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Forum: Pentax Medium Format 01-15-2011, 08:29 AM  
645D initial exposure workflow
Posted By Tim Wilson
Replies: 1
Views: 1,832
Here's a technique I've discovered for setting initial exposure with the 645D that is probably old hat to long-time Pentaxians, but new to us former Canonites. It's primarily applicable to handheld work.

Have the camera set to M mode, spot meter, with exposure compensation at plus 2 stops. You see some subject matter and look for an area that represents textured highlight. Place that area in the meter spot, press the green button. The 645D does two things: Sets the exposure to what it would use in P, even though you're in M, and does so using the plus 2 compensation for the highlights. Can't do that with a Canon. So let's say the shutter/aperture combo isn't exactly what you want. Press the AE lock button and turn the wheel to adjust the shutter speed and the aperture changes automatically to maintain EV. Can't do that with a Canon either. Fire a shot, check the histogram and hi-lo warnings. Quick adjust to tuck those highlight a little closer to the edge (or pull them back from the brink), and your off to the races.

Tim Wilson
Forum: Pentax Medium Format 12-31-2010, 03:32 PM  
645D lens test results
Posted By Tim Wilson
Replies: 20
Views: 8,463
I finally found time to do a little lens testing today. I used targets on a studio wall, and a carefully measured and aligned setup. All tests at 50x magnification (subject:sensor). Mainly looking for camera alignment problems and lemon lenses. I tested the new 55/2.8, FA 75/2.8, FA 120/4macro, FA 45-85 and 80-160 zooms. There's good news and there's bad news:

SMC Pentax-FA645 Macro 120mm f4---

GOOD news: Consistent with what others have reported, this is a really sharp lens. Good at f5.6. Really good at f8 or f11, OK at f16, downhill from there. f22 is soft. f32 is mushy. (All of these lenses are mushy at minimum aperture and soft one up from there.) No problems I could see with this individual lens.

SMC Pentax-FA645 75mm f2.8---

GOOD news: Another good sample, it looks like. The center is sharpest at f5.6-8, the corners are sharpest at f8-11. Second sharpest lens in the bunch.

SMC Pentax-D FA645 55mm f2.8---

GOOD news: Tack sharp in the center, at f5.6 or f8.

BAD news: As Lloyd Chambers has reported, really soft in the corners. Worst of all the lenses I tested in that regard. I'm thinking about sending it back.

SMC Pentax-FA645 45-85mm f4.5---

GOOD news: At 55mm, this lens gets sharp really quickly, by f5.6. That's where the center of the new 55mm f2.8 gets sharp, too, except that the zoom gets sharp all over. At longer settings it needs f8. I haven't tested 45mm yet. Most of the time, sharpness is close to what I'm seeing from the 75 f2.8. Looks promising, EXCEPT...

BAD news: at the longer end of the zoom range (75-85mm) the right sides of my test images are noticeably softer than the left sides. Looks like this particular lens is flawed somewhere. Not sure what to do about that yet.

SMC Pentax-FA645 80-160mm f4.5---

GOOD news: Another eBay find, this one just arrived yesterday. Very close in terms of sharpness and optimal apertures to the 45-85, also same layout, feel, filter size... would be a nicely matched pair if the 45-85 wasn't cockeyed. Fortunately, I don't see any asymmetries with this lens.


GOOD news: I see no signs of any camera alignment problems. And what limited focussing I did (AF center spot on a centered target) seemed to be accurate in all tests.

I'm really happy with the 120mm, the 75mm, and the 80-160. I think the 45-85 is a good lens in general, but mine has a problem that needs attention--a disappointment. The 55mm? I hate to say it but it's starting to look like Pentax screwed up on these, either with a design problem or with a serious manufacturing issue.

Tim Wilson
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