There’s been a lot of negative chatter on the Internet in the last several months about the Nikon SB-900 and its "thermal cut-out" feature which causes the flash to suddenly shut down when it overheats during heavy usage. Wedding photographers, in particular, have raised the loudest concerns about the flash cutting out at inopportune moments, such as during the all-important cutting of the cake during the reception.

At NY Fashion Week last September, I ran into a photographer who was also frustrated by the thermal cut-out feature and while I sympathized with him, I hadn’t experienced the problem when testing the flash for my August PDN review, or while shooting at Fashion Week.

Since a combination of factors contributes to increased heat in the flash unit, there are no hard and fast rules about how many images can be captured before the temperature warning indicators peak and the flash stops working. First on the list is that the SB-900, the most powerful Nikon Speedlight to date, uses more energy when firing than Nikon’s other strobes, including the SB-800 and the SB-400. The latter also has the thermal cut-out feature but because it uses a lot less power than the SB-900, you’d have to really work hard to have the cut-out kick in.

Cutting Out
While it comes as no surprise, Nikon explains that the SB-900’s internal temperature will rise significantly (and the temperature indicators will go from low to high sooner) when:

• Shooting at fast, short intervals
• Shooting at wide angle
• Using multiple full flash output
• Using daylight sync mode in high ambient temperatures or under direct sunlight

As expected, the SB-900 will heat up faster if you’re bouncing the flash off a high ceiling, shooting at full or near full power, etc.

While all that may make sense technically, it’s kind of like driving a Maserati that will only go short distances at 100+ mph. Still, having the thermal cut-out feature helps prevent your Speedlight from being toasted – "to prevent the degradation of components, beginning with the flash head” – and that’s not a pretty sight, especially for a $500 piece of gear.

Contrary to a few theories by photographers on various websites, when asked whether the type of batteries used affect the thermal cut-out point, Nikon responded that “There are no reported differences as long as any of the following types are used in both the SB-900 and the optional accessory battery pack SD-9 (which holds a total of 8 AA batteries):”*

• Four 1.5V LR6 AA alkaline-manganese batteries
• Four 1.5V FR6 AA lithium batteries (select Lithium batteries feature internal temperature regulation which can limit electrical output when overheating is detected)
• Four 1.5V ZR6 AA nickel-manganese (Panasonic AA Oxyride) batteries
• Four 1.2V AA Ni-MH rechargeable batteries

*Also note that batteries should be used in sets of 4 of the same type.

If you’ve been caught short when using the SB-900, one option is to turn off the thermal cut-out feature. The three-level temperature gauge will still show the increased levels and the warning beep (if you have that option turned on) will still sound, but you can keep on shooting, with the understanding that you may risk frying the flash.