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Which has shallower DoF?

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I'm not sure it really matters. More might depend on distance to subject and things like that. Besides, they are different focal lengths. The DOF of the 85 f/1.4 at f/1.4 is extemely shallow. It takes time to master. One eye can be in focus while the other isn't.

Here's a shot with my 85 f/1.4 on a crop camera (D300) to show DOF. It's the top of a chain link fence. I don't have a 70-200 f/2.8 so can't try it. I can't imagine wanting a shallower depth than this though. If you need some from full frame, I can toss some up.





--
Cheers, Craig

Equipment in Plan via Profile
 
Joel C said:
85mm f1.4 FX or 200mm f2.8 FX?

Thanks,

Joel C
Click to expand...
At what f/no?
At what distance?

There are DOF calculators everywhere. On the web. On iPhone, Android, Nokia smartphones.

Here's one. Plug then numbers in

http://www.dofmaster.com/dofjs.html

What you can't tell from the numbers and charts however, is how the perspective looks like, the bokeh - for that, even if you can calculate it, you really need to see it for yourself.

--



Ananda
http://anandasim.blogspot.com
https://sites.google.com/site/asphotokb

'There are a whole range of greys and colours - from
the photographer who shoots everything in iA / green
AUTO to the one who shoots Manual Everything. There
is no right or wrong - there are just instances of
individuality and individual choice.'
 
Joel C said:
85mm f1.4 FX or 200mm f2.8 FX?
Click to expand...
  • Strictly speaking, focal length isn't a factor in actual Depth of Field ... DoF being the front-to-back depth of the "apparently sharp" zone in an image.
  • In fact, all lenses have the same DoF if used at the same aperture and focused on the same target (at same distance). So, the 85mm and the 200mm are the same in DoF terms at all apertures they have in common ..which is f/2.8 and upwards.
  • This means the 85mm has shallower DoF at all apertures WIDER than f/2.8, which is two stop's worth (apertures f/2 & f/1.4 resp.) ...
But that isn't the end of the matter....
  • DoF scales and tables tell us nothing about the appearance of those areas NOT within the sharp zone we call Depth of Field ..... and it turns out that the degree of "apparent blur" in those UNsharp image zones is definitely NOT the same at all focal lengths.
  • Because longer lenses have a larger image scale (they "magnify more") the appearance of blur in the unsharp zones is also magnified... giving an impression of more separation between the sharp subject and the blurred background beyond....
  • .... which many people perceive as being "shallower Depth of Field"... but it is not, really! It is just more "apparent blur" in the image zones outside of Depth of Field... and that is not the same thing at all.
Unfortunately, I have not got either of the lenses myself, so I cannot tell if the longer length of the 200 magnifies the blur of the background enough to equal the extra blur that comes the 85mm having wider apertures....

...although I suspect that 200mm at 2.8 may equal the 85mm at or around f/2... and that the 85mm may pull ahead in the blurriness of background when opened up to full bore.

As I say, this is just my guess. DoF scales and tables are restricted to indicating the "apparently sharp"... they don't make any comment on how blurred is the "apparently blurred" That is somewhat outside their remit, as it were.

I hope this was clear, and possibly a bit interesting, even if it didn't tell you exactly what you wanted to know.

PS. Very concerned for the poor b*ggers in Queensland. :-(
--
Regards,
Baz

"Ahh... But the thing is, they were not just ORDINARY time travellers!"
 
Barrie Davis said:
PS. Very concerned for the poor b*ggers in Queensland. :-(
--
Click to expand...
They are having a hard time. With some loss of life.

http://www.google.com/crisisresponse/queensland_floods.html

http://mapvisage.appspot.com/static/floodmap/map.html

Some sorrow in other states as well.

--



Ananda
http://anandasim.blogspot.com
https://sites.google.com/site/asphotokb

'There are a whole range of greys and colours - from
the photographer who shoots everything in iA / green
AUTO to the one who shoots Manual Everything. There
is no right or wrong - there are just instances of
individuality and individual choice.'
 
If I assume that each lens is used to get the same field of view at the focus distance, then the f2.8 lens can get a smaller DoF. This means different focus distances which can impact perspective, etc. In regimes where shallow DoF is desired (focus distance large compared to DoF), the differences between the lenses will be small. As DoF becomes small compared to focus distance, DoF becomes mostly a function of the field of view.

At some point, as both focus distances become quite large, the DoF of the 85 lens will go to infinity, followed a bit later by the 200 lens. In this regime, a photographer is not likely worried about shallow DoF.
--
Leon
http://web.me.com/leonwittwer/landscapes.htm
 
Can I shoot the 200mm at f1.4 ?

No.

Can I shoot the 200mm as wide as the 85mm ?

No.

So what the heck does it matter ?

--
StephenG
 
sjgcit said:
Can I shoot the 200mm at f1.4 ?

No.

Can I shoot the 200mm as wide as the 85mm ?

No.

So what the heck does it matter ?
Click to expand...
Well, there is currently a big fad for extremely blurred backgrounds, which is usually expressed as "Shallow DoF," even though that is not quite the same thing.

Anyway, I expect that's why the OP was asking....

...the myth of the moment being that the more shallow the DoF is, the "better" it is!
--
Regards,
Baz

"Ahh... But the thing is, they were not just ORDINARY time travellers!"
 
Best answer goes to Barrie Davis -> voted by me.

I actually have both of these lenses, I should take shots and compare, but knowing the field of view would be different I wanted the technical answer that Barrie delivered.

Thank you very much.
Barrie Davis said:
Joel C said:
85mm f1.4 FX or 200mm f2.8 FX?
Click to expand...
  • Strictly speaking, focal length isn't a factor in actual Depth of Field ... DoF being the front-to-back depth of the "apparently sharp" zone in an image.
  • In fact, all lenses have the same DoF if used at the same aperture and focused on the same target (at same distance). So, the 85mm and the 200mm are the same in DoF terms at all apertures they have in common ..which is f/2.8 and upwards.
  • This means the 85mm has shallower DoF at all apertures WIDER than f/2.8, which is two stop's worth (apertures f/2 & f/1.4 resp.) ...
But that isn't the end of the matter....
  • DoF scales and tables tell us nothing about the appearance of those areas NOT within the sharp zone we call Depth of Field ..... and it turns out that the degree of "apparent blur" in those UNsharp image zones is definitely NOT the same at all focal lengths.
  • Because longer lenses have a larger image scale (they "magnify more") the appearance of blur in the unsharp zones is also magnified... giving an impression of more separation between the sharp subject and the blurred background beyond....
  • .... which many people perceive as being "shallower Depth of Field"... but it is not, really! It is just more "apparent blur" in the image zones outside of Depth of Field... and that is not the same thing at all.
Unfortunately, I have not got either of the lenses myself, so I cannot tell if the longer length of the 200 magnifies the blur of the background enough to equal the extra blur that comes the 85mm having wider apertures....

...although I suspect that 200mm at 2.8 may equal the 85mm at or around f/2... and that the 85mm may pull ahead in the blurriness of background when opened up to full bore.

As I say, this is just my guess. DoF scales and tables are restricted to indicating the "apparently sharp"... they don't make any comment on how blurred is the "apparently blurred" That is somewhat outside their remit, as it were.

I hope this was clear, and possibly a bit interesting, even if it didn't tell you exactly what you wanted to know.

PS. Very concerned for the poor b*ggers in Queensland. :-(
--
Regards,
Baz

"Ahh... But the thing is, they were not just ORDINARY time travellers!"
Click to expand...
 
Joel C said:
Best answer goes to Barrie Davis -> voted by me.

I actually have both of these lenses, I should take shots and compare, but knowing the field of view would be different I wanted the technical answer that Barrie delivered.

Thank you very much.
Click to expand...
That's kind of you. I'm glad what I wrote was helpful. However, on re-reading it (below) I see that I have made a mistake... and it is NOT an insignificant one. Please allow me to correct it.
Joel C said:
Joel C said:
  • Strictly speaking, focal length isn't a factor in actual Depth of Field ... DoF being the front-to-back depth of the "apparently sharp" zone in an image.
  • In fact, all lenses have the same DoF if used at the same aperture and focused on the same target (at same distance)
Click to expand...
Click to expand...
Correction....

No. NOT "same distance." It should read "same framing ," which, of course, will be at a different distance with the two lenses. With same framing image scale will be the same in either case, and that's why DoF is the same.

I apologise for this error. I think my fingers were ahead of my brain.

Further info: This is why changing to a shorter f-length doesn't not increase DoF. At the change, image scale is reduced, so we move forward to fill the frame, with the result that DoF reduces proportionately... right back to where it started. With the change in distance, perspective changes, but not DoF.
Joel C said:
. So, the 85mm and the 200mm are the same in DoF terms at all apertures they have in common ..which is f/2.8 and upwards.
Joel C said:
  • This means the 85mm has shallower DoF at all apertures WIDER than f/2.8, which is two stop's worth (apertures f/2 & f/1.4 resp.) ...
But that isn't the end of the matter....
  • DoF scales and tables tell us nothing about the appearance of those areas NOT within the sharp zone we call Depth of Field ..... and it turns out that the degree of "apparent blur" in those UNsharp image zones is definitely NOT the same at all focal lengths.
  • Because longer lenses have a larger image scale (they "magnify more") the appearance of blur in the unsharp zones is also magnified... giving an impression of more separation between the sharp subject and the blurred background beyond....
  • .... which many people perceive as being "shallower Depth of Field"... but it is not, really! It is just more "apparent blur" in the image zones outside of Depth of Field... and that is not the same thing at all.
Unfortunately, I have not got either of the lenses myself, so I cannot tell if the longer length of the 200 magnifies the blur of the background enough to equal the extra blur that comes the 85mm having wider apertures....

...although I suspect that 200mm at 2.8 may equal the 85mm at or around f/2... and that the 85mm may pull ahead in the blurriness of background when opened up to full bore.

As I say, this is just my guess. DoF scales and tables are restricted to indicating the "apparently sharp"... they don't make any comment on how blurred is the "apparently blurred" That is somewhat outside their remit, as it were.

I hope this was clear, and possibly a bit interesting, even if it didn't tell you exactly what you wanted to know.

PS. Very concerned for the poor b*ggers in Queensland. :-(
--
Regards,
Baz

"Ahh... But the thing is, they were not just ORDINARY time travellers!"
Click to expand...
Click to expand...
--
Regards,
Baz

"Ahh... But the thing is, they were not just ORDINARY time travellers!"
 
Leon Wittwer said:
If I assume that each lens is used to get the same field of view at the focus distance, then the f2.8 lens can get a smaller DoF. This means different focus distances which can impact perspective, etc. In regimes where shallow DoF is desired (focus distance large compared to DoF), the differences between the lenses will be small. As DoF becomes small compared to focus distance, DoF becomes mostly a function of the field of view.
Click to expand...
I should have said at the same f number. Thus the smaller f number lens can achieve less DoF at the same field of view.
Leon Wittwer said:
At some point, as both focus distances become quite large, the DoF of the 85 lens will go to infinity, followed a bit later by the 200 lens. In this regime, a photographer is not likely worried about shallow DoF.
--
Leon
http://web.me.com/leonwittwer/landscapes.htm
Click to expand...
--
Leon
http://web.me.com/leonwittwer/landscapes.htm
 
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