Lens for short focal length

Newbe question: What specs would I need to look for when shopping for a lens that gives you that short focal length so that you can blur the background behind a subject that you are filming? Is it the F stop? Would I look for F1.4 or something like that?
I'm lens shopping for my Sony A6300.
 

sfoster

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the two biggest contributing factors are aperture and focal length

primarily is the aperture like you say. i have a 50mm 1.8 that gets so shallow you cant use it for anything but tripod shots if you open it all the way.

something that is 400mm will have more bokeh than something that is 15mm all other factors being equal
but focal length changes a lot of other stuff too.
 
the two biggest contributing factors are aperture and focal length

primarily is the aperture like you say. i have a 50mm 1.8 that gets so shallow you cant use it for anything but tripod shots if you open it all the way.

something that is 400mm will have more bokeh than something that is 15mm all other factors being equal
but focal length changes a lot of other stuff too.
I'm basically wanting to interview people with this lens. Shots like this... https://assets.entrepreneur.com/content/3x2/2000/1413830260-interview-questions.jpg?width=700&crop=2:1
 
First, you need to uderstand what focal length actually is: the physical distance between the lens and the camera’s image sensor. It’s indicated in millimeters, and is what determines the field of view of the lens. A short focal lenth means a wide lens (15mm, 24mm). A long focal length means a long lens (85mm, 135mm). A zoom lens is able to move across several focal lengths.

What you’re actually asking about is depth of field, which is how much will be in focus in front of and behind the subject. Wider aperture generally means shallower DOF.

Focal length enhances DOF based on aperture. For example, a 16mm lens at f/2.8 will still look to be relatively in focus throughout, but an 85mm at f/2.8 will have a very soft background behind the subject.

For wider interview shots, stick with the 24mm/35mm neighborhood. For closeups where you want to get more intimate with the subject and really blur out the background, you’ll want 50mm or even 85mm. Pick your aperture based on how soft you want the background, and light to that.

The example you linked is a medium angle with only a slightly soft background. You could get that with a 50mm. But be very careful shooting at extremely wide aperture. A lens at f/1.4 is going to be nearly useless because the focal plane will be so narrow that even the subject taking a deap breath can knock them out of focus. Stick between f/3.5 and f/5.6. And practice with whatever lens you get so you have a feel for the actual depth of field at f/3.5, f/4, and f/5.6.

Are you looking for just one lens to shoot single-camera interviews? If that’s the case, you’re better off getting a constant-aperture zoom that covers the range you want, so that you can push in a little when the conversation gets emotional. Zoom range gives you versatility, and constant aperture means you don’t lose light when you zoom in.

Tamron makes a great 28-75mm f/2.8 that’s available in Sony mount. That would be an excellent lens for interviews.
 
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Tamron makes a great 28-75mm f/2.8 that’s available in Sony mount. That would be an excellent lens for interviews.
I watched some YouTube demos. I wound up ordering the Sony E 50mm f/1.8 OSS. Only $238. I like that it has image stabilization, which the Sony A6300 camera itself does not have.
 

jax_rox

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One thing that is often overlooked when it comes to depth of field is distance. Yes, opening up your aperture is going to decrease your depth of field. How close your subject is to the lens also affects depth of field. As an example, a 35mm lens with a subject at 5’ gives a similar field of view to a 15mm with a subject at 2’. In this case, with both appetures set at f1.4, the 15mm will actually have less depth (I.e. shallower) due to how close the subject is to the lens (leaving aside the other potential artifacts from a 15mm lens, and of course that the look of the bokeh will be very different).
 
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