|
Forum: Pentax SLR Lens Discussion
06-23-2013, 12:19 PM
|
| |
I only have experience with a Soligor 200mm F3.5 in M42 mount, also on a K10D. I think it is a re-branded Tokina RMC, there is definitely an almost identically looking Tokina with the same specs. The build quality is quite decent, and I got mine for less than 10 Euros. If you search a bit, then you will probably find a K-Mount version for not much more. However, sharpness is not great at 3.5, it becomes decent at F8. You probably need some post-processing (removal of CA and some sharpening) to make pictures taken at F3.5 look 'crisp'.
coon
|
|
Forum: Pentax News and Rumors
06-30-2012, 02:20 PM
|
| |
Yep, you are right, I completely skipped question 1 and tried to answer 2 only. If you then assume that everybody gives a rating = Pentax population mean + noise, then your standard error of the (sample) mean is given by the formula stdv(noise)/sqrt(N), if you have normal distributed noise (bell curve). Now we don't have normal distributed noise(=varying buyers experience) here, that's why I wrote "plausibility check". With respect to distribution independent tests (I assume the one you mentioned is one of those, I don't know it), I have no experience. But they all should give uncertainties in the same order of magnitude, if you don't have large outliers (and they couldn't vote <0 or >1000).
That much about theory. To my shame I must confess that I used 899 (which is the mean) for the standard deviation in my calculation, and this was indeed wrong. So to turn the argument around, having a statistically meaningful difference of 11 points in the mean for 810 (10% of the buyers) samples, the standard deviation in the noise must be significantly smaller than about 11*sqrt(810)=313. This is already the case for a uniform distribution between 0 and 1000 (stdv=289), probably not many people even voted with less than 500.
So yeah, right formula but wrong numbers... :o
coon
|
|
Forum: Pentax News and Rumors
06-29-2012, 09:57 AM
|
| |
But these 5% are equivalent to about 45 points (with a mean of 899 points). And the difference between Pentax and the industry standard is only 11 points or 1.24%. So not very meaningful.
I also did not calculate anything "correctly", I just applied the estimate 'uncertainty = mean/sqrt(N)', and that gives about 32 for mean=899 and N=810 (number of samples). It was more or less a plausibility check only.
coon
|
|
Forum: Pentax News and Rumors
06-29-2012, 08:29 AM
|
| |
Well, I don't want to spoil the fun, but with 8100 people participating and let's say 10% market share of Pentax, about 810 people who participated are not really enough to draw any conclusions. The uncertainties in the result are then about +/-32 points. Uncertainties for Canikon will be lower (higher market share), but the only real outcome seems to be that Panasonic gets ratings that are below the industry average. And they do not produce DSLRs (in the original sense, with movable mirrors inside...), do they? I can't really get rid of the feeling that this is another worthless survey result.
Hmm, now I did spoil the fun...
coon
|
|
Forum: Pentax News and Rumors
12-23-2010, 06:00 AM
|
| |
That's what I was asking myself as well. It seems to be rather long compared to the size of the rear element, in comparison with the da 12-24 (http://www.bdimitrov.de/kmp/lenses/zooms/_optics/12-24f4.jpg). The front element seems to be smaller as well, only about 2x the diameter of the rear element vs. ~3x for the 12-24. It's just speculation, of course, but if they built that lens with a length comparable to the 12-24, then it should be fairly small in diameter, maybe with a smaller filter size than 77mm as well, or maybe even with a rear element which is somewhat more recessed in the bayonet mount.
But maybe this is wishful thinking as well... ;)
coon
|
|
Forum: Pentax News and Rumors
09-01-2010, 05:17 AM
|
| |
Hmm, if that's true, then they could also make a 28/4 tilt-shift superrotator lens for 35mm with 13mm shift (ok, maybe a bit less due to tilt). The approx. 25mm difference in flange focal distance should give enough room for the mechanics if the rear element is not too far recessed in the 645's body.
It would allow to make a stitched 35MP image with ~15mm fov with a K10D, 50MP with K20D...:cool:
coon
|
|
Forum: Pentax News and Rumors
02-10-2009, 04:19 PM
|
| |
I just know some numbers from semiconductor industry (Intel etc.), but as CMOS for sensors shouldn't be much different from CMOS for CPUs and DRAMs, it should be more or less compareable.
What they have nowadays are 12'' waver. The costs for one waver are more or less the same, thus the more chips you get out of it, the lower the costs. Thus the costs of one chip is proportional to its area. Another effect is the probability of defects. They have a certain average number of defects per waver. You can calculate how many squares of a certain size in a circle with radius 6'' are lost, assuming a certain number of dust particles on the waver. If that number is small enough, the probability to loose one chip is proportional to its area as well. In the end costs are proportional to the square of area. Having a sensor which is 1.5*1.5=2.25 times larger than APS-C means that the costs are about 5 times as much.
coon
|
