K10D & 21mm Limited Lens Low Light Focusing Issues

[Benjamin Kanarek]

In my last shoot and in conjunction with the K10D and the 21mm Limited lens using a particularly difficult lighting for the AF sensor, Many of my images were out of focus on the models face and sharp on her feet. This is what I determined...

The problem with my K10D after extensive testing, seems to be a question of extreme low light conditions I utilise when shooting. After testing both bodies and several lenses, I have determined that the problem I was having was the difficulty associated with focus detection under adverse lighting and off axis subject matter. I solved the problem (I think), by doing a clutched manual over-ride. In tests, I have had about a 90 percent success ratio. As a result, I'll be using the K10D's for my next shoot called "Diva" for "Style Monte Carlo" Magazine. I'll post once the images are ready. I will shortly post "Citizen K International" once the magazine officially comes out.

The problem with Pentax in France is that their tech people have just started their orientation with the K10D and will not be prepared to solve these issues immediately. I will have to wait a few weeks to send them all of my material for a thorough bench test. I am sure that my problems are not exclusive to myself. However, for a certain type of lighting I employ, it is very taxing on the existing technologies, i.e. very low output lighting and severe angles to the subject etc.

Best Wishes
Ben

[Asher Kelman]

Thanks Ben for sharing with us in almost real time!

This allows Kyle and others to test this too which is helpful for Pentax.

This camera is a major additional choice for the Professional and your dedication will help others work through temporary of other problems.

All tools have some limitations or quirks one has to know how to deal with and this appears to be no exception. However, this ability to deal with the issues separates the men from the boys!

Asher

[Kyle Nagel]

This problem existed on the istD* as well, only Pentax has improved it on the K10D to some degree. What was happening is that it was "hunting" for focus in low light situations. In low light it has a hard time finding focus and will spend too much time searching for focus. When it is in the 11 point focus mode (green focus mode) it would usually find focus quicker, but it would "see" something at maybe only one of the focus points, but not necessarily the main subject, and it was usually a closer object, which made the center of the field of focus at a portion of the image that was not what I wanted as my center of focus.

What I have now done is to set it to center focus mode, this makes it very easy when hand holding the camera to aim the center point on the spot I want at the center of my field of focus, then press the shutter halfway to lock focus (in dim light it may "hunt" a little) on that point, then I quickly re-compose the shot and fire, this only takes me a second and forces it to focus on the point I want. When shooting on a tripod I use the "select" focus point mode, and move the focus point to the spot I want to focus on.

To be honest I frequently go into manual focus and Hyper-focus my lenses when shooting subject matter that isn't moving toward or away from the camera, but these situations aren't generally low-light situations so it may not be a solution for this problem, however if you are working in an environment where the subject matter and the camera are in fixed positions it should still work well for low lit conditions.

Basically the low light focusing has always been an opportunity area for Pentax, I'm not sure if you have used their other DSLRs, but they are worse at this than the K10D. Since there appears to have been some improvement in the K10D it looks as if they are aware and trying to correct it, though they still have some work to do to get it just right.

I have noticed a friend with a Canon Digital Rebel has problems with it sometimes missing the correct focus point in low light as well, it doesn't "hunt" for focus as much as the Pentax, but I think Canon has some sort programming in the firmware that tells it to give up at some point in the process and take the picture at the best point of focus it could find, at least that is what appears is happening as I have watched her use it and looked at the results. In my opinion Nikon probably has the fastest and most accurate focusing system of these three, especially in these low light conditions we are discussing.

Which begs the question, wouldn't the K10D be the perfect camera with Nikon's focusing system and one of Canon's full frame sensors? The best of all worlds. :>)

Kyle

[Benjamin Kanarek]

"Which begs the question, wouldn't the K10D be the perfect camera with Nikon's focusing system and one of Canon's full frame sensors? The best of all worlds. :>)"

Kyle

In my meeting with Pentax, they said "This is what we all aspire to accomplish."

Ben

[Benjamin Kanarek]

"Which begs the question, wouldn't the K10D be the perfect camera with Nikon's focusing system and one of Canon's full frame sensors? The best of all worlds. :>)"

Kyle

In my meeting with Pentax, they said "This is what we all aspire to accomplish."

Ben

As I cannot upload samples, here is a link to view the graphic representation and here is the explanation of the Graph..
Here is a graphic representation of a typical type of lighting I use on occasion where the problem has cropped up. The Black area represents parts of the image that are very dark with no illumination. The Grey areas are parts of the image illuminated but not part of the main subject. The Green area is the lower portion or bottom of the subject and the Red could represent the face of the subject. This is more than a Graphic representation as it mimics the lighting conditions used during my shoots. As you can see, it challenges the AF sensor to only focus on the Red section. Also remember that I am shooting at the Red section from the floor at a distance of about 3 meters.

http://forums.photographyreview.com/showthread.php?p=193388#post193388