RE: DOF in DSLRs - HELP ME PLEASE...
Lemme get this straight: From 36*24mm, you need to enlarge roughly 5 times to get a 5*7. From 24*16mm - surely you need to enlarge by 7 times to get the same 5*7? What has this to do with pixels? The size of a digital sensor isn't strictly dimensional. The number of pixels determines the real size of the image. If you enlarge BELOW that size, then you have to throw information away. This leads to a property of digital files that really confounds traditional photographers--which is that, in some cases, BIGGER prints have MORE detail than smaller ones. Not more apparent detail--more actual resolution. Here's a good basic reference: http://www.luminous-landscape.com/tutorials/understanding-series/und_resolut ion.shtml --Mike The life of an intellectual should be a permanent reproach to the idea that knowledge has to be handed down to us from authority. (unattributed: unidentified TV talk show guest) Find out about Mike Johnston's unique photography newsletter, The 37th Frame, at http://www.37thframe.com.
DOF in DSLRs - HELP ME PLEASE...
I have just read http://www.luminous-landscape.com/tutorials/understanding-series/dslr-ma g.shtml where again the lecture on DSLRs having greater DOF rears its head. Unless I am severely mistaken this is absolute hogwash! One other subtle benefit is the greater depth of field. To frame a head and shoulders portrait for example, a DSLR use will have to stand further away than a 35mm user with the exact same focal length lens. Subject distance determines DOF, for any given focal length and Circle of Confusion so it follows that the DOF will be greater by roughly 50%. Then he says: This is crucial. Depth of Field is an illusion based on minimum sized Circles of Confusion and is related to the enlargement factor of the final print... Which I do agree with. What he misses is that on a DSLR you will have to magnify more to get the same print size. In other words, the extra DOF only exists at the capture size which is smaller. I also don't see the point of his big shpeel where he gets all anal about the term 'focal length multiplier' - saying it doesn't exist. Perhaps we should call it 'extra enlargement required multiplier' so that he doesn't get upset and can understand it. He doesn't seem to acknowledge that this is required. I am not impressed! Rant over, please someone explain to me if I am wrong, but I don't see why DOF for the same shot with the same framing should be any different.
RE: DOF in DSLRs - HELP ME PLEASE...
Yeah, but presumably they also use the film format? I know fcalc prompts asking what format you want the COC for. Changing this from 35mm to APS (roughly what a DSLR does) reduced the DOF as a larger magnification would be required to compensate at the enlarging stage. Increasing your distance to subject presumably cancels this out so I would expect you to end up with the same DOF for the same framing within the format used. -Original Message- From: Antti-Pekka Virjonen [mailto:[EMAIL PROTECTED]] Sent: 28 November 2002 12:55 To: [EMAIL PROTECTED] Subject: Re: DOF in DSLRs - HELP ME PLEASE... At 06:43 28.11.2002 -0600, you wrote: Depth of field is a factor of reproduction ratio and aperture. Focal length doesn't enter into the equation. William Robb Hmm.. the equations (hyperfocal distance, near and far focus limits) I have seen or used all include the focal length of the lens. A very simple DOF explained can be found at Pentax University: http://www.pentax.com/university/photo101/index.cfm?photoconte nt=univ%5Fphoto%5F06%2Ecfm Antti-Pekka --- * Antti-Pekka Virjonen * Fiskarsinkatu 7 D * GSM: +358 500 789 753 * * Computec Oy Turku* FIN-20750 Turku Finland * Fax: +358 10 264 0777 *
RE: DOF in DSLRs - HELP ME PLEASE...
DSLRs use smaller sensors than 24 X 36 mm 35mm film does. Thus, for a given angle of view, they use shorter focal length lenses. Shorter lenses give better depth of field. I get great MACRO shots with my digicam that would be impossible with 35mm or God forbid 6X7. Seconded. It's exactly the same principle that gives 35mm better d.o.f. than an 8x10 view camera--shorter lens to cover the same angle of view. Frankly, I have had a blast shooting macro stuff with my little digicam. You can make macro pictures HANDHELD that would have required all manner of claptrap like tripods and big long macro lenses with 35mm. It's a lot of fun. --Mike You never know when the shot of a lifetime will appear before you. You do have a say in what kind of film is in your camera when it happens. (Mark Roberts) * * * Find out about Mike Johnston's unique photography newsletter, The 37th Frame, at http://www.37thframe.com.
Re: DOF in DSLRs - HELP ME PLEASE...
William wrote: Depth of field is a factor of reproduction ratio and aperture. Focal length doesn't enter into the equation. No. DOF has everything to do with focal lenght. Reproduction ration doesn't eneter the picture even if the DOF scale on your lenses are decided with reproduction ratio in mind. DOF is the relationship between whats in the plane of focus and whats outside it. This ratio won't change regardless of how much you magnify an image. Sharpnes does change with magnification. Eg. a lens has a certain sharpness regardless of how much you blow up the image; same with DOF at a certain focusing distance, subject magnification (on film), and aperture. I mean, talking reproduction ratio into DOF definition is like taking reproduction ration into lens sharpness definition. By that definition my Limited lenses sucks because my 8X10 meter images aren't sharp! DOF is dependent on four things only: 1. Aperture 2. Focal length 3. Size of the subject 4. Camera and subject distance If you shoot the same subject at the same subject size (angle of view) with the same subject camera distance at the same aperture but with differnt focal lengths, you'll get different DOF. This is the effect we are discussing here. Pål
RE: DOF in DSLRs - HELP ME PLEASE...
Yeah, but presumably they also use the film format? I know fcalc prompts asking what format you want the COC for. Changing this from 35mm to APS (roughly what a DSLR does) reduced the DOF as a larger magnification would be required to compensate at the enlarging stage. Increasing your distance to subject presumably cancels this out so I would expect you to end up with the same DOF for the same framing within the format used. But size is not determined by the size of the sensor in digital. Rather, the number of pixels determines the image size. --Mike You never know when the shot of a lifetime will appear before you. You do have a say in what kind of film is in your camera when it happens. (Mark Roberts) * * * Find out about Mike Johnston's unique photography newsletter, The 37th Frame, at http://www.37thframe.com.
RE: DOF in DSLRs - HELP ME PLEASE...
No, but the amount of enlargement is determined by the size of the sensor. Its now sounding as though enlargement isnt the main deciding factor in DOF, which goes against what I have been repeatedly told in the past. But then why does changing the format change the COC in fcalc? This is VERY confusing... -Original Message- From: Mike Johnston [mailto:[EMAIL PROTECTED]] Sent: 28 November 2002 15:20 To: [EMAIL PROTECTED] Subject: RE: DOF in DSLRs - HELP ME PLEASE... Yeah, but presumably they also use the film format? I know fcalc prompts asking what format you want the COC for. Changing this from 35mm to APS (roughly what a DSLR does) reduced the DOF as a larger magnification would be required to compensate at the enlarging stage. Increasing your distance to subject presumably cancels this out so I would expect you to end up with the same DOF for the same framing within the format used. But size is not determined by the size of the sensor in digital. Rather, the number of pixels determines the image size. --Mike You never know when the shot of a lifetime will appear before you. You do have a say in what kind of film is in your camera when it happens. (Mark Roberts) * * * Find out about Mike Johnston's unique photography newsletter, The 37th Frame, at http://www.37thframe.com.
RE: DOF in DSLRs - HELP ME PLEASE...
On 28 Nov 2002 at 12:12, Herb Chong wrote: Message text written by INTERNET:[EMAIL PROTECTED] From 36*24mm, you need to enlarge roughly 5 times to get a 5*7. From 24*16mm - surely you need to enlarge by 7 times to get the same 5*7? What has this to do with pixels? there is an additional factor, pixel count. think if you had 1 pixel per millimeter. it doesn't affect what gets focused on the sensor, but it does affect what you are able to see when you enlarge. Apart from the fact that DOF has everything to do with final print viewing distance. The limits of DOF are defined as the point at which the the image becomes visibly unsharp and the equation assumes that as prints are reproduced larger they should be viewed at an increased distance so as to maintain the apparent size. Conventional DOF calculations CAN NOT be directly applied to digital systems in all cases, consider the implications of using a 640 x 480 matrix to capture full frame 35mm images? Also consider that in all sensor except Foveon a single pixel in the print is formed by the computing its value form at least 4 other single colour pixels. Anyone want to take a stab at the math? Cheers, Rob Studdert HURSTVILLE AUSTRALIA Tel +61-2-9554-4110 UTC(GMT) +10 Hours [EMAIL PROTECTED] http://members.ozemail.com.au/~distudio/publications.html
Re: DOF in DSLRs - HELP ME PLEASE...
Close. DOF is determined by a combination of focal length and diaphragm opening diameter (aperture). All 150mm lenses @ f8 have the SAME dof (providing for minor variations because of varying lens designs). It doesn't matter if the coverage of the lens is for 24x36mm or 6x7cm or 4x5in. 150mm is 150mm and f8 is f8. Period As a photofinisher I must disagree. Technically only 1 point is in actual focus, everything else is increasingly out of focus (circle of confusion). So as you enlarge further, less area is perceived to be in focus. This is why I usually will use the guide for 1 F stop more open when using hyperfocal distance. So, although a 150mm lens is a 150mm lens, unless you are shooting film that you are not going to print (enlarge) then both format size( needs more/less enlargement for any given print size ) and print size contribute to what is perceived to be in focus, which is what depth of field is supposed to measure.
Re: DOF in DSLRs - HELP ME PLEASE...
- Original Message - From: Pål Jensen Subject: Re: DOF in DSLRs - HELP ME PLEASE... If you shoot the same subject at the same subject size (angle of view) with the same subject camera distance at the same aperture but with differnt focal lengths, you'll get different DOF. This is the effect we are discussing here. What you are describing is impossible. Think about it for a moment. William Robb
Re: DOF in DSLRs - HELP ME PLEASE...
William wrote: If you shoot the same subject at the same subject size (angle of view) with the same subject camera distance at the same aperture but with differnt focal lengths, you'll get different DOF. This is the effect we are discussing here. What you are describing is impossible. Think about it for a moment. Huh?? Thats exactly what you're doing when shooting exactly the same image with two or more formats. Pål
Re: DOF in DSLRs - HELP ME PLEASE...
- Original Message - From: Pål Jensen Subject: Re: DOF in DSLRs - HELP ME PLEASE... Depth of field is a factor of reproduction ratio and aperture. Focal length doesn't enter into the equation. No. DOF has everything to do with focal lenght. Reproduction ration doesn't eneter the picture even if the DOF scale on your lenses are decided with reproduction ratio in mind. DOF is the relationship between whats in the plane of focus and whats outside it. This ratio won't change regardless of how much you magnify an image. Sharpnes does change with magnification. Eg. a lens has a certain sharpness regardless of how much you blow up the image; same with DOF at a certain focusing distance, subject magnification (on film), and aperture. I mean, talking reproduction ratio into DOF definition is like taking reproduction ration into lens sharpness definition. By that definition my Limited lenses sucks because my 8X10 meter images aren't sharp! Reproduction ratio is how large the subject is on the film, not the print. If you keep the subject the same size on the film, then the DOF will remain constant at any given aperture and focal length. This is not format dependent. It is just aperture and subject size (reproduction ratio) dependent. William Robb
Re: DOF in DSLRs - HELP ME PLEASE...
Butch wrote: As a photofinisher I must disagree. Technically only 1 point is in actual focus, everything else is increasingly out of focus (circle of confusion). So as you enlarge further, less area is perceived to be in focus. The point in focus will be equally less sharp with magnification. The prceived DOF is related to the focus difference between the point in focus and the DOF zone. This is constant with magnification. Another issue is that larger images a viewed from a longer distance negating any reduction of sharpness due to magnification. Pål
Re: DOF in DSLRs - HELP ME PLEASE...
William wrote: Reproduction ratio is how large the subject is on the film, not the print. Then we agree... Pål
Re: DOF in DSLRs - HELP ME PLEASE...
- Original Message - From: Pål Jensen Subject: Re: DOF in DSLRs - HELP ME PLEASE... William wrote: If you shoot the same subject at the same subject size (angle of view) with the same subject camera distance at the same aperture but with differnt focal lengths, you'll get different DOF. This is the effect we are discussing here. What you are describing is impossible. Think about it for a moment. Huh?? Thats exactly what you're doing when shooting exactly the same image with two or more formats. NO!!!. If you change formats, and focal length, the subject size ON THE FILM will change, unless you also adjust the camera to subject distance. If the subject size is kept the same on the film (reproduction ratio), then DOF will also be the same at any given aperture, no matter what format you use. William Robb
Re: DOF in DSLRs - HELP ME PLEASE...
- Original Message - From: Pål Jensen Subject: Re: DOF in DSLRs - HELP ME PLEASE... William wrote: Reproduction ratio is how large the subject is on the film, not the print. Then we agree... More than likely. I suspect there might be a difference in semantics is all.
Re: DOF in DSLRs - HELP ME PLEASE...
William wrote: If the subject size is kept the same on the film (reproduction ratio), then DOF will also be the same at any given aperture, no matter what format you use. True. But that was not was I was getting at. I was talking about the same angle of view from the same shooting distance with different focal lengths. Then Eg. MF will have less DOF at the same aperture as the same image with 35mm. This is the DOF effect this thread was initially all about. Pål
Re: DOF in DSLRs - HELP ME PLEASE...
J. C. O'Connell wrote: DSLRs use smaller sensors than 24 X 36 mm 35mm film does. Thus, for a given angle of view, they use shorter focal length lenses. Shorter lenses give better depth of field. More DOF is not always better! Cheers, - Dave http://www.digistar.com/~dmann/
