|
Forum: Pentax SLR Lens Discussion
03-09-2012, 09:54 PM
|
| |
The proper fisheyes have 180 degrees diagonal view angle. In rectilinear projection, it is impossible to achieve this view angle so no matter what the rectilinear focal length is, it's always not as wide as fisheye.
Also, extreme wide rectilinear lenses produce unpleasant (for my liking) distortion effects near borders, where objects are stretched along radial direction and thus look unproportional. I think 12mm (cropped) is more than enough for wide angle, in fact even 15mm seems too wide for me, but maybe it's just me...
Anyway, about the 10-17 and 8mm lenses. As I said in another thread, the 8mm is a one trick pony - it's only good if you want to shoot the surroundings without focusing on particular object - the resulting shots are sharp across the frame, and the projection is such that no part of the frame has significantly changed proportions of objects. Also note that 8mm has pretty distant minimum focusing distance which augments the fact that it's not as good as Pentax 10-17 if you want to put an accent on some particular object.
Pentax 10-17mm is more traditional projection fisheye - it compresses the objects near frame borders (along radial direction) unlike rectilinear projection that stretches them. This means that central objects are much more detailed than objects closer to the borders. It also has very close minimum focusing distance so you can make artistic shots. Also the zooming ability allows to get shots that look more like rectilinear wide angle at 17mm end which makes it more versatile.
So, if you know you want Samyang 8mm (e.g. you need it to get detailed surrounding shots ONLY), get it. If not, you are more likely to prefer Pentax 10-17mm instead, unless you prefer 8mm's projection.
|
|
Forum: Pentax SLR Lens Discussion
09-29-2010, 05:59 AM
|
| |
Well if you already had 16-45 .. really, what exactly did you expect?
I think the main differences from zooms are
1. nice sun star effect at f/14. also almost no flares, zooms usually get plenty of them
2. maybe little less CA but perhaps it's sample variation.
3. perhaps less distortion but it's still not 0.
4. sharper perhaps but you need to use correct focus for that. if you focus on something in the middle with wide aperture, don't expect whole frame to be sharp.
oh and does dynamic range depend on lens? news to me ... i thought it's sensor only.
I've also got one a few months ago. Had mixed impressions too at first but after some experimentation I think I learned to use it, for landscapes at least.
In cloudy weather watch your shutter speed. Try 1/200 or faster.
I dont' know why exactly, but faster shutter images tend to be much sharper. Maybe it's related to shutter slap or image stabilizer, I don't know...
Also watch your aperture. Do not use f/4, it's very bad IQ. I think 1/5.6 is where it gets useful but maybe a bit wider is ok too, but definitely not f/4. Unless you don't care about sharpness of course, eg you use ISO 6400 or something.
Generally for landscape I use f/8 or f/14, I think it's about a sweet spot of this lens, it also draws much nicer light sources at f/14.
If you have to, increase ISO. I think ISO 320-500 is a norm for cloudy weather, and it still looks ok on my K-x. So don't hesitate .. and don't trust the camera - it will always set 1/50 shutter which is unacceptable. I just use Av and set ISO manually until I get desired shutter.
If I shoot in cloudy I usually set -1/3 EV correction so sky would not be overexposed (you can pull the shadows in PP). If it's sunny it's trickier though, sometimes you really need to make a few shots to get desired result... but it's not really lens related. Oh and if you want nice 14 ray star for a sun then you need to set f/14+ aperture and measure exposition on the sky... at f/8 it also produces star but with very thick rays and multi colored artifacts around the sun, which does not look very nice.
And another thing about focus. There is distance scale on the focus ring. Don't trust it for infinity. I compared MF using distance scale for my aperture to infinity, and the same shot with focus set all the way to infinity until it stops. The second shot was sharp across the frame, the first not sharp at edges. But in this frame all of the objects were really far so it might not work if there are closer objects .. I didn't yet figure which distance is acceptable for which aperture with full infty focus.
|
