Friday, April 11, 2008

Depth of Field and Stacking Close Photography

This is my first real post on photography. I'll try not to bore the crap out of you. (Oh, the pressure, the pressure.) Before I get rolling, though, I need to give you a splash of photography 101.

The two most basic functions of the camera are shutter speed and aperture (i.e., how big the lens opening is). Both control how much light gets into the camera, so in a way, they work against each other. For example, the faster the shutter speed, the larger the aperture must be to let in enough light. The slower the shutter speed, the smaller the aperture must be to keep too much light out.

The biggest factor in shutter speed is motion. If you are taking a picture of a racecar, you need a fast shutter speed to avoid blur. On the other hand, you might want a slow shutter speed to paint the movement of a waterfall. The thing to keep in mind, however, is that most people cannot hold a camera still below a shutter speed of 1/60 of a second. Therefore, unless you have a tripod, you can't realistically go much slower than that.

So, what about aperture? What the heck does that do? Well, the most important effect of aperture is depth of field, which in English means how much of the shot will appear to be in focus. According to some impressive formulas with funky mathematic symbols, the physics of light causes more of the picture to be focused when the lens opening is very small. Let me demonstrate.

These three pictures were taken with increasingly smaller apertures.

Here, only the middle blossom appears to be in focus and the background is very blurred. Large aperture.

With a smaller aperture, the depth of focus deepens and the background comes more into focus (actually, not a desirable thing if the background is distracting).

With even smaller of an aperture, most of the branch comes into focus, but the background is kind of busy.

As you can see, in close (macro) photography, the depth of field is very small. Who wants a gorgeous close-up of a flower where only a few specks of pollen are clear? Blech! So what do you do? Well, you could decrease the aperture like I did above to widen the field.

Well, not so fast. Unless your subject is very brightly lit, by the time you make the aperture very small, you will have to make the shutter speed too slow to handhold the camera. Add in some wind or entirely too much coffee, and you're screwed. Now what?

Well, you could add a flash to solve the light problem. However, the artful use of flash is whole other can of worms. I hate nothing more than a shot with heavy and harsh flash. It looks like the subject is a millisecond away from getting vaporized by an intercontinental ballistic missile.

Here is where stacking comes in. By keeping the aperture large (wide), you can isolate the subject from the background while creating an impossibly large depth of field. Using a tripod (sorry, you're stuck with one now), you inch the focus forward through the subject bit by bit in a series of photos. A stacking program then creates a composite image using only the clear portions.

Here is the process in action.

Note how the first photo is clear on the left, but blurry on the right. By the time you reach the 6th photo, the right is the clear side and the left blurry.

Now comes the fun part. Take these 6 otherwise pitiful pictures, and stack them with a program far smarter than I am. Voilà! You've done the impossible.

Okay, now you have some crazy mad tools. Go get stacked.


Geraldine said...

Thanks for these photography tips Jason, very interesting. I think that photography could be even more addictive than blogging, if a person could only find the time to really pursue it, in depth. I had a photographer friend (a seasoned pro) pay me a great compliment re: photography, many years ago. He told me that I had 'the eye' for being a great photographer, the technical 'stuff' anyone could learn,in time. It's a pursuit I hope to still find the time to devote to, and become really proficient at.

JaneyV said...

Thanks Jason! -That was so well explained I actually understood it. And at no point did it turn into blahdy blah blah which is what happens to me when I feel I'm being projected back to my physics class in university. That's a great talent. As well as the whole writing and photography thing - you're a great teacher too!

So now I have only my really mega-simple cheap camera to blame!

Sarah Hina said...

I second Janey's compliments--I took a photography elective in college, but your explanation cuts through the clutter (and by clutter, I mean those optical physics diagrams with all of those arrows...yawn). Very remarkable demonstration, too.

Thanks for the explanation! And for the beautiful progression. :)

SzélsőFa said...

Thank you for the description of the process!
What a useful little program you have!

Jaye Wells said...

Not boring at all. The last image is gorgeous.

ChristineEldin said...

Ditto everyone's comments!!
I understood all of it-your explanation was clear and concise.
Love the photos too!

iLL Man said...

All that made my brain hurt. I photograph by trial and error. Sometimes I get Jack S, other times it's Jackpot.

It's all good info, and well presented, but I'm stuck in my ways...........

As you can probably tell, I never read instructions........ :)

Beth K. Vogt said...

The pressure may have been on, but I followed your explanation aperture and shutter speed without wanting to bang my head on my keyboard just fine!
And the picture stacking--well, it looks like magic, but, thanks to your explanation, I know it's not.

katcampbell said...

Stacking is very cool. Is there anything software can't do? Great explanation.

jason evans said...

Geraldine, I really enjoy the photography element of this blog. Getting myself in situations for pictures is the tougher part, but when I do, I can get a lot of photos for later use. I have an archive built up now.

Janey, thank you for the compliment! I do enjoy teaching.

Sarah, I like that kind of laid back style of teaching. Probably not suitable for everything, but it seems to me that if a teacher doesn't see the knowledge as fun, the student won't either.

Szelsofa, I just sent you the link. Good luck exploring it!

Thanks, Jaye. I can't wait to use it on some of the forest critters.

Chris, anything cool in Dubai that you could capture?

Illman, whatever works for you is cool. Nothing wrong with organic, see-what-happens photography.

Beth, welcome! I love seeing new faces! It seems magical to me too. I can't imagine the mathematics going on behind the scene.

Kat, it seems like it must be a sophisticated process to do what the program does. I think the progression of focus from one side to the other is important. When I mixed up different, conflicting elements, the end result got very messed up.

anne said...

Excellent! Now... how does the software work, huh?! ;)

The Electric Orchid Hunter said...

That was a servicable primer, Jason, and much clearer and more fun to read than those complicated photography books. Great picture! I recently bought a Canon PowershotG9 to take on my upcoming Arizona roadtrip. I cannot wait to get out there and start experimenting!

Ello said...

Hey this is so cool! I love photography! Thanks for the lesson! And these were awesome pics! Ok so I just bought the aperture software for my niece who is a budding photographer and she loves it. Don't know what it does but i know she wanted it so I got it for her. I realized I didn't even know what aperture meant until you did this post!

Precie said...

Wow, that last pic is brilliant! And I never would have realized the effort and technique that go into that last pic without your explanation. I would just camera just doesn't do that.

Can we make requests? At some point, could you do some time-lapse stuff? :)