Although I have not outgrown my current DSLRs, I still dream about a new DSLR body, I dunno, doesn't cost anything to dream, I guess, :). I am using D70, Pentax DL, and Canon SD400 (carry around).
I created a list of features that I use to justify a possible purchase, and hopefully might be helpful to others who's looking into buying their first DSLR, or upgrade. The list is not in any order of importance:
- Existing gear.
- TYpe of memory card.
- Handling and feel of the camera.
- Purpose.
- Anti-shake, vibration reduction.
- Sensor cleaning feature.
- Size and resolution of LCD display.
- View finder.
- Keep your old digital P&S.
- Battery type.
1 - Do you currently own a SLR? Are the old lenses compatible with the DSLR system you are considering?
You will soon realize that your investment does not stop at camera body and the kit lens, but additional lens will soon be on your shopping list, and they don't come cheap. If you have considerable investment in quality glasses already, consider a DSLR with the same lens mount. For people who have older flashes, it actually does not make too much of a difference. Most modern DSLR incorporates a new type of TTL system that older flashes may not support. Don't throw them away, because it is possible for you to use them for off camera flash in the future.
2 - Existing memory cards: this is really not a big deal any more. The cost of compact flash and SD format are so cheap now, even if they are not compatible with the new system you are looking at, it is really not much to spend down the road. With 2GB SD card costing 20 bucks or so, this shouldn't be a limiting factor in the DSLR purchase any more.
3 - Handling: this is really more about how it feels in your hands.
Pick one up, and see how it feels. Wrap your fingers around the grip and see if it is comfortable. How does the surface of the camera feel? What about the size, is it too big, too small, too heavy?
Will your spouse/partner be using this camera, too? Get him/her to try it out also. Many newer cameras are heading towards the pettite size, some are comfortable, while some sacrifice comfort for people with larger hands - this might be important as you try to justify an upgrade later on, :~).
4 - Purpose: Define reasons why you are making this purchase.
Making larger prints? Faster autofocus performance, frames per second (sporting events)? Wildlife photography (super tele)? Perhaps going pro, or the business of Wedding photography?
I always refer to Thom Hogan's article on print size (
http://www.bythom.com/printsizes.htm) based on megapixel (MP). I have made 11x13 prints with images from my D70, I'd say I am very happy with the print. Since both of my cameras are 6mp, to make the jump based on MP, I really need to go to 10MP, since there's not a big difference between 6 and 8 MP to justify the upgrade - if that's the only feature.
Will I make bigger prints than that? I am not sure, most likely no. In my research, I am considering higher MP count mainly because I do considerable cropping on some shots. But if you see a need to make larger prints in your future, you do have to factor in higher megapixel count. But if your shots are mostly viewing on compurer screen, or occasional 5x7 (or even 8x10), 6 MP cameras will do just fine, the money saved can be put toward additional lens or other accessories (flash, tripod, bags, etc).
Regarding faster focus performance, or shutter lag, I am mainly comparing this with point and shoot digitals, and there's really no comparison. I have not used that many SLR systems, but I know between my Nikon and Pentax (with kit 18-55 mm lens), Pentax is on the sluggish side, but it should still satisfy normal every day use.
Lens availability - both new and used. I purchased the Pentax camera simply because I want to use some of the older Pentax offerings (screw mount and manual k-mount). They are cheap and widely available from Ebay and used camera stores, and some are incredibly sharp. The ability to use older Pentax screw mount lens is not limited to Pentax cameras only, Canon and Olympus both can utilize a mounting kit, and allow you to use these widely available lenses. But the idea is mainly for future growth. A camera maker may offer 50 plus lenses in their line up, but that does not mean you have to purchase everyone of them! But broader offering is a way to glance into the future of your current investment. You may not need it now, but once you move to the next level with your photographic skill, having that special lens as an available option can be important.
Wedding photography - This is one area where "image" plays an important part. Image as in the type of gear you are using. If you show up at a paid assignment with Nikon D40, which uncle Joe and a host of others might also be using, it may create an issue for future assignment, in which bride/groom may think "so and so can do this for us, he/she's got the same camera!". I know, its the final product that counts, but booming DSLR market has created a slight problem in this regard. I am not saying you should purchase a Canon Mark III, Nikon D3, that's not the case. But mid range prosumer models might be the minimum you have to purchase.
5 - Built-in stabilization/anti-shake: Since I have already bought into the Nikon line, and my next camera body will most likely be another Nikon, this does not look promising for me. If I am starting out now on a new system, I'd have to say this is a very nice feature to have. If you ever had to take your tripod with you to shoot low light scene, that extra weight and bulkiness of the tripod is really a drag. Having an in-body antishake option makes some low light shooting possible without the extra gears. The really nice thing about this feature is that it is not lens dependent, so every lens you can mount on this type of camera can take advantage of this feature. Nikon and Canon still offers vibration reduction (VR) and image stabilization (IS) with the lens, that means you have to puchase this feature with every lens - if that feature is even available! Check out Sony/Minolta (all models), Olympus/Panasonic (not all models), and Pentax (K10d, K100d) with this feature.
6 - Sensor cleaning: This is a really nasty issue. With film, since you advance the film every time you wind it, the dust/dirt have less of a chance to create an issue with your shots. But with digital sensor, since it is in a fixed position, so specks of dust will show up on your images. At this time, from what I have read on-line, Olympus' Super Sonic Wave Filter is really the only system that is useful. The other offerings at this time does not really do a good job. None of my cameras have this feature, so I can't comment on it.
Sensor cleaning is really not very hard, but it is more of an inconvenience to me. I usually detect the dust after a shoot, since I don't usually clean the sensor before each outing. If that's what I need to do, I guess I'll just have to include that function into my workflow, but it is a pain. So to me, since the effectiveness of this built-in sensor cleaning is questionable at this time, this is not really a must for me.
7 - BIG LCD display: This is pretty much the standard issue now with newer SLRs. But if you are considering an used DSLR, this might be an issue, but shouldn't be a real deal killer.
8 - View finder: I prefer the larger, brighter view finder of the Pentax DL compared to the D70. The real nice view finder I like is the old Minolta 7000 film SLR, what a difference. Check out the view finder in person. I have heard people complaining about the view finder of the Olympus cameras, it has some type of tunnel effect. I can't say I have noticed it, but I don't use that system.
9 - Whatever you do, if you already have a P&S digicam, don't get rid of it. DSLR is nice, but having a smaller carry everywhere camera means you have less of a chance of missing shots.
10 - Battery system: Most of the DSLR utilizes Lithium-Ion rechargeables. Strange thing is, it seems like everytime a new DSLR is introduced, a different battery/charger is introduced at the same time. My personal preference is using recharageable AA NiMH batteries. At this time, only Pentax is still using these batteries (except for K10d). I have had over 500 shots per charge of nicely matched high capacity AA batteries on my DL, and they are fairly easy to obtain, and in a pinch, you can run to grocery store to pick up a set.
If you have set your mind on AA batteries, there's not much choice, Pentax or older Fuji S1/S2/S3 Pro are the only choices.
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So at this time, my personal preference is to stay with the Nikon system, because of the investment I have made with Nikon equipment, it is really just simple economics; for better pricing, I have no problem going with used D80 or D200. I have 3 primary lenses that I use: 18-70 kit, 50mm f1.8 prime for portraits, and 80-200 f2.8 for tele and portraits (bought used).
This is really a hobby for me, and I do have to think about my retirement, :~). Pentax's K10D is a possibility with anti-shake, weather seal, 10MP, top notch prime lenses available (I do have to make new purchases).
Did I miss anything? Feel free to add your comments.
Yellowing issue with the SMC 50mm, pictures come out, well, yellowish. See above.
At f1.4
At f2.0
At f2.8
At f4
At f5.6
At f8
At f11
I have always wanted a dedicated macro lens, but I know if I am ready to buy one, I want a really nice one. Either the Tamron 90mm, or the Tokina 100mm, which are the top 2 contenders at this time for me. Either of these lenses will set me back about $400, so I have to save some money first, :~(
Cut out the material, and then lay it on the LCD screen one more time before you peel off the backing and expose the sticky side. 
Voila! It's on the camera, for continous protection. The hardest part of this little project is actually get the darn bubbles out, :).
