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View Full Version : Filters and Large(r) Apertures... Help

seandavid
20-Jun-2017, 20:33
Let's preface this by letting you all know (which you'll soon figure out) that I'm terrible with numbers.

I've been loosely trying to figure this out for a while, but thought I would ask on here, as I've had good luck before. Now, let's see if I can explain this properly...

I'm wanting to shoot one of my lenses in the F2.5- F/4 range on bright days (summer is actually here, apparently). Normally, this isn't my bag, but I'd like to give it a shot.

The problem I have (being pretty inexperienced with all the calculations...and math in general... and LF... and...) is figuring out how to compensate with my filters with the limited shutter speeds of my lenses (highest being 1/1000 on my speed graphic , and lowest being 1/400 on my Rodenstock).

I tried to experiment on my digital camera, but reducing the shutter speed according to full stop increments left things under-exposed. I'm sure I'm doing something wrong.

Ok, I guess my question is this (if you've made it this far)...

Example:

-Meter reads at 1/4000 at F/2.5

-I want to keep the aperture at F/2.5 (Don't judge me)

-My highest available shutter speed is 1/1000

-I have a 10stop filter and a 6 stop filter available to me

-What the heck do I do?

Did that even make sense?

brucetaylor
20-Jun-2017, 20:53
6 stop ND filter, your shutter speed is 1/60 @ f2.5
4000-2000 1 stop
2000-1000 2 stops
1000-500 3 stops
500-250 4 stops
250-125 5 stops
125-60 6 stops
And you are good to go.

Leigh
20-Jun-2017, 20:55
Example:
-Meter reads at 1/4000 at F/2.5
-I want to keep the aperture at F/2.5 (Don't judge me)
-My highest available shutter speed is 1/1000
-I have a 10stop filter and a 6 stop filter available to me
-What the heck do I do?
One stop equals a change in shutter speed by a factor of 2.
So going from 1/4000 to 1/2000 is 1 stop; from 1/2000 to 1/1000 is another stop for a total of 2 stops.

You need a 2-stop ND filter.

To use your 6-stop ND filter you must drop 4 more stops, thus:
1/1000->1/500, 1/500->1/250, 1/250->1/125, 1/125->1/60

So shooting 1/60 @ f/2.5 should work provided the metered light level is the same.

- Leigh

seandavid
21-Jun-2017, 14:37
Thanks, guys.

I did some tests, and I guess my filters are not exactly what they say. The 6 stop is a 7 stop, and the 10 stop is a 10 and 1/3 stop.

Thanks again!

xkaes
21-Jun-2017, 15:14
Just a couple of questions:

1. How are your ND filters marked, ex. ND6X, 3.0ND, 0.9, or ?

2. How did you determine their "actual" transmission? Was it with a camera meter or hand-held meter?

Leigh
21-Jun-2017, 17:18
I did some tests, and I guess my filters are not exactly what they say. The 6 stop is a 7 stop, and the 10 stop is a 10 and 1/3 stop.
Unless you have some really good optical test equipment, I suggest using the manufacturers' specs.

Very few filters or films are flat across the visible spectrum.
They tried to tailor the density based on the response characteristics of film.

- Leigh

jp
21-Jun-2017, 17:38
You can adjust your digital camera to work in half stop or third stop increments. perhaps half stop increments would help you understand it. The math is simple but important. Easily conquered with some practice.

I shoot FP4+ on bright summer days because it's a lot slower than my normal film (tmy2).

seandavid
21-Jun-2017, 23:16
Just a couple of questions:

1. How are your ND filters marked, ex. ND6X, 3.0ND, 0.9, or ?

2. How did you determine their "actual" transmission? Was it with a camera meter or hand-held meter?

They just say 10 stop and 6 stop on them (respectively). They're from a company called Breakthrough Photography https://breakthrough.photography/products/x4-neutral-density?variant=30850759697

My test sure wasn't scientific. I used my digital camera. I just metered a scene... meter read 1/1000 at F/4. Took a shot without the filter, Then threw on the 6 stop filter and reduced the exposure by 6 stops. It was dark. I then reduced it until the exposure (here's where it gets real, ummm "scientific") visually looked the same as the shot without the filter (which was a 7 stop reduction).

xkaes
22-Jun-2017, 05:37
Given the prices they charge for their ND filters, you deserve an accurate filter, as well as a free night at a luxury hotel.

Your test methods leave a lot to be desired but since I don't know your gear, all I can suggest is to put your camera on a steady support. Then meter a blank, midtone scene, such as a gray card or evenly illuminated wall -- with and without the ND filters. Hopefully your camera gives you some sort of f-stop and shutter speed readout that you can compare. Without that, I'm afraid you are just using your eyeball -- not too accurate.

Leigh
22-Jun-2017, 07:48
I used my digital camera. I just metered a scene...
Digital cameras are less than worthless for objective analysis. They're deceptive and manipulative.

They take a meter reading, then manipulate it to achieve the "best" appearance assuming a human subject.

Absolutely invalid for any reliable testing since they don't tell you what the algorithm is.

Get a hand-held exposure meter, preferably of the vintage variety though it really doesn't matter.
Use a sunlit white wall as the subject, standing where your shadow is not in the metered area.
Meter the wall without the filter, then with.

- Leigh

seandavid
22-Jun-2017, 08:43
Given the prices they charge for their ND filters, you deserve an accurate filter, as well as a free night at a luxury hotel.

Your test methods leave a lot to be desired but since I don't know your gear, all I can suggest is to put your camera on a steady support. Then meter a blank, midtone scene, such as a gray card or evenly illuminated wall -- with and without the ND filters. Hopefully your camera gives you some sort of f-stop and shutter speed readout that you can compare. Without that, I'm afraid you are just using your eyeball -- not too accurate.

Haha, yes. They are pricey and only one of the reasons I can't afford to stay in a luxury hotel.

Thanks for the tip. I'll try this method next and see what comes of it. And yes, my eyeballs have a lot to be desired.

seandavid
22-Jun-2017, 08:48
Digital cameras are less than worthless for objective analysis. They're deceptive and manipulative.

They take a meter reading, then manipulate it to achieve the "best" appearance assuming a human subject.

Absolutely invalid for any reliable testing since they don't tell you what the algorithm is.

Get a hand-held exposure meter, preferably of the vintage variety though it really doesn't matter.
Use a sunlit white wall as the subject, standing where your shadow is not in the metered area.
Meter the wall without the filter, then with.

- Leigh

I agree 100% re. digital cameras. I just don't want to experiment with actual film.

I am using a dedicated light meter. Always. Just taking the reading off of that and adjusting the settings on my camera.

I'll definitely try the method you described.

Thanks for your help and input!

Leigh
22-Jun-2017, 08:51
I agree 100% re. digital cameras. I just don't want to experiment with actual film.
The problem with digital cameras is they don't always give you the same information.

Film always responds the same way to the same conditions.

Admittedly, testing with film costs money, which is why I suggested a hand-held exposure meter.

- Leigh

xkaes
22-Jun-2017, 08:54
If you are using a hand-held, reflectance meter, a little caution is in order. Since it is an ND filter, if you simply hold the filter in front of the meter, some extraneous light might hit the meter's sensor -- stray light from the side or reflecting back off of the filter. So get the filter as close as you can to the meter's sensor. Sometimes having four hands helps.

Jerry Bodine
22-Jun-2017, 10:19
If you are using a hand-held, reflectance meter, a little caution is in order. Since it is an ND filter, if you simply hold the filter in front of the meter, some extraneous light might hit the meter's sensor -- stray light from the side or reflecting back off of the filter. So get the filter as close as you can to the meter's sensor. Sometimes having four hands helps.

Exactly. When I tested my ND gels I used my Sinar (monorail) camera with a bellows hood in front of the camera and a filter holder located between the hood and the camera; the hood kept all stray light off the front surface of the filter, then I removed the camera back so I could use a spot meter through the camera bellows and put a darkcloth over the camera and hood to keep stray light off the rear surface of the filter. Used blue floods (to simulate outdoor lighting) evenly illuminating a white mount board. All this setup was possibly overkill, but the filter factors were all exactly what the manufacturer said they were.