Lens shutter speed aperture and framerate confusion

J

Jay Laville

Well-known member
Hi guys sorry for another noob question, am newish still to having ability to shooting with different lenses and working out the maths to get correct exposure with 3 or 4 contributings factors if we take into account ISO as well. I read this article:

http://acg2.fullcoll.edu/FACULTY/MAHMOOD/ACG170/Exposure.html

which explains brilliantly iso, shutter speed and aperture for me which is great but I have a question. when shooting film look, I go 24p (25p pal) and shutter speed 1/50 which works fine. I understand there is a correlation between aperture and shutter speed and the two should change together in order to get best exposure, problem is If I need to change shutter speed due to changing aperture for a shallower or deeper dof will I come out of the realms of film look due to changing from 1/50 shutter speed? Am bit confused as surely cant stay at 1/50 if I have to change aperture or do I just relight the set differently to allow me to maintain aperture and shutterspeed at 1/50.... or rather than relight is this where ISo comes in as long as I dont go to high where noise level is apparent.... okay just lost myself :embarasse
 
It just depends on what you want, but you're right. If you change the aperture, the image is going to become darker/brighter whether you close/open the aperture. ISO can be a way around this, for example, if you open the aperture, lower the ISO, and vice-versa. Depending on how much light you have, and how high of an ISO you go with (higher the number, grainier the image as a rule of thumb), then yes, the image will get grainy. Shutter speed is usually the last thing you want to change for video, unless it's a stylistic choice, such as a high shutter speed for the "saving private ryan" type battle scene look.

Basically, every camera has its limtations. These are just some of them for the 7d/t2i. Lens choice can also factor in, as some allow for a lower aperture.

I hope I was able to answer your question. Feel free to ask more if you need to and hopefully I can help you out. :)
 
BryantStanton said:
It just depends on what you want, but you're right. If you change the aperture, the image is going to become darker/brighter whether you close/open the aperture. ISO can be a way around this, for example, if you open the aperture, lower the ISO, and vice-versa. Depending on how much light you have, and how high of an ISO you go with (higher the number, grainier the image as a rule of thumb), then yes, the image will get grainy. Shutter speed is usually the last thing you want to change for video, unless it's a stylistic choice, such as a high shutter speed for the "saving private ryan" type battle scene look.

Basically, every camera has its limtations. These are just some of them for the 7d/t2i. Lens choice can also factor in, as some allow for a lower aperture.

I hope I was able to answer your question. Feel free to ask more if you need to and hopefully I can help you out. :)
Click to expand...

Thanks you helped me out alot, Ill stay at the shutter speed and try adjust iso when changing aperture keeping in mind that too high will risk grainier footage, if needs be I can always light the set to allow iso to keep iso lower whilst maintaining shutter and playing with the aperture. Starting to make sense now thanks. When I want slow mo effect and shoot 60frames at 720p to put on 24p timeframe, does shutter change or still keep at 1/50 or change to 1/120?
 
Jay Laville said:
Thanks you helped me out alot, Ill stay at the shutter speed and try adjust iso when changing aperture keeping in mind that too high will risk grainier footage, if needs be I can always light the set to allow iso to keep iso lower whilst maintaining shutter and playing with the aperture. Starting to make sense now thanks. When I want slow mo effect and shoot 60frames at 720p to put on 24p timeframe, does shutter change or still keep at 1/50 or change to 1/120?
Click to expand...

Change to 120 for 60fps shooting. When shutter speed is locked into a value, your only other options are:

aperture
ISO
ND filters (darken only)
Lights (brighten only)
 
shaocaholica said:
Change to 120 for 60fps shooting. When shutter speed is locked into a value, your only other options are:

aperture
ISO
ND filters (darken only)
Lights (brighten only)
Click to expand...

ahh I get it now, Ive now graduated from the school of understanding the basics with lenses ha ha ha thanks
 
As shaocaholica points out adding ND filters of different strengths, will allow you open up your lens (have a wider aperture), whilst keeping your shutter speed constant. This is especially useful if you are filming bright exteriors.
 
If you're using aperture to control depth of field you will need to use ISO, light, or ND to control exposure. Whenever possible I try to control DOF with lens focal length...much less of a headache. Most films are shot if not at the same stop then within a small range (at least within a scene) and DOF is controlled with lenses because with film once you've setup your lights, picked your film-speed (ISO), and you never change shutter speed because you shouldn't usually, your scene will be exposed at a certain aperture value and you can't just change it without reloading film of a different speed or changing the light, both of which will usually be noticeable to the viewer.

As for what you were saying about changing values...this is called "equivalent exposure." Welcome to photography 101 :)

You should never change shutter speed for video unless it's being done for an artistic reason, and even then you typically only user faster shutter speeds for a stuttery look.

To one of the above posters: 1/120 is appropriate when shooting 60p if you plan to turn it into slow-motion, however, 1/60 is appropriate if it's going to stay as 60p or be converted to 24p in post...which is nice because you let in twice the light :). 1/50 is appropriate for 24p (well technically 1/48 but 1/50 is what these cameras do.)

Basically the best way to be shooting is this: lock aperture, light, ND, and ISO for a certain scene, and change lens focal lengths (either by zooming or changing lenses) to control DOF. Shutter speed never changes.

The way you will probably end up shooting indoors (though not ideal): lock light so your scene is properly exposed at the widest aperture you're using at ISO 100, ND (won't need them). Use aperture to control DOF, and push ISO higher when you are stopped down. Yes it will be noisy...but since your scene is exposed properly at ISO 100 which is very clean you have some leeway to push ISO. Lets say your widest aperture value for the scene is 2.8 and your most stopped down is f8...you will need to push ISO anywhere between 100 and 800. Not too bad. But seriously, the above method is MUCH better.

The way you'll probably end up shooting outside: hopefully light stays about the same, lock your ISO at something nice and clean...100 if you can. Use aperture to change DOF. If the scene is properly exposed at ISO 100 and f/16, then you'll need a whole lot of ND to get to f/2.8. A 0.9 ND filter cuts 3 stops...so one of those will let you push to f/5.6. Outdoor conditions aren't always predictable and it's sort of hard to tell what you're going to need until you get out there. I usually only carry a 0.9 ND filter with me and often that cuts too much light and I have to push ISO or end up splitting the difference on the DOF I want...not an ideal situation.

The most ideal way to be shooting is the first one I mentioned. Lock everything down and change lens focal length to control DOF. But...not everyone has the same access to glass, and sometimes you really want super super super shallow and super super super deep DOF in the same scene, which may be impossible with the range of glass you have if you're keeping aperture constant, and you'll have to resort to one of the other methods. But, if you're doing the first as much as possible, and only resorting to the other 2 when needed if the 1st fails, you'll get pretty good footage.
 
Last edited:
Hi Ben thanks for that informative post, never thought of changing dof by changing focal length instead of aperture but guess to keep same exposure constant its the done thing. Guess this is where a zoom lens helps rather than primes for quick access, would you normally pull in and out of focus with by foal length on zoom?

As for N.D I think im going to get a fador N.D, saves me buying three or four different filter glasses, this would be an all in one, and do some nice artifical night shots on sunny days for artistic purposes.
 
You must log in or register to reply here.
Back
Top