table of equivalent lens lengths for different formats

[johnielvis]

correct--these are all at the same distance--otherwise they wouldn't be equivalents

the mangification is the non-dimensional distance...you can go and expand into another column of distances...but for what---I think in terms of magnification required...not distance...but that's just me.

at any rate--the main amazing point here is that the smaller formats require a variety of focal lengths to do the job of a larger format with only one lens---

everybody keeps puzzling over the fact that the larger formats allow shorter lenses without getting perspective distortion showing up...this shows how that happens

[vitality]

everybody keeps puzzling over the fact that the larger formats allow shorter lenses without getting perspective distortion showing up...this shows how that happens

Sorry, I don't get it.
If you shoot with 18" lens (11x14) tight head shot you will be around 1m from a person, that's why you will get distortion (big nose comparing to ear). Not because of FL, not because of angle of view, but because of distance between lens (I think it's lens position what matters most, not film plane) and person.
To be free from face distortion when shooting portraits you need to be on certain distance from person (e.g. 3m), in that case distortion will be minimal. If you get closer relative distance between lens/nose and lens/ear gets higher ratio (e.g. 1m and 1,1m) that's where perspective distortion start to appear.

Correct me if I'm wrong, but that how I understand fact of perspective distortion in portraits - distance between person and lens matters, FL and angle of view doesn't change distortion.

[vitality]

Sorry, I don't get it.
If you shoot with 18" lens (11x14) tight head shot you will be around 1m from a person, that's why you will get distortion (big nose comparing to ear). Not because of FL, not because of angle of view, but because of distance between lens (I think it's lens position what matters most, not film plane) and person.
To be free from face distortion when shooting portraits you need to be on certain distance from person (e.g. 3m), in that case distortion will be minimal. If you get closer relative distance between lens/nose and lens/ear gets higher ratio (e.g. 1m and 1,1m) that's where perspective distortion start to appear.

Correct me if I'm wrong, but that how I understand fact of perspective distortion in portraits - distance between person and lens matters, FL and angle of view doesn't change distortion.

Never mind. I've finally got to the point, what you mean.

[Ken Lee]

Focal Length - Distance - Perspective - Angle of View: 4 sides of the same coin.

[jb7]

Correct me if I'm wrong, but that how I understand fact of perspective distortion in portraits - distance between person and lens matters, FL and angle of view doesn't change distortion.

Well, I'm glad you got it in the end, everyone seems to be having difficulty with the basic premise set out here, which, I suppose, is to illustrate the breakdown in the focal length equivalence charts between formats when magnification becomes a significant factor-

However since everyone is going off topic in this thread- 'Distortion' is a loaded term- and often it seems to be confused with the subjective unacceptability of the effects of a chosen viewpoint and focal length. If a nose is displeasingly large to you when viewed from a meter distance, then maybe the nose is just too large- or maybe the particular lens you're using is showing distortion- in which case, perhaps a better lens of the same focal length could be selected.

A nose, photographed from 1m, is not at all distorted, unless perspective is a distortion.

Similarly, a wide angle lens doesn't automatically produce distortion; it does, however, produce a projection that could be described as unnatural, particularly near the perimeter of its image circle. However, some lenses, of any focal length, do produce distortion- the worst offenders are zooms, and retrofocus types for slr's- in my experience. Lenses for large format are far better corrected.

Perhaps it's just a convention, and I shouldn't be concerned about the interchangeability of descriptive terms, but in my opinion, a nose photographed close up is just bigger, not distorted. Perspective is not distorted either, so if there is any distortion to be described, it is in the minds and tastes of the viewer. Even then, exaggerated might be a better description-

However, this is off topic, as I mentioned already...

[johnielvis]

distance provides the perspective or the angle of view of the subject---the FL provides the distance to get the particular "cropping" or magnification AT that distance...so one follows from the other...

it just kind of clicked in for me--how the scaleof the subject in relation to scale of the image is what causes this....

for example...if we all normally took pictures of things that were about 1" in scale, then the EXACT same thing would be noticed for 35mm cameras, since we'd all be shooting in the 1:1 range and the lens extensions would then be significant for the 35mm format....in this case 35mm would be "large format"....

Ijust never seen it quantified like that before...I made the table to stop with the back and forth with the calculator and then I see that this ONE lens 18" covers like from one focal length to almost double that focal length in 35mm.....and how that gradually happens...I've never seen it quantified like that before--I've only seen it said that large format is somehow different, but not HOW...this showed me HOW----it's all about scale.

[ic-racer]

I was thinking it would be nice to have a spread sheet that solved this equation and spit out focal length:
w=2*arctan(Y/(2f(M+1))
Where
w=angle of view
Y=film diagonal
M=f/(x-f)
x=lens to subject distance


For example if you liked the view of a 35mm camera with an 85mm lens at 2 meters from the subject (produces 28 degree view and 1 meter field), you would get a chart like this for your other formats (all with the same 28 degree view and 1 meter field at 2 meters):

35mm format = 82mm lens
6x6cm format = 148mm lens
6x9cm format = 190mm lens
4x5in format = 260mm lens
8x10in format = 460mm lens
16x20in format = 750mm lens
etc.

By comparison if one had used the simple infinity angle of view for each format and lens you would have erroneously bought a 570mm lens on ebay for the 8x10 camera

[johnielvis]

absolutely!!!

every time I see someone asking what's the equivalent and then seeing the infinity numbers that keep getting spit back...hell, even the calumet photo lens selection charts for the different formats says NOTHING about their equivalents being ONLY for infinity type distances---now, of course it's almost always true for smaller formats, where the subject is usually very large compared to the format size, but almost NEVER for the larger formats where you're usually shooting a size comparable to the subject--particularly in the studio.

it just seems to always get overlooked by everyone, including me, to the point that I never REALLY noticed how MUCH the formats begin to diverge as soon as one of them enters "the macro zone"