wide angle lens (angle of coverage question)

[GPS]

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]

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]

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.

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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...
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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]

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]

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...