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 Post subject: Burj Khalifa
PostPosted: Thu Dec 16, 2010 12:57 pm 
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Joined: Thu Oct 08, 2009 11:24 am
Posts: 1826
A nice morning today, with a few high whispy clouds so I thought I'd try a few long exposures. Here's one of the Burj Khalifa:

164 second exposure, F18, ISO 100, 13mm

Image

And then on the way home I found an interesting sculpture:

Image

Which had an interesting abstract view from directly underneath:

Image


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 Post subject:
PostPosted: Sat Dec 18, 2010 10:43 am 
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Joined: Thu Oct 08, 2009 11:24 am
Posts: 1826
and a couple more from the area this morning:

Image

Image


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 Post subject:
PostPosted: Sat Dec 18, 2010 2:08 pm 
I miss Dubai, went there for holidays back when I was in Bahrain! Nice shots there man, didn't know Burj was actually that tall..


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 Post subject:
PostPosted: Sat Dec 18, 2010 4:17 pm 
Those are some very majestic shots there dubaiphil!!

I particularly like the the long and bright exposure of the skyscraper and the fountains.

How did you manage to control exposure in such a bright setting and still have light hitting the sensor for a whopping 164 seconds??!

Cheers :-)


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 Post subject:
PostPosted: Sat Dec 18, 2010 4:28 pm 
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@LahLahSr - I used a 10 stop and 3 stop ND filter, stacked.

Doing the maths gave me an 80 second exposure, which wasn't enough as the clouds wouldn't have moved enough in that time, so I then dialled in ISO 100 from the D90's normal ISO 200, gaining an extra stop and doubling the time.


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 Post subject:
PostPosted: Mon Feb 14, 2011 2:04 pm 
Phil,
Would you mind explaining the "math" portion. I new and very intrigued with these photos and would like to learn more.


thank you


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 Post subject:
PostPosted: Mon Feb 14, 2011 5:11 pm 
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Joined: Sun Aug 29, 2010 11:52 am
Posts: 861
Location: Surrey, UK
Amazing photos as usual dubaiphil. I really love duabai and am hoping to go sometime in the summer holidays or maybe in october.

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 Post subject:
PostPosted: Tue Feb 15, 2011 2:33 am 
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Joined: Sat May 29, 2010 11:27 pm
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Location: Toronto, Canada
I love the abstract!

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 Post subject:
PostPosted: Tue Feb 15, 2011 6:01 am 
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Joined: Thu Oct 08, 2009 11:24 am
Posts: 1826
Thanks for the comments guys.

@ atrembla - for the maths...

My camera has a 'base' ISO of 200, but I can go lower to 100 if required. When using a 10 stop ND filter it can be difficult to see the composition if it is attached to the lens (sometimes Live View compensates). Therefore I compose the shot I want without the filter and make a mental note of the exposure I need for the shot.

So for example, if I compose with no filters on the lens at F8 and ISO 200 and the shot requires a 1/400th second shutter for a good exposure, then that's my base.

Then, if I add a 3 stop ND filter I can still see through the viewfinder (as it's not that dark). I know that the shutter speed will slow by 3 stops (or double three times over) - 1 stop reduces to 1/200th, 2 stops reduces to 1/100th, 3 stops reduces to 1/50th.

Then, if I add the 10 stop ND filter I cannot see through the viewfinder, so I have to calculate the additional 10 stops manually. 1/25th, 1/13th, 1/6th, 1/3rd, 1/1.6", 1", 3", 5", 10", 20".

So now, for the same exposure as the original base shot (F8 and ISO 200) by adding the filters I can slow the shutter from 1/400th second to 20 seconds.

Now, if I want to slow things further I can do several things:

1 - add another filter (stacking filters can compromise the image quality so I prefer not to)
2 - change the aperture of the lens (stopping down too much can again compromise the image quality)
3 - change the ISO

I prefer not to stop down beyond F18 if necessary. Here - remember my base shot is at F8, so if I reduce the aperture in 1/3 stop increments I can go from F8 through F9, F10, F11, F13 and F14 to F16. This reduces the light entering the lens by 2 further stops, so therefore I have to slow the shutter a further 2 stops to compensate.

Therefore F8 and ISO 200 with filters at 20 seconds moves to F16 and ISO 200 with filters at 80 seconds.

Now I have one other option to slow things down again, which is reducing the ISO. Reducing from ISO 200 to ISO 100 gains me another stop, meaning I can reduce the shutter speed further.

I can then go from F16 and ISO 200 with filters at 80 seconds to F16 and ISO 100 with filters at 160 seconds.

Clouds are a rarity in Dubai for 10 months of the year, so when there are some it helps with skies. Generally they are wispy and high so I wanted to blur them and induce a bit of movement, which I why I had to go to extreme lengths to get the effect I wanted! I also like to use the 10 stop for watery reflections where the long shutter smoothes the water and gives a cleaner reflection.

The more you stack filters, the more likely that image quality can be lost. Also, when using a really dark filter there is a colour cast as well. That's why I take a base shot without filters to match the original colour as accurately as possible to the filtered shot in Photoshop.

It takes a bit of practise but gives you the opportunity to add interesting effects into shots that have been taken many time before by many people (as in this Burj Khalifa shot) - it's not something you'd use all the time but I find it useful and if I'm out with a tripod then the filters are always in my bag along with a crib sheet below which I set up to help with the maths!



Image


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 Post subject:
PostPosted: Tue Feb 15, 2011 2:21 pm 
Wow Phil!!! Thanks for all the detailed information.


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 Post subject:
PostPosted: Thu Feb 17, 2011 10:24 pm 
My quick tip: don't buy cheapest ND filters, they will spoil your pictures both in terms of sharpness and color. My ones are so rubbish, I'd rather take a UV and smoke it, and still get better results. Avoid "Green.L" "brand".

If you don't have a ND filter with you, and your stream is still likely to be there in the evening, wait for a couple of hours, and you can enjoy long exposures again :)


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 Post subject:
PostPosted: Mon Feb 21, 2011 8:59 am 
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Joined: Thu Oct 08, 2009 11:24 am
Posts: 1826
Also, you have two styles of filter to consider. Screw in round and square/rectangular filters.

Both have their pros and cons. Ideally I'd go for a square/recangular set but I haven't stepped up to that yet. Generally the quality is higher for recangular high ND filters (Lee Big Stopper), as there is less of a colour cast. However they are never available and are a high price.

Stacking plain Hoya ND filters reduces the image quality in my experience, but I've stacked two B+W filters with no issues.


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