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Thread started 17 May 2011 (Tuesday) 22:32
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Why do I need a DOF calculator

 
dharrisphotog
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May 17, 2011 22:32 |  #1

Saw this on the app store for my iPhone/iPad. Why would one use this? What scenarios?


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krb
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May 17, 2011 22:40 |  #2

You would need one if you wanted to know what parameters would give you the DOF you want for a given shot.


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TuanTime
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May 17, 2011 22:42 as a reply to  @ krb's post |  #3

If you're referring to the app I'm thinking of it also gives you the hyperfocal distance as well. Really useful in landscape photography as a quick reference.

Of course the seasoned photogs would argue you should just know... but my memory of these things seem to fleet me at times that I need it.




  
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krb
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May 17, 2011 22:47 |  #4

TuanTime wrote in post #12430713 (external link)
Of course the seasoned photogs would argue you should just know...

I've never met a "seasoned photog" who would have claimed that, but I've met plenty of them who have said that the tables (or an app to calculate the info) are very good tools to have available.


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dharrisphotog
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May 17, 2011 23:05 |  #5

Ok, but how does one figure what kind of DOF he wants? Sometimes, all I know is "I want a blurry background, so f/2.8...


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Bendel
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May 17, 2011 23:17 |  #6

Razeus wrote in post #12430878 (external link)
Ok, but how does one figure what kind of DOF he wants? Sometimes, all I know is "I want a blurry background, so f/2.8...

Then there isn't anything else to figure out...One example of where you'd want a DOF calculator is if you were taking a picture of a landscape with something in the foreground for framing purposes. If you want both the foreground and background in focus, you would use a DOF calculator to figure out the aperture you need. You could always guess, but with the decease in image quality as you stop down you want the largest aperture possible to get the job done.


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hfgarris
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May 17, 2011 23:32 |  #7

So ... why don't the camera designers include a DOF calculator on the display screen? :confused:

They can read all the required inputs from the camera settings (you may have to perform a auto-focus half-press, but that is easy) and then display the results on the display screen. I think this would be more useful than having to dig out my phone, iPod Touch, or iPad and enter all the settings manually to see the DOF.:D




  
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Bendel
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May 17, 2011 23:36 |  #8

hfgarris wrote in post #12431030 (external link)
So ... why don't the camera designers include a DOF calculator on the display screen? :confused:

They can read all the required inputs from the camera settings (you may have to perform a auto-focus half-press, but that is easy) and then display the results on the display screen. I think this would be more useful than having to dig out my phone, iPod Touch, or iPad and enter all the settings manually to see the DOF.:D

Because how would the camera know what you want to be in focus? There is no quick way to enter a number into your camera...using the dials would take forever.

Besides, they already do. It's the depth of field preview button.


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May 17, 2011 23:45 |  #9

Bendel wrote in post #12431051 (external link)
Because how would the camera know what you want to be in focus? There is no quick way to enter a number into your camera...using the dials would take forever.

Besides, they already do. It's the depth of field preview button.

I would center-spot focus, half press the shutter release to lock in the distance, then check the display which would tell me the focus range around the focus point for that lens length setting at the exposure aperture value or setting.




  
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krb
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May 18, 2011 00:11 |  #10

Razeus wrote in post #12430878 (external link)
Ok, but how does one figure what kind of DOF he wants? Sometimes, all I know is "I want a blurry background, so f/2.8...

What happens if you are using your 85mm to shoot close-up portrait from 5 feet away? Is f/2.8 going to give enough DOF to keep the whole face sharp?


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May 18, 2011 00:58 |  #11

The intriguing thing about DOF calculators is that it assumes that you know the distance to the subject with some degree of accuracy...but AF lenses have so few distances indicated on the distance scale that true accuracy in DOF calculated is often a wasted effort!


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May 18, 2011 08:11 |  #12

I think they are most useful for when you are trying to MAXIMIZE depth of field for a given situation, such as with landscape, architecture, or macro photography. Modern AF lenses usually have an accurate enough focus scale at the close end for this to be very easy.

Also possible, but slightly less useful due to our crappy focus windows, is as mentioned above - a ballpark estimate to know if you have roughly the amount of DOF you need to keep an entire face or entire body within the focus plane.


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May 18, 2011 08:46 |  #13

MNUplander wrote in post #12432618 (external link)
I think they are most useful for when you are trying to MAXIMIZE depth of field for a given situation, such as with landscape, architecture, or macro photography. Modern AF lenses usually have an accurate enough focus scale at the close end for this to be very easy.

Unfortunately all too easy to disprove the utility of the few distances we have marked on the lens. Using two lenses as examples, on Tamron 28-75mm the longest marked distance is 7', on Canon 17-55mm the longest marked distance is 5'...

  • at 28mm and f/4 the hyperfocal is 14.5' and at f/11 is 41' for the Tamron, while
  • at 17mm f/4 the hyperfocal is 15' and at f/11 is 5.4' for the Canon.
So in only one of those four situations are we capable of reasonable use of hyperfocal. The other three require guessing about where to focus, and while 15' is a distance for a reasonably good guess, many folks are pretty poor (notice how often folks leave a space wasting one-car length gap between them and the car in front of them at the stop light, rather than 3-5'!)

... wrote:
Also possible, but slightly less useful due to our crappy focus windows, is as mentioned above - a ballpark estimate to know if you have roughly the amount of DOF you need to keep an entire face or entire body within the focus plane.

Fully agree with this statement, that a mental ballpark estimate is what many veteran users now rely upon for the most part. "large aperture = shallow DOF, , middle aperture = moderate DOF, small aperture = deep DOF" is the mental model in the absence of DOF scales (zooms) and with poor AF distance scales.
Using 17mm FL, the 10' subject distance the DOF zone is 11' at f/2.8, is 132' at f/5.6, and is Infinite at f/11..."large aperture = shallow DOF, middle aperture = moderate DIF, small aperture = deep DOF" :)


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May 18, 2011 08:49 |  #14

So what is the short cut? :-)


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dharrisphotog
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May 18, 2011 10:24 |  #15

krb wrote in post #12431209 (external link)
What happens if you are using your 85mm to shoot close-up portrait from 5 feet away? Is f/2.8 going to give enough DOF to keep the whole face sharp?

Trial and error.


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Why do I need a DOF calculator
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