Profile pictures in low light

[JBPhotog]

+1 @Derrel for Nikon's iTTL, it really does a nice job and one can add +/- 3 stops of flash compensation should they need more or less flash illumination.

A wee bit off topic but the principles apply here.
"Early 2000's" DSLR's (Nikon) were 2.7 to 6 megapixels DX bodies with photosites the size of golf balls, camera shake was rarely an issue back then. Today's densely packed sensors like in the D500 (20.9MP) with teenie tiny photosites requires a judiciously steady hand at low shutter speeds in order to get sharp results. This phenomenon became apparent with the launch of the D800(FX 36.3 MP) and Nikon released several tech papers on minimum required shutter speeds. Long gone are the days of 1 over/the focal length for minimum shutter speed without some sort of IBIS or VR tech working its magic.

I propose the OP take their D500 and SB700 and do some ambient + flash shots to discover his/her minimum shutter speed and work up the f-stop and ISO from there to get the results they seek.

 

[Derrel]

With a short focal length lens, hand-holdable speeds are wayyyyyyy lower than with a longer lens: with a 14-24, even 3× the focal length is 1/75 second... meaning 1/160 is roughly 6x the maximum focal length at the longest setting the lens offers....so, again, back to my advocacy for lower speeds... if the OP wants to shoot at 1/160....I shot a flash assignment with my D800 and used 1/80 for 700 frames with no issues using a 28-80 lens at f/7.1

As far as shooting four-person informal flash group shots at f/4, and 1/160,and ISO 1250, I WOULD GUESS the SB600 was probably putting out roughly a 1/4 power flash pop... not anywhere near the right baseline settings, IMO.

 

[JBPhotog]

Agreed, 1/160 is cutting into the flexibility of ISO and f-stop, no need for speeds that high in low light event work. And to bolster your post further, a 21mm (equiv) lens means the shooter has to get too close to fill the frame and distortion on the edges can be an issue, I prefer the 24-70mm for this type of work. and a minimum f-stop of 5.6. Take a look at the OP's original photo, the younger boy is way out of proportion to the other people.

 

[Derrel]

Try out JBPhoto's suggestion, and see what you can hand-hold with flash and your 14-24mm zoom. On a 1.53x sensor like the D500 has, multiply the focal length x 1.53. So,24mm is 36.72... at 2x the effective focal length, that would be roughly 1/75 second ...at three times it would be about 1/125 second...

The OP could also see about using FP Synch to shoot at quite a high speed, to make the backgrounds black or very dark.

 

[Derrel]

Back when dinosaurs roamed the earth, and 15 to 20 years before Nikons had TTL flash metering capability, Nikon used to make the 45 mm f / 2.8 GN lens, and the photographer would key in his flash guide number on the lens itself and the diaphragm was directly connected to the guide number ring, so whatever distance was focused at, the aperture would open or close so that it was in lockstep with the flash Guide Number. Not by accident this lens was a 45 mm,not a 24mm, not a 28mm, not a 35mm,not a 50mm. When the photographer is too close to people, there is ample opportunity for apparent perspective distortion; when the lens length is too short there is ample opportunity for plenty of distortion. The 17-55 f/2.8 would be my lens of choice for such photography using the Nikon D500.

 

[JBPhotog]

And that 45mm GN was a pancake lens and pretty sweet, so sweet in fact Nikon produced a P version and dropped the GN function that I almost bought.

 

[Derrel]

I bought a 45-P back in 2003...it's a good lens, a modern day Tessar, only 4 elements, but with 2003-era multicoating... here is a flatbed scan of the lens, and its special bowl-type lens hood, and its chrome-colored lens cap

 

[JBPhotog]

Ooh, nice! It looks mint there @Derrel. You use it much theses days(and no I’m not prodding you to sell it to me lol)?

 

[Derrel]

Don't use it much since 2012-2014. It's a good lens for landscaoes and for people photos. The last time I used it was to exaggerate a carpeter's forearms in a location portrait. The 45mm length is actually very useful; my first-ever SLR was a 1950's Zeiss-Ikon Contaflex, which had a 45mm f/2.8 Pantar, so some of my earliest photo learning was with the 45mm length. 45mm is an excellent length for some uses.