If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
Thread Tools | Display Modes |
#1
|
|||
|
|||
Please enhance my knowledge of dof scales
Hi, Trying to understand the theory behind the dof scales of my Nikon lenses I wonder what the distance between two f-stop marks stands for. I read in Merklingers " The Ins and Outs of FOCUS" that the dof scale is a ruler tha measures distances in the unit of the max allowable circle of confusion. But the distance between the f-stop marks is not the diameter of the circle of confusion, which is 0,03 mm in the case of Nikon. If I divide the distance between the focus mark and the mark for f/22 on my f/2,8 24 mm its 11 mm and 11 mm/22= 0,5 mm. Maybe the distance is coc*the pitch of the helicoid of the lens barrel?! Does someone know better? Best regards! Monica |
#2
|
|||
|
|||
Circle of Confusion in Nordhein-Westfalen
Monica Schulz (or is it Marc Wossner?) wrote:
Hi, Trying to understand the theory behind the dof scales of my Nikon lenses I wonder what the distance between two f-stop marks stands for. I read in Merklingers " The Ins and Outs of FOCUS" that the dof scale is a ruler tha measures distances in the unit of the max allowable circle of confusion. But the distance between the f-stop marks is not the diameter of the circle of confusion, which is 0,03 mm in the case of Nikon. If I divide the distance between the focus mark and the mark for f/22 on my f/2,8 24 mm its 11 mm and 11 mm/22= 0,5 mm. Maybe the distance is coc*the pitch of the helicoid of the lens barrel?! Does someone know better? Funny. Two posts via google groups, asking about Nikon DOF issues, and of a similar nature from "different people" at 83.135.226.213 (Bielefeld) 83.135.221.172 (Herne) http://tinyurl.com/yqejjj Cities less than 150km apart in Germany. Surely there is a Crop Circle of Confusion in Nordhein-Westfalen !! (Why do I get the feeling I know exactly who the poster is?) |
#3
|
|||
|
|||
Please enhance my knowledge of dof scales
"Monica Schulz" wrote
But the distance between the f-stop marks is not the diameter of the circle of confusion, which is 0,03 mm in the case of Nikon. If I divide the distance between the focus mark and the mark for f/22 on my f/2,8 24 mm its 11 mm and 11 mm/22= 0,5 mm. Maybe the distance is coc*the pitch of the helicoid of the lens barrel Yes, you need the distance from the film plane. How much you turn the lens is irrelevant and is dependant on the pitch of the helicoid. For 35mm work the relationship of lens movement to CoC is of little to no practical interest - just go by the scale on the lens. If you want 1/2 the mfg's CoC use 1/2 of the dof span marked on the lens. The acceptable CoC depends on the photographers desire for sharpness, the enlargement ratio and the viewing distance. Note that the CoC calculations assume a perfect ray bundle and this is not the case in real life. The rays don't come together at a point but form a 'sploge' at the film plane at the point of sharpest focus. The size of the splodge before and after the film plane is not as assumed in the DOF calculations. See the various aberrations he http://hyperphysics.phy-astr.gsu.edu...errcon.html#c1 -- Nicholas O. Lindan, Cleveland, Ohio Darkroom Automation: F-Stop Timers, Enlarging Meters http://www.darkroomautomation.com/index.htm n o lindan at ix dot netcom dot com |
#4
|
|||
|
|||
Circle of Confusion in Nordhein-Westfalen
Well done Alan but there is no mystery: Marc is my brother and as we share the same interest in photography we take part in posting to the usenet what we canīt solve on our own. Anyway, I wonder if there is a list out there that connects those ip numbers to the right cities?! Best! Monica |
#5
|
|||
|
|||
Please enhance my knowledge of dof scales
On 3 Jun., 00:21, "Nicholas O. Lindan" wrote:
"Monica Schulz" wrote But the distance between the f-stop marks is not the diameter of the circle of confusion, which is 0,03 mm in the case of Nikon. If I divide the distance between the focus mark and the mark for f/22 on my f/2,8 24 mm its 11 mm and 11 mm/22= 0,5 mm. Maybe the distance is coc*the pitch of the helicoid of the lens barrel Yes, you need the distance from the film plane. How much you turn the lens is irrelevant and is dependant on the pitch of the helicoid. Iīm sorry but thatīs not clear to me. Do you mean the distance between the f-stop marks equals or corresponds to the distance from the film plane? Monica |
#6
|
|||
|
|||
Please enhance my knowledge of dof scales
Monica Schulz wrote: On 3 Jun., 00:21, "Nicholas O. Lindan" wrote: "Monica Schulz" wrote But the distance between the f-stop marks is not the diameter of the circle of confusion, which is 0,03 mm in the case of Nikon. If I divide the distance between the focus mark and the mark for f/22 on my f/2,8 24 mm its 11 mm and 11 mm/22= 0,5 mm. Maybe the distance is coc*the pitch of the helicoid of the lens barrel Yes, you need the distance from the film plane. How much you turn the lens is irrelevant and is dependant on the pitch of the helicoid. Iīm sorry but thatīs not clear to me. Do you mean the distance between the f-stop marks equals or corresponds to the distance from the film plane? On the off chance that this is straight: The DOF marks indicate the distance limits for acceptable DOF. Say you focus at 5 meters and you are shooting at f/22. If one of the f/22 marks is now at 3 meters and the other is at 9 meters then the Depth Of Field or range of "acceptable" focus extends from 3 meters to 9 meters when focused at 5 meters at f/22 with that particular lens. |
#7
|
|||
|
|||
Please enhance my knowledge of dof scales
On Jun 5, 11:49 am, "
wrote: Monica Schulz wrote: On 3 Jun., 00:21, "Nicholas O. Lindan" wrote: "Monica Schulz" wrote But the distance between the f-stop marks is not the diameter of the circle of confusion, which is 0,03 mm in the case of Nikon. If I divide the distance between the focus mark and the mark for f/22 on my f/2,8 24 mm its 11 mm and 11 mm/22= 0,5 mm. Maybe the distance is coc*the pitch of the helicoid of the lens barrel Yes, you need the distance from the film plane. How much you turn the lens is irrelevant and is dependant on the pitch of the helicoid. Iīm sorry but thatīs not clear to me. Do you mean the distance between the f-stop marks equals or corresponds to the distance from the film plane? On the off chance that this is straight: The DOF marks indicate the distance limits for acceptable DOF. Say you focus at 5 meters and you are shooting at f/22. If one of the f/22 marks is now at 3 meters and the other is at 9 meters then the Depth Of Field or range of "acceptable" focus extends from 3 meters to 9 meters when focused at 5 meters at f/22 with that particular lens.- Hide quoted text - - Show quoted text - Bob has the right answer for you. The marks on the lens are to show the range of in focus with a certain f/stop. They really have not much to do with CoC or distance to the film plain to the lens opening. They allow you to "preset" your lens at a distance and with the proper f/ stop you can shot and run and still get an acceptable image. The f/stop is in direct relation to the opening size to the lens focal length. So a 50mm f/2 lens will measure 25mm across the opening. Okay? Nothing to do with the marks on the barrel. There isn't any stupid questions. Just some silly answers. Draco Getting even isn't good enough. Doing better does. |
#8
|
|||
|
|||
Please enhance my knowledge of dof scales
On Jun 5, 9:02 am, Draco wrote:
On Jun 5, 11:49 am, " wrote: Monica Schulz wrote: On 3 Jun., 00:21, "Nicholas O. Lindan" wrote: "Monica Schulz" wrote But the distance between the f-stop marks is not the diameter of the circle of confusion, which is 0,03 mm in the case of Nikon. If I divide the distance between the focus mark and the mark for f/22 on my f/2,8 24 mm its 11 mm and 11 mm/22= 0,5 mm. Maybe the distance is coc*the pitch of the helicoid of the lens barrel Yes, you need the distance from the film plane. How much you turn the lens is irrelevant and is dependant on the pitch of the helicoid. Iīm sorry but thatīs not clear to me. Do you mean the distance between the f-stop marks equals or corresponds to the distance from the film plane? On the off chance that this is straight: The DOF marks indicate the distance limits for acceptable DOF. Say you focus at 5 meters and you are shooting at f/22. If one of the f/22 marks is now at 3 meters and the other is at 9 meters then the Depth Of Field or range of "acceptable" focus extends from 3 meters to 9 meters when focused at 5 meters at f/22 with that particular lens.- Hide quoted text - - Show quoted text - Bob has the right answer for you. The marks on the lens are to show the range of in focus with a certain f/stop. They really have not much to do with CoC or distance to the film plain to the lens opening. They allow you to "preset" your lens at a distance and with the proper f/ stop you can shot and run and still get an acceptable image. The f/stop is in direct relation to the opening size to the lens focal length. So a 50mm f/2 lens will measure 25mm across the opening. Okay? Nothing to do with the marks on the barrel. But as Nicholas pointed out what is "in focus" is a bit subjective. And this will also depend on the camera that is being used. I find with either the 20D or the 350D that I have to use about 1 f/stop wider on the scale to get what I consider in focus. So for example if I am shooting at f/16 I use the f/11 marks on the lens. If I was shooting with a FF camera then I would likely find the f/16 marks to work much better. And if you are using a film camera then it will also depend on what film you are using since for example a ISO 800 print film will never be close to as sharp as say a 100 ISO slide film. Scott |
#9
|
|||
|
|||
Please enhance my knowledge of dof scales
On 5 Jun., 21:02, Draco wrote:
On Jun 5, 11:49 am, " wrote: Monica Schulz wrote: On 3 Jun., 00:21, "Nicholas O. Lindan" wrote: "Monica Schulz" wrote But the distance between the f-stop marks is not the diameter of the circle of confusion, which is 0,03 mm in the case of Nikon. If I divide the distance between the focus mark and the mark for f/22 on my f/2,8 24 mm its 11 mm and 11 mm/22= 0,5 mm. Maybe the distance is coc*the pitch of the helicoid of the lens barrel Yes, you need the distance from the film plane. How much you turn the lens is irrelevant and is dependant on the pitch of the helicoid. Iīm sorry but thatīs not clear to me. Do you mean the distance between the f-stop marks equals or corresponds to the distance from the film plane? On the off chance that this is straight: The DOF marks indicate the distance limits for acceptable DOF. Say you focus at 5 meters and you are shooting at f/22. If one of the f/22 marks is now at 3 meters and the other is at 9 meters then the Depth Of Field or range of "acceptable" focus extends from 3 meters to 9 meters when focused at 5 meters at f/22 with that particular lens.- Hide quoted text - - Show quoted text - Bob has the right answer for you. The marks on the lens are to show the range of in focus with a certain f/stop. They really have not much to do with CoC or distance to the film plain to the lens opening. They allow you to "preset" your lens at a distance and with the proper f/ stop you can shot and run and still get an acceptable image. The f/stop is in direct relation to the opening size to the lens focal length. So a 50mm f/2 lens will measure 25mm across the opening. Okay? Nothing to do with the marks on the barrel. Thank you Bob and Draco, itīs perfectly clear to me what the dof scales are beeing used for. What Iīm interested in is how the position of the f-stop marks are beeing derived. I know that they are based on the max allowable circle of confusion that the manufacturer thinks is appropriate. You can calculate that value for any lens using the formula that Norman Koren has on his website (http://www.normankoren.com/Tutorials/ MTF6.html#DOFscale): coc = f^2 / (Nmax(s-f) For most lenses itīs around 0,03 mm. But if I take a lens and measure the distances between the marks I find they are larger than this value. That was what made me ask if the pitch of the helicoid is involved in any case. - Nicholas said "Yes, you need the distance from the film plane." I still wonder if this means "Yes it is". Best regards! Monica |
#10
|
|||
|
|||
Please enhance my knowledge of dof scales
On 5 Jun., 21:34, Scott W wrote:
But as Nicholas pointed out what is "in focus" is a bit subjective. And this will also depend on the camera that is being used. I find with either the 20D or the 350D that I have to use about 1 f/stop wider on the scale to get what I consider in focus. So for example if I am shooting at f/16 I use the f/11 marks on the lens. If I was shooting with a FF camera then I would likely find the f/16 marks to work much better. snip As far as I know about the theory diffraction and pixel size might play a role in this case. At f/16 a lens produces a diffraction disk of 0,0217 mm diameter, at f/ 11 itīs diameter is only 0,0149 mm. If the 20D or 350D have pixel spacings much smaller than this the large diffraction disk will blur the image noticeably. And this is really the case. You can see it in a wonderful interactive sample on http://www.cambridgeincolour.com/tut...hotography.htm ("VISUAL EXAMPLE: APERTURE VS. PIXEL SIZE", middle of the page). Best! Monica |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Circle of confusion for nikons dof scales | Marc Wossner | 35mm Photo Equipment | 4 | May 27th 07 11:41 PM |
lack of knowledge about printing | Beach Bum | Digital SLR Cameras | 9 | January 16th 06 02:52 AM |
How to use knowledge of hyperfocal distance...? | [email protected] | Digital Photography | 11 | October 28th 05 03:36 PM |
FA: Darkroom Balance Chemical Scales | Dragonphoto1 | Darkroom Equipment For Sale | 0 | August 21st 05 11:34 AM |
To Acquire and Apply Knowledge | Ben Jimmie | Digital Photography | 3 | October 21st 04 03:29 AM |