image magnification is the ratio of the image size to the object size as formed by the camera lens. Not to be confused with format size, that doesnt matter in terms of DOF.
M = image size/object size M can be altered by changing lens f.l. at a given distance, or by changing distance from object to film plane, or both. JC O'Connell hifis...@gate.net -----Original Message----- From: pdml-boun...@pdml.net [mailto:pdml-boun...@pdml.net] On Behalf Of Larry Colen Sent: Tuesday, April 07, 2009 6:39 PM To: Pentax-Discuss Mail List Subject: Re: Trading resolution for depth of field 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. -- 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.
