Hi,
I regularly take my K10 and my Tamron 28-75 into a country western nightclub/bar and do photography there extesnively....
The conditions are really difficult... its dark, my camera has trouble focusing half the time, there are moving lights, and people are dancing and moving around constantly..
that said I think I do pretty good with all that...
Codiac26000's tips were ireally helpful to me, althought I never ended up purchasing a WailTail, for flash diffusion I went with my uncle's product instead ( abetterbouncecard.com ) so I hope this post will pay it forward too...
Initially when I started I was shooting wide open f2.8 with ISO 1600
but not shooting RAW ( I was shooting straight to Jpeg )
for example:
Here is a larger shot of the dance floor.. shot wide open at about 1/25th.. ISO 1600
You can keep a relatively low shutter speed and stay at about f2.8 or 4.0, whatever your flash is at will freeze the action regardless of whats in the foreground... what the ISO will do is add more noise but more ambient light will come in as a result...
Here is an image stopped by the on camera flash at a lower ISO but a lower shutter speed 1/10th f2.8 ISO 500
Then I stayed at that setting never going back to ISO1600 and I would just bring the background up a stop or two in raw using the fill light setting then reapplying black..... and I have not gone back on this yet since I started doing it... so my next tip is shoot raw because the RAW image captures so much ambient light information you can work with without destroying the image....
This was shot at f2.8 ISO 500 1/10th of a second but I brought the ambient light back in using RAW
Eventually I got a more powerful flash, one that carried far past the foreground so I found it unnecessary to use a higher ISO
so lately anytime I go in I normally stay at f4.0 for depth of field... about 1/15th to 1/20th for shutter speed and I work my ISO from 100-400 and always shoot in RAW which allow me to bring out the ambient light more later on in post processing.... you can go hgher in your ISO to bring out the ambient light and that is no problem but if you are using a semi auto or auto flash remember to dial down the power or every single one of your images will be blown out completely I have a sunpak super so I normally set it at auto green mode at ISO 400, and then depending on how close or far away I am from a foreground subject I will go up or down in my ISO and keep the same shutter speed cuz I know the flash will freeze whatever... and then just bring the background light up or down later in RAW
Also if you are going to be shooting into concert light.. and are far back and are going to be using flash for illumination I find that for that strong, very warm concert light off to the side is better.. .the K10 handles mixing the flash light and the hot concert light a little better if you are not direct.... at least this has been my experience...
for example here is the flash mixing with some strong concert lighting on the performer and I am front and center... not so good...
but here is another one where I was more at an angle with the flash as a fill and at least to me I think using the flash as an angled fill into that kind of lighting is much more pleasing to the eye...
To illustrate the technique where I shoot at a lower ISO and then bring out the background in RAW I've provided 2 examples so you can see the viability if you wanted to do the same...
the original ( f4, ISO 250, 1/25th )
I could have gone much slower with my shutter to let more ambient light in because my flash was going to freeze him either way...
AFter
Here is one more......
Before ( f4, 1/15'th, ISO400 - letting in just a little more ambient light this time )
The after
If you want to see the whole set of photos they are
Here!/
Hope this helps...