Canon 5D Mark 4 Not always firing in nightclub

[yansar]

I’m having a couple issues with my camera. I have a Canon 5D Mark 4 and am shooting with a flash and diffuser inside nightclubs. When I’m taking the photo sometimes it doesn’t fire because it’s so far so it seems like it’s trying to focus on something. I thought that it used to have a red light that would be on the subject just before taking the photo, but it’s not doing that anymore (I might have changed the settings). Also when I look through the view finder the image is blurry even though the photo is in focus.

Anyways, would love some help with these so I don’t miss any moments.

[rs-eos]

What exact flash are you using?   Is it on-camera or off-camera?

For your last statement "the image is blurry even though the photo is in focus"... sounds like you need to adjust the diopter which is a small dial near the upper-right corner of the viewfinder.  See page 57 in the User Manual for details.

[deebatman316]

Are you using a Canon speedlite if so what model. Some speedlites IR AF Assist is limited to the center AF point. Also the AF Assist Beam DOES NOT WORK with AI Servo. So use One Shot or AI Focus. Note some speedlites don't use an IR Grid Pattern for AF Assist. Some speedlites utilize Intermittent Flash Firing. If a color filter or flash diffuser is used. The AF Assist Beam is DISABLED. 

[ebiggs1]

First before anything reset the camera back to default. Second keep in mind if the camera can't obtain focus it will not fire. I would set only the center focus point and use One shot and no other specialty features. In a dark nightclub a flash and a diffuser isn't a good combo if the subject is at distance. Even if the subject is close it isn't, IMHO, the best way to go. A better choice, IMHO, would be a high ISO number as the Mk IV has pretty darn good high ISO performance.

You didn't mention what lens you are using and that may have an impact on how well the Mk IV does.