question about dx lenses

[chad79]

Hi there just got afew question about nikon dx and d series lenses.
Are dx lenses designed for crop sensor dslr such as d300?
So if i get a 20mm dx lens will it be 20mm or will it be something else on a d300.
D series lenses, are they designed for full frame dslr or cropped?
I know when i put on a d series lens on my d300 it is not what it is.

[kiwi]

DX lenses are designed specifically for DX cameras. They will still work on a FX camera but will typically exhibit vignetting.

Focal length of a lens is the same on any camera, a 20mm on a DX D300 is still 20mm on a FX D3. The crop factor is applicable to the sensor or camera not the lens and is effectively a crop of a FX sensor if that makes sense.

"D" lenses such as the 50 1.4 AF-D work on either FX or DX

[ricktas]

This page on the D3 on DPReview shows the difference in a DX lens to a D lens. Have a look down the page till you find the photo of the cat. It shows you the same image, but what you will capture using the various lens versions. : http://www.dpreview.com/reviews/NikonD3/page4.asp

So a cropped sensor camera doesnt give you a different zoom length, it gives you a smaller image circle, thus the final result is a photo that only captures the centre part of what a full frame lens and camera would capture at the same zoom length.

The actual photo is not 'zoomed' in more, rather the captured area is cropped, giving the effect that it was taken closer.

[MarkW]

Rick
This even screws with my head occassionly - if a 50mm DX lens is fitted to my D200 and a 50mm D lens is fitted to a D700 will they both give same image. I suspect the answer is no but in this issue maybe the way that manufacturers designate their lenses ie 50mm, 85mm, etc just doesnt help the end user. A better way might be to use the view angle ie 28 Deg, 23 Deg and so on.

[ricktas]

No they will not give the same image. BUT!

take your 50mm lens. It is a piece of hardware, just cause you put it on a cropped sensor body doesn't miraculously make it a different length lens. Its just a bit of glass, plastic and metal, no magical properties involved at all.

If you look at the one thing that is different between a full-frame camera and a cropped sensor camera, it is just that, the sensor. A cropped sensor captured a smaller part of the image that is sent at it through the lens, than a full frame camera can. Which is how the link in my above post shows it.

So your 50mm lens is still a 50mm lens, but the sensor is only capturing a central part of the image (cropped - hence the name).

Your capture from a cropped sensor doesnt make the subject look any closer, it just chops off all the side bits that a full frame camera can grab, and gives the illusion that it is was taken closer (or with a longer lens).

You could take the same photo with a cropped camera and a full frame camera. Then in photoshop, crop the full frame image to reflect the area a cropped sensor would capture and you would end up with two photos that basically looked the same. No magical change to the 50mm lens involved at all.

[arthurking83]

....
So if i get a 20mm dx lens will it be 20mm or will it be something else on a d300.
D series lenses, are they designed for full frame dslr or cropped?
I know when i put on a d series lens on my d300 it is not what it is.

the magnification of the 20mm lens is always 20mm, but you get the impression that it's a 35mm lens on a crop sensor, and that's only because the photo sensitive area of the camera is only seeing an equivalent image circle that you'd get if you were using a fullframe camera.
it looks more magnified to you if you concentrate on single subject matter.
That's why nature photographer on the whole prefer cropped sensors because they usually only want to capture the subject and blur out the periphery.

But if you're capturing a deeper DOF such as in a landscape, the distance between a closely spaced subject and the elements placed further back gets distorted(lets call that perspective distortion)

two kinds of perspective distortion we want to focus on(punintended) is extension(using an ultra wide lens) and compression(using a telephoto)

Somewhere between 35mm and about 75mm you start to see exaggerated effects of extension and compression distortion. That's what focal length(magnification) does.

So!

Lets say for arguments sake you prefer a 50mm lens for portraits, but that's on full frame cameras. So you only have a crop camera, and then you do the math and you figure out that you really need to get a 35mm lens(as that's usually the next best focal length you can get in prime lenses...

So you will see a similar field of view using both lenses on their respective formats, but you will see slightly more extension distortion, where the distance between the closer subject looks further away from the background.

For portraits this can be important as it gives the subject a slightly distorted look.

This is easily seen in the extremities of the focal length ranges currently covered by all available lenses.

That's why an(landscape) image taken at 10mm and then cropped to a pano format always looks different to a stitched image taken with a similar field of view but captured with a 50mm lens. The 50mm lens brings the background much closer to the foreground(and usually more definition with it) relative to how the 10mm lens seems to push the background further back.

if you have an extreme UWA lens you can see this for yourself, even without the benefit of having access to a full frame camera.

Zoom out to the widest zoom setting, hopefully 10 or 12mm and then zoom in to a closer zoom setting(multiplied by 1.5, so if at 12 then try at 18 if at 10, then try at 15)

Look how much further back the background is(distant mountains are best for that)

shoot a landscape at 200mm and you literally bring the mountains within reach, Shoot the same scene at 10mm and you really need a week to get to those same mountains, even though you only need to step back about 20meters or so to capture that same foreground subject with the 200mm compared to where you need to be with the 10mm lens.


it's usually not overly obvious as to how much difference there actually is, but the difference say between a crop camera and a view camera of 10x8 format size is enormous. Even a medium format camera is a fair amount of difference in the level of magnification relative to a crop camera, where a standard lens is 90mm, and it's not uncommon to use a 150mm lens to capture a landscape shot, that would give an equivalent FOV of approx 50mm on a crop camera. At 150mm you are starting to see a heck of a lot more compression distortion, where the background comes a lot closer to you than a simple few steps closer would yield.

alternatively if you have a compact P&S:
zoom out to it's widest setting. Usually that's about 4-6mm, which is equivalent to 28mm on FF. now using your DX camera set it to 18mm, roughly the same FOV of 28mm on a FF camera.
Does the far distance look further away from the near distance on the P&S compared to the DX camera?
Just remember that the more extreme the focal lengths, the perspective distortion becomes more pronounced by the respective cameras.

Hope that all makes sense.

[arthurking83]

THIS wiki info (http://en.wikipedia.org/wiki/Perspective_distortion_(photography)) on perspective distortion highlights how it all changes the difference between foreground and background distances.

To Mark: at 50mm of magnification, regardless of format, the difference between foreground and background distances will always look the same.

Whilst Rick said that there is an illusion that the image appears magnified, the illusion is real, just ask Tony(Tannin) as he;s already posted a fair bit on the subject too.
But the point of pixel densities hasn't been taken into consideration yet, so for an equivalent pixel density crop vs full frame camera(say the D300 vs the D3x) in Nikon terms the pixel density is close enough to being the same.
So if you were to crop a D3X(you can shoot in DX crop mode and you lose nothing!) to give the same FOV as the D300 the images would look more or less identical.. but compared to the 50D's 15Mp the Canon would look more magnified as it has a higher pixel density.
That's where the confusion lies in crop sensors vs FF sensors, as there was always a disparity between pixel densities of each format, but as FF sensors start to reach into the 40-50Mp count, and thus higher pixel densities they will start to look more attractive than APS-C sensors.

Nikon have been comparing the D3x to medium format cameras in their marketing BS, so they seem to have their sights set on trying to lure away at least some prospective MF devotees into their system. They have the lenses for it, and they've shown with the D3x that even with high pixel densities that high ISO quality can still look good, but at lower ISO's the images are totally noise free anyhow, so why not invest in a cheaper more compact 50Mp(or more) DSLR rather than a heavy cumbersome MF system?

Same arguments will be ensuing over the reason to stick with MF over 35mm format as there is/was with the APS-C vs FF domain.

But in that wiki explanation of perspective distortion, the difference between 50mm and 28mm is clearly seen, where a 28mm lens on a DX body will give a similar FOV(save for a few mm) as would a 50mm lens on FF.