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

[tripod]

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.

 

[stuken]

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.

 

[ampguy]

not with my lens

not with my lens

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.

 

[Chris101]

... 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.

 

[FrankS]

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!

 

[Toby]

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:

 

[gdi]

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:

 

[maddoc]

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 ...🙂

 

[FrankS]

Some good point you made, shallow DoF as an end in itself can be quite boring ...🙂

Quite shallow, actually.

 

[maddoc]

Quite shallow, actually.

Yep, that is what I meant, quite shallow.

 

[maddoc]

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.

 

[ampguy]

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. 🙂

 

[Ororaro]

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...

 

[maddoc]

Roland and Ned, you are right guys ... 😱 I am to much in science, when I just read or hear "discuss" the " I have to contribute" switch is triggered...😀

Roland, Danke fuer die Info ! Das war schnell 🙂

 

[ampguy]

not quite

not quite

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]

He's got to be moving pretty damn fast for that to take effect!

 

[Ororaro]

I can't beleive where this thread is going :Insert a Dizzy head exploding:

😉

 

[MikeL]

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.

 

[former member]

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.