Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
10-06-2008, 03:31 PM   #46
baw
Senior Member




Join Date: Dec 2006
Location: Neterlands
Posts: 189
Original Poster
DOF discussion

I feel the DOF concept isn't overly complex, especially if you separate the optical and the imaging/viewing part.
Optical results in CoC's on the sensor/film, imaging/viewing in a CoC limt, that decides which CoC's fall within DOF.

That's the gist of the "Back to the basics" post above. I'm interested in comments pro or contra this post to see if I have to change something in my reasoning

In practice you may be interested in this concept. It's a bit different from the hyperfocal focussing thing: focus on the background and stop down as needed to resolve foreground objects. useable for landscapes etc.

Problem with the DOF preview button to me is the small size of the LCD screen. Allmost everything seems to be sharp on that screen (or in the viewfinder, but then everyhing turns allmost dark when stopping down.

10-06-2008, 04:11 PM   #47
Veteran Member
sewebster's Avatar

Join Date: Jun 2008
Location: Vancouver, BC
Photos: Gallery
Posts: 535
QuoteOriginally posted by baw Quote
I feel the DOF concept isn't overly complex, especially if you separate the optical and the imaging/viewing part.
Optical results in CoC's on the sensor/film, imaging/viewing in a CoC limt, that decides which CoC's fall within DOF.

That's the gist of the "Back to the basics" post above. I'm interested in comments pro or contra this post to see if I have to change something in my reasoning

Like the other guys I have to say that I am tiring of the subject.

Your Back to basics post seems generally good, but I don't think your last example (25mm f/2 vs 100mm f/8) works. The DOF for those two cases is very different (around 20m for the 25mm and 3m for the 100mm). I don't think the final crop and enlarge on the 25mm lens photograph will actually decrease the perceived depth of field down to 3m.
10-06-2008, 04:29 PM   #48
Otis Memorial Pentaxian
stevebrot's Avatar

Join Date: Mar 2007
Location: Vancouver (USA)
Photos: Gallery | Albums
Posts: 37,931
QuoteOriginally posted by sewebster Quote

Like the other guys I have to say that I am tiring of the subject.

I...am...soooo...tired...zzzzzzzzzzzzzz :ugh:

Steve
10-07-2008, 02:30 AM   #49
Forum Member
brownargus's Avatar

Join Date: Sep 2008
Location: Rotherham, South Yorkshire, UK
Posts: 55
Fascinating discussion. I printed off all the posts to read and digest. Didn't realise that DOF could be so complicated. Accept that CoC is dependent on the final image (print) and agree that DoF can be difficult to assess in-camera using the DoF preview.

I shall continue to use the technique I have used for many years - ensure that the key point in the image is at the point of sharpest focus, e.g. the eye of the bird or head of a dragonfly and make sure that I maximise the DoF by using the smallest aperture commensurate with acceptable shutter speed. And use viewfinder magnifier and a tripod wherever possible.

Thanks all
John

10-07-2008, 07:32 AM   #50
baw
Senior Member




Join Date: Dec 2006
Location: Neterlands
Posts: 189
Original Poster
QuoteOriginally posted by baw Quote
To check my example, use DOFMaster. It has the option to select a CoC limit iso camera.
Just use a 4 x higher CoC limit for the 100mm because you magnify the 25mm crop 4 times. so .001 and .004 or .002 and .008 etc.
I still had this Excel sheet on my harddisk.
All distances are calculated using DOFMaster.
For those of you still interested:
Code:
Distance from lens where diff. CoC's originate from.		
Both lenses focussed at 10m.

CoC (mm) 25mm f/2 100mm f/8

0.12 2.1 5.1
0.11 2.2 5.3
0.10 2.4 5.6
0.09 2.6 5.8
0.08 2.8 6.1
0.07 3.1 6.4
0.06 3.4 6.8
0.05 3.9 7.2
0.04 4.4 7.6
0.03 5.1 8.1
0.02 6.1 8.6
0.01 7.6 9.3

0.00 10.0 10.0

0.01 14.7 10.9
0.02 27.7 11.9
0.03 235.8 13.1
0.04 infinity 14.6
0.05 infinity 16.6
0.06 infinity 19.1
0.07 infinity 22.4
0.08 infinity 27.3
0.09 infinity 34.8
0.10 infinity 48.1
0.11 infinity 77.6
0.12 infinity 210.6
Compare CoC 0.01 for 25mm vs. 0.04 for 100mm
Or 0.02 vs 0.08 or 0.03 vs 0.12
10-07-2008, 01:43 PM   #51
Veteran Member
sewebster's Avatar

Join Date: Jun 2008
Location: Vancouver, BC
Photos: Gallery
Posts: 535
QuoteOriginally posted by baw Quote
To check my example, use DOFMaster. It has the option to select a CoC limit iso camera.
Just use a 4 x higher CoC limit for the 100mm because you magnify the 25mm crop 4 times. so .001 and .004 or .002 and .008 etc.
I don't think it is that simple. Once the image is captured by the sensor, certain parts of it will be "permanently" sharp because the CoC was smaller than the pixel size. So you can enlarge the image without starting to detect out-of-focus.

I'm starting to get a little out of my comfort zone with this reasoning, but I would really doubt that your 25mm vs 100mm test works in practice. You could try it and post photos, but I'm not really super-interested at this point.
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
camera, dof, length, photography, ratio, relationship, reproduction, test
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
DA*16-50 dof Adam Lucas Pentax SLR Lens Discussion 3 08-30-2010 10:29 AM
DOF ,EV jolee1990 Troubleshooting and Beginner Help 4 12-15-2009 12:01 PM
Help with DOF RonMexico Post Your Photos! 3 02-02-2009 06:03 PM
dof menappi Pentax DSLR Discussion 11 07-12-2008 07:23 PM
How to get more DOF??? Help rmtagg Pentax SLR Lens Discussion 12 03-18-2008 07:10 PM



All times are GMT -7. The time now is 11:08 AM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top