What is ISO?
ISO can control how bright or dark an image is along with shutter speed and aperture, however, ISO is rather important as Image quality can be severely affected with incorrect use of this setting. ISO in basic terms controls the amount of light sensitivity on the cameras sensor.
Low vs High ISO
A large majority of cameras such as the Canon 5D MKIII (2012) for example have a lowest ISO setting of 100 and a high of 12,800, which can be expanded. Newer cameras (2017+) have even better ISO control and can be as low as 50 ISO and expand to 51,200 in the case of the Sony A7III (which is the camera I use). The lower the ISO number, the higher quality of image you will see (assuming correct exposure). The higher your ISO number the more noise you introduce into the photo as well as loss of dynamic range.
ISO 100 will provide the best image quality. The settings then double each time in what is called a 1-stop increment. Losing quality and introducing noise the higher you go. Here is a typical ISO range. 100, 200, 400, 800, 1600, 3200, 6400, 12800. There are of course values between those numbers.
Full Frame vs APS-C (cropped censor)
When it comes to wedding photography, a professional wedding photographer will have at least TWO professional cameras (1 being a backup incase of a camera failure). These two cameras will have great ISO control and be utilising a Full Frame censor which can create beautiful Images even at some higher ISO numbers (My typical range is 50 – 3200). An APS-C censor has less ISO control and as a result creates more noise in an image than a full frame camera. I personally had an APS-C camera when i started my photography journey and I never dared go past ISO 1600 as the image quality after that was horrendous. My current Sony A7III full frame camera is exceptional, Id happily capture an image at 6400 as the ISO control is brilliant. Not that I ever need to go that high as I use fast prime lenses which let in a lot of light.
How can this affect my choice in photographer?
As stated above, a professional wedding photographer will have a professional level camera with great ISO control. Think about a typical wedding for a second, apart from walking into church or having your couple photos, 80% of the day is inside. Due to being inside for most of the wedding day, the photographer is always shooting in dimly lit rooms etc so having great ISO control is very important to achieve great quality images. Couple ISO control with fast prime lenses and you have a winning combination for great quality photos. Obviously the photographer needs to be great too in order to capture the correct exposure.
Some photographers, especially those starting out in wedding photography may not have the best equipment, experience and knowledge to create high quality images, this includes hiring Uncle Bob or friends. There are even photographers who have been active for a number of years who produce poor quality Images, make sure to always review a photographers portfolio, It should be easy to spot the difference between an exceptional professional photographer and someone who likes to shoot a few weddings a year to make some extra money. Read How to find the perfect wedding photographer for tips.
I bring up amateur photographers and even some photographers who class themselves as ‘Professional‘ as typically they are not in full control of their cameras, i.e using Manual mode to set every value of the cameras ISO, Aperture and Shutter Speed. Instead they use assisted modes such as Aperture Priority, Shutter Priority and even worse Full AUTO mode. The problem with these assisted modes is the photographer is not in full control and when in dimly lit environments (80% of a wedding day) the camera adjusts each image to what ‘It Thinks’ is the correct exposure and in a lot of cases will raise the ISO to crazy high numbers. Which reading all the above and previewing the images below you can see totally degrades the image quality. If there is one question to ask a potential photographer is ‘Do you shoot in Manual?’ If they answer YES, you can be confident in the fact they know how to control every aspect of their camera which is important as they need to adjust to situations at the drop of a hat. If they answer NO, be cautious and again review their portfolio.
Professional: A photographer who is classed as professional means simply they are being paid for their work and shouldn’t be taken as a sign of their skill, quality or experience. Always review photographers portfolios, reviews, awards etc. I have personally seen people start to offer wedding photography after picking up a camera a few weeks prior and call themselves professional wedding photographers even without ever shooting a single wedding, crazy!
Examples of ISO Noise and degrading Dynamic Range.
Example of ISO in action can be seen below. The images were captured using a tripod and correctly exposed with increasing ISO. You can clearly see the image quality degrades the higher the number. Captured on a Sony A7III + Sigma MC-11 Adapter + Canon 70-200 F4L.