Question on digital cameras

[Ed Hansberry]

Looking hard at the Canon Powershot S1 IS. My wife wants one that can have the subject in focus and blur the background. http://consumer.usa.canon.com/app/pdf/d_camera/s1is_bro.pdf says the camera has something called. "selectable focusing point."

Is that what that means or is that something else?

[backpackerx]

Not sure if that's what it does or not but in photography, that effect is a result of the aperature setting. The bigger the lens aperature (smaller value) the shallower the depth of field or focus is. By using a small aperature value (large opening) you will get subjects in focus with backgrounds blurred. Any camera that allows manual aperature, f-stop settings can do this.

The distance of focal length (zoom), distance from camera to subject, and distance from subject to background affects this too but the cause is the aperature value.

[Lee Yuan Sheng]

No, that has nothing to do with having a shallow depth of field.

Selectable focusing point means you can tell the camera where in the frame you wish to focus. Generally cameras focus at the centre of the frame; with selectable focusing point you can select other areas. Where you can select depends on the camera itself. EOS 1 and 3 series have 45 points!

I'd like to add to backpackerx's comments that there's an additional factor, and that's how much you want to enlarge the photo by.

If your wife needs a fairly shallow depth of field, I'm afriad most of these cameras can't do it, due to the smaller sensors leading to very short focal lengths. Your options are then to get a DSLR, or to use Photoshop to do the blurring instead.

Perhaps you can give us an example of how shallow the depth of field, and the amount of background blur that is needed?

[Ed Hansberry]

http://consumer.usa.canon.com/ir/controller?act=ModelFeaturesAct&fcategoryid=144&modelid=9824 at the very bottom. The boy/girl hugging each other with the trees in the background blured. I know that is on the Canon page, but that doesn't mean that camera did that.

[Lee Yuan Sheng]

Yea, it's not impossible.. but you'll probably need to use the maximum 10x zoom and stand at the appropriate distance to the subject to get that. It'll also depend on the distance of the background to the subject.

If you absolutely need to get that kind of blur consistently, then you'll probably need to follow one of the two points I made above, that is, get a DSLR, or use Photoshop (or similar software).

[SassKwatch]

To add one more point.....

The separation of subject/background by blurring the latter is also affected by the distance between the main subject and the background.....and even by the distance between the photographer and the main subject. In the pic you cited at the Canon site, the background is clearly quite some distance behind the boy & girl. Hence, with a large aperture opening, the blurry background. Had they been standing right at the edge of the wood line, the blur effect would have been far less pronounced....even with a large aperture set on the camera. Chances are, the background would still have been somewhat blurred, just not as demonstrably as in this pic.

'Back in the day'......lens makers used to put Depth of Field markers on the lens barrel. So, if one's subject/focal point was at 8ft from the camera and the aperture was set at say, f16, it was easy to glance at the lens barrel and tell that everything between 5 ft and 25 ft (or whatever) would be 'in focus'. These DOF markets are FAR less common these days, and I think it's a pity. It was a handy little tool.

[Lee Yuan Sheng]

Well, sinze everyone wants zoom lenses nowadays, DOF markers aren't practical, unless some LCD panel is installed to provide an on-the-fly calculation of DOF.

[SassKwatch]

Well, sinze everyone wants zoom lenses nowadays, DOF markers aren't practical, unless some LCD panel is installed to provide an on-the-fly calculation of DOF.
Zoome lenses don't matter. Lens focal length has nothing to do with DOF.

http://www.luminous-landscape.com/tutorials/dof2.shtml

[Lee Yuan Sheng]

Heh, knew someone would post that up sooner or later.

If you look at the mathematical equations for DOF calculations, you'll see the variables include:

1. Focal length
2. Distance to subject
3. Circle of confusion (related to the enlargement factor I was talking about)
4. Aperture size.

What that article demonstrates (and states at the beginning) is that when magnification remains the same, the DOF remains the same too. However what it neglects to mention is that magnification is dependent on focal length and distance to subject; double one and you'll have to double the other to keep magnification constant, and thus the experiement is flawed as it is changing TWO variables at the same time. I'm not going to torture everyone (including myself) by doing the derivation for the DOF equations, but you can try plugging in the numbers into a DOF calculator and you'll find that is indeed the case.

edit: ack, brain freeze, edited the bit on keeping magnification constant.

[Lee Yuan Sheng]

I just remembered, there is a camera that'll show you what your DOF is even with a zoom lens, and that is the extremely gadgety Minolta Dynax/Maxxum 7 SLR. I assume the digital version has the same feature. With a D lens, pressing the DOF preview button on the camera will show you the DOF (with a diagram even) right on the rear LCD!

[SassKwatch]

If you look at the mathematical equations for DOF calculations, you'll see the variables include:

1. Focal length
2. Distance to subject
3. Circle of confusion (related to the enlargement factor I was talking about)
4. Aperture size.

Technically, you're correct. But the following from the cited article is the most relevant portion from my perspective......

"Yes, I know that there are some flaws...But, from a practical point of view, what really counts to photographers working in the real world is what ends up on a print in front of them. The fine points of optical theory are one thing, prints hanging on the wall are another. My orientation as a photographer and as a teacher is toward the pragmatic. "

[Lee Yuan Sheng]

It still doesn't excuse the fact that the article is misleading. After all, because of it, you did think that DOF markings would be possible on zoom lenses (it isn't).

[Gordo]

Your question is really: How can I take a shot where the subject is in focus and the background is out of focus?

The point about the "selectable focusing point" has already been answered.

On the camera in question you would need to select one of “Portrait Shooting Mode” or Creative Mode.

I assume that with Creative mode you will have full control of the camera settings. You want the camera to take the shot with a small aperture value. The smaller the aperture value the smaller the depth of field.

The quicker method is to use “Portrait Mode” which by default will choose a small depth of field.

[flooder]

I just remembered, there is a camera that'll show you what your DOF is even with a zoom lens, and that is the extremely gadgety Minolta Dynax/Maxxum 7 SLR. I assume the digital version has the same feature. With a D lens, pressing the DOF preview button on the camera will show you the DOF (with a diagram even) right on the rear LCD!

Nope. It was one of the things that was taken away. That and the eye start are what come to mind. I did not have the 7 so I never used this feature.

I would challenge anyone to draw the silkscreen of the DOF diagram for 28-300 lens. I'll put it on my wall!

What I do is print out the table version of DOF and carry it in my bag. I don't referance it very often but it's there. I know Tamron publishes it for their lens.

[Lee Yuan Sheng]

[Nope. It was one of the things that was taken away. That and the eye start are what come to mind. I did not have the 7 so I never used this feature.


Now that's a pity. It's one of the more nifty and actually useful functions on the D7. I suppose the feature which shows which areas on the honeycomb is being under/overexposed is gone too, given that it's digital?

[flooder]

Now that's a pity. It's one of the more nifty and actually useful functions on the D7. I suppose the feature which shows which areas on the honeycomb is being under/overexposed is gone too, given that it's digital?

It must be as I haven't run into that function. When looking at the histrogram it does flash the under/over areas. This is, after the fact, of course.

[Lee Yuan Sheng]

Before I go on, I think the thread has gone off topic.. can someone help move this and the previous 3 posts to a new topic on the D7D?

Back to the D7D, does (IIRC) pressing the AEL button togehter with the DISP button show anything?

[flooder]

[quote="Lee Yuan Sheng"]Before I go on, I think the thread has gone off topic.. can someone help move this and the previous 3 posts to a new topic on the D7D?quote]

Agreed. I replyed over in the hardware section.


TOPIC

Ed, if you want real control you are going to need a (d)SLR. If not, it's going to be a lot of guessing and trial and error.

[SassKwatch]

It still doesn't excuse the fact that the article is misleading. After all, because of it, you did think that DOF markings would be possible on zoom lenses (it isn't).

Been meaning to come back to this for a while.....

Given that DOF is a mathematical equation (I stand corrected on that), there's still no reason the information couldn't be provided for zoom lenses. Not on the lens barrel itself obviously, but it could be calculated and displayed in the viewfinder. Even if it was a user selectable option for display there, so be it. That would be better than not having the info at all.....for those of us who find it useful, anyway.

[Lee Yuan Sheng]

I know what you mean, and I agree, that's why I mentioned the Dynax 7.. however, as mentioned above, the digital version doesn't seem to have that feature. :(

[Macguy59]

As was just pointed out by a previous poster quite a few cams have a "portrait" mode which does provide some of that effect.

[Don Tolson]

...and if you're camera doesn't have manual aperature settings, you can also achieve the same effect 'in the darkroom', using your imaging software. :wink: