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View Full Version : Does more stops help DOF?



BowerR64
02-02-2007, 03:03 AM
Say i have 2 cameras one has F2.8-F11 and one is F2.8-F8.0 will the first one get better DOF because it has more Fstops?

It almost seems like it does but i wasnt sure why One is 8X zoom and one is 12X

The HP 945 has theF2.8-F11 and the canon S3 has the F2.8-8.0

cdifoto
02-02-2007, 03:09 AM
The quantity of stops doesn't make a difference. The actual stop you used does. Assuming your distances to subject, focal lengths, and sensor sizes are identical. That said, the ability to use f/11 vs "maxing out" at f/8 with everything else mentioned equal would definitely render deeper depth of field - again assuming everything else is equal. HOWEVER, with cameras such as these and sensors so small, almost everything is in focus at f/4 and normal focal lengths anyway so it's kinda moot until you get into extremes.

Riley
02-02-2007, 05:30 AM
cdi pretty well nailed it, except to say
small sensor cameras can do appreciably well at F2.8 as well
the best point of focus should be a third out over your target area

there are sensible limits to DoF via F stop too
the circle of confusion influences the sharpness of the image
so that on a small sensor camera, F8 or so is probably the sharpest aperture
but as DoF can be huge at that, there is little need to go further unless for some reason you require a slower speed

AlexMonro
02-02-2007, 09:15 AM
Depth of Field depends on many factors, some of the most important of which are aperture and actual focal length (as opposed to "35mm equivalent FL"). Things that tend to increase DoF are smaller aperture (higher f-number), shorter focal length, greater focus distance, smaller sensor, and greater print viewing distance. Note that stopping down too far with small sensor digicams can lead to overall softness due to diffraction effects.

There's a detailed discussion, together with an online calculator, here (http://www.cambridgeincolour.com/tutorials/depth-of-field.htm).

BowerR64
02-02-2007, 07:07 PM
Actualy they arnt the same, the HP wich has an F11 apature has a 1/1.8" sensor, the S2 and S3 use the smaller 1/2.5

So is there any benifit to having more Fstops?

What can this camera do that the canon cant with the more stops?

Im just wondering wich to get rid of, i dont need em both and i thought because it has more stop i might want to keep it insted.

http://i5.photobucket.com/albums/y191/BowerR64/Camera/HPcopy.jpg

Rhys
02-02-2007, 08:11 PM
Depth of field is controlled by three things:
1. Sensor size
2. Aperture
3. Distance to the subject

If we have an aperture of f4 on a larger sensor then the DOF will be less than the DOF on a smaller sensor.

If we have an aperture of F4 the DOF increases with distance from the subject but decreases as we get closer to the subject.

If we use a smaller aperture then DOF increases.

mattdm
02-02-2007, 08:34 PM
There are several sites online which know the characteristics of many popular models and can calculate information like this for you. Here's one. (http://www.dofmaster.com/dofjs.html).

Using that, I see that (and knowing that the Canon and HP's real focal lengths are 6-72mm and 7.6-61mm, respectively), you can find that at the wide end, both of these cameras have an effectively infinite depth of field no matter what the aperture.

At the tele end, though, where the HP can apparently actually stop down to f/12.4, you can find that the HP has a DOF of about 11 feet when focused 30 feet away. Meanwhile, also zoomed completely out, the S3 has a DOF of only a little over 4 feet at that distance.

Of course, that's a lot more zoomed in. At the equivalent focal length (50mm on the S3 = 61mm on the 945), it's more like 9 feet -- so closer. Close enough, in fact, that I don't think this can be considered an important difference between these cameras.

BowerR64
02-03-2007, 01:43 AM
You know what i forgot somthing, i keep getting this DOF term mixed up. Whan i say i want more DOF im actualy wanting less. Im wanting these to perform in a similar way SLR cameras perform where the subject is in good focus but the back ground or everything else is out of focus. I get confused because im so use to everything being in focus like on most P&S cameras.

So actualy what im wanting is a more narrow DOF. Is this the right way it works? narrow is how an SLR is?

cdifoto
02-03-2007, 02:09 AM
You know what i forgot somthing, i keep getting this DOF term mixed up. Whan i say i want more DOF im actualy wanting less. Im wanting these to perform in a similar way SLR cameras perform where the subject is in good focus but the back ground or everything else is out of focus. I get confused because im so use to everything being in focus like on most P&S cameras.

So actualy what im wanting is a more narrow DOF. Is this the right way it works? narrow is how an SLR is?

The concepts are the same no matter what camera you have. Narrow isn't how an SLR works. You control how much DOF you have.

Because the sensors of the P&S type cameras (pretty much any non-SLR) are so tiny, it's more difficult to get the narrow DOF, sometimes even impossible if the camera doesn't have a long enough lens and short enough minimum focus distance.

In order to get the most narrow DOF possible you need to zoom to the longest, get as close to the subject as the camera will focus, use the widest aperture (smallest f number) capable, and have as much distance between the subject and the background. You still won't have what you can get with a dSLR+fast lens combo but it might be acceptable.

Getting another non-SLR camera won't change things, and the various specification differences might make it even more difficult yet.

AlexMonro
02-03-2007, 03:48 AM
OK, to get the minimum DoF, you want maximum aperture and max zoom (assuming you can step back far enough).

Plugging the numbers in to the DoF calculator mattdm linked to earlier (which allows intermediate f/stops), and assuming a subject distance of the equivalent focal length, to give the same apparent size, we get:

HP 945: f/3.2 @ 61mm f/l (300mm equiv), subject distance 3m, DoF total 0.09m

Canon S3IS: f/3.6 @72mm (432mm equiv), subject distance 4.32m, DoF total 0.13m

(the closest f-stops on the calculator to the actual max apertures at full zoom were slightly smaller, so in practice you might get slightly shallower Dof, though I doubt you'd notice the difference).

So the HP gives you slightly shallower DoF (about three quarters).

However, there's not a lot in it. If you really want to explore shallow DoF, you really need a DSLR and a wide aperture portrait lens - something like the Canon 85mm f/1.8 (or the f/1.2 if you can afford it!:) )

Riley
02-03-2007, 04:09 AM
and then there are macro lenses used as long optics

you really dont have to drop your bundle for adequate bokeh
and no-one will know the difference if you dont