NEW YORK CITY) By DAVID POGUE (By David Pogue, NYTimes) June 16, 2005 - Predicting the future just by extrapolating from current trends can be risky business. One megabyte of memory in 1985, for example, would have cost you about $400. By 1995, the same amount cost about $35. You might conclude that memory makers will eventually have to start paying you.

Still, watching prices of popular technologies crash to earth is always exciting while it lasts. Take the highly regarded digital single-lens reflex cameras from Nikon, for example. Over the years, prices for Nikon S.L.R.'s hit $5,000 (the D1 in 1999), $4,000 (the D1H in 2001), $2,000 (the D100 in 2002), $1,000 (last year's D70) and $900 (last month's slightly upgraded D70S).

Nikon's latest data point represents a delicious addition to the line: the D50, due next week. It takes the same spectacular photos as the bestselling D70S - for a list price of $750.

(These prices are for the body only - bring your own lens. With a great starter lens, the D50 will be priced at $900. Prices online will be even lower once the camera has been on sale for a few weeks.)

Now, $900 may still sound like a lot, but these are professional cameras - or were, until amateur shutterbugs started snapping them up. And that price frees you from the teeth-grinding annoyances of everyday consumer cams.

For example, the D50 powers up in two-tenths of a second, so you don't miss shots because your camera's not ready. You don't worry about running out of battery power by lunchtime at Six Flags, either; the D50's battery lasts for weeks on a charge. (It has a 2,000-shot capacity, compared with 200 to 400 on a pocket-size consumer cam.) And a digital S.L.R. reduces shutter lag - the half-second delay after you press the shutter button - to zero.

But a digital S.L.R.'s most important advantage is that it takes infinitely better pictures than those little pocket cams. These are big, bright, sharp, professional-looking photos, with ultra-sharp subjects and gently blurred backgrounds. You can freeze motion, making a pool splash look like crystallized ice; you can shoot in the dark, leaving the shutter open to record the orange trails of car taillights; and you can fire off several shots a second, improving your odds of catching the bat meeting the ball, the cork exiting the Champagne bottle or the 5-year-old sitting still.

What you can't do with a digital S.L.R., though, is capture digital movies, compose shots using the back-panel screen (you must look through the viewfinder) or put the camera in your pocket; a digital S.L.R. is bulky. Harsh trade-offs, yes, but that's the ballgame.

Still, the explosive success of Nikon's D70 and Canon's Digital Rebel proves that millions of consumers will overlook those cons to gain the pros - and to shoot like pros. So Nikon was smart to design, in the D50, a camera that offers the same stunning photographic quality as the D70 in a more family-friendly package. (You can see some examples at here.)

What does "family friendly" mean? It would be easy to say that the D50 is just a stripped-down D70, but that wouldn't be accurate. The D50 is certainly a modified D70, but it adds as many new features as it takes away.

The lower price is a key feature. But so is the reduction of size and weight, made possible in part by a switch in memory format (from Compact Flash to SD card). In conjunction with its new, compact 18- to 55-millimeter starter lens (a 3X zoom, the equivalent of a 28- to 80-millimeter zoom lens on a film-based S.L.R.), the fully assembled D50 makes a much less intimidating-looking package than its predecessor. (It's 5.2 by 4 by 3 inches, vs. 5.5 by 4.4 by 3.1 on the D70.)

If you can afford a second lens, Nikon's new, equally compact 55- to 200-millimeter telephoto lens (equivalent to an 80- to 300-millimeter lens on a film camera) makes a great choice at $250. Its zoom picks up where the starter lens leaves off, bringing you 11 times closer to soccer goals, school plays and shuttle launchings.

The D50 also features an improved autofocus system; in sports mode (one of its six scene presets), for example, it can track a subject as it moves. The D50's rubber eyepiece is larger and more comfortable than the D70's.

The displays have been rewritten for better clarity; the confirmation message when you delete a photo, for example, now tells you not only which button to press to proceed, but also which button cancels the operation. And the scene dial's new child mode is supposed to offer a magical combination of vivid clothing colors and natural flesh tones, although the pictures are generally indistinguishable from those of the auto setting.

The four-way controller's left and right arrow buttons now summon the previous and next photos. (On the D70, it was the up and down arrows, which always felt wrong.) Zooming in on a photo is still an awkward two-handed procedure that should send Nikon back to the drawing board - but at least on the D50, you can scroll through your pictures at the same magnification level, without having to rezoom each one.

So Nikon giveth, but it also taketh away - in this case, a bunch of tweaky features that nonprofessionals, it believes, won't miss. The D50's fastest shutter speed is 1/4000th of a second (slower than the 1/8000th of the D70). You can't choose any I.S.O. (light sensitivity) settings between 800 and 1600. The D50 can't drive a wireless flash attachment, as the D70 can. And the D50 lacks its predecessor's compositional grid option for the viewfinder, clip-on plastic screen protector and depth-of-field preview button. (The D.O.F. preview button closes down the lens aperture before shooting to give you an accurate view of what foreground and background elements will be in or out of focus at the selected aperture setting.)

In most cases, Nikon was right; for the amateur, most of these omissions are of advanced, fussy or obscure features. But in two cases, Nikon slipped with its scalpel, hacking off features that you may indeed miss in everyday shooting.

First, the burst mode captures only 2.5 frames per second, down from 3. That may not seem like a radical difference. But when you're trying to snap just the right instant in a skydiver's flight, the dog's trick or the children's ride on the Tilt-a-Whirl, every little frame helps.

Second, the L.C.D. status window on the top of the camera is no longer illuminated, which means you can't read it in dim light. To change flash, ISO or white-balance settings, for example, you're supposed to turn a dial - but without being able to see the status display, you have no idea how far you've cycled through the choices. (Note to D50 buyers: keep a keychain flashlight in your camera case. Note to Nikon: O.K., fine. Put the backlight back in, and raise the price 85 cents.)

Sold on the idea of a digital S.L.R. but not sure which one to buy? If you already own lenses for a certain brand, well, then, your decision is made. (Technical note: Remember though, that because a digital S.L.R.'s sensor is smaller than a frame of 35-millimeter film, traditional lenses act as though they are 1.5 times as long when they are mounted on a digital camera body. A 200-millimeter lens, for example, will give you an effective focal length of 300 millimeters.) )

Here are the D50 and the two current market leaders in a nutshell. (Pentax and Olympus also make sub-$1,000 digital S.L.R.'s.)

NIKON D50 Smaller, lighter and easier to use than the D70. The status-panel back light is the most serious missing frill. Price, with lens: under $900. (Discounting online hasn't yet begun.)

NIKON D70S Greatest photographic flexibility. Loaded with features that come in handy, if only occasionally. Best battery life (2,500 shots per charge). Wireless flash option. Awkward playback controls, slow U.S.B. transfer. Online price, with lens: $1,120.

CANON DIGITAL REBEL XT Highest photo resolution (8 megapixels, vs. 6.1 on the Nikons), yet least expensive. Shortest battery life (600 shots) and smallest screen (1.8 inches vs. 2.0 on the Nikons). Inferior starter lens. Awkwardly shrunken handgrip. Online price, with lens: $835. (The older, slower, larger original digital Rebel is still available, too, for as little as $660 online.)

The prices of digital S.L.R.'s haven't finished their long, slow descent from the stratosphere. He who waits longest, pays least - but misses out on a lot of spectacular photo ops. In the meantime, the Nikon D50 is a great camera, a mouth-watering option for the family amateur who wants to take professional pictures.