#1. "RE: D40 + SB600 + on camera flash" In response to Reply # 0
You will not be able to open the internal flash door if you have the SC-28 cable in the hot shoe.
Offhand, I would say no to TTL flash or the D40, but one way that would work is this:
You could add an optical trigger hot shoe accessory to fit the SB-600 foot, so that it was optically triggered remotely by any other manual flash. (The SB-800 already has such optical trigger in it, named SU-4 mode). You would have to switch the internal flash to Manual flash mode, to prevent the preflash from triggering the manual remote. That would work, the internal flash would trigger the external flash, both in manual mode. Manual users could be happy, but it may not be what you imagined.
To do two remote TTL flashes with the D40, you need 1) two flashes of SB-600 or SB-800 type, and 2) the Nikon SU-800 hot shoe controller to trigger them.
#2. "RE: D40 + SB600 + on camera flash" In response to Reply # 1
Thanks Wayne for your quick response. I noticed that when the flash is mounted on the camera the built in flash will not work. I was hoping there might be a way with the cord to maintain ttl functions. Now I have mounted an old SB16 on the camera and noticed that the built in flash will pop up, but will not fire.
I agree with your solution of a photo sensitive trigger for the remote flash, and still have the use of the built in flash in manual mode. I considered the SU800, but with only a few dollars more I can buy a complete SB800 (put it in my dream book).
#3. "RE: D40 + SB600 + on camera flash" In response to Reply # 2
>I considered the SU800, but with only a few dollars more I can buy >a complete SB800 (put it in my dream book).
Yes, adding the SB-800 would seem a good way to go. It can substitute on the hot shoe (or on a SC-17 or SC-28 cord) for the internal flash. And the SB-800 can be CLS Commander, to control the remote SB-600, all in CLS TTL mode. And of course, the SB-800 has much more power than the internal flash, so it can match the SB-600 and be really useful in a two light situation.
The shortcoming is that to be Commander, it must be hot shoe mounted, but including via the SC-17 or SC-28 cords. The SC-17 and SC-28 cords are quite short, really only about two feet effective, but a fill flash umbrella should be near the lens anyway, and the cord could do that job. You can chain two or three of the cords together for length, and some people boil them (heat and stretch) to straighten them out to about 8 feet.
SC-17 cords are plentiful on Ebay, most seem to go for about $30 including shipping. They are the same as the newer SC-28 cords, except they do not have the tiny hole to accept the flash units rotating pin lock. I have a couple of SC-17, and have been tempted to drill the little hole for the SB-800 lock pin, but have not, because it really does not seem to matter... rotating the pin lock seems to just clamp down, and there has never been any issue about it holding.
#4. "RE: D40 + SB600 + on camera flash" In response to Reply # 3
thanks again for your response. I guess for now I will use the SB600 on the camera for fill (in manual mode to prevent the preflash) and my two SB16's as the remote units with photosensitive triggers. I've been using a similar setup with my F3 for so long that the manual aspect is not a hassle for me. I can see where the future addition of an SB800 would be most welcome.