Photoclubalpha

The first and foremost - once again we get a lousy LPF and tons of false detail. Moreover, the 16Mp with weak LPF also produces a lot of extra 'grain' as spatial intermodulation components (spatial beat frequencies) between the natural photonic noise spatial distribution and the spatial density (frequency) of the sensor. (It's of the same nature as ugly hissing trebles you get at low sampling freqs with digital audio.) That false grain shows too much even at the low ISO and well into bright midtones; it even may cause shiny objects to look somewhat matted.
The problem may be overcome with special demosaicing and/or noise processing, and I understand that Nikon does it for the D7000 files with NX2. But Lr/ACR processing takes too much NR to kill that false grain. This problem is common between a55/a580 and the D7000, the Pentax K-5 seems much better in that regard.

The second problem that's also common between a55/a580/D7000/K-5 and the a33 - there's too much purple fringing under certain conditions. That fringing seems to result from secondary reflections between the sensor/microlenses surface and the IR filter, and it is very sharply defined geometrically; and it is at that different from the normal purple fringing that happens (I believe) due to reflections between sensor wiring and the microlenses and is more shapeless.
The examples of that fringing/ghosting can be seen in these IR raw samples for a55/D7000 - http://216.18.212.226/PRODS/AA55/FULLRE ... 001003.ARW http://216.18.212.226/PRODS/D7000/FULLR ... 001003.NEF . You may find there the samples for other cams mentioned here too. (Btw, the Canon 60D is nothing better at that. It's so quite interesting that Sony has recently filed a patent application where they put the IR filter onto the SLT mirror - no more fringing of that particular type!)
Below you may see an inflated and somewhat exaggerated crop showing the problem quite clearly -

I'm not real sure what all that stuff means but it must be good because these cameras take some very good looking photographs.

well I'm not likely to be peeping so closely at my pixels,thank god

My Tamron 70-200 2.8 "fringes" like crazy on A55, while it was great on A900.
70-300G is much better though, almost no fringing.

All kinds of purple fringing depend the most on the exit pupil distance and the aperture value. Longer exit pupil distance and smaller apertures make the flux hitting the sensor more collinear, but the exit pupil distance is more important here.
It generally means that a physically long lens should cause less fringing, as the lens length normally goes along with the exit pupil distance; though that's not necessarily connected directly.

And the a55 is no worse at fringing than the a580/d7000/k-5/60d are - there's just some common modern design trend affecting that particular property of those cams.

Does the length of a lens hood for example affect the exit pupil didtance? what I mean is does the exit pupil have to be a glass element?

Javelin wrote:Does the length of a lens hood for example affect the exit pupil didtance? what I mean is does the exit pupil have to be a glass element?

Optical experts may have a better explanation, but exit pupil distance would only be affected by zoom setting (on zoom lenses) lens construction and focus distance. Assuming a single lens. Various lenses have differing exit pupil distances based on their construction and flange distance.

A lens hood will have no bearing on any of this - unless it severely vignettes the lens.

Dusty

supernovak wrote:My Tamron 70-200 2.8 "fringes" like crazy on A55, while it was great on A900.
70-300G is much better though, almost no fringing.

I got to test the Tamron on the Canon 50D which had fairly high res on a small sensor - that's why I didn't buy it. The Sigma at the time was maybe not as 'crisp' but also was free from wiry edges and colour fringes.

David

The lens hood can have no effect on the exit pupil diameter and distance, the exit pupil is at the rear of the lens and will remain the same even if you put a small hole in front of the lens instead of a lens hood.

David

Dusty wrote:

Javelin wrote:Does the length of a lens hood for example affect the exit pupil didtance? what I mean is does the exit pupil have to be a glass element?

Optical experts may have a better explanation, but exit pupil distance would only be affected by zoom setting (on zoom lenses) lens construction and focus distance. Assuming a single lens. Various lenses have differing exit pupil distances based on their construction and flange distance.

A lens hood will have no bearing on any of this - unless it severely vignettes the lens.

Dusty

We were mentioning somewhere else on this forum that a55/33 probably had no IR filter...

Doc, had there been no IR filter, you IR remote LED would appear about 8-10 stops brighter in the image captured

AFAIK the Leica M cameras use a very weak IR-filter on their sensor because of their compact built. They use optional lens IR-Filters when the IR light is distracting. How does it look like, when IR-light is captured in a normal colored photo (e.g. from a light bulb)?

Neonsquare wrote:AFAIK the Leica M cameras use a very weak IR-filter on their sensor because of their compact built. They use optional lens IR-Filters when the IR light is distracting. How does it look like, when IR-light is captured in a normal colored photo (e.g. from a light bulb)?

The Dimage 7 had a weak IR sensor. The biggest issue was identified on some forums was that black clothing appeared brownish under stage lighting. (That little black dress and black tux didn't look so nice.)

I'm not sure if other issues were noted.
tom

Please, forget about 'weak' IR filters. Below are the images made with a55 and Nex. Now imagine what it would look like if that were the red LED light...

I've noticed some outrageous purple fringing with some of my lenses on the NEX-5.