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### AuthorTopic: Depth of field, f-stop and focus point  (Read 8042 times)

#### richarddd

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##### Depth of field, f-stop and focus point
« on: March 15, 2013, 01:41:58 PM »

How exactly do you decide where to focus and what f-stop to use, especially when you want lots of DOF, for example for a landscape?

I'm interested in what people actually do in the field, rather than underlying theory or a link to an article showing someone else's technique.

Assume shutter speed and ISO are not concerns (e.g., on a tripod with a stationary subject). Assume we all know the basics of DOF. Don't forget diffraction.

Alternatives include

1) Guess, shoot, chimp with magnification, adjust, repeat. A 3" LCD isn't the best viewer, but it's what you have.

2) Use rules of thumb, such as focus 1/2 or 1/3 of the way into the scene and use something around f/11 or f/16 for deep DOF. This could be the main method or a first step in method (1).

3) Use a DOF calculator (readily available on most smartphones).  Limitations include estimating distance (just what is 60m away) and determining an appropriate circle of confusion (calculator defaults may not be appropriate for your purposes)

4) Use Merklinger's method: focus at infinity (or the furthest thing you want to be sharp), decide the size of the smallest near object you want to be identifiable, divide focal length by that size (in mm), result is f-stop.  For example, if you are shooting at 22 mm and want a 2mm near object to be identifiable, shoot at f/11

5) Other

#### RFPhotography

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##### Re: Depth of field, f-stop and focus point
« Reply #1 on: March 15, 2013, 03:31:45 PM »

Would hyperfocal fit into your 'Other' category?
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#### David Sutton

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##### Re: Depth of field, f-stop and focus point
« Reply #2 on: March 15, 2013, 05:17:33 PM »

I decide on the day where my priorities lie. To some extent it's often a trade-off between sharpness, DOF, dynamic range and so on. Normally I would decide what points I want sharp and make an image at each point at between f/8 (my sharpest aperture) and f/22. I find problems with diffraction overrated. At f/22 I need to use deconvolution sharpening, which is another step and makes for a more complicated workflow, but the results are almost identical to f/8.
After that I focus blend. Having three or four layers with different focus points allows me to more closely match what I saw. It allows the subject to be sharp, but extraneous detail in the same focus plane to be subtly defocussed. Which is how my eyes work.
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#### Slobodan Blagojevic

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##### Re: Depth of field, f-stop and focus point
« Reply #3 on: March 15, 2013, 05:54:42 PM »

#2 (assuming that the main point of interest is within that range too).

Front-to-back absolute sharpness is overrated. It is actually more natural-looking that very near and very far objects are slightly out of perfect focus. That is why it is beneficial to have lenses with nice bokeh: even when they are more than slightly out of focus, they tend to deliver pleasing rendering.

Besides, when in the field, I prefer to try to "feel" the place, breath the air, listen, sense, etc., rather than fiddling with numbers, theories, apps, etc. Otherwise, I would have become a topographer, not photographer

When I was shooting medium format film with prime lenses that had hyper-focal inscriptions, I would use the next f/stop on that scale, just to be safe (i.e., if shooting at f/16, I would use f/11 hyper-focal markings on the lens).

#### richarddd

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##### Re: Depth of field, f-stop and focus point
« Reply #4 on: March 15, 2013, 06:02:13 PM »

Would hyperfocal fit into your 'Other' category?
In my case, it would fall into the DOF calculator category, since I don't have distance scales on any of my lenses and usually can't do the calculation in my head.

#### dhancock

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##### Re: Depth of field, f-stop and focus point
« Reply #5 on: March 15, 2013, 06:06:53 PM »

Having a DSLR, if I want front to back sharpness, I set the aperture at f/22 and adjust the shutter speed while looking at the camera's estimated exposure guide in my viewfinder. Then, I check the photograph and histogram on the LCD for underexposure/overexposure; if necessary, I'll repeat. Unless I have a massive scene, setting my focus near affinity with the f/22 aperture normally works. At night, I pull out my charts for better focus accuracy and larger apertures.
« Last Edit: March 15, 2013, 06:09:07 PM by dhancock »
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#### richarddd

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##### Re: Depth of field, f-stop and focus point
« Reply #6 on: March 15, 2013, 06:09:26 PM »

#2 (assuming that the main point of interest is within that range too).

Front-to-back absolute sharpness is overrated. It is actually more natural-looking that very near and very far objects are slightly out of perfect focus. That is why it is beneficial to have lenses with nice bokeh: even when they are more than slightly out of focus, they tend to deliver pleasing rendering.
Having far objects out of focus is sometimes a useful depth cue.  http://en.wikipedia.org/wiki/Aerial_perspective I often see this in landscape paintings.

On the other hand, there's often enough haze or just atmosphere between the front and a far subject in the back that it's at least a bit out of focus no matter what we do.

Besides, when in the field, I prefer to try to "feel" the place, breath the air, listen, sense, etc., rather than fiddling with numbers, theories, apps, etc. Otherwise, I would have become a topographer, not photographer
That can be a general concern with photography, especially if you have a heavy tripod and a bunch of lenses. On the other hand, few non-photographers get up to watch the sunrise.

When I was shooting medium format film with prime lenses that had hyper-focal inscriptions, I would use the next f/stop on that scale, just to be safe (i.e., if shooting at f/16, I would use f/11 hyper-focal markings on the lens).
I used to do the same with film SLRs.

#### richarddd

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##### Re: Depth of field, f-stop and focus point
« Reply #7 on: March 15, 2013, 06:14:25 PM »

Having a DSLR, if I want front to back sharpness, I set the aperture at f/22 and adjust the shutter speed while looking at the camera's estimated exposure guide in my viewfinder. Then, I check the photograph and histogram on the LCD for underexposure/overexposure; if necessary, I'll repeat. Unless I have a massive scene, setting my focus near affinity with the f/22 aperture normally works. At night, I pull out my charts for better focus accuracy and larger apertures.
Using f/22 for deep DOF seems reasonable and is much easier than worrying about fine tuning (I had assumed away exposure issues; I prefer blinkies to histograms, but that's going off-topic).

Some would say diffraction can be a problem at f/22 and that you usually can get enough DOF at a slightly smaller aperture. I tend to ignore that thought.

Where do you focus - infinity, 1/2, 1/3, somewhere else?

#### elf

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##### Re: Depth of field, f-stop and focus point
« Reply #8 on: March 15, 2013, 11:11:23 PM »

Is there any DSLR that isn't heavily into the diffracted zone at f/22?
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#### ErikKaffehr

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##### Re: Depth of field, f-stop and focus point
« Reply #9 on: March 16, 2013, 02:25:27 AM »

Hi,

Diffraction is a function of aperture, nothing else.

Same for Holga or Leica.

The more you have the more do you have to loose. Sharpening can recover much of the sharpness lost to diffraction.

This is a practical study I made:

http://echophoto.dnsalias.net/ekr/index.php/photoarticles/49-dof-in-digital-pictures?start=1
http://echophoto.dnsalias.net/ekr/index.php/photoarticles/49-dof-in-digital-pictures?start=2

Best regards
Erik

Is there any DSLR that isn't heavily into the diffracted zone at f/22?
« Last Edit: March 18, 2013, 12:35:01 AM by ErikKaffehr »
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#### Petrus

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##### Re: Depth of field, f-stop and focus point
« Reply #10 on: March 16, 2013, 04:49:34 AM »

I think we are carrying too much film era thinking with us here. When shooting expensive film there was a need to calculate ideal focus and exposure for the one shot. If we do not know the ideal values, we can now bracket focus, F-stop and exposure much faster and costing nothing, than calculating the theoretical values. Simply pick the best looking frame at home and delete the rest...
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#### scooby70

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##### Re: Depth of field, f-stop and focus point
« Reply #11 on: March 16, 2013, 08:30:51 AM »

I very rarely use extremely small apertures for front to back DoF and if the DoF is going to vary I'd prefer it to vary into the distance. Mostly I focus on what I want to be in focus and pick what I think is a suitable aperture for the effect I want. Sometimes I like DoF to gently drift into the distance but sometimes I want DoF to be more obviously thinner.

I'm not a great user of DoF tables and in the field I think I'd rather use the Merklinger method than refer to DoF tables.
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#### RFPhotography

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##### Re: Depth of field, f-stop and focus point
« Reply #12 on: March 16, 2013, 09:17:57 AM »

If you're worried about getting maximum depth of field and minimising diffraction, you may also be able to do focus stacking.

Merklinger claims that all of the work to use his method requires no math, no tables, etc.  I'm not quite sure I see it being as simple as he makes it out to be.  Focusing at the furthest point where you want sharpness is fine.  But figuring out what aperture to use to get the closest object desired sharp doesn't seem as simple.  You need to know the size of that near object and how its true size will be translated onto the sensor.  To me, that's not a simple thing to figure out.  It seems that you need to know the size of the object, the distance to the object and the magnification ratio of the lens at that distance.  Oh, and the 'focus error' which I don't know how to determine with any manner of simplicity.
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#### scooby70

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##### Re: Depth of field, f-stop and focus point
« Reply #13 on: March 16, 2013, 12:34:16 PM »

If you're worried about getting maximum depth of field and minimising diffraction, you may also be able to do focus stacking.
I'm not worried

Merklinger claims that all of the work to use his method requires no math, no tables, etc.  I'm not quite sure I see it being as simple as he makes it out to be...

It's simple and much easier than trying to memorise DoF tables but not as simple as pulling a DoF table out of your pocket What he says is... divide the focal length by the size you want to resolve to determine the aperture. So, if we have a 50mm lens and want to resolve a 3mm blade of grass we divide 50 by 3 and get an aperture of... call it f16.

It isn't perfect end neither are DoF tables but much of the time it'll do.
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#### Fine_Art

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##### Re: Depth of field, f-stop and focus point
« Reply #14 on: March 16, 2013, 02:29:50 PM »

If you're worried about getting maximum depth of field and minimising diffraction, you may also be able to do focus stacking.

Merklinger claims that all of the work to use his method requires no math, no tables, etc.  I'm not quite sure I see it being as simple as he makes it out to be.  Focusing at the furthest point where you want sharpness is fine.  But figuring out what aperture to use to get the closest object desired sharp doesn't seem as simple.  You need to know the size of that near object and how its true size will be translated onto the sensor.  To me, that's not a simple thing to figure out.  It seems that you need to know the size of the object, the distance to the object and the magnification ratio of the lens at that distance.  Oh, and the 'focus error' which I don't know how to determine with any manner of simplicity.

That is the long lost art of pressing the DoF preview button with manual focus.
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#### RFPhotography

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##### Re: Depth of field, f-stop and focus point
« Reply #15 on: March 16, 2013, 09:31:17 PM »

Scooby, there again, you have to know the size of the object you want rendered sharp.  And what if that object is 4' long?  That doesn't seem to fit into the equation.

Fine_art, the issue with DoF preview; and you don't need manual focus to use it, is that at higher f-stop values it becomes very difficult to see what's in focus and what isn't because the viewfinder becomes too dark.
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#### Fine_Art

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##### Re: Depth of field, f-stop and focus point
« Reply #16 on: March 16, 2013, 10:50:19 PM »

Scooby, there again, you have to know the size of the object you want rendered sharp.  And what if that object is 4' long?  That doesn't seem to fit into the equation.

Fine_art, the issue with DoF preview; and you don't need manual focus to use it, is that at higher f-stop values it becomes very difficult to see what's in focus and what isn't because the viewfinder becomes too dark.

I have electronic VF. Your live view LCD should also show a properly lit scene.
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#### RFPhotography

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##### Re: Depth of field, f-stop and focus point
« Reply #17 on: March 17, 2013, 08:30:38 AM »

With the exception of video, where I have no choice, I've never once used Live View.
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#### Slobodan Blagojevic

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##### Re: Depth of field, f-stop and focus point
« Reply #18 on: March 17, 2013, 09:54:58 AM »

... I've never once used Live View.

Shush! Do not let anyone ever find out

#### Fine_Art

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##### Re: Depth of field, f-stop and focus point
« Reply #19 on: March 17, 2013, 12:07:15 PM »

With the exception of video, where I have no choice, I've never once used Live View.

Old school.
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