Fx and Dx lens conversions

bandit993

Senior Member
I may have asked this before, so if I did, I apologize. I know when you put an Fx lens on a dx body, you multiply by 1.5. But does a Dx lens already have the crop factor figured in? An example would be my 18-55mm Dx lens. Is that a 12-37mm fx lens? I am thinking of buying a wide angle zoom. But to be wider than 18mm , would I have to buy a 10mm or less Fx lens? I hope you understand what I am getting at. Thank you .
 
I may have asked this before, so if I did, I apologize. I know when you put an Fx lens on a dx body, you multiply by 1.5. But does a Dx lens already have the crop factor figured in? An example would be my 18-55mm Dx lens. Is that a 12-37mm fx lens? I am thinking of buying a wide angle zoom. But to be wider than 18mm , would I have to buy a 10mm or less Fx lens? I hope you understand what I am getting at. Thank you .

There is no difference in the crop factor between DX and FX lenses on a DX camera. A DX lens on a FX camera will not work as a FX lens.
For example. I have a D7100 and a D750 I use my 70-300 FX lens on my D7100 it acts like a 105-450 If I use it on my D750 it is a 70-300.

DX lenses are not designed to work correctly on a FX camera.
 

RocketCowboy

Senior Member
Say what? :confused:

Then why on earth did Nikon add 'DX Mode' to all FX bodies?

I have yet to hear of a DX lens 'not working correctly' on a FX body.

By "work correctly", you could also substitute "work optimally".

Does DX Mode on a D610 still result in an image that 24mp? The image is cropped down to the area of the sensor that is covered by the DX lens, but it is a smaller image than what an FX lens would produce on the FX body.
 

alan92rttt

Senior Member
If you have a DX body any lens you put on it you multiply by 1.5. DX, FX , Tameron, Sigma, .... It does not matter. Multiply by 1.5.

If you put a DX lens on a FX body the image projected will not fill the sensor. If your FX camera has the "DX mode" option the camera will crop the image.
 

480sparky

Senior Member
........Does DX Mode on a D610 still result in an image that 24mp? The image is cropped down to the area of the sensor that is covered by the DX lens, but it is a smaller image than what an FX lens would produce on the FX body.

All this information is readily available on Nikon's website for each FX camera body, as well as in every FX body instruction book.
 
Say what? :confused:

Then why on earth did Nikon add 'DX Mode' to all FX bodies?

I have yet to hear of a DX lens 'not working correctly' on a FX body.

Not correct in the FX mode. Many people try and use them on an FX camera and are disappointed. I did try it and you get smaller files and not really as good as the same lens on my D7100
 

Danno

Senior Member
I may have asked this before, so if I did, I apologize. I know when you put an Fx lens on a dx body, you multiply by 1.5. But does a Dx lens already have the crop factor figured in? An example would be my 18-55mm Dx lens. Is that a 12-37mm fx lens? I am thinking of buying a wide angle zoom. But to be wider than 18mm , would I have to buy a 10mm or less Fx lens? I hope you understand what I am getting at. Thank you .

They do not change the numbers on a DX lens. The DX 18-55 viewable area would be approximately 27- 82mm on a DX Body.
 
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480sparky

Senior Member
Not correct in the FX mode. Many people try and use them on an FX camera and are disappointed. I did try it and you get smaller files and not really as good as the same lens on my D7100

You need to compare apples to apples. You need to compare the same lens on an FX body that will, in DX mode, give the same pixel size as you would get in a DX body. IE, an FX body in DX mode that produces, say, 16mp and a DX body that produces the same 16mp image size.

Otherwise, you'll just be spinnin' your wheels. Comparing an FX body in DX mode at 16mp to a 24 or 32 mp DX body is an exercise in futility.
 

lokatz

Senior Member
All Nikon FX bodies introduced since 2007 support DX mode. By default, they switch automatically to DX mode when a DX lens is used, meaning that only the center part of the sensor is used and you lose resolution. Your lens will have the "1.5x DX factor", though. ALL lenses for Nikon SLRs are spec'd with their 35mm-equivalent focal length, which tends to cause confusion at times.

On all or most (not sure which) FX bodies, you can override and switch to FX mode with a DX lens. That will give you full resolution, with the DX lens now effectively at 35mm focal lengths, but in most cases with substantial quality losses at the edges and corners, including blacked-out corners in some cases. I assume that's what Don referred to with "will not work correctly".
 
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hark

Administrator
Staff member
Super Mod
Contributor
No matter whether you use an 18mm FX zoom or an 18mm DX zoom, you will get the same field of view when those lenses are mounted on a DX body.

When an 18mm DX zoom is mounted on FX, and IF the FX body is set to automatically identify a DX lens, the image you see through the viewfinder should look like it normally would for an FX body (remember, there isn't any crop factor visible when viewing through an FX viewfinder). BUT the size of the file will be smaller from the FX body because part of the image you saw through the viewfinder is cropped away in camera--and the image you see afterwards will be the cropped image.

If the FX body isn't set to automatically sense there is a DX lens mounted, then you will get a full resolution file that usually has vignetting and loss of quality at the corners. Those areas that have the loss of quality and vignetting are the areas that would normally be cropped away IF the FX body was set to automatically sense a DX lens. So what you'd need to do in those circumstances is to crop the image yourself. And you still wind up with a smaller sized file.

Just remember that the field of view is different when looking through a DX body vs. FX even when the FX body is set for a DX lens. DX bodies have the 1.5 crop factor applied to the viewfinder. On an FX body, you will only see the FX field of view, not the cropped DX view no matter how the body is set.

Clear as mud, I'm sure. ;)
 

480sparky

Senior Member
No matter whether you use an 18mm FX zoom or an 18mm DX zoom, you will get the same field of view when those lenses are mounted on a DX body.

When an 18mm DX zoom is mounted on FX, and IF the FX body is set to automatically identify a DX lens, the image you see through the viewfinder should look like it normally would for an FX body (remember, there isn't any crop factor visible when viewing through an FX viewfinder). BUT the size of the file will be smaller from the FX body because part of the image you saw through the viewfinder is cropped away in camera--and the image you see afterwards will be the cropped image.

If the FX body isn't set to automatically sense there is a DX lens mounted, then you will get a full resolution file that usually has vignetting and loss of quality at the corners. Those areas that have the loss of quality and vignetting are the areas that would normally be cropped away IF the FX body was set to automatically sense a DX lens. So what you'd need to do in those circumstances is to crop the image yourself. And you still wind up with a smaller sized file.

Just remember that the field of view is different when looking through a DX body vs. FX even when the FX body is set for a DX lens. DX bodies have the 1.5 crop factor applied to the viewfinder. On an FX body, you will only see the FX field of view, not the cropped DX view no matter how the body is set.

Clear as mud, I'm sure. ;)

And this is why I wish the 'crop factor conversion' idea should disappear from the face of the earth. Erase it. Delete it. Send it to the Trash Bin. Eradicate it. As if it never existed.

What I find amazing is back in my film days, there was no such thing as a 'conversion factor' to compare lenses between 135, 120 and 4x5 formats. I never heard of a number to multiply (or divide by) when changing from 35mm to 6x4.5 format, or to 6x7 format, or to 4x5 format. I never had to 'convert' the 80mm lens of my Mamiya 645 to 'the equivelant of __mm on my 35mm camera". Nor convert the 150mm on my 4x5 to 'the equivelant of __mm on my RB67 camera".

I understand why the manufacturers created the 'conversion' factor. It was a marketing tool to help sell fledgling digital SLRs to an uneducated populace. The populace that had grown up with one format: 35mm. Everyone and their uncle owned a 35mm lens. Most carried a 50mm 'standard' lens. Many purchased 28mm wide-angles and 135mm telephotos. So that was 'the gold standard' back then.

Then along came digital. But the sensors were smaller than a 35mm frame due to manufacturing costs. So the makers needed an easy way for those transitioning to digital to 'relearn' how focal length related to FOV. "Conversion factor' seemed like the perfect choice. And it was. At least back then.

But today, we have an entire generation that has never even SEEN a 35mm film camera, let alone understand focal length, sensor/film plane size and how the two relate to FOV. So today, the 'conversion factor' has royally muddied the waters. Not to mention the internet, and it's ability to spread incorrect information that will be accepted as gospel.

And next, the assumption (and even firm belief with some) that the 'conversion factor' applies to other properties of the lens, such as aperture and minimum focus.

I say it's time to deposit 'the conversion factor' to the dustbin of history. Let it reside the the Hall of Useless Technology, next to ice picks, buggy whips and 8-track tapes.
 

Texas

Senior Member
Nikon, and All other lens makers, labels their lenses with actual focal length. A property of lenses unrelated to FX DX or 35mm equivalents.
 
And this is why I wish the 'crop factor conversion' idea should disappear from the face of the earth. Erase it. Delete it. Send it to the Trash Bin. Eradicate it. As if it never existed.

What I find amazing is back in my film days, there was no such thing as a 'conversion factor' to compare lenses between 135, 120 and 4x5 formats. I never heard of a number to multiply (or divide by) when changing from 35mm to 6x4.5 format, or to 6x7 format, or to 4x5 format. I never had to 'convert' the 80mm lens of my Mamiya 645 to 'the equivelant of __mm on my 35mm camera". Nor convert the 150mm on my 4x5 to 'the equivelant of __mm on my RB67 camera".

I understand why the manufacturers created the 'conversion' factor. It was a marketing tool to help sell fledgling digital SLRs to an uneducated populace. The populace that had grown up with one format: 35mm. Everyone and their uncle owned a 35mm lens. Most carried a 50mm 'standard' lens. Many purchased 28mm wide-angles and 135mm telephotos. So that was 'the gold standard' back then.

Then along came digital. But the sensors were smaller than a 35mm frame due to manufacturing costs. So the makers needed an easy way for those transitioning to digital to 'relearn' how focal length related to FOV. "Conversion factor' seemed like the perfect choice. And it was. At least back then.

But today, we have an entire generation that has never even SEEN a 35mm film camera, let alone understand focal length, sensor/film plane size and how the two relate to FOV. So today, the 'conversion factor' has royally muddied the waters. Not to mention the internet, and it's ability to spread incorrect information that will be accepted as gospel.

And next, the assumption (and even firm belief with some) that the 'conversion factor' applies to other properties of the lens, such as aperture and minimum focus.

I say it's time to deposit 'the conversion factor' to the dustbin of history. Let it reside the the Hall of Useless Technology, next to ice picks, buggy whips and 8-track tapes.

The problem is that back then my 35mm film lenses would not even fit on my Mamiya 645 so it was not even a question. Now we have DX and FX cameras that to the eye look no different and can interchange lenses.
 

480sparky

Senior Member
The problem is that back then my 35mm film lenses would not even fit on my Mamiya 645 so it was not even a question. Now we have DX and FX cameras that to the eye look no different and can interchange lenses.

Yet today, it shouldn't be an issue. The idea of 'conversion factors' is an concept whose time has come and gone. Long ago. It's merely a vestige of an age where it is no longer needed. It's target market no longer exists. Us old farts understand it because we made the transition. But the young-uns today are merely confused because the need to understand it has never part of their indoctrination into photography.

If you want to properly educate people today, do it right. Explain to them the difference between an FX and a DX sensor. Not some crap about "Oh, just multiply by 1.5." That's helping no one. Then, just like we did back when Kennedy what in the White House, they'd readily understand that shooting with a 645 takes a different mindset when dealing with focal lengths.

It just goes to show you how brainwashed people are becoming, bowing down to Madison Avenue and getting a degree in Sound Bites.
 

lokatz

Senior Member
... What I find amazing is back in my film days, there was no such thing as a 'conversion factor' to compare lenses between 135, 120 and 4x5 formats. I never heard of a number to multiply (or divide by) when changing from 35mm to 6x4.5 format, or to 6x7 format, or to 4x5 format. ...

You might have missed it altogether, but sorry, this statement is not correct. Many years ago, I owned one of the first (film) APS-C cameras, which is exactly the same concept we now call DX: Nikon's Pronea S. The crop factor applied there, too.

Beyond this small correction, I have to admit I'm lost in your ramble: what's so hard to understand about cropping images? If a only use a smaller area of my sensor, the resulting image will look the same as if I had used a longer lens. As someone often shooting wildlife, I crop all the time.

Since DX sensors are 1.5x (well, actually it is 1.5x in either direction, so 2.25x in area) smaller than their FX equivalents, a 1.5x longer focal length is what you get with them. Hard to grasp? I don't think so, and I certainly see more value in it than a marketing ploy. For 'wildlifers', having smaller sensors that nonetheless have high resolution is a godsend.
 
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Bukitimah

Senior Member
after reading, i am more confused than before reading. my understanding is, new FX cameras have features to accept DX lenses. of course you aren't going to enjoy the full FX sensor you paid for. That is a vwry straight forward answer for me.
 
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