Originally posted by Jrolandphotography I would not say I completely understand the basics. I have spent quite a bit of time on YouTube and Pentax Forums, however understanding concepts and putting them into practice are two different things.
From my understanding ISO has to do with light sensitivity, aperture has to do with depth of a photo, and shutter speed is how quickly an image is capture. Is this correct?
Buy this book:
Understanding Exposure, Fourth Edition: How to Shoot Great Photographs with Any Camera: Bryan Peterson: 9781607748502: amazon.com: Books?tag=pentaxforums-20& (use affliate links from the forum however to help the site)
Basic theory:
ISO (yes sensitivity) + aperture + shutter speed = an exposure. A given calculation for an exposure will result in a particular value chosen for all three. Making adjustments to any of them without changing in a related way others will result in an exposure with more light or one with less light than the original calculated exposure (we can pretend and call this the normal exposure for now). More light = overexposure; less light = underexposure from the "normal" one calculated. Note I'm not saying how this was calculated - you can use the camera meter, the sunny 16 rule, a light meter, etc.
Assume ISO is set to 100 and isn't changing (not set to AUTO ISO).
Assume the "normal" exposure calculated was 1/125s at f/8.
If you wanted to have less depth of field and were willing to adjust aperture - if you lowered f/8 to f/5.6 you would have increased the light by 1 "stop". This could be compensated by reducing the time of the shutter opening to 1/2 (every stop is based on this factor in time) so the new "normal" would be ISO 100, f/5.6, 1/250s. The same can be accomplished by moving the ISO so you could keep 1/125s if you adjusted to ISO 50 - but most cameras won't go that low. Alternatively if the original ISO had been 1600 and the same exposure you could lower it to 800. The only value that isn't adjusted in direct multiples of 2 is aperture which is based around ratios of openings and does relate back to 2x the light but the numbers are a bit weirder. In aperture 2x = 2 stops. So f/4 to f/8 is two stops with f/5.6 between.
It's a lot to absorb.
Neutral Density filters simply take away light and add the need for more stops of light to come from the camera so you can take a bright beach and shoot a long exposure with shallow depth of field if you want. The combinations are quite large but don't get overwhelmed. Start with the image you want to make, take a benchmark "normal" shot and look at the exposure parameters the camera set for you. Let's say it was ISO 1600, f/4, 1/250s. To get a blurred effect you might want a 1/2 sec exposure lets say. Adding light from 1/250 to 1/125 to 1/60 to 1/30 to 1/15 to 1/8 to 1/4 to 1/2 is a lot of stops (7 to be exact). You could drop from ISO 1600 to ISO 800 to ISO 400 to ISO 200 to ISO 100 (4 stops), then you could change aperture from f/4 to f/5.6 to f/8 to f/11 (3 more stops) to get the effect you wanted. (These numbers are just made up btw - the ratios are right but the numbers are just pulled out of thin air.)
Another important fact: time is in ratios of 1/time - so the larger numbers are smaller values. Aperture is a ratio of size of the opening to the focal length so again larger numbers represent smaller openings with less light admitted. ISO is a value that goes up with increased sensitivity so increasing ISO makes the needed light for a given exposure go down.
Higher ISO = higher noise (to a degree)
Higher Aperture = more depth of field, likely higher sharpness to a point and then loss of sharpness due to magical fun called diffraction
Higher shutter speeds = faster action can be stopped, flashes will not sync easily over a set value based on the camera, etc.
This is only scratching the surface.