The trouble with focal lengths

[Martin Evans]

I am reading a book by a well respected author, who has written many books about the technicalities and art of photography. Early on I find in a photo caption: "... the shot was composed with a 20 mm lens ..."

What a meaningless number this now is! For most of our lifetimes, it would probably have meant a lens with a 20mm focal length fitted to a 35mm film camera. What might it mean nowadays? Probably not a lens on a quarter-plate camera, and maybe not even on a medium-format camera. But is it on a 35mm or 'full frame' camera, an APS-C sensor camera, or one of the innumerable smaller digital sensor cameras? On a 35 mm camera, a 20 mm lens would definitely be a 'wide-angle'. On the Canon compact that I carry with me when I don't have my dSLR, 20mm is medium-telephoto, equivalent in view to a 100 mm lens on a 35mm camera.

What can we do about this? The immediate answer would be to specify angle of view rather than focal length. But even angle of view is not precise. If we specify angle of view across the diagonal of film or sensor, we have to remember that not all sensors keep the old 24 x 36 mm ratio of 135 film. Furthermore, virtually all optical maths revolves around a focal length measurement.

I thought that Doug might touch on this in his detailed essays about the "reach" of a lens, or perspective and focal length, but we have become too used to talking about focal length simply in terms of millimetres.

It will be an uphill battle to change this nomenclature for the 100 million or thereabouts photographers in this world - let alone the powerful manufacturers. But has anyone any useful suggestions about proceeding in a more rational and precise direction?

Idle thoughts on a Friday night...

Martin

 

[fahim mohammed]

Hello Martin.

Agreed that a clarification in circumstanes you mention is needed. Might it not be possible that the authors of such books be the ones that should clearly indicate the equivalency of the focal lengths used rather than the manufacturer/user accepted understandings and nomenclature.

After all the majority of us use km, liters, kg while some continue to use miles, gallons, lbs. It does get confusing, no doubt.

Leica did have the Summitar, Summicron and the Summar lenses designated in cms rather than
mm back when. e.g the Summar 5cm f/2 in the 30s.

Best.

 

[Asher Kelman]

Martin,

If only people would tell us something about the event and the position they took for the picture. Sometimes we know. So that a table of ten people at a wedding reception, Bar Mitzva or fundraiser of Mitt Romney and Condolisa Rice would be an 80 mm lens for MF and 50 mm for 35mm format. We sense it.

I'd hope that no one would think of getting those pictures with a little digicam, even a 4/3 Olympus. It would be indecent! No one would want to pay the photographer. Without some black bulk or white lenses, the respect and fees would plummet.

So real cameras will still have focal lengths that mean business.

Asher

 

[Tom dinning]

Focal length is and always will be a property of the lens. Its a physical quantity irrespective of where and how it is used. To provide a different naming system based on sensor size would be incorect and confusing. I agree with Asher. If we all stuck to decent cameras instead of those piddly little pseudo thngies people call cameras we wouldn't have the problem. Get rid of anything less than 135 and concentrate on effect.
Now where's my Rollieflex with the 60mm lens. Now that's an effect!

 

[Jerome Marot]

Do we really need a very precise determination (except when buying a lens, of course)? I always had the feeling that there are just 5 focal lengths (35mm equivalent):

• very wide (16-20)
• wide (24-35)
• standard (35-70)
• small tele (85-135)
• long tele (200-600)

 

[Asher Kelman]

For almost all photography, except birding and sports, just 3 lenses suffice,

1. In practice 24 mm is a good focal length to start with and it doubles as a super wide by stitching two adjacent fields.
   
   
2. Then I'd go to 50mm 1.2 as it's both a portrait lens and a reception lens for events.
   
   
3. With a 70-200 lens one can then handle almost anything.

1. 
   

Add a macro screw in lens, or a true macro and one has a good kit and a x for 2.0 extra reach and mostly we're covered.

Asher

Those times when a costly lens like a 600 mm is needed, I rent. I must admit to owning more. The 28-105mm gets a lot of use in events.

 

[Doug Kerr]

Hi, Martin,

What can we do about this? The immediate answer would be to specify angle of view rather than focal length. But even angle of view is not precise. If we specify angle of view across the diagonal of film or sensor, we have to remember that not all sensors keep the old 24 x 36 mm ratio of 135 film. Furthermore, virtually all optical maths revolves around a focal length measurement.

I thought that Doug might touch on this in his detailed essays about the "reach" of a lens, or perspective and focal length, but we have become too used to talking about focal length simply in terms of millimetres.

Field of view

To the extent that field of view is the issue (something else a little later), of course the rigorous thing is to speak of the field of view (an angular property) in both directions. That is complete and a natural way to do it, independent of folklore.

If we would be willing to move toward field of view expression, but don't want to specify it in both directions, we have no choice but to compromise (such as the use of the diagonal field of view as the basis for our metric). One cannot thoroughly state the size of a generalized computer screen, for example, with a single number, no matter how much we might wish we could.

I do encourage us to think in terms of field of view. The convention of "full-frame 35-mm equivalent focal length" (to give its full name, as we must if it is to be definitive) becomes more and more "stale" as the range of cameras of interest expands. It is as though guides for travelers stated the distances between cities on the basis of the time to travel based on a speed of 30 miles/hour, assuming an hour for meals every four hours.

The "reach" of a lens, or maybe of a camera

Now the matter of the "reach" of a lens is another thing. That concept can have several meanings. One is some sort of inverse of the metric of field of view (and again, we would probably work with the incomplete notion of the diagonal field of view). This would work exactly like "full-frame 35-mm equivalent focal length", but might be defined so the numbers are different.

Perhaps we would decide, when establishing this standard, to make 100 units correspond to the diagonal field of view given by a 50-mm lens on a 36 x 24 mm format. It would then turn out that the "reach factor" of a lens was exact twice its full-frame 35-mm equivalent focal length. But the metric does not (by its name) suggest anything having to do with a full-frame 35-mm camera (except of course we know that the definition of the scale was first conceived in those terms). (Remember, the definition of the inch was first chosen based on the length of some king's thumb, but the unit is now a standard unit and we don't think of it as having anything to do with a thumb.)

But others have reminded us that, in sophisticated photography, the decision to use a greater focal length does not come from the need to have less of the scene on the image. Rather it comes from the need to cover the actual subject with as many resolution units (thing, simplistically, pixels) as possible. Otherwise, we could shoot everything at 35 mm and crop tighter for smaller or more distant subjects.

Those guys then suggest that a simple true measure of the "distant subject potential" of a lens and body combination (a "camera") is its angular resolution. That is, if the resolution of certain camera, expressed on an angular basis, in terms of cycles (line pairs), with a lens of focal length 80 mm, is 0.0003 radian (this would be a resolution of 1000 cycles across a 24-mm frame height), then (assuming for now that the resolution at the focal plane is not limited by lens performance) with a 160 mm lens, the angular resolution would be 0.00015 radian.

But would want our "reach" number to increase with greater focal length - with "finer" angular resolution. So we would define our "reach" metric as the reciprocal of the angular resolution as I have discussed it above. And the unit would have to be the reciprocal radian (no sense concocting something else - that's how it comes out.

So in the first case, the "reach" of the camera (lens and body together, since that's what affects the result we get) would be 3333 reciprocal radians (rad^-1). For the second case above, the "reach" would be 6667 rad^-1.

Now, to make it really meaningful, we would need to take recognize that the focal plane resolution depends on the lens. That does not at all change the concept of the metric we use to express "reach".

Overview: ain't progress complicated!

Now I know this all sounds rather esoteric and nerdlich (as did photography when it was first invented, and then exposure metering, and then digital photography, and then digital image editing. But if we really want to have more accurate ways to describe things of importance to us, we can't do it in terms of Mickey's big hand or the length of a favorite stick.

Best regards,

Doug

 

[Jerome Marot]

With a 70-200 lens one can then handle almost anything.

I used t like long lenses but today I rarely use the 70-200. Interestingly, I took pictures of the local gay parade today and noticed that many people used a 70-200 or even longer. I didn't.

 

[Asher Kelman]

I used t like long lenses but today I rarely use the 70-200. Interestingly, I took pictures of the local gay parade today and noticed that many people used a 70-200 or even longer. I didn't.

Jerome,

In my work with models or where I'm assembling tableaux, I find the advantage of narrowing the depth of field but also having to go further away to flatten the perspective.

However, I'm now enjoying the 100 mm macro for full length body shots. It's often a little too long and I'm pressed against the farthest wall to get everything included.

Asher

 

[Jerome Marot]

I find the advantage of narrowing the depth of field but also having to go further away to flatten the perspective.

True. When I take portraits, I also use a 85 of 135mm lens.

 

[Mark Hampton]

True. When I take portraits, I also use a 85 of 135mm lens.

90mm tse canon.. that my lens collection :0

 

[Martin Evans]

Thanks, Doug, for a carefully considered comment. I can appreciate the gist of what others have written: that we should assume that the millimetre figure for focal length will apply to "full frame" or at least not much smaller than APS-C sensors. If one ignores the smaller ones (and I'm not sure that one should ignore 4/3) then the ballpark figure will give a good idea of whether the view was wide-angle, long telephoto, or whatever. I suppose that is what Michael Freeman was getting at: that the specific object in the photo was small compared to the expanse of sea and sky captured by a wide-angle lens.

But Doug will appreciate that scientists and technicians will not usually find ballpark figures acceptable. Like Doug, I was thinking again today of the need to specify angle-of-view in both the X and Y axes to be really precise. Or the long and short dimensions, since X & Y will reverse depending on whether one is using landscape or portrait orientation - or even something in between.

I also suppose that technical folk will be using radians and not degrees, minutes and seconds. Oh horror! What will working photographers make of that? It will flummox most, in the same way that talk of lux and lamberts must have dismayed those brought up to think in terms of foot-candles or Weston Units.

Idle thoughts on a Sunday night... It must be Sunday, because I made porridge for breakfast this morning - it's the only way to distinguish weekends from weekdays when one is retired.

Martin

 

[Robert Watcher]

I think that most of us can quickly learn what the focal length of the lenses are that we use with our cameras. Really, we only have to know and make the choice when we purchase the one or two or three lenses that we may end up owning. There may be a short learning curve as the sales guy or any research we do, tells us what the popular focal lengths are for the camera we intend to buy.

In the days of past, there was no difference. Funny thing was that 50mm became a normal only to 35mm cameras - which few professional photographers other than sports and newspaper photographers used. For a square 6x6 format like Hassy and Bronica the normal lens was an 80mm. For my RZ67 it was a 90mm to 110mm depending on your liking. for 6x4.5 it would be the 75mm. Wide angle may have been 50mm to 75mm, but then Hassy had a great camera that I used for commerical shoots many times that was I believe 30mm - - - we just called it superwide because we knew the undistorted wide view effect that it could give. Then for those who shot large format, you decided on a 120-150mm for a slightly wide to normal view with 4x5 inch film - and then there was 5x7, 8x10, 11x14, etc, etc. . . . Every serious photographer knew those few lens focal length numbers, off by heart - and where you would likely use them if you even needed them.

I have now had Nikon Digital as well as Olympus Digital and I know roughly what any particular focal length is going to provide me on either system or even on the Canons (APS-C does not mean all the same mulitplication factor). Just another one of those few technical things that are useful to learn - like fstop, shutter speed and depth of field. Just a few numbers and their relationship.

For my purposes, I have never had a use for the "normal focal length" (except for the 110mm on my RZ67 which provided great shallow DOF and an image quality with that standard lens, that no 50mm normal lens of a 35mm film camera or todays supposed Full Frame Digital cameras can provide). As a result, I never had to figure out what the "normal" lens was for my Nikon D200's because I find that focal length boring and in my film days when the 50mm was included with a camera, may have used the 50mm once or twice to hang a filter on. 18mm gave me wide angle and I was set for portrait because I used a full range zoom. The 50mm that many buy as portrait, is too short for me on the smaller Nikon sensor and so I never owned it.

With my Nikons I had a wonderful 85mm and knew that it was too long for what I prefer for my portraits. I didn't find that out because of needing to know the focal length - - - but because I couldn't comfortably take portrait length shots in normal rooms that I regularly encountered in my wedding and portrait work. Most of the time I was shooting with an 18mm to 200mm and mainly used each end of it for wide and long. So for my Olympus cameras I just know that for normal wide angle I will be using a 12-14mm lens - for portrait it will be the 50mm and on the long end is 150 to extreme 300mm. The thing is that I use all zooms and so don't bother checking specifically what focal length I am using. I just zoom in and out according to my needs - of course knowing the effect of using a wide setting and a longer setting, and using the end of the zoom that suits my vision. But if I do end up getting single focal length lenses for my E-PL3, they will be 12mm wide angle and 45mm portrait - - - only 2 numbers to remember. The only time that I check to see what focal length I have used, is after the fact and someone wants to know for a forum post or I decide to include that data for interests sake. Other than that, I have no need to know once I've taken my shot.

I would be lost if there were some new standard like field or angle of view. I wouldn't have a clue what it meant if someone gave me those numbers. To me those numbers of degrees make no sense as I can't visualize those parameters in my shooting environment. So I am happy if it stays as-is just learning which lenses will give me the results I need with my camera. There are some standards in numbering that are best kept. Yes they changed ASA to ISO - but the numbers stayed the same - so no damage.

 

[Robert Watcher]

I used t like long lenses but today I rarely use the 70-200. Interestingly, I took pictures of the local gay parade today and noticed that many people used a 70-200 or even longer. I didn't.

The longer the better for me. My preference has always been super long or superwide.

In the film days with my Olympus Om4's (the 80's and 90's), my absolute - absolute favourite lens was my 300mm f4. The quality of image it produced was spectacular. It was a mainstay in my studio for tight portraits (studio area was 25 wide by 45 feet long) and went on the road with me to auto races and sports events as well as on my shoulder as I biked around the city looking for content to shoot. My other favourite unbelievable lens was my 21mm f3.5. Everything I shot with 35mm film, I shot with the 21mm, 65-200 f4 and the 300mm f4. I needed nothing else.

If I could have back then, I would have had a 600mm - but couldn't afford it (read - could not justify spending such money). Now I can with my Olympus system and my most used lens is my 70-300 (140mm to 600mm in 35mm film equivalent). I'm good for headshots from 6 or 8 feet away - to shooting down the street for a compressed viewpoint that I love or into treetops in the jungles of Central America.

In fact, yesterdays Buskerfest was an exercise in the benefits of the 70-300 (used on my lighter weight E-510).

This shot was taken from around a block away at the full 300mm (600mm in 35mm film equiv.), while I was shooting some music going on in front of me. I just swivelled and shot goings on at the same time in the distance. There is no other shot taken that day that has this unique perspective of the town and its gradual hills that look stacked here:

And then shooting from the sidelines about 40 or 50 feet away with 263mm (526mm in 35mm film equiv.), I got lots of shots like this:

And for close and intiment from about 10 feet away with 150mm (300mm in 35mm film equiv.):

BTW - the event took place around high noon, so controlling the extremes of contrast weren't a priority as it wasn't possible unless someone was under an overhang on the shade side of the street.

 

[Martin Evans]

Hello Martin.

Agreed that a clarification in circumstanes you mention is needed. Might it not be possible that the authors of such books be the ones that should clearly indicate the equivalency of the focal lengths used rather than the manufacturer/user accepted understandings and nomenclature.

Fahim: I think you are right in that. My initial irritation was caused by slack editing. The publishers ought to have asked the author to specify what camera the 20mm lens was on. Then we would have been quite clear about the extent of the view (assuming that there was no PP cropping!).

It was only later that I, as a retired scientist, began to wonder whether or not the 'field of view' of a published image could not more generally be expressed in terms of the included angle. This angle will be the same for a scene taken with a 50mm (or 5 cm) lens on a 135 film camera as it will be for a 6 inch lens on a quarter-plate camera (rounding down the inches a bit). I can't be bothered to work out what the angle is in degrees, and I'll leave it to Doug (who is better educated in engineering terms) to tell us what it might be in radians, if he feels like it.

It's hard for us to switch from familiar numbers to new "scientifically correct" ones. My father was used to the DIN speed system, and in his younger days probably encountered the Weston system. Now, as Robert has written, we are happy with ISO. Even us Brits have eventually become used to a monetary system that is decimal based, and does not have 12 pennies to a shilling - not to mention farthings, half-crowns, groats and nobles. We are still a bit uneasy with temperatures in Celcius and weights in kilograms, but our grandchildren are wondering what feet and yards are.

Martin

 

[Jerome Marot]

I can't be bothered to work out what the angle is in degrees

2 x atan (2f/d), where d is either the diagonal or the width of the format, according to taste.

 

[Robert Watcher]

2 x atan (2f/d), where d is either the diagonal or the width of the format, according to taste.

Thank you. I will put that right into practice. LOL

(oh how I miss smileys that provide the intent of my replies - just have to put up with my LOL or HeHe then)

 

[Robert Watcher]

I just thought I'd throw something else out there.

So it was mentioned about how difficult it is for us older ones to learn Celsius or the metric system or other such refinements to long held traditions we may have been raised on. So being that I was raised on Fahrenheit I fully understood what every degree of F temperature meant - from top to bottom - - - and could spill out those numbers if anyone asked. When Canada changed to Celsius, I was obviously lost. It was difficult if not impossible to relearn every scenario in that new scale.

But what I came to understand quickly was comparisions. So as a reference for myself when other people talk in both systems or when I travel and have to go between both systems - what I came to know was that 36 degrees C was very hot and 100 degrees F was very hot. I already knew that 32 degrees F was freezing and Celcius made it so much easier with 0 degrees being freezing. Any setting lower starts to get very cold. The same was the case when kilometers per hour was instituted where I was used to 60 miles per hour and now had to associate 100 kilometers with the same sensation (speed limit in most cases) - - - and for driving in town the 30 miles per hour became 50 KPH.

Of course much like our lenses, when it comes to the speed I should be driving I don't have to figure anything out when using the new system. The signs are right in front of me just like the numbers on the lenses. But I also don't feel the need to learn the different systems in depth or try to remember popular conversion algorithms so that I can figure out exactly what 63 degree F is in C right on the spot. The reality is that I will only be dealing with 3 or 4 numbers from each system - that I must know in any scenario that I might face. The other in between ones I can guess at to get close - or if I have to write something down for someone else, I have online converters on the web and a calculator on my desk. So for me it is the same thing with lenses system conversions. With the particular medium format camera that I used, I knew what could be expected from each of the lenses I purchased for it. Because 35mm was also popular, I became aware that 110mm was standard as 50mm was standard - - - wide angle and mild tele. That was about it.

One of my favourite mentors when it came to figuring out measurements, accuracy and efficency came to be the fellow on the "Router Workshop" tv show (probably only here in Canada). He used no rulers or tape measures when creating his woodwork pieces. His methodolgy was to have a small set of square pieces of metal to stick in between the router bit and the guide for distance. Dove tails or any other precise joint, fit together like precision without measuring and measuring again to make sure. It didn't really matter whether the measuring system he adhered to was inches or centimeters. He was able to complete very complex projects within the timeframe of the single episode.

His philosophy was that it is more important to have consistency that accuracy of numbers. If a cut was 1/16 inch longer than intended, it was more important to make sure all sides were that exact same amount over or under by defining the length with a set piece of wood clamped to the table to but up against - instead of measuring each piece. I ended up applying this to my picture framing business where I had struggled getting corner joints to fit perfectly, even thugh I was painstakingly measuring each piece for precision. Once I just starting setting up a wood "stop" that was very close to the length I needed and bumped each piece of wood up against and never measured other than the first time - - - my corners were perfect.

Actually lightling master Dean Collins - as technical and precise as he was - preached consistency over accuracy when it came to light metering as well. This methodology allowed him and can allow us to work quickly and accurately because of not fussing the small details, trying to figure out if we have it "right", or spend endless time trying to calculate and convert.

OK - I've totally confused you now - - - - in summary, learning a few essential numbers in each of the 2 or 3 systems that we will be using or need to be aware of at any given time - - - - will get us roughly where we need to go. The old lens standards not related to any real number - like small metal bars of a few thicknesses to gage distance or length - seem to work best for me when describing how I got a shot. I probably should use those more for the aid of people viewing my images where I am including shooting details. Generally that involves Ultrawide, Wide, Normal, Portrait, Tele, SuperTele - some of which we might never use. And then if we know the numbers in milimeter measurement related to those generalities - and know them for a couple of different sensor formats - - - we can probably guess close enough what the in-between numbers will give us.

I am strong in math and am a computer programer who loves hand coding from scratch and even created my own operating system back in the late 80's without any books to guide me. I am capable of doing the exact calculations - - - but that conflicts with my mentality of "things being simple" and "just doing it". I think that is one reason that I have been very efficient in my life and get a lot done in a short period of time. I'm not saying this to bolster myself - - - but to allow others who are so inclined, to see that things don't have to be that complex in life - and yet that lack of complexity doesn't have to hinder your ability to produce at the highest level.

Hey - am I off topic yet? LOL

 

[Doug Kerr]

I am delighted by the array of really apt observations that have been made her in the matter of stating various properties of lenses and/of the cameras of which they form a part.

I think they have well illuminated the way in which our species has developed ways of communicating that relate well to our actual "living and working". I liked the thing about the little pieces of metal used to set the router depth! But of course I wouldn't be able to draw upon that in sending Will a note telling him how to reproduce a cut needed to accept a certain cable in the face of a board.

I only urge that in a situation where we, for whatever reason, aspire to be "rigorous", we really do it.

So you will understand why, sometimes, when someone says "full-frame equivalent", I will jibe him, saying, "Do you mean full-frame 35-mm equivalent . . .?"

Or, when someone says "35-mm equivalent", I will jibe him, saying, "Do you mean full-frame 35-mm equivalent . . .?"

As Carla says, "it is all well and good to call a bison a buffalo, until the ones you ordered from the wild animal dealer arrive."

Best regards,

Doug

 

[Robert Watcher]

I think they have well illuminated the way in which our species has developed ways of communicating that relate well to our actual "living and working". I liked the thing about the little pieces of metal used to set the router depth! But of course I wouldn't be able to draw upon that in sending Will a note telling him how to reproduce a cut needed to accept a certain cable in the face of a board.

That is true - - - we need a reference point to start with - but that could be a full scale picture of the object to lay the measurement pieces on to create them - it could be a description to a body part like the length of a forearm or foot or some well known object - or it could be a specific measurement like inches or millimeters if that is recognized by the person.

And that is to me where general terms of Wide, Normal, and Tele are probably of more use in their generality when it comes to taking pictures. If we want to get somewhere close in reproducing an image, we should have an idea of what those terms mean with our own gear. Is it going to be identical - no - - - does it matter - not likely. For precision scientific creation, all of the specific calculations may be relevant. I don't really look at photography or art as fitting in that category. if you are a camera manufacturer - yes.

So you will understand why, sometimes, when someone says "full-frame equivalent", I will jibe him, saying, "Do you mean full-frame 35-mm equivalent . . .?"

Or, when someone says "35-mm equivalent", I will jibe him, saying, "Do you mean full-frame 35-mm equivalent . . .?"

You are correct. What is full frame? It was my 4x5 camera - it was my RZ67 - it was my 35mm Olympus OM4 - and it is my Olympus 4/3 believe it or not.

I think that at this time it is safe to assume that whoever coined the term Full Frame to relate to cameras with sensors the physical size of 35mm film cameras - - - has had success in getting that across. Most people are aware of that term and what it represents, and so we can safely use it as a "starting reference" to any other sensor size. That might change in the future - we will see.

It is easy to use the now common term Full Frame as it refers to the 35mm film frame with its 35 mm width (actually 36×24 mm) that we knew as a standard - and so it compares with the larger FF digital sensor with it's 36×24 mm dimmension. Most lenses of course, were and are produced for that standard - and so provide the same perspective when used on either.

 

[Doug Kerr]

Hi, Robert,

I think that at this time it is safe to assume that whoever coined the term Full Frame to relate to cameras with sensors the physical size of 35mm film cameras ...

Well, the frame size of full-frame 35-mm cameras (admittedly the most common type), which is exactly my point. That outlook ignores the fact that were were many cameras ("half frame 35-mm cameras") that used type 135 film (to be precise about the film) and had a frame size of 18 x 24 mm, not 36 x 24 mm.

Best regards,

Doug

 

[fahim mohammed]

Hi Doug.

For me, this is the best advice one can find; on any subject.

My best regards to the Mrs. and yourself.

....
As Carla says, "it is all well and good to call a bison a buffalo, until the ones you ordered from the wild animal dealer arrive."

Best regards,

Doug

 

[Robert Watcher]

Hi, Robert,


Well, the frame size of full-frame 35-mm cameras (admittedly the most common type), which is exactly my point. That outlook ignores the fact that were were many cameras ("half frame 35-mm cameras") that used type 135 film (to be precise about the film) and had a frame size of 18 x 24 mm, not 36 x 24 mm.

Best regards,

Doug

I realize that was your point Doug. I think we can get into all kinds of technicalities that have little to do with the perception that most people have though - - - and that is that it is expected I think, that the reference to "35mm film equivalent" or "Full Frame equivalent", means the same thing based on a frame size of roughly 35mm in length - that will result in a specific use of the common lenses that are designed for that standard. Even with my 33 years of making my living at photography and even being an Olympus devotee, I have never shot with - let alone seen - a half frame film camera. I know about them through osmosis from being around the industry so long. But I doubt that many people would confuse a "35mm film" reference to anything other than a full frame 35mm film frame.

Even so, that standard only matters if someone has posted their shooting details with their images and the viewer decides they need a reference point to understand what that data relates to when using their camera system. Or when we are buying a camera - but then a quick Google seach or the camera salesman will let us know what focal length works for wide angle, normal and tele in that standard - so that we can make a good choice based on the sensor or film frame size we desire.

 

[Doug Kerr]

Hi, Robert,

I realize that was your point Doug. I think we can get into all kinds of technicalities that have little to do with the perception that most people have though - - - and that is that it is expected I think, that the reference to "35mm film equivalent" or "Full Frame equivalent", means the same thing based on a frame size of roughly 35mm in length - that will result in a specific use of the common lenses that are designed for that standard.

I understand.

Gotta go to the door - I think our bison have arrived.

Best regards,

Doug

 

[Robert Watcher]

Hi, Robert,


I understand.

Gotta go to the door - I think our bison have arrived.

Best regards,

Doug

Hehe -------

 

[Jerome Marot]

You are correct. What is full frame? It was my 4x5 camera - it was my RZ67 - it was my 35mm Olympus OM4 - and it is my Olympus 4/3 believe it or not.

I tend to consider "full frame" as linked to the lenses. So "full frame" is the frame the lenses were designed for. In the first days after I bought a camera with a sensor of 24mmx36mm, I was delighted that my old lenses worked as intended... at last! They gave the perspective and depth of field I wanted.

 

[Robert Watcher]

I guess that is why the Olympus 4/3 and micro 4/3 cameras are considered Full Frame as well - - - the sensor and lenses were built from the ground up to support the new format.

But then I guess going by that analogy, why would lenses specifically made for the APS-C sensor not make that system full frame? Ones like my 18-200 VR or any of the other DX lenses.

 

[Doug Kerr]

Hi, Robert,

I guess that is why the Olympus 4/3 and micro 4/3 cameras are considered Full Frame as well - - - the sensor and lenses were built from the ground up to support the new format.

Well, and this is what makes this whole scheme so - well, you fill in the adjective.

Best regards,

Doug

 

[Jerome Marot]

IBut then I guess going by that analogy, why would lenses specifically made for the APS-C sensor not make that system full frame? Ones like my 18-200 VR or any of the other DX lenses.

Because, then, people would not understand what size of sensor for a given mount you are talking about? "Full frame" as a wording only makes sense when there is more than one size of sensor (film is a sensor) for a given lens mount. And then, it means the image size the original lenses were designed for in that mount.

So:
-four thirds: no "full frame" needed because there is only one size of sensor.
-Canon/Nikon/Sony: full frame is 24mmx36mm, the size the original lenses were designed for in the EF-, F- or A- mount.
-Mamiya RB/RZ: full frame is approximately 56mmx67mm (as opposed to smaller digital backs).

 

[Michael Nagel]

For me the designation of 'full frame' is not very precise, it has entered common language as 36x24mm negative/sensor equivalent.

A lens designed for a 1/2.5" sensor and being used with this sensor is used full frame.
Same goes for a 4/3 lens used on this sensor, APS-C lens on the adequate sensor and so on up to a MF lens used on a MF sensor. In all cases the sensor fills the image circle in the best possible way.

Tilt/shift lenses and LF lenses are a different breed as these have an image circle considerably larger than the negative/sensor these are being designed for to permit for corrections (e.g. Scheimpflug).

A photographer being only used to 4/3 not having any other reference will refer to 20-25mm as his 'normal' focal length.

A photographer being only used to APS-C not having any other reference will refer to 30-35mm as his 'normal' focal length.

A photographer being only used to 36x24mm sensor/negative not having any other reference will refer to 40-50mm as his 'normal' focal length.

A photographer being only used to MF sensor/negative not having any other reference will refer to 75-90as his 'normal' focal length.

The 36x24mm sensor/negative is - being most common during the dominance of film - currently the best common ground for many people to establish a link between focal length (what is marked on the lens) and angle of view. The crop factor is just a mnemonic trick to get to this reference dimension.

I wonder if future generations of photographers will still use it when sensor formats might use sizes other than in the list above and 36x24mm might have become just an obscure reference...

Best regards,
Michael