Digital cameras & depth of field (my experience)

My $.02: I've had both a point-and-shoot and a digital SLR. I'll take the digital SLR hands-down. My primary reason is that I'm both nearsighted and now
getting a bit farsighted, so I depend on the autofocus plus the viewfinder (versus the LCD display) to frame photos. Your mileage may vary :-) The newer point-and-shoot take great photos (my wife has this little tiny thing that does great still photographs, also video with sound, and is about the size of a deck of cards!)
Depth-of-field is a function of aperture. The smaller the aperture the larger the depth-of-field. Depth-of-field is the "length" of things that are in focus. Narrow depth-of-field is used to take photos of flowers, etc, where you want the flower in the photo to be in focus, and don't want the rest of the photo to be in focus (as it would distract). The opposite tends to be true for things like photos of trains, where you want to see not only the locomotive itself, but all the cars and the caboose.
The problem with depth-of-field is that it restricts light, meaning you need a longer exposure time.
Most of the point-and-shoot digital cameras have limited aperture control. With a digital SLR, you pick the lens with the right depth-of-field. F/22 or greater is usually recommended for hobby photography to get the best depth-of-field, and someone used to sell pinhole lenses that were something like f100 or so.
I currently have a first generation Canon Digital Rebel (not the newer XT). For my recent trip around-the-world, I bought the new Canon EF-S 17-85 f4-5.6 IS USM lens. Here's how to parse this lens description: It's an autofocus lens (EF) that only works with the smaller digital imagers (-S). The digital imagers on most, but not all, digital SLRs are smaller than 35mm. This saves a lot of $$, but it shows up as a change to focal length. The Canon Rebel line has a multiplier of 1.6, so the 17-85 lens has an effective (35mm film camera equivalent) minimum focal length of 27mm (pretty much 'normal wide angle') and a maximum effective focal length of 135. That's a very good all-round zoom lens. f4 is the -maximum aperture- at the minimum focal length. f5.6 is the max aperture at max focal length. This determines exposure time. For the same light, you'll need more time to get the right exposure at f5.6 than you will at f4. What we care about, though, is the minimum aper ture. On this lens it's f22 (OK for depth-of-field) at 17mm, and 32 (much better) at 85mm. IS means that the lens is Image Stabilized. This is a very good thing when shooting freehand (and useless when using a tripod.) The practical effect of IS is to get sharper pictures than you could get from a non-stabilized lens, particularly in low light (such as interior photos.) Finally USM is ultrasonic motor, which is how this lens does its autofocus. That lens will cost you about $550 or more.
You can find a first-gen Digital Rebel for about $650 or less (it was $1000 including the lens when it first came out), and the newer XT (shoots much faster and has a better and bigger imager) goes for about $800. (Check out http://www.dealcamera.com for deals and current best price.) Canon makes about 50 different lenses that fit their SLRs, and all Canon auto-focus lenses fit every digital SLR (but see the comment above about the effect of smaller imagers.) The original lens that came with my Canon is nice, especially for the price, but it's nowhere near as good as this new lens. As you can probably tell by now, I'm -super happy- with both the camera and the lens.
You'll notice I haven't said a word about "megapixels". That's a whole 'nuther topic, but anything greater than 3m pixels on a relatively new camera will give you images good enough for the web or for 5x7 prints. The best place to learn about this is http://clarkvision.com . A great site for general photo info and superb camera reviews is http://www.dpreview.com . Much of what I know about digital camera technology and plusses & minuses comes from these two websites.
So this was a long note, and I'm no expert, but I've learned a lot over the last couple of years and I wanted to share.
                dave
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
++++++++++++++++++++++++++++
This is not about the depth of field of digital cameras itself but rather about how to see the results more clearly before taking the picture.
If you can, connect a television to the video output of the camera so that there is a much larger image to view when focusing and then when the lens stops down when the shutter release is pressed to the half way position the depth of field will be displayed.
It's not perfect but it is better than the small display on the camera itself.
Take plenty of bracketing shots as well, I understand the film is really cheap on these cameras.
Rob.
-----------------------
Model Railroad & Misc. Electronics
http://home.cogeco.ca/~rpaisley4/CircuitIndex.html
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
++++++++++++++++++++++++++++
This is not about the depth of field of digital cameras itself but rather about how to see the results more clearly before taking the picture.
If you can, connect a television to the video output of the camera so that there is a much larger image to view when focusing and then when the lens stops down when the shutter release is pressed to the half way position the depth of field will be displayed.
It's not perfect but it is better than the small display on the camera itself.
Take plenty of bracketing shots as well, I understand the film is really cheap on these cameras.
Rob.
-----------------------
Model Railroad & Misc. Electronics
http://home.cogeco.ca/~rpaisley4/CircuitIndex.html
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.