I bought my first digital camera about four years ago. It was a Canon A20 - 2 megapixels. I love that camera. It’s done everything I’ve ever needed from a camera and has produced many wonderful shots of my family over the last four years.
However, I’m now at the point where I am looking for a new camera. I’d like one that can produce larger images and maybe has some more features. I’d love to get another Canon - they completely won me over with the last camera.
That is, with the exception of one feature.
The only real complaint I have about my A20 is the fact that the flash is really limited. If I take a picture across a room (even a small one) the picture comes out very dark. Of course, I could go into manual mode and hold the shutter open a bit longer, but then I risk severe blurring (I don’t want to have to carry a tripod around with me all the time).
Is there a way that I can reliably measure in a camera how well the flash is going to work and it’s range, so that I know that in my camera I will get a better flash?
Look for the flash guide number. Basically, the higher the guide number, the more intense the flash. The other important factor is film speed. The higher the number, the more sensitive the film is and the less light required for an exposure. The upshot of all this is that a high guide number and a high film speed equates to a longer distance over which the flash will be effective.
Obviously, a camera with a faster lens will require a less powerful flash. However, most small cameras compromise on the flash – it’s just not feasible to put a very powerful flash in a small camera body. So if you really want acceptable flash photos, your best bet is to get a camera with a hot shoe or at least a flash sync cord and use an external flash, possibly mounted on a flash bracket.
If you can find the “guide number” of a flash (it should be expressed in feet) a larger value means greater power. Note that the effective guide number varies with aperture; that is, the smaller the aperture at which you’re talking an exposure, the lower the effective guide number.
Um, actually we know that the guide number of a flash is the distance times the aperture. So Canon gave us everything we need to know to compute the guide number. Assume the maximum aperture of the camera is 2.0 (not likely, but it makes for easy math), then the guide number would be 27.6. So, if you set your aperture to f10.0 for some reason, you could successfully take a flash picture at a whopping 2.76 feet.
(Oh, guide number is usually computed at ISO 100. Canon’s brochure doesn’t explicitly say that. So it’s conceivable that they could be fudging if they expect you to jack up the ISO in order to take your flash pictures.)
Since all of the experts are here, and I don’t want to waste a whole, new thread on a related topic (digital cameras, or cameras in general), maybe I can make a slight hijack:
Can someone briefly explain optical lengths and/or lens sizes? Specifically, when I got my current camera, I was disappointed as hell in its so-called “zoom.” A brief explanation. I was an early pioneer with my Epson PhotoPC 500 digital camera – the model number indicated its price, and it predates the invention of the word “megapixel.” It still takes awesome photos for on-screen (low res) use, and its indoor photos and flash are superior to my current camera. In any case, this was a camera without any zoom at all. All of its photos were “life size” – by that, I mean that when I looked through the view finder, there was no zooming in or out, everything was normal, life size, and my pictures came out as framed in the viewer.
Some time ago, Apple came out with Mac OS X and then iPhoto, and it was time to get a camera that didn’t need a serial to USB adapter and third party program to get the photos off the camera. Also, it would be really, really, really good to have zoom! I ended up selecting a refurbished Kodak DC-4800 camera (3.2 mega pixels!) with a heavy basis on its supposed 3x optical zoom. As it turns out, at maximum optical zoom (I don’t use digital, which it has) is the same normal, life size frame that I had thought was minimum zoom. So at it turns out, the fscking thing has no effective zoom whatsoever! When “zoomed out” it just makes everything farther away. It still bugs me crazy to this day, and I still want a camera that does real zooming.
So, thanks for bearing that little tale. For my next camera purchase, then, what numbers do I need to concentrate on, and what do they mean?
The Kodak DC-4800 has a zoom lens with a range from 28-84mm, if it were on on 35mm camera. In actuality the lens is more like a 7-21mm, but the digital camera CCD is much smaller than a 35mm negative so it has a multiplier factor. None of that is really important, the 28-84 is imporant.
With a 35mm film camera, a 50mm lens gives you no magnification at all. A 100mm lens will bring you twice as close to the subject, 200mm will bring you 4 times closer. Your lens starts at 28mm which means it’s a fairly wide angle lens, more than most point and shoot cameras which have lenses that start around 35mm. So your camera is great for taking wide shots.
The penalty for this lens is that its largest zoom is 84mm, which as you learned isn’t much of a zoom. It will bring you less that twice as close to your subject, which doesn’t amount to much. But it’s still a 3x lens since the widest focal length is 3x as small as the longest focal length.
Most P&S cameras with a 3x lense have a 35mm - 105mm equiv. That gets you somewhat close to your subject without sacrificing too much on the wide angle end. Still, many people want that extra oomph on the wide end and so a 28mm lens is a big selling point. There are 4x and 5x zooms on compact digital cameras now that go from 35mm to 140mm or 35mm to 175mm, these are new on the market.
There are also ultrazoom cameras that have anywhere from 8x to 12x, usually starting at 35mm on the wide angle end. You can do the math on much zoom they have.
So, look for the low and high end equivilent range of the zoom. The 3x or 4x doesn’t tell you the whole story, you need to know the 35mm equivilent focal length of the lens. Most folks are happy with 35 to 105, but you don’t have to settle for that. Your 28 to 84 is more of a wide angle setup.
And to bring the topic back to flash photography, the longer zooms on the P&S cameras will also force the f-stop down to smaller apetures. Zooming out to 105, 135, 185 is great, but the lens will stop down to f11 or smaller;
the smaller apeture coupled with the distance from the camera will make for underexposed or just dark flash pictures.
So be careful about how far away the subjects of your indoor flash shots are. Even if your camera can zoom in on people thirty feet away, your flash may only be good for fifteen feet at the given apeture.
(And 28-85 is a pretty decent range for a ‘waliking around’ lense on a 35mm or DSLR.)
Focal length is the distance from the rear node of the lens to the film plane at infinity focus. Visualize a pryamid with a base the same size as the sensor/film plane and the altitude the same as the focal length. The angles of the sides are the field of view of the lens at infinity focus.
For reference this page (scroll about halfway down) has some data on common sensor sizes of digital and 35mm film cameras. Note that a lot of common consumer digicams have even smaller sensors than shown here.
Because digital cameras have many different sensor sizes it’s not practical to use the focal length to express field of view so many makers put the equivalent focal length for a 35mm camera so you have a frame of reference. It isn’t a perfect system as the aspect ratios of the frames is different but it gets you in the ballpark. Zev’s Canon A20 has a lens that is about the same as a 35-105mm zoom which is modestly wide angle to modestly telephoto.
Aperture is expressed in the diameter of the iris opening relative to the focal length. An f2.8 aperture means the aperture is 1/2.8 of the focal lenth. The advantage of expressing it this way is that a relative aperture number gives you the same exposure on any size camera.
Telemark, I know I’m picking nits but I have to disagree with how you are using the term magnification. All lenses magnify but only if you are shooting macro closups is the ratio greater than 1. 50mm is considered nominally normal because images usually look neither particularly telephoto or wide angle. For years when rangefinders were popular 35mm lenses were considered normal.
It’s also a common myth that a 50mm lens has the same field of view as the human eye. If your field of vision were that narrow you would probably not be able to safely drive a car and might even be considered legally blind.
Zev, I agree with Finagle that you should probably look at a camera with a hot shoe for an external flash. As to which one depends on how much you want to spend and how involved you want to get in the process. I currently shoot a DSLR which is pretty expensive though some new models are as low as $900 and a Canon A75 which is pretty similar to what you have now.
I can’t think of a single camera in the Point and Shoot or SLR category where the long end of the zoom only allows an aperture of f11 or smaller. My Minolta Dimage 7Hi, with a 7-50mm (28-200 equivalent) zoom allows f3.5 at the long end. And even a fairly slow 80-200mm SLR lens will usually allow f5.6 at 200mm.
Your second sentence is true enough. But usually, when a photo magazine or book trots out the “50mm = human eye” comparison, they make clear that they are not talking about the eye’s complete field of vision, but the main field of view at the centre of our field of vision, the area that we comfortably call the centre of our attention. And it’s only ever meant to be a rough analogy anyway.
The 7Hi hardly compares to the Canon A20. Your Minolta is much more advanced than the point and shoots I refer to. And there’s no comparison between a P&S and a 5.6 200mm SLR lens.
Padeye gives a good explantion; I’ve always diagreed with the ‘50mm=human eye’ as well.
And DPreview has a another examination of sensor sizes Here.
Well, the f11 is probably an exaggeration. But the point is valid and the effect is more pronounced for smaller lenses. My lil’ Sony point and shoot is a fine camera in bright light, but once you zoom, you lose at least a couple of stops of speed. Which means that at night or when taking flash photography, it’s just dismal for telephoto shots. I’ve learned to keep it wide and do my cropping in Photoshop under those circumstances.
So I guess they didn’t give us quite everything. I agree with your figuring once you make your assumptions but it’s too many assumptions to be able to compare the flash on the A20 to another flash. Especially if you have to make similar assumptions on the other flash as well.
Sure, but i’d still be rather surprised to learn that even cheap point-and-shoot cameras can’t do any better than f11 at the long end. If anyone can show me a camera* that does indeed have f11 as maximum aperture, i’ll happily concede the point.
And, no, a telephoto lens for an 8x10 large format camera doesn’t count.
Oy. The f2.0 example was just because I was too lazy to go to the Canon site and look the real number. It wasn’t that it was unavailable. And the ISO 100 assumption really isn’t all that big a jump.