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Usage of hyperfocal length

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sridhar125
 
Posts: 2

Usage of hyperfocal length

Post Thu May 14, 2009 10:18 pm


Hello, am always perplexed by usage of the hyperfocal length. Let us say, I have a chart with me based of my camera and targeted fstop and focal length and let us say it comes up as 18 ft.

Now if I am shooting a mountain from its base, then I can measure 18 ft from my tripod and manual focus to get that spot in focus (because my zoom lens does not have a DOF scale )

However, if I am shooting grandcanyon and want the little branch/shrub in front and distant mountains, how to go about it. 18 ft there, would lead me to the empty space between 2 objects...Also what happens if the 18 ft point is not part of the framed picture i.e if you want to compose beyond the point (maybe that will never be possible, but I dont know).

thanks
Sri

dougj
 
Posts: 2276

Re: Usage of hyperfocal length

Post Fri May 15, 2009 12:02 am


Hyperfocal distance - The acceptable range of focus (somewhat subjective) is from 1/2 the hyperfocal distance to infinity. In the 18 foot example, the distance range for acceptable focus is 9 feet to infinity. This is a little different from Depth of Field, but not too much. Some definitions state the hyperfocal distance as the point of focus (then objects 1/2 the distance to infinity will be in focus), this is the more common definition. I've also seen it defined as the shortest focus distance - objects closer will be out of focus and all others will be in focus - but this is less common.

These may help:
http://www.dofmaster.com/dofjs.html
http://www.cambridgeincolour.com/tutori ... stance.htm

Edit: I had to leave for awhile. Let's try an example, I'll base this on the data from the first link, DOF master

We want to take a landscape type photo that includes a small mountain 500 feet away. We use a DSLR with a sensor that has a 1.6 'crop' factor and shoot at f/11 with a 50mm lens. The calculations from DOF master tell us:

DOF
When we focus on the mountain 500 feet away, the near limit for what will be in focus is about 35 feet from the camera, and the far limit is infinity. Again, this is focusing on the mountain.

Hyperfocal distance
The same website tells us the hyperfocal distance is 38.5 feet, if we focus on an object that is 38.5 feet away from the camera, objects that are as close as 38.5/2 feet = 19.15 feet will be in focus and the range of acceptable focus is to infinity.

In your 18 foot and Grand Canyon example, assuming a 50mm lens, you need a smaller aperture and to focus a little beyond 18 feet to get both in focus. If there is nothing at about 30 feet, you could estimate it and use manual focus.

I hope it helps.

sridhar125
 
Posts: 2

Re: Usage of hyperfocal length

Post Fri May 15, 2009 8:37 pm


Doug, thanks for the response. I have a EOS 5D, with 17-40 lens and using the chart from
http://www.pbase.com/eos5d/hyperfocal

The various charts differ based of circle of confusion factor, seems like. Going with the
chart above, measuring the distance given and placing a stone there and manually focussing
there (2ft for me), did NOT really give me shapness from 1ft to infinity like it should. When
I looked at the image in PS, it seemed a little soft. Again, perhaps I have to shoot at different
distances to see the difference I suppose ?

dougj
 
Posts: 2276

Re: Usage of hyperfocal length

Post Fri May 15, 2009 11:22 pm


The Circle of Confusion size will influence the DOF calculations and manufacturers use different values. I've seen 0.025-0.035mm stated, Canon publishes a CoC of 0.035 in their Lens Works II and III guides, I believe Leica might use 0.025mm. It's all relative, as is DOF, there is only one point of true, sharp focus, the rest is termed 'acceptably in focus', what's acceptable to one person may not be to another. The intended use comes into play as well, 800px images for web galleries are more tolerant than an 8" x 10" print.

In your example of a 2 foot focus point, the DOF calculation using a COC of 0.3mm indicates a range of 1 foot to infinity at f/22, however there are some issues: 1. What is 'acceptable' in terms of in focus, 2. The calculations are on the borderline and accuracy is questionable, also this range is really pushing the limits of the lens, and, 3. Diffraction at f/22 has softened the photo. Apertures smaller than about f/11 introduce diffraction that may become visible, depending on the final image size that we view.

http://www.luminous-landscape.com/tutor ... tion.shtml

If you really need a photo with everything very sharply in focus from 1 foot to infinity, you could consider a technique called focus stacking - taking multiple shots at different focus points and combining in software. I haven't used this, however I've seen macro photos very well done with DOF that can not be achieved with a single shot.

The last point to consider is sharpening and other adjustments in post processing, you might already do this but I thought I would mention it.

Just my 2 cents, there might be some other comments and suggestions that come along.

madlights
 
Posts: 911

Re: Usage of hyperfocal length

Post Fri May 22, 2009 9:01 pm


On a somewhat related topic: I used to sit and wait and wait forever for my point and shoot to focus in the dark for home type snaps. I happened to read about a great photographer (Alex Majoli) who uses point and shoots for war and a lot of other types of photography, and his methods of using those cameras...so went to DOF master and looked up my P+S cameras...and wondered what I'd been doing when smaller sensor cameras had such a tremendously deep DOF compared to my DSLR (which focuses reasonably fast in low light). The bigger sensors are of course lower in number in COC but I never had a clue before that if I kept my Fstops up (numerically) as much as possible, and my lens as wide as possible...how much DOF I could get just pre-focusing and using manual aperture and shutter settings for flash and still get acceptably in focus shots with a point and shoot (diffraction can become a real problem for them and many are limited to F8 or F11). I think a lot of street shooters like Bresson used to do this(pre-focus) with his Leica, and think in bringing this up you've done a service...since so few people use this method...or think too much about it. I, like Doug, have read that it isn't exactly accurate always...more like "reasonably accurate"...I would imagine with a full frame high resolution camera like yours you'd notice the limits more quickly than those like me with 1.5-1.6 cropped DSLR's...or my small sensor point and shoots for sure...and like Doug says the bigger you enlarge, the more you'll notice that maybe something won't be extremely in focus. But for those of you with point and shoots that focus slowly for flash photography, set your lens wide - f stops as high as your flash allows (external flash helps with this) get close, do the walkingzoom - set your focus manually say at 4-5 feet and be surprised at the results (it also eliminates a lot of lag). This method even for outdoor shots, has turned my "point and shoot" cameras into completely different cameras...when set to an aperture priority setting that allows for fast enough shutter speed, the zoom on a wider setting and the focus on a predetermined manual length (some point and shoots don't have manual focus though) The difference in lag is truly astounding..but then I'm not blowing my point and shoot photos up to poster size usually. The trade off with them to me is more than worth it. I honestly haven't tried it with my DSLR yet...but will..out of more or less necessity if I get some adapters and manual focus lenses (especially if they have no DOF scales).
I've seen some incredible results with focus stacking too, it's very tedious though from what I've heard, and don't know for positive but think any movement ruins it... but can have great results DOF wise.
To the OP... There is a DOF wheel at DOF Master that you can construct yourself which is very handy for field use, and hyperfocal charts that you can download and print. It's a great site...and has really opened up my eyes (well they are starting to open) to what's possible and what may not be. Yep like Doug says...anywhere from 'around' 9 feet to infinity should be in reasonable or acceptable focus at a a hyperfocal length of 18 feet...depending on how critical you are, or how big the print will be.
http://www.dofmaster.com/dofjs.html
http://www.tawbaware.com/maxlyons/calc.htm


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