The 50 mm as standard - how it came to be

[Bill C]

... and while there is a little difference, they look pretty close in terms of angles. The main difference being DOF. Both taken at f11, ISO 400.

 

Hi, to match the DOF, you want the physical diameter of the lens apertures to match, rather than the f-numbers. (Physical aperture diameter is focal_length / f-number.)

 

Since you used fls of 50 mm and 14 mm, try, for example, 50 mm at f/11 vs roughly f/2.8 or f/4 (actual f/3.1) on the 14mm lens.

 

In other words, the 14 mm lens should be opened up about 3 1/2 f-stops more than the 50mm lens. This should get the DOF pretty similar. (If you are shooting closeups the rule won't hold exactly, as the 50 mm lens has to be "racked out" a little more; perhaps you would only need to open up about 3 f-stops, etc.)

[Ed_Ingold]

The effect of the focal length or size of the sensor, at the same distance, is the same as cropping a print. No matter how you cut, the shape/perspective of objects in the image are unchanged. This principle is often used in camera advertisements to illustrate the effect of different focal lengths.

[Bill C]

Also, each lens by each manufacturer is a little different in terms of what it "sees". I found that out tonight as I was making some tests with two 135 lenses to see which one I wanted to keep. I was quite surprised to see what I saw in the viewfinder (and on an SLR, what I saw was what the lens was actually recording). Placing the camera at exactly the same distance from a stationary subject, one lens recorded the subject as being quite a bit further away than the other lens! Has anyone else seen this sort of thing?

 

Hi, this can happen if the subject is relatively close, depending on the lens design. When you are trying to match the subject coverage, your actually want to keep the subject distance constant from what is known as the "entrance pupil" of the lens. (The entrance pupil is the place from which the lens "sees" the subject, and it is not necessarily where you think it will be; it depends on the lens design.)

 

I'd guess that your two 135 mm lenses will match closer when the subject is a long distance away.

 

If you're interested, I can given you a relatively crude but straightforward way to find the approximate pupil position. If one of the lenses is a zoom you'll probably be surprised at how much the entrance pupil moves while you zoom. Although it really doesn't make much difference for most practical purposes, unless you are trying to match a field of view.

[Sandy Vongries]

unless you are trying to match a field of view.

Even with GPS position, same camera, same lens, that is quite a trick. I used to need to do that on a job I had for half a dozen years - finally had to settle for good enough, bringing prints of the previous photos, best match with live view.

[Uhooru]

Here are the 2 picks. Roughly similar, the 14 mm seems to include a bit wider background than the 50, but that could be caused by human error or specific qualities of the lens. Also DOF is a bit different. The 14mm shows a little wider area in the background and foreground but the relationship of the object on the table and the box in background are basically the same. 50 mm

[Uhooru]

Hi, this can happen if the subject is relatively close, depending on the lens design. When you are trying to match the subject coverage, your actually want to keep the subject distance constant from what is known as the "entrance pupil" of the lens. (The entrance pupil is the place from which the lens "sees" the subject, and it is not necessarily where you think it will be; it depends on the lens design.)

 

I'd guess that your two 135 mm lenses will match closer when the subject is a long distance away.

 

If you're interested, I can given you a relatively crude but straightforward way to find the approximate pupil position. If one of the lenses is a zoom you'll probably be surprised at how much the entrance pupil moves while you zoom. Although it really doesn't make much difference for most practical purposes, unless you are trying to match a field of view.

Thanks Bill, that's really more than I want to do with this, plus I also want to show the DOF difference, its actually part of the test.

[Ed_Ingold]

The entrance pupil is how the lens sees the world. The exit pupil is how the film sees the lens, and consequently the DOF. They are one and the same for a simple lens, but can vary widely with compound lenses. If you compare focal lengths and formats, DOF is inversely proportional to the absolute magnification at the film plane. A subject which just fills the frame will have 1.5x the DOF on an APS-C camera vs an FX camera. Absolute magnification depends on both focal length and distance. If you crop a print and enlarge the cropped portion, the apparent DOF will decrease proportionately.

 

Zooming a lens affects the apparent diameter of the diaphragm (~ entrance pupil diameter) when viewed from the front of the lens, but not necessarily its position. How much the entrance pupil position varies when you zoom a lens depends on the lens design. When you take a series of images for a stitched panorama, it is important to rotate the camera on an axis coincident with the front pupil, so that nearby (< 50' or so) don't move with respect to the background. Empirically, you observe this shift and adjust the axis so that the shift is minimized. In the lens I used most often for this application, a Nikon 28-70/2.8, the entrance pupil shifts less than 1/4" over the entire zoom range, and can be essentially ignored once set.

[Bill C]

Here are the 2 picks. Roughly similar, the 14 mm seems to include a bit wider background than the 50, but that could be caused by human error or specific qualities of the lens. Also DOF is a bit different.

 

Hi, thanks for the results, but the reason they look different is because the camera is not in the same place - I'm guessing that you just went handheld. Looking at the bag of Rapid-Set, it's pretty clear that the camera has shifted to the right for the 50 mm lens shot. (Look at the angle of the white stripe on upper right of bag.)

 

Regarding DOF, if you want it to match you can't stay at the same f-number, the more important thing is the physical diameter of the entrance pupil (basically how large the stopped-down aperture appears as you look into the front of the lens). If you deal with these two things, and possibly a small distance shift due to different entrance pupil positions, then the images should be virtually indistinguishable, aside from pixel density differences, etc.

[Bill C]

Thanks Bill, that's really more than I want to do with this, plus I also want to show the DOF difference, its actually part of the test.

 

I should have been more clear that I was trying to explain, for Steve Mareno, how two lenses, with same focal length, might have a different subject coverage when camera position is fixed. Because he apparently experienced it (I have also, but measured things to discover what was going on).

 

The difference can be pretty significant at studio distances, but as Ed points out, it depends on the lens design. I wouldn't be surprised, and have seen more than a few, where the pupil at the long end of a zoom might shift to the rear, some distance behind the back of the camera. (You might measure 8 feet from the front of lens to subject, but the lens actually "sees" from over 9 feet away; consequently it can't zoom in as tight as you might otherwise expect that it ought to.)

 

(My awakening came 'bout 30 year ago, doing design work on a front projection system (these went mostly defunct when chromakey on digital says got "good enough"). Anyway, for front projection it is necessary to match the virtual positions of both camera and projector lens pupils to control what's often called a shadow line. Consequently one needs to know where the pupils are, distance-wise.)

Edited July 5, 2018 by Bill C

[Uhooru]

Hi, thanks for the results, but the reason they look different is because the camera is not in the same place - I'm guessing that you just went handheld. Looking at the bag of Rapid-Set, it's pretty clear that the camera has shifted to the right for the 50 mm lens shot. (Look at the angle of the white stripe on upper right of bag.)

 

Regarding DOF, if you want it to match you can't stay at the same f-number, the more important thing is the physical diameter of the entrance pupil (basically how large the stopped-down aperture appears as you look into the front of the lens). If you deal with these two things, and possibly a small distance shift due to different entrance pupil positions, then the images should be virtually indistinguishable, aside from pixel density differences, etc.

 

Yes, I understand and I did handhold, sitting in the same spot, but with the 14 I had to make sure that it was reasonably rectilinear and thus maybe moved it a little. But really for these purposes I was after it confirmed for me what Ed was stating, DOF aside. Thanks for all the technical explanations Bill and Ed. I understand about matching or trying to match DOF as well, but that's not what I was interested in. Practically I only really wanted to see if the photos looked similar in their perspectives when the 14 was cropped to match the 50.

[Ed_Ingold]

You're welcome. Now you have another "sharp tool" in your skills kit - perspective. Too often we stand pat and use a zoom lens to get "closer" or "further". On many occasions I venture forth with only prime lenses, often only one, to polish my ability to see. It is perhaps true when your only tool is a hammer you look for nails, but not always the same nails ;) I still prefer zoom lenses. When you stand at the edge of a 3000 foot abyss (Grand Canyon), getting closer by foot is not a plan. At other times, a zoom lens gives you the ability to crop once you are standing in the "right" place.

[Uhooru]

With my DSLR days (D700 and D200), I used mostly zooms. I had a fast 50 for low light work, but as I was shooting weddings I tended to use the lovely and heavy 24-70 and nice but even heavier 70-200. But my favorite street lens was the 17-35 which mated so perfectly to the D700 and I took some of my favorite street/documentary sets with that combo. Though its a little risque, and if you haven't and are interested, take a look at my "Folsom Street Fair" set here on p.net. Always interested to see your thoughts on that, but there is some public nudity so just be aware.

 

Now with the Fuji X I'm using basically primes but have been thinking of getting something like 18-55 which is supposedly a very capable kit lens that isn't crazy expensive. But really from my rangefinder days I am really used to and enjoy the 35mm equivalent lens, sometimes the 14mm (21 equivalent) and surprisingly the 50 f2, a lens that I really ended up liking. I got it because I was shooting some friends' bands and a couple of weddings and I just needed a little better reach, though obviously the zoom would be handy in those situations. The 50 is also a nice portrait lens IMO. My philosophy is basically "love the one your with". I rarely, if ever, say I wish I had another lens with me. Those are only vapor ware of the mind :) The only pictures that exist from moment to moment are the ones you can take with what you have with you.

[Tim_Lookingbill]

Though its a little risque, and if you haven't and are interested, take a look at my "Folsom Street Fair" set here on p.net.

Are you Barry Fisher? That's the person's gallery I get when I click on your Photo.net gallery link.

 

I haven't found Uhooru gallery. Couldn't find "Folsom Street Fair" since there's nothing labeled as such on Barry Fisher gallery. I get a lot of Untitled and one that says Bergens1.

[Uhooru]

Yeah I'm Barry Fisher let me check out what you have. I have several what do we call them, albums? Clearly labeled so let me look at mine and see what the profile says.

[Uhooru]

Tim the Gallery is called Folsom Street Fair (through the eyes of a tourist). Here's hopefully a link to my galleries.

Photo.net - Where Photographers Inspire Each Other

[JDMvW]

To sum up - From the Life Library of Photography

[Tim_Lookingbill]

Tim the Gallery is called Folsom Street Fair (through the eyes of a tourist). Here's hopefully a link to my galleries.

Photo.net - Where Photographers Inspire Each Other

That link sends me to my gallery. What was the point of that, Uhooru?

 

Why couldn't you just provide a link to the Folsom Street Fair gallery?

[Tim_Lookingbill]

It's OK, Uhooru.

 

This site is run by robots so I'm guessing hyperlinks within its own navigation of the site don't even work now.

 

This is why I only spend time posting images to No Words and Abstracts forums and engage in an occasional discussion of interest like this one. At least now I know how broke this site has become.

[Uhooru]

Must be so, as I took that url from the folsom set. What happens when you just click on my icon and navigate over? That should work.

[glen_h]

The article says that they used 25mm lenses with 35mm movie cameras, presumably with 18x24mm frames.

 

Converting to a 24x36mm frame would not double the focal length, but, as I calculate about 36mm.

 

So, even as described in the article, the normal lens should not be 50mm.

 

When I bought my own camera in 1979, I bought a Nikon FM with AI 35/2.0.

 

Previously, I was using my father's Canon VI, for which I had 35mm, 50mm, and 135mm lenses.

 

For indoors with flash (Vivitar 283, which covers 35mm) and outdoor scenery, my preference was 35mm.

 

Not so much later, I bought a used Nikon AI 35-70/3.5 zoom, which I used for many years,

often in the 35mm position.

[Ed_Ingold]

Fact check: 35 * 24 / 18 = 47.2.

 

However a "normal" focal length depends on the application. For unplanned photography (e.g., street photography) the preferred lens is often 35 mm, or even 24 mm (gaining status for me). Statistically, over half of my landscapes are shot at 50 mm, except in the mountains and foothills, where 70-90 mm is the norm. Unless there is something interesting in the foreground, even a 35 mm lens flattens the landscape too much.

 

All of this attention on 50 mm prompted me to take a couple of hours off for a stroll in the Chicago Botanic Garden, with a single lens, a strictly manual 50 mm f/2 Loxia.

[Uhooru]

35mm is a very popular lens for street, but HCB mostly used a 50 and Winogrand liked the 28mm. I think you're using "normal" in a different sense then what the thread started out as.

[Ed_Ingold]

50 mm is an objective fact, whereas "normal" is a subjective term. HCB assumed the role of a detached observer, for which a 50 mm lens allowed him to maintain a distance. Street (sks documentary) photography, as presented in PNET seems to portray life as a participant, for which 35 mm (or shorter) is appropriate.

[Uhooru]

"50 mm is an objective fact, whereas "normal" is a subjective term."

All well and good. But in photography despite some inaccuracy, a 50mm is generally called a "normal" lens. Maybe you have objections scientifically to that in-exact terminology, but if you go to any photo store, or any photo department equipment checkout and ask for a normal lens, for a 35mm camera, they will hand you a 50mm no matter whether you agree with the term or not. Its just a convention. Likewise if you have a medium format camera and ask for a "normal" lens they will hand you an 80mm. Of course its a bit subjective but so what?

[Ed_Ingold]

I have never asked a camera shop for a "normal" lens, nor do I know anyone who has done so. If I want a 50 mm lens, that's what I ask for. I haven't asked for advice on which camera (or lens) to buy either. I do my homework first, including reading specifications, credible reviews and manuals. On the other hand, many knowledgeable photographers consider 35 mm to be a "normal" lens, because that's what they normally use. Judging from your portfolio, I suspect that's what you do too.

 

I confess that when a complete novice asks me which lens to buy, I suggest 50 (or 35 for DX), describing it at a "normal" lens, or a 28-35 mm "wide angle." When mixing it up between FX and medium format, I tend to think, "wide, middle (normal), and tele," rather than specific focal lengths. That was especially true in Iceland, where the wind stings your face with dust, thumb-sized pebbles roll across the road, and changing lenses outside the car is inadvisable.

Edited July 7, 2018 by Ed_Ingold