tag:blogger.com,1999:blog-27557058.post2662518677247684110..comments2024-01-18T05:34:40.549-07:00Comments on Behind The Lens: Up Close And Out Of Focus (mostly)George Barrhttp://www.blogger.com/profile/06745541057122821349noreply@blogger.comBlogger7125tag:blogger.com,1999:blog-27557058.post-62456672229899933192011-08-20T12:17:39.998-06:002011-08-20T12:17:39.998-06:00For the fun of it: As long as your object is signi...For the fun of it: As long as your object is significantly closer than the hyperfocal distance, the term f^4 is much bigger than N^2c^2s^2. Hence you can in ignore the latter in this cases. Then the formula gets reduced to:<br /><br />2Ncs^2/f^2<br /><br />Not exact any longer, but a pretty good approximation.<br /><br />What does this tell us? Well, the DOF increases with the square of the distance. And it increases when we close the aperture.<br /><br />Let us compare the approximated value and the correct value assuming c equals 0.03 mm. If I used my 85 mm f/1.8 fully open to shoot a portrait from a distance of 1.5 m, the correct value would be a DOF of 33.64 mm, the approximated value one of 33.63. Not much difference and explains why in this case the tip of the nose looks blurred already when I get the focus spot-on the eyes. If I want the nose sharp, I'll have to stop down to 5.6, giving me a DOF of 104.76 mm (approx. 104.64). That is good to know (and matches with my experience).<br /><br />Different example: I want to take a shot of a belltower from a distance of 50 m with f set to 24 mm. Can I use the approximation? Definitely not, as the hyperfocal distance is that short for all f-numbers I can set, the 50 m will be more.<br /><br />Completely different again when using telephoto lenses. Say I have a 500 mm I want to use at f/8. What is the hyperfocal distance now? Believe it or not, over a kilometre. So the approximation will be good for anything much closer than that, say 100 m. <br /><br />Boring? Maybe, not for me, pretty useful I think.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-27557058.post-61905583495436638022011-08-20T10:24:20.177-06:002011-08-20T10:24:20.177-06:00We as photographers are so spoiled nowadays with o...<i>We as photographers are so spoiled nowadays with our fancy digital cameras... it's so much easier now than it used to be to take great photos without having to know all the physics and formulas. </i><br />Sorry, mate. The laws of physics apply to digital cameras as well as they did to the "old" analog ones. You don't have a digital lens, it's still glass, it's still refraction, focal length, aperture and eventually diffraction, too. Nobody needs to keep that formula in mind, but knowing the fod is proportional to one over square of focal lenght helps understanding. As well as getting to know your lenses does.<br /><br />Cheers<br />HenkkiAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-27557058.post-29244414241772165482011-08-18T03:41:55.797-06:002011-08-18T03:41:55.797-06:00I am not interested in the hairs on your warts; I ...I am not interested in the hairs on your warts; I want to see into your eyes. Need but a little DOF for that (even though I do like to see where the nose ends...).<br /><br />Enter the formula into Excel, make some plots and carry them laminated with you. However, you'll find that the "constant" of the formula is kind of arbitrary. Anyway, there's also an A_dep setting on your camera...Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-27557058.post-21251025780443866042011-06-23T10:43:02.613-06:002011-06-23T10:43:02.613-06:00it's so much easier now than it used to be to ...<i>it's so much easier now than it used to be to take great photos without having to know all the physics and formulas</i><br /><br />I never knew a single photographer who knew this formula by heart. It's great for understanding why DOF works the way it does, but it little or no practical application for those of us who jockey a camera. Now, if George can find the formula for good images, I'll try and remember that one.Chuck Kimmerlehttp://www.chuckkimmerle.com/noreply@blogger.comtag:blogger.com,1999:blog-27557058.post-62058495698096653412011-06-21T12:48:09.867-06:002011-06-21T12:48:09.867-06:00Haha, this is total greek to me. We as photograph...Haha, this is total greek to me. We as photographers are so spoiled nowadays with our fancy digital cameras... it's so much easier now than it used to be to take great photos without having to know all the physics and formulas.Tien Froggethttps://www.blogger.com/profile/16360861032800438835noreply@blogger.comtag:blogger.com,1999:blog-27557058.post-67229448549545450272011-06-20T03:23:32.619-06:002011-06-20T03:23:32.619-06:00You've reminded me of an utterance by a photo-...You've reminded me of an utterance by a photo-club judge: "If you'd focussed a third of the way in, that would be hyperfocussing and everything would be sharp". The subject-matter: a table-top flower still-life about 10-30cm away where hyperfocussing would require f/1024 or narrower, guaranteeing *nothing* sharp.<br /><br />Thanks for throwing that idiocy into sharper relief. I know who I'd rather believe ;)Timhttp://www.shinyphoto.co.uk/noreply@blogger.comtag:blogger.com,1999:blog-27557058.post-37125667904956014712011-06-19T22:06:52.392-06:002011-06-19T22:06:52.392-06:00Oh man... Physics and formulas again.
I was trying...Oh man... Physics and formulas again.<br />I was trying for ages to memorize the hyperfocal distance formula, and guess what; a fail. I still can't remember a character.<br />The irony is, I'm a physics graduate!TJhttps://www.blogger.com/profile/08018919311091160354noreply@blogger.com