Is my 50mm lens actually a 60mm lens???

[Ororaro]

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...

 

[venchka]

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]

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!)

 

[Ororaro]

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!)

😀 😀 😀

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?

 

[Ororaro]

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.

 

[Rob-F]

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.

 

[Bryce]

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.

 

[tripod]

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]

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

 

[Toby]

* 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

 

[Ororaro]

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.

 

[Ororaro]

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?

 

[Ororaro]

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)?

 

[ampguy]

it's self-correcting

it's self-correcting

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...

 

[Toby]

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.

 

[tomasis]

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]

So is it a bad thing if I hang around in a forum where everyone talks about COC?

 

[Ororaro]

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 ;-)

 

[Ororaro]

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.

 

[tomasis]

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.