By magnification do you mean the size of the image as projected on the sensor or film?
On Tue, Apr 07, 2009 at 06:26:17PM -0400, JC OConnell wrote: > The problem with this post below is the word "perceived". For my purposes, if the viewer can't tell that something is out of focus, I don't care whether it is in focus or not. Granted, it's generally better if I can achieve this effect with a bigger image, but life is all about compromises. > The REAL DOF increases with lower magnification, not the > perceived DOF. If you could build a high quality tiny > sensor and had a real short FL lens of unlimited resolution, > you would end up with a camera with immense DOF capability, So, if I want to increase DOF at the same aperture, I could use a smaller sensor? And if I don't have a smaller sensor, then I could use a wider lens and crop down to the smaller portion of the sensor, in effect giving me a smaller sensor and less magnification? (Albeit at the cost of image resolution) Just like I asked in my first post? > EVEN WITH LARGE PRINTS MADE. The viewing angles and print > sizes dont matter. Its the in-camera maginification that > makes the difference, a REAL difference. > > JC O'Connell > hifis...@gate.net > > > > -----Original Message----- > From: pdml-boun...@pdml.net [mailto:pdml-boun...@pdml.net] On Behalf Of > Luiz Felipe > Sent: Tuesday, April 07, 2009 5:55 PM > To: Pentax-Discuss Mail List > Subject: Re: Trading resolution for depth of field > > > Hard as it is to remain serious in this thread, I'll try. :-) > > Magnification is one of the keys, and very important. For a while, let's > > keep the aperture and circle of confusion effects out of the equation > (make them constant to all the scenarios below). So for this moment, > magnification is our tool. > > Zooming out or stepping back would reduce image size, increasing the > perceived DOF. > > But that's part of the problem, since we have now a pic a little smaller > > than we wanted. So we enlarge said photo back to the desired size, and > we MAY keep the perceived DOF, as long as we don't degrade the image in > the process. Best if we have some megapix stored just in case. Taking > this to a limit, the circle of confusion that was acceptable in the > small image becomes unacceptable in the enlargement. > > But there is still another point to consider - viewing distance of the > final, enlarged photo. Looking too close is another way of enlarging the > > photo, and there go the perceived DOF and sharpness away. Keep the > distance and the image keeps looking sharp - small, but sharp. > > Small sensor P&S cameras use so small images they offer some serious DOF > > - offset by other considerations very quickly. As you move up in sensor > size (assuming of course you use a corresponding larger image) the > perceived DOF will drop. Want it back? Small image, to be enlarged later > > if the number of pixels remains on our side. > > Now, about that light at the end... ;-) > > LF > > Larry Colen escreveu: > > On Tue, Apr 07, 2009 at 09:32:47AM -0300, Luiz Felipe wrote: > >> You're actually saying if one zoom out (reduce the magnification of > >> the > >> subject) and crop back to the desired composition the DOF will be > >> increased, right? So the pic taken with the zoom at 35mm will present > > >> greater DOF than the one taken at 70mm, after you enlarge both to the > > >> same subject size, right? > > > > This is the premise behind point and shoots having greater depth of > > field than APS which has greater depth of field than Full Format. Or > > conversely if you want to limit DOF at a particular angle of view, you > > > may need to go to FF. > > > >> ...so the K20d has greater DOF than the *ist DS, right? > > > > Because you can shoot with a shorter lens and crop, since DOF is based > > > on focal length squared and CoC as a linear value. > > > > Mind you, if you down res a photo from 2000x3000 pixels to 400x600 > > then an edge that had been 5 pixels wide is now only 1 pixel wide so > > even if DoF can't be changed in post processing, there will be a lot > > more lattitude in what you cannot see is out of focus. > > > >> I love numbers... :-) > >> > >> LF > >> > >> JC OConnell escreveu: > >>> depth of field is determined solely by in camera magnification and > >>> working fstop. So cropping/format is not a factor but changing > >>> lenses from a given distance will affect DOF, likewise moving > >>> further away with the same lens and stopping down more will also > >>> both increase DOF. > >>> > >>> JC O'Connell > >>> hifis...@gate.net > >>> > >>> > >>> > >>> -----Original Message----- > >>> From: pdml-boun...@pdml.net [mailto:pdml-boun...@pdml.net] On Behalf > > >>> Of Larry Colen > >>> Sent: Monday, April 06, 2009 4:35 PM > >>> To: Pentax-Discuss Mail List > >>> Subject: Trading resolution for depth of field > >>> > >>> > >>> Perhaps someone has already done the math, or the experimentation, > >>> and can just give me the answers. > >>> > >>> Scott's pictures of his Nishiki inspired me to shoot some of my > >>> mongrel legnano. I rode it to lunch today, and on the way back to > >>> the office was getting some shots of it with some lupin by the side > >>> of the trail. > >>> > >>> I didn't have quite as much depth of field as I'd like, so I decided > > >>> to try zooming way out and then just cropping. Smaller sensor, > >>> shorter lens, more depth of field. If the equation is linear, I > >>> should get the same DOF by downresing (downrezzing?) a longer lens > >>> over the whole sensor, as I would using a shorter lens and cropping. > >>> > >>> This would also mean that a K20 would have a lot less DOF than my > >>> K100 at the same focal length, assuming that they were blown up > >>> large enough that the sensor resolution became a factor. > >>> > >>> So, if I'm willing to trade resolution for depth of field, am I > >>> better off using a wider angle lens and cropping (my intuition says > >>> yes), or do I get the same benefit by just combining pixels (which > >>> would also reduce > >>> noise) for a larger circle of confusion? > >>> > >>> > >> -- > >> Luiz Felipe > >> luiz.felipe at techmit.com.br > >> http://techmit.com.br/luizfelipe/ > >> > >> -- > >> PDML Pentax-Discuss Mail List > >> PDML@pdml.net > >> http://pdml.net/mailman/listinfo/pdml_pdml.net > >> to UNSUBSCRIBE from the PDML, please visit the link directly above > >> and > >> follow the directions. > > > > -- > Luiz Felipe > luiz.felipe at techmit.com.br > http://techmit.com.br/luizfelipe/ > > -- > PDML Pentax-Discuss Mail List > PDML@pdml.net > http://pdml.net/mailman/listinfo/pdml_pdml.net > to UNSUBSCRIBE from the PDML, please visit the link directly above and > follow the directions. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > -- > PDML Pentax-Discuss Mail List > PDML@pdml.net > http://pdml.net/mailman/listinfo/pdml_pdml.net > to UNSUBSCRIBE from the PDML, please visit the link directly above and follow > the directions. -- The fastest way to get your question answered on the net is to post the wrong answer. Larry Colen l...@red4est.com http://www.red4est.com/lrc -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
