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11-21-2010, 03:10 AM - 1 Like   #16
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QuoteOriginally posted by GregX999 Quote
No quick-shift focusing, and no switch on the lens. So you have to hit the switch on the body to disengage the screw-drive
A quick and easy way to have "quick-shift": with my right hand's middle finger I press the lens release button on the body, this disengages the screwdrive AF mechanism and I can freely turn the focus ring.

01-04-2011, 07:34 AM   #17
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QuoteOriginally posted by simico Quote
A quick and easy way to have "quick-shift": with my right hand's middle finger I press the lens release button on the body, this disengages the screwdrive AF mechanism and I can freely turn the focus ring.
Everyone needs to know this!!!

Thanks!
01-04-2011, 02:32 PM   #18
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This sounds like playing with fire to me...
01-04-2011, 02:51 PM   #19
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QuoteOriginally posted by CWyatt Quote
This sounds like playing with fire to me...

I tend to agree, this may be perfectly fine but it would just make me uncomfortable. Not so much about the lens falling off (though I guess that may be possible, too, with an especially exuberant MF'er), but about the de-coupling of the lens while using. I don't know...

01-05-2011, 01:02 PM   #20
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Pushing lens release button is not harmful - you're twisting the focusing ring, not the lens. Not very convenient though, but after some practise it could be done quickly.
01-17-2012, 01:17 PM - 1 Like   #21
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QuoteOriginally posted by simico Quote
A quick and easy way to have "quick-shift": with my right hand's middle finger I press the lens release button on the body, this disengages the screwdrive AF mechanism and I can freely turn the focus ring.
A better way might be to reassign AF to a read button. Then you can MF the lens and override as needed without risking anything.
01-17-2012, 05:04 PM   #22
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I don't have the HSM version of it, but the regular AF version has field curvature. Sharpness at the AF point is fine, but in extreme edges, the camera needs to move a bit forward. I got very good sharpness at the edges.
01-18-2012, 04:40 AM   #23
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QuoteOriginally posted by nater Quote
What, no shout-out for the Sigma 28mm f/1.8 EX DG Aspherical Macro? A full-frame (with aperture ring), autofocus, modern 28mm lens that sells for $350... and it never seems to get mentioned.
There are 2 versions of the Sigma 28mm and they differ in filter size (58mm/77mm). The Sigma 30mm is superior to the Sigma 28mm (77mm) from my informal testing.

01-18-2012, 01:06 PM   #24
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QuoteOriginally posted by CWyatt:
If you want a fast (say, f/2 or faster) standard auto-focus lens on a Pentax camera, you options are limited to the renowned FA 31mm f/1.8, this Sigma 30mm f/1.4, or the FA 35mm f/2.... The Sigma 30mm f/1.4 gets mixed reviews. I've had it for a few months and have taken thousand of shots in many conditions with it on a K-7. I bought it for street photography and low-light photography. Here are my thoughts:
....
IQ is very high in the centre right from wide open. This is great and one reason I bought a f/1.4 lens is to be able to use it at f/1.4. By f/2 to f/2.8 centre IQ is about as high as anyone could want. The extreme corners are never great, poor wide open (although hardly ever in the field of focus), and only get to a moderate level stopping down. It's certainly geared towards performing well in the centre wide open....
Just thought I'd give my 2 cents worth. The corners are not nearly as bad as advertised, (at least on my copy on my on a K-x), and the corner sharpness problems are largely limited to field curvature which probably doesn't effect shots at a reasonable distance when the lens is stopped down. I've had a fair amount of success using the Sigma as a landscape lens, often paired up with the Pentax DA15. Some of my recent Sigma 30mm posts include https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/149865-sigma-3...ml#post1755643 and https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/149865-sigma-3...ml#post1740987. I decided to test the 30mm F/1.4 Sigma corner/center sharpness for myself, at F/2 and at F/8. For comparison, I also tested my Tamron 28-75mm (at 30mm), at F/2.8 and F/8 for center and corner sharpness. In the 1:1 crops below, I thought the Sigma did pretty well. I can't see any difference in the corners between the Sigma at F/8 and the Tamron 28-75mm at F/8, except that the Sigma looks slightly better. Surprisingly, the Sigma at F/2 looks better than the Tamron at F/2.8, in both the centers and in the corners! I focused using live view, and I think I got it focused almost perfectly, for both the center and corner shots for both lenses. As expected, center sharpness is excellent, and corner sharpness is pretty good stopped down. I don't know whether I have a better copy than most. Also, the Sigma has a very large amount of field curvature which might not go away completely when focused at infinity, but at F/8 for a reasonably large landscape print, the corners on the Sigma would not be noticeable worst than the center. This would certainly be ok for 12"x18" print, and probably a 16"x24" print. Probably a 20"x30" print would be pushing it for my K-x at 12 megapixels, but usually such larger prints are done on less glossy paper than the smaller prints. The test chart is an 8.5x11 sheet of paper, perhaps 12 feet from the camera; there are links to the full size Sigma 30mm test images below the 1:1 crop images.

For comparison, here are the Tamron 28-75mm test shots.


for reference, full size 30mm Sigma center test shot
http://www.sheltx.com/share_stuff/IMGP5700.JPG
for reference, full size 30mm Sigma LL corner test shot
http://www.sheltx.com/share_stuff/IMGP5697.JPG

- Shel, my photos, Shel and Miriam's home page ....

Last edited by sheld; 01-18-2012 at 01:42 PM.
01-19-2012, 05:31 AM   #25
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QuoteOriginally posted by JohnBee Quote
A better way might be to reassign AF to a read button. Then you can MF the lens and override as needed without risking anything.
Huh? It's a screwdrive AF lens. No matter what button you assign to AF, you can MF only if you disengage / decouple the screwdrive mechanism - either by the AF/MF switch or lens release button.
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