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DX multiplier factor

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sengngo

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I've seen people talk about multiplier factor on DX and I find it misleading. Please correct me if I'm wrong. My understanding people are explaining it as "a 50mm lens on a DX is the equivalent to a something like an 80mm lens." However, isn't this incorrect? Isn't that a 50mm lens on a DX gives you the magnification of 50mm but it is cropped so it gives you the field of vision of a 80mm lens?

Therefore, its basically the field of vision that changes not "reach" of the lens. I can't see how a sensor can increase the magnification of a lens.
 
The focal length is a factor of the lens not the camera. But us old timers like to compare our lenses to the 35mm film equivalents.

The DX sensor is smaller, a fraction of the size of an FX sensor or 35mm film.

So the DX sensor is only reading part of the light the lens is capable of transmitting.

So the math works - for Nikon, Pentax, Sony, they have an APS C sensor that is 2/3 the size of a FX sensor, so you multiple the DX lens length by 1.5 to get the equivalence - which lens it would correspond to in film/FX.

So a 50 mm film lens, mounted on a DX camera, would be like a 75mm lens mounted on an FX/Film camera -same angle of view.
 
JamesRL said:
The focal length is a factor of the lens not the camera. But us old timers like to compare our lenses to the 35mm film equivalents.

The DX sensor is smaller, a fraction of the size of an FX sensor or 35mm film.

So the DX sensor is only reading part of the light the lens is capable of transmitting.

So the math works - for Nikon, Pentax, Sony, they have an APS C sensor that is 2/3 the size of a FX sensor, so you multiple the DX lens length by 1.5 to get the equivalence - which lens it would correspond to in film/FX.

So a 50 mm film lens, mounted on a DX camera, would be like a 75mm lens mounted on an FX/Film camera -same angle of view.
Click to expand...
Right, the angle of view is the same but not the magnification?

Basically what I'm asking is that if a DX and FX camera take the same exact image using the same lens, it would be the same image. The only difference is the FX would extend out due to the larger sensor size?
 
sengngo said:
Right, the angle of view is the same but not the magnification?

Basically what I'm asking is that if a DX and FX camera take the same exact image using the same lens, it would be the same image. The only difference is the FX would extend out due to the larger sensor size?
Click to expand...
Now for this argument I mean to use an FX lens. Not a DX on a FX body.
 
The angle of view is smaller as well.

--
A Beginning Amateur Photographer
 
sengngo said:
JamesRL said:
The focal length is a factor of the lens not the camera. But us old timers like to compare our lenses to the 35mm film equivalents.

The DX sensor is smaller, a fraction of the size of an FX sensor or 35mm film.

So the DX sensor is only reading part of the light the lens is capable of transmitting.

So the math works - for Nikon, Pentax, Sony, they have an APS C sensor that is 2/3 the size of a FX sensor, so you multiple the DX lens length by 1.5 to get the equivalence - which lens it would correspond to in film/FX.

So a 50 mm film lens, mounted on a DX camera, would be like a 75mm lens mounted on an FX/Film camera -same angle of view.
Click to expand...
Right, the angle of view is the same but not the magnification?

Basically what I'm asking is that if a DX and FX camera take the same exact image using the same lens, it would be the same image. The only difference is the FX would extend out due to the larger sensor size?
Click to expand...
Yes, this has to be true because the lens is the same and the image it produces iis the same. But the images on the sensor are not the same. You noted the difference yourself: the FX image covers more field. So the field of view of a 50 mm lens on a DX camera is the same as the field of view of a 75 mm lens on an FX camera.

What happens is that people print pictures. If you print a DX file to 20" X 30", you're magnifying it 32X. If you print an FX file to the same size, you're magnifying it 21X. So that's where the crop factor comes in: if you take an image with an FX camera, you generally don't want to waste the outer half of it. So for any given print size, FX requires less magnification between the sensor size and the final image.

--
Leonard Migliore
 
sengngo said:
Basically what I'm asking is that if a DX and FX camera take the same exact image using the same lens, it would be the same image. The only difference is the FX would extend out due to the larger sensor size?
Click to expand...
You are correct in that the angle of view is the issue - the focal length is a function of the lens and stays the same regardless of what camera you put it on. If you put a 50mm lens on a DX sensor, and FX sensor, or a Medium Format sensor, the lens still has a focal length of 50mm. What does change, however, is the angle of view .

Let's say you've got two cameras - an FX, full-frame, 35mm-equivalent camera, and a DX, APS-C sized crop-sensor camera.

You get out your 24mm lens and put it on your full-frame FX camera. The (horizontal) angle of view is about 74 degrees. Imagine standing in a circle drawn on the ground - it has 360 degrees. With your camera, you can see about 74 degrees of the total 360 around you.

Now you take that same 24mm lens and put it on a crop-sensor DX camera. Nothing about the lens has changed, but because of the smaller sensor, the sensor "sees" a smaller portion of the image cast by the lens. This causes a change in the angle of view.

Since Nikon's crop factor for their DX cameras is 1.5, your angle of view is now only 53 degrees - standing in your 360-degree circle, only about 53 degrees of the total 360 is available.

Anyway, this is why people say "35mm equivalent". A 24mm lens on a FX camera has the same angle of view as a 16mm lens on a DX camera (16 x 1.5 = 24).

The only difference between lenses are badged "DX" and other lenses is that the DX lenses have smaller diameter pieces of glass in them, and only cast an image big enough to cover the DX sensor. This means that they are cheaper to manufacture and lighter in weight, but the downside is that when you put on on an FX camera, the image cast by the lens is not large enough to cover the sensor and you see black borders through the viewfinder (darkened image edges are also known as "vignetting").

If you want to get into the math behind this, or more detail, this is a good page: http://www.bobatkins.com/photography/technical/field_of_view.html
 
rob-t said:
Anyway, this is why people say "35mm equivalent". A 24mm lens on a FX camera has the same angle of view as a 16mm lens on a DX camera (16 x 1.5 = 24).
Click to expand...
This is basically why I started this thread. Because I think to beginners (myself included) when I first heard this I assumed that a 24mm lens had both the magnification and field of view as a 35mm on an FX body. Which I never understood but people kept saying "equivalent".
rob-t said:
If you want to get into the math behind this, or more detail, this is a good page: http://www.bobatkins.com/photography/technical/field_of_view.html
Click to expand...
I'll take a look into this.

Thank you for clearing things up everyone.
 
The use of the words "multiplier" and "magnification" are problematic.

The better term to use is "crop", and the best is "angle of view" because it is a term that is absolute. Crop or multiplier are relative terms, relative to 35mm film. If you think in terms of 35mm film, then these concepts may be useful. But if you are new to DSLR photography, these terms are confusing and not very useful.

Second, camera lenses don't magnify anything. Quite the reverse - they gather light from the actual size world and concentrate it on a very small sensor.

Angle of view is the term that is the least confusing; i.e. this focal length lens has an AOV on that sensor size. Once we do that, then we can say that a 20mm lens on DX has an AOV equal to a 30mm on FX, and it all makes sense.
 
Chas B said:
Second, camera lenses don't magnify anything. Quite the reverse - they gather light from the actual size world and concentrate it on a very small sensor.
Click to expand...
I'm not sure I understand this. I get that lenses gather light but how does that not create a magnified image? I mean isn't something being magnified the point of Macro lenses?
 
sengngo said:
Chas B said:
Second, camera lenses don't magnify anything. Quite the reverse - they gather light from the actual size world and concentrate it on a very small sensor.
Click to expand...
I'm not sure I understand this. I get that lenses gather light but how does that not create a magnified image? I mean isn't something being magnified the point of Macro lenses?
Click to expand...
Here's an example. The piece of silicon that makes an FX sensor is about 35mm x 24mm in actual, physical size. Yet your camera is taking an entire scene, say a mural on a wall that is 35 meters x 24 meters, and using the lens to gather and condense light - in this case, reducing 1 meter in real life to 1 millimeter on the sensor.

To put it another way, the area of the mural is 35x24m = 840 square meters = 840,000 square millimeters. You camera reduces the mural by a factor of 1000, down to 840 square millimeters, to fit on the sensor.

A Macro lens typically has a 1:1 magnification ratio. 1:1 is usually at the lens' closest focus point only - i.e. the object, like a flower is at the minimum focus distance of the lens, say about 3cm or something.

1:1 means that an object at that closest focus point is going to be projected at the same size on the sensor that it is in real life. So if you've got a postage stamp that measures 35mm x 24mm, a 1:1 macro lens on your FX camera, and the postage stamp is at the minimum focus distance of 3cm (for that lens), then the 35x24mm stamp is going to take up the entire 35x24mm sensor, and the entire 'frame' of the image.

If you've ever used a microscope in school, they typically have a magnification power, and sometimes multiple lenses with different magnifications. Microscopes do the opposite of a camera lens. They take something very small (a bacterial cell for example) and enlarge it to be visible to the eye.

Let's say you've got an expensive 1000x digital microscope. It could take something that's 35x24 micrometers in size, and blow it up to 35x24 millimeters in size so that it would cover the microscope's FX-sized digital sensor. (A micrometer is 1/1000 of a millimeter).

A good 1:1 macro lens is the equivalent of a 1x microscope - it makes something the same size on the sensor as it is in real life. But most non-macro camera lenses have magnifications in the range of 0.01x to 0.5x, depending on the lens design and the focus distance - the lenses make real life smaller on the sensor. Most microscopes have lenses that have magnifications of 10x-1000x (they make real life bigger on the sensor.)
 
rob-t said:
Here's an example. The piece of silicon that makes an FX sensor is about 35mm x 24mm in actual, physical size. Yet your camera is taking an entire scene, say a mural on a wall that is 35 meters x 24 meters, and using the lens to gather and condense light - in this case, reducing 1 meter in real life to 1 millimeter on the sensor.

To put it another way, the area of the mural is 35x24m = 840 square meters = 840,000 square millimeters. You camera reduces the mural by a factor of 1000, down to 840 square millimeters, to fit on the sensor.

A Macro lens typically has a 1:1 magnification ratio. 1:1 is usually at the lens' closest focus point only - i.e. the object, like a flower is at the minimum focus distance of the lens, say about 3cm or something.

1:1 means that an object at that closest focus point is going to be projected at the same size on the sensor that it is in real life. So if you've got a postage stamp that measures 35mm x 24mm, a 1:1 macro lens on your FX camera, and the postage stamp is at the minimum focus distance of 3cm (for that lens), then the 35x24mm stamp is going to take up the entire 35x24mm sensor, and the entire 'frame' of the image.

If you've ever used a microscope in school, they typically have a magnification power, and sometimes multiple lenses with different magnifications. Microscopes do the opposite of a camera lens. They take something very small (a bacterial cell for example) and enlarge it to be visible to the eye.

Let's say you've got an expensive 1000x digital microscope. It could take something that's 35x24 micrometers in size, and blow it up to 35x24 millimeters in size so that it would cover the microscope's FX-sized digital sensor. (A micrometer is 1/1000 of a millimeter).

A good 1:1 macro lens is the equivalent of a 1x microscope - it makes something the same size on the sensor as it is in real life. But most non-macro camera lenses have magnifications in the range of 0.01x to 0.5x, depending on the lens design and the focus distance - the lenses make real life smaller on the sensor. Most microscopes have lenses that have magnifications of 10x-1000x (they make real life bigger on the sensor.)
Click to expand...
Thank you! That makes a lot of sense.
 
sengngo said:
I've seen people talk about multiplier factor on DX and I find it misleading. Please correct me if I'm wrong. My understanding people are explaining it as "a 50mm lens on a DX is the equivalent to a something like an 80mm lens." However, isn't this incorrect? Isn't that a 50mm lens on a DX gives you the magnification of 50mm but it is cropped so it gives you the field of vision of a 80mm lens?

Therefore, its basically the field of vision that changes not "reach" of the lens. I can't see how a sensor can increase the magnification of a lens.
Click to expand...
Sounds like you have a pretty good handle on it.

Bottom line is if you photograph a duck with a 50mm lens on a D300, and your buddy standing next to you takes a photograph of the same duck with a 75mm lens (invented a few seconds ago) on a D3, then the prints of both photographs will look practically identical.

I like to be practical about the whole affair... and visuals get straight to the nitty-gritty.

http://www.pbase.com/teiladay/full_frame_vs_cropped_examples

Notice how the 35mm on the D7000, D2hs or D300 basically equates to using a 50mm on a Canon 5d2, D3, or D700?

No matter what people want to call it (field of vision, angle of view, magnification, etc.) the fact of the matter is simple:

1. Whatever lens you have on your FX camera, if you divide the focal length by 1.5 and stick the resulting focal length on a DX camera, then practically speaking, both cameras now have the same lens on... and when taking a photograph of an object from the same spot, both cameras will basically take the exact same photograph.

2. Whatever lens you have on your DX camera, if you multiply the focal length by 1.5 and stick the resulting focal length on a FX camera, then practically speaking, both cameras now have the same lens on... and when taking a photograph of an object from the same spot, both cameras will basically take the exact same photograph.

... that is if I haven't confused myself ;)
--
Teila K. Day
 
sengngo said:
rob-t said:
Here's an example. The piece of silicon that makes an FX sensor is about 35mm x 24mm in actual, physical size. Yet your camera is taking an entire scene, say a mural on a wall that is 35 meters x 24 meters, and using the lens to gather and condense light - in this case, reducing 1 meter in real life to 1 millimeter on the sensor.

To put it another way, the area of the mural is 35x24m = 840 square meters = 840,000 square millimeters. You camera reduces the mural by a factor of 1000, down to 840 square millimeters, to fit on the sensor.

A Macro lens typically has a 1:1 magnification ratio. 1:1 is usually at the lens' closest focus point only - i.e. the object, like a flower is at the minimum focus distance of the lens, say about 3cm or something.

1:1 means that an object at that closest focus point is going to be projected at the same size on the sensor that it is in real life. So if you've got a postage stamp that measures 35mm x 24mm, a 1:1 macro lens on your FX camera, and the postage stamp is at the minimum focus distance of 3cm (for that lens), then the 35x24mm stamp is going to take up the entire 35x24mm sensor, and the entire 'frame' of the image.

If you've ever used a microscope in school, they typically have a magnification power, and sometimes multiple lenses with different magnifications. Microscopes do the opposite of a camera lens. They take something very small (a bacterial cell for example) and enlarge it to be visible to the eye.

Let's say you've got an expensive 1000x digital microscope. It could take something that's 35x24 micrometers in size, and blow it up to 35x24 millimeters in size so that it would cover the microscope's FX-sized digital sensor. (A micrometer is 1/1000 of a millimeter).

A good 1:1 macro lens is the equivalent of a 1x microscope - it makes something the same size on the sensor as it is in real life. But most non-macro camera lenses have magnifications in the range of 0.01x to 0.5x, depending on the lens design and the focus distance - the lenses make real life smaller on the sensor. Most microscopes have lenses that have magnifications of 10x-1000x (they make real life bigger on the sensor.)
Click to expand...
Thank you! That makes a lot of sense.
Click to expand...
BUT ..."magnification" should be "magnification ratio". When you correctly express it as a ratio, 10:1 and 1:10 both make sense, but one is sorta a negative magnification, in that the image is 10X smaller than the object.

A better term is "reproduction ratio", because "reproduction" by itself doesn't mean anything confusing. :-)

As others have said, unless you are grounded in 35mm film technology, it's a bit difficult to understand the "crop factor" concept! A much better approach is to simply talk about the FoV w/ a specific lens or perhaps a "FoV factor"?

--
Charlie Davis
Nikon 5700, Sony R1, Nikon D50, Nikon D300
HomePage: http://www.1derful.info

"If ever a time should come, when vain and aspiring men shall possess the highest seats in Government, our country will stand in need of its experienced patriots to prevent its ruin."
-Samuel Adams, 1776
 
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