jlw
Rangefinder camera pedant
I'm going to start a new, separate thread (under 'And Now for Something Completely Different,' since it's not specifically RF-related) with some visual examples which I hope will clear all this up a bit!
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S
Sean Reid
Guest
Here's a quick one: http://bj.canon.co.jp/english/photoshooting/technihsc/howtophotograph/howtophotograph08.html
Sean
Sean
LCT
ex-newbie
Yes of course.
Forgot what i've learnt in my youth.
Thanks Sean.
Best,
LCT
Forgot what i've learnt in my youth.
Thanks Sean.
Best,
LCT
pfogle
Well-known
Sean... your quote from Puts puts (no pun intended 
) it well. I think that some of the confusion comes from the fact that the 'magnification' he mentions arises from the enlarging/printing process as well as from the lens. However, DOF does not scale the same way in enlarging/printing as it does in changing the focal length of the lens.
I guess the upshot of all this, and the point I was (not very well) trying to make, is that what we are interested in is the characteristics of a *system* ie the whole shebang up to the finished print, and the R-D1 is a different system, in the same way that MF is a different system. So a 50mm on a 35 body is a different system to a 50mm on an R-D1, and will have it's own unique character.
I'd just like to say at this point how much I appreciate your work, and the input of all the other people who contribute to this forum - it really is a special place!
cheers
Phil
) it well. I think that some of the confusion comes from the fact that the 'magnification' he mentions arises from the enlarging/printing process as well as from the lens. However, DOF does not scale the same way in enlarging/printing as it does in changing the focal length of the lens. I guess the upshot of all this, and the point I was (not very well) trying to make, is that what we are interested in is the characteristics of a *system* ie the whole shebang up to the finished print, and the R-D1 is a different system, in the same way that MF is a different system. So a 50mm on a 35 body is a different system to a 50mm on an R-D1, and will have it's own unique character.
I'd just like to say at this point how much I appreciate your work, and the input of all the other people who contribute to this forum - it really is a special place!
cheers
Phil
S
Sean Reid
Guest
jlw posted a separate thread here: http://www.rangefinderforum.com/forums/showthread.php?t=5121 and his summary point is: "But it's the distance change, not the lens or format change, that causes the perspective relationship to change." I think that statement points out that, for the sake of precision, we should be talking about the "perceived" or "effective" spatial compression of longer lenses. It's a similar distinction I always try to make when writing about DOF (and now need to make with respect to spatial compression). DOF, in a pure sense, is exactly the same for all lenses (at a given aperture) regardless of focal length *if* the primary subject is kept exactly the same size on the capture medium. That means, of course, coming closer to the subject with a wide lens and further from the subject with a long lens. So that's an absolute property of DOF. Yet, we generally experience DOF much differently because we do not always keep the subject the same size on the sensor or film. Our actual experience of lenses, usually, is that we see more DOF in pictures we make with wide angle lenses than we do with pictures made with telephoto lenses based on the way we actually work with these lenses. In absolute terms, a 12mm lens has exactly the same DOF (at a given aperture) as a 300mm lens (again, if the subject size is kept exactly the same on the capture medium). In practice, though, few of us would be comfortable zone-focusing a 300mm whereas we might readily do that with the 12mm (in our normal picture-making). The way we tend to actually use these lenses leads us to perceive that the "effective" DOF is greater with the wider lenses. For example, the wide angle end of a Digilux 2 lens is 7mm. If subject size on the sensor was kept absolutely constant, that 7mm lens would have exactly the same DOF as a 300mm lens. But to accomplish that we'd need to be almost pressing that 7mm lens up against the subject's nose (for example). It's a property that's true in an absolute sense, but not very true to our experience. That's why it seems unbelievable to many of us that all focal length lenses could have exactly the same DOF.
I think the distinction is similar here for the relationship between spatial compression and focal length. In actual practice, we tend to use wider lenses closer to our subjects and longer lenses further from them. A concrete example: When Garry Winogrand was working in the streets of NYC, for example, he was often working with a 28mm lens about 6-10 feet from his primary subjects. His framing is often such that the height of the pictures (made at that distance) is defined largely by the height of his primary subjects. His work was mostly made with 28mm and 35mm lenses, working fairly close to his primary subjects. Now imagine a young photographer who is interested in Winogrand's subject (nominally people) but feels too shy to work close in to people. So he starts working from much further away with a 135mm lens. The figures perhaps appear the same height in his frame that they did in Winogrand's pictures but the spatial compression seen in the latter pictures is vastly different (as is the drawing of the figures themselves). In general, we use longer lenses when we stand further back and as such the truth of our experience (generally) using these longer lenses is that space is compressed, just as our experience of using wide angle lenses (at the distances we normally work with them) is that they have a greater DOF.
Cheers,
Sean
I think the distinction is similar here for the relationship between spatial compression and focal length. In actual practice, we tend to use wider lenses closer to our subjects and longer lenses further from them. A concrete example: When Garry Winogrand was working in the streets of NYC, for example, he was often working with a 28mm lens about 6-10 feet from his primary subjects. His framing is often such that the height of the pictures (made at that distance) is defined largely by the height of his primary subjects. His work was mostly made with 28mm and 35mm lenses, working fairly close to his primary subjects. Now imagine a young photographer who is interested in Winogrand's subject (nominally people) but feels too shy to work close in to people. So he starts working from much further away with a 135mm lens. The figures perhaps appear the same height in his frame that they did in Winogrand's pictures but the spatial compression seen in the latter pictures is vastly different (as is the drawing of the figures themselves). In general, we use longer lenses when we stand further back and as such the truth of our experience (generally) using these longer lenses is that space is compressed, just as our experience of using wide angle lenses (at the distances we normally work with them) is that they have a greater DOF.
Cheers,
Sean
LCT
ex-newbie
You're opening new perspectives in my FoV Sean ;-)
Always a pleasure to read you.
Best,
LCT
Always a pleasure to read you.
Best,
LCT
S
Sean Reid
Guest
Thanks LCT.
Cheers,
Sean
Cheers,
Sean
Phil_Hawkes
Established
Yet Another DOF question
Yet Another DOF question
Hi all,
I've been thining about DOF issues. I gather that (without considering the field of view) the depth of field on the R-D1 using focal length f at aperture x would be the same as on a M6 using focal length f at aperture x/1.5.So the photo I take with 50/1.0 on the R-D1 has the same depth of field as a 50/0.7 on M6. A few comments I've seen on this forum seem to confirm that this is the accepted view.
I was reading a few threads on this, and came across Sean's comment...
What stood out to me was this..
I haven't heard that comment before. I was wondering if there are some references/links to some diagrams or text that explains this. I'm intrigued!!!
Cheers
Phil
Yet Another DOF question
Hi all,
I've been thining about DOF issues. I gather that (without considering the field of view) the depth of field on the R-D1 using focal length f at aperture x would be the same as on a M6 using focal length f at aperture x/1.5.So the photo I take with 50/1.0 on the R-D1 has the same depth of field as a 50/0.7 on M6. A few comments I've seen on this forum seem to confirm that this is the accepted view.
I was reading a few threads on this, and came across Sean's comment...
Sean Reid said:
What stood out to me was this..
Sean Reid said:
I haven't heard that comment before. I was wondering if there are some references/links to some diagrams or text that explains this. I'm intrigued!!!
Cheers
Phil
Doc William
William
Sean Reid said:
Sean,
I would only warn those people that are converting in CS2 that the new Adobe RAW converter has a white balance picker. Bruce Fraser in his recent book "Real-World Camera Raw with Adobe Photoshop CS2" warns that you should pick a white in your image that is not blown out rather than the neutral grey card we are all used to, to get everything into balance. Again, that is with the new Adobe RAW converter in CS2.
Peace,
bill
Phil, in your first paragraph, there are two necessary elements not considered... First is subject distance or magnification, and second is the user's choice of "circle of confusion" that are both used in the computation. If the focal length is the same, the aperture diameter is the same, the subject magnification is the same, and you choose the same circle of confusion, then Depth of Field is the same regardless of format dimensions or cropping, etc.
The thing in comparing DoF with different sensor/film sizes is that the enlargement ratio is likely to be different, and for that reason CoC would likely be chosen differently. You blow something up larger, it gets fuzzier before and behind the point of focus, so apparent DoF is less... the CoC has been magnified as well. To keep the apparent DoF the same, the CoC must be kept smaller at the sensor, requiring a smaller aperture...
Since there are a number of related factors, and it all boils down to human perception in the end anyway, it gets difficult! There are a few DoF calculator web pages online that are fun to play with...
http://www.dudak.baka.com/dofcalc.html
Here's one in the form of an Excel spreadsheet (the blur circle mapper)
http://www.smartgroups.com/vault/lens_grading/Public/
The thing in comparing DoF with different sensor/film sizes is that the enlargement ratio is likely to be different, and for that reason CoC would likely be chosen differently. You blow something up larger, it gets fuzzier before and behind the point of focus, so apparent DoF is less... the CoC has been magnified as well. To keep the apparent DoF the same, the CoC must be kept smaller at the sensor, requiring a smaller aperture...
Since there are a number of related factors, and it all boils down to human perception in the end anyway, it gets difficult! There are a few DoF calculator web pages online that are fun to play with...
http://www.dudak.baka.com/dofcalc.html
Here's one in the form of an Excel spreadsheet (the blur circle mapper)
http://www.smartgroups.com/vault/lens_grading/Public/
MarkEDavison
Member
Let me suggest an actual experiment which can clarify some of these matters, and which is fun to conduct (I just now did it myself).
Take your R-D1 and mount it on a tripod facing a scene like a room with furniture where there are plenty of features which will provide persepective cues. Without moving the camera, photograph the scene with, say, a 15mm, 35mm, and 50mm lens, stopped way down so in each case the entire scene appears to be in focus. Pull the images into Photoshop. Find a pair of distinguishing points (which appear in all three images) where you can easily measure the distance between the points using the ruler tool. Use the resulting measurements to figure out the relative scale difference between the three scenes. Now shrink the 35mm and 50mm scenes by the appropriate scales, and overlay the shrunken images on the 15mm scene. You will find that they match almost exactly. That is, in terms of geometric perspective, the images produced by the 35mm and 50mm lens are identical to crops from the 15mm image. Just such an overlay is attached below. The 35mm image overlay is colored yellow, the 50mm overlay sort of grayish blue. I admit that the images don't align exactly perfectly, but they are very very close.
Beware if you do this experiment yourself--some lenses display differing amounts of barrel or pincushion distortion. These are departures from ideal rectilinear perspective which will cause the images not to align.
The academic conclusion is that if we just had a good enough 15mm lens (with infinite resolution) and a digital sensor with high enough resolution we could dispense with carrying lenses of different focal lengths and simply carry the 15mm, and magnify crops from images produced with that lens.
But in point of fact, we do not have infinite resolution in either lenses, or sensors. We use different lenses because they draw the fine details differently, not because there is some generic difference in the way they render geometric perspective.
Now why do photographers insist that telephoto lenses compress space, and wide-angle lenses foreshorten in? Because we typically create prints that are all the same size, and then view the prints from the same distance. With telephoto lenses, we are viewing the prints from a point which is closer to the print than the center of perspective, or natural viewpoint, and this creates compression. For wide angle lenses we are viewing the prints at a position which is further from the print than the natural viewpoint, and this produces foreshortening.
I think you will find that if you take an R-D1 image with a 50mm, and then take a 35mm image with a 75mm lens, the two images will be identical in terms of geometric rendering, but different in terms of rendering of fine details and depth of field effects.
Take your R-D1 and mount it on a tripod facing a scene like a room with furniture where there are plenty of features which will provide persepective cues. Without moving the camera, photograph the scene with, say, a 15mm, 35mm, and 50mm lens, stopped way down so in each case the entire scene appears to be in focus. Pull the images into Photoshop. Find a pair of distinguishing points (which appear in all three images) where you can easily measure the distance between the points using the ruler tool. Use the resulting measurements to figure out the relative scale difference between the three scenes. Now shrink the 35mm and 50mm scenes by the appropriate scales, and overlay the shrunken images on the 15mm scene. You will find that they match almost exactly. That is, in terms of geometric perspective, the images produced by the 35mm and 50mm lens are identical to crops from the 15mm image. Just such an overlay is attached below. The 35mm image overlay is colored yellow, the 50mm overlay sort of grayish blue. I admit that the images don't align exactly perfectly, but they are very very close.
Beware if you do this experiment yourself--some lenses display differing amounts of barrel or pincushion distortion. These are departures from ideal rectilinear perspective which will cause the images not to align.
The academic conclusion is that if we just had a good enough 15mm lens (with infinite resolution) and a digital sensor with high enough resolution we could dispense with carrying lenses of different focal lengths and simply carry the 15mm, and magnify crops from images produced with that lens.
But in point of fact, we do not have infinite resolution in either lenses, or sensors. We use different lenses because they draw the fine details differently, not because there is some generic difference in the way they render geometric perspective.
Now why do photographers insist that telephoto lenses compress space, and wide-angle lenses foreshorten in? Because we typically create prints that are all the same size, and then view the prints from the same distance. With telephoto lenses, we are viewing the prints from a point which is closer to the print than the center of perspective, or natural viewpoint, and this creates compression. For wide angle lenses we are viewing the prints at a position which is further from the print than the natural viewpoint, and this produces foreshortening.
I think you will find that if you take an R-D1 image with a 50mm, and then take a 35mm image with a 75mm lens, the two images will be identical in terms of geometric rendering, but different in terms of rendering of fine details and depth of field effects.
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