Need Help Selecting Lens Configuration for Portrait Photography

[bluehabit]

I need to take some portraits later today. I am using a Panasonic GH4 and have a metabones speed booster. My question is which of these configurations will allow me to achieve a nice blurry background / bokeh the easiest while still capturing the portrait?

Camera: Panasonic GH4
Lens: Sigma 18-35 f1.8

1. (no speed booster) 35mm equivalent focal range 36 to 70, max aperture f1.8

2. (with speed booster) 35mm equivalent focal range 23 to 45, max aperture f1.4? (not sure what the full stop reduction is from 1.8 using the speed booster)

It seems like option 2 might be the best, but you hardly have any range to zoom in with, and having more of a telephoto lens seems to be ideal for portraits.

Thank in advance

 

[ronlane]

Not familiar with Panasonic camera or what speed booster is but you should be able to get bokeh with either 1.8 or 1.4 with no problem. The depth of field is so small there that it shouldn't be hard to do at all.

 

[tirediron]

^^ What Ron said. I would go for the longest focal length (70mm) and largest aperture (smallest f#) you can.

 

[bluehabit]

Thanks guys. I took some practice shots yesterday and I didn't really like the results. It felt like I had to get really close to the subject (several feet away from her face) to get nice bokeh at 70mm f1.8

With all other factors being constant (focal length etc), would a f 1.8 on a full frame sensor have superior bokeh compared to f.1 on a micro 4/3rds sensor? Because the panasonic GH4 is a m4/3rds camera.

 

[ronlane]

Thanks guys. I took some practice shots yesterday and I didn't really like the results. It felt like I had to get really close to the subject (several feet away from her face) to get nice bokeh at 70mm f1.8

With all other factors being constant (focal length etc), would a f 1.8 on a full frame sensor have superior bokeh compared to f.1 on a micro 4/3rds sensor? Because the panasonic GH4 is a m4/3rds camera.

How far is your subject from the background? This will play a role in the bokeh.

The anwer to the ff vs 4/3's is that it's not the camera, it's the lens and aperture that has more to do with it. Yes, a ff with quality fast glass will beat a 4/3's camera in bokeh.

 

[bluehabit]

[
How far is your subject from the background? This will play a role in the bokeh.

She was very, very close to the background. We were using some tall flowers as a the background and she practically had her back touching them. I guess if we move her away form the background the bokeh should improve?

The anwer to the ff vs 4/3's is that it's not the camera, it's the lens and aperture that has more to do with it. Yes, a ff with quality fast glass will beat a 4/3's camera in bokeh.

Right, but lets assume you have the same quality of glass for both the 4/3's and the FF camera. You are able to get both lenses open to f 1.8 and and take the shot on both cameras at the same 35mm equivalent focal distance. Would the bokeh quality in the shots not be equal, or would the FF camera still have better bokeh quality even though all factors are the same?


Thanks for your help so far everyone, much appreciated.

 

[ronlane]

Yes, if you moved her 4-5 feet away from the flowers, you will start to see the blur. You may have to move her 10-15 feet away in order to get it like you want it.

In theory, I guess they should be equal. At that point you would then get into a lot of technical stuff that I'm not that good with. I would question at this point would the sensor size and processor of the ff make the quality better. Not to mention the question of can you get 4/3's glass with the same quality as a ff glass?

 

[KmH]

Digital Camera Sensor Sizes: How it Influences Your Photography
Understanding Depth of Field in Photography
Online Depth of Field Calculator

Your GH4 has a 4/3 size image sensor and a crop factor of 2x.
The smaller an image sensor, the higher the crop factor, the harder it is to achieve a shallow depth-of-field (DoF).
Bokeh is not adjustable and is an inherent property of whatever lens you use.
Bokeh and a shallow DoF are not the same thing.

It is not helpful when others only mention lens aperture when making recommendations regarding achieving a shallow DoF.

How far the point-of-focus (PoF) is from the camera has as much, if not somewhat more, to do with achieving a shallow DoF than a wide open lens aperture does.
The shorter the PoF distance the shallower the DoF gets.

Many have focus control issues when using a shallow DoF because they do not understand just how shallow the DoF can become.
The PoF creates a plane of focus that is parallel to the plane of the image sensor in the camera. If you tilt the camera up/down/sideways you also tilt the plane of focus.

 

[mcap1972]

For portraits I prefer longer lenses/range like 70mm to 200mm.

 

[Derrel]

[
How far is your subject from the background? This will play a role in the bokeh.

She was very, very close to the background. We were using some tall flowers as a the background and she practically had her back touching them. I guess if we move her away form the background the bokeh should improve?

The anwer to the ff vs 4/3's is that it's not the camera, it's the lens and aperture that has more to do with it. Yes, a ff with quality fast glass will beat a 4/3's camera in bokeh.

Right, but lets assume you have the same quality of glass for both the 4/3's and the FF camera. You are able to get both lenses open to f 1.8 and and take the shot on both cameras at the same 35mm equivalent focal distance. Would the bokeh quality in the shots not be equal, or would the FF camera still have better bokeh quality even though all factors are the same?


Thanks for your help so far everyone, much appreciated.

Yes, Ron is entirely right: if the subject is close to the background, then the defocused nature of the background will berather unremarkably defocused, because the subject and background are CLOSE to one another, and the depth of field will have the in-focus and the out of focus distances quite close to one another.

The easiest way to get a very out of focus background is 1) have the subject CLOSE to the camera: this is very critical and then 2) Have the background be as far behind the subject as is practical. These TWO factors are the primary ways to get strongly defocused backgrounds. Coming in at 3) is Use a longer focal length lens, rather than a shorter lens and 4) Use a rather wide aperture, such as f/2,f/2.,2, f/2.5,f/2.8, f/3.2, f/3.5, or f/4,etc..

As to the m4/3 versus FF debate. The simple physics are this: the smaller the format, the MORE you get in-focus with the SAME picture angle. So...a telephoto lens length used on a m4/3 camera has MUCH more depth of field than say, a 250mm lens used on a 6x6 cm rollfilm camera that is capturing the SAME picture angle. The larger the film or larger the sensor, the more difficult it is to achieve deep, expansive depth of field. This means that smaller-sensored cameras, like smart phone cameras and compact P&S and compact superzoom and bridge cameras can all make deep depth of field shots very,very easily. The inherently deep depth of field that small-sensor digital cameras posses can be viewed as an advantage in many situations, and a liability in other situations.

m4/3 has significantly MORE depth of field than FF digital does, and that characteristic,at least to me, makes the m4/3 cameras better choices for social photography situations and documentary/street shooting where having MORE in-focus, or with less critical focus needed for every shot, a really big advantage for that camera format. IF on the other hand, a person wants to "blow out the background", then the m4/3 camera's smaller capture size and correspondingly shorter lenses makes it LESS of a plus, and more of a negative.

 

[bluehabit]

Great Post Derrel, but I wanted to point out one thing.

3) is Use a longer focal length lens, rather than a shorter lens and 4) Use a rather wide aperture, such as f/2,f/2.,2, f/2.5,f/2.8, f/3.2, f/3.5, or f/4,etc..

I was actually taught to believe that its easier to get a shallow DoF using a telephoto lens compared to a wide/ or mid range lens. However, that is actually a misnomer. The only thing that changes is how close or far you have to be from your subject to achieve that DoF.

 

[Derrel]

Great Post Derrel, but I wanted to point out one thing.

3) is Use a longer focal length lens, rather than a shorter lens and 4) Use a rather wide aperture, such as f/2,f/2.,2, f/2.5,f/2.8, f/3.2, f/3.5, or f/4,etc..

I was actually taught to believe that its easier to get a shallow DoF using a telephoto lens compared to a wide/ or mid range lens. However, that is actually a misnomer. The only thing that changes is how close or far you have to be from your subject to achieve that DoF.

Depth of field is a complex subject that many people do not fully understand. As to the way to get shallow depth of field while using just ONE sensor or film format size, the list I provided with the 1,2,3,4 steps in order of importance is correct. You are correct that camera-to-subject distance is a critical factor in achieving shallow depth of field. HOW CLOSE the camera is to the subject is a very big factor in how deep the depth of field is in the normal distance ranges of from 5 to 60 feet, especially with lenses in the so-called portrait length. And the degree of out of focus of the background is hugely dependent upon subject/background distance, yes.

Depth of field varies a bit in the macro range, at normal distance, and then as the focused distance approaches the hyperfocal distance of the lens in use. For example: with an 85mm lens shot at 10 feet at f/2.8, there is not much depth of field; but with the same 85mm lens at f/2.8 at 75 feet, the depth of field is quite deep! [Oly E-series sensor, 85mm f/2.8 lens focused at 10 feet, DOF is 9.83 feet to 10.2 feet, or 0.35 feet total; at 75 foot focus, near focus comes in to 66.2 feet, far focus extends to 86.6 feet, for a total DOF band depth of 20.4 feet.]

For example, with an Olympus E-series sensor, at f/16 with an 85mm lens, focused at 75 feet, the DOF is from 42.7 feet near limit, to 308.1 feet, for a total depth of field band of 265.4 feet. Same camera, same f/16 aperture, but focused at 7 feet? Near limit 6.55 feet, far limit 7.51 feet, for a total DOF band of 0.96 feet.

Online Depth of Field Calculator

 

[xzyragon]

FF cameras give a shallower DoF with the same lens because your distance to your subject decreases by the crop factor to get the same framing.

For your 4/3's format (or 2x crop body), you could stand 10 feet away to frame your subject.
On a FF equivalent (using the same lens), you'd stand 5 feet away to similarly frame the shot.

Because the distance to your subject is reduced, the DoF is smaller, which can enhance bokeh if the background is closer.

 

[bluehabit]

FF cameras give a shallower DoF with the same lens because your distance to your subject decreases by the crop factor to get the same framing.

For your 4/3's format (or 2x crop body), you could stand 10 feet away to frame your subject.
On a FF equivalent, you'd stand 5 feet away to similarly frame the shot.

Because the distance to your subject is reduced, the DoF is smaller, which can enhance bokeh if the background is closer.

That's not necessarily true. Thats why I specifically stated in 35mm equivalent. Whatever lens you are shooting on FF, APS-C, or m 4/3's if the effective focal length of your lens WITH crop factor applied is the same (for example 50mm) your distance to subject for framing and DoF will be the same assuming all other factors are the same (glass quality etc).

 

[Derrel]

Back to the ACTUAL camera and lens, the Panny and the Siggy 18-35mm f/1.8: the difference in defocused background degree between f/1.8 and f/1.4 will barely be visible, but the loss of focal length would be noticeable, and it would be better I think to use the Sigma zoom lens at the longest focal length setting of 35mm (70mm equivalent in 135-format), rather than get a slightly wider effective f/stop but a shorter focal length. And of course, shoot from close-in distance, and keep the background as far behind the subject as is convenient and which gives the right overall "look" to the shot. so, skip the Metabones and just mount the Siggy right on the camera.