Should I try to swap my Nikon D70 for a D40?

I think they are worth about the same on the used market, plus or minus a few. The D70 is a much more serious camera, but quite a bit larger and heavier, and older, with a noisier CCD according to Roger Clark's measurements. Also I have a lot of manual focus Nikkor lenses which won't meter on either the D70 or the D40. They will meter on the D200 and D300, which are out of my price range new. But now that the D300 is out, used D200's are becoming affordable. So I'm thinking of buying a used D200.

The D200, on the other hand, is larger than the D70 which is already near the limit of what I can conveniently carry very often. Add the MB-D200 battery pack to run it on AA's (I hate lithium ion) and it's even bigger. So I think if I got a D200, I'd use it mostly for those occasions that needed MF lenses, remote flash, etc, or for shooting at home (which I do a fair amount). That leaves me wanting a smaller camera, and my Canon A530 P/S recently crapped out (built-in flash stopped working).

So an upward trade (sell D70, buy D200) doesn't really work, it leaves me with a cumbersome camera. Instead I'm thinking of buying a D200 and trading/cross-grading the D70 for a D40, which is very small for a DSLR though of limited capability. The limitations are less of a problem since I'd have a D200 available. What I really want is a hypothetical D400 with a full frame sensor (priced about like the current D300, i.e. a little bit below the directly competing Canon 5D), and I figure I'll buy it when it happens since it's the last digicam I'll ever want (hah!), but I figure that's at least a year away.

Let me know if this sounds nuts.

I'm a nikon user myself. Personally, if one follows the technology has to offer, one can get really poor fast. Yes it is nice to be able to get the latest tech has to offer, but buying slr bodies nowadays is like buying PCs. Get the most of your buck if not save up.
I bought the D2h when it first came out, then there was problems with the board, autofocus etc but nikon took care of that as well (phew), then the D2x came out, then D2hs, D3 etc.....but I took no notice and still use the humble d2h. Its three years old and around 120k shutters but its still going strong. I can still manage to get around 750 jpegs on a full charge and I'm still with the original battery. So what I am trying to say is that, if it is still working why trade it? Might as well use it until it falls apart. As it is I can't really get a good resale value anyway.
Anyway all the best in your choice.....

Thanks. I guess there's two things going on:

1) I'm interested in a D200 specifically to use old tech, i.e. my manual focus Nikon lenses. The D200 itself is old tech in that it's been replaced by the D300.

2) The D40 is newer tech than the D70 but my main interest in it is that it's so much smaller. Also, the D40 and D200 both have sensor performance close to the theoretical limit for a sensor that size, so that particular aspect won't get obsoleted (by very much) through newer tech, as I understand it.

What I really want is a D3, but that's just way too expensive for my purposes. Even the D200 is pushing it in terms of expenditure, but I figure at this point it would keep its resale value for a while. These things don't collapse nearly as fast as laptops. I've had my D70 around 2 years and it's worth maybe 60% of what I paid for it, which isn't too bad. A laptop that I bought at about the same time is now worth about 25% of what I paid for it.

4) I think the FX format DSLR (which right now means the D3) is basically the final completion of the Nikon F series that started in 1959. There is basically not much more they can add in the framework, except continuing to make the camera smaller, less power-hungry, cheaper, etc. So once there's an affordable FX camera I really do (famous last words) think that it will satisfy me once and for all, I won't seriously desire upgrades, just like I've never especially wanted to upgrade my F3 to an F4/F5/F6. I could imagine wanting more than one such camera since I do some shooting with two-camera setups, but that's a different matter.

Anyway, thanks for the thoughts, and I agree that the D2h is a great machine and I'd consider it a good alternative to the D200. But I think a D200 is somewhat cheaper.

I think the most important aspect is getting the right body lense combination that suits us. Getting something less would leave one unsatisfied and thus regret comes into play. On the other hand budget is important and D200 is a nice body that have the necessary programmability IMO.
As for a D3, well its on my wish list. In fact it still cheaper than what cannon has to offer. I have invested quite a sum for prime nikon lenses and I am happy that I have taken the right route as lenses do not change as fast as bodies do.
I wouldn't recommend getting a 2nd hand body unless its from nikon themselves. I have bad experience with 2nd hand bodies (D100 and F5) that I stay clear from them. Bodies being electronics and mechanical in design tend to fail at sometime. Its always best to get new but again budget do come in play.....

I have a D40, and it is my first DSLR. I don't have experience with the other cameras mentioned.

I must say that I am very happy with it. It is light enough that I have taken it on daywalks and it has excellent battery life. It has a simple, intuitive interface and is simply a joy to use.

If you're looking for negatives, I would give the following:
-no bracketed exposure
-occasionally the autofocus can get confused and won't focus on anything
-if you're publishing, the 6mp of the D40 may not be accepted by some people/authorities (I didn't expect that I would be publishing but it has proved a PIA!)
-I have also read that it can't take certain kinds of leneses.

You should bear in mind that a lot of the old manual focus Nikkor lenses are not up to the standard of the D200 image sensor. Both the resolution and the anti reflection coatings are just not good enough. There are a few exceptions of course. IMO, It seems like a bit of a waste to spend all that money on a d200 just to use with your manual lenses and if it's too heavy for your everyday needs.

Here's a crazy idea: buy a canon eos 350d/rebel which you can pick up for very cheap now and buy a nikon adapter for it. This will meter with your manual nikon lenses (with stop down metering) and is also very small and light. If you replace the d70, go for the D40x since this uses a much newer 10mp sensor whereas the d40 uses the dated 6mp sensor from the d100 and d70.

The Canon idea is interesting, I've heard of it but never really looked into it. Do those adapters really work? Do they have problems focusing to infinity or anything like that?

The D40 uses a 6mp sensor similar to the D50, which is a generation newer than the D70 sensor (and close to a full stop less noisy) and two generations newer than the D100 sensor. I think I'd want it over the D40x because the larger pixels work better in low light. Also the D40 costs a lot less.

The MF lenses I'm most interested in using are 1) 35/1.4, 2) 105/1.8, 3) 180/2.8. These are around 150 bucks each used but the AF versions would be at least 5x more. I missed a chance to get a 300/2.8MF for 450 bucks. The current AF-VR version is around 4K. But I'm probably better off without it.

I use the adapter on my EOS 20D and it works very well on aperture priority if you can live with stop down metering. Infinity focus is preserved. My adapter is a very cheap $10 model and I haven't noticed any problems with it. You can buy really expensive models if you want. I think it's ironic that the cheaper nikons can't meter with manual lenses but the canons can. Do check compatibilty before buying a 350d though (don't just take my word for it)

I definitely read that the D70 uses the same sensor as the D100 but with better image processing. I may be wrong about the D40 though.

I would avoid the 35mm f1.4. It's supposed to be very poor when used wide open. the 35mm f2 AF is better.

You might be right about the D70 vs D100 sensor, the D100 was sort of before my time so I didn't pay close attention. I'm quite sure the D40/D50 sensor is newer and better, based on Roger Clark's measurements. Thanks for the advice about the adapter. Maybe I'll buy one if they're just $10, and try it on a friend's Canon. Can you say where you got your adapter and who made it? The only one I see at bhphoto.com is a Novaflex that's way expensive. (Edit: Adorama has one for $50 but that's still a lot more than $10).

The adapter was one of those cheapo generic branded ones from ebay. Like this one: http://cgi.ebay.co.uk/Nikon-Lens-to...ryZ30059QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

I guess there could be some variation in the quality of these adapters. One thing I did notice was that there is a small amount of play with the nikon lens mounted on the canon although this does not seem to affect the pictures. I expect the novaflex has no play at all.
This is one of my favorite photography websites:

http://www.16-9.net/

It tells you everything you need to know about mounting non EOS lenses onto EOS bodies. Lots of lenses are reviewed too. Check out the Zeiss 21mm review. It basically destroys anything that Canon has to offer at the same focal length. The Olympus 21mm f3.5 is also very good and much cheaper.