Questions about F-Stops

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Shanec8mm
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Questions about F-Stops

Post by Shanec8mm » Sun Jun 27, 2010 10:49 pm

OK so I am researching and trying to understand the F-stops for shooting higher speed movie film outdoors. I recently bought a roll of ektachrome 100D Super 8 and shot the roll in my Minolta Autopak 8 D6. I decided to try it without a ND filter under sunny conditions, and shade. Filming in the sun the camera gave me readings ranging from 32 to 16. 32 being in the brightest conditions. In the shade I recall seeing an F-stop of around 8. I set the film of for processing and will wait to see the results when it returns this week. In the mean time I purchased a Hoya ND filter #4. Reading my Minolta owner's manual the F-stops for the Autopak 8 are from 45 to 1.8. Now if I wanted to apply the Sunny 16 rules to shooting with the ND filter should I start at the F22 and go from there, or start at F45? Example if the Minolta read an Fstop of 16, in sunny conditions, with the ND filter installed would this have been metered from F22 or from a lower f-stop setting? I just want to get a better understanding at what I am seeing and whether the camera is making the proper exposures.
One more Question. If the Minolta (ND Filter installed) gave me an F-stop value of 16 while filming at the beach, sunny conditions of course, would this be correct with the filter in place? Or should the f-stop be F11or F8? If the fstop is showing 16 can I open up another 1/2 stop and get a good exposure?

richard p. t.
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Re: Questions about F-Stops

Post by richard p. t. » Mon Jun 28, 2010 1:23 am

g'day shane,
look, its a little hard to follow your trains of thought in your post. I'll have a go.
The most important thing you need to find out is 'is my camera's light meter still giving correct exposures?'. The only way to know that is to shoot a test roll on reversal film. You can't second guess that. Sure, by contemplating the sunny 16 rule, or by using another camera you can decide if the camera's reading 'sounds about right'. But you can't know just how right without a test roll.
As for using an ND filter, no problem. Screw it on and use the camera as normal. The camera's meter will see through the nd and expose accordingly. I am not sure what nd factor the hoya #4 has. Usually one thinks of factors in terms of thirds of a stop. A full one stop factor (or three thirds of a stop) is called a '.3' So I am not sure what a #4 is. But not to worry, you can find out by simply using it on your camera and seeing the difference.
As for opening up half a stop, what was that about? Were you thinking this because a beach is a typical 'back light' situation? If so, then that is fair enough. Depends how back lit the subjects are though.
I hope some of that helps.
I run Nano Lab - Australia's super8 ektachrome processing service
- visit nanolab.com.au
richard@nanolab.com.au

bakanosaru
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Re: Questions about F-Stops

Post by bakanosaru » Mon Jun 28, 2010 7:07 am

Still photography filters often seem to use the confusing system which is only in full f-stops of 2,4,8, etc. Each doubling is a halving of the amount of light (one stop).
So a ND4 is the equivalent in cine filters of a ND6, two stops less light.

That doesn't answer your question. But if your light meter is TTL (through the lens) like most super 8 cameras adding the ND filter should not put your exposures out assuming your camera is working.

mauka
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Re: Questions about F-Stops

Post by mauka » Mon Jun 28, 2010 12:18 pm

BTW, If you want to use your cameras TTL lightmeter, it's good idea to buy grey card. It is very helpful in most situations.

Shanec8mm
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Re: Questions about F-Stops

Post by Shanec8mm » Mon Jun 28, 2010 10:28 pm

Thanks to all of you for your help here. First I should say that yes the automatic exposure works very well! I have used this camera many times with 64T. As I stated earlier I am now using Ektachrome 100D. I shot a roll on Father's day, and that is now being processed. Once it returns I will see how it turned out. The camera does read 100D film so it should be fine. I guess my real question was, after installing a ND filter, what Fstop does the camera open up from? Another words what is the starting Fstop the camera is metering from to open the aperture after the ND filter has been added? Let's say I see an Fstop of 16 after the ND filter has been installed, would this mean the starting Fstop was 32? Or does the camera start from an F22? I am using the Sunny 16 logic here but with a twist I suppose. Hopefully this makes sense to someone ha ha! I guess I also would like to find out if I can open the aperture a little more at the beach if I see an Fstop of 16, could I go to F11? Or would this bring in to much light? I like brighter images when I project them on the screen. I have used this method a few times with 64t and all looks good. I guess my lack of experience has me wondering if anything larger than say an F16 at the beach would be to much for 100D, even with a ND filter. Also I would assume that if the Nd filter opens the aperture up 2 more Fstops than 16 would be probably correct at the beach? I am not looking for exact calculations just something to gauge by when shooting in different light. The sunny 16 rule is something to look at when shooting under certain lighting conditions. With 100D is it a little different. Hope all of this makes sense. In my mind it seems too.

mauka
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Re: Questions about F-Stops

Post by mauka » Tue Jun 29, 2010 8:31 am

Shanec8mm, if your lightmeter reads f16 behind ND4 filter then correct aperture without the filter is f32.

Bakanosaru, ND4 is not same as ND6, but ND4 is the same as ND.6. The so called "cine ND filters" are also in the same scale, they are just named after their optical density: ND.3, ND.6, ND.9, etc.

bakanosaru
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Re: Questions about F-Stops

Post by bakanosaru » Tue Jun 29, 2010 11:13 am

You're right it should be ND.6=ND4

Shanec8mm
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Re: Questions about F-Stops

Post by Shanec8mm » Tue Jun 29, 2010 9:24 pm

mauka wrote:Shanec8mm, if your lightmeter reads f16 behind ND4 filter then correct aperture without the filter is f32.

Bakanosaru, ND4 is not same as ND6, but ND4 is the same as ND.6. The so called "cine ND filters" are also in the same scale, they are just named after their optical density: ND.3, ND.6, ND.9, etc.

Thank you this answers my question. f32 is what I thought the camera would be metering from. Yes the Hoya filter I am using reduces light by 2 stops.
So when I ran film on Father's day the f32 I saw in bright light was probably correct then. I was not using a ND filter when filming that day. The Minolta has never left me down so it will probably do just fine at the beach, and areas around the beach.

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