Fov

was_a_guru

Senior Member
I posted this question on a different Photography site and got some conflicting answers. So I’ll ask it here. Suppose with my D7500 mounted on a tripod and focused on a busy landscape scene, I take a picture using my Nikon 70-300 (DX) lens at a focal length of 300mm.

I then replace that lens with a Nikon (FX) lens (keep it pointed in the same direction) and take a shot.

Will the FOV (field of view) of the two shots be the same, different, and if the latter by what angle?

interested in your opinions. Thanks
 

480sparky

Senior Member
FWIW, any 300mm lens with an image circle large enough to cover a DX sensor would produce the same FOV. Even one of these (if you could mount it to the D7500 somehow):

182258953_nikon-nikkor-w-300mm-f5-6-large-format-lens.jpg
 

mikew_RIP

Senior Member
As said the actual FL would be the same but the DX sensor crops a smaller image out,this can make you think the efective FL is longer on DX than FX.
The apparent change in FOV is nothing to do with the lens in you quoted set up its the crop factor of the sensor.
One reason for FX and DX lenses is an DX lens normaly will not give full coverage on an FX sensor so they are easier and cheaper to make.
 

hark

Administrator
Staff member
Super Mod
Contributor
A 300mm lens is 300mm no matter what body it's on. So 2 different 300mm lenses on the same body will produce the same FoV.

My guess is some of the people who responded might have been incorrectly comparing the FoV of a 300mm lens on a DX body vs. an FX body. THEN the FoV would be different due to the different size of the sensors.
 

480sparky

Senior Member
And this is why I wish the 'crop factor conversion' idea would 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 film camera. 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. So the manufacturers 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 Hall of Useless Technology, next to ice picks, buggy whips and 8-track tapes.
 

was_a_guru

Senior Member
Thanks to all who responded. The answer, "same", is what I had anticipated. And based on that I believe that that FX lens on a FF sensor camera would give the same FOV but at 450mm fl. I now understand why some people have been telling me my 18-400 Tamron DX is really a 27-600. But I agree with 480sparky in his/her later comment that all this conversion factor nomenclature is confusing and a waste of time. What matters (to me) is not specific numbers but rather how well my equipment performs and how good (hopefully) my work is.
 

Dawg Pics

Senior Member
Me too. I found that so confusing and pretty useless. I couldn't understand why I should care how my crop sensor compared to a 35mm film camera. I needed to know file size and image size. I can look through the viewfinder and see what the FOV is.
 
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