a landscape guy, and my gear sees some serious use. I just taped some parts of the camera that tend to scratch (based on the years of experience with the 645d).

I tested the lens with a B+W uv filter and a Lee-type adapter ring stacked and they work just fine. Although these are thin wide-angle types so I can't say about regular filters and regular adapter rings.

I will be on a week-long field trip starting tomorrow, so I will post some real-world samples when I am back. Thanks!

I did some initial testing with mine yesterday and although it is inconclusive, I think what I saw was field curvature also.

I took some photos in a rainforest, focussing on a nearby tree in the very foreground, then another shot focussed on a tree at least 100m away. I found that the foreground corners and extreme corners had better sharpness and contrast when focussed at the furtherest tree, not the closest tree. This would indicate forward field curvature towards the edges of the frame.

For landscape I can only think of this as a good thing, being that you will technically gain additional depth of field for foreground subjects at the bottom of the frame, as mostly the sky is at the top so no real loss there.

Also as a side note, the focus ring has a great long throw to it, so its great for fine manual focus in live view.


09-22-2014, 12:48 PM   #47
RonHendriks1966's Avatar

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QuoteOriginally posted by harklee Quote
1. The lens is insanely big, it dwarfs the D-FA 25mm. It looks even bigger than the 645z body.
I hold it on Photokina and wow is that true, this lens is big.
09-22-2014, 05:39 PM   #48
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Join Date: Dec 2011
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Now if Metabones would only make a Speed Booster for the Pentax 645, then that lens would be even more of an attractive buy.
I asked them in an email if they had any plans to build one for the 645 and they said no, not at this time.
Maybe Pentax could design and build one of their own? I know I'd jump at the opportunity to get one.

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