Originally posted by HavelockV Why would anyone say using the FF camera he get's "more DoF control" using any of the lenses?
That is one of the biggest lies or misconceptions I hear about why people want you to buy a full-frame or why they bought a full-fame camera.
DOF does NOT change! They don't get more control! And a lens being made for FF or crop does not affect DOF nor its control.
OK, there are some differences of refraction due to pixel size, etc causing changes in circles of confusion, etc.... but I don't know if I would consider that changing DOF and I don't see it making that big of a difference in the end.
To make things worse, professionals meaning well, try to simplify explanation of Crop v.s. Full frame by saying "a 50mm lens on a crop sensor is *equivalent* to a 75mm on a full frame". First, the "angle of view" is equivalent*. Unless they get into how DOF is affected as a result, the lenses are NOT EQUIVALENT! I just saw this yesterday from several prominent professionals. It irritates me to no end.
DOF is a result of three physical properties; focal length, aperture and distance to subject. These are basic *physical* properties that cannot be changed without changing how the Universe is built and operates. (doing so would be *bad*
)
Basically, the crop sensor does just what it says... it crops in on the circle of light that is created on the sensor plane by the lens.
As a result, the DOF area covers a larger area of the entire resulting image on a crop sense.
Take a full frame camera and aim it at a picket fence running along a road.
Focus on a spot 10 feet away. Lets say at a given focal length and aperture, from where you're standing there ate three out of 20 posts in focus.
You stand in the same location and focus to the same spot with the same focal length and aperture... what will you see?
You'll see the *SAME* three posts in focus! BUT, you will maybe only see 13 posts in total.
Did DOF change? No!
Does the DOF area on the crop sensor take up a larger portion of the screen? Yes.
That is what confuses people. They simply do not understand what is going on.
What is interesting is people also say you can never create the same DOF effect on a crop sensor camera as you can on the Full frame.
May use terms like "you get better control" with Full Frame. BS!
Well that may or may not be true depending on the settings and capabilities of your equipment. Often any limitation is a one sided limitation. Fiip over and it becomes a open window that the other cannot get through. i.e you can make arguments for FF or for crop.
Remember three things affect DOF; distance to subject, aperture and focal length.
- You cannot move, distance to subject dictates perspective, and any change in your location completely changes the resulting image.
- The easiest method to change DOF is to change focal aperture. But as in the example above, you don't get the same image. (left with 12 posts instead of the desired 20)
- The next easiest is focal length. Lets say you are able to zoom out to see the 20 posts but now your DOF changes.
So mix them.
- Decrease your focal length by 1.5x (75mm full frame changes to 50mm crop frame)
- Decrease your aperture by a full stop. (F8 on full frame changes to f5.6 on crop sensor)
You should now have the equivalent image on your crop sensor as was seen on the full frame.
The only problem comes in when you cannot decrease your aperture or change your focal length to compensate.
On the flip side, if your crop sensor is at the long end of the range and you twang to make equivalent photo on FF, they may be limited by not being able to reach another stop higher, or get to a wider focal length to meet the crop'd body's capabilities.
Long story short, the 1.5 change in focal length is only *equivalent* if you also drop your aperture by a stop.
It is really not so difficult, but is is important.