Extreme long exp. in daylight - 30 mins?

LERsince1991

macrumors 65816
Original poster
Jul 24, 2008
1,245
37
UK
Hi,

I'm looking to get an extremely long exposure in pure daylight of a busy highstreet to track movements. i.e. busy vs quite areas.

How can I get the longest exposure possible on a low budget?
I've used variable ND filter that I borrowed once before, with ND400 I'm pretty sure I got 20-30seconds. so if I had an nd8000 or so filter that should make it about 10 mins which might do.

So whats the best way to get the longest possible exposure, need some extreme sunglasses ;) for this!

The highest Neutral density filter I can find is 400. Do they go higher?

Thanks,
Luke
 

srf4real

macrumors 68040
Jul 25, 2006
3,000
26
paradise beach FL
What you need is time lapse, not long exposure. There are programs for this where you can tether your camrera and store directly to your computer's hdd.
Take a still photo with normal exposure every few seconds for thirty minutes I think is what you want?
 

snberk103

macrumors 603
Oct 22, 2007
5,503
87
An Island in the Salish Sea
A pinhole might also do. Get a spare camera body cap, drill out a small hole - half inch or so - and then attach the pinhole over that.

Read up on pinholes, there is lots of info on the web. If you need a sharp image the diameter of the pinhole is important....you can't just go to the smallest one. I suspect you could shoot through a ND filter in case you can't get to 30 minutes using just a slow ISO.

Luck.
 

TheDrift-

macrumors 6502a
Mar 8, 2010
877
1,370
What you need is time lapse, not long exposure. There are programs for this where you can tether your camrera and store directly to your computer's hdd.
Take a still photo with normal exposure every few seconds for thirty minutes I think is what you want?
You can buy a shutter release with a timer built in which does a similar job.
 

jabbott

macrumors 6502
Nov 23, 2009
326
7
You can stack ND filters (e.g. an 8x stacked with a 1000x becomes ~8000x). For such a long exposure though you'll notice that moving objects disappear from the photo altogether. Here is a good ND reference - look at the Anzac bridge photo to see what I mean. I agree with the earlier post that a time lapse series would probably work better for your application. Then you could layer the photos in Photoshop using an additive blending mode such as Overlay to see where the busiest areas are. Just be sure to keep the camera on a tripod and oriented the same for each shot. Best of luck.
 

TheDrift-

macrumors 6502a
Mar 8, 2010
877
1,370
Then you could layer the photos in Photoshop using an additive blending mode such as Overlay.
Eh? How does that work? That will just make the image really contrasty won't it? Have you tried this or am I missing something?

Maybe something like an image stacker..the type of things they use for star trails etc could work.....not sure about that overlay blend tho?
 

LERsince1991

macrumors 65816
Original poster
Jul 24, 2008
1,245
37
UK
Just a quick question, will get back to you all fully later;

If I stack ND filters would I times their values together?

For instance if I bought and stacked together 4x ND8 filters would I get an ND 4096 filter? (8x8x8x8 or 8^4) :)

I'm thinking of this mount;
http://www.ebay.co.uk/itm/Filter-mo..._adaptors_ET&hash=item1c20d809de#ht_804wt_986

and 4 of these ND8 filters
http://www.ebay.co.uk/itm/Grey-Neut...Filters_JN&hash=item2a132efdbe#ht_1301wt_1219

Seems like the cheapest way to do it?
I know image quality will be degraded a bit, I don't mind if it looks abstract as I'm only after people's movements. On a busy highstreet this should make a good image? but if the highstreet isn't busy enough the movement will be invisible?

Luke
 

admwright

macrumors regular
Sep 11, 2008
207
30
Scotland
I'm only after people's movements. On a busy highstreet this should make a good image? but if the highstreet isn't busy enough the movement will be invisible?
As others have said, a long exposure with ND filters will cause people walking about to 'disapear'. Only if someone stands still will they register in the image. You need to take a long series of 'normal' pictures to register each person and where they move. Then stack the pictures.

All the best
Andrew W.
 

LERsince1991

macrumors 65816
Original poster
Jul 24, 2008
1,245
37
UK
ok long exposures won't work, I've taken another look at some tests I've done and it would have to be extremely busy for it to work properly, thanks for the help.

I've done a test with a HD video, converted the video frames to layers in photoshop, made them all a single smart object, used the stack mode - "Variance" and also "standard deviation", these give very similar results but variance has more depth to the intensity of people.

Heres what I'm working on for tests. With more layers this should suffice, this was 160 layers. photoshop has a limit of 8000 layers but will most likely crash above 800 so I will try it will 800 layers from a 30 minute video on a high end mac pro and see what it does :) I'll probably use 16 bit mode.

I will then reduce the number of colours using either gif format or posterizing (probably noise reduce or blur the image before this though so its a bit smoother).
These colours in the image will then be used as gradient lines, then converted to vectors in illustrator, then imported to 3d software and processed as contour lines to produce a 3d shape, I'll then use smoothing and nurbs smoothing in 3ds max to create a nice smooth model and work from there. Will see how it goes!

Other threads I've been working with are;
https://forums.macrumors.com/showthread.php?p=14173648#post14173648
http://forums.adobe.com/thread/951032
http://forums.adobe.com/thread/952387
https://forums.macrumors.com/showthread.php?p=14194321#post14194321

Thanks
 

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LERsince1991

macrumors 65816
Original poster
Jul 24, 2008
1,245
37
UK
Just a quick question, will get back to you all fully later;

If I stack ND filters would I times their values together?

For instance if I bought and stacked together 4x ND8 filters would I get an ND 4096 filter? (8x8x8x8 or 8^4) :)

I'm thinking of this mount;
http://www.ebay.co.uk/itm/Filter-mo..._adaptors_ET&hash=item1c20d809de#ht_804wt_986

and 4 of these ND8 filters
http://www.ebay.co.uk/itm/Grey-Neut...Filters_JN&hash=item2a132efdbe#ht_1301wt_1219

Seems like the cheapest way to do it?
I know image quality will be degraded a bit, I don't mind if it looks abstract as I'm only after people's movements. On a busy highstreet this should make a good image? but if the highstreet isn't busy enough the movement will be invisible?

Luke
Would stacking filters like this work the way I've said? i.e. 4x ND8's will be 8x8x8x8 = ND4096?
Might get them anyway as a separate project :)
 

Doylem

macrumors 68040
Dec 30, 2006
3,858
3,640
Wherever I hang my hat...
To OP... Since no-one else seems to know any more than you do, it's time you became your own expert. Stack up a load of ND filters, conduct loads of controlled experiments, discover some new and wonderful way to express yourself... then come back and report your findings... :)
 

Edge100

macrumors 68000
May 14, 2002
1,557
10
Where am I???
As others have said, a long exposure with ND filters will cause people walking about to 'disapear'. Only if someone stands still will they register in the image. You need to take a long series of 'normal' pictures to register each person and where they move. Then stack the pictures.

All the best
Andrew W.
A famous example:

 

jabbott

macrumors 6502
Nov 23, 2009
326
7
Eh? How does that work? That will just make the image really contrasty won't it? Have you tried this or am I missing something?

Maybe something like an image stacker..the type of things they use for star trails etc could work.....not sure about that overlay blend tho?
It works for a few images but yes it does become more contrasty. I didn't realize the OP was going to have 800 images. ;) If you wanted a somewhat normal looking non-contrasty image then yeah you'd want to stack using mean, median, etc. for the stacking mode, but even then people might disappear (or become a blurry mess of people). If people are still lost then maximum or other stacking modes may work better.

As for stacking NDs (in case you want to do that for another project), they stack as follows: you can multiply the light reduction amounts together, or add the optical densities together. For example, let's say you have 8x (optical density 0.90309... seen as 0.9 on the package) and 1000x (optical density 3.0) ND filters, where 8x and 1000x are the respective amounts of light reduction. You could either multiply the light reduction amounts together to get 8000x or you can add the optical density numbers together to get 3.9. To convert optical density numbers to their ND equivalent, the calculation is 10^(optical density). So for the example above, it would be 10^(3+0.90309) = 8000x light reduction.
 

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