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  #1  
Old 05-05-2005, 01:56 AM
bboss bboss is offline
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Join Date: Nov 2004
Posts: 565
Default Hyperfocal confusions

So imagine I am trying to get the most in focus photo I can of a scene with a very close foreground subject whilst retaining as much focus as possible at infinity.
I understand that small aperture gives me large DOF, but also that most lens are sharpest over the whole frame at around f8. I understand the lines on my zoom lens are designed to give me a guide as to what will be in focus, (even if they are a little approximate) as dof is related too focal length.
So is the idea to focus in between the front and back object at a point the lines on the lens tells me, or should I put the focus on the front object and set aperture to give me what the lines tell me will be a good focus at infinity (whilst keeping as close to f8 as possible). Or is there another way? and have I got this right?
Any help on this will be much appreciated.
many thanks, David

btw I use an old nikon f3 with a 24mm lens and a 35-200 zoom.
(if I used digital I would just go out and experiment a lot, but film is expensive!)
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  #2  
Old 05-05-2005, 03:06 PM
GrahamB GrahamB is offline
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Join Date: Mar 2004
Posts: 97
Default Re: Hyperfocal confusions

Hi David.

This is the way I do it.

As you say, this size of the DOF is dependant on the aperture set – the smaller the aperture the bigger the DOF - and there is always twice as much sharp area beyond the focal point as in front of the focal point. If you focus on infinity you are ‘wasting’ the DOF beyond the infinity point, as nothing is further away than infinity. Hyperfocal Focussing is a way of using the wasted DOF to get more of the scene in focus.

So, using a 24mm Nikkor lens as an example, as I have one in front of me and can never explain this from memory. If I focus the lens to infinity and have the aperture set to f22 the DOF scale shows that at the closest point that will also be in focus is at 0.8m. Now I focus the lens to 0.8m and if you look at the DOF scale it shows that the furthest point in focus for f22 is still infinity, and the closest point is now just over 0.4m. So using this method you can get more of the foreground sharp. As this is not often an exact science when you are in the field, it may be better to base your calculations on the next f-number up say f16 but keep your lens set at f22 so that you have a bit of tolerance. Hope that makes sense.

I think you are right about most lenses giving best results at around f8 but that doesn’t always give you enough DOF –everything’s a compromise I guess. I can’t see much quality difference between f8 and f16 on my 24mm lens but I’m not a pro so maybe not so critical.

Graham
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  #3  
Old 05-06-2005, 12:52 AM
bboss bboss is offline
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Posts: 565
Default Re: Hyperfocal confusions

Hi Graham, and many thanks for taking the trouble to answer my rather confused question. You have clarified things for me but a few confusions remain. I had been doing things as you describe happily for some time until I saw the charts for hyperfocal points and saw that they were fixed and not relative like I had imagined (although still subjective). This then threw up questions as how to use them to obtain as sharp as possible pictures.
I am still confused when you say 'always twice as much sharp area beyond the focal point as in front of it', or its corollary that I have seen in some explanations - focus a third of the way into the scene.
So I was right in thinking that in order to maximize the dof its best to focus further away than the close subject (even though this will not be the best focus for that subject in isolation), but by how much. A third of infinity is still infinity, or maybe I could try guessing exactly how many kilometers the distant mountains are away, and then focus at 5km? This cannot be right, so I imagine you are meaning to use the non-linear markers as they appears on the lens focusing scale, and what a third means relative to that I dont know. If for instance I am focusing at 4m (hyperfocal point is 3.71m at 35mm, f11) my lens says infinity will be in focus, but what is a third in front of 4m? ( if 4m to infinity is 2/3). The other guide line points at 2m, which (as the lines are symmetrical) must be exactly the same distance (logwise?) in the other direction - 4m is midway between 2m and infinity. So where does the third come into it?
Maybe I am being stupid but this is confusing to me. Please could you clarify this bit a little.
cheers, David
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  #4  
Old 05-07-2005, 03:08 PM
GrahamB GrahamB is offline
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Join Date: Mar 2004
Posts: 97
Default Re: Hyperfocal confusions

Ermm...I was hoping someone who knew what they were talking about would have stepped up by now!

I have never looked into it in much detail - just followed the method I mentioned (maybe I should have listened more during the night class I did recently)
The 1/3 in front, 2/3 beyond the focal point ratio is just a physics/optics thing I think. The size of these areas of 'acceptable sharpness' is dependant on the aperture as we have said. I think we need to ignore the 'how far is 2/3 beyond infinity' question because as you say nothing is further than infinity. But now I think about real distances the maths doesn't seem to add up.
In my example if I focussed on 0.8m then infinty was still sharp beyong this (2/3) and 0.4m was still sharp in front(1/3) ?????

You are correct that you can focus furhter than the closest object you want sharp and use the DOF to keep it sharp - this then gives you more sharp area further into the scene - I have always just used the lens markins as a guide but I am now as confused as you.

I think I need to read some books!
In the mean time if anyone else can explain this then feel free.

Cheers for now.
Graham
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  #5  
Old 05-08-2005, 02:09 AM
bboss bboss is offline
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Join Date: Nov 2004
Posts: 565
Default Re: Hyperfocal confusions

Hi Graham
well I have now looked into it at reasonable length so I can summarise a few of the things I have learnt. I am actually quite surprised by the lack of discussion on the subject of focus in TE, I mean how much more basic can you get? A discussion on the merits of one lens over another will generate many many lengthy discussions, but something as basic as getting a photo as in focus, virtually none. I guess that auto-focus digital cameras are destroying the art of photography to some degree. Many people just let the camera focus, end of story. I am not even sure you can use this technique with autofocus cameras - a sensor cant focus on an theoretical point, it has to focus on a thing. Apparently most new lens don't even have the markings for hyperfocal. (maybe I am wrong as I know nothing of auto-focus cameras).

This is what I have learnt -
The "hyperfocal distance" is the nearest distance that you can focus a given focal length/aperture combination at and still have "infinity" in focus. Practically speaking, this is the deepest possible depth of field for that focal length/aperture combination. At the hyperfocal distance then the every point between half of the hyperfocal distance to infinity will be sharp. (in theory at least).

- the 2/3 1/3 thing is fairly meaningless, but maybe useful as a approximation sometimes.

- hyperfocal distance is subjective. The idea of there being an exact hyperfocal point is not true however scientific the charts and calculations appear. 'In focus' is a subjective value.
It all depends on how demanding you are. Charts can be different, it all depends on the value for the circle of confusion. For 35mm film a value of 0.02501mm is used (or 0.025-0.03mm).
Some people say you should use the next smaller aperture setting as the 'in focus' is just not in focus enough (ie use DOF settings for f8, and then ajust aperture to f16) . It depends on your final print size, viewing distance, taste etc
Also marking on lens aren't always accurate, so beware.
-using hyperfocal focusing will not necessarily give you the sharpest picture even if you need a very large DOF, as psycologically we tolerate foreground out of focus much less than background out of focus.
-You shouldnt use this technique for the smallest aperture setting on the lens as diffraction will spoil the sharpness.

As I am far from being expert, and there are many confusing things written about this, I may have got some of this not quite right. But I am trying.

cheers, David
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