Nikon DX lens question

[duraace]

Is the stated focal length on a DX lens what you get on a DX body?  Eg.   Is 18mm DX actually 18mm on the DX camera?  If it's not a DX lens, the 1.5x crop factor comes in to play, right?

[Richowens]

An 18, whether DX or not, when used on a DX body has the field of view of a 27 on full frame. It just doesn't have enough image circle to cover full frame.

HTH

 Rich

[duraace]

An 18, whether DX or not, when used on a DX body has the field of view of a 27 on full frame. It just doesn't have enough image circle to cover full frame.

HTH

 Rich
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I'm bit confused with the reference to a full frame.  Can you confirm an 18mm DX lens is 27mm on both a DX camera and a full frame camera?  I just purchased a 14-24mm f2.8, so I'm assuming I'll get a wider angle than with the 18-200mm DX, on my D300.  Is that correct?

[Mort54]

I'm bit confused with the reference to a full frame.  Can you confirm an 18mm DX lens is 27mm on both a DX camera and a full frame camera?  I just purchased a 14-24mm f2.8, so I'm assuming I'll get a wider angle than with the 18-200mm DX, on my D300.  Is that correct?

An 18 mm DX lens (or any 18 mm lens, period) is 18 mm on a full frame body, and the equivalent of a 27 mm on a DX body. All you have to remember is that on a DX body, mulitply the focal length by 1.5 to get the equivalent focal length. On a full frame body, you simply multiply the focal length by 1.

Whether a lens is DX or not doesn't make any difference as far as the multiplier goes. However, a DX lens typically will vignet badly on a full frame body.

[Panopeeper]

The focal length of an 18mm lens is 18mm, no matter which lens and on which camera. This is important, for the focal length is a factor in the depth of field, circle of confusion, bokeh and minimum shutter time when shooting hand-held (what else?)

Another aspect is the angle of view: that depends not only on the focal length but on the diameter of the captured image as well.

As the DX projects a smaller image than the FF, the angle of view on a FF camera is smaller than of a "normal" lens (if it can be mounted at all). On the other hand, an FF lens projects a larger image than the cropping camera can use, so the angle of view of the captured image is smaller than on the FF camera - actually 1.5 times smaller.

[TMcCulley]

I'm bit confused with the reference to a full frame.  Can you confirm an 18mm DX lens is 27mm on both a DX camera and a full frame camera?  I just purchased a 14-24mm f2.8, so I'm assuming I'll get a wider angle than with the 18-200mm DX, on my D300.  Is that correct?
[a href=\"index.php?act=findpost&pid=189840\"][{POST_SNAPBACK}][/a]

Imagine that you have a D3 and a D300.  On the D3 the image circle of your 18-200 will be cutoff in all the corners because it projects a smaller image circle.  

If you set 24mm (or any other common focal length) on both of your lens they will give you the same view on each camera but the view will be different between the cameras and the 18-200 will vignette badly on the D3.

Tom

[01af]

Is the stated focal length on a DX lens what you get on a DX body?[a href=\"index.php?act=findpost&pid=189830\"][{POST_SNAPBACK}][/a]

Yes, sure it is.

E. g. Is 18 mm DX actually 18 mm on the DX camera?[a href=\"index.php?act=findpost&pid=189830\"][{POST_SNAPBACK}][/a]

Yes, sure it is.

If it's not a DX lens, the 1.5x crop factor comes in to play, right?[a href=\"index.php?act=findpost&pid=189830\"][{POST_SNAPBACK}][/a]

Wrong. The 1.5× crop factor comes into play when you are using an APS-C-format camera and your mind still is set on the focal-length-to-angle-of-view relation that you're used from 35-mm format. It has absolutely nothing to do with the lens being DX or not.

Can you confirm an 18 mm DX lens is 27 mm on both a DX camera and a full frame camera?[a href=\"index.php?act=findpost&pid=189840\"][{POST_SNAPBACK}][/a]

No, of course not. An 18 mm lens, whether it's DX or not, will always be 18 mm on both DX-format (= APS-C-format in Nikon speak) and 35-mm-format cameras. Of course, on the smaller-format camera the angle of view will be smaller.

I just purchased a 14-24 mm f/2.8, so I'm assuming I'll get a wider angle than with the 18-200 mm DX, on my D300.  Is that correct?[a href=\"index.php?act=findpost&pid=189840\"][{POST_SNAPBACK}][/a]

If you just purchased it, why don't you simply take a look through the viewfinder? 14 mm is shorter than 18 mm so yes, you'll get a wider angle at 14 mm than at 18 mm. On any camera.

And in case you're still wondering: With both lenses set to 18 mm, you'll get the same angle of view from both, on a D300.

-- Olaf

[duraace]

An 18 mm DX lens (or any 18 mm lens, period) is 18 mm on a full frame body, and the equivalent of a 27 mm on a DX body. All you have to remember is that on a DX body, mulitply the focal length by 1.5 to get the equivalent focal length. On a full frame body, you simply multiply the focal length by 1.

Whether a lens is DX or not doesn't make any difference as far as the multiplier goes. However, a DX lens typically will vignet badly on a full frame body.
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Great thanks. That means my new 14-24 will be wider angle than the 18 and upward compatible whenever I move to full frame.

[BJL]

The focal length of an 18mm lens is 18mm, no matter which lens and on which camera. This is important, for the focal length is a factor in the depth of field, circle of confusion, bokeh and minimum shutter time when shooting hand-held
[a href=\"index.php?act=findpost&pid=189859\"][{POST_SNAPBACK}][/a]

I disagree a bit on depth of field, circle of confusion and minimum shutter time when shooting hand-held.

Since prints (of the whole recorded image) of the same size require greater degree of enlargement from a smaller format (1.5x more in this case), the acceptable circle of confusion in the image formed by the lens at the focal plane needs to be reduced in proportion to format size. Thus, DOF will be less (in proportion to the linear format factor) if you use the same focal length and aperture and print the uncropped images from the two formats at the same size and view them under the same conditions.

Similarly for hand-holding: less motion of the image across the sensor due to camera motion is acceptable with a smaller format due to that greater degree of enlargement for same sized uncropped prints, so a higher shutter pseed is needed for handholding with equal focal length, about in proportion to format factor, meaning that the "effective focal length" is a better right measure of needed shutter speed.

So what counts for hand-holding is angular field of view, as indicated by effective focal length, not actual focal length. Well, factors like camera weight count too, but smaller format cameras are generally lighter, making camera motion worse if anything.

[Panopeeper]

Since prints (of the whole recorded image) of the same size require greater degree of enlargement from a smaller format (1.5x more in this case),

You are mixing different, independent issue. The enlargement (upresing) depends on several factors, one of them is the pixel count of the camera. There is no such rule, that an FF camera has higher pixel count than a cropping one. As the matter of fact, there are opposite examples.

If we don't separate the independent issues, then we can debate forever without any result. The final result depends on several factors, and all of them need to be analyzed on their own.

[Morgan_Moore]

Is the stated focal length on a DX lens what you get on a DX body?  Eg.   Is 18mm DX actually 18mm on the DX camera?  If it's not a DX lens, the 1.5x crop factor comes in to play, right?
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Trying to find a simple answer for you

an 18 is very wide on a D3 full frame and averagely wide on a DX size camera like the D80 or the D300

when buying a small chip camera you need to budget on getting wider lenses to acheive a certain field of view

with my D3 I need a 17-35 as a wide zoom for a D300 a 12-24 is required

S

[BJL]

If we don't separate the independent issues, then we can debate forever without any result.
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I agree, but to me, the final image size and viewing conditions (like viewing distance) are amongst the factors to be chosen independently, and "final image size" is a better choice than "degree of enlargement" as one of the independent factors.

I would count pixel count or "sensor detail" in lines per picture height as another independent factor. (In the Nikon example under discussion, the D300 and D3 have equal pixel counts!)

Mine is also the approach taken in traditional DOF tables and DOF scales on lenses, which are based on a standardized print size and viewing distance combination, corresponding to viewing distance about equal to print diagonal size.

[BJL]

when buying a small chip camera you need to budget on getting wider lenses to acheive a certain field of view
[a href=\"index.php?act=findpost&pid=190013\"][{POST_SNAPBACK}][/a]

No, you need shorter lenses to get equally wide angular field of view. (Meaning shorter focal lengths.) If the shorter lens is designed for the smaller format, it can be equally wide in angular field of view.

Only people who insist on using wide angle lenses designed for a larger format with a sensor of smaller format need to use wider than necessary lenses to get a given degree of wide angle coverage. The format mismatch is the problem here.

With a mixture of format sizes, we need to stop using "width" as a synonym for "focal length". (Along with the confusion of identifying either f-stop or ISO speed as a measure of "camera speed", when the two in fact interact in a way that is somewhat format dependent.)

[Tony Beach]

With a mixture of format sizes, we need to stop using "width" as a synonym for "focal length".
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This thread and many like it are the direct result of understandable confusion caused by the peculiar tendency to refer to focal lengths based on a single format.  It would be more useful and less confusing if we were to say that 18mm was 90 degrees (horizontal on a 3:2 aspect ratio) on an FX or 135 film format, but it's 67 degrees on a DX format.  Most of us can visualize 90 degrees, or even 67 degrees; few of us can visualize 18mm regardless of what format it's used on.

[duraace]

This thread and many like it are the direct result of understandable confusion caused by the peculiar tendency to refer to focal lengths based on a single format.  It would be more useful and less confusing if we were to say that 18mm was 90 degrees (horizontal on a 3:2 aspect ratio) on an FX or 135 film format, but it's 67 degrees on a DX format.  Most of us can visualize 90 degrees, or even 67 degrees; few of us can visualize 18mm regardless of what format it's used on.
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Basically all I wanted to know is ... "will more stuff fit into the picture with a 14mm (non DX) lens than with an 18mm DX lens, on a DX camera?"

Simple yes or no ... I'm assuming "yes" based on the feedback above.

[Tony Beach]

Basically all I wanted to know is ... "will more stuff fit into the picture with a 14mm (non DX) lens than with an 18mm DX lens, on a DX camera?"

Simple yes or no ... I'm assuming "yes" based on the feedback above.
[a href=\"index.php?act=findpost&pid=190069\"][{POST_SNAPBACK}][/a]

Short answer is yes.  Ironically, getting to that answer causes a great deal of confusion because of references to "equivalent" focal lengths; and you asked in your OP "Is 18mm DX actually 18mm on the DX camera?" which clearly indicates you were confused about what 18mm is on DX lens.  The reason lenses are designated DX or EF-S isn't because they are using "equivalent" focal lengths, it's because the image circle they produce isn't designed to cover a larger format.

[francofit]

Basically all I wanted to know is ... "will more stuff fit into the picture with a 14mm (non DX) lens than with an 18mm DX lens, on a DX camera?"

Simple yes or no ... I'm assuming "yes" based on the feedback above.
[a href=\"index.php?act=findpost&pid=190069\"][{POST_SNAPBACK}][/a]

Others have already answered in some way, but it seems that the OP is still confused and/or in search of an answer...

Hoping to not add confusion, let a beginner-dilettante (myself) try to be of help:

The answer to your question is YES, but not because the 14 mm is non DX and the 18mm is DX.
The answer is yes "the 14mm does fit more stuff than the 18mm one" because a shorter Focal Length lens has a wider angle of view than a longer one.

Explanation:

a- "more stuff fitting into the picture" (angle of view) does NOT depend on the DX or not DX type of the lens mounted on the same camera

b- on the same camera, a 14mm lens does always "fit more stuff into the picture" than a 18mm one, independently of the DX or FX type of the lens.
The angle of view of a 14mm lens is wider than that of a 18mm one

c- the angle of view of a (e.g.) whatever 14mm lens on a DX camera is equivalent to  that of a 21mm(14*1.5) mounted on a FX camera

Added for hopefully   further clarification:

If you buy for your DX camera (1.5 "crop factor") a given lens and you want to know the FX (35mm) Focal Length equivalent angle of view, you have to multiply by 1.5 the focal length of the lens you are considering, being it a special one for DX or not.  So, on a DX camera you have always to multiply the Focal Length by the "crop Factor" 1.5.
You have to judge the opportunity to buy a DX lens v/s a non DX lens on other factors than the Angle of view (on the same camera, same Focal Length = same Angle of View).

Hope to not have written anything wrong or confusing.

Cheers

[Panopeeper]

a- "more stuff fitting into the picture" (angle of view) does NOT depend on the DX or not DX type of the lens mounted on the same camera

It DOES depend on the lens. I posted this before: the angle of view of a lens does not depend alone on the focal length but on the image diameter as well. The DX lens projects a smaller image than the "full frame lens", therefor the angle of view is smaller. If you mount a DX lens on a FF camera (if the mirror does not hit the back of the lens), then the projected image does not cover the entire sensor; accordingly, the view is smaller than with an FF lens of the same focal length.

b- on the same camera, a 14mm lens does always "fit more stuff into the picture" than a 18mm one, independently of the DX or FX type of the lens.
The angle of view of a 14mm lens is wider than that of a 18mm one

Not so. A FF 18mm lens on a 1.5x cropping camera projects a larger image (with a larger FoV) than a 27mm DX lens; however, the camera does not capture the "excess image".

Consequently the view with an FF 18mm lens on a cropping camera is the same as the view with a DX 27mm lens.

[duraace]

Thanks for confirming my assumptions. In buying the 14mm I wanted not only the wider angle of view, but also the other qualities that this particular lens has to offer. The DX signifies for me an unacceptable compromise when moved to a full frame camera, as I'd like my lenses to be forward compatible without compomise.