Aperture depth of field question

[sbr]

Hi,
Assuming you have comparable quality lenses. Would you get the same depth of field at say f5.6 with a 50mm prime lens as you would with a 18-140mm set at the same f5.6 and at same 50mm? Basically I am asking do you get the same depth of field with a zoom vs a prime if the aperture and mm's are the same?

 

[480sparky]

They would be identical. Prime or zoom, focal length is focal length.

 

[sbr]

Thanks

 

[Overread]

A few things to note that may cause confusion if you're comparing lenses:

1) As said focal length is focal length, a cheap 50mm, a high end L 50mm and a zoom set to 50mm will all still be 50mm. This the depth of field (assuming you use the same aperture on them all) will be identical.
What will change is contrast, clarity, sharpness, colour saturation, and the nature of the blur (some lenses give a more "creamy" blur and others harsher) also if you have highlights in the background the shape of the light "rings" will vary depending on the shape of the aperture blades inside the lens (this is why sometimes they appear as rings, sometimes ovals and others as hexagons or similar multi-sided shapes).

2) Many lenses (not all) have some degree of focal length adjustment through their focusing range. This means that when you're focusing at the closest focusing distance the lens might have a shorter focal length than stated. (this is true for primes and zooms, however the degree to which there is, if any, change will vary lens to lens - there is no general rule nor pattern). You can often read of this in lens reviews if its a very significant focal length change.

3) When using lower end zoom lenses the maximum aperture (smallest f number) can vary through the focal range. This change is reported to the user through the camera.


If you want there are depth of field calculators online and even aps on phones that you can use. These will give you; for a given series of properties that you enter, the actual depth of field. They'll also give you some other handy information. They can be a valuable resource if you need to know what kind of depth of field you'll be working with for a given set of settings.