Why does my D40 have a shutter lag when using the pop-up flash in full manual mode? There isn't a lag when shooting in any of the auto modes.
I'm shooting in single shot mode. It is a constant lag between shots.
This is highly likely due to the charging time of the flash. Depending on the camera, one of the following happens in manual (M) mode:
For #1, you will get the full recharge cycle of your flash every time. If you were in any Automatic mode, then the camera may not need to fully charge the flash and you would get a shorter lag.
For #2, the flash recharge cycle will be depending on the aperture and ISO you set. Try the highest ISO and widest aperture you have and then the opposite, to see if this is the case.
For #3, see the Custom Setting Menu on the D40, the lag will be depend on the manually chosen power setting. Try different power settings and you should see the lag change, particularly if you choose 1/32.
On some cameras, there is a setting in the setup menu which lets the camera take a shot even if the flash is not sufficiently charged. From memory, I do not recall the D40 having this.
You are using your flash on 'red eye removal' Icon: thunder+eye, put it on normal flash Icon: just the thunder.
You did not mention if it is a constant behaviour, or if it happens on continuous shooting. If the latter, then the flash's capacitor needs time to recharge before you can shoot again. This is true for manual, as well as automatic modes.
I suspect you're firing in rear-curtain sync mode, which means the flash is fired at the end of the exposure. Switch your flash mode to "auto" and I bet you'll see the delay disappear.
FYI, after literally years of being unable to figure out the lag in taking shots on my d3300 - I discovered the painfully obvious. The memory card was not fast enough for the camera. Finally replaced it with a high speed card (90mb/sec) and it shoots fast for once.