Sensor size & focal length question

JerryLove

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The other side of all this is that a not-full-frame lens lies about its focal length in order to remain consistent with honest full-frame lenses.
 

480sparky

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The other side of all this is that a not-full-frame lens lies about its focal length in order to remain consistent with honest full-frame lenses.


Huh?
 

Braineack

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The other side of all this is that a not-full-frame lens lies about its focal length in order to remain consistent with honest full-frame lenses.

clarify.
 

JerryLove

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Think I'm wrong as I'm not dealing with changes in flange length. I am thinking solely in terms of AoV and how focal lengths are reported.

While I understand the whole crop / full frame effects with a given lens, how lenses are measured in regards to circle of light vs flange distance vs AoV is still a little muddled.

For example.

FFvCropNewSmall.jpg
Is the lens that makes the blue circle, and its smaller AoV, really the same mm as the lens that puts out the white circle and its wider AoV? Or is the mm listed as "equivalent to"?
 

Ysarex

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Think I'm wrong as I'm not dealing with changes in flange length. I am thinking solely in terms of AoV and how focal lengths are reported.

While I understand the whole crop / full frame effects with a given lens, how lenses are measured in regards to circle of light vs flange distance vs AoV is still a little muddled.

For example.

Is the lens that makes the blue circle, and its smaller AoV, really the same mm as the lens that puts out the white circle and its wider AoV? Or is the mm listed as "equivalent to"?


Angle of view is a function of focal length AND sensor size.

Joe
 

Dao

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Personally, I do not think the 35mm equivalent means much unless you are going to use it for comparison, it is just a reference point. It means a lot for someone who use 2 formats. So the photographer know what to expect once he/she switch camera bodies with different format. And different format (size) affects the Angle of View (or Field of view) only. The focal length of the lens is the physical property of the lens so it stay the same with different recording medium/format.

OP, as a photography beginner, and if you only have one camera body, it is better to know what you will expect as far as field of view goes when you pair a lens (set with a particular focal length) with your camera. Knowing what it may looks like in a different camera does not mean too much.
 

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The image projected by a given focal length is always the same size.
The projected image size is dependent on the design of the lens and the flange focal distance of the camera. Flange focal distance - Wikipedia, the free encyclopedia.

Camera makers and 3rd party lens makers design some of their lenses so they project a reduced size image for use on crop sensor cameras.
By doing so the lens makers can produce lower cost lenses. Lens cost less to make and sell because the lens can be shorter and can use smaller diameter lens elements.

By the same token lens makers design lenses to project a larger image circle for medium and large format cameras.

In other words, you can have multiple 50 mm lenses, each for a different image sensor format that each project a different size image.

Canon designates their crop sensor lenses EF-S. Nikon designates their crop sensor lenses DX.
 

JerryLove

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Angle of view is a function of focal length AND sensor size.
If that were true: telescopes would not have AoVs.

No. There is a fixed angle in the circle of light put out by the lens. While a sensor may or may not be placed to grab all of it, it's still fixed. A number above which no sensor can pass.
 

JerryLove

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The image projected by a given focal length is always the same size.
The projected image size is dependent on the design of the lens and the flange focal distance of the camera. Flange focal distance - Wikipedia, the free encyclopedia.

Camera makers and 3rd party lens makers design some of their lenses so they project a reduced size image for use on crop sensor cameras.
By doing so the lens makers can produce lower cost lenses. Lens cost less to make and sell because the lens can be shorter and can use smaller diameter lens elements.

By the same token lens makers design lenses to project a larger image circle for medium and large format cameras.

In other words, you can have multiple 50 mm lenses, each for a different image sensor format that each project a different size image.

Canon designates their crop sensor lenses EF-S. Nikon designates their crop sensor lenses DX.
What determines the mm of the lens?

I've read the wiki page on it, but don't fully grok it.

Is it the AoV of the resulting circle?

If mm and AoV are not dependent: two 50mm lenses could give different AoV circles?
If the two *are* dependent, then an EF-S lens marked as 50mm is actually more than 50mm because the circle produced by it as a smaller AoV.

I'm not talking about the chunk pulled out by the sensor... the sensor doesn't affect the lens.
 

Ysarex

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Angle of view is a function of focal length AND sensor size.
If that were true: telescopes would not have AoVs.

No. There is a fixed angle in the circle of light put out by the lens. While a sensor may or may not be placed to grab all of it, it's still fixed. A number above which no sensor can pass.

Yes. Angle of VIEW is a common photo term that we use to specify what we'll record from a 360 degree circle when taking a photo. For example a 80mm lens on a Hasselblad camera has a 41 degree angle of view. That same lens on a 35mm camera has an angle of view 25 degrees.

Joe
 

Ysarex

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The image projected by a given focal length is always the same size.
The projected image size is dependent on the design of the lens and the flange focal distance of the camera. Flange focal distance - Wikipedia, the free encyclopedia.

Camera makers and 3rd party lens makers design some of their lenses so they project a reduced size image for use on crop sensor cameras.
By doing so the lens makers can produce lower cost lenses. Lens cost less to make and sell because the lens can be shorter and can use smaller diameter lens elements.

By the same token lens makers design lenses to project a larger image circle for medium and large format cameras.

In other words, you can have multiple 50 mm lenses, each for a different image sensor format that each project a different size image.

Canon designates their crop sensor lenses EF-S. Nikon designates their crop sensor lenses DX.
What determines the mm of the lens?

I've read the wiki page on it, but don't fully grok it.

Is it the AoV of the resulting circle?

If mm and AoV are not dependent: two 50mm lenses could give different AoV circles?
If the two *are* dependent, then an EF-S lens marked as 50mm is actually more than 50mm because the circle produced by it as a smaller AoV.

I'm not talking about the chunk pulled out by the sensor... the sensor doesn't affect the lens.

The focal length of the lens is the distance from the lens nodal point to the film/sensor when the lens is focused at infinity. The lens focal length does not have a fixed relationship with the lens's projected image circle. Two lenses of the same focal length can project different image circles. However on the same camera they will have the same angle of view.

Joe
 

JerryLove

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Angle of view is a function of focal length AND sensor size.
If that were true: telescopes would not have AoVs.

No. There is a fixed angle in the circle of light put out by the lens. While a sensor may or may not be placed to grab all of it, it's still fixed. A number above which no sensor can pass.

Yes. Angle of VIEW is a common photo term that we use to specify what we'll record from a 360 degree circle when taking a photo. For example a 80mm lens on a Hasselblad camera has a 41 degree angle of view. That same lens on a 35mm camera has an angle of view 25 degrees.

Joe
I don't see how that is possible (unless you are cropping, which is not what I'm discussing).

If I put an infinite piece of paper behind the lens, how many arc-seconds of the terrain in front of me would be visible on that paper?
 
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JerryLove

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The focal length of the lens is the distance from the lens nodal point to the film/sensor when the lens is focused at infinity. The lens focal length does not have a fixed relationship with the lens's projected image circle. Two lenses of the same focal length can project different image circles. However on the same camera they will have the same angle of view.
Since we can "free lens" on a camera, the flange length is not fixed to one number by the lens (if it were, "freelensing" would be impossible because of the new flange length).

So since the length (50mm) is the distance from the nodal point (that is fixed?) to the sensor (which is not fixed), we cannot say that a lens is 50mm? We can only say that a lens is 50mm at a given distance from the sensor or film?
 

Ysarex

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If that were true: telescopes would not have AoVs.

No. There is a fixed angle in the circle of light put out by the lens. While a sensor may or may not be placed to grab all of it, it's still fixed. A number above which no sensor can pass.

Yes. Angle of VIEW is a common photo term that we use to specify what we'll record from a 360 degree circle when taking a photo. For example a 80mm lens on a Hasselblad camera has a 41 degree angle of view. That same lens on a 35mm camera has an angle of view 25 degrees.

Joe
I don't see how that is possible (unless you are cropping, which is not what I'm discussing).

If I put an infinite piece of paper behind the lens, how many arc-seconds of the terrain in front of me would be visible on that paper?

You used the term AoV (angle of view). I'm telling you how that term is commonly understood, defined and used by photographers. If you're discussing something else, use the right terminology for whatever that something else is.

Joe
 

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