Understanding dof Part 3:Focus Stacking

So we know about hyperfocal distance. But what happens when we are close to an image?  Here is an image of an old speaker. I wanted to get the top face in focus. My settings were ISO 400 f32 and 1/6 sec exposure with my 90mm lens.

Image taken at f32

No editing was done with this image. As you can see, the image has good depth of field but the back of the speaker is a bit soft. I cannot dial in more aperture and I don't really want to have the decking totally sharp. So what is a solution? Yeap - focus stacking.

Photographers, both landscape and macro, often use focus stacking to enhance the sharpness. The reasons for using this method include:
1. When we stop the aperture all the way down (f32 etc), dof increases but lenses suffer from diffraction causing a loss of sharpness.
2. Poor light but good dof is still needed.
3. Artistic reasons to use the aperture wide open (say f1.2) and play with focus and blur with other elements in a scene.

If you are going to focus stack, then in the field remember:
1. Use tripod to keep the scene fixed.
2. Set your exposure
3. Take several shots from near to far where only the point of focus is changing.

All we are really doing is creating a smaller dof by using say f4 or f8 and overlapping these windows of sharpness to cover the scene in question. Then in post processing (say in Photoshop) we blend them together to create 1 sharp image. 

Going back to the speaker, I used f8 ISO 400 and 1/80 and took a series of images where the front, the middle and the rear of the speaker were respectively in focus. After blending the images, here is the result.

The grill is sharp all the way to the back.

Here is how I used Photoshop (CS6).
1. I shoot in "raw" so I opened each image and saved as a tiff. I used meaningful names like near.tiff, mid1.tiff, mid2.tiff, far.tiff
2. To open all of the images so that each layer in photoshop is one of these images simply: File -> scripts -> load files into stack then find and select your images.
3. Once all of the images are loaded, you will see the image names as a new layer. (giving a decent name to the image makes sense now :-)) highlight each layer. Now we need to align then. Edit -> auto-align layers.   At this point make sure all geometric corrections are deselected.
4.  Once aligned we get Photoshop to blend them to create one sharp image.... Edit -> auto-blend layers choose the "stack images" option and the "seamless tones and colors" option.
5. Sit and wait.

Don't forget to save your image :-)

load the images into a stack

choose files to add

highlight layers before aligning

align layers

make sure to turn off all corrections

after aligning it is time to auto blend

after PS has gone to work we get a blended image

deselect layers to see the composition of the blended image

have fun! ☺

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Understanding dof Part 2: Time to go Hyperfocal

I think that when the auto focus was a feature of a camera lens more than twenty years ago, a great many photographers never got to understand depth of field and hyperfocal distance.

Take this quick true or false test to see how you go.

1. The only way to have an object in focus is to use the auto (or manual) focus to focus on it.
2. The depth of field does not change with distance from the object.
3. The depth of field does not change when you focus on different parts of a scene.
4. The only way to ensure everything is in focus is to use the largest f-stop possible eg f29, f32 etc, and use a tripod.

How did you go, here are the answers: False, False, False, False ....

let me clarify all this for you.

We know that the depth of field depends on three things: 1. focal length of the lens your are using (17mm, 40mm, 70mm, 90mm, 200mm etc) 2. Where we focus within the scene ie the distance this object is away from us. 3. The aperture setting we have set ie f4, f8, f16 etc.

With today's cameras having auto zoom and auto focus, it is no wonder why it is easy to forget about depth of field (since the dof is changing as we zoom in as well as what we focus on).

Imagine that for a given lens (say 90mm)  it has a "window" of sharpness. When I point at a spot and focus, there is a window of sharpness around this spot. The size of the window (aka dof) will depend on how near or far the spot is from me as well as the aperture setting.

Here is a table of distances (in feet) for my 90mm lens

 

Distance to Subject		f/4	f/8	f/16
10 feet		9.6-10.5	9.2-11	8.5-12
50 feet		41-64.5	34.5-90	26-490

 
A couple of things stand out:
1. As the f-stop increases the window (aka dof) grows.
2. The further into the scene I focus the greater the dof.

 My question now is, what is the distance I need to focus at within a scene to get the biggest possible dof? That distance is called the hyperfocal distance. 

 Here are the hyperfocal distances (in feet) for my lenses.   

 

Lens: 17mm		f/4	f/8	f/16
Hyperfocal distance		8	4	2
	dof	4- ∞	2- ∞	1- ∞

 

Lens: 40mm		f/4	f/8	f/16
Hyperfocal distance		44	22	11
	dof	22- ∞	11- ∞	5.5- ∞

 

Lens: 70mm		f/4	f/8	f/16
Hyperfocal distance		134	67	34
	dof	67- ∞	34- ∞	17- ∞

  

Lens: 90mm		f/4	f/8	f/16
Hyperfocal distance		220	110	55
	dof	110- ∞	55- ∞	28- ∞

 

Lens: 200mm		f/4	f/8	f/16
Hyperfocal distance		1094	547	274
	dof	547- ∞	274- ∞	137- ∞

Some things to note:
1. With a 40mm lens, you can get infinite dof with f16 if you focus 11 feet from you.
2. When focusing at the hyperfocal distance, the dof starts half way between you and the focal point and extends to infinity. Now that is cool!!
3. fast zoom lenses are cool bis of glass but they dont give us much dof.
4. Since there is a nice pattern in the data, I just remember the hyperfocal distance at f/4 for each lens and go from there.

The final part to this study on depth of field will look at how to create super sharp images with deep depth of field when we are close to an image, or the lack of light means we must use a small f-stop say f4 or if our lens gives too much diffraction at large f-stops (f22, f29, f32 etc) but we still need a sharp image with large depth of field.

 If you want to know the hyperfocal distance of your lens, here is a cool calculator I use. hyperfocal calculator

 have fun! ☺  

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Texture ...

When was the last time you took a photo that had real texture?

Taking photos with texture is all about the time of the day: the angle of the sun and the strength of the sun's rays. Shallow angles dancing across a rough surface can bring out the texture. Just watch you don't over expose the shot as the shadows are needed to create depth to the texture.

have fun! ☺

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Movies and Munchies

I was watching I am Legend recently, I love the introduction to the movie where the character played by Will Smith is driving his red Mustang through the streets of NY. Many different perspectives were used with cool effect.

This also got me thinking about when I grab some fast food. When choosing from the menu, we are looking at the work of some of the best food photographers in the business. Studying how they compose their images and emulating some of those elements when we compose images with people etc will raise our standard.

The world is a visual place, and gifted photographers and cinematographers enhance our experience. Studying their work whenever we see it will make a difference to our own work.

Here are two quick shots using my phone to show you the difference.   Yes the chips tasted so good!


  

have fun!  ☺

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Is your camera a hammer or a scalpel?

Look at a scene, point the camera and shoot... and you  probably have a reasonable image. But you have just used the most expensive hammer you own. Did you set the exposure yourself? Did you set the white balance or use AWB? Did you know what parts of the scene were in focus and what wasn't? Did you move yourself into a better position or shoot from a different angle or perspective? Have you ever taken a shot whilst lying down?

Have fun taking the time to learn how to use your camera as a scalpel, artistically removing unwanted elements from a scene to reveal the beauty you saw subconsciously. Here are some ideas to get you started:

1. Learn how to adjust the focal length of each lens you own to control the depth of field in a scene. You can practise this by shooting along the railing of a staircase.

2. How does the perspective of a scene change when you crouch down or lay down? How about experimenting with images that are taken from waist height only?

3. If you usually take big picture shots, how about experimenting with small scale images.

4. Find a scene with a large tonal range and explore black and white photography.

5. Take a  risk and turn your camera off manual. Set the time for an exposure and play with the ISO and focal length to see what happens.


Here is a shot I took - the subject matter is a little left of center. After thinking for a while I decided to turn these sweet potatoes into a conversation, so I worked hard to make sure that only the middle part of the scene was in focus and hopefully the result is the viewer focusing in on this  "conversation".

I would love to hear how you went with your project.


have fun :-)

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Should your images be on a diet?

Less is so much more.

I recently spent a week working on a project. Every day I would shoot with the early morning light and the late afternoon light, all for really one or two images. I didn't have a clear vision of how I wanted it to look, only how I wanted it to feel. I shot hundreds of images, thinking about the light, the shadows, where the focus should be and the narrative. After a week of shooting, I realized something: my story was not clear, but rather too muddled. I tried to do too much with the images, or I had elements in the shot that detracted the viewer from the story. So I put my images on a diet: paired them down, used simple elements, gave my story more clarity by getting closer. Guess what? I got a better result.

Do your images need to be on a diet too?

have fun :-)

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