For discussion: DoF 2 article on LL.

amateur6 · 01-18-2008, 05:48 AM

First, let me say that I'm very respectful of Michael H. Reichmann and thankful for Luminous Landscape. But I was just doing some digging and came across this article:

DOF2

And while I won't take issue with the technical aspects (although I think the demonstration isn't complete enough to prove it), I think he's missed the point. Effectively, any discussion about DoF is subjective, and to my eye, you can see an obvious difference in focus just between the 400mm and the 200mm!

Granted, this is probably not due to a change in DoF, but the simple fact that in the image from the shorter lens the tower is smaller and thus will obviously appear "sharper" (because the eye can only resolve so much). The only way to really confirm the DoF would be to make an enlargement where the tower from the 17mm is the same size as the tower in the 400mm image -- and the result would be essentially academic anyhow because, after all, no one would actually to crop a 17mm image that severely.

Thoughts? Am I just being picky? Okay, yes, I am -- but because I think he started it by saying "Most photographers [are wrong]."

Last edited by amateur6; 01-18-2008 at 05:49 AM. Reason: typo

MRRiley · 01-24-2008, 07:07 PM

My turn to say I'm not stalking YOU... LOL

Saw you mention this thread and had to take a look. I think most of us were paying an inordinate amount of attention to the K20D threads and ones like this got lost in the wash.

Actually I think Mr. Reichmann has it right. From an optical standpoint, DOF does not change based on focal length. I think the problem is that DOF depends more on "distance of prime focus". I can't remember where I read the explanation but if I can find it I will post it.

p.s. loving the "magnification" thread... LOL

p.p.s. Found a good explanation here.

amateur6 · 01-25-2008, 03:42 PM

Originally posted by MRRiley

My turn to say I'm not stalking YOU... LOL

Actually I think Mr. Reichmann has it right. From an optical standpoint, DOF does not change based on focal length. I think the problem is that DOF depends more on "distance of prime focus". I can't remember where I read the explanation but if I can find it I will post it.

p.s. loving the "magnification" thread... LOL

p.p.s. Found a good explanation here.

Hey, stop trying to bury me in FACTS!

First, thanks for looking and having a good attitude. I think I was getting a little snarky over in Crop Factor (I haven't had a chance to go back to it yet!) and I appreciate that you, at least, didn't take it personally.

Okay, I'll accept as given that the math/facts support the assertion (not that I read them... zzzz...), but -- and this IS totally subjective -- just looking at the 400 and the 200 images over at LL (http://www.luminous-landscape.com/images/gremlin-400.jpg and http://www.luminous-landscape.com/images/gremlin-200.jpg), you don't think that the 200 looks "sharper"?

It definitely does to me, and here's my explanation: the tower is smaller in the 200. That means that even if the blur of its edges (actually, none of it is in focus, but stay with me) is the same percentage from one to the next, the physical measurement of the blur in the image is going to be smaller. And most people, I think, will interpret that as being "more in focus". Which is how you get the apparently mass delusion that "shorter focal length = more DoF"...

Make sense? Even if you disagree with the conclusion?

Jonson PL · 02-14-2008, 02:22 PM

Thanks a lot for the link to the LL article, I had been thinking about it quite a bit.

I think the reason people feel that WA lenses have more DOF, is that we rarely crop to compare to a 50 mm lens, etc.
This makes it easy to simply shoot with e.g. the Pentax 15/3.5 lens, and get most in focus. With a manual focus 50 mm attached, we would have to take much more care in acquiring focus.

With a 15 mm on a film camera, one would generally have to make a massive enlargement or crop, to run into DOF problems.

Also useful answer by Nick Rains in the LL article

And thanks to MRRiley for the Cambridge in colour link

Last edited by Jonson PL; 02-14-2008 at 02:27 PM.

01-18-2008, 05:48 AM	#1
amateur6 Senior Member Join Date: Mar 2007 Location: Rhode Island Photos: Gallery Posts: 177	For discussion: DoF 2 article on LL. First, let me say that I'm very respectful of Michael H. Reichmann and thankful for Luminous Landscape. But I was just doing some digging and came across this article: DOF2 And while I won't take issue with the technical aspects (although I think the demonstration isn't complete enough to prove it), I think he's missed the point. Effectively, any discussion about DoF is subjective, and to my eye, you can see an obvious difference in focus just between the 400mm and the 200mm! Granted, this is probably not due to a change in DoF, but the simple fact that in the image from the shorter lens the tower is smaller and thus will obviously appear "sharper" (because the eye can only resolve so much). The only way to really confirm the DoF would be to make an enlargement where the tower from the 17mm is the same size as the tower in the 400mm image -- and the result would be essentially academic anyhow because, after all, no one would actually to crop a 17mm image that severely. Thoughts? Am I just being picky? Okay, yes, I am -- but because I think he started it by saying "Most photographers [are wrong]." Last edited by amateur6; 01-18-2008 at 05:49 AM. Reason: typo

01-24-2008, 07:07 PM	#2
MRRiley Veteran Member Join Date: Feb 2007 Location: Sterling, VA, USA Photos: Gallery \| Albums Posts: 6,275	My turn to say I'm not stalking YOU... LOL Saw you mention this thread and had to take a look. I think most of us were paying an inordinate amount of attention to the K20D threads and ones like this got lost in the wash. Actually I think Mr. Reichmann has it right. From an optical standpoint, DOF does not change based on focal length. I think the problem is that DOF depends more on "distance of prime focus". I can't remember where I read the explanation but if I can find it I will post it. p.s. loving the "magnification" thread... LOL p.p.s. Found a good explanation here. Last edited by MRRiley; 01-25-2008 at 10:38 AM.

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01-25-2008, 03:42 PM	#3
amateur6 Senior Member Join Date: Mar 2007 Location: Rhode Island Photos: Gallery Posts: 177 Original Poster	Originally posted by MRRiley My turn to say I'm not stalking YOU... LOL Actually I think Mr. Reichmann has it right. From an optical standpoint, DOF does not change based on focal length. I think the problem is that DOF depends more on "distance of prime focus". I can't remember where I read the explanation but if I can find it I will post it. p.s. loving the "magnification" thread... LOL p.p.s. Found a good explanation here. Hey, stop trying to bury me in FACTS! First, thanks for looking and having a good attitude. I think I was getting a little snarky over in Crop Factor (I haven't had a chance to go back to it yet!) and I appreciate that you, at least, didn't take it personally. Okay, I'll accept as given that the math/facts support the assertion (not that I read them... zzzz...), but -- and this IS totally subjective -- just looking at the 400 and the 200 images over at LL (http://www.luminous-landscape.com/images/gremlin-400.jpg and http://www.luminous-landscape.com/images/gremlin-200.jpg), you don't think that the 200 looks "sharper"? It definitely does to me, and here's my explanation: the tower is smaller in the 200. That means that even if the blur of its edges (actually, none of it is in focus, but stay with me) is the same percentage from one to the next, the physical measurement of the blur in the image is going to be smaller. And most people, I think, will interpret that as being "more in focus". Which is how you get the apparently mass delusion that "shorter focal length = more DoF"... Make sense? Even if you disagree with the conclusion?

02-14-2008, 02:22 PM	#4
Jonson PL Veteran Member Join Date: Dec 2006 Location: Copenhagen Photos: Gallery Posts: 1,842	Thanks a lot for the link to the LL article, I had been thinking about it quite a bit. I think the reason people feel that WA lenses have more DOF, is that we rarely crop to compare to a 50 mm lens, etc. This makes it easy to simply shoot with e.g. the Pentax 15/3.5 lens, and get most in focus. With a manual focus 50 mm attached, we would have to take much more care in acquiring focus. With a 15 mm on a film camera, one would generally have to make a massive enlargement or crop, to run into DOF problems. Also useful answer by Nick Rains in the LL article And thanks to MRRiley for the Cambridge in colour link Last edited by Jonson PL; 02-14-2008 at 02:27 PM.