Understanding a True 50mm on MFT or Super35 Body, confused. Help!!

[bjoern]

Hi I'm new here
And I'm trying to wrap my head around this topic...

From what I understand, if I put a 25mm Lens (SLR 35mm film) on a MFT-camera (crop-factor 2x) then I get roughly
a field of view of a 50mm lens (SLR 35mm film). Problem is a 25mm will have a very noticeable distortion even though I crop allot out on MFT Body's.

Question: Does a MFT lens like for example the "voiglander 25mm" has a equal "small" Image distortion (almost none visible)
like a 50mm lens (SLR 35mm film)?
Which I'm guessing,if true, could be achieved doe to the shorter flange distance, correct ??
Or is the 25mm from an image distortion equal?


Different Scenario, similar problem:
Comparing here Super35 (cropfactor 1.6) to SLR 35mm full-format in terms of FOV.
Question: Cinema lenses are build with a super35 dimensions in mind. Which does "NOT" cover a full-format sensor ( at least the older lenses).
I'm wondering which of these possibility's is then true:
A: a 50mm lens Build for super35 is = 50mm lens in terms of FOV (SLR 35mm film)
Yes, because the Flange distance is different?
B: a 50mm lens Build for super35 is = 80mm lens in terms of FOV (SLR 35mm film), here is the crop-factor applied.
Answer: Yes, Because "SLR 35mm film" got established first (still cameras) And now everything get's calculated from this base?


Another Scenario
Question:If I want a true "SLR 35mm Film" look (Distortion, FOV, BOKEH) Lense: 50mm f/2,
with super35 (APS-C) sensor I would need:
A: 31mm focal-length (31 x 1.6 = 50mm), but with a distortion of a 50mm lens like for Full-frame format (not Wideangle distortion !!!).
B: f/1.4 Aperture. The lens needs to be 1 Stop Faster! Otherwise the Bokeh is only half as Shallow/blurry.

Thx, for any input this is realy frying my brain....
sorry for the mixed up english...
ps.: I'm not interested in what "feels" right. I'm looking for what is optically from a science standpoint right.

[pnodrog]

The only lens that will give you the perspective of a 50mm lens is a 50mm lens. You can achieve an equivalent viewing angle by using a 25mm lens on 2x crop sensor but the perspective is altered. As you indicated the increased depth of field that a 25mm lens has compared to that of a 50mm lens at the same aperture can be compensated for by opening the aperture but you will not change the perspective.

This behaviour can be an advantage with a long focal length lens on a cropped sensor camera. However for soft out of focus backgrounds with wider angle lenses a full frame sensor or larger format is the best tool - hence the move by many photographers back to using a full frame camera.

[Manfred M]

Hi – welcome to CiC.

Hi I'm new here
And I'm trying to wrap my head around this topic...

From what I understand, if I put a 25mm Lens (SLR 35mm film) on a MFT-camera (crop-factor 2x) then I get roughly
a field of view of a 50mm lens (SLR 35mm film). Problem is a 25mm will have a very noticeable distortion even though I crop allot out on MFT Body's.

I think that this is going to be dependent on your lens. I have used a Tokina f/2 11-16 mm crop frame lens on my mFT video camera (Panasonic AF100). This means I was using the centre part of the lens and did not notice any distortion.

Question: Does a MFT lens like for example the "voiglander 25mm" has a equal "small" Image distortion (almost none visible)
like a 50mm lens (SLR 35mm film)?
Which I'm guessing,if true, could be achieved doe to the shorter flange distance, correct ??
Or is the 25mm from an image distortion equal?

First of all, are referring to the mFT f/0.95 25mm Nokton or the full-frame f/4 25mm Color-Skopar? The Nokton is a speciality fast lens with a very narrow DoF that is very popular with video shooters, and hence has a lot of trade-offs to get this effect. The full-frame lens has a larger image circle and will give you superior, low distortion results. In terms of FoV, both lenses will give you the same size of image. The Nokton would be designed for the mFT image circle, while the Color-Skopar would cover the image circle for a 35mm or full-frame camera.

The flange distance is relevant to where the lens focuses. I seem to remember reading that when Leica brought out the M8, the sensor that they used angled microlenses on the sensor to correct for the relatively acute angle that resulted from the short flange distance. I would assume that there would be a similar issue in mirrorless cameras like mFT.[/QUOTE]

Different Scenario, similar problem:
Comparing here Super35 (cropfactor 1.6) to SLR 35mm full-format in terms of FOV.
Question: Cinema lenses are build with a super35 dimensions in mind. Which does "NOT" cover a full-format sensor ( at least the older lenses).
I'm wondering which of these possibility's is then true:
A: a 50mm lens Build for super35 is = 50mm lens in terms of FOV (SLR 35mm film)
Yes, because the Flange distance is different?
B: a 50mm lens Build for super35 is = 80mm lens in terms of FOV (SLR 35mm film), here is the crop-factor applied.
Answer: Yes, Because "SLR 35mm film" got established first (still cameras) And now everything get's calculated from this base?

Even today the APS-C lenses are not designed to cover the full image circle of anything other than the 1.6 crop factor (Canon) or 1.5 crop factor (pretty well everyone else). Full-frame lenses are designed to cover the image circle of a full-frame sensor.

The FoV will be the same for both types of lenses. I have a full frame camera, a crop frame camera and a mFT video camera. I can use my full-frame lenses on any of the cameras, but if I try to use the crop frame lenses on the full-frame camera, I get less than full coverage because the image circle is too small.

As stated before, the flange distance is important for focus, not FoV. I use my full frame and crop frame lenses on my mFT video camera through an adaptor. The adaptor does two things, it allows me to use my Nikon lenses on my Panasonic video camera because it has the appropriate lens mounts AND it adjusts the flange distance for proper focusing.

Actually 35mm still frame was not established first, the first 35mm still camera used movie film, but covered two frames. Nominally 35mm still film uses a 24mm x 36mm image and movie film uses roughly 18mm x 24mm (the actual sizes vary amongst different formats).

Question:If I want a true "SLR 35mm Film" look (Distortion, FOV, BOKEH) Lense: 50mm f/2,
with super35 (APS-C) sensor I would need:
A: 31mm focal-length (31 x 1.6 = 50mm), but with a distortion of a 50mm lens like for Full-frame format (not Wideangle distortion !!!).
B: f/1.4 Aperture. The lens needs to be 1 Stop Faster! Otherwise the Bokeh is only half as Shallow/blurry.

Thx, for any input this is realy frying my brain....
sorry for the mixed up english...
ps.: I'm not interested in what "feels" right. I'm looking for what is optically from a science standpoint right.

It depends on what you mean by "SLR 35mm Film". The answer is somewhat complicated by the fact that no DSLR actually shots that way. These cameras are HD cameras and shoot either 720 x 1280 or 1080 x 1920 formats, and the frame rates vary. If you look at the sensor sizes in any still camera, you will see that the only way that these formats are achievable is through downsampling, i.e. throwing away most of the data.

If you want the 35mm look, you need to shoot with a full-frame camera; nothing else will work, especially when it comes to Depth of Field (DoF). I strongly suspect that this is why Cosina introduced the 25mm Nokton; to get the shallow DoF that is normally associated with the larger full-frame sensor. Bokeh, by the way is dependant on the lens design, not the camera. I think you are mixing up DoF and Bokeh; they are totally different things. Depth of field is the out of focus area (foreground and background) and Bokeh is the aesthetic appearance of the out of focus areas, especially the highlights.

I am not sure if this helped clarify things at all.

[oleleclos]

The only lens that will give you the perspective of a 50mm lens is a 50mm lens. You can achieve an equivalent viewing angle by using a 25mm lens on 2x crop sensor but the perspective is altered.

I'm afraid I'd have to disagree with Paul's last statement. Perspective is not controlled by the use of a specific focal length but by the choice of viewpoint, or camera position if you like. Given the same camera position and the same image sensor size, the focal length, and therefore viewing angle, of any given lens only decides the cropping of the scene.

In other words, lenses of different focal lengths produce the same perspective from the same viewpoint, but different crops - as long as the sensor stays the same. When you compare a full frame and a 2x crop sensor, a lens of half the focal length will therefore produce the same crop on the small sensor - and the same perspective, given the same camera position.

[Inkanyezi]

The answer from oleleclos is correct and easy to understand.

Perspective always and only depends on the distance from your subject, and is not influenced by focal length or sensor size.

A 50 mm lens on any camera is always a 50 mm lens, no matter what sensor size it is. But sensor size will govern the angle of view. Hence, the 50 mm, which is regarded a "normal" lens on a "full frame" camera, i.e. a camera with an image size of 24x36 mm, will be more like a "portrait lens" on µ4/3 or APS-C sensors. It is equivalent in angle with the 100 mm lens on the FF camera, when it is used on µ4/3 and equivalent in angle to 75 or 80 mm when used on APS-C format.

25 mm lenses generally do not have much distortion, whether full frame 24x36 or smaller formats. However, viewing distance may present a distorted view, when you view the image from a distance that makes it occupy a smaller viewing angle than the angle it captures. When you bring the wide angle image closer to your eye, the apparent perspective becomes normal.

A "normal" lens is so called, because when you view the final image at a suitable viewing distance, perspective seems "normal". Generally, a somewhat larger focal length than the diagonal of the image creates the normal perspective, so portrait lenses of about 1½ of the sensor diagonal mostly will render the most natural perspective, when you look at the final image at a convenient distance. Hence a 10 mm focal length might be the one that makes perspective appear "normal" in the final image, if your camera is a compact p&s, while 30 to 35 mm might render the same for most DSLR cameras. For µ4/3 it is 25 mm. All of those present the same angle of view and will give similar images, differing only by the purely technical properties of respective sensor sizes and physical aperture. Thus the smaller cameras will show greater depth of field and the larger ones shallower.

And yes, for your "Super 35" that has the same size as APS-C, you'll need a 31 mm lens at f/1.4 to render the same DOF and FOV as f/2 with a 50 mm lens on a full frame camera (24x36). On a µ4/3 camera you would need f/1 at 25 mm.

[jcuknz]

Another vote for OLE

[Inkanyezi]

I am rather familiar with using various focal lengths on µ4/3. The image below, with the Carl Zeiss Planar 1,4/50 T* was taken as an illustration to how to get your model to look openly into the camera for portraits. The open eye, when half the face is exposed, will indicate that you are not hiding behind a black box, and it makes it much easier for your victim to focus on the right spot, where the camera is. And yes, I can focus and frame with both eyes open and looking past the camera with one. I've been doing this for about fifty years now.

[bjoern]

WOW, thx for this crazy amount of details...

okay, but what confuses me then.. What would an old-school cameraman do with a super35 camera that wants to shoot,
from the perspective of a Human eye. Like lets say replacing a persons head in an Interview with a camera.

If you would use a Full-format censor and 50mm as this head-replacment. The perspective would be correct (as close as you can get).
But you could "never" use a 50mm for this with a super35/APS-C sensor and just zoom with your Feed. This will not give you the same perspective!

But would I read everywhere is that to replicate a human eye overall you should just use a 50mm and zoom with you feet. Which has to be absolutely wrong! right?
So if a oldschool cameraman wanted to reproduce a Human eye in terms of FOV, they would have to use a 35mm or a 28mm lense (on super35). But 50mm does not make sense what so ever...

wikipedia states for example this, I know its wikipedia... but that is where my journey started...:

Normal lense:
35 mm, sound (super35)
50 mm focal length
http://en.wikipedia.org/wiki/Normal_lens


But in terms of FOV again. This is wrong. You cannot use 50mm as a normal lense unless you zoom with your feed. But again then you change the perspective, and how things are Overlaying (think of a Forrest) in front of you.

sorry its more a filmcamera related answer that I'm looking for. But it seems to me that this forum is by far more knowledgeable than
most film-DSLR forums...

[bjoern]

I'm afraid I'd have to disagree with Paul's last statement. Perspective is not controlled by the use of a specific focal length but by the choice of viewpoint, or camera position if you like. Given the same camera position and the same image sensor size, the focal length, and therefore viewing angle, of any given lens only decides the cropping of the scene.

In other words, lenses of different focal lengths produce the same perspective from the same viewpoint, but different crops - as long as the sensor stays the same. When you compare a full frame and a 2x crop sensor, a lens of half the focal length will therefore produce the same crop on the small sensor - and the same perspective, given the same camera position.

This makes absolute perfect sense! And this is why I don't understand that people tell me: if you want to replicate
a human eye/Normal lense on super35/APS-C just zoom oldschool with your feed....

cause this seems to me complete nonsense!

[Inkanyezi]

I think that question was already answered. On double-8 we had 13 mm lenses, and 5.5 mm was considered wide angle. Movie cameras often had rather narrow FOV. Even though, for the audience, the screen was enormous in cinemas, and we looked at those images at a much wider angle of view than they were taken.

So there is not one, but many answers to the FOV quandary. It depends on the size of the screen where the movie is played and its distance from the audience. If the movie is viewed on a small TV screen, a narrow angle is appropriate, but if you view it on a cinema screen from the middle rows, a wider angle lens will give a more natural perspective.

The direct comparison between 50 mm for the miniature camera and 30 mm for the super 35 is reasonable. The half frame Olympus had a frame size of just a little less than 18x24 mm, which was its nominal frame size, that corresponds to the normal 35 mm frame. Its *normal* lens was 38 mm.

So you'll have to consider the audience situation in order to calculate what FOV would give a natural perspective. If objects that are registered take up the same angle of vision for the final viewer of the work, the perspective is correct. It depends on the size of the projected image and the distance to the viewer.

[bjoern]

I think that question was already answered. On double-8 we had 13 mm lenses, and 5.5 mm was considered wide angle. Movie cameras often had rather narrow FOV. Even though, for the audience, the screen was enormous in cinemas, and we looked at those images at a much wider angle of view than they were taken.

So there is not one, but many answers to the FOV quandary. It depends on the size of the screen where the movie is played and its distance from the audience. If the movie is viewed on a small TV screen, a narrow angle is appropriate, but if you view it on a cinema screen from the middle rows, a wider angle lens will give a more natural perspective.

The direct comparison between 50 mm for the miniature camera and 30 mm for the super 35 is reasonable. The half frame Olympus had a frame size of just a little less than 18x24 mm, which was its nominal frame size, that corresponds to the normal 35 mm frame. Its *normal* lens was 38 mm.

So you'll have to consider the audience situation in order to calculate what FOV would give a natural perspective. If objects that are registered take up the same angle of vision for the final viewer of the work, the perspective is correct. It depends on the size of the projected image and the distance to the viewer.

Okay I think I'm getting it slowly, thx again for the detailed help!
This means I always have to take in to account where my audience would see the picture?
So lets say (with a super35 camera) if I do something for TV where my Audience is looking at a relatively close and small screen, I should pick a 30mm lens.
But If I shoot for the Cinema I should shhot (on super35) with a 50mm to give the Audience a experience that is close to the human eye? Correct?

[bjoern]

Okay I think I'm getting it slowly, thx again for the detailed help!
This means I always have to take in to account where my audience would see the picture?
So lets say (with a super35 camera) if I do something for TV where my Audience is looking at a relatively close and small screen, I should pick a 30mm lens.
But If I shoot for the Cinema I should shhot (on super35) with a 50mm to give the Audience a experience that is close to the human eye? Correct?

Okay I just figured, that above was wrong:

If I have the perfect setup: Cinema-screen with a viewer in the right distance in relation to the screen-size. Filmed with a 50mm on super35.
Then everythig is correct. But now I would stand up and walk slowly towards the screen and the screen would scale down proportionally, Nothing would change! right?
I should still use 50mm on super35. Because the Window I'm looking though feels the same size. I'm closer, but the window is smaller scaled in proportion to how much I cam closer. right?

So if that is true, then using a 30mm lens on APS-C seems to make no sense to me "now" (to achieve the human eye feeling/normal lense), if I assume my Audience is in the right distance in relative to the Screen-size (like in the cinema). Unless the distance of the viewer get adjusted accordingly.

So I guess 30mm on APS-C makes only sense for Still photography (for a humaneye/Normal lense) where the Audience
has a different distance to the image

[Inkanyezi]

Man piaba rings in my ears. Clear as mud, but it covers the ground...

The final product of a photoshoot sits on a shelf and is viewed from a certain distance. With the "portrait" lens, and a 5x7 inches print, the perspective will be pretty normal at arm's length if the lens was a 50 mm on a µ4/3 camera. Now we move the scenario to a movie theatre with a screen that is 30' wide. In the back row about 40' from the screen, you have a rather normal perspective with a 30 mm lens on what was shot with a super 35 camera. Moving closer will distort perspective, flatten it, and the angle of view toward the screen would be much wider than the camera FOV.

On the other hand, if it is projected to a size of about 20', even those in the middle of the audience would have a reasonably correct perspective. Still it would be flatter when you are close and somewhat, but not much, wider when you are farther away. In the back row, the focal length of the camera lens would be shorter than ideal for such a small screen.

But this is a tradeoff we always have to make in order to show the footage to a large audience. All of them cannot sit at the exact spot that corresponds to a normal perspective. Often cinematographic effects are used where size is exaggerated, and not much is thought about using that particular focal length, which gives perfect perspective for the guy in the middle row. Telling a story with images is much more than "correct perspective". But it sure helps. I think that if I shot movies with a super 35, the 30 mm would be my favourite for close shots. However, I would use wide angle sometimes too, but hardly ever a long lens. I remember that 25 mm was a much used focal length for 16 mm, and that would be something more like 40 or 50 mm on the super 35. But movie sizes also corresponded to smaller screen sizes. 16 mm was not blown up as 35 mm, and we looked at screens that were at best up to 10' wide from about 20' distance.

[bjoern]

Man piaba rings in my ears. Clear as mud, but it covers the ground...

haha I did not know that one... but I just checked it on youtube... haha
I can't convert inch in relation to mm and meters in my head in realtime... being a german with bad math..
And I get what you are saying that its more about the viewers experience and there are more viewers than just the guy in the middle row.
But to be a pain in the ass

Just as a rehearsal, cause my brain gets a bit fried processing all this English through my German brain.
And I need to safe something as the correct base in my head
If I have only 1 viewer in the Middle row sitting in the cinema, in a correct designed cinema (screen-size for super35 ,seat distance to screen), and the film is filmed with a super35mm Camera with a 50mm lens. Than this will give me the most natural experience
close to the human eye/ standart lense.
Correct?

[Manfred M]

This makes absolute perfect sense! And this is why I don't understand that people tell me: if you want to replicate
a human eye/Normal lense on super35/APS-C just zoom oldschool with your feed....

cause this seems to me complete nonsense!

Carefully said, a "normal lens" is generally viewed as a lens whose focal length is the same as the diagonal of the sensor / film size, i.e. the image circle. For the nominal Super35 mm film of 24.9mm x 14mm, this is 28.56mm. So any lens between 25mm and 30mm will be just fine.

That being said, there is no "rule" that you have to shoot this way. If I shoot video and do head shots or 3/4 shots, I treat the shot very much like I would with a still camera and shoot with a short zoom. On my mFT video camera this means somewhere between 40mm and 65mm. If you shoot headshots with a "normal" lens, you will get distortions of the subjects face, just like you would in still photography.

If I shoot landscapes, I tend to shoot a bit wider angle; the best I can do with the lenses I own, without going to a fisheye is 11mm.

The issue on mFT is of course DoF. Cosina has sold tons of f/1.1 50mm Noktons to mFT and DSLR videographers. The Voigtländer (Cosina) mFT f/0.95 17.5mm and 25mm Nokton lenses are very much aimed at that crowd. You need to have an ultra fast lens in mFT to get the shallow DoF that is very fashionable right now.

[bjoern]

Carefully said, a "normal lens" is generally viewed as a lens whose focal length is the same as the diagonal of the sensor / film size, i.e. the image circle. For the nominal Super35 mm film of 24.9mm x 14mm, this is 28.56mm. So any lens between 25mm and 30mm will be just fine.

from what I understand this is in terms of cinema this is not correct. Quoting from wikipedia:

In cinematography, a focal length roughly equivalent to twice the diagonal of the image projected within the camera is considered normal, since movies are typically viewed from a distance of about twice the screen diagonal.

So 50-60mm should be more appropriate choice for cinema shoot with super35

[Inkanyezi]

If I have only 1 viewer in the Middle row sitting in the cinema, in a correct designed cinema (screen-size for super35 ,seat distance to screen), and the film is filmed with a super35mm Camera with a 50mm lens. Than this will give me the most natural experience
close to the human eye/ standart lense.
Correct?

If this one person views the screen at the same angle as the scene was viewed with the 50 mm lens on the super 35, it would be correct, but I would think that the theatre is very oblong with a rather small screen for such a wide film format.

If we assume that the movie is shot on super 35 with a 31 mm lens, and the viewer sits 10 metres from the screen that is 7.5 metres wide, Then the perspective will be perceived as it was shot, normal. If shot with a 50 mm lens, with the same size on screen, the viewer should move to 16 metres from the screen to get the same perspective as the images were shot. So for most movie theatres, the most natural perspective would be from the back row, because screens are often wider than 7.5 m and few movie theatres have such oblong layout. Very often the audience sits uncomfortably close to the screen, the front row only a few metres away from it.

By the way, I am also more used to the metric system, and I would spell "bjoern" Björn, which is Swedish for Bär in German. :-)

[Manfred M]

from what I understand this is in terms of cinema this is not correct. Quoting from wikipedia:


So 50-60mm should be more appropriate choice for cinema shoot with super35

I guess I don't know anyone shooting mFT or DSLR who is aiming at shooting for the big screen. Most of the small format shooting is aimed at large screen TV or small theatres. If you are shooting for feature film, I am out of my league.

[bjoern]

thx guys! This is awesome. I learned so much from this thread!
@ Inkanyezi
And yes my name is Björn haha But I'm working in canada... got so much used to the engl keyboard layout...

[Manfred M]

Bjorn - if you are looking at shooting video, I suggest signing up at a video site, rather one that focuses on still photography.

DVXUser is a very good one I use: http://www.dvxuser.com/V6/