ND and HDR technique - help please.

D

Dan1502

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Dan
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My apologies for the mega long post.

Being new to this I’m trying to work out the technical aspects in advance so that when I get out in the field I am more productive and can hopefully master them more quickly, allowing me to start concentrating on the artistic side more.

I’m trying to plan my first serious attempt at using ND filters and probably combining with HDR. By this I mean using HDR rather than graduated filters and have prepared the following as my guess at how to go about it. Please correct any mistakes, add to it and criticise it.

1. Set up tripod, attach camera, remote control and compose.
2. Set exposure bracketing
3. Set drive to fast
4. Set focus point
5. Set metering mode
6. Set ISO
7. Set to aperture priority
8. Set aperture
9. If helpful, press DOF review button to check DOF
10. Take bracketed shots with a few different brackets
11. Review shots and check histograms

When ND filter too dark for autofocus and metering:

12. Half press shutter and note exposure reading
13. Switch lens to manual focus (and adjust if necessary)
14. Switch to manual mode and check aperture, ISO etc
15. Work out exposure based on number of stops of the ND filter using noted reading
16. Attach relevant filter
17. Attach viewfinder cover
18. Take shots using remote control manual shutter and stopwatch if applicable
19. Review shots and histograms


Questions

How much should you bracket by at different levels of ND? Is one to two stops still about right but bearing mind that on longer exposures a stop can be quite a long time?

What metering mode is best to use? What should the metering target be?
When doing long exposures combine with HDR should spot metering be used for say above and below horizon before composing, readings noted and exposures being calculated for each separately based on number of stops ND?

Is exposure bracketing irrelevant for long exposures?

Is deciding which level of ND filter to use just a matter of experience or are there any helpful guidelines to start? (I have a variable ND filter so can easily try various degrees but would need to keep calculating exposures).

Is there an iphone app for calculating exposures quickly?

Is there an iphone app for DOF calculations? (may be abroad and not have data services for web based app).

Thanks

Dan
 
I think I know what you're wanting to do.. you want to create long exposure HDR images. I've not tried it, although I do regularly do normal HDR and non-HDR long exposures. In the absence of anyone else commenting, I can suggest what I might try on the basis of how I go about each technique seperately (using a 40D, so it should relate). This assumes using a relatively fast lens to allow using live view to focus/meter.

  • Switch the camera to Manual mode
  • Switch focussing to manual
  • Attach ND filter
  • Set the camera firmly on a solid tripod, attach remote shutter and compose the scene
  • Set Aperture
  • Set ISO to something stupidly high (1600/3200/higher)
  • Switch to Live View
  • Manually focus (with a fast enough lens you should still be able to focus with Live View, if not you'll have to set focus before attaching the ND filter)
  • Spot meter the scene to get a shutter speed (you can take a test shot at the higher ISO just to check the overall exposure)
  • Calculate the shutter speed back from the initial ISO to ISO100 (using a variable-ND filter you have the option of strengthening/weakening the filter to manipulate the shutter-speed you start with)
  • Change the ISO to ISO100
  • Check the focus again
  • Take the shot, check exposure on screen
  • Shorten the shutter speed by 1-stop (obsessive) or 2-stops (relaxed) depending on your attitude to HDR
  • Take second shot, check the exposure on the screen
  • Keep shortening the shutter speed until the exposure is almost completely black
  • Go back to your initial shutter speed
  • Now increase the shutter speed by 1- or 2-stops
  • Take the shot, check the result on the screen
  • Keep increasing the shutter speed until the exposure is almost completely white
The bits in italics are my usual ND technique and works for me for anything up to welding glass levels of light stopping (13-14 stops). The rest is my usual HDR technique. This will capture the full dynamic range of the scene for the best possible input to the HDR process.

I'm not sure how this will work with long exposures. With skies there is going to be a considerable variation in cloud movement, and with waves I'll be interested to see the effect that the frequency of the waves has on the final result.

I've had a quick search through Flickr, but the majority of the one's I can find that combine longs exposures and HDR look like tone-mapped single exposure shots. I did find a few genuine multiple exposure HDRs that included some very long exposures, but none of these used ND filters.

What sort of scene are you wanting to try this on?


For DOF, I generally look up some representative tables for typical focal lengths (10, 20, 30, 50, 85, 105mm) that either match (primes) or cover the range (zooms) of the focal lengths of the lenses I use most often. I then print these out and put them in the camera bag. For landscape shots you'll generally find you only really need one to three printed tables to give you enough of an idea. Alternatively.. you just need one table with focal length vs hyperfocal distance, and again you can download and print these from several websites.


What would be interesting to try with a variable-ND would be to keep the shutter-speed, aperture and ISO constant and use the variability of the variable-ND filter to adjust the overall exposure to get a -2, -1, 0, +1, +2 five shot bracket.
 
Thanks, just what I was looking for really. I hadn't thought of the ISO reduction technique and associated calculation of exposure.

I am looking to get used to HDR and use of the ND filter separately and envisage trying coastal scenes first as I shall be going on holiday to the east coast of Spain shortly.

My thinking was that it might be worth combining the two techniques to get the long exposure effect but also capture good dynamic range and without the need for ND grads and avoiding the features above the horizon problem with these. I might be being daft as I'm very new to this but was just thinking. I hadn't properly thought through the movement issue you highlighted and was thinking that as they're long exposures anyway it might not matter too much. The best thing is probably to give it a go and see.

So far I have only produced one HDR image and that was from two shots and looked very natural. Do you use several images combined into one and which post processing technique do you use?

If it works then using the scale on the variable ND would be a very simple solution. I'll give that a go.

A possible weak point in my setup (apart from me!) is my tripod which is an old Velbon with no hook but it's probably about as heavy as I could take away with me and I can't spend any more on kit for a while so I'll just have to hope its not too windy.
 
Dan1502 said:
How much should you bracket by at different levels of ND?
Click to expand...
Depends on the scene, but it's no diferent to with the filter in. If you need two stops difference between sky and foreground with the filter off then you'll need the same with it on.

Is one to two stops still about right but bearing mind that on longer exposures a stop can be quite a long time?
Click to expand...
One stop is always doubling or halving the amount of light, so twice or half the shutter speed. Depends how you blend but that could really affect how movement is recorded throughout the scene, for example if one of your shots is when a wave is coming in, one when it's going out.

What metering mode is best to use? What should the metering target be?
When doing long exposures combine with HDR should spot metering be used for say above and below horizon before composing, readings noted and exposures being calculated for each separately based on number of stops ND?
Click to expand...
Don't overthink. Take a meter reading however you usually do, shoot, check the histogram and adjust as you need to. I tend to meter once, stick it in manual and just make sure I look at the histogram after each shot as the light changes.

Is exposure bracketing irrelevant for long exposures?
Click to expand...

No. If you need to bracket with the filter off then you need to bracket by the same amount with it on.

Is deciding which level of ND filter to use just a matter of experience or are there any helpful guidelines to start? (I have a variable ND filter so can easily try various degrees but would need to keep calculating exposures).
Click to expand...

Why would you need to keep calculating? Let the camera meter and shoot, compensate as desired.

I might be wrong but you seem a little confused about exposure in general. Do you fully understand what a stop is in photographic terms? If not it might help for you to read a bit on it :)
 
Thanks, I do understand what a stop is and that there are various ways of achieving a stop difference (Exposure, ISO, Aperture, ND Filter). I guess with this post I was just throwing down my thoughts without fully thinking them through (late at night after getting a bit overwhelmed by variables). The responses are just what I wanted though - helping me consolidate my thinking. Quite a few of the answers are what I expected which is good.

I haven't tried metering in very low light (or strong ND) yet so wasn't sure how the camera copes and was thinking that there might be a maximum exposure time before manual shutter release is required which would require manual calculation of exposure time rather than auto bracketing (though this is where the vary ND might be very helpful).

I think I'm probably at the stage where I need to go out and experiment and see how the camera behaves. I've only tried one shot of my garden so far with +1 -1 bracketing on a cloudy day and it worked well. I think I know enough now to be getting on with and will probably to quite a few stops difference if I find a really good subject. Then I'll be asking about post processing with mulitple exposures!
 
Dan1502 said:
Thanks, just what I was looking for really. I hadn't thought of the ISO reduction technique and associated calculation of exposure.

I am looking to get used to HDR and use of the ND filter separately and envisage trying coastal scenes first as I shall be going on holiday to the east coast of Spain shortly.

My thinking was that it might be worth combining the two techniques to get the long exposure effect but also capture good dynamic range and without the need for ND grads and avoiding the features above the horizon problem with these. I might be being daft as I'm very new to this but was just thinking. I hadn't properly thought through the movement issue you highlighted and was thinking that as they're long exposures anyway it might not matter too much. The best thing is probably to give it a go and see.

So far I have only produced one HDR image and that was from two shots and looked very natural. Do you use several images combined into one and which post processing technique do you use?

If it works then using the scale on the variable ND would be a very simple solution. I'll give that a go.

A possible weak point in my setup (apart from me!) is my tripod which is an old Velbon with no hook but it's probably about as heavy as I could take away with me and I can't spend any more on kit for a while so I'll just have to hope its not too windy.
Click to expand...

There's a risk of over-analysing any new technique.. just get out there and have a go, see how you get on. Try both HDR and ND techniques seperately before combining the two.

In answer to your questions.. I use as many exposures as I need. I used to use three with +/-2 AEB, but I noe ignore AEB completely, use Manual settings and I frequently now use as many as 14 exposures.. it depends on the scene and what mood I'm in.. taking sequences of 1-stop exposures from 1/250 to 2 minutes can be a very relaxing way of spending a quiet afternoon in a pleasant church interior after a busy morning meeting. To be honest I could probably get the same result using 2-stop intervals and half as many exposures.. I'd certainly run less of a risk of having to vacate the scene quickly via a side door when a funeral starts to arrive! (why do they never advertise these things?).

Nothing wrong with a Velbon.. I have a trusty Velbon Delta.. the only thing that means I'm likely to replace it soon as that it's d'd awkward operating the camera when it's hanging upside down from a reversed column. It's certainly heavy enough for a long exposure even in a bitterly cold blustery wind when down on the beach.

AEB will not go above 30 seconds.. if you meter the scene at 30 seconds and set the camera to AEB +/-2 you will get exposures at 30 seconds, 7 seconds and 30 seconds. It will repeat the 30 seconds and won't do "+2".

I do the HDR and tonemapping with FDRtools and further processing with Lightroom (or GIMP if I want to layer on a darker exposure).
 
Do your focussing and metering BEFORE putting the ND on. If using a large stop ND, you won't see much even in live view with high ISO and you are introducing something else to forget or get wrong.

Set your working ISO.
set focus, composition and check exposure.
Fit ND.
Adjust exposure according to ND factor (I have done a little chart on the actual filter holder - on the inside of the see through box with permenant marker! If I have the ND with me, I have the exposure chart too...saves my head with maths!

Take your shots. Job done.
 
I'm not sure what to do with several exposures yet as I've only tried combining two so far.

Regarding attaching the ND filter after focussing/metering, the advantage of the variable ND I've bought should be that I can set it to mimimum for focussing and metering then crank it up after. First impressions of it are very good - it fits my 11-16 without vignetting. I've not used it yet though - just messed about with it in the house.

I go to Spain in a few weeks and am going to have a few days before my wife joins me so hopefully I should have a chance to have a go without trying her patience!

Thanks guys.
 
Lensflare said:
Do your focussing and metering BEFORE putting the ND on. If using a large stop ND, you won't see much even in live view with high ISO and you are introducing something else to forget or get wrong.
Click to expand...

I've never really had a problem with my 10 stop. unless in low light, live view shows everything clearly. It meters pretty well too if I seal the viewfinder properly. I only have problems with my 13 stop welding glass.
 
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