visualopsins
Joined: 05 Mar 2009
Posts: 10362
Location: California
Expire: 2021-06-22
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 Posted: Sun Oct 21, 2012 8:37 pm Post subject: |
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visualopsins wrote:
I think the reason why dof of 50/2 with 2X TC is equivalent to dof of 100/4 lens is in the definition of focal length. The FL of a lens is defined as the difference in magnification of a subject at two different distances. The 2X TC simply changes magnification of subject at each distance by 2, thus the difference, the FL, will double.
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Cameras: Sony A7Rii, Spotmatics II, F, and ESII, Nikon P4
M42 Asahi Optical Co., Lenses:
Takumar 1:4 f=35mm, 1:2 f=58mm (Sonnar), 1:2.4 f=58mm (Heliar), 1:2.2 f=55mm (Gaussian), 1:2.8 f=105mm (Model I), 1:2.8/105 (Model II), 1:5.6/200
Tele-Takumar 1:5.6/200, 1:6.3/300
Macro-Takumar 1:4/50
Auto-Takumar 1:2.3 f=35, 1:1.8 f=55mm, 1:2.2 f=55mm
Super-TAKUMAR 1:3.5/28 (fat), 1:2/35 (Fat), 1:1.4/50 (8-element),
Super-Multi-Coated Fisheye-TAKUMAR 1:4/17
Super-Multi-Coated TAKUMAR 1:4.5/20, 1:3.5/24, 1:3.5/28, 1:2/35, 1:3.5/35, 1:1.8/85, 1:1.9/85 1:2.8/105, 1:3.5/135, 1:2.5/135 (II), 1:4/150, 1:4/200, 1:4/300, 1:4.5/500
Super-Multi-Coated Macro-TAKUMAR 1:4/50, 1:4/100
Super-Multi-Coated Bellows-TAKUMAR 1:4/100
SMC TAKUMAR 1:1.4/50, 1:1.8/55
Other lenses:
Carl Zeiss Jena Flektogon 2.4/35
SMC PENTAX ZOOM 1:3.5 35~105mm, SMC PENTAX ZOOM 1:4 45~125mm
Nikon Micro-NIKKOR-P-C Auto 1:3.5 f=55mm, NIKKOR-P Auto 105mm f/2.5 Pre-AI (Sonnar), Micro-NIKKOR 105mm 1:4 AI, NIKKOR AI-S 35-135mm f/3,5-4,5
Tamron SP 17mm f/3.5 (51B), Tamron SP 17mm f/3.5 (51BB), SP 500mm f/8 (55BB), SP 70-210mm f/3.5 (19AH)
Vivitar 100mm 1:2.8 MC 1:1 Macro Telephoto
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Nordentro
Joined: 24 Jun 2010
Posts: 4719
Location: Lillehammer, Norway
Expire: 2015-01-29
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| Posted: Sat Mar 02, 2013 12:13 am Post subject: |
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Nordentro wrote:
| fermy wrote: |
| martinsmith99 wrote: |
Short simple answer...
Teleconverters will not affect DOF. Your 200mm F4 (for example) lens is still a 200mm F4 with the same DOF. |
| visualopsins wrote: |
Dof scale on lens is valid with or without TC.
Without TC, lens set at f/2, use distances between f/2 marks for dof.
With 2X TC, lens set at f/2, 2X TC loses 2 stops, so use distances between f/4 marks for dof. |
Folks, this makes no sense! Suppose you focus at 2m with the lens @f2. As you yourself just explained, 2x TC just crops the picture and enlarges the crop to the original size. Well, do this with any picture, it will look blurrier! That means that DOF has effectively shrunk compared to the shot taken with naked lens @f2. The DOF scale for F4 shows even greater DOF than DOF for F2 so it can not be accurate either. So to answer OP, DOF scale is inaccurate with TC.
What is true, is that if you maintain the same magnification then DOF will remain the same. However, in order to do so with TC, you'll have to step back. In other words, you'll have to focus at different (larger) distance, say 4m. In this scenario (same magnification), you can read DOF from F4 DOF scale for 2m. However, this is not how TC is typically used. |
Yes, true 
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Lars | Lens collection | Manuellfokus.no |
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