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PostPosted: Fri Jul 22, 2011 5:10 pm 
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Do you still have to add crop factors if you mount a DX lens on a DX camera body. Because nothing would be cropped right?

But some people say you still have to add crop factor. But I dont see how because nothing is cropped. Can somebody explain it?

I show an image below that explains it a bit. I still dont understand about the crop factor, becuase that will happens only if you use a FX lens on a DX body, or am I missing something.
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PostPosted: Fri Jul 22, 2011 6:03 pm 
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Hi nikonfreak,

You are right in that the focal length of a lens is the same whatever sensor it's in front of. Cropping can occur either because the sensor is small or because only a portion of a larger sensor is used - if a crop is made then that reduces the field of view and it's the equivalence between fields of view that is really being compared when we talk about equivalent focal lengths. The other gotcha is that if a lens is designed for use with a cropped sensor then it's unlikely to produce acceptable results much outside such a cropped sensor.

Bob.

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PostPosted: Fri Jul 22, 2011 7:56 pm 
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I don't understand your answer. You are talking about DX lens on FX-cameras? sensors, yes of course that wont work.

But my question is did they redesign the DX lenses so 35mm lenses are not cropped and it will be truely the full 35mm FOV. Or did they take a FX lens and did they cut of the outerpart of the lens that normally does not fall on the sensor, so its a waste of glass. So even though the extra glass is not there it is still a crop and it still has a 52mm FOV.


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PostPosted: Fri Jul 22, 2011 9:49 pm 
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nikonfreak wrote:
I don't understand your answer. You are talking about DX lens on FX-cameras? sensors, yes of course that wont work...

Check out the third paragraph of Gordon's D700 review:
    Unlike Canon’s full-frame models you can still use lenses designed for cropped bodies on the D700. Fit a DX lens and you can either shoot in a cropped 5.1 Megapixel mode, or with the full sensor area and resolution – albeit with a reduction in quality beyond the DX frame.
Bob.

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PostPosted: Sat Jul 23, 2011 1:32 pm 
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I guess there are hundreds of thousands of photographers out there who are confused about crop factors. A DX lens is designed for DX bodies, which means its image circle (the circle of light it projects onto the sensor) has a smaller diameter than the one of an FX lens. This allows Nikon and other lens manufacturers to design smaller and lighter lenses.

Does the focal length of a DX lens change or not?
Unless you zoom a lens its focal length never changes. A 50 mm lens is a 50 mm lens on every camera you use it on. The crop factor was an aid for the millions of 35 mm film users to act as a "would-be" multiplier. They were used to a 35 mm being a moderate wide-angle lens. On a DX body the lens roughly offered the field of view of a 50 mm. So they learned that their camera had a "1.5x teleconverter" built-in.
A smaller sensor/film is not a teleconverter though. A teleconverter alters the focal length of your lens, but a smaller/larger sensor only affects the field of view.
The AF-S 35mm/1.8G DX NIKKOR lens for example is a 35mm lens on an FX camera as well as on a DX camera. DX just means it has a smaller image circle and that's it.


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PostPosted: Sat Jul 23, 2011 3:00 pm 
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I just have a very simple question which is apparently to difficult to answer.

Does a DX lens on a DX body still have a crop factor yes or no? And if it does why? Only reason I can think of: they take a FX lens, cut of the excess glass (The FX image circle) put whatever is left of the glass in some plastic tube and call it a DX lens.

I know a 35mm lens is a 35mm lens. It says so on the lens it self it not very complicated. But some people (including famous reviewers) say that 35mm becomes a 52mm lens which is not true of course. It just has 52mm Field of View not 52mm focal length.

But what I dont understand does a 35mm DX lens have 35mm FOV or 52mm FOV.


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PostPosted: Sat Jul 23, 2011 4:19 pm 
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All lenses have a crop factor if they are put in front of a sensor which is smaller than 35mm film/full frame; whether they are designed for DX or FX does not matter. A DX lens is designed for the smaller image circle of a DX sensor.

We talk about crop factor because we compare to 35mm film/full frame. You only really need to consider the crop factor to compare with camera systems with other sensor sizes

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PostPosted: Sat Jul 23, 2011 4:25 pm 
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Does a 35mm DX lens have 35mm FOV or 52mm FOV?
As I wrote – DX means the lens has a smaller image circle just as FX lenses have a smaller image circle than medium format lenses. Therefore a 35 mm DX lens has a 52 mm equivalent field of view– relative to full frame, of course.

Every FX lens can be used on any digital Nikon F-mount camera.
Every DX lens can be used on any digital Nikon F-mount camera (in cropped mode on FX cameras, which is 5.1 megapixels on a D700 for example).

Personally I think mentioning the crop factor to photographers who start out with DX is the worst thing to do. They just get confused and why would they care about the wider field of view on a different camera?


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PostPosted: Sat Jul 23, 2011 4:47 pm 
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No no no. As I tried to indicate in my original answer lenses don't have crop factors: only sensors have crop factors. A lens might be optimised for a smaller image circle to save costs. There are mechanical constraints as well with Canon's DX equivalent lenses (the EF-S lenses) as they can have rear elements closer to the sensor - if Canon hadn't taken steps to prevent EF-S lenses being fitted to a full-frame body the mirror could end up hitting the rear of the lens.

But I digress as this is a Nikon thread. Repeat after me: lenses don't have crop factors, sensors do. :lol: :lol: :lol:

Bob.

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PostPosted: Sat Jul 23, 2011 8:40 pm 
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Of course, I miswrote :oops: Sensors have crop factors, not the lenses
Bob, please forgive me!

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PostPosted: Sat Jul 23, 2011 9:17 pm 
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It is a minefield, isn't it! :)

P.S. Not really a topic for the forum but it would be remiss of me not to express the hope that your friends and family are safe after the tragic events.

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PostPosted: Sat Jul 23, 2011 10:24 pm 
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My friends and family are all safe. Thanks, Bob

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 Post subject: DX lens on FX body
PostPosted: Fri Jan 27, 2012 1:15 pm 
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You can set a D700 to DX mode Bob , I have not tried it cause I don't have
a Nikon DX lens . I was thinking of buying one 18-200 but one of the moderators says there is a FX 18-200 MM one ( I can't find it )
IS THERE ?

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PostPosted: Fri Jan 27, 2012 5:46 pm 
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Nope there isn't, see my comment over there, Drecked.

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PostPosted: Sat Jan 28, 2012 7:08 am 
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A DX lens does not get its image cropped BUT you must apply the crop factor when calculating the effective focal length. That means that an 18mm DX lens is effectively a 27mm lens if you want to estimate focal length. This is because focal lengths are given in 35mm equivalent terms, this means that an 18mm DX lens will have the same field of view as an 18mm FX lens on the DX sensor.

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