DX vs FX focal lengths?

[darkblue-x]

Getting back to the OP's question:

Which brings me to my question, an FX lens, the 24-120mm...what length would that be exactly in DX terms. How do you calculate these?

As has already been explained, the actual focal length of any lens does not change by mounting it on a different body. Call it the equivalent field of view, and you'll have a better grasp of the concept.

In Nikon, the ratio of sensor sizes is 1:1.5, so you simply multiply the actual focal length of your FX lens by 1.5 and you get the equivalent of that lens when mounting it on a DX camera.

Therefore; the 24-120mm FX lens would appear to be a 36-180mm when mounted on a DX camera.

Would an Fx 35mm prime be the same or are they the same whether on dx or fx

Are you ever going to use an FX body?

I plan to upgrade to perhaps a D750, but that wont be for at least a year or two.

so I'd suggest to stop buying DX only lenses now. If you want 50mm on you current body, just know that it will seem a lot shorter when you bolt it on your D750. But you want to try to have an arsenal of lenses that are compatible.

I'm thinking of buying a Tamron 35mm F/1.8 VC as a portrait/creatives lens (this over the sigma art bc of the weight and size difference, VC, weather proofing and light macro ability.
Would this be the same focal length as my current Nikon DX 35mm f/1.8g looks through my D7100? Tbh I still don't get it.

As far as walkaround lens I have found my Nikon DX 16-85mm f/3.5-5.6g VC lens to be a great focal length range...a lot of the FX lenses seem to start at 24mm...kind of a bummer.

 

[Designer]

I'm thinking of buying a Tamron 35mm F/1.8 VC as a portrait/creatives lens (this over the sigma art bc of the weight and size difference, VC, weather proofing and light macro ability.
Would this be the same focal length as my current Nikon DX 35mm f/1.8g looks through my D7100? Tbh I still don't get it.

As far as walkaround lens I have found my Nikon DX 16-85mm f/3.5-5.6g VC lens to be a great focal length range...a lot of the FX lenses seem to start at 24mm...kind of a bummer.

Yes, the respective fields of view from those two 35mm lenses (of different makes even) will look very much alike.

Why are you disconcerted about the FX lenses starting around 24mm? Is there something else that you're going for?

 

[Ysarex]

Would this be the same focal length as my current Nikon DX 35mm f/1.8g looks through my D7100? Tbh I still don't get it.

A 35mm is a 35mm is a 35mm -- all 35mm lenses are 35mm lenses. Moving the lens between cameras doesn't change the lens. Here's what happens:

The whole image above is a 35mm lens on a FX camera. Don't move at all. Use the same lens but switch camera bodies to a DX camera and you'll get the photo inside the red lines. That's because by using the DX body you switched to a smaller sensor and so you're now recording less. Perspective is the same because you didn't move. The smaller sensor is cropping what you can record relative to the larger sensor. The lens is still a 35mm lens.

As far as walkaround lens I have found my Nikon DX 16-85mm f/3.5-5.6g VC lens to be a great focal length range...a lot of the FX lenses seem to start at 24mm...kind of a bummer.

A 24mm lens on an FX camera has the same field of view as a 16mm lens on a DX camera. That means if you take a photo with a 24mm lens on an FX camera and then don't move -- just pick up a DX camera with a 16mm lens and take the photo again you'll get the same content/framing in both photos -- basically taking the same photo but with a slight difference in DOF.

Joe

 

[Frank F.]

Field
Of
View

is important. My 1.4/58G is a decent portrait lens on my D500.

For the same effect I take my D850 with a 1.8/85G attached.

That is the real world apart from theoretical rants.

 

[WayneF]

I dont get it.
I have a DX lens for instance that is Nikkor 16-85mm and they say that the 16mm end is a 24mm equivalent on FX, I believe.
Which brings me to my question, an FX lens, the 24-120mm...what length would that be exactly in DX terms. How do you calculate these?

A lens does not change focal length by putting a different size sensor on it. If it is 24-120mm, it is always 24-120mm, on any body. All that changes is a smaller sensor "crops" the larger full size image that a larger sensor would see. With the same lens, smaller sensors see a smaller field of view. What we compare is the focal length of a different lens on a different sensor (specifically on a 35 mm film camera as the standard) that would give the same smaller field of view on that other camera.

The significance is that if we know what field of view that the "equivalent" 24 mm lens does on 35 mm film (and many people do have years of experience on 35 mm, even if some others have never seen a 35 mm camera), then we know what the 16 mm does on DX, which might be new to them.

That does NOT affect what the lens does on your camera with a smaller sensor. The 24-120 mm FX lens on your DX body will simply be a bit longer than the 16-85mm lens on same body, exactly as the numbers would make you expect. But due to the smaller DX field of view, the 24 mm will not offer very much wide angle on a cropped DX sensor.

It is a little tricky. 16 mm on DX has the FX Equivalent 24 mm. However, when that same 24mm is on DX, its field of view on DX now has an FX Equivalent field of view of 36mm. The lens is still the same, but we are comparing field of view of the sensor size.

See Camera Sensor Crop Factor and Equivalent Lens Focal Length. Calculate Crop Factor for more, including the calculator you might seek.

But even shooting pro, NOT ONCE did I ever need to convert the FL of one format to another. I cared not that the 80mm for my 6x45 was close to what a 50mm on my 35mm SLR would capture. Nor did I convert my 6x7s 250mm to "the equivalent of" either the 6x45 or 35mm.

But you did know to buy the different focal length lens, right? That certainly was the FL conversion for film format. Photographers (that ever used a different camera type) always knew that different size film cameras required different focal lengths to get the same expected field of view. The only difference today is that our DSLR cameras might mount and use the exact SAME physical lens, and the sensor sizes make a different field of view possible with the same lens. That adds confusion that makes it a subject of discussion.

There was a time when cameras had no electronics and no automation. This required that we learned a few basics. Or at least the film box had a Sunny 16 data sheet in it that mostly worked if outdoors in sunlight. I miss that time when most everybody knew at least a little about using the camera. However, the pictures are a lot better today, digital has made it tremendously easier.

 

[darkblue-x]

Yep. Still dont get it.
Disregarding what the sensor covers completely...I'm only talking about what I see in the viewfinder the whole fkn rectangle ,while disregarding any sensor crop lines or what have you.
At 16mm on my DX im able to go right beside something and have the viewfinder cover the whole thing for instance.
FX doesnt make lenses like that 16-85. Does the 24mm fx looks like it would for my dx in the viewfinder at that same focal length? Will the angle be as wide as that that i see on my Dx setup

 

[Overread]

The angle of view (what you see through the viewfinder and get on the sensor) of DX at 16 is equivalent to FX at 24mm.

To convert the angle of view of a DX to FX you multiply the DX focal length by 1.5
To convert the angle of view of a FX to DX you divide the FX focal length by 1.5


NOTE focal length is always the same, a DX 16mm lens and an FX 16mm lens on a DX camera body will give you exactly the same angle of view. With Nikon many of their FX camera bodies can let you use a DX lens on it by activating only a portion of the central area of the sensor, as a result you'd get the DX lens performing as if it were on a DX camera body

FX = fullframe or 35mm
DX = crop sensor (cropped in terms of comparing it to 35mm)

 

[Designer]

FX doesnt make lenses like that 16-85. Does the 24mm fx looks like it would for my dx in the viewfinder at that same focal length? Will the angle be as wide as that that i see on my Dx setup

You can get fairly close with the 24-70.

No.

Wider.

 

[astroNikon]

Yep. Still dont get it.
Disregarding what the sensor covers completely...I'm only talking about what I see in the viewfinder the whole fkn rectangle ,while disregarding any sensor crop lines or what have you.
At 16mm on my DX im able to go right beside something and have the viewfinder cover the whole thing for instance.
FX doesnt make lenses like that 16-85. Does the 24mm fx looks like it would for my dx in the viewfinder at that same focal length? Will the angle be as wide as that that i see on my Dx setup

Your viewfinder may not show 100% of what your sensor sees. It may only show 95%. So composition of a subject has to take that into consideration if no post processing.

The MIRROR's size is based on the sensor size. Thus the VIEWFINDER will only show you what the Mirror reflects. Technically you could have a mirror 3x the size of the sensor and the viewfinder would show you a gigantic area of which most won't be captured.

Generally, The lower end camera the darker and less of the actual subject size is shown - it's not by much but it's still there.
viewfinder info ==> APS-C field of view

But that mirror size, based on the Sensor size - the sensor defines the FOV which may change what a lens "sees".

If you have a lens that is a 24-70 that lens is designed as a 24mm-70mm.
On a Full Frame Camera which is considered 1x (as it's the base) makes that lens FOV as a 24-70.
On an APS-C camera which is considered 1.5x makes that lens FOV as a 36-105.

To compensate on a APS-C camera you need a 16mm lens to get the (16x1.5) FF 24mm equivalent on a FF sensor.
==> DX Lens Focal Lengths

 

[darkblue-x]

Yep. Still dont get it.
Disregarding what the sensor covers completely...I'm only talking about what I see in the viewfinder the whole fkn rectangle ,while disregarding any sensor crop lines or what have you.
At 16mm on my DX im able to go right beside something and have the viewfinder cover the whole thing for instance.
FX doesnt make lenses like that 16-85. Does the 24mm fx looks like it would for my dx in the viewfinder at that same focal length? Will the angle be as wide as that that i see on my Dx setup

Your viewfinder may not show 100% of what your sensor sees. It may only show 95%. So composition of a subject has to take that into consideration if no post processing.

The MIRROR's size is based on the sensor size. Thus the VIEWFINDER will only show you what the Mirror reflects. Technically you could have a mirror 3x the size of the sensor and the viewfinder would show you a gigantic area of which most won't be captured.

Generally, The lower end camera the darker and less of the actual subject size is shown - it's not by much but it's still there.
viewfinder info ==> APS-C field of view

But that mirror size, based on the Sensor size - the sensor defines the FOV which may change what a lens "sees".

If you have a lens that is a 24-70 that lens is designed as a 24mm-70mm.
On a Full Frame Camera which is considered 1x (as it's the base) makes that lens FOV as a 24-70.
On an APS-C camera which is considered 1.5x makes that lens FOV as a 36-105.

To compensate on a APS-C camera you need a 16mm lens to get the (16x1.5) FF 24mm equivalent on a FF sensor.
==> DX Lens Focal Lengths

So then 24mm FX is the same FOV as 16mm on DX?

 

[Tomasko]

Yes. It's really just the most basic multiplication/division...

 

[darkblue-x]

Yes. It's really just the most basic multiplication/division...

soooooo then the FOV that an FX lens 24-70 gives off is similar to a standard zoom FOV on a DX of 16-45 or 50?

 

[Tomasko]

70 / 1.5 = roughly 46,67

 

[Ysarex]

Yes. It's really just the most basic multiplication/division...

soooooo then the FOV that an FX lens 24-70 gives off is similar to a standard zoom FOV on a DX of 16-45 or 50?

Yes.

 

[darkblue-x]

70 / 1.5 = roughly 46,67

Okay finally. I made that calculation weeks ago, everything else ITT served to confuse me further.

that's an okay focal length on the lower end, lacking a bit on the longer end though...
I saw that nikon makes a 24-120 lens though.. should I move on to FX maybe I should get that.
third party lenses are the same thing arent they?
and what if its a PRIME FX lens like 35mm? are they the same between DX and FX? Id imagine they make the DX lenses to make the FX equivalent in DX format and same with FX.
I may just be best going to the Camera store, I am a visual learner it may be easier having someone show me with the cameras and lenses physically for it to fully compute.