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Gerald
![Level 3 Level 3](rating3.gif) Joined: 25 Mar 2014 Posts: 1196 Location: Brazil
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Posted: Wed Jan 13, 2016 8:37 pm Post subject: |
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Gerald wrote:
The idea behind the lens shade is very simple. An ideal lens shade should:
1) allow the passage of ALL image-forming rays to the lens
2) block ALL non-image-forming rays
Failure to satisfy condition 1 produces vignetting. However, even if the condition 1 is fulfilled, image-forming rays have potential to produce flare and gosthing due to internal reflections in the lens. Make it certain that if a strong light source like the sun is included in the field of view, the effectiveness of lens shade to prevent flare is zero!
Failure to satisfy the condition 2 means that non-image-forming rays can penetrate the lens. However, this does not necessarily imply the occurrence of flare or gosthing. It all depends on specific details of each lens.
L = F x D / d
where:
L = lens hood length
F = focal length
D - lens hood diameter
d = sensor diagonal
This formula, which I had presented in a previous post and repeat here for convenience, gives the length of the lens hood that satisfies both the conditions 1 and 2 above, by assuming the lens aperture is small (large f-number). That formula is very simple and serves as a good starting point to analyze real cases in which lens aperture cannot be ignoredl.
When the aperture of the lens is taken into account, it is easy to see that the hood's diameter must be increased, or length must be reduced to prevent vignetting. Theoretically, for a lens with finite aperture, the hood dimensions must be infinite for simultaneously having a total absence of vignetting and blocking of all non-image-forming rays. In practice, a lens hood is not infinite, of course, but to be really efficient, its size must be huge, much bigger than most commercial lens hoods. Commercial lens hoods are in general sub-sub-sub-optimal from an optical point of view. Nonetheless, as said before, they can be useful to protect the lens from bumps, rain, snow, etc. And most people like the appearance of a lens with a hood. They think the lens looks cool...
Below a situation where no lens shade in the world would help as the sun is in the field of view of the lens (a Sigma fisheye 16mm). By the way, would the picture be better without gosthing?
![](http://forum.mflenses.com/userpix/20161/8001_DSC05431gosthing_1.jpg) _________________ If raindrops were perfect lenses, the rainbow did not exist. |
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Analog lex
![Level 1 Level 1](rating1.gif) Joined: 10 Nov 2013 Posts: 95 Location: East Europe
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Posted: Wed Jan 13, 2016 11:23 pm Post subject: |
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Analog lex wrote:
I prefer to use lens flares as art effect. ![Tuzki with lens](images/smiles/tuzki-bunny-lens.gif) _________________ =-=Canon eos 1100D=-=Zenit-E=-=
[RMC Tokina 35-105 macro FD][CZJ Sonnar 135mm f4 Exa][Jupiter-11 135mm f4 (silver)M39][Helios 44m-6][Helios-44-2 2/58][Vega-11u m39][Industar-50u][Tair-3fs][Mir-1B 2,8/37 (ВОЗМ)] |
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meanwhile
![Level 1 Level 1](rating1.gif) Joined: 29 May 2014 Posts: 225 Location: Australia
Expire: 2016-11-28
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Posted: Mon Jan 18, 2016 5:41 am Post subject: |
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meanwhile wrote:
Quote: |
The idea behind the lens shade is very simple. An ideal lens shade should:
1) allow the passage of ALL image-forming rays to the lens
2) block ALL non-image-forming rays |
OK, but lens hoods are not just simple cylindrical tubes - for a reason.
Given your use of the word ideal, you also left out:
3) Ergonomic
4) Practical _________________ In my bag: Sony A7II - Olympus OM 21mm f/3.5 - Minolta M-Rokkor 40mm f/2.0 - Konica Hexanon 57mm f/1.2 AR - Olympus Zuiko OM 100mm f/2.8 - Pentax 135mm f/3.5 |
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calvin83
![Level 4 Level 4](rating4.gif) Joined: 12 Apr 2009 Posts: 7555 Location: Hong Kong
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Posted: Mon Jan 18, 2016 5:56 am Post subject: |
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calvin83 wrote:
meanwhile wrote: |
Quote: |
The idea behind the lens shade is very simple. An ideal lens shade should:
1) allow the passage of ALL image-forming rays to the lens
2) block ALL non-image-forming rays |
OK, but lens hoods are not just simple cylindrical tubes - for a reason.
Given your use of the word ideal, you also left out:
3) Ergonomic
4) Practical |
I will add one more:
5) Aesthetic _________________ https://lensfever.com/
https://www.instagram.com/_lens_fever/
The best lens is the one you have with you. |
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anktonio
![Level 1 Level 1](rating1.gif) Joined: 20 Oct 2012 Posts: 219 Location: Spain
Expire: 2017-02-22
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Posted: Wed Feb 03, 2016 8:41 pm Post subject: |
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anktonio wrote:
meanwhile wrote: |
I know, obviously ... but we see glare too, sometimes I can see less than the camera, sometimes the other way around, depending on what kind of light, glare, reflections, etc. It's not necessary only in the photo. |
On the second photo, the light and the image were captured as your eye could have seen in the room, this day at that time. The good contrast and colour given by the lens was destroyed on the first photo, first: not having a good coating and second... not using a hood!
Happy shots! |
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Gerald
![Level 3 Level 3](rating3.gif) Joined: 25 Mar 2014 Posts: 1196 Location: Brazil
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Posted: Wed Mar 02, 2016 12:48 pm Post subject: |
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Gerald wrote:
A Thought From A Lens Hood Addict
"Shooting naked will make you vulnerable to... disapproval and even wrath from fellow photographers who religiously practice shooting with hoods."
http://oldlenses.blogspot.com.br/2016/02/a-thought-from-lens-hood-addict.html
... naked, disapproval, wrath, religion, addiction, lens hood ![Laugh 1](images/smiles/laugh-1.gif) _________________ If raindrops were perfect lenses, the rainbow did not exist. |
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padam
![Level 1 Level 1](rating1.gif) Joined: 09 Oct 2012 Posts: 175 Location: Hungary
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Posted: Thu Mar 03, 2016 12:59 pm Post subject: |
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padam wrote:
If you use a rangefinder, you cannot be sure about how the flaring will affect your image, so it is safer to have a lens hood on (even if it adds a little finder blockage)
But yes, it is more important that it looks badass
![](https://lh3.googleusercontent.com/-VKnY9_23-JE/Vtg03CqkB7I/AAAAAAAALgU/bRJI4amSix8/s1200-Ic42/DSC01799.JPG) |
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