There is no law against a working photographer using an entry-level camera and vice versa.

However the working photographer will look for a number for things that an entry-level photographer may not.

Robust construction - will the camera wear out before it is obsolete? Can I trust it totally when on a shoot, knowing that I will not have to face a client's rage at not getting images. Blow a shoot and lose a client - working photographers must aim for a zero failure rate. Clients hold photographers responsible for camera failures.

Does the camera really fit my hands both in horizontal or vertical position? Or will I spend the next two years fighting with an awkward camera, losing shots because it is so hard to hold still?

Are the controls well placed so I don't accidentally bump them and change them drastically?

Can the menu be customized to my choices?

Is the body well sealed against the environment? I work in any weather, in any location where I am sent.

Speed - what is the interval between shots, how many shots can I take before saturating the buffer, and how quickly will it move shots from the buffer to the card. Does the camera start and respond quickly?

Is autofocus fast and positive, specially with long lenses under poor light? Can I instantly switch to manual focus, if autofocus fails?

Is the viewfinder bright and clear with all the lenses I use? Can I fully trust what I am seeing?

Does the flash sync at speeds high enough that I can use fill flash effectively out-doors? Does it work well with multiple flash setups, remote flash setups, wireless, etc.?

Is there quick access to the histogram and is exposure compensation uncomplicated to use?

Have the batteries sufficient capacity that I will never run out during a shoot? If I do run out of power, can they be changed quickly with little interruption? Do they recharge quickly? Are there over-the-counter batteries that can be bought in an emergency, or are these strictly proprietary?

Does it use cards that are available in the size and speed I need? CompactFlash still rules, but others are trying hard to catch up.

Can I use it with a GPS - a VERY handy thing when traveling. I came back from a travel shoot in the Pacific Northwest of the USA - film in this case - and had a very difficult time identifying locations. One bit of spectacular Pacific coastline is pretty much matched by the next bit of spectacular Pacific coastline. EXIF has a field for GPS data that would have made identification a breeze.

Can I use it with a WiFi transmitter? Very handy for news and sports coverage. Hard to meet deadlines when stuck in a traffic jam after a game or a race. Great to be able to relay shots in near real-time to the city desk or sports desk during the event.

Can I easily remote control the camera if needed?

Does it have an interval timer? Long timed shutter speeds?

Is the sensor large enough and of high enough quality that I can shoot with reasonably high shutter-speeds in low light without noise levels that render the pictures useless for print?

At lower speeds, will it provide the superb quality that my picky clients accustomed to medium and large format film, demand?

Can I meter through my superb manual prime lenses?

Does it have a full frame sensor so my old lenses will continue to work as they did with film, specially super-wide lenses?

Are there loads of options beyond the menu, to customize the camera to the way I work?

Are there any hidden "gotchas" that could ruin a shoot? When on a shoot, one needs to put 100% of ones attention on the content-creation aspect, letting camera operation mostly take care of itself. What one REALLY does not want to do, is to constantly have to work around bugs and bad design that are distractions.

There are probably more, but those were the first things that came to mind. You may also notice, that price was not mentioned. A working camera is expected to pay for itself in short order.

thanks Larry thats very informative. Although i'm not a professional photographer, it is my passion. thanks again

Yes, Larry's answer is very helpful. I thought I'd give the perspective of another serious amateur like you. My main points will be the features that are make-or-break-the-shot difference makers. Without repeating another post I started on whether anyone except Nikon or Canon will ever make truly pro DLSRs, the context for my thoughts is that I am waiting very impatiently for next Spring to see if Olympus finally comes through. If they don't I'll keep my E-330 because of its live view (for shooting people I'm relating to) but go over to Nikon. (I've owned two "pro" Nikon film cameras, the S3 rangefinder and F3 slr - and given away a lot of Nikon gear to a local school; I've also used Leica and Mamiya film cameras so I have a feel for pro film gear.) It was and still is much easier to buy fairly cheap pro film gear than used pro digital gear, partly because the latter becomes obsolete much faster.
There are five areas that I can see where the pro models can make a shot that could be lost otherwise.
One is digital noise, although this may be changing as some amateur cameras, like the Nikon D80, now handle noise very well. I agree with Larry that this makes or breaks a photograph. Current pro models all control noise well and many amateur DSLRs do not. One thing that reviews tend not to notice is long exposure noise, and while a camera that handles high ISO noise well will probably do the same for long exposure noise they aren't the same so this is something to check when you look at a camera.
The second area is focusing. After using so many manual focus cameras I was surprised to find how badly autofocus tends to work in low light, even in manual mode. The top models do much better.
Third is processing speed. I understand that the top Canon model can even handle the dark image that takes care of long exposure noise while the next image is being taken. That's processing power. And it doesn't get long exposure noise at exposures that most cameras would. (Nikons also do well here.)
Fourth is one that I may have missed in Larry's very comprehensive list: resolution. This is a bit more controversial with so many amateur DSLRs in the 10mp range. 10mp is actually not all that more in practice than 8mp; I think the gap is meaningul once that sensor reaches the mid teens. Obviously this is only make or break in some circumstances: larger prints than one normally makes, client requirements (for pros) and serious cropping. Personally I think the mid teens would be worthwhile. Larger? Hard to say. I already have three hard drives for heaven's sake.
Fifth, another of Larry's: the durability of the camera. My sense is that Canon and Nikon protected the "pro" feel of their top DSLRs by giving their entry level models a cheesy plastic feel (though they took very good photos). I also think that some amateur models are pretty tough (and the Pentax K10D looks very promising). Moreover you really need a backup body no matter what model you have. But with these qualifications, if you take a lot of shots the durability is clearly a make or break issue.
Currently there are amateur models that do well on at least some of these variables, but it isn't clear to me that any do well on all of them, and if I'm right about megapixels there aren't any on the market right now.

As you say, resolution is controversial, and I trod lightly. Now I will expand a bit.

I have read a number of forum postings from people saying "Why should I lay out $30,000 to $50,000 for a digital Hasselblad system with the 39MP back, when almost all my stuff goes on the web?" More and more, the web is where publication is moving. What is the point of shooting a 6400 x 4800 image and then throwing away all but the pixels needed for a 640 x 480?

Even for very large prints, the 39MP is overkill. At a print resolution suitable for viewing at reading distance, a 39MP shot will yield a print larger than 20x30. However, to see the whole shot, one needs to take a couple of steps back. At this distance print resolution can be dropped dramatically, meaning that you can use a much lower resolution camera.

Viewing distance is key. For decades, Kodak had a series of backlit photomurals above the concourse at Grand Central Station in New York City, in the USA - 18x60 FEET!! Many were done from 35mm shots. Up close, the dye clouds were the size of golf balls, but from the floor, the photos looked fine grained and sharp.

Megapixels is an easy thing to understand - noise is very difficult to quantify in a meaningful way. Most professionals would far rather have excellent pixels than more pixels. However, resolution has become the main marketing tool. Newcomers to digital want the maximum ratio zoom and the most megapixels they can for their kopecks.

Numbers sell. I look in horror at 10MP cameras with 1/1.65" sensors. There is barely enough space on such as small sensor for 4MP of clean image. Noise control needs to be so aggressive that the picture ends up almost posterized, even at low ISO settings.

Numbers also sell to photography buyers. While there certainly are art directors out there who thoroughly understand the whole photography/publishing process, many got their job because they were the owner's nephew or in similar ways. To be safe, they accept nothing less than a 22MP image for a quarter page shot in the magazine, when a 2.2MP image would reproduce beautifully at that size. Stock agencies too often demand outrageously high resolution images, realizing that their buyers don't really know what they want, but they do want more pixels than the next guy. Meanwhile newspapers are getting excellent quality, full page width pictures, from 4MP cameras like the Nikon D2H.

Noise - more accurately signal to noise ratio - is an unfortunate term. Film grain is rather aristocratic, while noise sounds like filth. At any given ISO setting, even entry-level cameras with APS-sized sensors produce images with less noise than 35mm cameras would produce grain. However, if you encounter noise, there is the impulse to immediately wash your hands and swallow an antibiotic. Some of my best shots on film, used grain as a visual gesture.

Had company market droids called noise "grain" there might be less obsession with it. When shooting film in the ISO1600 to 3200 range, grain was neither good nor evil - it simply was.

Digital photography is barely a decade old, and there is bound to be a lack of understanding. Kodak's first dSLR was about 1MP, huge and cost $13,000US. We have come a long way in that decade. Back in the 1800s, when photography was being invented it took ten years from the first image - that would not quickly fade away - to the first negative/positive print that Fox Talbot made. Almost 3/4 of a century passed before the first colour appeared, and it really did not become practical until the 1930s when Kodachrome hit the shelves. In relative terms, more than a century of analogue development has been compressed into this past decade of digital development.

Digital cameras are passing out of their adolescence into mature image capture devices. From here on in, there will be very little actual innovation, but rather refinement more or less at the pace of Gordon Moore's Law.

I wonder if this is true of long exposure noise the way it is (arguably) about high ISO noise. The latter can look like grain and there are shots that may be improved by adding noise with CS2 or some other program. However, in my somewhat limited experience - I've shot about 2000 medium long exposure shots in the last three to four months - long exposure noise is neither pleasant nor easy to deal with. The noise reduction programs I have (Noise Ninja and the CS2 utility) are worse than useless: they soften a lot and leave the noise. It has to be removed manually and if there's a great deal of it this takes too long and leaves an overly softened shot anyway. So I have lost a few shots this way. It's a bit ironic that ISO noise is called "random" and long exposure noise is called "fixed pattern" because the former looks like a (possibly pleasant) pattern and the latter like an outbreak of digital blackheads and zits (the former being minor and the latter flaming). I gather the "fixed" refers to the moment of the shot and the camera's ability to take the dark image exposure that lets it then remove (almost all) the noise.
Regarding the current topic, the better DSLRs - not all of them actually pro models - handle this kind of noise well, and many less expensive DSLRs handle it poorly.

wow, thanks for the input. after reading all this i checked most of the areas you told me about. As i stated b4 i own the E-500 from Olympus and i have to say it's an amazing camera , however i see your point about digital noise. i tried a couple of pictures with the ISO set to 1600, and the noise is visible quite easily, but in my case i don't plan on using this setting often. as for rugged construction this camera feels solid although i don't think it would do well as war correspondent's camera. anyone have any feedback for the e-500? i checked the e-330 before buying the e-500 , however i find it ugly and clumsy looking.

If I may quote myself

Quote:
Robust construction - will the camera wear out before it is obsolete?

This is the big change from film. My Nikon F3 was purchased for a single reason - that it was the least expensive Nikon there was for a working shooter. One would go through 20 entry-level cameras before the F3 even needed a routine cleaning and calibration. Of course each of the entry-level cameras would break on a crucial shoot, so not only would you be out the bucks for the camera, but you would lose a client as well, most likely. When the total cost of ownership was considered, an F-series Nikon provided the greatest economy. However, with a given lens, the picture was indistinguishable from the entry-level camera.

With digital cameras, the "film" is now the heart of the camera - the sensor. Each generation gets better and better, so all one needs is to have a trustworthy camera until the next generation arrives.

For a working photographer, the payback is extremely quick when compared to film shooting, but not in the cost of supplies - that is where the enthusiast gains. Supplies are billed to the client anyway. The savings is in time.

In a commercial studio doing photography for fliers or catalogues with film, the tabletop is styled, lit and a sheet of film is exposed. It must then go to the lab, be digitized and distributed to the agency and client and approved before the tabletop can be struck. The tripod remains in the exact spot and the lights can not be moved. Not only does this take a bunch of time, but it ties up valuable studio real-estate.

Shooting with a scanning back, or even a one-shot back, the image is transferred to the tethered computer, and the art-director or client can approve it on the spot - or ask for a reshoot with changes. When using film, if a reshoot was needed, the whole lengthy procedure would begin all over again. With the flier on the printing press, if a change had to be made with a picture, the cost would be enormous. With digital, the delay would be hardly more than minutes.

Digital not only saves studio staff time, but time all the way down stream as well. The digital shot can be sent via server to everyone concerned, it is ready for separation for printing plates the moment the image hits the computer. Dozens of people may be involved in every image that is published and the hours really do add up.

Scanning backs for view cameras are actually very inexpensive, start around 56MP and go to 384MP. Even the 384MP back costs under $18,000US, and the 56MP back can be had for under $6,500. Considering the cost per megapixel, they are very economical. They are a pain in the field, but a breeze to use in the studio. However, for landscapes of incredible quality, people do use them in the field as well.

For the enthusiast, the savings are both in supplies and in time. Now shooting as an enthusiast myself, I figure that each of the three digital cameras I have owned have paid for themselves in film and processing savings alone in well under six months. They also save me a trip to drop off the film at the lab, and another to pick it up. I closed my last fume-room two decades back, and the fun went out of personal photography. Now with the digital darkroom, the whole process has returned to me. Ink-jet prints are as good as anything I ever made in the fume-room or obtained from a top pro lab, and in spite of the cost of ink and paper, are vastly cheaper to make.

I only print what I want to see on paper - most of my work goes on the web. A 19" monitor is roughly the size of an 11x14 print so printing is fairly minimal. While it takes a day or more and often more than a box of paper and the chemistry necessary for processing to make a single portfolio quality print in the fume-room, it takes a maximum of half an hour in Photoshop, and the first print nails it. Now a run-of-the-mill, give-away print for a friend is of equal quality to the best print in my professional portfolio!