View Full Version : Is my 50mm lens actually a 60mm lens???
Okay, so I shoot a M4-P on 35mm film with a 2:3 ratio frame.
I develop the film and print on 8x10 paper. Of course I need 8x12 paper in order to print the totality of the film. Since I can't do it, I crop. I want to keep the 8 inch intact so I end up cropping 2 inches up and down to make a 8x10 print.
Does this make my 50mm lens a 60mm lens? Do I gain DOF in the image?
What do you have to say on this?
Please discuss...
Well, if you had a 50mm Summicron, it is really a 51.9mm lens. Otherwise, no to all of your questions. Cropping doesn't change the optical qualities of your 50mm lens.
Chris101
02-04-2008, 14:28
Oh hell yeah! When you crop the image the lens (that took the picture last week) suddenly changes it's focal length. It's just like quantum mechanics - spooky action at a distance. (Ask any dslr user!)
Oh hell yeah! When you crop the image the lens (that took the picture last week) suddenly changes it's focal length. It's just like quantum mechanics - spooky action at a distance. (Ask any dslr user!)
:D :D :D
Chris, maybe you will answer this one too:
What happens if I'm in total darkness and with my Super Cat vision I open a Tri-X film, take a Black marker and blackout 4 sides of a 24mmx36mm frame and load it in the camera and take a picture on that particular frame (please note I don't blackout the Mirror of the SLR but only the film)? And what happens when I wind the film to the next frame and shoot the same scene (but this time the film hasn't been blacked out and I'm always standing on the same spot)?
Granted, I end up with two 8x10 prints. One with a 8x10 image and the other with a 5x7 image in the center (which is indeed a 8x10 print with huge Black borders). I then cut the borders and end up with a 5x7 image.
Now, when I take the 5x7 print and place it over the 8x10 print the 5x7 print will blend-in perfectly, right?
Has Depth of Field changed? Did the Black marker add depth of field magically?
Why do everybody send me to dofmaster.com? Why does Fred come up with hyperfocus distance in orer to prove the above isn't correct?
Of course, I understand the COC illusion. If I take an image with 1mm dof and enlarge it as big as the galaxy, the dof will seem to be as big as planet earth to my puny human eyes. But that's a whole different story.
Chris, any answers for your old Brother Ned?
nikonhswebmaster
02-04-2008, 15:23
Of course, I understand the COC illusion. If I take an image with 1mm dof and enlarge it as big as the galaxy, the dof will seem to be as big as planet earth to my puny human eyes. But that's a whole different story.
Now you are beginning to get it, that is the only thing that counts, how it appears to the viewer.
Now you are beginning to get it, that is the only thing that counts, how it appears to the viewer.
I am "beginning" to get it?
This, Fred, was never the topic. Sistemistic and some others introduced it and started the confusion. Typical blind leading the blind kind of situation.
Anyhow, I'm glad it's finally sorted out.
You know, Fred, I'm kinda extremely deceived at the way you led this whole thing. You kinda lost the authority you seem to like to show about yourself in all your posts.
Your 50mm lens becomes a 60mm equivalent only in terms of horizontal angle of view. Remember, the vertical angle of view has not changed, since you are using the full height of the negative. But unless you have backed off from the subject to reclaim the lost horizontal coverage, the perspective has not changed, nor has the DOF.
nikonhswebmaster
02-04-2008, 16:53
Ned my opinion continues to be that you really add to the confusion. (as does Sitemistic)
While some of the statements made by others, are not absolutely correct, they are methods of visualizing, a mental metaphor for them to use when taking photos, so to speak.
Quote:
"Granted, I end up with two 8x10 prints. One with a 8x10 image and the other with a 5x7 image in the center (which is indeed a 8x10 print with huge Black borders). I then cut the borders and end up with a 5x7 image.
Now, when I take the 5x7 print and place it over the 8x10 print the 5x7 print will blend-in perfectly, right?
Has Depth of Field changed? Did the Black marker add depth of field magically?"
Ned-
Your analogy doesn't include the final step to make the comparison that DOF scales are based on: enlarging the 5x7 piece of the original picture to the same size as the 8x12 it was originally identical to the center of.
At that point, the image as well as its blurry spots are made bigger.
Were the lens designed to make the more greatly enlarged, smaller negative in the first place, its DOF markers would have told you to stop down a bit further to compensate.
Notice how the photo on the left appears to have deep depth of field, and the photo on the right appears to have very shallow depth of field?
In your example photos, the right one (cropped) lacks sharpness and looks out-of-focus. Sorry, but I can't see any increasing shallow DoF due to the cropping process !? :confused:
Ned, IMO you are wrong, and NikonWebMaster, sitemistic and Dave in the other thread, and others are correct.
You seem to think that film or sensor format plays no role in the DOF rendered, but it does and the reason why is simply this: The format determines the focal length that is considered normal (as opposed to wide and telephoto).
When taking a pic of a person showing head to toes for example with different formats:
with 35mm format the normal focal length is about 50mm (let's not argue that point in this discussion). To get that shot, you would have to stand, say 10 feet back. Let's say we use an aperture of f2. The zone of focus (DOF) for a 50mm lens at this aperture at this distance is, say 8 to 12 feet.
with aps format, the normal focal length is about 28mm. This plces you at the same 10 feet from the subject to get a head to toes shot. At 10 feet at f2, a 28mm lens has a greater zone of focus (greater DOF), probably 6 to 20 feet.
with a 6x7 film camera, the normal focal length is about 100mm. This places you the same 10 feet from your subject to get a head to toes shot. At 10ft at f2, a 100mm lens has a smaller zone of focus (DOF) than a 28mm lens (which is the normal focal length for APS format.) DOF for a 100 mm lens at 10ft at f2 is probably, what, 9 to 11ft?
(The numbers that I've given here are relative only, I didn't quote DOF charts. They may be off, but their relative sizes are accurate.)
So you see, film and sensor format plays a pivital role in DOF, and this is why lots of photographers are not happy with cropped digital sensors, they cannot get the same limited DOF effects as with a full frame sensor.
Benjamin Marks
02-05-2008, 04:30
Oy vey. Twenty lashes with a roll of wet Tri-X for everyone and repeat 36 times, "I will go take some pictures with my favorite lens and breath deeply before participating in any more DOF threads."
Bemusedly (and ducking),
Ben Marks
nikonhswebmaster
02-05-2008, 06:08
In your example photos, the right one (cropped) lacks sharpness and looks out-of-focus. Sorry, but I can't see any increasing shallow DoF due to the cropping process !? :confused:
Those are Ned's photos.
I just removed them. I tried using his photos for an illustration, but he shoots wide open (at least in the photos he has online) so there is such very shallow depth of field. He is going for a very soft dreamy look in his work.
* sound of a deep intake of breath and then a mournful sigh *
DOF field is decribed by the point where the dots of light that a photographic image is made out of turn into discs. This is where the sharp areas of an image turn blurry - think sharp areas dots, blurry area discs.
Enlargement is of course central to how many dots (sharp areas) and how many discs (blurry areas) are perceived by the viewer. Enlarge any picture big enough and it becomes totally blurred -there are no sharp areas. Enlarge the same image to 6x4 and it appears sharp front to back.
How does this effect the properties of a 50mm lens across different formats?
If you compare two images shot with the same lens but one shot with a FF sensor the other with a smaller APS sensor on if you enlarge them two the same size print more of the APS sensors 'dots' will be enlarged to the point where they become discs hence DOF field drops for the print from the smaller format. This is the COC in action
Of course I am wrong if you imply I have to move and recompose with a different lens. But you are totally missing the point and all I've said on the subject. You haven't read, have you?
Ned, IMO you are wrong, and NikonWebMaster, sitemistic and Dave in the other thread, and others are correct.
You seem to think that film or sensor format plays no role in the DOF rendered, but it does and the reason why is simply this: The format determines the focal length that is considered normal (as opposed to wide and telephoto).
When taking a pic of a person showing head to toes for example with different formats:
with 35mm format the normal focal length is about 50mm (let's not argue that point in this discussion). To get that shot, you would have to stand, say 10 feet back. Let's say we use an aperture of f2. The zone of focus (DOF) for a 50mm lens at this aperture at this distance is, say 8 to 12 feet.
with aps format, the normal focal length is about 28mm. This plces you at the same 10 feet from the subject to get a head to toes shot. At 10 feet at f2, a 28mm lens has a greater zone of focus (greater DOF), probably 6 to 20 feet.
with a 6x7 film camera, the normal focal length is about 100mm. This places you the same 10 feet from your subject to get a head to toes shot. At 10ft at f2, a 100mm lens has a smaller zone of focus (DOF) than a 28mm lens (which is the normal focal length for APS format.) DOF for a 100 mm lens at 10ft at f2 is probably, what, 9 to 11ft?
(The numbers that I've given here are relative only, I didn't quote DOF charts. They may be off, but their relative sizes are accurate.)
So you see, film and sensor format plays a pivital role in DOF, and this is why lots of photographers are not happy with cropped digital sensors, they cannot get the same limited DOF effects as with a full frame sensor.
Fred, what are you trying to illustrate? All I know is the dof stays the same. The ILLUSION changes. But are we talking ILLUSION or real DOF?
More Cock value?
Mine is big. But if you look at it from far, you don't see it. It becomes small.
Do you want to talk about REAL values (measured in centimeters) or do you want to talk about ILLUSION values? (Cock of confusion)?
given that you're using an RF, film, and all, the 2/3 becomes 4/3 through the process. It think a Hicks and Francis book also confirms this...
Okay, so I shoot a M4-P on 35mm film with a 2:3 ratio frame.
I develop the film and print on 8x10 paper. Of course I need 8x12 paper in order to print the totality of the film. Since I can't do it, I crop. I want to keep the 8 inch intact so I end up cropping 2 inches up and down to make a 8x10 print.
Does this make my 50mm lens a 60mm lens? Do I gain DOF in the image?
What do you have to say on this?
Please discuss...
Mine is big. But if you look at it from far, you don't see it. It becomes small.
Do you want to talk about REAL values (measured in centimeters) or do you want to talk about ILLUSION values? (Cock of confusion)?
There are no constant values for depth of field. The scale for DOF on a lens is usually worked by assuming a print enlargement range of a certain size. You're trying to find an absolute value for sharpness where none exists.
ned, you insist about croping and croping. If you nailed the frame perfectly with the camera and you cannot crop the image in the darkroom (not even by any inch or centimeter) otherwise it'd ruin the composition. So do you see that type of argument doesn't hold, are you getting my point?
antiquark
02-05-2008, 07:12
So is it a bad thing if I hang around in a forum where everyone talks about COC?
given that you're using an RF, film, and all, the 2/3 becomes 4/3 through the process. It think a Hicks and Francis book also confirms this...
I don't need a book nor a website to confirm anything, really. A calculator is enough in this instance.
2/3 =1.5 ratio, which is the same as 36mm/24mm= 1.5.
4/3 =1.33 ratio and a 8x10 print is 1.25 ratio.
So no, 2/3 doesn't become 4/3 and doesn't self-correct unless you play with your enlarging easel the way you like it ;-)
ned, you insist about croping and croping. If you nailed the frame perfectly with the camera and you cannot crop the image in the darkroom (not even by any inch or centimeter) otherwise it'd ruin the composition. So do you see that type of argument doesn't hold, are you getting my point?
Is it me who insists on cropping or is it the market that insists on selling cropped sensors?
Of course, we're only having a discussion and it's amazing how discussions go all over the place. Still cool.
ned, you know that manufacturers are slowly milking us by releasing smallest sensors then introduce a bigger and so on. Same with megapixels race. Ridiculous, isn't? But we are familiar with the way of dealing with capitalism, yeah? We have somewhat accept that size of sensors is not always related to marketing, needs of consumers , photographers but also laws of physics :( I don't worry though and in future it will be very exciting times for us with a nice arsenal of amazing optic pieces anyway.
nikonhswebmaster
02-05-2008, 08:47
Fred, what are you trying to illustrate? All I know is the dof stays the same. The ILLUSION changes. But are we talking ILLUSION or real DOF?
I hate to be the bearer of bad tidings, but these photos are all an illusion, we have a flat image with appears to have shape and depth.
You can prove this to yourself, try putting your hand into one of your prints, you will find it is all just an illusion.
Reality is merely an illusion,
although a very persistent one. (Einstein)
:)
If I am incorrect in my understanding of format size and DOF effects, I would only welcome enlightenment. An ignorant man is not one who does not know something, it is one who does not want to learn.
I have been under the impression for years, that limited DOF effects are relatively more difficult to achieve with relatively smaller formats. I've heard many complain about this with the small digicams. I notice this too using different film formats. Isn't it also why front tilt is so useful in LF to achieve large DOF in a landscape photo?
Please educate me.
nikonhswebmaster
02-05-2008, 09:10
If I am incorrect in my understanding of format size and DOF effects, I would only welcome enlightenment. An ignorant man is not one who does not know something, it is one who does not want to learn.
I have been under the impression for years, that limited DOF effects are relatively more difficult to achieve with relatively smaller formats. I've heard many complain about this with the small digicams. I notice this too using different film formats. Isn't it also why front tilt is so useful in LF to achieve large DOF in a landscape photo?
Please educate me.
Format does not have anything to do with that. That is related to the fact that most lenses on small point-n-shoot cameras simply do not have large enough f-stops to produce shallow DOF.
An example:
My little Lumix comes with a Leica Vario Elmarit 6.3~25.2 Zoom, but the widest f-stop is only 2.8, which changes to 4.9 as the lens goes to 25.2.
In 35mm terms that would be the same as a 28mm 2.8 lens, which is going to give you rather deep depth of field. At the other end the telephoto is shut down to 4.9 which is also going to give a lot of DOF.
If the lens was faster, say a 1.4, all through the zoom range (which would be a HUGE piece of glass) then the DOF would be more limited. 2.8 at the long end would give shallow DOF, but not 4.9.
Increasing or decreasing DOF on any given film/sensor size (at a specific focal length) is only a product of what f-stop you use. The smaller the f-stop the greater the DOF.
Adding to this issue is that most people use point-n-shoot camera on Program, so the camera often closes the lens down even more in bright sunlight, thus even further reducing the blurred background effect some are looking for. The more stopped down, the more EVERYTHING looks more or less, in focus. This effect of everything more or less appearing in focus is what is called hyperfocal distance (as a simple explanation), the area in a photo where there is no out-of-focus, front to back.
Having everything in focus is what makes a photo appear more "real" in the sense this is the way we see with our eyes and brain. Our eyes shut down in bright sunlight, and everything appears in focus, and our brains fool us also into thinking as we re-focus far and near that everything is sharp.
Out of focus backgrounds and foregrounds look very unnatural, since we never see the world that way. Some photographers like Ansel Adams, proponents of natural photography, worked very hard to get every detail of a photo in focus, and in fact their movement was named f-64.
Fashion photographers in the 60's really began to experiment with shallow depth of field, sometimes using 300 mm lenses at f 2.
Deliberate, out of focus, has never however reached the mainstream to any degree, and is particularly unpopular right now in museum shows. Hyper-sharp is now pretty much the norm.
Clearly whomever deemed them cirlces of confusion had this certain phenomenon aptly named.
I did not read the entire thread, so sorry for doubling up if it is the case. You are not changing the focal lengh of the lens, you are changing its effect focal lengh. You will acheive the same perspective, and compression ect in the image, it will just be rendered differently according to format. 50mm on a 4x5 is very wide, but only because of the senser(film) size. if you cut out a 24x36 peice of neg from the very center of that 4x5, it would have the same characteristics as if it were taking on a 35mm camera.
antiquark
02-05-2008, 10:10
Deliberate, out of focus, has never however reached the mainstream to any degree.
With the exception of the bokeh craze:
http://flickr.com/search/?q=bokeh&ss=2&s=int
When I use the DOF indicator on the lens, with my aperture at infinity, everything to infinity (and beyond) is in focus. 4x6, 5x7, 8x10, if costco prints that size, it's in focus and sharp!
There are no constant values for depth of field. The scale for DOF on a lens is usually worked by assuming a print enlargement range of a certain size. You're trying to find an absolute value for sharpness where none exists.
nikonhswebmaster
02-05-2008, 12:16
With the exception of the bokeh craze:
http://flickr.com/search/?q=bokeh&ss=2&s=int
Bokeh seems to be totally an online concept, frankly in 40 years I have never heard of it before dropping by the RFF. I do see however there is enormous interest in it, B&H is even mentioning it in lens descriptions!
I personally have no idea what it actually is, but remain open.
Chris101
02-05-2008, 12:19
... Chris, any answers for your old Brother Ned?DOF is a whole 'nuther animal, one I will stay away from. Since I print from very small prints you hold in a book or hand, to HUGE things that dominate a wall, it's easy to see that DOF is pure illusion. What looks nice and crisp in a small version when viewed from across the room, is a blurry mess when printed 48x72 and examined with a magnifying glass.
So I never try to calculate DOF. I focus as needed, and stop down for more, open up for less. From there it's out of my hands.
I find it really interesting/surprising that there is either an unclear understanding about a fundamental photographic principle by many folks here, or there is simply an inability to communicate these thoughts clearly. I find depth of field differences among different size formats like tripod. Let's hear from some real experts on this to straighten us out, please!
nikonhswebmaster
02-05-2008, 12:55
When I use the DOF indicator on the lens, with my aperture at infinity, everything to infinity (and beyond) is in focus. 4x6, 5x7, 8x10, if costco prints that size, it's in focus and sharp!
Now that is metaphysical... What is beyond infinity? Nirvana?
FrankS you are right, just think of an infinity aperture. Makes that Noct 1.0 look slow by comparison!
I am pretty much done trying. Ned was just annoying me, so I kept posting, but I am working on control.
When I use the DOF indicator on the lens, with my aperture at infinity, everything to infinity (and beyond) is in focus. 4x6, 5x7, 8x10, if costco prints that size, it's in focus and sharp!
Infinity is one point. DOF describes the zone of sharpness between two points. so what's your point? Or is this just pointless:bang:
nikonhswebmaster
02-05-2008, 13:04
He is thinking of
"To infinity and Beyond"
I had completely forgotten that technical point when I posted. That would be two points, Infinity, and Beyond, and the zone between them.
With the exception of the bokeh craze:
http://flickr.com/search/?q=bokeh&ss=2&s=int
Truly a fad among aperture geeks. Those who think a Noctilux (or its really fast competition) was designed to wear 2 x ND8 filters to take daylight closeup shots of twigs to display the nauseating blurred and swirling background, and twisted coma. :bang:
depends on the lens, for some leica lenses it is beyond a certain # of miles as defined for infinity in the advanced leica m book. Go read it!
Now that is metaphysical... What is beyond infinity? Nirvana?
FrankS you are right, just think of an infinity aperture. Makes that Noct 1.0 look slow by comparison!
I am pretty much done trying. Ned was just annoying me, so I kept posting, but I am working on control.
Truly a fad among aperture geeks. Those who think a Noctilux (or its really fast competition) was designed to wear 2 x ND8 filters to take daylight closeup shots of twigs to display the nauseating blurred and swirling background, and twisted coma. :bang:
Some good point you made, shallow DoF as an end in itself can be quite boring ...:)
Some good point you made, shallow DoF as an end in itself can be quite boring ...:)
Quite shallow, actually.
Quite shallow, actually.
Yep, that is what I meant, quite shallow.
Okay, so I shoot a M4-P on 35mm film with a 2:3 ratio frame.
I develop the film and print on 8x10 paper. Of course I need 8x12 paper in order to print the totality of the film. Since I can't do it, I crop. I want to keep the 8 inch intact so I end up cropping 2 inches up and down to make a 8x10 print.
Does this make my 50mm lens a 60mm lens? Do I gain DOF in the image?
What do you have to say on this?
Please discuss...
I thought some time about your question and my two cents are:
It is important to distinguish between two image-producing processes, the first is the projection of the 3D subject onto the 2D film, that is where the camera optics is the key factor, and the second is the projection of the 2D 24x36 frame onto the 2D 8x10 inches photo-paper. In the first process the selected aperture and distance to your subject determines the DoF with respect to the choosen FL of 50mm, the FL of 50mm further determines the FoV. The resulting negative is a 2D "plot" of the former 3D distributed subject, so parts of the subject are "in focus" and parts are "out-of-focus", since the complete 3D information can`t be transformed into 2D using normal photographic processes (with Holography it can to a certain point). On the negative all details "in-focus" can be clearly distinguished, since they are sufficiently separated (minimum distance 0.03mm = CoC).
Now, in the second process, the enlargement onto the photo-paper, the 2D information of the negative is enlarged by a factor of ~ 8 (24mm = ~ 1 inch) and so are the details. The formerly 0.03mm separated details are now separated by 0.24mm. This separation is still small enough to be seen as "sharp" by the eye.
If you now crop during the enlarging process, there won`t be any change to the detail separation, so the DoF shouldn`t change. (Since you keep the same enlargement factor of 8) What changes is the FoV, so on your final print, you will see everything of the subject as maybe a 60mm lens would have recorded initially but the DoF and perspective of the 50mm lens will be the same.
OK, so Leica uses a few more miles than I thought for infinity, namely 1,057,206,276 x 1035 miles for their lens designs.
Still no match for Buzz L. :)
Gabor, my original question wasn't serious (as I knew the answer) altough it gives food for thought once one starts thinking about it.
Thanks for the thoughts...
Roland and Ned, you are right guys ... :o I am to much in science, when I just read or hear "discuss" the " I have to contribute" switch is triggered...:D
Roland, Danke fuer die Info ! Das war schnell :)
I hate to be the bearer of bad tidings, but these photos are all an illusion, we have a flat image with appears to have shape and depth.
You can prove this to yourself, try putting your hand into one of your prints, you will find it is all just an illusion.
Reality is merely an illusion,
although a very persistent one. (Einstein)
:)
I am 6'1. No matter how near or far, even if I'm 100 yards far and look like I'm smaller then your thumb, it doesn't diminish the fact that I am a solid 6'1 and that your thumb is an inch or two. Perception changes but reality is real.
At some point one has to get real and stop the nonsense.
If you are horizontal and moving, and your tape measure is stationary, then the faster you are moving, the shorter you are relative to the stationary measuring unit, as you cross past it.
I am 6'1. No matter how near or far, even if I'm 100 yards far and look like I'm smaller then your thumb, it doesn't diminish the fact that I am a solid 6'1 and that your thumb is an inch or two. Perception changes but reality is real.
At some point one has to get real and stop the nonsense.
Chris101
02-06-2008, 13:11
He's got to be moving pretty damn fast for that to take effect!
I can't beleive where this thread is going :Insert a Dizzy head exploding:
;)
If you are horizontal and moving, and your tape measure is stationary, then the faster you are moving, the shorter you are relative to the stationary measuring unit, as you cross past it.
Don't forget the density of each and orientation as well.
nikonhswebmaster
02-07-2008, 09:09
I am 6'1. No matter how near or far, even if I'm 100 yards far and look like I'm smaller then your thumb, it doesn't diminish the fact that I am a solid 6'1 and that your thumb is an inch or two. Perception changes but reality is real.
At some point one has to get real and stop the nonsense.
So you don't believe Einstein?
So you don't believe Einstein?
Are we now getting into Einsteins special theory of relativity? Hoochi Mumma! thats heavy stuff. I have read book after book after book on it and while I am perfectly prepared to accept what those books tell me my head still spins and I think I am going nuts every time I read about it.
And if you think that stuff is reality testing pick up a book on Quantum Mechanics for Dummies (or whatever) and read what it has to say about reality. Shrodinger's Cat, here I come!
Brian Sweeney
02-08-2008, 01:58
It's a 50mm lens. If you want it to be 60mm, move the rear optics out a few millimeters, shim the lens, and then cut a spiral into the RF cam for the new focal length.
vBulletin® v3.6.8, Copyright ©2000-2010, Jelsoft Enterprises Ltd.