Web Analytics RiceHigh's Pentax Blog: When the Diffraction Limit is Reached..

Sunday, July 31, 2011

When the Diffraction Limit is Reached..

First see the Physics formulae for the calculation:-

http://egami.blog.so-net.ne.jp/2011-07-11

After all, the following is obtained for the Diffraction Limits, against different F-numbers (for 550nm Green light):-

F-number
[f/]
Resolution [μm]
1.00.67
1.40.94
2.01.34
2.81.88
4.02.38
5.63.76
8.05.37
117.38
1610.74
2214.76
3221.47

So, just say that the Diffraction Limit at f/2.8 is in 1.88um, which means that the pixel pitch size of the sensor have to be larger than that limit in order to avoid resolution loss owing to diffraction. Now, let's look back at the pixel pitch size of the Pentax Q sensor, which is in 1.55um only, that means that a faster lens with a larger aperture has to be used. In this case, a f/2.0 lens could just make it.

Btw, with that small sensor size and hence pixel pitch, what miracle should we expect? Will it work against the Law of Physics? And, should the Q user stop down the lens when shooting outdoor under brighter environment? But then the resolution will be decreased and Image Quality suffers.. And most importantly, we all knew that optics are not in optimal performance when used near wide opened. Besides, how about when the "02" kit zoom is used? In fact, it is just too slow and has gone beyond the diffraction limit by one to 2.5 f-stops already even when it is used wide opened! :-o


Related:-

Comparison of Sensor Specifications

When the Sensor Outresolves the Lens.. (How Meaningful is a 24MP APS-C Sensor?)

Comments (6)

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calculation that for a K7 with 4672 Pixel on a length of 23,4mm would mean a 5µm Pixel size - and according to the list above taht all apperatures smaller than 8 would have the same problem at a current DSLR. This is not in line with the practial experiences.
1 reply · active less than 1 minute ago
Various different lens resolution tests on APS-C DSLRs do have already verified that f/8 is the turning point where the resolution starts to decrease owing to the diffraction effect.
But will people using the Q notice the diffraction on a 6*4 (150*100) print or on a computer monitor notice it? Probably not.
This diffraction problem is so serious for 1/2.3 sensor size camera that nobody has bothered to try to make a serious hobbyist camera with such a small sensor. This Q is a toy, a very expensive toy that those who have more money than photography knowledge.
1 reply · active 710 weeks ago
Yes, if this toy is not sold at that very high price, it would be somehow more acceptable.
Probably why they include an ND filter in their lenses, so you can use wide apertures in high light levels.

ChrsJ

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