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DPChallenge Forums >> Tips, Tricks, and Q&A >> Fake ND filter with multi-exposures in-camera?
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Showing posts 1 - 12 of 12, (reverse)
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07/15/2011 12:52:01 PM · #1
Hi,

I suddenly have a chance to shoot some waterfalls. I never do, and I don't live near the sea or any interesting moving water. Hence, I'm light on neutral density filters. That, and the lens I use most often doesn't accept filters.

It's too last-minute to buy one. I've called all the shops an hour in each direction and no one can ship to me by tomorrow.

So, question is: Could I use multiple exposures in-camera to simulate a neutral density filter/longer exposure effect for the water? Or would it go all slightly off? If it would work, auto gain off, right?

Thanks for any tips.
07/15/2011 01:01:16 PM · #2
Shoot at dusk or at night.
07/15/2011 01:05:17 PM · #3
Yes, you can. Set the smallest aperture you can, and the lowest ISO to get the longest possible shutter open time. Expose normally (don't intentionally under-expose). Take as many shots as you wish, and combine in post. Combine them the same way you would if combining night sky exposures:

- Layer 1 (first image) at 1/1 or 100% opacity
- Layer 2 (second image) at 1/2 or 50% opacity
- Layer 3 at 1/3 or 33% opacity
- and so forth.

You can increase your exposure time slightly by using a polarizer as an ND filter.

ETA: careful with aperture. Using f/22 may result in visible softness from diffraction. I tend to limit myself to f/16, or even f/11 if I want the best in sharpness.

Message edited by author 2011-07-15 13:06:39.
07/15/2011 01:19:24 PM · #4
Thanks, kirbic. (And while a good idea, DC, the specifics of this trip don't allow that.)

I was thinking more along the lines of combining them in camera instead of post, but I suppose post would work as well.
07/15/2011 01:20:06 PM · #5
You may want to do this and mask it only to the waterfall if you can. Moving foilage may confound your plans.
07/15/2011 01:29:40 PM · #6
Originally posted by DrAchoo:

You may want to do this and mask it only to the waterfall if you can. Moving foilage may confound your plans.


Moving foliage *will* confound, however not any more than if an ND is used to achieve long exposures. For example a single 10-second exposure, vs. 10 1-second exposures will give visually almost identical results.

ETA:
This challenge entry of mine was shot using this technique:
' . substr('//images.dpchallenge.com/images_challenge/1000-1999/1003/120/Copyrighted_Image_Reuse_Prohibited_770020.jpg', strrpos('//images.dpchallenge.com/images_challenge/1000-1999/1003/120/Copyrighted_Image_Reuse_Prohibited_770020.jpg', '/') + 1) . '
The exposures were long already, but I increased the smoothness of the water flow by incorporating multiple exposures. Note the movement of the tree in the foreground.

Message edited by author 2011-07-15 13:32:54.
07/15/2011 01:35:47 PM · #7
Originally posted by DrAchoo:

You may want to do this and mask it only to the waterfall if you can. Moving foilage may confound your plans.

But I wasn't planning on moving any foliage. ;)

Thanks, kirbik. I'm feeling better already about not having that specific piece of gear I thought i'd desperately need.
07/15/2011 01:36:27 PM · #8
Originally posted by kirbic:

Moving foliage *will* confound, however not any more than if an ND is used to achieve long exposures. For example a single 10-second exposure, vs. 10 1-second exposures will give visually almost identical results.


True. I almost always bracket my waterfall shots and use the fast exposure for everything but the water. Then I manually blend the longer water exposure into the shot.
07/15/2011 01:47:56 PM · #9
Originally posted by DrAchoo:


True. I almost always bracket my waterfall shots and use the fast exposure for everything but the water. Then I manually blend the longer water exposure into the shot.


I've tried that, but my blending tools keep getting soaked :-P
07/15/2011 02:30:12 PM · #10
Originally posted by kirbic:

Originally posted by DrAchoo:


True. I almost always bracket my waterfall shots and use the fast exposure for everything but the water. Then I manually blend the longer water exposure into the shot.


I've tried that, but my blending tools keep getting soaked :-P


You know Doc's not afraid of getting his gear wet.
07/15/2011 03:54:54 PM · #11
Originally posted by DrAchoo:

Originally posted by kirbic:

Moving foliage *will* confound, however not any more than if an ND is used to achieve long exposures. For example a single 10-second exposure, vs. 10 1-second exposures will give visually almost identical results.


True. I almost always bracket my waterfall shots and use the fast exposure for everything but the water. Then I manually blend the longer water exposure into the shot.


Excellent advice, Doc. Thanks a lot.
07/15/2011 05:08:00 PM · #12
Just a reminder that you can use two polarizer filters to get somewhere between 1-4 stops of exposure compensation. I already had a circular polarizer, and I bought a used linear polarizer for about $10. These are a couple of test shots I made. The blur is a little deceptive because I only had the camera on a little mini-tripod and it was quite windy, but the second one should still give you an idea of the exposures you can get this way. Both are shot at ISO 80, f/8.0.

2 second exposure, edited: ' . substr('//images.dpchallenge.com/images_portfolio/0-4999/1031/120/Copyrighted_Image_Reuse_Prohibited_943126.jpg', strrpos('//images.dpchallenge.com/images_portfolio/0-4999/1031/120/Copyrighted_Image_Reuse_Prohibited_943126.jpg', '/') + 1) . ' 4 second exposure, unedited: ' . substr('//images.dpchallenge.com/images_portfolio/0-4999/1031/120/Copyrighted_Image_Reuse_Prohibited_943135.jpg', strrpos('//images.dpchallenge.com/images_portfolio/0-4999/1031/120/Copyrighted_Image_Reuse_Prohibited_943135.jpg', '/') + 1) . '

It's cool because you can vary the opacity quite a bit by altering the orientation of the two filters with respect to each other, but you also have to be careful (or creative) because with certain combinations and at certain angles to the sun you can get a sudden, bright-blue color-shift, almost like switching to a Tungsten White-Balance setting.

There's a whole separate thread on this technique, but I don't have time to find/link it right now ...
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