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Forum: Pentax K-5 & K-5 II
09-05-2013, 09:14 PM
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Best cathedral photos I´ve ever seen. Congratulation on an excelent application of a non distortion corrected lens.
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Forum: Pentax K-5 & K-5 II
08-21-2013, 08:57 AM
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If you only want to look at some charts based on one specific way of testing, ok. But, from the same review:
 Quote: MTF (resolution)
Testing a fisheye lens is a bit experimental. The Imatest toolkit freaked out regarding all the wild curves at the image borders at the 10mm setting. The 17mm MTFs should be quite accurate whereas the border resolution figures at 10mm should be only taken as a very rough guidance.
Keeping this in mind the Pentax SMC-DA 10-17mm f/3.5-4.5 ED[IF] Fisheye produced good to very good results in the lab. At 10mm the center performance is already very high at wide-open aperture and the borders follow not far behind. Stopping down produces only marginally sharper results. The local sweet spot is at f/8. At 17mm there's a performance drop - not in the center but the borders suffer a bit. The situation is better at f/8 or f/11 where the border quality recovers to good+ levels.
The Tokina variant in Nikon mount performed somewhat better so the tested sample may not have been the very best one. If you rather some real world samples, here´s a very unscientific comparison between 10-17 and 18-55WR. both wide open, same exposure, shot in RAW and developed without adjusting anything expect white balance and tint to be the same. The full resolution samples are there for download.
DA10-17 @17mm - f/4.5 por Fran Mora, en Flickr
DA18-55 @18mm - f/3.5 por Fran Mora, en Flickr
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Forum: Pentax K-5 & K-5 II
08-21-2013, 07:08 AM
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This is an interesting fact. I´ve experienced it not only with the 10-17 but also at the wide end of wide and normal zooms. Even in P&S cameras.
On th other hand I think this is not correct. Keeping every other variable equal, 10mm/4 = 2.5mm aperture, while 50mm/4 = 12.5mm. so technicaly, a 50mm f/4 lens lets in more light than a 10mm f/4 lens (movement blur is another issue) but the final result will depend on the subject size and distance. This is a good read on the topic: www.Clarkvision.com: Exposure and Digital Cameras
Resolution and sharpness are different things but the first one will dictate how much we can exploit the latter. So, for example, if shooting a subject with the kit lens at 18mm and the fisheye at 17mm and making sure the subject fills the same "ammount" of frame in the same way for both lenses, (so that the number of pixels on the subject is the same) then you could evaluate sharpness between the two. I am guessing the 10-17 will have a small advantage when both wide open.
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