Critical Guidelines For F-Stop Numbers? (Newbie Question)

Oct 19, 2013
hi guys.just got into photography recently, and have signed up for a few courses..I have read about F stop numbers with regards to Aperture , Shutter Speed and ISO and am trying to understand it.To my understanding, an example of full stops would be as follows

Aperture 2, 2.8, 4, 5.6, 8, 11, 16, 22

( Bigger Aperture to Smaller Aperture , Cutting by Half, amount of light with each stop) (low DOP to high DOP)

Shutter Speed 1/15 , 1/30 , 1/60 , 1/125 , 1/250 , 1/500

( Slower Shutter Speed to Faster Shutter Speed , Cutting by Half , amount of time Shutter is open with each stop , thereby also cutting light by half with each stop ) (

IS0 100 , 200 , 400 , 800 , 1600 , 3200 , 6400

( Increasing Sensitivity of Light of Sensor by 2 with each stop )

1) So for example if i have a correct exposure of Ap - 5.6 , SS - 1/60 , ISO 400 and want to get shallower DOP , if i increase Ap by 2 Full Stops to 2.8 , i can either increase Shutter Speed or ISO by 2 stops to maintain exposure or increase each by 1..Correct?

In the same with , if i'm getting correct exposure with the above but want to stop some movement i'm getting, i can increase SS to 1/125 and reduce ISO by 1 stop yes?

2) Whats a good rule of thumb for Shutter Speed value when holding handheld to avoid camera shake and also to Freeze general movements of people interacting in a Family function for example (lets say im using 50mm lens on my T3i crop sensor)

3) Whats a good rule of thumb for ISO limit when shooting in a dark lit location like hotel lounge with dim lights that i will still be able to get photos which are visually usable even when printed on a 4R size(lets say im using 50mm lens on my T3i crop sensor)


Staff member
Sep 27, 2004
Punggol, Singapore
1) Correct.

if you cut down two stops from one, you either open up one stop each for the other twos, or two stops for either one of the other two.

2) General rule of thumb, 1/focal length, but also have to depend do apply correct hand held technique.

3) it depends on what is your subject, you can get away with ISO 1600 for close up of single head shot, but not for a group photos of 50 pax, and provided you do make correct exposure in the first place.
when you pull the exposure from an underexposed image, it will create even more noise.

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