# ND Filters and Long Exposure: Calculate or Automate (Part Deux)



## lilmsmaggie (Apr 13, 2015)

Earlier this year, I posted this question: How do you determine your exposure time when using ND filters (especially 8 stops or more?)

Some of you reported using iPhone apps without identifying the app and some asked the question: What apps do people use? Well, I'm about to choose an app for my iPhone for a trip to Yosemite in 2 weeks and thought maybe a poll might be helpful to ask just that question: 

What phone apps do people use to calculate a long exposure using ND filters? Feel free to elaborate, especially if you use some other method to derive your exposure. The information you provide will be valuable to those who are testing the Long Exposure waters for the first time.


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## wsheldon (Apr 13, 2015)

Not sure what the challenge is here. I use the exposure meter in the camera unless it gets over 30sec, then I either adjust aperture until I can meter <30 sec and figure out how many stops from my preferred aperture that is, or take a reading with the filter off and adjust for additional stops of shutter speed based on the ND strength. For variable ND I think you'd need to stick with the meter pretty much all the time, or bracket.


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## Stu_bert (Apr 13, 2015)

Less than 30 seconds, just let the camera calculate. I know there are some who prefer to do it the way these apps suggest - never had to personally.

Over 30 seconds, typically in low light conditions I adjust the ISO until the camera is happy to calculate. Let's say this is ISO 800 at 20 seconds. Every time you drop an ISO, you double the time. So my exposure would be 160 seconds. Depending on how low the light it, and the time of the year (determining how quick till dark), then I may add on some time to my calculation to compensate for the fading light and of course to ETTR.

If you get chance, practice a little in your back yard before you get to Yosemite - I tend to be in awe of amazing locations and sometimes get too easily distracted


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## lion rock (Apr 14, 2015)

When I got the Lee Big Stopper, it came with a little card that gives a range of normal shutter speeds (from 1/1000 second to 2 seconds exposure time) to Big Stopper speeds (1 second to 32 minutes).
Of course, when I was in the fields doing my long exposure, did I have the cheat sheet with me? No!
I know my normal exposure time, aperture and ISO, and I know the ND is 10 stops, so I just did a best estimated calculations. First few shots come out over exposed badly, next few shots came out way under. But, it eventually got dialed in correctly. What did I waste? No more than a few electrons, shutter counts and some space on the cards, none of which mattered much. I did stand there waiting, but, the scenery was captivating.
-r


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## lilmsmaggie (Apr 14, 2015)

The challenge is not necessarily myself, although I've used long exposures they have generally been night scenes. I have a set of LEE filters but I will not be taking them this trip. Lodging will be sleeping bags and Yosemite housekeeping camp. 

This outting will actually be a mix of college students, some of which have maybe some experience with long exposure photography but not using ND filters. It will be a mix bag. Some of the students have never been to Yosemite. Some will be checking out and using equipment they're not familar with. I'm anticipating we will be paired or maybe in groups of 3 or more students. Invariably, someone will not know how to calculate the proper exposure. And dollars to donuts many will have some flavor of smartphone with them. There were no prerequisites for the class. More like Oh WOW! I get to go to Yosemite for the weekend and earn college credit 8) 

They all (myself included) will be using screw-in filters and not Cokin or Lee's, so there won't necessarily be a handy-dandy exposure chart (well, maybe). 

There's only 2 class meetings before the field trip. Being college students, they won't necessarily have a lot of funds to play with. The instructor actually suggested they purchase this set of ND filters 

http://www.amazon.com/Altura-Photo-Professional-Photography-MagicFiber/dp/B007SXJ1VG/ref=sr_1_3?ie=UTF8&qid=1428977130&sr=8-3&keywords=altura+ND+filters

I don't think these are optical quality glass - most likely plastic.

Anywho, just thought a phone app might come in handy and might even be helpful as a learning tool that's all.




wsheldon said:


> Not sure what the challenge is here. I use the exposure meter in the camera unless it gets over 30sec, then I either adjust aperture until I can meter <30 sec and figure out how many stops from my preferred aperture that is, or take a reading with the filter off and adjust for additional stops of shutter speed based on the ND strength. For variable ND I think you'd need to stick with the meter pretty much all the time, or bracket.


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## benperrin (Apr 14, 2015)

I use exposure calculator which is an android app. Didn't need anything fancy. Usually my process is to set everything up with the nd filter off and take a test shot to figure out any issues. This is the most essential step. Don't try to figure out focus issues with the big stopper or similar attached. Then I use the calculator to figure out the exposure time. It makes life very simple. My filter is around 10 and two thirds stops dark (b+w). From there I usually just guess the exposure time as the sun fades and make adjustments as necessary. A remote helps and a sturdy tripod and head are essential with long exposure. Also try getting your students to play with mirror lockup if possible. Not sure if that's available on lower end cameras.


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## benperrin (Apr 14, 2015)

Also once your focus is correct switch your lens to manual or use back button focus. No point in trying to focus with a dark ND filter on.


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## Hillsilly (Apr 14, 2015)

I use the Triggertrap ND calculator. Its part of the free trial version. Very easy to use.

If I need a timer, I use "ND Filter Timer", which is also easy to use.

These are both free Android apps, but I assume you can get the for Apple.


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## scotia (Apr 15, 2015)

Why not get the students to put together their own tables? This will give them a truly free resource and it will not matter which type of phone they have (or even if they have a phone). It doesn't take long to do and it might help them to understand how the exposure times work. Given that some filters are not exactly 10-stop (my Big Stopper needs to be calculated as 11-stop to get the exposure correct, and one of my friends has one that is closer to 9-stops) it can be useful to know how to calculate exposures for yourself. I can do the calculations in my head (counting stops on my fingers) in less time than it takes to work out in which pocket I stored my phone. 

Several of my camera club seem to think I am some sort of mathematical genius (if only!) because I can produce a tables for them quickly when their mobile phone battery runs out/they forget their mobile phone/they drop their iphone off a jetty (it happened)….


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## mackguyver (Apr 15, 2015)

Um, you left one off:

I use my brain


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## lilmsmaggie (Apr 16, 2015)

scotia said:


> Why not get the students to put together their own tables? This will give them a truly free resource and it will not matter which type of phone they have (or even if they have a phone). It doesn't take long to do and it might help them to understand how the exposure times work. Given that some filters are not exactly 10-stop (my Big Stopper needs to be calculated as 11-stop to get the exposure correct, and one of my friends has one that is closer to 9-stops) it can be useful to know how to calculate exposures for yourself. I can do the calculations in my head (counting stops on my fingers) in less time than it takes to work out in which pocket I stored my phone.
> 
> Several of my camera club seem to think I am some sort of mathematical genius (if only!) because I can produce a tables for them quickly when their mobile phone battery runs out/they forget their mobile phone/they drop their iphone off a jetty (it happened)….



It's an 8 week class and it meets twice before the trip. The first class meeting was last week, the next will be on April 24. Listening to the introductions the students were giving, I got the impression that photographiy skill level is all over the board. A lot of students didn't know what a ND filter was; some will be shooting film; some want to shoot MF film; some asked about using LF; and as mentioned previously, some signed up because they viewed it as a fun and easy way to earn a few college credits and go to Yosemite. And last but not least, some don't even own their own camera equipment.

I wouldn't be surprised if someone showed up with a P&S (even though the course description said it didn't qualify), and there's probably 45-50 students in the class. 

BTW - I'm not the instructor




mackguyver said:


> Um, you left one off:
> 
> I use my brain




I think that comes under Other ;D


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## mackguyver (Apr 16, 2015)

lilmsmaggie said:


> mackguyver said:
> 
> 
> > Um, you left one off:
> ...


I'm just being silly, but if you set your exposure stops to full instead of 1/3 stops, it's not too hard to click down however many stops you need for the ND - or triple that if using 1/3 stops. If you adjust ISO and shutter speed, it's a bit more complicated, but still not too bad.

I have ND Filter Calc on my phone but have never used it.


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## lilmsmaggie (Apr 16, 2015)

Gotcha -- I downloaded NDTimer last night. Not sure if I like it. The interface is different than what you may come across online e.g. Scott Kelby, but it functions pretty much the same. The version available for download now is more recent than the one I've seen Kelby use.

You dial in your shutter speed and ND filter density and it will display a countdown for the exposure time. If you're stacking two filters, you have the option of adding the filter density for that too. There is no option for adding 3 filters but you can probably combine the densities for two filters and use that to calculate a 3-filter combination



But its pretty straight forward. I'll just have to play with it and see how it works 

The image below shows 1 filter, 11 stops. +None = no filters being stacked 




mackguyver said:


> lilmsmaggie said:
> 
> 
> > mackguyver said:
> ...


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## geekpower (Apr 16, 2015)

multiplying by 2 is hard! :-X


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## charlesa (Apr 17, 2015)

Better calculate and know the expected shutter time, as if mid exposure you see the light changing you can alter the time leaving the shutter open by an appropriate degree up or down.


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## lilmsmaggie (Apr 17, 2015)

So, it appears that less than 30% (28.5%) of those responding to this survey use an automated means such as a phone app to calculate a long exposure. 

The vast majority 71.5% of respondents use some other method, e.g. quick reference table, manually calculate exposure or perhaps some combination thereof.


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