The post Try this DIY Neutral Density Filter for long exposure Photos first appeared at Digital Photography School. It is written by Rick Ohnsman.
Have you seen those landscape photos where the water is silky soft, the ocean waves more like fog or the clouds have moving effects? How are they done? They are photos with a long exposure time. The shutter speed is often measured in whole seconds instead of a fraction of a second. Some even measured in minutes of exposure. In low light, you can sometimes reduce the shutter speed by reducing the aperture size and setting the ISO as low as possible.
Of course, if you work in bright light, you'll find that even with the smallest aperture and the lowest ISO, you still can't get the shutter speed slow enough to achieve the desired effect while still maintaining the correct exposure. What can you do then? It is time for a neutral density filter.
So what are they, how do they work, and how can you achieve a similar effect without immediately capturing around $ 100 US dollars for one? Read my friend.
What is ND and why use it?
On a sunny day you can look for sunglasses to reduce the amount of light in our eyes. A neutral density filter (ND) is almost the same for your camera. The "density" portion of that term refers to how dense or dark the filter might be. The "neutral" part of the term refers to the color that the filter could add to the image.
If we take color photos, we want a filter that would help reduce the amount of light, while remaining neutral in color and not putting color cast on our images. That is why we want a neutral filter that can cut off the light in situations where the ambient light is too bright to get a slower shutter speed that is higher than that that can be obtained with a combination of the lowest ISO and the smallest aperture.
Types of ND filters
The do-it-yourself approach to long-exposure photography discussed here uses a method that was never designed for photography, but allows you to try this technique "cheaply". Instead of spending around $ 100, it will cost you a tenth of that. Before I enter the ' secret ' Reveal, let's talk first about the commercial photographic ND filters that you may purchase.
Camera filters usually fall into two types:
Screw fixing – Those that screw into the filter wires on the front of your lens
Square filters – Those mounted on the lens with a filter holder.
Both are available in different degrees of density. How dark the filter is is usually described in how many "stops" light it reduces compared to an exposure without the filter.
For example, if you have made a good exposure with ISO 100, f / 5.6, 125 seconds and then after the filter is mounted, you had to slow the shutter speed to 1/2 second to get the same exposure (assuming you had left the ISO at 100 and f-stop at 5.6), that filter would be a 6-stop ND filter. (1/125 -> 1/60 -> 1/30 – 1/15 -> 1/8 -> 1/4 -> 1/2 second). The density of the filter would have reduced the amount of light by 6 stops.
You can buy both screw mounted and square filters in different "strengths" or the number of stops that they reduce the light.
For example, this 77-mm screw-mount 6-stop ND filter made by B&W runs around US $ 71, while this popular 10-stop square-mounted ND filter, the Lee "Big Stopper," currently $ 129 00 writes.
Variable ND filters – Another type of ND filter uses two polarized filters that are mounted together so that they can be rotated in a way that produces variable density. You might think that this is a better solution than a fixed ND filter, which gives the photographer the means to set the desired stops of reduction.
That would be ideal, and it works – to a certain extent.
The problem with variable ND filters is sometimes that they can produce annoying "artifacts" that spoil the image, especially with wide-angle lenses at higher density settings with less expensive variable ND filters.
More expensive variable ND filters will be better, but will of course cost even more.
The "One Weird Trick" ND filter
You've seen that "one rare trick" phrase on the web before, right? Usually it is less for a gimmick than a quality product. I have to admit, what I'm going to suggest here is a bit of a gimmick and no, won't produce the results of the more expensive photography ND filters. You need a few solutions to produce decent results and mounting it on your camera will be a bit … "funky," shall we say? The advantage is that it probably costs about 1/10 part of what a true photographic ND filter is.
So it could be a nice introduction to photography with a long exposure time, while you can explore this technique with a limited budget to see if this is for you.
So here's the big revelation …
What you are going to use is a piece of welding helmet glass.
Have you seen welders wearing helmets while working and perhaps noticed a glass "window" through which they look to observe their work? The intensity of arc welding is so great that without a way to darken the welding spark the welder would be blinded. So, a piece of very dark glass, a "density filter", is what they have in their helmets. The common denominator is that the welder wants to darken the welding arc and that you as a photographer want to darken the light that enters your lens.
What and where to get it
What you are looking for is a piece of welding glass used in a helmet. Pieces can only be purchased (as a replacement for helmets) and in various sizes and "qualities". You may have a local welding shop where you can buy it or buy it online. Here is a link to an example. The glass measures 4.5 "x 5.25" (114.3 mm x 133.35 mm), which is large enough to cover most camera lenses. It comes in classes 4, 5, 6, 8, 10, 11, 12 and 14 where the higher numbers are darker / denser.
This graph can help you determine the conversion from "grade" to the amount of f-stop reduction:
To keep things simple, you usually use a 6-stop or a 10-stop ND filter. A popular brand of ND filters is Lee. Their "Little Stopper" is a 6-stop filter and their "Big Stopper" is a 10-stop filter. So if you consult the graph, if you want a 6-stop welding glass filter, get a mark of 6 and get a mark of 8 for a 10-stop reduction.
Density Yes, neutral … not even close
This is probably the biggest disadvantage of using a piece of welding glass as an ND filter. You can get very dark pieces of welding glass, so density is no problem. The problem is that most welding filters have a very pronounced green or in some cases golden color cast.
Dedicated photography ND filters can fade a bit, but try to be as neutral as possible. You pay more for more neutral filters because you prefer to get dark without coloring. So what to do when using a welding glass filter?
Three options for dealing with the color cast
There are three things you can do to reduce the different coloration that a welding glass filter causes:
- Make a recording in Raw (what you do, right?) And adjust your white balance during editing to compensate.
- Set a custom white balance in the camera
- Make plans to make your images monochrome, where color casts are no problem.
Let's discuss these options.
The first is simple enough. Yes, when you view your photos after taking photos on the camera's LCD monitor, they look whole green. (I only used the green welder glass, not the gold). Just know that you will add a lot of from magenta, (the opposite of green), to your white balance when editing. Even then, a good color can be a struggle.
The second option, setting a custom white balance, is a good idea. To do this, mount your welding glass filter (more about this in a minute) and make an exposure of the sun or clear air. Then use the custom white balance function of your camera (consult your manual on how to do this), save that image and white balance on it, and create a custom white balance that you can record when using your laser glass filter.
The advantage of this is that image display on your LCD will be closer to a normal color.
Additional adjustments will probably be needed in post-processing, but this might help you a little when shooting.
The third option (and perhaps the best) is not to fight the color cast and plan to make your welding glass filter shots monochrome. Long exposure images have an "ethereal" appearance that is often enhanced in a monochrome image. So instead of fighting to restore a good color to that alien green image, embrace your monochrome.
If you decide that you like long-exposure photography, you are probably buying a photographic ND filter that will take much better color photos.
Calculate your exposure
Before you mount your welding glass on your lens, you just want to take your shot as usual. You also want to get a good focus. Do this first because you cannot see much with the mounted welding glass.
Once focus is obtained, switch the focus to manual. Consider placing a piece of tape on the focus ring so that it is not moved later.
Take a photo with good exposure without the filter. You will change your shutter speed once the filter is mounted, so choose an aperture and ISO. Which setting you choose depends on the depth of field that you need and also how long you want your exposure to be. The slower the shutter speed that you set here (while still getting good exposure), the longer your exposure can be with the filter.
Your subject largely determines the desired exposure time and the look that you are trying to achieve. A silky waterfall may only require a 2-second exposure, while the smoothing of ocean waves can take 30 seconds and clouds in the sky shoot away for a few minutes. There is no formula here – with trial and error you can learn what works well.
Use an app to calculate the shutter speed with the filter
Your meter will probably be useless once you have mounted the welding glass ND filter, so you must calculate the shutter speed yourself using the previous exposure information as a starting point. There are countless smartphone apps available to help you. I love the one made by Lee Filters (Android / iOS). Made for use with their Little (6-stop) / Big (10-stop) / Super (15-Stop) filters, you'll have to adjust a little if you use it with your welding glass. However, it will take you to the baseball field and you can adjust from there.
Let's use an example: you took a picture without the filter and with the ISO set to 100 and the aperture at f / 22 you can reduce the shutter speed to 1 / 15th of a second and get a good exposure. You have purchased both a class 6 (6.67 stop) and a class 8 (10 stop) piece of welding glass. What should your new shutter speed be when each filter is installed? With the help of the Lee app we can see that the 6-stop reduction would bring us between 4 and 8 seconds and the 10-stop reduction to 1 minute.
Again, plan to use these adjusted settings as a starting point. Try them out and adjust your shutter speed (or any other settings) as necessary. Certainly intend to make multiple recordings while calling things in. Photography with a long exposure time is not so fast.
Attach the welding glass filter
You have set up the camera, assembled it, focused it, enclosed everything, calculated your new shutter speed and were ready to mount the welding glass ND filter. I think I mentioned the word ' funky ' earlier in the article. used to describe how to attach your DIY ND filter to your lens. The photo here, which shows how the reversing of the lens cap on your lens and the use of rubber bands kind of represent the technique.
Something to improve it a bit – put some black tape on the edges of your welder glass. This gives the rubber bands a surface with more friction to grip. (It also helps you to hang on the glass). I'm not sure if the edges of the glass would transfer light to the image, but the tape also prevents this from happening. If your lens does not have a hood to reverse, try larger tires that allow you to stretch them back around the camera housing.
Do not attempt to disturb the focus ring when mounting the filter. You can no longer check the focus once the filter is in place.
Take the picture
If the welder's glass filter is mounted, you will fly "blindly". You will not be able to see anything through the viewfinder and maybe, if your filter is not too dark, you might see a little bit with live view if your camera supports this. You've composed and focused better before you mount the filter, as you can't see doing it now. Your meter also does not work with so little light.
Although you could use the 2-second timer to turn off recording, I would suggest an external release. You certainly also need one if you illuminate for more than 30 seconds (on most cameras ' s), in which case you put your camera in Bulb mode.
A release with which you can lock the shutter open during exposure will help a lot here. The Lee exposure calculator app also has a countdown timer. Activate this when you open and count down the shutter and beep at the end of the calculated exposure time to indicate when you should close the shutter.
You can also consider using the noise reduction function of your camera. Noise can be a problem with long exposures. The noise reduction function makes a second black image frame the same length as your first shot and then subtracts random noise or warm pixels from your image using the black frame as a reference.
However, keep in mind that the exposure of the black frame is just as long as the original shot. For example, if you take a 2-minute recording, your camera will be in for four minutes. I already told you that you don't have photography with a long exposure in a hurry.
Back in post production
You edit your long exposure photo ' s just like with any regular shot, with the big exception of that crazy color cast. There are many web resources that tell you how to correct for that cast, so I won't spend any time on this. Just know that with this welding glass technique you will never get the color as good as without the filter. I still believe that monochrome is the way to go here.
Frustrations and limitations
I have since bought a real ND filter, the 6-stop B + W that I have mentioned, so my welding glass did not use much until I had finished making this article. When taking the photos of the wind turbine, I found what I think (after some comparison tests) a glass of class 10, very dark but still not dark enough to even take a short shot of 1.6 seconds (the shutter speed I set was the best to get the hint of movement I wanted on the turbine blades.) Longer exposures simply caused the blades to disappear completely.
A side note: long exposures can be a great way to make a crowd disappear when photographing a busy urban landscape. People move and disappear during a long exposure while the static buildings and the like remain standing and appear on the photo.
To make the photo even darker, I placed a polarizer on the lens, (dropped the exposure 2 stops) and stacked the glass ND of the welder over it. It was not a good combination. Too much, as the British say, ' sneak around & # 39 ;, and I probably have slackened my attention somewhat. Also by photographing both the polarizer and the welding glass, too much "cheap glass" was placed between the camera and the image, leaving the sharpness to be desired.
A second trip to the Boise River provided an opportunity to see how a long exposure would depict the fast-moving spring drain. I could use much longer exposures here, a few more than two minutes. I also made a 30 second exposure with the sun in the photo, something that would not have been possible without a filter, even with the minimum ISO of 50 and the smallest aperture of f / 22. Taking long shots in bright light is an important reason to use an ND filter.
When to buy one really ND filter
You may find the welder glass technique a fun way to dip your photographic toe into the waters of long exposure photography. If you find yourself enjoying it and like the types of images you can take, you can save and buy a good ND filter. However, if the technique is interesting, but not really your bag, then you have discovered that you have only spent a few euros on the DIY version of your welder.
Either way, you learn a lot more about using your camera controls creatively to take exciting photos and that is what it's all about. Learn and enjoy!
The post Try this DIY Neutral Density Filter for long exposure Photos first appeared at Digital Photography School. It is written by Rick Ohnsman.