How to focus 1/3 into the frame.

<p>Hi Guys,<br /> I know this probably sounds like a silly question, but I've been trying to learn about hyper-focal distance and focusing at 1/3 to presumably get a good DOF, but i don't really understand how. I understand the concept but how do i precisely select 1/3 of the frame and focus on that point? It must be really easy but i just can't find anything in google that explains the focusing part. Everything just says "focus 1/3" and doesn't actually explain how to physically do it with the camera. I currently have a 450D.<br>

Sorry if this is in the wrong forum section!</p>

<p>Thanks in advance</p>

<p>Jon,</p>

 

<p>Live View on your 450D has made hyperfocal technique obsolete.</p>

 

<p>Turn on Live View. Hold down the Depth of Field Preview button while simultaneously manually

adjusting both focus and aperture. Your eyes will tell you when you have achieved the optimal

combination of settings for that particular combination of camera and scene. For bonus points, zoom in

with Live View, and for super bonus points, use a tethered laptop.</p>

 

<p>Cheers,</p>

 

<p>b&</p>

<p>Hi Ben,<br>

Cheers for that! i rarely use the live view function and mainly look through the view finder.<br>

Thanks that really helps.</p>

<p>Jon, is it possible you're confusing hyperfocal distance with the rule of thirds?</p>

<p>Hi Alan,<br>

Yeah possibly, in all honesty i'm not entirely sure. I thought the rule of thirds relates purely to composition and not focus. When reading about hyper focal distance i kept coming across the 1/3 focus technique i thought it was key to getting a sharp image. I really need to improve my technical understanding! I'm very much self taught, some things just go over my head.</p>

<p>Ok, I did a little googling and see there's also a 1/3 rule in hyperfocal focusing as well. Somehow I'd never stumbled on it.</p>

<p>That being the case, perhaps the problem is your lens doesn't have a distance scale? Many lenses have a distance gauge to tell you where you're focused, and it's easy to do the 1/3 thing by just doing a little math and turning the ring. But there are some lenses, including most of the kit lenses, which don't have the distance gauge, and for those it's going to be more difficult.</p>

<p>I have one lens with the distance gauge which is the sigma 10-20 mm. I think i need to read up on how to make best use of it. Up until now i've just been setting my aperture, zooming and focusing and not necessarily looked into the gauge and how it works. I find it difficult to understand where i'm focusing unless i'm directly next to the subject! <br>

Cheers for the help Alan </p>

<p>DOF and the advice traditionally given, such as the 1/3 rule you mention, are subject of much debate. Mainly because the basic assumptions are in need of an update.<br /> I'd recommend to read <a href="http://www.trenholm.org/hmmerk/DOFR.html">Depth of Field Revisited</a> for an alternative approach that has worked very well for me. On a side note, even the large, high-resolution screens on the newer cameras are only good for rough estimates of DOF. They're certainly better than a darkened viewfinder image though.</p>

<p>Martin,</p>

 

<p>I’ve never bothered to check the actual figures, but the 10× preview of the 5DII Live

View function is as close to actual pixels as makes no difference. If you can’t get good focus that

way, even a loupe on LF ground glass won’t do you any good.</p>

 

<p>And you can view 200% actual-pixels magnification with a tethered laptop…on an 8″

× 10″ (or bigger) display….</p>

 

<p>Cheers,</p>

 

<p>b&</p>

<blockquote>

<p>DOF and the advice traditionally given, such as the 1/3 rule you mention, are subject of much debate. Mainly because the basic assumptions are in need of an update.</p>

</blockquote>

<p>If used correctly Depth of field scales on old manual focus lenses work very well (auto focus lens scales are not as good or are often not even printed on the lens). With all do respect I didn't find the article you linked to very helpful at all and I doubt Jon would find it useful either. At the end of the article when the author outlines his methode he fails to explain how he determined the focus distance. So without knowing how he is setting his focus his methode is not useful. Furthermore his example of why the old way wouldn't work (90mm, hyperfocal distance 106 feet, F8 for a subject 30 feet away with the background at infinity is not correct. The correct hyperfocal distance is 111 feet (a small but critical error) and F8 is not even close to being narrow enough to get the needed depth of field. If those were the number he got off of his lens he either has a very cheep lens with a bad scale or he is not reading the scales correctly.</p>

<p>For Jon I would recommend you set your camera to use the center focus point. Put the center focus point on the most distant object that will be in the picture and focus. then look at your lens scale and mark the position or write the number down. Then put the center focus point on the closest object and focus the camera. Again look at the lens scale and mark or write down the focus distance. You now know the distance for fhe closest object and most distant object. Subtract the two for the depth of field needed and divide by 3. Add the result to the minimum distance you recorded earlier. Set the lens to manual focus and use the focus scale on the lens to set the distance to the calculated number. Then take the shot. </p>

<p>To be honest I have not used the 1/3 rule (I din't know it existed) so I don't know how well it works. I have used lens scales (manual focus lenses) with great success or depth of field preview on the camera with mixed results. I currently don't have a camera with live view. But based on quick calculation I did this 1/3 focus rule should be close as long as you stop the lens down enough. Use depth of field preview on your camera to check before you take the picture. You might also find this <a href="http://www.dofmaster.com/dofjs.html">depth of field calculator </a>helpful. Granted you generally can't bring your computer with you put you can used it creat a small table that may be useful. Addtionally you might find this <a href="../learn/optics/dofdigital">article from Bob Atkins </a>very helpful. </p>

<blockquote>

<p>At the end of the article when the author outlines his methode he fails to explain how he determined the focus distance.</p>

</blockquote>

<p>Steven, the entire article was about where he focused, and why.</p>

 

<p>I have a 450D. I tried to use Live View for some Macro work. However, I could not find a way for Live View work while shooting RAW/Av/M. So, if you want to use those modes, you may not be able to use Live View. If you do find a way to use Live View for those modes and RAW, please let me know.<br>

DS Meador</p>

<p>I wonder if two optically related but practically different issues are mixed together in the OP's question.</p>

<p>I think the 'focus 1/3 of the way into the picture' idea comes from the fact that at certain focal lengths, more of the DOF lies behind the point of focus than in front. However, this affects primarily short lenses. For some #s about this, see http://www.cambridgeincolour.com/tutorials/depth-of-field.htm</p>

<p>Hyperfocal distance obtains when DOF extends to infinity. This is one of the explanations on DOFmaster: "When the lens is focused on the hyperfocal distance, the depth of field extends from half the hyperfocal distance to infinity." (there is a useful diagram on the same page, http://www.dofmaster.com/hyperfocal.html). One can't focus 1/3 of the way to infinity....</p>

<p>My knowledge of optics is limited, but I think the fact that DOF shifts toward the front with increased focal length (the first link above) is the reason why short lenses are the ones where hyperfocal focusing is most useful.</p>

<p>Cheers for the advice, guys and your recommended reading material. I'm going to try this out and get back to this thread with my results. Thanks again</p>

<p>Focusing at 1/3rd comes from the fact that aproximately 1/3rd of the acceptable sharpness is located in front of the focus plane and 2/3rds are located behind the focus plane. E.g if you focus at 4m distance, then objects at 4m will be in focus, while objects from 3m up to 6m will be acceptably sharp (you have to find out which apperture setting gives those numbers for given lens). Mind that this are only aproximate values, so you'll need to close down apperture a bit.</p>

<p>So in practical terms, once you've settled on nearest and farmost objects that you want sharp and figured out required apperture, you find a point aproximately 1/3rd away from nearest object (not from you!).</p>

<p>If you want to know more about it, have a look at Ansel Adams "Camera" book.</p>

<p>Unfortunately this 1/3 - 2/3 guideline is only an approximation, and it's usually not even close to reality. For instance, if you're using the hyperfocal distance, the ratio of usable focal depth forward of the point of focus to the depth behind the point of focus is actually zero. If you're using a rather shallow DoF and are focused at a close/moderate distance, the ratio is closer to 50:50.</p>

<p>I second any recommendation you're gotten for Harold Merklinger's excellent articles. Good reading.</p>

<p>In addition to Merklinger, I'll offer the following guideline that works with MOST lenses: Focus on the nearest point you want in focus. Mentally note its position on the focus scale. Then focus on the farthest point, and note its position. Finally, rotate the focus ring so that the two marks you mentally noted are equidistant ON THE FOCUS SCALE from the focal distance mark. I'm not referring to the numbers on the scale, but rather the degrees of rotation of the focus ring -- the physical distance along the circumference of the focus scale. That will be the center point of focus you need to use. From there, you'll have to determine the aperture that yields the DoF you desire, according to whatever circle of confusion you wish to select. Our modern-day focus scales don't help us much with that, of course. Anyway, if you set your focus by my method, the near and far points will be equally sharp/blurred on MOST lenses and very, very close to equally sharp/blurred on most of the remaining lenses.</p>