A ND filter is essentially a dark piece of glass that reduces the amount of light entering the lens. For this project, the ND filter will reduce the amount of light by 10 STOPS! Why would anyone want to reduce the amount of light entering the camera? Well, by reducing the amount of light, we can use a slower shutter speed. This will create motion blur (great for moving water). Another popular reason for using a ND filter is to use a larger aperture, creating thinner depth of field without over exposing. If you want to know more about ND filters, check out the Wikipedia article: http://en.wikipedia.org/wiki/Neutral_density_filter.
If you're ready, lets begin.
Things you will need:
- Welder's Glass/Lens Green Shade #10, <$10 on Amazon
- DSLR or camera with manual controls
- Lens or lens adapter that accepts threaded filters
- A spare UV filter. These are pretty cheap, sometimes free if you buy camera related items on sites such as Amazon
- Remote for your camera
- Lens cleaning supplies
- Black or dark electrical tape. Must be dark to prevent light leaks
- Working knowledge of long exposures
- Optional: Step down rings
Step 1: Clean Your Glass
Step 2: Positioning Your UV Filter on the Welder's Glass
Step 3: Securing Your UV Filter to the Welder's Glass
For extra security, glue the UV filter to the welder's glass, then use electrical tape. I personally wouldn't do that, as I want to be able to use the welder's glass on other lenses with different filter sizes or use the welder's glass in a welding mask.
Step 4: Finishing Touches to Your ND Filter.
Step 5: Setup Your Camera to Use the 10-Stop ND Filter
First, mount your camera to your tripod. Do not mount your ND filter yet. We need to meter the scene. Set your camera into Raw. You can do this with JPG, but it is easier to post process with RAW. Now you can compose your scene. Focus on your subject and switch your camera into manual focus or lock your focus. You will not be able to focus with the filter on.
Now we need to meter the scene. Set your camera to Manual mode. Set your aperture and iso. Lower the iso for less noise. Perform a meter reading. Your camera meter should tell you if you're over exposing or under exposing. Adjust your shutter speed so you get a proper exposure to your liking.
Adjust Exposure Settings
Next, note your shutter speed. This is your shutter speed without the ND filter. Since the ND filter reduces the amount of light by 10 stops, you can lower the shutter speed by 10 stops too to compensate for the ND filter. Most cameras will allow shutter speed adjustments at 1/3 stop increments. So every 3 clicks of your dial equals 1 stop.
Bulb Mode for Long Exposures
The only problem you will run into is your shutter speed limit. Most cameras will only allow you to go down to 30 seconds for shutter speed. If you're getting a 1/30 sec for your shutter speed without the ND filter, you will need about 32 seconds for the shutter speed to compensate for the 10 stop ND filter. To go beyond the 30 second limit, you will need to set your camera into BULB mode. To use bulb mode, you need a remote shutter release with a timer or with a remote with the hold feature. Nikons can also use the IR remote in bulb mode (press once to start, press again to stop).
You can observe your shutter speed before using the filter then calculate the appropriate shutter speed for 10 stops with a calculator too. Instructions on how to calculate shutters could be found all around the web. If you just want a handy guide for 10 stops compensation, look below.
Normal Exposure = With ND Filter
1/1000 = 1
1/500 = 2
1/250 = 4
1/125 = 8
1/60 = 16
1/30 = 32
1/15 = 64
1/8 = 2 min
1/4 = 4 min
1/2 = 8 min
1 = 16 min
2 = 32 min
Step 6: Taking the Shot
Set your shutter speed to compensate the 10 stops of light reduction. Screw on your ND filter. Press the shutter button. To reduce vibrations, you can use your in camera self timer to trigger the shutter.
If you are using a wired remote release with a timer, set your remote for the appropriate time length the shutter will be open for. Now attach the ND filter. Trigger your shutter with your remote and set the hold. If you are using a manual remote without a timer, use a stopwatch or a timer to keep track of how long your shutter should be open for. Once the time has passed. Your remote with a timer should close the shutter. If youre using a manual remote, release the hold to close the shutter. If you're using an IR remote like Nikon's, one press to open the shutter. Then press again to close the shutter.
If your photos are coming out dark, use a slightly longer exposure. But following the chart should give you an exposure thats not dark. Welder's glass is not designed to be exactly 10 stop ND filter. Thus, sometimes you might need to use a longer exposure than what the calculated times "should" be. You can also use a different shade of welder's glass if you do not need 10+ stops.
You might consider closing or covering your eye piece to prevent light leaks.
To speed up this process, turn of the noise reduction.
You might see hot spots in your photos if you are doing really long exposures, or repeated long exposures. This is your camera sensor overheating. Some cameras will warn you when your sensor is overheating.
Remotes work differently on each camera. See your camera's user guide for instructions.
Step 7: Conclusion
Thats it! Now go out there and be creative with a ND filter. There are tons of resources on the web regarding the use of ND filters and how to build filters out of different types of glass. Enjoy!
You can use step down ring adapters and attach it to other lenses instead of re-taping a another filter onto the welder's glass.
Don't trash the packaging of your welder's glass. You can reuse it for storage of your new ND filter.
You might get more lens flare than usual as the welder's glass is not coated.
Want to use the ND filter on another lens? Just remove the tape!
Depending on the type of Welder's glass you buy, you might be able to make a 15 Stop ND filter.
Crank up the ISO to use a faster shutter speed.