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johnielvis
22-Nov-2011, 05:46
this is a more descriptive title as it has NOTHING to do with portraits...here's the title...here's the orignal post, etc...

NOTE now there are TWO tables attached--one based on diagonal measurement as most people are comfortable with...they show nearly IDENTICAL results:

I've done so many of these calculations one at a time, I finally made a table of equivalents...and, when all the information is all tablulated together, it is extremely useful to see what is going on when you compare the "equivalent lenses" for different formats. Note that the equivalent lens CHANGES based on the magnification required--by the visual field that is covering the image area. This is what always seems to confuse people because it doesn't change in any seemingly predictable way and it is responsible for the non-intuitive concept that short lenses are "ok" for close up portraits for larger formats. The attached table was made for an 18" lens (457mm) for the 11x14 format. for the format characteristic lengths, I didn't use the diagonal, but rather the square root of the area...so for square hasselblad, the characteristic length is 2.25 inches = sqrt(2.25*2.25)....for 8x10 it is sqrt(8*10)=8.9 inches....don't worry...it's the RATIOS that matter with format characteristic lengths..and that is what is used in these calculations.

You'll see that for the 11x14 format column, the equivalent length is all 18" for every magnification....this is, of course true, since the table is for 18" on 11x14....

the very interesting thing is the smaller formats--you'll see that the 18" lens at magnification of zero (infinity focus) is equivalent to a 43mm lens on 35mm or an 83mm lens on hasselblad 2.25...this is like "normal" lens coverage for infinity focus....

NOW....you'll see that as you move down the table to magnification of 1.0 for the 11x14 format (very tight head shot on 11x14), the equivalent lenses are 79mm for 35mm and 140mm for hasselblad---THESE ARE PORTRAIT LENGHTS FOR THOSE FORMATS.....

so you see that the 18" on 11x14 BEHAVES like you having a zoom from 43mm to 79mm for 35mm or a zoom from 83mm to 140mm for hasselblad format.

So THIS is a better explanation of what is going on when you are talking equivalent formats.....I saw this all tabulated and a light went off....AHHHHH!!!!!! THAT's it!!!!

so you see, all you need for 11x14 is your 18" lens...shoot landscapes with it at "normal" coverage and get close up and automatically get portrait lens angle of view!!!! This should help IMMENSELY when selecting a lens and camera for your new format of choice.....See attached printout for various magnifications on 11x14 format with the 18" lens and all of the equivalents from 35mm to 11x14....

Asher Kelman
22-Nov-2011, 06:24
Johnielvis,

So Elvis is alive! In what way is your approach different from others?

Could you make your picture larger so that it can be printed on an 8x10 sheet clearly. It's to small! Also, if this is an Excel spreadsheet, why not extend the table starting from 8mm 35mm equivalent lenses? That would be interesting.

Asher

johnielvis
22-Nov-2011, 07:02
yes...Ill add the 8mm and 16mm equivalents...

OH...what are the frame dimensions for 8mm and 16mm? I don't know these...the cine or the micro camera?

I'll upload the spreadsheet with a couple of exemples for different formats other than 11x14 and then you cna play with it and see what I'm talking about.
\
well...just found that I can't upload spreadsheets...I'll see if I can zip them later tonite and upload them that way.....got a couple of filled in ones to show how to change it to suit your needs....

johnielvis
22-Nov-2011, 09:08
it looks like spreadsheets cant be uploaded...so here's pdfs of the three spreadsheets that will give you an idea of how they work...EMAIL ME at johnielvis@aol.com and I'll send you the xls spreadsheets to play with and add 8mm or 16mm or 20x24.

here are the .pdfs of the three spreadsheets--the first is the 11x14 with 18" lens originally posted

the second is the famiiliar 50mm lens on 35mm camera....note--since 1.0 magnfication on 35mm is a closeup of an eyeball, I erased all magnifications past .1...which is the close tight head shot.

the third is the 14" 360mm lens on 8x10 format--note that a 1.0 magnification for 8x10 is a GREATER than 1.0 magnification for 11x14....it is an ENLARGEMENT to 11x14...so that is the eqivalent focal length for a greater than 1.0 magnification on 11x14 shown there...ALSO..this one uses the DIAGONAL for characteristic length for familiarity....

ic-racer
22-Nov-2011, 10:14
What would be helpful is a table of subject distance vs angle of view. What you need to know is that when keeping perspective the same (same subject distance, like 6 feet) what lens you need on a 11x14 to match the angle of veiw of say 6x7cm camera with a 120mm lens. And so,on.

johnielvis
22-Nov-2011, 10:26
thats what these show..identical angle of view at the identical distances for the same view field--the only thing that changes through the formats is the relative magnification--have another look......

the distance you want is given by the magnification---distance is just (1+M)*focal length...so the distance is given non-dimensionally in terms of magnification....which is more useful it seems to me....

email me and I'll send you the spreadsheets and you can play around with them/ tailor them to your lenses or formats of interest...

Ed Kelsey
22-Nov-2011, 10:40
See the Alpa calculator, you can plug in two different formats and compare focal lengths.

http://www.alpa.ch/dms/products/tools/alpa-comparable-focal-length-calculator/ALPA_CFL_Calc_V217B.xls

timparkin
22-Nov-2011, 10:40
Don't 35mm lenses have a bellows factor in the same way as large format? I see magnifation increasing as I focus closer on my OM1..

E. von Hoegh
22-Nov-2011, 10:58
Don't 35mm lenses have a bellows factor in the same way as large format? I see magnifation increasing as I focus closer on my OM1..

Of course. Set up your camera pointed at anything. Watch what the meter does as you focus from infinity to the closest distance - this will be more pronounced if you are using say a 55mm Micro-Nikkor, which will focus from infinity to one-half lifesize.

22-Nov-2011, 11:56
Use of the square root of the nominal format area is an interesting approach.

However, I believe the relation of the focal length of one format to that of another is less important than subject distance. Notice that in order to answer questions like "what focal length do I need to do a head and shoulders portrait on 4x5?", one must first decide the subject distance. Isn't focal length more-or-less always predicated on and indeed, dictated by subject distance and desired image size?

johnielvis
22-Nov-2011, 16:05
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
23-Nov-2011, 02:09
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
23-Nov-2011, 05:02
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
23-Nov-2011, 05:16
Focal Length - Distance - Perspective - Angle of View: 4 sides of the same coin.

jb7
23-Nov-2011, 05:56
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
23-Nov-2011, 07:20
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
23-Nov-2011, 18:01
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
24-Nov-2011, 01:35
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"