Question About Prime Lenses

[table1349]

so you close the aperture to 8 or 11

Sorry if the answer is obvious, but by closing the aperture that high in order to focus on the body as well, how do you then achieve the shallow dof?

The easiest way is to understand the math behind DOF. The second easiest way is this. Basically Plug and Play.

 

[bryanwstai]

The second easiest way is this.

Thanks for the link gryphon, got some values which I was confused about and tried reading the bottom bit with the information but I'm still confused. What I got out of that was that the circle of confusion defines the amount a point needs to be blurred to be unsharp etc.

But how do you use those actual values in a practical situation? Are you meant to?

eg.
Nearest Acceptable Sharpness: 1.94m (Max/min distances you should stand fromyour subject?)
Furthest Acceptable Sharpness: 2.06m
Total Depth of Field: 0.12m

for a DSLR 1.5x CF and a 50mm lens at f/1.8

 

[Frank F.]

so you close the aperture to 8 or 11

Sorry if the answer is obvious, but by closing the aperture that high in order to focus on the body as well, how do you then achieve the shallow dof?

By opening the aperture!

As you calculated above at f/1.8 the 50mm lens on a crop sensor delivers 12cm DOF.
The 105mm on a Full Frame Sensor at f/1.4 at the same distance delivers 3cm DOF.

In your first picture you have a 3/4 body portrait on a balcony, so you need something like one meter of DOF, so I would take a 24mm on a crop sensor, still the same distance and get 118cm DOF @f/4.0. On a full frame sensor with a 35mm lens I only achieve 80cm of DOF @f/4.0, so I close to f/5.6 and get 117cm of DOF.

That is called "equivalence" by some people although the term is misunderstood by many people

 

[droaingsong]

so you close the aperture to 8 or 11

Sorry if the answer is obvious, but by closing the aperture that high in order to focus on the body as well, how do you then achieve the shallow dof?

By opening the aperture!

As you calculated above at f/1.8 the 50mm lens on a crop sensor delivers 12cm DOF.
The 105mm on a Full Frame Sensor at f/1.4 at the same distance delivers 3cm DOF.

In your first picture you have a 3/4 body portrait on a balcony, so you need something like one meter of DOF, so I would take a 24mm on a crop sensor, still the same distance and get 118cm DOF on a crop sensor @f/4.0. On a full frame sensor with a 35mm lens I only achieve 80cm of DOF @f/4.0, so I close to f/5.6 and get 117cm of DOF.

That is called "equivalence" by some people although the term is misunderstood by many people

That is an equivalent answer for "equivalence" . I learned something new today.

 

[droaingsong]

1) Since my camera is a crop sensor, is 50mm a good focal length for portraits? I heard that it'll be a 75mm since it's on crop sensor.

You heard one of the common myths. Focal length is Focal length period. Sensor size does not change focal length. A 50mm is a 50 mm. What you are getting on a crop sensor is the field of view that falls on the sensor is approximately equivalent to what a 75mm lens would produce.

Personally I prefer the 85 to 100mm range for portraits on either a FF or a crop for the particular characteristics of that range.

Various focal lengths shooting the same subject filling the frame as close to the same as possible.

As for which 50mm, since I don't shoot Nikon these days others would be better suited to answer whether to spend the extra on the f1.4 vs the f1.8. If you were shooting Canon then the choice is easy, the f1.4 is far better.

I would suggest that when the budget allows, if you still want a 50mm in your arsenal of lenses look at the Sigma Art 50mm f.14: Sigma 50mm f/1.4 DG HSM Art Lens for Nikon F 311306 B&H Photo

This is a really nice and informative set.

So true. Didn't knew Sigma Art 50mm f/1.4 can be used for this.

 

[bryanwstai]

still the same distance and get 118cm DOF @f/4.0. On a full frame sensor with a 35mm lens I only achieve 80cm of DOF @f/4.0

Thanks Frank! I've got the jist of it now and have been reading up more about it. Just one quick question, you mentioned the first picture would require and approximate DOF @ ~1metre. How did you come up with that estimate?

Thanks,
Bryan.

 

[Frank F.]

still the same distance and get 118cm DOF @f/4.0. On a full frame sensor with a 35mm lens I only achieve 80cm of DOF @f/4.0

Thanks Frank! I've got the jist of it now and have been reading up more about it. Just one quick question, you mentioned the first picture would require and approximate DOF @ ~1metre. How did you come up with that estimate?
Thanks,
Bryan.

I estimated the distance from her knee to her hair and added something for insecurits focussing. If you are experienced you can do this shot with f/4
The second shot can be done at f/1.4 to f/2.8, depending on experience

more portraits @f=1.4