Digital on a budget - Depth of field rambling

[oldgreygary]

The Canon G2 has got a range of aperture setting from f/2-f/8. I was looking for a shallow depth of field to get the main subject in focus with the background blurred. I used Av mode and set the aperture to f/2.8 and when I looked at the results everything was in focus!? Initially this didn't make any sense. Until I read an article about fixed lens digital cameras which the Canon G2 is. Apparently, on this type of camera f/2.8 is the equivalent of f/11 on a 35mm camera. Now things started to make a bit of sense. But that leaves me with the problem of can I get a shallow depth of field with the G2? I haven't managed so far, so I guess the option that would be open would be to do something in post processing? Or perhaps I perhaps there is a method of using the camera to do it?
I'll leave those as a open questions and if anyone wants to comment? It would be interesting to hear any thoughts.

Cheers for now

Gary

[anita]

Hello, Gary.

I'm having the same problem understanding the DOF, but you could try to get close to your subject, that in teory should minimize the DOF. I am not sure if this concept is aplying to your camera too, but worth a try .

[Donald]

....... perhaps there is a method of using the camera to do it?

Have to confess to not having heard of the f2 = f11 thing before. But that's just my ignorance.

The problem is that you are not going to get a shallow DoF. You're going to have what you have, if you see what I mean. Given that depth-of-field is about the range that something is in focus from front-to-back, the most obvious method is to ensure that the distance between the subject and the background is maximised - subject in focus and background far enough away to be out-of-focus.

You don't tell us what the subject was that you were trying to get in focus and what the background was that you were trying to get out-of-focus. But maybe you need to explore the options for getting as close as possible to the subject and getting background as far away as possible.

[oldgreygary]

Ana, Donald,

I will try exploring the option of getting nearer to the subject set the aperture to wide open and see what results from this. I guess that it's all part of finding the limitations/capabilities of the camera and working with these.

Thanks for replies

Cheers for now

Gary

[herbert]

Hi Gary,

You could try using the longest focal length you have. For an equivalent framing of the subject the background will appear more blurred. (This is because it is more magnified with the longer focal length. The blur is the same but you see it spread out more.)

Getting low is a good idea. This will usually increase the distance to objects in the background. Imagine a shot of a child taken looking down and you will notice the floor right behind them. If you crouch to the child's height then the background may be dozens of meters away. One good rule for this I like to keep is to take portraits at the eye level of the subject, be it a cat, child, bird or adult.

Blurring a select few images in post processing is easy. I do it when my backgrounds are not blurred enough or have some nasty Bokeh (the quality of the blur). Nasty Bokeh is usually seen when straight lines get blurred. However blurring thousands is not easy. You should be selective about the ones you really want to show off.

Alex

[William W]

The Canon G2 has got a range of aperture setting from f/2-f/8. I was looking for a shallow depth of field to get the main subject in focus with the background blurred. . . . Apparently, on this type of camera f/2.8 is the equivalent [aperture]of f/11 on a 35mm camera. Now things started to make a bit of sense. But that leaves me with the problem of can I get a shallow depth of field with the G2? I haven't managed so far . . . It would be interesting to hear any thoughts.

I understand the Canon G2 has a 1/1.8” sensor with a 7mm to 21mm F/2~2.5 zoom lens.

If we describe this Compact Camera in terms of 135 Format (i.e. “A Full Frame DSLR”) by addressing “Equivalence” (which is what the equating of DoF and Aperture stops is about) – the we get this approximate description of the lens: 35mm to 105mm F/10~13 zoom lens.

The “crop conversion” for the focal length “equivalent” is pretty commonly discussed, and for brevity, trust me that the DoF Equivalence is about +4⅔ Stops – a statement which can be easily researched.
[Equivalence – Depth of Field – Lens Aperture – Sensor Size].


***


The (generic) problem you have with small sensor cameras is the inability to make really shallow Depth of Field, even with a very fast lens.


To leverage what you do have, you can influence the appearance of the Background Blur, (Bokeh), and this is different to the Depth of Field.
For example the first step is achieved by situating the Subject far away from the Background.
Often choosing a different lighting type on the background to the Subject will add to the illusion of better Separation - for example you could chose a Camera Vantage Point such that the background is in open shade and there is more direct lighting on the Subject.


The next consideration is the composition of the shot (for example a Portrait) - it needs to be as tight as possible.
For example you will have more success with a Tight Head Shot than a Bust Shot and an Half Shot will be even more difficult to accommodate.
And this is no matter WHETHER you use the Wide Angle or the Telephoto end of the zoom.
The DoF will be the same for any given framing of The Shot if the Aperture remains the same.

And, importantly the looser The Shot**, the MORE DoF you will make, so if you want shallow DoF you need to make The Shot as Tight as possible**, whilst still keeping it pleasing to you. (** see Footnote)


Which leads us to the next consideration – the Aperture: it should appear obvious that you use the largest aperture. But remember that many zoom lenses on micro format cameras have a VARYING Maximum Aperture Lens – so for your camera, you will want to use F/2 –but that likely will only be available to you from about FL = 7mm to FL ≈ 9mm (equiv. ≈ 35mm to 45mm). So, it would leverage your cause if you used the range of FL, whatever it might be, to allow you to use F/2


These are the general guidelines that I recommend you employ.


***


Examples of Shallow DoF and Bokeh with a micro format camera:

These are two examples shot with a Canon Powershot S5 IS which has a sensor size 1/2.5".
This camera therefore renders an Equivalence Aperture factor of +5⅓ when compared to 135 Format (e.g. a 5DMkII)

Both these images were shot at Aperture F/3.5 (Equivalence F/22); both at about the same Subject Distance (Shooting Distance) and both have similar Framing; both are taken with the Subject in Open Shade, but the first with a Background in Open Shade and the second with the background in Bright Sun; the solid Background is about the same distance form the Subject, in each shot;
(pls. note in the second shot there is Fly Screen about 3ft (1mtr) behind the Subject which renders the small square pattern).

The DoF is about 12” (30cm) in both pictures and both are made using Available Light and no Light Modifiers.





and





WW


** A "Tight Shot" and a "Loose Shot" are NOT referring to the Focal Length of the Lens - but are referring to how "tight" we are in "on the Subject".

An Head Shot, is a very "Tight Shot"; an Half Length Portrait is a "Looser Shot"; A Full Length Portrait is a "Looser Shot", still.

i.e. it is a description of the FRAMING of the MAIN SUBJECT within the SCENE.

[Ryogenetic]

I cant seem to find the source but I read an article back when I was shooting with my GE X5 Superzoom, that a technique for shooting shallow DOF was to put the camera into Macro mode. Here is an example:



I note that it is not super shallow but you do get some of the Bokeh that Bill was referring to and this was the best setting I could get for it. But if must have some separation there are ways to mimic it with post processing. Same picture edited in Photoshop:



took original image copied to new layer, added gaussian blur at 50pixels, and painted back in the Schweppes and table foreground.

Hope that helps
Ryo

[oldgreygary]

Bill, Ryo. Thanks very much for your comprehensive replies which have clarified the problem. I will incorporate for future shots.

Cheers for now

Gary