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Forum: Pentax K-5 & K-5 II
08-21-2013, 08:02 PM
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HUH?!? since when are we not allowed to compare the sharpness from lenses with a different focal length? (You should mail Photozone quickly; they're out of a job!) Sharpness, or the lack of it, can be compared just fine. The lack of sharpness in the DA 10-17 is not a characteristic of it being so wide. Otherwise the other UWA's would suffer from the same. It's just an indication. The DA 10-17 is not sharper then the 18-55 and the DA 12-24 is ultra-sharp, compared to the 18-55. Simple.[/QUOTE]
Ok, Came home from work, had some dinner and was reading some posts.....- HUH?!? since when are we not allowed to compare the sharpness from lenses with a different focal length? (You should mail Photozone quickly; they're out of a job!) - I did not state you were not allowed to compare sharpness from lenses of different focal lengths. I was pointing out, when you have two lenses that differ in their type (fisheye vs. normal) and have a substantial difference in their Angle of View or Field of View (180 - 100 degrees for the fisheye vs. 76 degrees for the wide end of the kit lens), it makes little sense. The fisheye is 30% wider on the diagonal than the kit lens just on Pentax's field of view specification. Of course the fisheye is going to have worse sharpness, and that is what I was pointing out - and also listing the reasons why. Two different lenses were designed for completely different purposes. Their performance point that out.
- Sharpness, or the lack of it, can be compared just fine. - I did and do not disagree, it was just obvious to the casual observer. Folks tend to get confused - a fisheye at 17mm vs a normal lens at 18mm - gee they must be pretty similar. Two completely different projections on to the sensor. Two different uses. Two completely different optical designs - apples and oranges. Two completely different types of distortions, and one is corrected, while the other is not. You can certainly compare sharpness - but to me its a fool's errand.
- The lack of sharpness in the DA 10-17 is not a characteristic of it being so wide.- This is where we disagree. There are two main points in this respect. 1) The size and resolution of the sensor does not change when you swap lenses. Each pixel on the fisheye is going to represent more area than the same pixel with the kit lens mounted. It is just pure physics. 2) In addition, the fisheye has the fisheye distortion that is uncorrected, and will certainly pull the edges and especially in the corners. Even though the fishiness is pretty mild at the 17mm end, its still present. When the two of these are combined, there is no question that sharpness is degraded.
- Otherwise the other UWA's would suffer from the same. It's just an indication. - There are differences between UWAs, in the case of the 10-17, its a fisheye with a Angle of View of 180 to 100 degrees (corner to corner diagonal). The 12-24 at 12mm is 100 degrees wide (at 12mm). Other UWA's also suffer. There are no normal or rectilinear UWA lenses as wide as a fisheye - that is why fisheys lenses were developed. It is a function of each individual lens' actual width or Angle of View. They suffer (in sharpness) in direct proportion to their Angle of View. The wider the lens, the more area each pixel will need to represent, and that will degrade the overall sharpness.
- The DA 10-17 is not sharper then the 18-55 and the DA 12-24 is ultra-sharp, compared to the 18-55. Simple - The 10-17 complements the 12-24. Between the two lenses, you have a seamless coverage of AoV from 180 to 60 degrees. The 12-24 is much sharper than the 10-17. I never said it was. The two lenses however, also are substantially different in their optical design. One (10-17) is an uncorrected fisheye, while the 12-24 is a highly corrected (for distortion) normal rectilinear lens. Comparing the 12-24 to the 18-55 kit lens is easier, since each is a normal rectilinear zoom, and have a common overlap (18-24mm). I would suspect that the 12-24 being highly corrected, with better lens elements, would be sharper. The 12-24 has its optimum resolution at 18mm and it trails off into the 24 area. The 16-45 is sharper at the 24mm mark than the 12-24. The 16-45 is sharper and has better IQ than the kit lens, however that is expected, since that was its design purpose.
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Ok, not to beat a dead horse errrr cow, here is an image comparison tool. I am using the same images that carrrlangas provided (thanks!)
I used the image comparison tool located atThe left hand is the first image from carrrlangas the 10-17 at 17
The right hand is the second image from carrrlangas the 18-55 at 18
The difference across the three supplied images are increased scaling - equal on each sample, and a shift left and right, respectfully in order to be able to compare the musical notes side by side. Also, assuming that all things are equal in terms of the images (focusing distance, rotation of the cow, etc.)
I think that you can start to see that the width and sharpness is slightly different between the left and right. The elongation of the vertical marks. Some of this is due to the distortion.
So, I'll just leave the rest of the analysis up to the collective.....
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Forum: Pentax K-5 & K-5 II
08-21-2013, 04:35 AM
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I don't believe that the 10-17 was designed to compete with the kit lens. It can't. Let's take the sensor, something near the K5 - 3000 x 4000 pixels. When you swap lenses, the sensor's size does not change, it remains the same. What changes is the focal length (which is a difficult indicator to gauge). A more important aspect to the lens is the Angle of View. The AoV is tremendously larger for the 10-17 than the 18-55. What that translates to is that each pixel has a much larger of area to represent. The 10-17 at the 17mm end has an AoV of 100 degrees, while the 18-55 at the 18mm end has an AoV of 76 degrees. So that is about 50% more area (when taking length x width into account).
So, its 2 different lenses, each of which has their own use, and the types of each of the lenses are quite different, so it's apples to oranges comparison. The similar focal lengths is a real red herring.
Yes, wide angle lenses in general have this quality of great color and improved contrast. The wider you go the greater the richness.
One other quality is how they (wide angle lenses) handle light. The wide angle lenses tend to be somewhat slow in the aperture, around f4 usually. However, since they are so wide and are capable of pulling in so much light, they tend to meter slightly different that one might expect. They tend to actually perform a bit faster that their relatively slow aperture would indicate.
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Forum: Pentax K-5 & K-5 II
08-20-2013, 07:39 PM
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I have had my 10-17 for almost 5 years now. As others have posted its a fisheye across the entire range, however at the widest - 10mm it appears to be a true fisheye. As you progress through out the range to the narrowest end, the fisheye effect appears very subdued. It is still there, but you really need to look.
Another approach to judge is the Angle of View (AoV). At 10mm its 180 degrees corner to corner, while at 17mm its 100 degrees. The DA 12-24 has a an AoV that starts at 100 degrees (12mm) and goes to 60 degrees (24mm). Based on these two lenses AoV wise they complement each other perfectly, however based on focal length there appears to be a substantial overlap. This is due to one being a fisheye while the other a normal or rectilinear lens.
It is indeed a specialty lens, however it is incredibly fun to use. I doubt that you would want to use it daily, however there are applications that it just excels at. Getting close to very large objects, and then grabbing a wide shot where you have things in motion and stitching will just not work.
The fisheye effect is very pronounced when you shoot objects with very straight lines and square corners. Scenes with lots of natural curves - trees, mountains and the like the fisheye effect can be very gentle. You, as the photographer, are able to determine where you want to place the "bend" in the image by ever so slightly tipping the camera up or down. You can have a very straight horizon also.
Just one word of caution - when using it, check the frame for where your toes are - as its easy to get your feet in the bottom edge of the frame.
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