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markinwaterloo
14-Aug-2008, 18:43
Hello all,

When comparing 2 lenses of varying focal legths that I'm considering purchasing, I've come across a question that I was hoping someone more experienced could help me with. I was considering both the Nikkor SW 75mm with a listed angle of coverage of 106 degrees and a Fujinon SWD 65mm with an angle of coverage listed at 105 degrees.

My question is: is the 75mm a wider lens than the 65mm? Will I get a wider view with this longer lens? It doesn't seem to make sense to me at all and Im not quite sure how a longer lens can give a wider angle of coverage . . . if anyone can explain this I would really appreciate your help!!

Best regards!

Mark

Ron Marshall
14-Aug-2008, 18:52
The 65 will give you a wider perspective than the 75, but the 75 will permit a bit more movement than the 65.

See the rise possible for the 65 and the 75 on this chart:

http://www.largeformatphotography.info/lenses/LF4x5in.html

Jan Pedersen
14-Aug-2008, 18:57
The 75mm with 106 degree coverage have an image Circle (IC) of 199mm
The 65mm with 105 degree coverage will have an image Circle of 169.4mm
Imagine the circle behind the lens when it is focused on something at infinity. This is what projects the image on your film.
To cover a 4x5 sheet of film you will need about 154mm IC so the 65mm barely covers.

Jeff Keller
14-Aug-2008, 22:42
It sounds like you are coming from the 35mm world. For large format there are a few different aspects you have to pay attention to:

1.) As in the 35mm world a shorter focal length provides what you refer to as a wider angle.
2.) Lenses can not illuminate an infinitely large piece of film. The angle of coverage refers to how much film the lens can cover. An angle of coverage is a good way to specify this because as the lens is focused at closer objects the lens moves further from the film and can cover a larger piece of film.
I3.) f you use camera movements such as shift or tilt, the film probably won't be centered in the area that the lens illuminates. Typically you want lenses which can cover an area significantly larger than the film


Jeff Keller
(http://www.julianalee.com - real estate for sale images)


Hello all,

My question is: is the 75mm a wider lens than the 65mm? Will I get a wider view with this longer lens? It doesn't seem to make sense to me at all and Im not quite sure how a longer lens can give a wider angle of coverage . . . if anyone can explain this I would really appreciate your help!!

Best regards!

Mark

Jiri Vasina
14-Aug-2008, 23:06
angle of coverage indicates the diameter of image circle illuminated. You can calculate the exact image circle size if you know the angle of coverage and focal length using goniometric functions (tangens and like). I don't know the exact formula, though...

It has nothing to do with "angle of view", which describes how wide the lens is (like the focal length). Maybe there lies the confusion.

GPS
15-Aug-2008, 04:41
angle of coverage indicates the diameter of image circle illuminated. You can calculate the exact image circle size if you know the angle of coverage and focal length using goniometric functions (tangens and like). I don't know the exact formula, though...

It has nothing to do with "angle of view", which describes how wide the lens is (like the focal length). Maybe there lies the confusion.

Unfortunately Jiri, you couldn't be more wrong on this.
The angle of coverage does not indicate the diameter of image circle. You can have two lenses, one that has a huge image circle -without being a wide angle lens- and the other that has a much smaller image circle and is a wide angle lens. Compare the huge Schneider 1100mmXXL (not a wide angle at all, despite its enormous 900 mm image circle) and the Schneider Super Angulon XL 72mm with its much smaller image circle - "just" 229 mm which is a wide angle lens. Why? Because the former has a coverage angle just some 44° and the latter whole 115°!
And you can have a lens with the same angle of coverage and different image circles (because of a different focal length), to make it more "complicated", and lenses with the same image circle and different angle of coverage.
The angle of coverage is in degrees, the image diameter in mm/in. Think of it...
The angle of view doesn't describe at all how "wide a lens is", only how wide it sees for the given film format. Think of it...



Hello all,

When comparing 2 lenses of varying focal lengths that I'm considering purchasing, I've come across a question that I was hoping someone more experienced could help me with. I was considering both the Nikkor SW 75mm with a listed angle of coverage of 106 degrees and a Fujinon SWD 65mm with an angle of coverage listed at 105 degrees.

My question is: is the 75mm a wider lens than the 65mm? Will I get a wider view with this longer lens? It doesn't seem to make sense to me at all and Im not quite sure how a longer lens can give a wider angle of coverage . . . if anyone can explain this I would really appreciate your help!!

Best regards!

Mark

Mark, it's simple. The wider lens of them is the one with a bigger angle of coverage.
But the angle of view depends on the film format you use. If you use the same film format the longer focal length will see less than the shorter one (for the same taking distance), even if the longer has a wider angle of coverage - you just don't use it fully with the same film format...

Nick_3536
15-Aug-2008, 06:05
Mark, it's simple. The wider lens of them is the one with a bigger angle of coverage.


Well no. If you take two 150mm lenses with different angles of coverage one isn't wider then the other. Sure a big angle of coverage might let you use it on a bigger format and therefore it can be a wide lens for a bigger format. But angle of coverage indicates coverage. Even the 80degree "normal" lenses can be wide on the next step up in format.

Jiri Vasina
15-Aug-2008, 06:24
GPS, I think I'm not that wrong.

Angle of coverage together with the focal length do describe the image circle (and yes, that is precisely the reason why the 1100XXL with only 44° angle of coverage but with the focal length of 1100mm has such a huge image circle. But relatively to its focal length, it's small). I have stated that in my previous post, although maybe not as clearly. You can calculate any one of the remaining parameters if you know the other two: angle of coverage, focal length, image circle. They are all part of one imaginary optical triangle.

GPS
15-Aug-2008, 08:59
angle of coverage indicates the diameter of image circle illuminated. You can calculate the exact image circle size if you know the angle of coverage and focal length using goniometric functions (tangens and like). I don't know the exact formula, though...

It has nothing to do with "angle of view", which describes how wide the lens is (like the focal length). Maybe there lies the confusion.


GPS, I think I'm not that wrong.

Angle of coverage together with the focal length do describe the image circle
-snip
I have stated that in my previous post, although maybe not as clearly. You can calculate any one of the remaining parameters if you know the other two: angle of coverage, focal length, image circle. They are all part of one imaginary optical triangle.

Sorry Jiri, not to beat the horse ad nauseum, but in your first post, first phrase you mentioned the angle of coverage (without any focal length!) as an indication of the image circle. That is clearly incorrect and that's why I corrected it. Only then, in the second post, did you add the focal length to it... Nobody denied the possibility of calculations, provided you know at least two input values.
Also, the angle of view doesn't "describe how wide the lens is" , as you say, only how wide the lens sees - two very different things, aren't they... If you put a 6x6 film format on the SA XL 72mm you will have a normal lens, although the lens is a wide angle lens. Put there the 6x17 film format and abracadabra,the lens is a wide angle lens... Thus both statements, written as they are, were misleading. Hence my correction.

Leonard Evens
15-Aug-2008, 09:10
Let me split a hair. The image circle is not the same as the circle in which there is adequate illumination. It is the circle in which the definition is considered adequate. That will generally be smaller than the circle where there is enough light to produce an image. In some circumstances, where one doesn't care about sharpness at the edges, you can shift beyond the boundary of the circle of coverage. An example might be where that part of the image consists of open sky or clouds which need not be sharp.

GPS
15-Aug-2008, 09:20
Well no. If you take two 150mm lenses with different angles of coverage one isn't wider then the other. Sure a big angle of coverage might let you use it on a bigger format and therefore it can be a wide lens for a bigger format. But angle of coverage indicates coverage. Even the 80degree "normal" lenses can be wide on the next step up in format.

Well no. The angle of coverage indicates the angle of coverage, not just coverage. Notice that coverage as such could be also expressed simply in mm of the covered format length (it covers 6x17 easily... ect.) What you say about the 80 lens as normal or not has to do with the angle of view, given by the format. I wrote about that too.

GPS
15-Aug-2008, 09:28
Hello all,

When comparing 2 lenses of varying focal legths that I'm considering purchasing, I've come across a question that I was hoping someone more experienced could help me with. I was considering both the Nikkor SW 75mm with a listed angle of coverage of 106 degrees and a Fujinon SWD 65mm with an angle of coverage listed at 105 degrees.

My question is: is the 75mm a wider lens than the 65mm? Will I get a wider view with this longer lens? It doesn't seem to make sense to me at all and Im not quite sure how a longer lens can give a wider angle of coverage . . . if anyone can explain this I would really appreciate your help!!

Best regards!

Mark

Mark, before it makes you dizzy - the bigger the angle of coverage, the wider the lens is in terms of coverage (because it allows the use of a bigger format). The longer the focal length of a lens is, the less (in terms of angle of view) it sees on a given film format. Go by that and you will not get lost...

Jiri Vasina
15-Aug-2008, 09:57
GPS, I might have been not precise enough but


angle of coverage indicates the diameter of image circle illuminated. You can calculate the exact image circle size if you know the angle of coverage and focal length using goniometric functions (tangens and like).




... Also, the angle of view doesn't "describe how wide the lens is" , as you say, only how wide the lens sees...

And yes, yours is better wording. I omited the clarification that the angle of view does describe how wide the lens is on a given image format in comparison to a different lens with different angle of view on the same format. My answer might have been hasty and not precise enough, leaving out some assumptions (and wordings) I considered apparent.

---- edit ---
If not considering any specific image format, angle of view is related to the image circle. And when you compare two lenses you have to either consider the common image circle, or common image format. Or you might want to find a lens with a specific angle of view for a certain format if you know the focal length/angle of view for a different format - eg. a question like "If I like 24mm lens on a 35mm camera, what lens do I need to use on 4x5" - to answer this question, you use the calculation of angle of view...
-----

But I don't understand this part


...
The angle of coverage is in degrees, the image diameter in mm/in. Think of it...
...


This is exactly the place where goniometric functions come to place

GPS
15-Aug-2008, 10:50
Yes, we both know where the problem is, no problem with it:)
Now, if we don't consider any film format, then of course the angle of view is the angle of coverage, but so what:)
"When you compare two lenses you have to either consider the common image circle...etc." - well, depends what you want to compare in them...
"The angle of coverage is in degrees, the image circle in mm/in, think of it..." related to the first phrase of your first post. I wanted to show that the angle of coverage (with no mention of the f. length!) cannon say anything about the mm/in of the image circle, hence...
And yes, no problem with calculations so I don't touch that. Shame on you that you forgot the tgn formula learned in your fundamental school (but only in high school in the US,:) ) Back to your literature...;)

GPS
15-Aug-2008, 13:53
Let me split a hair. The image circle is not the same as the circle in which there is adequate illumination. It is the circle in which the definition is considered adequate. That will generally be smaller than the circle where there is enough light to produce an image. In some circumstances, where one doesn't care about sharpness at the edges, you can shift beyond the boundary of the circle of coverage. An example might be where that part of the image consists of open sky or clouds which need not be sharp.

Well, while we're at splitting the hair... let me split it even more:) I don't entirely agree with considering the illumination circle as a possible image circle. It's not only a question of sharpness that fails but also of the illumination evenness. The sky in question could be perturbed by a shady circle. In some cases...:)