Saturday, December 18, 2010

Focus Stacking

I feel like it is pretty self explanatory. If it isn't, well this post is for you. Its an explanation and some of my first examples.
So focus stacking, is as it sounds. Multiple images stacked, or merged, to form one with a greater range of focus than any individual image's range of focus. It is similar to HDR in the way that it compensates for limitations in equipment to show something that is not normally possible.

[unfortunately I broke a lot of links to images on my blog, and have lost these ones in particular, despite having been able to find almost all the other broken blog's images. Maybe a new focus stacking demo coming soon! November 2012]
In between the time of starting writing this post, and this point here, I endeavored to make a quick visual example of what focus stacking can do. Though not the best example, it will certainly give you an idea.  And as in almost all my photos, the most important steps lie is how you take your initial shots. Keep that in mind.


So in these three images, there are actually five component images. All made while camera was completely motionless on a tripod, fired with a cable release trigger.  On my Canon 50D with a 50mm prime. First image; as marked at f/1.8 focus on 'ultrasonic' for the 70-200f/4L's cap. Second image; focus on same location as first, but with aperture stepped up to 4.5 Still not an aperture that will get you a lot of depth. Third image; the combined product of three other images shot at f/9 with focus points lying in a different spot for all three.  Then taking only the best (aka sharpest) part of each photo to make the final composite.

Granted, with this particular image, its very possible I could have cranked the aperture up to f/22 or f/18 gone 'hyperfocal'.  That is beside the point. Now for a basic 'how-to' breakdown and a couple more examples. 

When looking through an optical viewfinder and changing your lenses focus, it is apparent that as a subject moves from in focus to out of focus, its size will vary and distort. I cannot go into detail about why that happens. It affects your 'focus stacked' image because although camera remains stationary, your objects will not sit flush on eachother indefinitely. This means some layer blending, opacity changing, and layer freeform distortion are necessary.  The amount of distortion you get can vary widely based on the amount of depth in your scene/subject and your focal plane's orientation to it.

In a stack of three images, I use the 'center focus' image as the base image. Use either one of the remaining two next. start with a 50% opacity and ensure that the most flush overlaps of the image lie between the center (or base) focal point and the one your working on now. Here is where you would apply a very slight, and precise distortion to line up your object's lines even better. After, apply a layer mask to this layer and make anything that is not more in-focus than the layer below it, invisible. Set the opacity back up to 100% Consider this layer finished. Lock it if you can. Now repeat this paragraph for your third and final image.

So where does this apply best? Mostly to macro photography and still life's. Basically anywhere you deal with long focal lengths, or are experiencing limits in your depth of field.  Also the process certainly doesn't lend itself to anything outside of tabletop photography very well. The first time I saw any focus stacked imaged was of a tarantula, and was so sharp, to a point that no ordinary lens, or processing could produce. This inspired me to learn more about it.  The images in here were all made today and my first attempts at applying focus stacking techniques.

My next application of this process I hope to do with a deep macro on either food or an insect. Considering its winter and insects are scarce, its likely going to be some food. All three photos in this post were done with a 50mm so a pretty average depth of field at that focal length, I will certainly be trying next in the 200mm area where the effects will be even more pronounced.


Enjoy


and I think hyperfocal distance is a good cousin of focus stacking to cover in a future post! look out for it