*SOLVED* Baffled by ND filter test results

[parkgt]

Does white balance stay the same with or without the filters? What happens if you adjust EV back to 0?

The white balance should stay the same, that is the "Neutral" in ND. But I have observed some slight change in color cast testing some NDs.

You should be adjusting the EV back towards 0. Of course some have their reasons for shooting slightly over or under exposed.

In the long run it doesn't really mater whether a particular set is exactly on the mark as far as the f- stop reduction. You will quickly figure out based on the amount of ambient light and the brightness of the subject which of your NDs will be most appropriate for what you are trying to accomplish.

 

[Lon Denard]

The white balance should stay the same, that is the "Neutral" in ND. But I have observed some slight change in color cast testing some NDs.

You should be adjusting the EV back towards 0. Of course some have their reasons for shooting slightly over or under exposed.

In the long run it doesn't really mater whether a particular set is exactly on the mark as far as the f- stop reduction. You will quickly figure out based on the amount of ambient light and the brightness of the subject which of your NDs will be most appropriate for what you are trying to accomplish.

Good point! I guess it doesn't really matter as it's totally relative. If you have on an ND4 and you want it two stops darker, you pop on a ND16, right? Makes sense.

Funny story I asked a professional photographer what the relationship between variable aperture and ND filters was and he couldn't answer. Perhaps you can.

Every doubling of the filter is a halving of the incoming light, correct? If you install an ND2 which cuts the available light in half, does changing the aperture from F2.8 to F4 result in 1/4 off the available light or 1/8? In other words, does it move the scale from 1/2, 1/4, 1/8, etc, to 1/4, 1/8, 1/16, etc or 1/4, 1/8, 1/32, etc? Does it start one stop lower and continue one stop at a time as you change the aperture or does it now double it's light reduction?

 

[parkgt]

Mio

Good point! I guess it doesn't really matter as it's totally relative. If you have on an ND4 and you want it two stops darker, you pop on a ND16, right? Makes sense.

Funny story I asked a professional photographer what the relationship between variable aperture and ND filters was and he couldn't answer. Perhaps you can.

Every doubling of the filter is a halving of the incoming light, correct? If you install an ND2 which cuts the available light in half, does changing the aperture from F2.8 to F4 result in 1/4 off the available light or 1/8? In other words, does it move the scale from 1/2, 1/4, 1/8, etc, to 1/4, 1/8, 1/16, etc or 1/4, 1/8, 1/32, etc? Does it start one stop lower and continue one stop at a time as you change the aperture or does it now double it's light reduction?

Moving from 2.8 to 4 halves the light that was available before the change; it doesn't matter what ND it has on it or not. If you have a ND2 on it before the change you will get half as much light after. If you have an ND64 on it you will get half the amount of light as you had before the change in f-stop moving from f-2.8 to f-4.0.

 

[Chopstix Kid]

Problem figured out. Due to lighting conditions I had to run a very high ISO and that appears to be what caused it. This morning I was able to run the tests again at ISO-200 and everything aligned as expected. I'll post my test data and an overview later today. Cheers.

 

[Lon Denard]

Mio


Moving from 2.8 to 4 halves the light that was available before the change; it doesn't matter what ND it has on it or not. If you have a ND2 on it before the change you will get half as much light after. If you have an ND64 on it you will get half the amount of light as you had before the change in f-stop moving from f-2.8 to f-4.0.

So if you have an ND16 on the camera and go from F2.8 to F5.6 it's like having an ND64?

I know I'm over thinking it but I can't figure that moving from an ND4 to an ND8 AND changing from F2.8 to F4 only results in two stops! For some stupid reason, I want it to be more. Geez, thanks for your patience!

 

[Lon Denard]

So if your ambient light is 1000 lumen (just a number) and you switch from 2.8 to 4, the light that hits the sensor is 500 lumen. If you then install an ND4, it then becomes 125 lumen. However, if you then switch to F5.6 it then becomes 62.5 lumen which is 1/16th of 1000. Which is 4 stops. Gotcha.

 

[SteelFlyer]

Just for complete trivia sake, the easy way to remember the number of stops is that the ND number is equal to 2 taken to the power of number of stops. For instance 2 to the second power is 4 thus ND4 is two stops. 2 to the third power is 8 so ND8 is three stops, etc.

 

[Garritynet]

The ND numbering is a "filter factor". An ND 2 adjust the light by one stop giving you 1/2 as much light. An ND 8 adjust by three stops so one half of one half is one fourth and one half of that is 1/8 as much light. One half of that is 1/16 as much light so a four stop filter is a ND16 and so on.

If you filter out three stops of light and adjust your shutter speed or aperture by a stop in either direction you don't have to do any calculations or adjustments. A stop is a stop is a stop.

What are you metering against? If it's not against a uniform surface the meter may be trying to overexposed so as not to lose as much shadow detail. Or the other way of its too bright. Not all meters attempt to maintain reciprocity, they usually do some form of matrix metering where they want to give the best overall exposure so if you're not already testing against a flat uniformly lit surface try that.

Also a third of a stop variation isn't anything to worry about, especially on inexpensive filters. 1/3 stop might be noticeable in very low light as it can be the difference between slight shadow detail and shapeless blobs but in bright scenes where you would normally use them I doubt almost anyone can perceive the difference.