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02-17-2013, 05:55 PM   #1
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Night Photos and Focus

I often read about focusing difficulties with wide angles in low light levels with manual lenses and am a bit puzzled with these statements.

For instance, if my desired subject are buildings at night like a skyline shot, my DOF android app says if shooting with a 14mm at f/5.6 then anything over 5.5 feet should be in focus to infinity. With a 28mm at the same f-stop, near focus limit is 15.7 and hyperfocal is 22.86 feet so anything of greater distance will be in focus. So I guess the question is why fool around eyeballing through the focus screen at all so long as the focus ring is turned to a distance somewhat greater than the minimum?


Last edited by arcturus; 02-17-2013 at 06:05 PM.
02-17-2013, 07:10 PM   #2
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One reason is, if you look at the focus scale of your M28 f/2.8, is that you would be hard pressed to know where 22.86 ft actually is.
(Compared to say, the scales on the P67 lenses which have graduations in this range.)
Anyway, I took that M28 f/2.8 lens outside and shot the garage door at a guess of 23 foot and f/5.6.
( the Door was about 35 foot away)
https://www.box.com/s/1hgle9m4rupkawu3s8pg

Although I didn't do it, stopping down below what the calculator suggests will always make a sharper shot, until maybe f/16 or so.
02-17-2013, 07:14 PM   #3
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I don't know which camera you use, but if no live focus how are you going to compose if you do not use the view finder? Which uses the focus screen.
02-17-2013, 08:30 PM   #4
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QuoteOriginally posted by wombat2go Quote
One reason is, if you look at the focus scale of your M28 f/2.8, is that you would be hard pressed to know where 22.86 ft actually is.
(Compared to say, the scales on the P67 lenses which have graduations in this range.)
Anyway, I took that M28 f/2.8 lens outside and shot the garage door at a guess of 23 foot and f/5.6.
( the Door was about 35 foot away)
https://www.box.com/s/1hgle9m4rupkawu3s8pg

Although I didn't do it, stopping down below what the calculator suggests will always make a sharper shot, until maybe f/16 or so.
Looks nice and sharp. My post was directed more in circumstances where items being photographed such as a skyline is no where near the minimum focus distance .

02-17-2013, 08:36 PM   #5
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QuoteOriginally posted by patrick9 Quote
I don't know which camera you use, but if no live focus how are you going to compose if you do not use the view finder? Which uses the focus screen.
Right, the focus screen is still needed for composition of course.
02-17-2013, 08:40 PM   #6
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Sure, in that case use judgement in the knowledge of HF distance, for example a whisker under infinity on your M 28 mm.
I learned this method with 18mm lenses on M43 camera which has no focus confirmation and focus zoom is a chore.
On the 9~18mm zoom I added an adhesive label with the f/4 Hypers, and use judgement to set the focus longer.
02-17-2013, 10:06 PM   #7
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All depth of field calculators start with an assumption: the smallest amount of detail you want. They might call it circle of confusion. That means the results they quote are "everything between 5 feet and infinity is sharp enough to show that point size you chose or sharper". They use this number because there really is a plane of focus, just one distance away from the lens. Everything in front or behind that is not quite as sharp as that plane. So you want your important details to be as close to that plane as you can get them.
In practice, all focus methods have weak spots, and that's the weak spot of depth of field calculators.
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