Category Archives: News

Shoot now, focus later?

Reading about some novelties in the camera world I stumbled upon the announcement of Lytro “light field” camera, promising to be a whole new revolution in photography. Now, there are new digital cameras coming out every other week, so what is it that makes Lytro any different from all the others?

Well, the novelty of the so-called “light field” cameras (as described by the company in the website) can be summarized in the punchline “shoot now, focus later”. That’s it, they are advertising a camera in which the focusing process can be postponed until the postprocess and even later. There is a gallery displaying some examples of what would this actually imply, here I reproduce one of them:

The novelty of this pics is that they can be refocussed on the fly by clicking on different spots of the image (try the to left corner to get close focus at the window and on the car to get distant focus). f this would work as advertised, this might indeed mean a great improvement on today’s cameras. I have seen quite a fuss about this announcement on several media, but I have to admit that I am a bit skeptical myself.

Why is that? Well, as a scientist (I do scientific research as a 9-to-5 job when I am not taking pictures) I am bond to be skeptical, so first thing I did after reading the announcement was going to Lytro’s website and checking out the science inside section.

I have to say there are a lot of buzzwords floating around there. The whole “light field” concept sounds more marketish than scientific, but let us blame that on aggressive marketing techniques and cut to the chase. The diagram showing how the whole thing works looks like this (image taken from the Lytro website):

What is wrong with this diagram? Well, nothing indeed. The fact is that this represents exactly how all cameras work. Camera lenses take in light coming from all angles within a range (given by their field of view) and making them converge into the sensor area to capture the light. Which is exactly what is depicted on the above diagram. What does the focus have to do with this? Well, the “focus” plane signals the part of the image that will be perfectly sharp. Actually, more than that plane will be focused; how much else will be focused will depend on the depth of field (maybe I will talk about this later) which depends on the focal length (or “zoom level”) and the lens aperture. Roughly, to wider aperture/longer lens will correspond a narrower depth of field (meaning that only a little portion of the picture will be focused and the rest will be blurred). Now, the whole depth-of-field and focusing phenomena are purely optical ones, they have nothing to do with the digital nature of the camera or the sensor itself.

There are ways in which we can trick this behavior, but before that let us go back to the sample image. If you click through it, you will notice that there are essentially only three different focus planes you can achieve by clicking on different parts of the image. If (as they claim) the new camera was capturing “all possible angles”, one might expect a smooth variation of the focusing plane, but this is not the case in any of the examples on their gallery. So my guess is that this whole “light field” technology doesn’t really involve much more than several camera sensors (maybe three or four) stacked together (maybe with angle-sensitive light reception) and perhaps a lens divided in parts to focus the light using a different focal length (and hence depth of field) for each of this sensors. If this is the case, the same effect could “easily” be achieved with a current technology DSLR if they added a “focus bracketing” option (i.e. by taking a burst of images with a different focus in each of them) similar to the “exposure bracketing” often used to produce HDR files.

Needless to say there would be an advantage to get all the focuses in a single image file, but if the camera works as I believe the whole business will be limited to three or four focal planes. A real “focus after you shoot” camera would be priceless for many kind of photographers (I can think of sports action, nature and wildlife, editorial and street photographers) in many situations in which one simply doesn’t have the time to fine tune the focus and must shoot with whatever the autofocus chooses. But a small number of focusing planes is not going to help moving the focus on a portrait to the model’s eye from the tip of her nose.

I might be wrong here, but by the explanations and the images shown in Lytro website I really doubt this “new technology” is that much of a game changer.

 

Disclaimer: I should mention that I haven’t tried a Lytro’s “light field” camera myself, so all that is written above is based on my impressions from the information available on their website and my knowledge of physics and optics, so it might be the case I am completely wrong. I would love if that was the case, but I won’t believe in this revolutionary technology until I get to try it by myself.