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DPChallenge Forums >> Hardware and Software >> Macro DOF: extension tubes/reversed lens/macro
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Showing posts 1 - 15 of 15, (reverse)
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 10/15/2007 11:55:33 AM · #1
How do they compare?

With my 50mm on 62mm of extension tubes, actually beat 1:1, getting about 1.2:1 magnification.

I also can shoot at a usual range of apertures, from 1.8 to 22.

So magnification and exposure aren't the issue, it's DOF.

How does the DOF vary among all options for getting to 1:1? Do macro lenses have deeper DOF than lenses on extension tubes? And how about reversed lenses?

Thanks!
 10/15/2007 12:00:26 PM · #2
Originally posted by levyj413:
How do they compare?

With my 50mm on 62mm of extension tubes, actually beat 1:1, getting about 1.2:1 magnification.

I also can shoot at a usual range of apertures, from 1.8 to 22.

So magnification and exposure aren't the issue, it's DOF.

How does the DOF vary among all options for getting to 1:1? Do macro lenses have deeper DOF than lenses on extension tubes? And how about reversed lenses?

Thanks!


Assuming a constant aperture for all of the variations, DOF is solely a function of magnification.
 10/15/2007 12:06:29 PM · #3
I'm going to post a writeup on my experience with my 50mm reversed on my 70-300mm when the Macro challenge is over. I estimate my magnification to be 2.9-8.75x out of the setup, and it's only $240 worth of lenses and a piece of tape (the reversing ring is on order now =)

But I agree, DOF was a huge pain at those levels. At max magnification, I estimated my frame was 4mm wide, making the DOF teeny tiny - I'd estimate on the order of 1/10mm. Talk about splitting hairs.

Message edited by author 2007-10-15 12:07:03.
 10/15/2007 12:07:52 PM · #4
PS - the 70-300 only goes to f/20 at 300mm. I notice that true macro lenses, like Canon's 180mm go to f/32. Now I know why!
 10/15/2007 12:09:26 PM · #5
Originally posted by smurfguy:
I'm going to post a writeup on my experience with my 50mm reversed on my 70-300mm when the Macro challenge is over.


Thanks, I'm sure that'll be very interesting. Please start a new thread., though. I wasn't clear enough - here I'm asking solely about DOF, and whether it varies among various macro options. If everyone agrees with spazmo, above, then this can be a very short thread. :)
 10/15/2007 12:15:58 PM · #6
Spazmo is correct. At distances much smaller than hyperfocal, the DOF is approximated by the formula: DOF = 2Nc(m+1)/m^2, where N is lens focal number, c is the circle of confusion (about 0.018mm for APS sized sensors), and m is the magnification. So, using that formula, and Jeffrey's example of magnification 1.2, assuming f11, then the DOF is about 0.6 mm!

One thing to remember, increasing the f-number too high will start to introduce diffraction blur, so the image will not be as sharp as more moderate apertures.
 10/15/2007 12:22:39 PM · #7
Originally posted by brownsm:
Spazmo is correct. At distances much smaller than hyperfocal, the DOF is approximated by the formula: DOF = 2Nc(m+1)/m^2, where N is lens focal number, c is the circle of confusion (about 0.018mm for APS sized sensors), and m is the magnification. So, using that formula, and Jeffrey's example of magnification 1.2, assuming f11, then the DOF is about 0.6 mm!

One thing to remember, increasing the f-number too high will start to introduce diffraction blur, so the image will not be as sharp as more moderate apertures.


N is the f-stop? F/1.8, F/16, etc?

Thanks for the info, both to you and spazmo. It seems the main benefit then of getting a real macro lens is in something like a 100mm+ focal length so I can back up from my subjects. With my extension tubes, the lens front was only about an inch from the subject.
 10/15/2007 12:24:38 PM · #8
GEEK!!!!
Originally posted by brownsm:
Spazmo is correct. At distances much smaller than hyperfocal, the DOF is approximated by the formula: DOF = 2Nc(m+1)/m^2, where N is lens focal number, c is the circle of confusion (about 0.018mm for APS sized sensors), and m is the magnification. So, using that formula, and Jeffrey's example of magnification 1.2, assuming f11, then the DOF is about 0.6 mm!

One thing to remember, increasing the f-number too high will start to introduce diffraction blur, so the image will not be as sharp as more moderate apertures.
10/15/2007 12:26:40 PM · #9
Originally posted by brownsm:
One thing to remember, increasing the f-number too high will start to introduce diffraction blur, so the image will not be as sharp as more moderate apertures.

Interesting - I'll have to look this up. I could swear that my f/20 shots weren't any sharper than my larger aperture shots, and now I know why! Some of my favorite shots were in fact in the fairly normal f/5.6 - f/11 range.
 10/15/2007 12:34:01 PM · #10
Com on now. If you don't have anything nice to say... :)

Originally posted by bassbone:
GEEK!!!!
Originally posted by brownsm:
Spazmo is correct. At distances much smaller than hyperfocal, the DOF is approximated by the formula: DOF = 2Nc(m+1)/m^2, where N is lens focal number, c is the circle of confusion (about 0.018mm for APS sized sensors), and m is the magnification. So, using that formula, and Jeffrey's example of magnification 1.2, assuming f11, then the DOF is about 0.6 mm!

One thing to remember, increasing the f-number too high will start to introduce diffraction blur, so the image will not be as sharp as more moderate apertures.
10/15/2007 12:34:23 PM · #11
Originally posted by levyj413:

Thanks for the info, both to you and spazmo. It seems the main benefit then of getting a real macro lens is in something like a 100mm+ focal length so I can back up from my subjects. With my extension tubes, the lens front was only about an inch from the subject.


Yes, the benefit to longer FL macro lenses is that they allow a longer working distance.

Keep in mind though that to get the same magnification with a longer FL lens will require a longer extension tube.
 10/15/2007 12:36:55 PM · #12
You just sounded way too much like an engineer. You analytical types just need to leave those technical discussions to the boys in development...

Actually, it was a great summary of magnification for everyone. The punchline about the mid range fstops being sharpest really hits home...Nice summary Steve

Originally posted by brownsm:
Com on now. If you don't have anything nice to say... :)

Originally posted by bassbone:
GEEK!!!!
Originally posted by brownsm:
Spazmo is correct. At distances much smaller than hyperfocal, the DOF is approximated by the formula: DOF = 2Nc(m+1)/m^2, where N is lens focal number, c is the circle of confusion (about 0.018mm for APS sized sensors), and m is the magnification. So, using that formula, and Jeffrey's example of magnification 1.2, assuming f11, then the DOF is about 0.6 mm!

One thing to remember, increasing the f-number too high will start to introduce diffraction blur, so the image will not be as sharp as more moderate apertures.
10/15/2007 12:39:34 PM · #13
Originally posted by Spazmo99:
Originally posted by levyj413:

Thanks for the info, both to you and spazmo. It seems the main benefit then of getting a real macro lens is in something like a 100mm+ focal length so I can back up from my subjects. With my extension tubes, the lens front was only about an inch from the subject.


Yes, the benefit to longer FL macro lenses is that they allow a longer working distance.

Keep in mind though that to get the same magnification with a longer FL lens will require a longer extension tube.


you also get the ability to focus to infinity. with the extension tubes, you lose that ability.
 10/15/2007 01:51:46 PM · #14
Originally posted by brownsm:
Originally posted by Spazmo99:
Originally posted by levyj413:

Thanks for the info, both to you and spazmo. It seems the main benefit then of getting a real macro lens is in something like a 100mm+ focal length so I can back up from my subjects. With my extension tubes, the lens front was only about an inch from the subject.


Yes, the benefit to longer FL macro lenses is that they allow a longer working distance.

Keep in mind though that to get the same magnification with a longer FL lens will require a longer extension tube.


you also get the ability to focus to infinity. with the extension tubes, you lose that ability.


Yes.

That said, extension tubes are also popular with bird photographers (and similar) to decrease the minimum focusing distance of super tele lenses.
 10/15/2007 02:08:26 PM · #15
If you are using flash, the lens will sometimes shade the area that you are shooting, esp with "on camera" flash using longer set ups, like a tele reversed, or on ext tubes. It happens with an older 55mm Ai micro nikkor and several other lenses that I like to use with extension tubes.
I like the 180mm 2.8 and a 11mm extension tube best for good bokeh and little critter shots. I don't think the setup gets into the 1/1 range, but it is great for walk around shooting out to about 8 ft and closer.
I also have a Vivitar 2X "macro" telextender that I like a lot, as it is a TC + a macro focusing ring that allows focusing to almost touching the object with the M N 55mm lens. It works well with the Ai 105 2.5 for small things too.
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