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View Full Version : F Stop confusion!!! Advice needed..



cat
03-15-2006, 08:55 AM
I don't have a 'proper' SLR type camera ( would be too scared of dropping one for starters! ) but am enjoying playing with the manual controls of my Canon S2. I've tried reading up on f stops and have a vague understanding ( ie my mind is just totally blanking on the whole subject!!! ) of what it's meant to do but can't seem to get the results I want! As in the photo I've posted below my problem is I want to get the whole of the flower in focus but retain the blurry background, I'm getting some bits in focus but not others and how ever much I fiddle I can't seem to improve on this. Is this just a case of me expecting too much or is there an optimal setting for this type of photography that would improve my results? would really appreciate any feedback.

These are the settings that I used;

Shooting Mode: Manual
Photo Effect: Off
Tv (Shutter Speed) : 1/30
Av (Aperture Value) : 5.0
Light Metering: Evaluative
ISO Speed: 50
Lens: 6.0 - 72.0mm
Focal Length: 6.0mm
Digital Zoom: None
IS Mode: Shoot Only
Image Size: 2592x1944
Image Quality: Superfine
Flash: Off
White Balance: Auto
AF Mode: Continuous AF
AF Range Mode: Super Macro
Color Space: sRGB
File Size: 1699KB
Drive Mode: Single-frame shooting


http://www.snappycat.co.uk/garden23-1.jpg

erichlund
03-15-2006, 09:54 AM
I don't know how much control you have over the stops on your camera. F stops are a numeric representation of the aperture of the lens. There are partial stops between these, but the basic scale is f1, f1.4, f2, f2.8, f4, f5.6, f8, f11, f16, f22 and f32. For each increase in number, half as much light is allowed to pass through the aperture of the lens (for a given exposure time). You indicated f5, which would be about 1/3 stop below f5.6.

The larger the number, the larger the depth of field, and conversely, the smaller the number, the shallower the depth of field. What you want is a number large enough to get the whole flower, while not so large that the background comes into focus. So, for instance, if you could select f8, that may work, while f16 may bring the background into focus. Again, I don't know what ranges are available on your lens.

Another way you can control your depth is to choose a different distance from your subject. To get the same framing, you have to have a wider angle when you get closer and a narrower angle when you move farther away. However, if you have the latitude to move a little closer and widen your angle of view, then your depth of field increases.

Of course, you also get closer to your hyperfocal distance, where everything will appear in focus from halfway between camera and subject out to infinity. One of the problems with P&S cameras is that you are nearly always flirting with this condition, especially when working close to your subject. This all has to do with the mathematics of small lenses, small sensors and associated circles of confusion. If you really want to know gobs about this, do a web search on depth of field (other subjects - hyperfocal distance, circle of confusion).

cat
03-16-2006, 01:48 AM
Fantastic!!! I think I've got that :D My aperture options are f/2.7, f/3.2, f/3.5, f/4.0, f/4.5, f/5.0, f/5.6, f/6.3, f/7.1, f/8.0 so I can go up 4 more stops to try and improve the depth of field. I was aware that increasing the fstop was making the image darker ( although hadn't really grasped the why! ) and was adjusting my shutter speed to compensate - although with shooting from above the slower shutter speed becomes problematic!!! Guess I need a brighter day or a steadier hand!!!!! Many Thanks for the advice - have read loads on fstops and wasn't making any sense at all!!! Itching to go and have another attempt now but has decided to snow :rolleyes:

EdBoy
03-18-2006, 03:36 PM
F-stops your problem... the bigger your F-stop the greater the depth of field (focus)