Depth of Field Problem w/ my G3

[lasercomp]

Hi guys and gals, I don't know if it is a problem with my shooting style or my camera or maybe even my lens but here goes. I try to take pictures where I want the subject in the foreground to be sharp but blur out the background. For some reason it never works for me. I set my F/stop value to a low number such as 2 and when I want to take the picture, the shutter speed turns red telling me the f/stop setting is too low so I have to step down on the f/stop until the shutter speed is good. Sometimes, it forces me to go up to like f/4. When I get home and load the pictures, I notice the foreground and background is both sharp. I have tried many different subjects with no luck. I am trying this at about 10 in the morning with nice weather so it is pretty light out. Any suggestions/recommendations would be greatly appreciated. Thanks

[slejhamer]

Ah, the wonderful world of consumer-level point-and-shoot digital cameras.

As I understand it, the sensors are much smaller than a frame of film, and combined with the apertures used in these cameras you get very small circles of confusion. Thus, even a wide-open lens on a p&s digicam will give you much greater depth of field than you would get in a 35mm film camera.

(Someone with more technical expertise can give you a better basis of understanding; the above is just my attempt at a lay explanation.)

You can try using a +1 diopter and long focal length (zoom out) but the result is still not quite the same as you would get with a digital SLR.

In the following pic I was at f2.5, and the DOF is obviously not what you would expect from that setting on a full-frame film camera:

http://www.photography-on-the.net/forum/showthread.php?t=10121

[GordonSBuck]

Trying to attain limited depth of field in digital cameras with small sensors (like our G3s) is somewhat of a problem. You have the right idea -- using a large aperture (small F stop number like 2, 2.8, etc) but the effect is not as as obvious as in a 35mm film camera. To get the blurred background, you really have to force the largest aperture (smallest F stop number) possible.

Put the G3 in Av mode. Zoom to maximum telephoto setting. Set the smallest F stop possible. Use the LCD panel to confirm the focus point and shutter speed that the G3 will automatically select. Focus on the subject and notice the shutter speed. If such a low shutter speed is selected that the G3 gives the "shaky" warning, then put the camera on a tripod or otherwise brace it and take the photo. Take a second photo but this time focus in front of the subject.

Exposure-wise, for a given ISO setting and amount of light, a fast shutter speed matches a large aperature (small F stop) and slow shutter speed matches a small aperture. For example, if you were to force F 2 and the corresponding shutter speed were 1/30 second then if you forced F4 the corresponding shutter speed would be 1/8 second.

If there is ample available light, the G3 ISO number should be at "50" when using the larger apertures. In fact, it is really best to use the ISO 50 setting whenever possible to maximize image quality.

If there is a lot of available light, even the fastest G3 shutter speed may not be fast enough to force F 2 -- perhaps that is your problem. In that case, be sure to set ISO 50, then go to the G3 menu and turn on the internal "ND Filter". The ND (neutral density) filter is a light absorbing filter that intentionally reduces the amount of light striking the image sensor. It is a "three stop" filter so that if the exposure would have been, say, 1/1000 sec at F2 without the ND filter, the exposure with the ND filter would be 1/125 second at F2.

Hope this helps. Good luck with your experimenting.

[getg3]

Mitch,

Gorgeous picture!

[lasercomp]

Mitch, at first I'd like to say, you take some awesome pictures. You know the picture you have in your gallery with a pelican or whatever that bird is sitting on a boat? That picture is what I am trying to do with blurring out the background. What settings did you use or was it PS doing the work?. Thanks for your input and I will try some suggestions you and Gordonsbuck offered. I will post some of my pics when I get home so maybe they can get critisized a bit.

[slejhamer]

Hey thanks to you both!

The blurred background in the heron pic was partially faked in PS, I am sad to admit. I used a gradient mask to get a somewhat realistic blur. I also used the pen tool to select the bird a few pixels at a time using channels, and then smudged the background so that the colors wouldn't halo (bleed) around the bird when I applied the blur. Not a fun exercise that I recommend... but that was going to be my next suggestion to you - if all else fails, fake it!

:D

P.S. Gordon's advice is very good!

[Dana]

Depending on the position of the subject, wouldn't the built in portrait mode work well in some of these cases?

Dana

[lasercomp]

dana wrote:
Depending on the position of the subject, wouldn't the built in portrait mode work well in some of these cases?

Dana


I am thinking the portait mode would give me the highest f/stop (lowest #) and since I am trying to do the same when switched to Av mode and the smallest I get is like 4, then that is probably what I would get in portrait mode. All the portrait mode does and please correct me if I am wrong is give a low f/stop # to attempt to focus on subject and blur out background??

[gaz63]

use full zoom, lowest f no possible, iso 50, and nd filter... this should give you about f3.0 at full telephoto, you could even manual focus too close so the depth of feild " starts too early " in effect ?

Try it

good luck
Gaz