Noob to the site and photography

Whiskeyman

Whiskeyman

Senior Member
zhead86 said:
Ok, so I did say I am a NooB... And I also just figured this out. At 18mm I have f/3.5 varying to f/5.6 at 55mm..... Never thought I could embarrass myself on the internet but... go figure
upset.png
Click to expand...

I'm sure you're not the first person to be confused over this. You are in the smaller group that could figure it out on your own.

Try going on vacation and being unable to even get your camera to turn on, and when taking it to a store for service, having the repairman come out to the counter and ask if you have the batteries with you. And no, it wasn't me, but a friend. Whenever I see him, I still ask if he's got batteries in his camera.:)

Welcome to nikonites.com.

​WM
 
J

jwstl

Senior Member
Mycenius said:
Always assumed DX lens focal length was actual
Click to expand...

They are actual. Focal length is a measurement of distance from focal point to the film/sensor and that distance doesn't change on any camera, DX or FX.


So there are 2 good reasons not to include the DX equivalent focal length on DX lenses:

1. Because it's wrong. A 24mm lens is 24mm to the sensor on both DX and FX. It just happens to have the field of view of a longer lens on DX because the sensor is smaller. This is why all lenses, DX and FX, have that "crop factor" on DX.

2. Let's say they included the DX focal length equivalent on lenses. What do you do if you decide to switch to a different size DX sensor and the crop factor changes? You would need to change your manufacturing of DX lenses to include the new numbers and the numbers on the existing DX lenses would be inaccurate for the new cameras.

So they did the right thing and kept the actual focal length.






Sent from my iPad using Tapatalk HD
 
W

WayneF

Senior Member
zhead86 said:
If it's made for cropped frame cameras why would it get that effect on the focal length? Doesn't make sense.... I mean, I understand why the cropped frame does it to "normal" lenses but if it's made for cropped frame you'd think they would adjust it
Click to expand...


The lens is always the marked focal length. The lens does not change regardless what FX or DX camera body you put it on.

All that does change is the DX sensor is smaller, therefore it only sees a smaller central part of the area that the lens does project. IOW, the DX image is simply cropped smaller. This smaller sensor does not see a view as wide as if it were not cropped. So the angle of view does change (smaller), and so it then looks as if we stood in the same place, but used a lens focal length 1.5x longer on FX (which would also crop so to speak, zoomed in longer to a smaller view). This 1.5x DX Equivalent Focal Length is just the number of what the smaller view "looks like", if it were compared to FX.

But the lens is definitely still as marked, which never changes. The same lens always does the same thing, regardless. All that changed was the cropped smaller view, and the resulting smaller angle of view on the smaller DX sensor.

See FX - DX Lens Crop Factor for more
 
Last edited:
Top