Depth of Field? Focus?

Re: Depth of Field? Focus?

Garrett in Victoria

>Hi Jennifer

The rule of thumb is that the higher the f stop the greater the depth of field, or in simpler terms, the more the lens diaphragm is stopped down (closed) the more is in focus.

You have at least a couple of options:

1) leave the camera on auto focus, but move it farther away. Then use the imaging software that came with your camera, or Irfanview that you can download free, to frame and crop the portion of the photo you want to keep and enlarge it to the size you require.

or

2) set the camera on manual, choose aperture priority, and set the aperture (f stop) to f11. If that works, i.e. focus and light are good, you're done. If more focus still required, increase the aperture one stop. Since shutter speed drops as aperture number increases, at some point, you might have to use a tripod, or add light.

Cheers, Garrett

Re: Depth of Field? Focus?

Bill Howatt

>Don't know about the details for your particular camera but lack of light may be causing it since it will try to open the lens up to get more light. The wider the lens opening the less the depth of field.

Can you overide any of the auto settings? On other cameras if you can set the shutter speed slower then it wouldn't open the lens as much. The ASA number may provide an option for this since the ASA number I'm familiar with was the film speed so a higher number would mean less lens opening. However, I don't know if that would give you good brightness overall.

Hopefully, you will get a more informed response. You did read the manual didn't you?

Bill

Re: Depth of Field? Focus?

Greg W. in NC

>Jennifer,

Depth of field (DOF) is controlled by your aperature. As Garrett said, you need to reduce your aperature by setting a higher F stop if you can. To get the maximum DOF, set the aperature as high as possible. Though I'm not familiar with that particular camera, you would probably do that by setting to aperature priority and then manually setting to the highest F stop you can.

You probably want to use a tripod, as setting the F stop higher lets less light in, and you have a slower shutter speed, so you need stability in the camera when taking the picture. Therefore, shutter speed doesn't really become an issue since your camera will be still.

Autofocus has little to do with it, as you want the whole bowl focused. You can move to manual focus if you want. The ASA setting basically allows the camera to be more 'sensitive' to light, but as the ASA is moved to a higher setting, you can pick up 'noise' (erratic dots) that way too, which is undesirable.

Feel free to email me if you have further questions. Good luck!

Re: Depth of Field? Focus? *LONG* *LINK*

Scott in Douglassville, PA

>Hi, Jen -

The S330 has a manual mode, but I can't tell if it's for manual focus or manual exposure setting. To manually set the aperture (the f/stop), you need manual exposure ability. If you've got it, stop the lens down (read: set the f/stop for a higher number) as far as you can and shoot. Note, there's a reciprocal relationship between aperture (the physical opening allowing light through a lens) and shutter speed when the exposure is the same; that is, for a given exposure, if you use a smaller aperature (higher f/stop), you need a longer shutter speed to get the same amount of light to the film/CCD. If you use a large aperture that allows more light through, you need less time to get the same amount of light. Confused?

The term "f/stop" comes from the fact that the number is derived from the aperture diameter and the focal length. A smaller f/stop means the ratio of focal length/aperture diameter is smaller, and therefore, that the two numbers are closer in magnitude. A larger f/stop suggests that the focal length is much greater than the aperture; therefore a high f/stop implies a small aperture.

Due to a bunch of physics and the nature of light, smaller lens openings equate to more depth of field (that is, more of the scene in front of and behind the point you're actually focussing on) is sharp. When you start in to magnifying things while shooting them, depth of field gets smaller for a given f/stop. So, if you're shooting a bowl from, say three feet, you can use a smaller f/stop than if you're shooting it from, say, 10" to get the same depth of field.

In practice, if you're got manual exposure settings, use a higher f/stop. Depending on the resulting shutter speed, you may need a tripod, or some kind of support for the camera. Experiment a bit. If your camera has an aperture priority mode (usually signified by an a_v on Canon cameras), use it - you set the f/stop, and the camera sets the shutter speed.

If you don't have manual exposure setting, back up a bit and get more light on the subject. You'll get more depth of field, and you can crop the image down in software.

If you're still confused (probably are from my explanation), read this description of f/stop.


A Tedious Explanation of the f/stop

Re: Depth of Field? Focus?

John Lucas

>Jennifer

Bill and Garrett both had some good points. Try to use manual focus if you can. Focus 1/3 of the way through the vessel. Depth of field increases 1/3 in front and 2/3's in back of the focus point as you increase the depth of field by stopping the lens down. Go to the smallest aperture you have it could be f11 or f16 or even f22 if your lucky. You will need a tripod to steady the camera because this will slow your shutter speed down.

Garret mentioned one good possibility for digital camperas and that was to back off so the immage is smaller. This increases depth of field a lot.

One last option. The close the object is to being parallel to the film plane the more depth of field you have. If you stood directly over the bowl and shot straight down you would get the whole thing in focus assuming a shallow bowl, lets say 4". When you shoot the same bowl from a low angle you would probably loose the front and back edges assuming the bowl was 10 to 12 inches wide. Does that make sense, I don't think I described it well. My latest article on Pen photography has some photos that show this very well. It is in American Woodturner, one of the last 2 issues I think.

Re: Depth of Field? Focus?

Russ Fairfield

>I am not oneof the experts here, but I took a lot of photos with a digital camera that didn't have very much in the way of manual controls of anything. But, it did have the ability to lock whatever setting it was at by partially depressing the shutter button.

I was able to cheat the auto-seting by putting a strong vertical line like the edge of a piece of cardboard to the side of the piece and about centered on it for depth. Then I let the camera lock on the edge of the cardboard, hold the shutter button part way down to lock the setting, and then move to the object and push the button the rest of the way to take the photo. It usually too a couple placements of the vertical line until I got it right, and the swing of the camera was easy to do with a tripod.

Re: Depth of Field? Focus?

Jim R

>Jennifer - Not being familiar with it, I googled the canon S330. It does have manual settings so you can use all the advice to reduce the F-stop with a resulting slower shutter speed. That is the normal procedure. A couple of uh-ohs: I believe your camera is a 2 mp with a min. f-stop of 4.7. That means it does not have a real small minimum aperture which means depth of field may not be enough for your purpose. Also 2mp is not very much which means you are limited in how much you can crop a full frame and still retain real good sharpness. I am not saying that you cannot get the depth of field you want, just that the limitations of your camera, which is a very good one I might add, may not allow it.

Re: Depth of Field? Focus?

Bruce McElhaney Spring Lake, MI

>Jenifer, as an ex-professional photographer I can give you the short answer: and that is to use more light--a lot more light. That will cause the auto-exposure system to close down the lens thereby giving you more depth of focus. Also, backing off the distance to the bowl a bit will increase the depth of focus. You can always crop in some on in the final print to correct its size. (just use make sure you use a higher than normal resolution setting) There are other and perhaps much better ways to acheive more depth of field, but this is the easy way. If these things don't do it let me know and I can go into more detail.

Great Camera

Tony - Memphis

>We have that one and the older 300 (his and hers - I got the older one). Anyway, make sure that you aren't getting closer than you should. The book gives the distances at wide open zoom and no zoom. Can't recall them right off hand. I've had great luck with this camera. Try using the zoom and playing with the macro too. I have also found that playing with the white balance settings sometimes helps.

Tony

Thank you!

Jennifer@Indy.USA

>You guys are fantastic! Thanks so much I have homework to do!

Jen :)

One more thing

steve antonucci

>I forget who (you know who you are) mentioned that in addition to the f-stop, shooting distance affects dof. Some cameras have a "macro" mode for close up work, which adjusts for this automatically. For some reason, it is usually depicted with a flower icon.

By putting it in macro mode, you should be able to "zoom" in close with all of the dof you require.

steve

Re: One more thing

John Lucas

>Steve

I hate to argue with you but macro mode on most cameras lets you physically get closer so the object fills the frame more. This will give you less depth of field.

Well actually that's only partly true. If you zoom in or get closer so the object is "bigger" you will get less depth of field.

If you shoot a bowl at the wide angle setting and then shoot it again at the telephoto setting and each time you fill the frame so the bowl will be the same size you will have the same depth of field on both shots.

I don't disagree, but...

steve antonucci

>Let's take an average hollowform/bowl- 10"?

Since I can only see the "front", I am only concerned with a DOF of ~5". While I do not dispute the reduced DOF claim, I think that the macro setting will allow the shooter to select WHICH 5" are in focus.

It should produce an image that is sharp front to back, edge to edge- for anything in that 5".

Does that make sense?

Steve

Re: Depth of Field? Focus?

John Lucas

>Russ

Very good idea. I've done that when manual focusing. sometimes it's just hard to see exactly where to focus so I will put a ball point pen or something in the set and focus on that. John

Re: I don't disagree, but...

john Lucas

>Steve

On a hollow form I would agree with you if it's a shallow piece. A John Jordan piece would be 10 to 12 Inches deep and would need to be sharp over that whole range. Bowls and Platters are where everyone has trouble with depth of field because they tend to be very deep in terms of the amount of area that needs to be in focus.

Macro mode only allows you to focus closer than normal. This does affect depth of field but like you said if all the important areas are sharp then it doesn't matter how you got there, only that you did.

Re: I disagree

Bruce McElhaney Spring Lake, MI

>Macro mode will get you closer and fill the frame, but it will result in less depth of field, not more.

Venturing further OT, but... *LINK*

Scott in Douglassville, PA

>...for an exhaustive look at depth of field across formats and into the macro realm, Bob Atkins (an optics engineer) has a good write-up on photo.net...


Depth of Field and the Digital Domain

Back to my original point...(dead horse arguement)

steve antonucci

>I never said that DOF was increased with a macro lense... Anyone that has ever used one knows that's preposterous.

What I did say is that a macro setting allows me to control where I place the "acceptably sharp" part of the image. I think this is supported (at an extremely intense level of detail by this link) by any of the participating posters to my comment.

For anyone looking to validate or disprove my claim, I offer the following experiment: take any camera with a macro setting and point it at the some flowers. Once the lense autofocuses, move back and forth very slowly, and watch other parts of the image come in and out of focus.

My whole contention was that with a macro setting, I could pick a very limited DOF, and be "sharp" in the part of the image that I cared about (the bowl for instance), and fuzzy in the part that I didn't (like a backdrop cloth). This would allow me to shoot the details of the bowl (like shape, wood grain, finish) and avoid having to edit out all the fuzzy backdrop stuff most of us crop...

dead horse.

steve