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View Full Version : A brief note on Neutral Density filters



dmdigital
22nd March 2009, 06:41 PM
Neutral density (ND) filters can be a handy addition as they allow you to stop down (reduce aperture or shutter speed) and to get more sharpness (or softness) in the image.

In my case they are particularly useful as there is usually an over abundance of light and so taking nice soft shots of water really is hard unless its a very rainy day or you catch everything in that 30 minutes of almost twilight we get up here in the north. For this reason I tend to only use either an ND6 or ND10. I have an ND3 but that's usually left at home.

The idea is the filter simply blocks some of the light and doesn't alter the colours. The common ND's are 1, 2, 3 and 6 stop and they can be stacked to get an additive effect. So if you have a ND1 and an ND2 you can stack them together and in effect have an ND3.

So for instance if you want to shoot a shot a 1/30 second f/16 then with an ND3 filter you could take the same shot at either 1/4 sec and f/16 or 1/30 sec and f5.6

The ND10 is a 10 stop filter and the best description is dark welding glass. This is good for turning bright sunny day into something useful as even at f/22 I can often not shoot as low as 1/30 second. So its impossible to get those nice smooth water shots with the angle hair effect of the water on the rocks.

So as an example here are two shots. The first I'll freely admit is a bit blown out and was just snapped off in a hurry. This was taken in program mode and the EXIF shows it as 1/50 sec and f/3.5.
https://www.aulro.com/afvb/images/imported/2009/03/697.jpg

So here's the shot set up with the ND10 filter. The camera was on a tripod, tethered shutter release and in manual. The EXIF on this is 120 seconds and f/18.
https://www.aulro.com/afvb/images/imported/2011/06/158.jpg

Of course the other aspect of ND filters is graduated ND's. With these one half of the filter is ND and one is clear. These are highly effective at removing the over exposure of a scene because of the sky given the darker lower light reading of the land. I can't give any examples as these are something I haven't used for a long time and presently don't own any.

Of course for a much more complete explanation of the ND filters its best to do a few Google searches.

werdan
23rd March 2009, 07:30 AM
Hey DM, have you ever tried 2 polarisers together?

Back in 'the day', you could buy linear polarising filters rather cheaply. By adding 2 together, you had an inifintely variable ND filter. In phase the filters let most light through and at 90deg out of phase, no light (more or less).

The problem is, linear polarisers interfere with CCD auto-focusing systems on SLR cameras. Therefore it became common to only use the much more expensive circular polarisers. I haven't tried using 2 circular polarisers together and was wondering if the variable ND effect still works. Since a polariser is the only true 'must-have' effects filter left since digital and photoshop came in, it might be a better option to spend another $100 on a second one instead of buying a few different strength ND filters.

dmdigital
23rd March 2009, 07:37 AM
No I haven't. Have a look at the Singh-Ray VariND (http://www.singh-ray.com/varind.html) I believe this uses 2 CPL's.

I always thought the CPL was introduced because of auto-focus initially and now because of other TTL sensors as well.

werdan
23rd March 2009, 08:41 AM
Yeah, I heard someone flogging the Singh-rays on a podcast the other week which reminded me of it. Charging $340-$390US for gluing 2 CPLs together seems rather cheeky.

My first camera was a Minolta 7000 and I remember paying $14 for a Linear PL at Kmart, then having to go back and pay $40 for a CPL. <grumble, grumble> The pitfalls associated with being an 'early adopter'. :)

mfc
4th April 2009, 11:55 PM
[QUOTE=werdan;940162]Hey DM, have you ever tried 2 polarisers together?

Back in 'the day', you could buy linear polarising filters rather cheaply.

you can still buy linear pol filters...{hadent seen them used this way but ill give it a burl

in regards to grad nd filters , ive been after a set of lee filters for over a year and there continuosly sold out{usa and gb}...likley ue to dig sensors crap response to contrast

plus there realy expensive:eek:

Maggot4x4
14th April 2009, 08:42 AM
I have some Cokin graduated ND filters

CowsGoMoo
17th April 2009, 10:34 PM
[quote=werdan;940162]Hey DM, have you ever tried 2 polarisers together?

Back in 'the day', you could buy linear polarising filters rather cheaply.

you can still buy linear pol filters...{hadent seen them used this way but ill give it a burl

in regards to grad nd filters , ive been after a set of lee filters for over a year and there continuosly sold out{usa and gb}...likley ue to dig sensors crap response to contrast

plus there realy expensive:eek:

I've got a Lee holder (from GB) and Grad ND filters from Sing-Ray to fit. Works very well. I'm glad I got the larger size. I know a number of people who went the smaller size and ran into problems with wider shots.

I've also go a Vari-ND. Very handy for waterfalls and moving water after the sun has come up.