LumoLabs: Pentax K-5 low light focus study is published

Started Feb 23, 2011 | Discussions thread
janneman02 Forum Pro • Posts: 15,733
Real world meaning???

First of all, good work, thank you for the research but I do have a few questions....

falconeyes wrote:

LumoLabs: Pentax K-5 low light focus study is published

1. The K-5 as it presently ships indeed has a flaw in its phase detect autofocus module or software which causes it to front focus in low light below a lens-dependent threshold in EV.

I do not really understand lens threshold.... Is that at optimal exposure and does it change when , for example in night shootingI stop down to get the picture dark enough to be realistic.

For example next pic:

1/30s f/2.0 at 24.0mm iso1600

If I use "green button it wold get much brighter but in order to refelct teh situation I stopped down or used faster exposure to get a more real life view.

2. If it does, it seems to consistently focus ≈ 255 µm behind the sensor plane (although with a significant ± 75 µm scatter of results which is about twice as large as the normal scatter of result).

The 75 µm scatter is indeed significant, more that 1/4th. But that 255 µm, how much FF would that really mean in an image (ofcourse depending on FL but someone must know how much that is on a 31, 50, 100 or whatever mm FL.
Then we can use a DOf calculator etc etc....

3. Faster lenses seem to keep working in lower light but of course, are prone to more blur when the front focus does eventually happen. Slower lenses can already start to front focus at light levels metering as 4 EV or 6 EV even. A fast lens may work down to 0 EV in white light.


4. Light sources other than daylight emphasize this problem as they simply appear darker to the AF module. Moreover, it seems to be moderately color blind for red which further emphasizes the effect in deep tungsten light.

Mayb that explain that K-7 and K20D also hade FF or BF probs in certain sitiations I know???? (Actually in there my K-5 (stained version) did better than the others...)

5. The effect is real and can negatively impact the daily work of a photographer. On the other hand, it is possible to run into a low light tungsten situation without the problem.

shouldn;t that be "nightly" work?

Please, refer to the full study and accompanying material before discussion. I am available to answer questions. Enjoy the read

Oh man, I have enough reports of meetings and decisions to read now already....

The difference between genius and LBA is that genius has its

  • Janneman ( adaptation of the Kings quote from Albert Einstein)

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