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LucisPictor
Joined: 26 Feb 2007 Posts: 17633 Location: Oberhessen, Germany / Maidstone ('95-'96)
Expire: 2013-12-03
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Posted: Wed Sep 29, 2010 7:48 pm Post subject: Some thought about "sharpness"... (or rather " |
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LucisPictor wrote:
In a photo magazin from 2009 I have found a nice essay about "sharpness" and the problems to achieve it.
It's in German. Allow me to summarize the main aspects:
- The higher pixel count causes an increasingly dense pixel pitch. A 15 MPix APS-C-Sensor needs an optical modulation of the image which is twice as high as on (analogue) film.
- Not only the lens needs to have higher resolution power, also the precision of the whole focus mechanism and the bayonet need to be more precise to focus directly on the sensor level.
- Thus Curvature of Field, focus shift or variation of rendering within one lens copy are also more visible, since there is a displacement of the AF-calculated and the real focus level.
- Lenses that are controlled and focused by small motor rods have a normal free play which prevents the necessary exactness. That's one of the reasons why more and more manufacturers change to lenses with internal focus drive.
- Many photographers want a faster AF which can be achieved by lighter focus elements which moves faster but needs more play and by a steeper thread translation. Both methods cause a less precise focusing. The good old volution of highly precise manual lenses are not suitable for fast-focusing AF lenses. (Tell us about it! )
- Contrast-AF of compact cameras is more precise than the phase-AF of DSLRs but much slower so it is not used.
- The possible solution "manual focus" (hear, hear!) is often not usable, due to the super-bright matte screens inside the cams. In order to produce a bright viewfinder image with slow lenses (f/5.6 zooms), these superbright screens deflect the air image and thus do no longer base on a genuine matte screen*. The air image then does not have a defined position because the eye can re-focus on different levels estimating each one as "sharp".
- AF field indicators and other symbols that are casted on the screens distract the eye and impede the ability of the eye to focus correctly.
- APS and esp. 4/3 cams sport a smaller viewfinder and thus hamper precise focusing as well.
- Even LiveView does often not equal the image resolution (not even with the magnifying function) so that a mis-focus still is easily possible.
Conclusion: precise focusing is only possible when a lens with a not too steep focus translation and a suitable matte screen are used. (What a surprise! )
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*Some replacement screens can still do that (e.g. the EE-S for the 5D) _________________ Personal forum activity on pause every now and again (due to job obligations)!
Carsten, former Moderator
Things ON SALE
Carsten = "KAPCTEH" = "Karusutenu" | T-shirt?.........................My photos from Emilia: http://www.schouler.net/emilia/emilia2011.html
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Old list: http://forum.mflenses.com/viewtopic.php?t=65 (Not up-to-date, sorry!) | http://www.lucispictor.de | http://www.alensaweek.wordpress.com |
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Last edited by LucisPictor on Sun Oct 03, 2010 8:10 am; edited 2 times in total |
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Orio
Joined: 24 Feb 2007 Posts: 29545 Location: West Emilia
Expire: 2012-12-04
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Posted: Wed Sep 29, 2010 8:19 pm Post subject: |
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Orio wrote:
So you mean that we've been correct all the time? _________________ Orio, Administrator
T*
NE CEDE MALIS AUDENTIOR ITO
Ferrania film is reborn! http://www.filmferrania.it/
Support the Ornano film chemicals company and help them survive!
http://forum.mflenses.com/ornano-chemical-products-t55525.html |
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ludoo
Joined: 18 Sep 2009 Posts: 1397 Location: Milan, Italy
Expire: 2011-12-05
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Posted: Wed Sep 29, 2010 8:59 pm Post subject: Re: Some thought about "sharpness"... |
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ludoo wrote:
LucisPictor wrote: |
AF field indicators and other symbols that are casted on the screens distract the eye and impede the ability of the eye to focus correctly. |
That was also one of my main gripes with the 5D, whose focus points in the vf were incredibly distracting. I bought a spare screen (the one that sits on top of the focusing screen) so as to cut away most of it in order to free my vf from the focusing points. In the end it was easier to switch to the K-x, which has no focus indicators and coupled with an EE-S screen (cut to size) gives me a totally naked viewfinder.
Thanks for summarizing the article! |
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visualopsins
Joined: 05 Mar 2009 Posts: 10967 Location: California
Expire: 2025-04-11
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Posted: Wed Sep 29, 2010 10:53 pm Post subject: |
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visualopsins wrote:
Thanks for summarizing the article LucisPictor! I am enjoying all of your recent informative posts.
This essay might have been about 'Focus' imho. _________________ ☮☮☮☮☮☮☮☮☮☮☮☮☮☮☮☮☮☮☮☮☮☮☮☮☮☮☮☮☮☮☮☮ like attracts like! ☮☮☮☮☮☮☮☮☮☮☮☮☮☮☮☮☮☮☮☮☮☮☮☮☮☮☮☮☮☮☮☮
Cameras: Sony ILCE-7RM2, Spotmatics II, F, and ESII, Nikon P4
Lenses:
M42 Asahi Optical Co., 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
M42 Carl Zeiss Jena Flektogon 2.4/35
Contax Carl Zeiss Vario-Sonnar T* 28-70mm F3.5-4.5
Pentax K-mount SMC PENTAX-A 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 (151B), SP 500mm f/8 (55BB), SP 70-210mm f/3.5 (19AH)
Vivitar 100mm 1:2.8 MC 1:1 Macro Telephoto (Kiron)
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bogolisk
Joined: 20 Dec 2009 Posts: 448
Expire: 2011-11-18
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Posted: Thu Sep 30, 2010 12:38 am Post subject: |
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bogolisk wrote:
I believe: focusing, PD and CD, AF and MF, in the future will all move to the main sensor (a la Fuji). _________________ When I try to be a photographer I manage to add an f to art. |
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LucisPictor
Joined: 26 Feb 2007 Posts: 17633 Location: Oberhessen, Germany / Maidstone ('95-'96)
Expire: 2013-12-03
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Posted: Thu Sep 30, 2010 2:56 pm Post subject: |
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LucisPictor wrote:
Orio wrote: |
So you mean that we've been correct all the time? |
It seems so.
visualopsins wrote: |
This essay might have been about 'Focus' imho. |
Yes, perhaps. But in this essay dissatisfying sharpness was mainly reduced to misfocus. _________________ Personal forum activity on pause every now and again (due to job obligations)!
Carsten, former Moderator
Things ON SALE
Carsten = "KAPCTEH" = "Karusutenu" | T-shirt?.........................My photos from Emilia: http://www.schouler.net/emilia/emilia2011.html
My gear: http://retrocameracs.wordpress.com/ausrustung/
Old list: http://forum.mflenses.com/viewtopic.php?t=65 (Not up-to-date, sorry!) | http://www.lucispictor.de | http://www.alensaweek.wordpress.com |
http://www.retrocamera.de |
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Transit
Joined: 20 Jun 2010 Posts: 52 Location: Wanganui
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Posted: Sun Oct 03, 2010 12:37 am Post subject: Re: Some thought about "sharpness"... |
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Transit wrote:
LucisPictor wrote: |
.......
Conclusion: precise focusing is only possible when a lens with a not too steep focus translation and a suitable matte screen are used. (What a surprise! )
....
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Thanks for the translation.
I knew there was a reason I was doing this again
http://www.pentaxuser.co.uk/forum/topic/split-focus-screen-for-k100d-adventure-22770
Pete _________________ Pentax K-1 K-01 Q7 some len |
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