School me on Angle of View

Hey everyone,

It's been a while since I last posted around these parts. Hell, last time I popped in, it was still APUG.

My question is: when is a 90mm not a 90mm? I was doing some research today, and I've seen all kinds of things about different lenses of the same focal length having different angles of view and it kind of bent my mind around a bit, as I always took for granted that a focal length and angle of view worked correspondingly.

What's the deal with this?

Suppose there will be more correct explanations, but what I think you mean is, it has to do with the format you are using. 90mm is wide angle on 4x5 and it is tele on 35mm.
Regards,
Frank

Frank53 said:

Suppose there will be more correct explanations, but what I think you mean is, it has to do with the format you are using. 90mm is wide angle on 4x5 and it is tele on 35mm.
Regards,
Frank

Click to expand...

+1

The angle of view is relative to the usable image circle a lens covers and the format used. Actual circle of illumination might be larger but may not be sharp towards the edges.

I use a 90mm f6.8 Angulon from the eraly 1960's coverage is limited by vignetting but will cover 5x4 with noreal room for movements, a pre-WWII version of the same lens has a touch more coverage, there was a slight design change, probably newer glasses as well. The newer 90mm f5.6 Super Angulon is much larger and heavier lens and can be used on a 7x5 camera having 105º coverage compared to the Angulon's 81º.

Ian

As Ian partly introduced, there is much confusion about the concept of "angle of view" especially among people who use fixed formats like 135 or 120 films, because in books etc. they often see graphs in which different focal lenghts are associated with different angles of view. Indeed with few exceptions, if the format is kept fixed (let's say 35mm), a lens with a shorter focal lenght has a wider angle of view (and is used as a wideangle).

Large format users are instead more accustomed to the fact that focal length and angle of view are not related. A (say) 50mm lens can be designed to cover a very small negative/area like 35mm, and will thus have a narrow angle of view, while another lens again with the same focal lenght of 50mm can be designed to cover a much larger format/area like 4x5 inches and will have a much wider angle of view, but as said the focal length will still be 50mm.

In general, the larger the area that the lens will cover, the harder it will be to design the lens, the harder it will be to design it with a high aperture, and the harder it will be to keep size and weight into reasonable limits. That's why high aperture 50mm for small formats are compact, common and cheap, while good 50mm for large format cost a fortune and have apertures rarely higher than f:4.5.

Here s why. Think of full frame sensor in the drawing as large format and cropped sensor as 35mm. Forget the green lines and just look at the red and blue and the one front lens in the diagram. The larger sensor or film format sees a larger angle of view of light rays from the same lens.
https://goo.gl/images/Kg6bWY

Since the 70's when I bought a used Olympus Pen F to use along with my full frame 35mm SLR I've dealt with this concept. One way to think of it is what happens when you crop a negative in the darkroom. So, if I have a 100mm lens and take a picture down a street but then enlarge only a 8X12mm portion from the center of the negative for a 6X9inch print the angle of view on the print will equal the same as if I had taken the picture with a 300mm lens and did not crop the negative. The problem being of course that the cropped print will have a lot more grain and not have as much resolution as the same print made using the 300mm lens. But both prints will look the same and have the same perspective.

There you go. Clear as mud?

Angle of view should be distinguished from angle of coverage, which is related to image circle and potential view camera lens movements, which varies not only with lens design and focal length, but also lens aperture and acceptable degree of enlargement. That's the whole point of view cameras, and not just point-blank shooting. I often use some of the same lenses on 6x9 roll film backs as with 4x5 and 8x10 sheet film. A lens which a relatively wide angle of view on 8x10 film will behave like a long focal length (telephoto-like) on much smaller roll film formats.

DREW WILEY said:

Angle of view should be distinguished from angle of coverage, which is related to image circle and potential view camera lens movements, which varies not only with lens design and focal length, but also lens aperture and acceptable degree of enlargement. That's the whole point of view cameras, and not just point-blank shooting. I often use some of the same lenses on 6x9 roll film backs as with 4x5 and 8x10 sheet film. A lens which a relatively wide angle of view on 8x10 film will behave like a long focal length (telephoto-like) on much smaller roll film formats.

Click to expand...

Yes of course. I mounted a Kodak 105mm f4.5 Anastar lens from a 6X9 folder on my 4X5 just to see how much coverage it had. Not near enough it turns out (no surprise there). At f8 at infinity it produced a round image about 4.5 inches in diameter before fading to black in the corners. Guess this is why those modern ultra wide lenses for 4X5 have such large front and rear elements. With my OM and Pen set up though I was only dealing with 35mm. The half frame has a 30mm diagonal and I had a Pen F to OM mount adapter so all my OM mount lenses could be used (all manually) on my Pen F body. Although I had several Pen F primes, from 20mm to 100mm if I wanted a longer or faster lens I could always mount my OM Zuikos on the Pen. For using my 24mm f2.8 Zuiko I had a home built rig that would let me shift the lens up or down a bit for perspective correction. I could shift it about 6mm up or down along the long axis of the Pen frame.

Pretend you are in the middle of the lens. In LF terms you would be looking back at the film. Your angle of view might take in just a portion of the film. This indicates a narrow angle of view. If you could see all the film and even more around the edges that lens would have a wide angle of view. These angles are expressed in degrees.

The angle of view in LF becomes important when you want to insure you have enough coverage to enable movements.

So the angle of view is the designation for the amount of coverage at infinity on a certain format?

EASmithV said:

So the angle of view is the designation for the amount of coverage at infinity on a certain format?

Click to expand...

Not quite. The lenses angle of view is static, it's a result of the design. The f stop chosen does effect it somewhat but you shouldn't add another variable to your confusion at this point.

EASmithV said:

My question is: when is a 90mm not a 90mm?

Click to expand...

Pretty much never.

EASmithV said:

My question is: when is a 90mm not a 90mm?

Click to expand...

ic-racer said:

Pretty much never.

Click to expand...

Convertible lenses excepted .
It would be nice if large format lenses were described by what angle of view they accurately project.
But instead that information is reported as coverage.
Of course, coverage can be converted to angle of view with a bit of geometry.
After saying this, I expect Dan Fromm will post with a link that does report angle of view - if anyone knows of one, he will.

EASmithV said:

So the angle of view is the designation for the amount of coverage at infinity on a certain format?

Click to expand...

Angle of view is measured at the subject side of the lens, coverage at the film side.

Sorta-Kinda maybe(ish). Any 90 will give the same image size from any camera. The angle of coverage depends on the format the lens is designed for.

If you take a picture with the SAME 4X5(90mm) lens and were to make a negative on 35mm-6X9 film, you should be able to place the smaller negative on top
of the larger neg and presuming nothing has changed relative to camera position they should align. There will be a difference in contrast and grain
but size is the same.
*The coverage on any lens does increase when it's focused on a closer subject.
*There may be a slight difference in size with different lenses because a lens may be 89mm or 101mm actual fl.

EASmithV said:

So the angle of view is the designation for the amount of coverage at infinity on a certain format?

Click to expand...

Eric Rose said:

Not quite. The lenses angle of view is static, it's a result of the design. The f stop chosen does effect it somewhat but you shouldn't add another variable to your confusion at this point.

Click to expand...

Manufacturers aren't clear about what they mean by angle of view, it can be measured horizontally, vertically or diagonally, it's often the horizontal that's quoted, but sometimes the diagonal, never the vertical !!! The angle of view of an LF is for the largest format the lens can be used with.

Perhaps a better term with a specific format is field of view for a lens, this is the practical angle of view focussed at Infinity with the particular lens/camera combination.

I'm not sure the Angle of view is static though, the usable Image Circle is so a lens used on a 5x4 camera won't be as wide (horizontally) as the same lens used on a 6x17 camera.




This brings us to a dimensional area rarely discussed where a lens can be wide angle in one dimension and yet normal in another.

I use a 75mm f8 Super Angulon on my 6x17 camera, this is a normal focal length lens on a 6x6 camera so in that respect is "Normal" for the vertical dimension with 6x17, on the other hand it's very wide angle in the horizontal dimension.

Ian

EASmithV said:

Hey everyone,

It's been a while since I last posted around these parts. Hell, last time I popped in, it was still APUG.

My question is: when is a 90mm not a 90mm? I was doing some research today, and I've seen all kinds of things about different lenses of the same focal length having different angles of view and it kind of bent my mind around a bit, as I always took for granted that a focal length and angle of view worked correspondingly.

What's the deal with this?

Click to expand...

The basis you just have to learn: (in concern of your question) is :
A standard lens has 50mm with this lens you have an angle of view like humans have (55mm). But you should know - this is only in regard of 35mm film (or "full frame" digital systems). So if you load your camera with a 135-36 cassette everything counts (like from my example).Now you put a 35mm lens on your camera - and the angle of view is changing (wide shot) with 28/25mm you have a more wide shot. 21mm lenses can give you an exteme wide shot. Today you can use "modern" lens constructions with18/15/12mm = heavy (extremest) wide shot.That is in concern of "no fisheye" effect.

In the past lenses with ~ 12 mm/15mm had no real correction to a normal photographcal use. So that lenses have been in use to special effect shots.
In easy explanation : You should be aware of : not to find your own legs with shoes into your picture.
That is all in concern of 35mm film cameras.
Comming to the other side : Tele lenses. the first simple normal use Tele is a 85mm (for portraits) sometimes you can find special lenses today with 100mm and wonder about pricing - this are often lenses with "macro" function. Then following 135mm (as the first "real tele" lens) and 180mm/200mm.
Extreme tele lenses for "extreme" tele shots are allways beginning with 300/400 mm up to 1000/1200/2000 mm (heaviest tele shots).
What will hapen when the format is changing? Notice : your focus lenght never changes (a 90mm ALLWAYS have 90mm) in ANY case - so focus lenght isn't able to change.
But with a higher format you got a new angle of viev. On a 6 x 7 negative is much more space. The same shot (with also 90mm lens) on 35mm film would in comparison just show the inner circle of that what you might see regarding you 6x7 negative (shot with also a 90mm to midt format cameras).
This is in direct concern of the space of your negative. Just try to imagine : the 6 x 7 negative shoes you more.
You can see the surroundings in that much bigger negative - as compared with the same shot on your ( much more little) 35mm negative.
Does that mean the midt format lens is from characteristic a wide shot lens ? Quite good (because the wider angle let you see more on your 6 x7 negative/ 35mm negative is just showing the middle/inner circle).
So you should never forget this example to understand the mechanism. So at last your 90mm lens to midt format is no wide shot lens but (not forgotten) your 90mm lens with 135-36 film is a "little" Tele lens (for portraits).
If you would have make this comparison with 50mm standard lens on 35mm film and with 90mm lens on higher format (6x7) you would have make the experience :
Both negatives are showing nearly the same - it looks like the same angle.
R I G H T - when 50mm is a standard focal lens with 35mm film 90mm has just to be a compariable standard focal lenght on midt format (120film) cameras.
(105mm lens is the real right standard lens on 6x7 - but we should not care soo much).
If you want to compare these different formats you have to double the focus lenght from 35mm film to 120film. A nice 135mm tele lens on 35mm film is a tele - the nearly same tele shot on 120film would have the need of ~250mm lens to have the same angle on bigger negatives. 4x5 inch has much more format (the nearly double of 6 x 9 with 120film) so you will need a lens with ~ 500mm guess 600mm is more precisly. But then this 600mm on 4x5 inch does not work as an extreme tele it is just a normal tele same as 250mm on 6x7 or 135mm on 35mm.
So if you want to shot "wide angle shots" on 135-36 you would be "brave" to use 21mm lens AND you should use (same shot intended) 40mm with 120 film and 90mm with 4x5. What about you will shot 8 x10 film ? Wow that has around 4times more negative space in comparison to 4x5 you should first rent a lens at around 400mm and try out.
400mm can be a real wide angle lens ? (Hope my explanation is "half the way" correct - little doubts.....) - I never shot 8x10 but you know what I mean.

with regards

PS : Due to extrem small sensors on digital amateur cameras you may notice there lenses (zooms) with focus lenght (written in front of that lenses - I never bought such stuff
for expample 1,9 mm - 4,6mm
W O W what the hell wide shots will they do digital ?
No that are normal shots in comparison to 35mm - 135mm with 35mm/full frame cameras.
But The deep of sharpness is quite
enourmous such like extreme wide angle lenses of 15mm (35mm version ) and much much more.
Estimated : 19 cm - endless sharpness. (don't care about but the possible next theme : lenght/deep field sharpness of different focus angles)

Ian Grant said:

Manufacturers aren't clear about what they mean by angle of view, it can be measured horizontally, vertically or diagonally, it's often the horizontal that's quoted, but sometimes the diagonal, never the vertical !!! The angle of view of an LF is for the largest format the lens can be used with.

Perhaps a better term with a specific format is field of view for a lens, this is the practical angle of view focussed at Infinity with the particular lens/camera combination.

I'm not sure the Angle of view is static though, the usable Image Circle is so a lens used on a 5x4 camera won't be as wide (horizontally) as the same lens used on a 6x17 camera.

View attachment 201118


This brings us to a dimensional area rarely discussed where a lens can be wide angle in one dimension and yet normal in another.

I use a 75mm f8 Super Angulon on my 6x17 camera, this is a normal focal length lens on a 6x6 camera so in that respect is "Normal" for the vertical dimension with 6x17, on the other hand it's very wide angle in the horizontal dimension.

Ian

Click to expand...

Sorry Ian I'd better read your post before - your explanation is a little simular to mine.Or let's better say : " I made it a little like your example in comparison with different formats. ..."
So I compared the focus lenght lenses of 21mm (35mm) 40 (120film ) and came to 90mm at 4x5 inch (you stated simular " very wide angle" with 75mm ) not to 4x5 inch format but "panorama" 6x17 is comming nearly to 4x5 dimentions (little higher indeed) in horizontal characteristic.
I came to 400mm with 8x10 (as real wide shot lens) from theoretical consideration.
BUT SEAMS THIS TO BE CORRECT
( 400mm widest shot on 8 x 10 )I must have made a misstake (doubts).....
with regards

hi eric

this should help clear things up
https://en.wikipedia.org/wiki/Angle_of_view

john

Ian Grant said:

Manufacturers aren't clear about what they mean by angle of view, it can be measured horizontally, vertically or diagonally, it's often the horizontal that's quoted, but sometimes the diagonal, never the vertical !!! The angle of view of an LF is for the largest format the lens can be used with.

Perhaps a better term with a specific format is field of view for a lens, this is the practical angle of view focussed at Infinity with the particular lens/camera combination.

I'm not sure the Angle of view is static though, the usable Image Circle is so a lens used on a 5x4 camera won't be as wide (horizontally) as the same lens used on a 6x17 camera.

View attachment 201118


This brings us to a dimensional area rarely discussed where a lens can be wide angle in one dimension and yet normal in another.

I use a 75mm f8 Super Angulon on my 6x17 camera, this is a normal focal length lens on a 6x6 camera so in that respect is "Normal" for the vertical dimension with 6x17, on the other hand it's very wide angle in the horizontal dimension.

Ian

Click to expand...

I use the horizontal for comparison because the diagonal for a 35mm does not compare well with 6x6, 6x7, 6x9, 4"x5".

I scale normal focal lengths to the format that I want to compare:



.