Blitz and GN

To classify flash, there are several classifications that can be used. First, based on availability in the camera, flash is divided into a built-in flash and external. Built-in flash is flash that is included in the camera it self while external flash is flash as an addition to a camera, usually connected through the cable or to the camera hot shoe. We also can classify based on the type / brand camera. We know dedicated flash and non-dedicated flash. Dedicated flash is a flash that is made for the special features in a certain specific camera. Usually the manufacturer of the camera release a special flash for its camera. Meanwhile, blitz has a non-dedicated functions releas for general cameras irrespective ofits type / brand. This type of flash, not like a dedicated flash that has already obtain information about the camera, requires a lot of calculation. There are also the type of flash that the output power of it(GN) can be arranged and there are also which can not (fixed GN).

In photography using flash we always find many calculation about object lighting. Therefore, we will meet with what is often called the GN (Guide Number) or flash strength. In short we can say that larger flash, it will be more light and can reach a more distant object.

Basically, GN is a simple calculation of the strength of flash. It’s  usually measured with m (meters) or feet (feet).

GN is the result of the multiply of the distance and the aperture (f / stop) on a certain conditions (ISO / ASA 100/35mm/m or ISO / ASA 100/35mm/feet). For example, if we want to use flash to take a picture of a person standing on the distance of 5 m from us using a 35mm lens and we want to use f/2.8 then we need flash with GN of 14.

Film SLRs vs. Prosumer Digital Camera vs. DSLRs

One thing to remember is that the film camera and digital camera is different. And there are two type of digital camera, pocket camera (usually using additional flash) also called prosume digital camera and Digital SLR (DSLR).

The first difference, of course,the comparison of the size of the sensor/film to the lens. Because the digital camera sensor smaller than 35mm film, then we will be stuck on the comparison of different length of the lens. To get a same angle, for example the 35mm, the sensor in the camera with 1/1.8 ” will use approximately 7.5mm lens, D100 will using 24mm lenses and 10D will use a 20mm lens. This is the effective length of the lens to start the calculation using the GN flash.

Second is the zooming. At the PDC, zooming will cause changes in f / stop to be slower (large numbers) and also on using consumer zoom on the SLR / DSLR. For example, we know the lens 35-70 f/3.3-f.5. That is, the largest aperture on 35mm is f/3.3 and the largest aperture on 70mm is f/4.5. This will affect the object.

The use of zoom on the camera is usually followed with the use of the flash zoom head. Tele lens / zoom will narrow the lens scope angle and the zoom head on flash will shrink the  light dispersion of the flash in other words increase the intensity so that it can reach further. Zoom head on tele position and lens at the wide position will cause some part of your object have do not get a light, or so called vignet. Zoom head on the wide position and lens at the tele position will cause flash light can not reach the far object. That this also will happen if we pair 35mm lens on the DSLR and then we do the calculation with fixed flash using the calculation for the normal SLR cause actually the angel is equivalent to 50mm or more (depending on multiply factors). Actually does not mean there is a problem that appears, but we ‘throw’ light are just useless.