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kentcr
07-25-2005, 06:01 PM
What is the best way to control depth of field on a digital camera? Specifically how can you reduce it? I have been playing around with my first Digital camera and it has a 10 x optical zoom. It is hard to get an apature big enough to get a nicely blurry background on a close up, even with the cameras built in closeup settings. What I have found is that by using the zoom I can effectivly reduce the background focus but I still would like more. Any ideas?

Craig

eastbluffs
07-25-2005, 06:32 PM
Was just having a DOF discussion on another forum and said I'm too off topic and need to bring it here.


At lunch, I read the definition of f-stop. Simply put, its the focal length of the lense divided by the diameter of the light portal (apeture).

Read the chapter on DOF. They give 3 means of controlling it.
1. f-stop - larger apeture means less DOF
2. increase focal length - longer lenses (at same distance to subject) have less DOF.
3. distance to subject - closer subjects have less DOF.


It was more of a Digital SLR thread, and I had to stretch my memory so went to the photo books. Sounds like you're pretty aware of the physics involved. So the question would be, what Digital camera do you have and does it allow Apeture control?

speaklightly
07-26-2005, 04:32 AM
Brad-

You are exactly correct. Depth of Field (DOF) is affected by the focal length of the lens on the camera, the aperture being used, and to a somewhat lesser degree by the size of the imager, if you are using a digital camera.

Generally speaking, the larger the imager, the easier it is to have greater control over the depth of field.

In the attached photo, taken with a Pentax 1stDS using a Sigma 70-300mm lens, a blurred back ground was achieved primarily due to the long focal length of the lens. The camera uses a smaller APS sized imager, which however, is larger than most consumer point and shoot digital cameras, and the aperture used.

Sarah Joyce

jamiehs
07-26-2005, 05:47 AM
Hi, i'm new to all this, so please, be easy on me :)

I was playing with my 5400 yesterday and I was trying out different apertures and I was wondering how the camera compensates for a smaller / larger aperture and how exactly that affects the DOF, other than the size of the sensor, what other factors come into play?

I'm sorry, I just saw the teach me about Aperture thread :rolleyes:

TheObiJuan
07-26-2005, 08:20 AM
Was just having a DOF discussion on another forum and said I'm too off topic and need to bring it here.



It was more of a Digital SLR thread, and I had to stretch my memory so went to the photo books. Sounds like you're pretty aware of the physics involved. So the question would be, what Digital camera do you have and does it allow Apeture control?

Just wondering who told you "I'm too off topic and need to bring it here."
It is your right to learn, and learning about DOF certainly teaches you about aperture. So it is not really off topic. Just a specif subject within aperture.


edit: nevermind, I looked back and saw it was regarding another thread.

TheObiJuan
07-26-2005, 08:43 AM
Hi, i'm new to all this, so please, be easy on me :)

I was playing with my 5400 yesterday and I was trying out different apertures and I was wondering how the camera compensates for a smaller / larger aperture and how exactly that affects the DOF, other than the size of the sensor, what other factors come into play?

I'm sorry, I just saw the teach me about Aperture thread :rolleyes:

the aperture, focal length, and size of sensor determine DOF.

The smaller the actual focal length, as is the case with point and shoot cameras, (like 7-21mm = 35-114, or something similar to that), the greater the depth of field at the same aperture will be.
At 7mm (35mm equiv) the depth of field at f/2.8 may be from 5ft to 16ft, when focused at 5ft.
A technique for learning how to use DOF to your advantage is to learn where to focus.
If you use f/2.8 and focus at 3ft instead, and the background is not immediately behind the person, then you will get good background seperation and blur. The depth of field will be reduced to 2ft - 5ft.

With p&s cameras, the best way to get 'bokeh' in your pics is to shoot at longer focal lengths, and as low of an aperture as possible.
Something like 114 f/2.8 (usually not feasible). Take a head and shoulders portrait with that setup and you will see some good background blur.

Sadly, most cameras wont allow large apertures at longer focal lengths. There are exceptions, like the fz series.

Rhys
07-26-2005, 11:37 AM
Here are two images - or rather the same photo - before and after editing.

This is after editing. I have used a swirl but I could equally have soft-focussed the background in it.
http://sageworld.smugmug.com/photos/29838573-O.jpg

This is the image before editing. Pretty bland.
http://sageworld.smugmug.com/photos/29838574-O.jpg

This is another version that I did which didn't win a competition entitled "beer".
http://sageworld.smugmug.com/photos/27497203-O.jpg

kentcr
07-26-2005, 06:14 PM
So to answer eastblufs question I have a Kodak Z7590. It has a 6.3-63.3 optical zoom. So what I have noticed is that if I use the longer focal length and stand back a bit and have lots of distance between my subject and the background I can get a good blurry background. Unfortunatly as was mentioned above at this focal length the largest aperture I can get is f/3.7 not the f/2.8 that it is capable of at the shorter focal length. I am coming from 30 years of using an AE-1 so I feel like I am going back to photo 101. But learning new things is always fun. I do have one question. People refer to point and shoots and DSLR's. There is quite a spectrum of digital cameras out there some called "Prosumers". Can any one tell me where the Z7590 fits into this spectrum. It has alot of manual capabilities and has a LCD view finder which is kind of like looking through the lens of an SLR which is why I got it.


Craig

TheObiJuan
07-26-2005, 07:50 PM
So to answer eastblufs question I have a Kodak Z7590. It has a 6.3-63.3 optical zoom. So what I have noticed is that if I use the longer focal length and stand back a bit and have lots of distance between my subject and the background I can get a good blurry background. Unfortunatly as was mentioned above at this focal length the largest aperture I can get is f/3.7 not the f/2.8 that it is capable of at the shorter focal length. I am coming from 30 years of using an AE-1 so I feel like I am going back to photo 101. But learning new things is always fun. I do have one question. People refer to point and shoots and DSLR's. There is quite a spectrum of digital cameras out there some called "Prosumers". Can any one tell me where the Z7590 fits into this spectrum. It has alot of manual capabilities and has a LCD view finder which is kind of like looking through the lens of an SLR which is why I got it.


Craig


The 7590 would be an ultra zoom digital camera, but not prosumer.
The G6 is prosumer.
There is no control over image type, other than size, there is no WB option, really, the only option is exposure.

Don't get me wrong, it ain't a bad camera, but not a prosumer.

kentcr
07-30-2005, 06:03 AM
So what defines a prosumer camera?

TheObiJuan
07-30-2005, 10:58 AM
A camera that has a high build quality, usually a great lens, perhaps faster than usual, and or IS, it has manual controls, many, and for every asect of picture capturing.
ISO performance is usually improved, too. They have a hot shoe for external flashes, etc etc...

JTL
07-30-2005, 01:57 PM
Technically speaking...while focal length may change the apparent depth of field, it actually does not change the actual depth of field at all. This is a proven scientific fact. It is well explained here...http://www.dofmaster.com/dof_imagesize.html
Also many photographic experiments have been done to prove that this is the case...

TheObiJuan
07-30-2005, 03:59 PM
Technically speaking...while focal length may change the apparent depth of field, it actually does not change the actual depth of field at all. This is a proven scientific fact. It is well explained here...http://www.dofmaster.com/dof_imagesize.html
Also many photographic experiments have been done to prove that this is the case...


that's right, and that's why those little 5-15mm lenses on P&S digicams give so much DOF. It's great, actually. Sharp pictures are far more common. :p
Focus and recomposing doesn't make cause OOF shots.