FX - DX confusion

[tonye]

Hi to everyone, I'm slightly confused here. I presently have a D600 FX and a D5200 DX and all sorts of lenses, some afs DX and others that are FX. The misunderstanding by myself is a DX lens says 70-300, has the crop already been calculated or is it really a 105-450 lens on my D5200 DX. I get that a 100 FX on my D600 is 100 and can be used on my D5200 DX and equates to 150 but is a DX lens already worked out for the crop on a DX camera. Thanks in advance, Tony.

 

[BF Hammer]

Focal length is an absolute value and is not adjusted for sensor size. The answer you are looking for is no.

The focal length describes the size of the image projected on the plane of the sensor or film. But the size of that sensor or film stock can range from tiny to huge. We have settled on crop factor to describe the slice of the image you will record. Full frame 35mm became the arbitrary reference size by historic popularity. In film large-format, a 100mm lens is actually close to a normal field of view.

Edit: Don't take that to mean you could use a DX lens to shoot on a Hasselblad medium format. Lens construction means the light is projected in a narrow beam. Like looking through a straw versus peering through the middle of a donut.

 

[tonye]

Thanks for the reply BF, so as i understand it a 100mm FX lens on my DX camera will produce an image as if i had used a 150mm, and a DX 100mm would also produce an equivalent of a 150mm image due to the crop factor. If this is the case why bother with DX lenses in the first place and why call it a 100mm instead of a 150mm on a DX.

 

[Burt]

Thanks for the reply BF, so as i understand it a 100mm FX lens on my DX camera will produce an image as if i had used a 150mm, and a DX 100mm would also produce an equivalent of a 150mm image due to the crop factor. If this is the case why bother with DX lenses in the first place and why call it a 100mm instead of a 150mm on a DX.

What I like about DX lenses is the size and weight... I think there is room for both... But it is definitely a steep learning curve, especially when you have two cameras that do take the two different format... BF helped me as well trying to figure out the differences between the two...
It did really help to use the 1.5 formula... DX xx multiply by 1.5=FX (approx). Same story apply in reverse... FX xx divided by 1.5= DX format

 

[BF Hammer]

Thanks for the reply BF, so as i understand it a 100mm FX lens on my DX camera will produce an image as if i had used a 150mm, and a DX 100mm would also produce an equivalent of a 150mm image due to the crop factor. If this is the case why bother with DX lenses in the first place and why call it a 100mm instead of a 150mm on a DX.

The answer is that it is 100mm for both size sensors. A DX format lens is projecting a smaller circle of light to cover a smaller sensor, but the physical size of the image is still for 100mm focal length. FX 100mm lens projects the same size image but the circle of light is larger.

Micro Four Thirds lenses also work like this, but the crop factor is 2. You buy a 100mm MFT lens, you get a photo equivalent to 200mm full frame in a more compact package.

This confused me also years ago when I would shop for lenses. But imagining the lens projecting on a wall with 2 different sized screens is how I learned to resolve that. The size of the subject is identical on the wall, but you are only seeing a limited part of the image framed on those screens. Then you can imagine an even larger screen for medium format, and a very tiny screen for a cellphone camera. But that lens is still the same focal length in each case as it never moved.

 

[Needa]

This may help. https://www.nikonusa.com/learn-and-explore/c/products-and-innovation/the-dx-and-fx-formats

 

[nikonbill]

If this is the case why bother with DX lenses in the first place and why call it a 100mm instead of a 150mm on a DX.

As pointed out the DX lens are lighter and more compact and cheaper to manufacture, FX lens are fully capable on both formats so when you have "both" bodies it is wisest to have FX lens unless you have a very particular use for a DX lens on your DX camera. Nikon allows DX lens to function on FX bodies but its not desirable to do so as you loose data you would likely want. Some may like to keep DX lens as they are a lighter product and only use them on their DX bodies. As most things in photography, there is no right or wrong way.

Some editing software does list the "35mm equivalent" focal length (could help maybe in understanding).

BF hammer did a great job explaining why they call the lengths what they do Needa and Burt gave good perspectives also.

It comes down to history I think in some cases. Sometimes in our efforts avoid confusion we can create some.

 

[tonye]

Thanks to everyone especially Needa with the link info, i get confused easily at my age. FX or DX as long as it looks right in the end, unless one of you folk know better

 

[hark]

When a 70-300mm DX lens is used on a DX body, your field of vision will be 1.4x greater than 70-300mm ... so the image will appear as being taken with a field of view of 98-420mm (the comparable viewing range of an FX body). That's because a DX body is a crop factor body. It's field of view is 1.4x greater than what it would be on an FX body.

IF you use the 70-300mm DX lens on an FX body, you should have a settings choice – to be able to choose between what it would look like if using it on an FX body or the DX view where the image already appears cropped by the 1.4x sensor. You will also lose pixels with this last option since the image gets cropped in camera.

Here's the problem ... when a DX lens is used on an FX body, and the camera body is set to record the image as though it was taken with an FX body, you will get a lot of vignetting around the edges of the photos (this will be the option to not have the images cropped in camera). But when setting the FX camera body to use the DX lens as a DX lens, it will automatically crop the image so no vignetting will appear. It's the potential vignetting that causes issues when using a DX body on an FX body. So most people simply have their FX bodies set to automatically adjust the images to be cropped in camera and to record the DX field of view.

Clear as mud, I'm sure. It's all due to a DX body having a field of view that is amplified by 1.4x the view of an FX body.

 

[Clovishound]

Another issue is that a lot of Nikon FX cameras will not let you use the entire sensor when a DX lens is mounted. I would like to try the Pup's 10-20 DX lens on my Z7ii or Z8 in full frame mode, but it won't let me. I know that I would get vignetting, but that might be a plus for some images. At any rate, I'd like to try.

 

[nikonbill]

Another issue is that a lot of Nikon FX cameras will not let you use the entire sensor when a DX lens is mounted. I would like to try the Pup's 10-20 DX lens on my Z7ii or Z8 in full frame mode, but it won't let me. I know that I would get vignetting, but that might be a plus for some images. At any rate, I'd like to try.

I think that's correct operation, the way I understand the D850 manual the DX lens will trigger DX mode and cannot be overridden - I only have one DX lens left I keep on the D7200

 

[Clovishound]

Yes, this is how the engineers designed the system. It will not let you override DX mode with a DX lens mounted. I think this being the default setting when a DX lens is mounted is sound design, but the user should be able to override to FX mode, and use it at your own risk.

 

[Burt]

Yes, this is how the engineers designed the system. It will not let you override DX mode with a DX lens mounted. I think this being the default setting when a DX lens is mounted is sound design, but the user should be able to override to FX mode, and use it at your own risk.

I just tried and yes, the Option Chose Image area is not available... That means Nikon only allows to use DX image area when the FX lens is used, that behaves just like a digital zoom...