the Depth of Field (DoF) focal width is directly tied in with four parts (in order of importance):
.
Aperture setting
Focal Length
Distance to your center of focus (CoF) or distance to object (subject)
Circle of Confusion or Camera Type
If you go to DOF Master (<- click here), you can enter the respective values and get a feel for just how wide the predicted DOF will be for each shot.
You have two cameras you shot with (or will be shooting with), so you could have variable number 4 mean something, but for most folks, they only have one camera, so that particular variable should not change, once it is entered into the calculator.
Now, arguably, the Aperture setting will probably have the biggest impact on the DOF, for lenses shorter than 70mm. When it comes to the longer lenses... distance is your most operative factor.
Again, using the calculator will allow you to know in advance the parameters of the closest and furthest distances you have to work with.
Try it out and see if that is helpful. Since the plant is a subject that is NOT moving... by use of a tripod and an electronic release (<- click here), frame the image and then tighten down the tripod head adjusters so that the camera cannot move. This will allow you to make the shutter speed to go very long... and increase time of exposure in order to compensate for "stopping down" the aperture. Remember, Shutter Speed does not affect DoF.
If you are not comfortable with MANUAL Mode settings, DoF-shots should be done in Aperture Priority Mode, this will allow the camera to automatically calculate the shutter speed for your proper exposure (Ev0).
Last edited by DonSchap; 01-16-2012 at 08:56 PM.
Don Schap - BFA, Digital Photography A Photographer Is Forever
Look, I did not create the optical laws of the Universe ... I simply learned to deal with them.
Remember: It is usually the GLASS, not the camera (except for moving to Full Frame), that gives you the most improvement in your photography. flickr® & Sdi
Those types of orchids are a particular challenge. Even if they are in focus it can be difficult to find a 'pose' that works as a 2D composition. I have had little success on those myself in our local botanical garden orchid house. I think you would find it worth your time to learn to use the shallow DOF to your benefit in this case. The out of focus areas of the image can be used to help spotlight a particular feature of the flower and add a sense of depth to the image. This is especially true if you can work with color and contrast in the flower as a part of the composition. It will not be easy, but it is a good exercise in fine art or abstract photography.