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Old 25-10-2013, 11:16 AM
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AstroJason (Jason)
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DIY Neutral Density Filter for Ultra Wide Angle Lenses

Hi all,

Before I begin with this I want to point out that if you do try this, you do so at your own risk and I will not be held responsible for any damage you do to your lens and or camera!

Not sure how useful this will be to people but I thought I would share a recent DIY project I undertook. Sorry in advance that this is a bit of a long post.

I love landscape photography and ultra wide angle lenses. As you can see in my signature I own the Sigma 8-16mm lens. As far as I am aware it is the widest lens for crop sensor DSLRs which is not a fish eye. It is a fantastic lens and images taken with it are amazing. The one issue with this lens and other ultra wide angle lenses is the bulbous front element. The front element sticks out of the lens which makes attaching filters to it very difficult and expensive. The element on the Sigma 8-16mm is so bulbous that it creates a natural polarising effect so there really isn’t a need to attach polarising filters to this lens. The filter I wanted to attach to it is a Neutral Density Filter (ND) so I could take long exposures during the day. I really like the silky look people get with these filters when they take shots of waterfalls and waves crashing on a beach. I wanted to try my hand at these types of shots. There are a couple manufacturers out there that make holders and filters for ultra wide angle lenses but they are super expensive (upwards of $200-$300 depending on the kit you get). Not wanting to fork out so much money on something on consider a small side hobby to astronomy I decided to look for alternatives.

I came across people using Welding Glass as a cheap alternative. But they still used expensive attachments to mount the Welding Glass to the front of the lens. So I decided to try make the holder for this as well. I bought the welding glass from a seller on ebay from the UK and it cost $3 including shipping to Australia! I then proceeded to make a holder for this welding glass. I based the build on commercial filter holders I had seen for sale. The issue with using welding glass as a ND filter is that it creates a very heavy green cast to images. Some people are able to white balance these images and get good results, however, I was unable to do this with my Canon 60D. I also think the welding glass I bought is too dark. Also the filter holder I ended up making is huge and bulky and really looks ridiculous!

So this made me look for alternatives. I had heard of gel filters before so I thought I would explore options here. I originally intended to use a gel filter over the front of the lens, just like how I used the welding glass. However, I was aware that there are some lenses out there that allow you to apply a gel filter to the rear of the lens. Looking at the back of the Sigma 8-16mm lens there is threading on the inner barrel of the lens so it looks like it accepts rear filters. I am yet to make a “screw on” type rear filter but I was able to make a simple filter which sticks to the back of the lens.

I bought a sheet of Lee Filters ND filter sheet with a 1.2 density off ebay. This sheet just cost $15 including shipping from the US and its larger than an A3 piece of paper. Making the rear filter holder was very simple. I basically stacked 2 layers of stiff cardboard onto each other and then layered the filter gel on top of each other. I was aiming to get nicely exposed 30 second exposures at ISO100. So I experimented with the amount of layers and found that 3 layers was the perfect balance for exposure brightness Vs colour cast. 2 layers was too bright in broad daylight even at f/22. 4 layers was too dark and created a red colour cast in the image. 3 layers allows you flexibility with exposure levels and allows you to even open up the f stop or increase ISO to allow more light in and have brighter exposures in lower light situations. 3 layers does not create any colour cast either so all exposures come out with good white balance. Also 3 layers is just enough to allow the camera to auto focus, this is a big bonus when you have a filter attached to the back of the lens!

The only thing that some people might not like about this filter is how I am attaching this filter to the rear of the lens. It is just currently attached to the rear of the lens using Blu-Tack, I am still trying to explore other options here. Obviously if you do attempt this do everything you can to NOT attach anything to the electrical component contacts on the rear of the lens. Again, it goes without saying that if you try this you do so at your own risk and I will not be held responsible if you damage your lens/camera!

If you’re still interested in trying this out continue to the below links…

Below is the link to my Flickr account which shows detailed shots of the various filters I made (too many shots to attach here), how they attach to the lens including hires, unedited test shots along with the same shots with only white balance applied where it was required.
http://www.flickr.com/photos/5900499...7636643810703/

If you have a similar lens and are interested in exploring these cheap DIY options below is the link to the ND Gel Filter sheet I purchased off ebay:
http://www.ebay.com.au/itm/Lee-Filte...4f1b293&_uhb=1

If you’re interested in the Welding Glass option here is a link to the same glass I used below:
http://www.ebay.com.au/itm/4-x-3-4-x...96dfd8b&_uhb=1

I hope that this was helpful to someone!

Cheers,

Jason
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Last edited by AstroJason; 25-10-2013 at 11:39 AM.
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Old 27-10-2013, 07:52 AM
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AstroJason (Jason)
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After visiting some friends yesterday I had some time in the afternoon to really put this DIY filter to the test. Went out to Garie Beach yesterday and found the perfect setting for some silky water shots on the rocks. Here are some examples below.

All these are 30 second exposures at ISO100. I'm so pleased with these results considering how much real ND filters cost to fit to this lens. I'm positive this concept can be adapted to all other ultra wide angle lenses.

Going to work on getting a screw in type filter holder machined to thread onto the back of the lens.
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Old 29-10-2013, 07:34 AM
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ZeroID (Brent)
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Have a look at camera shops for bargains on filters. I picked up 5 for $10 at one of our big dealers. Apparently DSLR's just don't use or need them with AWB fixing the pix. I found a blue 80A that fitted my 300mm and when I fitted it to the lens it went blue for about a second then corrected !! Take it off and same process in reverse. So Filter sales are down in the dumps.

But !!
What I did pick up was a pair of polarising filters with rotating eements. Fit the two together and voila you have a variable ND filter all for $4.

The 80A will hopefully counteract some LP for widefeild instead of a LP filter. Just playing with ideas.
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Old 29-10-2013, 08:47 AM
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AstroJason (Jason)
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Interesting Brent, I will check out some camera shops for these bargain filters. Might even just be worth doing that to see if I can get the filters and pop them out of their threaded barrels to use the barrels for my purpose.

However, I have just found this technique which can be used as well for that "silky water" look without the need for any filters at all. Basically take approx 15-20 normal exposures during the day and then stack them in photoshop. The result is pretty much the same as using an ND Filter. Link to the video describing this technique: http://www.youtube.com/watch?v=09njDK4TsEw
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Old 29-10-2013, 10:25 AM
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ZeroID (Brent)
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On the SONY at ISO 50 and F 22, gives about 1/8 sec exposure in cloudy daylight. Seems to be enough for the effect, just.
The polarizers I found only fit my 300mm. Must go back to see if they have any at 62mm.
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