is 50 50?

[obzelite]

is the Nikon 50mm f1.8 a 50mm film lens or a 50mm digital lens, meaning its accounting for the crop factor?

i could probably google this, but its easier to ask here

[digitor]

A 50mm lens is a 50mm lens even if it's not mounted on a camera at all - its focal length is 50mm. What will vary when a lens is used with different film (or sensor) sizes is the field of view which is captured on the medium.

Cheers

[jamesw]

yes, the focal length refers to its physical focal length. thus a 50mm lens is a 50mm lens, regardless of what sensor crop it was designed for.

the question you are asking is a little confused, i will try and answer it though.

i'll start off by saying that nikon digital bodies have a 1.5x crop. this 1.5x crop is a comparative term, when compared specifically wtih the 35mm format.

that means that any lense's focal length is effectively 1.5x longer when mounted on a digital body, than on a 35mm body.

eg.

50mm lens, when mounted on a nikon digital body is effectively 75mm if you are thinking in terms of the 35mm equiv.

30mm lens, when mounted on a nikon digital body is effectively 45mm if you are thinking in terms of the 35mm equiv.

that basically means that what was considered a normal lens (50mm) on the 35mm format is no longer a normal focal length... its more suited to portrait work but still the length is a bit odd ball.

if you were wanting a normall lens i suggest looking at the sigma 30mm f1.4 (effectively 45mm) or the nikon 35mm f2 (effectively 52.5mm)

to further emphasize my point, medium format guys have 30mm fisheyes (with DX its a 10.5mm for full fish, for 35mm its 15-16mm for full fish) and 80 odd mm normal lenses. this is because their sensor/film is larger

hopefully that answers your question.

[Greg B]

Good question.

And good answer.

50mm is indeed 50mm. The convention that 50mm is a "standard" lens
(on 35mm cameras) is based on the field of view being similar to the human eye.

A 50mm lens is still a 50mm lens on a dx format digital camera, but the FoV is
roughly equivalent to a 75mm lens on a 35mm camera.

On a 6x7cm camera, the FoV of a 50mm lens on a 35mm camera is
achieved with a 90 mm lens.

It could scarcely be more confusing.

[obzelite]

thats what i thought, what i want is a lens for a d200 that will give me a photo that compared to a 35mm film camera photo looks the same.

so its a 35mm for me

[ATJ]

Note that the focal length refers to the optical focal length not the physical size of the lens. For example, a mirror lens can achieve the same focal length in a much shorter physical size. Many of the newer lenses use compound glass to achieve focal lengths longer than the physical size of the lens.

Also note that the focal length is for the lens focus at infinity. As you focus closer the angle of view may change.

[jamesw]

thats what i thought, what i want is a lens for a d200 that will give me a photo that compared to a 35mm film camera photo looks the same.

so its a 35mm for me

30mm lens, when mounted on a nikon digital body is effectively 45mm if you are thinking in terms of the 35mm equiv.

that basically means that what was considered a normal lens (50mm) on the 35mm format is no longer a normal focal length... its more suited to portrait work but still the length is a bit odd ball.

if you were wanting a normall lens i suggest looking at the sigma 30mm f1.4 (effectively 45mm on a 35mm crop) or the nikon 35mm f2 (effectively 52.5mm on a 35mm crop)

either a somewhere between 30-35mm is considered the 'normal' focal length on DX crop

[digitor]

Many of the newer lenses use compound glass to achieve focal lengths longer than the physical size of the lens.

The telephoto design (a lens with the optical centre outside the physical lens) was first used towards the end on the 19th century, and doesn't depend on exotic modern glass for its properties. There's a good summary here: http://en.wikipedia.org/wiki/Telephoto_lens

Cheers

[ATJ]

either a somewhere between 30-35mm is considered the 'normal' focal length on DX crop

I'm not sure I agree with this statement. While the statement appears to true by definition:

A lens of focal length equal to the diagonal of the film size it is intended to cover is said to be of normal focal length.

DX cameras are a crop of the film size even though they are effectively 35mm. i.e. it is just like taking a photograph with a 35mm camera and then cropping the resulting photograph to a smaller size. With a normal lens you don't get the same distortion you get with a wide angle lens or the same foreshortening you get with a telephoto. Lenses slightly longer than normal are used for portraiture to ensure there is no distortion.

If you were to take a photograph with a 50mm lens on a 35mm camera, a photograph with a 35mm lens on a 35mm lens and crop the second photograph, I don't believe the two photographs would look the same.

[ATJ]

Many of the newer lenses use compound glass to achieve focal lengths longer than the physical size of the lens.

The telephoto design (a lens with the optical centre outside the physical lens) was first used towards the end on the 19th century, and doesn't depend on exotic modern glass for its properties. There's a good summary here: http://en.wikipedia.org/wiki/Telephoto_lens

Good point. I was thinking of some of the newer lenses which a significantly smaller than their focal length but you are correct, almost all are smaller.

[jamesw]

either a somewhere between 30-35mm is considered the 'normal' focal length on DX crop

I'm not sure I agree with this statement. While the statement appears to true by definition:

A lens of focal length equal to the diagonal of the film size it is intended to cover is said to be of normal focal length.

DX cameras are a crop of the film size even though they are effectively 35mm. i.e. it is just like taking a photograph with a 35mm camera and then cropping the resulting photograph to a smaller size. With a normal lens you don't get the same distortion you get with a wide angle lens or the same foreshortening you get with a telephoto. Lenses slightly longer than normal are used for portraiture to ensure there is no distortion.

If you were to take a photograph with a 50mm lens on a 35mm camera, a photograph with a 35mm lens on a 35mm lens and crop the second photograph, I don't believe the two photographs would look the same.

chill. i do understand the point you are making. but for the purpose of the original post, you are going to get a similar FOV with a 30-35mm leens as you would a 50mm lens.

i think the discussion is getting overly technical when it does not need to be. and i dont think perspective issues are particularly relevant...

if you are looking for a lens to give you a similar fov to a 50mm just get a 30-35mm lens, it will be fine. although there may be differences between the two, i sincerely doubt you will notice then.

[ATJ]

I guess we'll just have to agree to disagree.

[jamesw]

I guess we'll just have to agree to disagree.

dont get me wrong i agree with you and im not disputing your point. there are bokeh / dof differences between the lenses, as well as differences in distortion.

i just think for the purposes of this particular discussion that a 30-35mm lens serves the same purpose as a 50mm lens when discussing FOV.

if you want the bokeh and perpective of a 50mm - buy a 50mm. if you want the FOV you are accustomed to with your 50mm on a 35mm body, get a 30-35mm lens.

do we agree now hehe

[obzelite]

If you were to take a photograph with a 50mm lens on a 35mm camera, a photograph with a 35mm lens on a 35mm lens and crop the second photograph, I don't believe the two photographs would look the same.

that's actually true, something i didn't think about.
the perceived distance between object in the foreground and background increase the smaller the lens size. so side by side although the fov would prob be the same, but the picture would be different

[phillipb]

Let me ask an hypothetical question here.
Let's say I use a 35mm film camera with a 50mm lens, a Dslr with 1.5crop factor with a 35mm lens and another Dslr with 1.5 crop factor with a 50mm lens.
I take a photo of a person from the same position (ie. camera to subject distance stays the same). If I imported into photoshop all 3 photos as layers, but I crop them so that they all have the same size subject within the frame, eg. head touching the top of the frame, feet touching the bottom, do you think that the layers would match?

[digitor]

Let me ask an hypothetical question here.
Let's say I use a 35mm film camera with a 50mm lens, a Dslr with 1.5crop factor with a 35mm lens and another Dslr with 1.5 crop factor with a 50mm lens.
I take a photo of a person from the same position (ie. camera to subject distance stays the same). If I imported into photoshop all 3 photos as layers, but I crop them so that they all have the same size subject within the frame, eg. head touching the top of the frame, feet touching the bottom, do you think that the layers would match?

Yes.

Perspective effects (which ATJ refers to above as wideangle distortion and telephoto foreshortening) have nothing to do with the focal length of the lens, nor the format of the film/sensor. Not a jot. Zero. Zilch.

They are a function of the subject to camera distances. You don't need a camera to test this - just hold your hands out in front of you, and make a frame with your thumbs and forefingers, and move your hands to and fro. Does the perspective of the scene you can see within the "frame" change? No. The amount of the scene visible to you through the frame does change, but the perspective remains constant, because you haven't moved relative to the scene.

Cheers

[jamesw]

Let me ask an hypothetical question here.
Let's say I use a 35mm film camera with a 50mm lens, a Dslr with 1.5crop factor with a 35mm lens and another Dslr with 1.5 crop factor with a 50mm lens.
I take a photo of a person from the same position (ie. camera to subject distance stays the same). If I imported into photoshop all 3 photos as layers, but I crop them so that they all have the same size subject within the frame, eg. head touching the top of the frame, feet touching the bottom, do you think that the layers would match?

Yes.

Perspective effects (which ATJ refers to above as wideangle distortion and telephoto foreshortening) have nothing to do with the focal length of the lens, nor the format of the film/sensor. Not a jot. Zero. Zilch.

They are a function of the subject to camera distances. You don't need a camera to test this - just hold your hands out in front of you, and make a frame with your thumbs and forefingers, and move your hands to and fro. Does the perspective of the scene you can see within the "frame" change? No. The amount of the scene visible to you through the frame does change, but the perspective remains constant, because you haven't moved relative to the scene.

Cheers

you sir have a far superior brain than i!!!!!!!!

[obzelite]

ok, i found these to illustrate what i had forgotten when considering the 35mm. the scene is the same, but the focal length of the lens changes the final result.
So although with a 35mm at 1.6 crop would be a similar fov to a 50mm on a 35mm full frame camera the picture would be different.

24mm
<A HREF="http://www.cs.mtu.edu/~shene/DigiCam/User-Guide/990/ON-CAMERA-LENS/p-024mm.jpg"><IMG SRC="http://www.cs.mtu.edu/~shene/DigiCam/User-Guide/990/ON-CAMERA-LENS/p-024mm-s.jpg" BORDER=2></A>

38mm
<A HREF="http://www.cs.mtu.edu/~shene/DigiCam/User-Guide/990/ON-CAMERA-LENS/p-038mm.jpg"><IMG SRC="http://www.cs.mtu.edu/~shene/DigiCam/User-Guide/990/ON-CAMERA-LENS/p-038mm-s.jpg" BORDER=2></A>

75mm
<A HREF="http://www.cs.mtu.edu/~shene/DigiCam/User-Guide/990/ON-CAMERA-LENS/p-075mm.jpg"><IMG SRC="http://www.cs.mtu.edu/~shene/DigiCam/User-Guide/990/ON-CAMERA-LENS/p-075mm-s.jpg" BORDER=2></A>

[jamesw]

ok, i found these to illustrate what i had forgotten when considering the 35mm. the scene is the same, but the focal length of the lens changes the final result.
So although with a 35mm at 1.6 crop would be a similar fov to a 50mm on a 35mm full frame camera the picture would be different.

24mm
<A HREF="http://www.cs.mtu.edu/~shene/DigiCam/User-Guide/990/ON-CAMERA-LENS/p-024mm.jpg"><IMG SRC="http://www.cs.mtu.edu/~shene/DigiCam/User-Guide/990/ON-CAMERA-LENS/p-024mm-s.jpg" BORDER=2></A>

38mm
<A HREF="http://www.cs.mtu.edu/~shene/DigiCam/User-Guide/990/ON-CAMERA-LENS/p-038mm.jpg"><IMG SRC="http://www.cs.mtu.edu/~shene/DigiCam/User-Guide/990/ON-CAMERA-LENS/p-038mm-s.jpg" BORDER=2></A>

75mm
<A HREF="http://www.cs.mtu.edu/~shene/DigiCam/User-Guide/990/ON-CAMERA-LENS/p-075mm.jpg"><IMG SRC="http://www.cs.mtu.edu/~shene/DigiCam/User-Guide/990/ON-CAMERA-LENS/p-075mm-s.jpg" BORDER=2></A>

those photos only illustrate the pespective differences between a wide to normal to longer lens.

i believe digitor is on the money. sorry.

if someone has the time and energy, as well as a FF digi and crop digi, they could prove it, but i believe digitor is on the bling...

[Matt. K]

digitor is correct. Only camera to subject distance alters perspective, not focal length. Now...think on how you might use that information to your advantage.

[digitor]

ok, i found these to illustrate what i had forgotten when considering the 35mm. the scene is the same, but the focal length of the lens changes the final result.

No.

What has changed the final result here, is that the photographs were taken from different positions.

Cheers

[Yi-P]

50mm is indeed 50mm. The convention that 50mm is a "standard" lens
(on 35mm cameras) is based on the field of view being similar to the human eye.
.

Long ago, I got told that 50mm being "standard/normal" lens is because their image projection is equivalent or very close to typical 35mm film plane. And many other say it is close to human eye (on 35mm equiv)...

My curiosity is that which is true or both are true??

[jamesw]

50mm is indeed 50mm. The convention that 50mm is a "standard" lens
(on 35mm cameras) is based on the field of view being similar to the human eye.
.

Long ago, I got told that 50mm being "standard/normal" lens is because their image projection is equivalent or very close to typical 35mm film plane. And many other say it is close to human eye (on 35mm equiv)...

My curiosity is that which is true or both are true??

i dont know about the first,

but i too have been told on numerous occassions that the 50mm lens on a 35mm body gives the same FOV as what a typical human sees.

but then i remember this experiment that an art teacher taught us in grade 5 or 6 where we learnt that girls have a wider FOV that guys.

[phillipb]

I've known for a long time that girls have better colour vision then men (hence why they usually made up the bulk of employees at the kodak lab) but I've never heard about them having wider FOV.

[sirhc55]

I've known for a long time that girls have better colour vision then men (hence why they usually made up the bulk of employees at the kodak lab) but I've never heard about them having wider FOV.

Most women have eyes in the back of their head, so I suppose you could class this as a wide FOV

[ATJ]

Ah... I stand corrected. It would also explain the couple of photographs today. With the camera mounted on the tripod, I shot a simple seen at both 18mm and 70mm and cropped the 18mm version and they looked much the same.


Shot with the lens at 18mm, cropped and resized


Shot with the lens at 70mm and resized

As my D70's sensor is 23.7 x 15.6mm, a normal lens would be around 28mm*.


* (23.7^2 + 15.6^2)^0.5 = 28.3734