Blurred Backgrounds, Depth of Field, using different Nikon 300mm prime lenses

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joe43

Well-known member
I have a technical question concerning blurred backgrounds, depth of field , maximum (widest) apertures and minimum focus distances.

For two different Nikon 300mm prime lenses, used to take the same image on the same camera at the same f stop, would the Nikon 300mm f2.8 result in the same degree of background blurring as the Nikon 300mm f4 pf lens, all other things being the same? Or would the 300mm f2.8 result in more blurring?

The depth of field calculator I used shows the same depth of field data for each lens using the assumptions below: https://www.dofmaster.com/dofjs.html

Assumptions are:
(1) D850, 300mm f2.8, aperture f4, focus distance 8 ft:
and (2) D850, 300mm f4 pf, aperture f4, focus distance 8ft.

I do know that the Nikon 300mm f4 pf has a closer focusing distance than the 300mm f2.8, but I used a focus distance that was close to the minimum focus distance of the 300mm f2.8 to keep things consistent.

Since I own both lenses I might do my own tests. Before doing so I would like to have some idea as what results to expect.
 
On a related thread, same f/stop, same distance to subject/background. Will a DX body give more or less or the same DOF? In other words is DOF sensor size dependent? Asking cause I just purchased my first full frame and started wondering.
 
I think with a DX and a FX camera at the same distance and same lens, the DX would have shallower DOF (subject would be larger in DX frame). At the same image size, DX DOF would be greater ( you would be further away with DX). DX vs FX DOF can be confusing.
 
Re the query about a DX camera.

D500, F4, 300mm and 100 feet from the point of focus = 5 feet area of sharpness.

D850 with same input details, area of sharpness is 8 feet.

Not a lot of difference but still significant depending on the subject.

The distance from camera to the point of focus has a big effect on what the sharp area will be. For example. change 100 feet to 150 feet and the area of sharpness increases dramatically.
 
"D500, F4, 300mm and 100 feet from the point of focus = 5 feet area of sharpness.

D850 with same input details, area of sharpness is 8 feet. "

But the subject is much smaller in the FX frame.
 
I have a technical question concerning blurred backgrounds, depth of field , maximum (widest) apertures and minimum focus distances.

For two different Nikon 300mm prime lenses, used to take the same image on the same camera at the same f stop, would the Nikon 300mm f2.8 result in the same degree of background blurring as the Nikon 300mm f4 pf lens, all other things being the same? Or would the 300mm f2.8 result in more blurring?

The depth of field calculator I used shows the same depth of field data for each lens using the assumptions below: https://www.dofmaster.com/dofjs.html

Assumptions are:
(1) D850, 300mm f2.8, aperture f4, focus distance 8 ft:
and (2) D850, 300mm f4 pf, aperture f4, focus distance 8ft.

I do know that the Nikon 300mm f4 pf has a closer focusing distance than the 300mm f2.8, but I used a focus distance that was close to the minimum focus distance of the 300mm f2.8 to keep things consistent.

Since I own both lenses I might do my own tests. Before doing so I would like to have some idea as what results to expect.

DOF is the result of Focal length, used aperture, shooting distance and sensor size.
So with your settings both lenses will achieve the same DOF, but I wonder why would you use an expensive full stop faster lens stopped down?
Most people I know buying this F/2.8 primes buy them for that extra stop of light, the sharpness wideopen, the better contrast and the better background isolation...
(Just asking, not offensive)
 
On a related thread, same f/stop, same distance to subject/background. Will a DX body give more or less or the same DOF? In other words is DOF sensor size dependent? Asking cause I just purchased my first full frame and started wondering.

Yes DOF is sensorsize dependant, the larger the sensor the larger the DOF will be (compared with a smaller sensor)

An informative site on this subject
 
Thern, you asked a good question. I often use my 300mm f4 and 300mm f2.8 lenses to photograph captive raptors. I am often close to them, shooting at the minimum focus distance. The 300mm f4 has a shorter focus distance than the 300mm f2.8. At these close distances, DOF is quite short for each lens when the aperture is set to wide open. (Only about .17 inches for the 300mm f4 and .34 inches for the 300mm f2.8 both shot wide open at their own specific close focus distance on Nikon full frame camera.) If you want to get the eyes in sharp focus and the beak also in sharp focus, you usually have to stop down the lens to f5.6 or f8. And you have to be prepared to step back from the subject as greater distance increases the DOF range. And if you use a crop sensor body the DOF ranges are even smaller. At these close distances, about 50% of the usable DOF range is in front and the remaining 50% is in the rear. I will try and attach two images both taken with the 300mm f2.8 at f6.3 on a D850
AS_Eyeing You_N_SmithJ.jpg
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M_Red-tailed hawk_N_SmithJ.jpg
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" And if you use a crop sensor body the DOF ranges are even smaller. "

That is true if you're at the same distance, but if you maintain the same subject size, the DX camera/lens will have to be 1.5 times the distance away with a greater DOF.

For example:

DX @10', f/4, 300mm - DOF is 0.05'
FX @ 10', f/4, 300mm - DOF is 0.07'

but DX @ 15' (to maintain subject size in frame) - DOF is 0.11'
 
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