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Are Lens Shades Really Necessary?
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PostPosted: Mon Jan 11, 2016 1:25 pm    Post subject: Reply with quote
Gerald wrote:
The article by Marco Cavina has dozens of interesting photos of the Mirotar, one of a best mirror lenses ever built in the world, but I found no lens hood for Mirotar. Again, where is it?


Not sure, do you mean the one that Zeiss themselves recommend using?

"It is generally recommended to use the lens hood. For this, pull it out until it snaps in."

http://www.zeiss.com.au/content/dam/Photography/new/pdf/en/downloadcenter/contax_yashica/mirotar8_500mm_e.pdf

(It may not be the exact lens - but it is a Zeiss 500mm Mirotar - that Zeiss built the hood into - because it's useful)


PostPosted: Mon Jan 11, 2016 1:36 pm    Post subject: Reply with quote
Or maybe you mean this hood:



That is built to lock onto the 3 metal prongs on the inside of the front of the lens ...


You also conveniently forgot to mention the huge lens hoods shown that came with the 500 f/4 CZJ lenses, on the same page you got your Mirotar photo. Accidentally, I'm sure.

Last edited by meanwhile on Mon Jan 11, 2016 1:56 pm; edited 1 time in total


PostPosted: Mon Jan 11, 2016 1:55 pm    Post subject: Reply with quote
meanwhile wrote:
Not sure, do you mean the one that Zeiss themselves recommend using?

"It is generally recommended to use the lens hood. For this, pull it out until it snaps in."

http://www.zeiss.com.au/content/dam/Photography/new/pdf/en/downloadcenter/contax_yashica/mirotar8_500mm_e.pdf


First, that lens is not a real Zeiss Mirotar. I think it's a rebranded Yashica 500mm F8.

Second, I think Zeiss recommends using lens hood basically for the sake of mechanical protection.

Third, to effectively block ALL non-image-forming rays, the length of a lens hood would be excessive. Indeed, the length of a lens hood actually effective is given by:

L = F x D / d

where:

L = lens hood length
F = focal length
D - lens hood diameter
D = image sensor diagonal

For a full-frame camera, d = 43.2mm

For a 500mm lens, a REALLY effective lens hood with a diameter of 100mm should be 1157mm long!
For a 1000mm F5.6 Mirotar, a REALLY effective lens hood with a diameter of 200mm would be 4630mm long!!! Whoo Turtle
Obviously, these lens hoods are not practical.

As I said before, the shallow lens hood that some mirror lenses comes with is basically for the front lens protection against bumps and rain.

Last edited by Gerald on Mon Jan 11, 2016 2:03 pm; edited 1 time in total


PostPosted: Mon Jan 11, 2016 1:59 pm    Post subject: Reply with quote
Quote:
As I said before, the shallow lens hood that some mirror lenses comes with is basically for the front lens protection against bumps and rain.


Great, so you acknowledge their usefulness. Well done, you have grown.

I won't worry about your wiggle words by using ALL and REALLY (just like your use of "good" earlier, so you could change what you mean on the fly), and just leave it with you acknowledging that they do block some, and also have other uses. I think I'll put your conclusions to use and start utilising lens hoods. Thanks, Gerald!


PostPosted: Mon Jan 11, 2016 3:44 pm    Post subject: Reply with quote
meanwhile wrote:
Or maybe you mean this hood

That is built to lock onto the 3 metal prongs on the inside of the front of the lens ...


Possibly that short lens hood is non-standard, I don't know. The 3 metal prongs are basically to attach the lens cap.

Here a sales ad on ebay for Zeiss Mirotar 500mm F4.5. I see no lens hood, do you see?

"RARE mirror lens all in original condition"
http://www.ebay.ca/itm/MIROTAR-1-4-5-f-500mm-RARE-MIRROR-ZEISS-CONTAREX-SUPER-CAMERA-PLANAR-1-2-50-LENS-/201141396711?hash=item2ed4f624e7

It is obvious to me that this lens was designed from the start to work perfectly well without any lens hood.
(The other high-definition pictures in the ad are worth seeing, by the way)


PostPosted: Mon Jan 11, 2016 3:56 pm    Post subject: Reply with quote
What a beautiful Contarex with a Planar 50 f2 , mint condiiton and.......... an orinigal lens hood.


PostPosted: Mon Jan 11, 2016 4:20 pm    Post subject: Reply with quote
memetph wrote:
What a beautiful Contarex with a Planar 50 f2 , mint condiiton and.......... an orinigal lens hood.


I thought the original hood for the Contarex 50/2 Planar was rectangular . . . at least, mine was. And nicely made in metal. But ii did wobble a teensy weensy bit when on the lens. The Contaflex ones for the standard lenses were rubber and screwed in, rather than having a bayonet fitting. They didn't wobble.

I think I may take up collecting lens hoods.


PostPosted: Mon Jan 11, 2016 4:41 pm    Post subject: Reply with quote
scsambrook wrote:
memetph wrote:
What a beautiful Contarex with a Planar 50 f2 , mint condiiton and.......... an orinigal lens hood.


I think I may take up collecting lens hoods.

Yes they work even better without lens.


PostPosted: Mon Jan 11, 2016 4:41 pm    Post subject: Reply with quote
memetph wrote:
What a beautiful Contarex with a Planar 50 f2 , mint condiiton and.......... an orinigal lens hood.


That is creative imagination! Laugh 1


PostPosted: Mon Jan 11, 2016 4:54 pm    Post subject: Reply with quote
Best lens hood is transparent lens hood:



PostPosted: Mon Jan 11, 2016 4:58 pm    Post subject: Reply with quote
vanylapep wrote:
Best lens hood is transparent lens hood:


Like 1 Like Dog


PostPosted: Mon Jan 11, 2016 5:00 pm    Post subject: Reply with quote
Gerald wrote:
memetph wrote:
What a beautiful Contarex with a Planar 50 f2 , mint condiiton and.......... an orinigal lens hood.


That is creative imagination! Laugh 1


sometimes my humour is not understood....I have no idea how the original looks like....my humour was irony...towards you, dear Gerald.


PostPosted: Mon Jan 11, 2016 5:12 pm    Post subject: Reply with quote
I've got it, memetph.
A good use for your lens hood: Razz



Further details here:
http://petapixel.com/2013/02/13/a-wooden-hanging-lamp-shaped-like-a-giant-nikon-12-24mm-lens/


PostPosted: Mon Jan 11, 2016 5:56 pm    Post subject: Reply with quote
Seriously, Zeiss is using transparent lens hood.



PostPosted: Mon Jan 11, 2016 6:04 pm    Post subject: Reply with quote
Nordentro wrote:
It`s very easy to see flares thru a good EVF. Many of my lenses has uncommon filter sizes, so therefor I just use my hand on those (block the sun with my left hand) Wink


This is exactly what I do and you have to really look through the VF to make sure you don't miss flare. I do try to use the hoods on my longer lenses especially if they are the slide out type.
Pete


PostPosted: Mon Jan 11, 2016 6:11 pm    Post subject: Reply with quote
vanylapep wrote:
Seriously, Zeiss is using transparent lens hood.


The hood has to be trendy. Otherwise, it won't look good on the iPhone.
https://www.gottabemobile.com/2016/01/06/exolens-puts-zeiss-lenses-on-your-iphone-camera/


PostPosted: Mon Jan 11, 2016 6:48 pm    Post subject: Reply with quote
vanylapep wrote:
Seriously, Zeiss is using transparent lens hood.



Oh my Gosh! Et tu, Brute Zeiss?
How can I defend my position now that a lens hood is indispensable to prevent flare and gosthing?


PostPosted: Mon Jan 11, 2016 9:02 pm    Post subject: Reply with quote
Quote:

L = F x D / d

where:

L = lens hood length
F = focal length
D - lens hood diameter
D = image sensor diagonal


It's an interesting formula, where did it come from?
It seems to presume the use of round lens hoods?


PostPosted: Mon Jan 11, 2016 9:56 pm    Post subject: Reply with quote
meanwhile wrote:
Quote:

L = F x D / d

where:

L = lens hood length
F = focal length
D - lens hood diameter
D = image sensor diagonal


It's an interesting formula, where did it come from?
It seems to presume the use of round lens hoods?


Consider the diagram below:


I used the relation for similar triangles:

L/D = F/d

so:

L = F x D / d


PostPosted: Mon Jan 11, 2016 10:39 pm    Post subject: Reply with quote
Lens hoods to me seem to be used for the same reason people wear caps. Even if you are not looking directly at the sun, it helps you see without getting as much glare etc.

I usually use lens hoods because I don't use general purpose UV or skylight filters to protect the front element; they help protect again general (gentle) knocks and scrapes.


PostPosted: Mon Jan 11, 2016 10:45 pm    Post subject: Reply with quote
Accordion to some of the stuff I've looked at (which is just stuff on the internet, obviously) there's a slightly more complex way that adds in the variable of what diameter is needed at different hood lengths.

Helen B on APUG uses the following (and it went through some pretty rigorous checking and theorising in a wacky 10 page thread that makes this one look like paradise, complete with fake users pretending to be other people and all).

Quote:
f = lens focal length
S = film diagonal
L = diameter of front lens element
d = distance lens hood protrudes in front of front element, measured from the periphery of a convex front surface, not the vertex.

H = diameter or diagonal of lens hood

All measurements should be consistent, eg all in millimetres. It gives hoods that are slightly larger than George's. The formula is based on similar triangles, with the fundamental one being the one formed by the film diagonal and the focal length.

Strictly speaking it only applies for a round hood, but the correct calculation for a rectangular or square hood would require the aperture, and it would be more complicated. The error should not be great, though the error does reduce the size of the hood to slightly below what it would be with a rigorous calculation.

H = S.d/f + L


And then hoojammyflip added another calculation for rectangular hoods.

Quote:
If you want a more efficient design, imagine fitting the rectangular hood inside the circumference of the round hood. For a 2:3 35mm format, the hood will have sides of 0.55xRHD:0.83xRHD, which again comes from simple Pythag stuff.


http://www.apug.org/forums/forum51/33564-lens-hood-length-avoiding-vignetting-10.html


PostPosted: Tue Jan 12, 2016 12:32 am    Post subject: Reply with quote
Gerald wrote:
meanwhile wrote:
Quote:

L = F x D / d

where:

L = lens hood length
F = focal length
D - lens hood diameter
D = image sensor diagonal


It's an interesting formula, where did it come from?
It seems to presume the use of round lens hoods?


Consider the diagram below:


I used the relation for similar triangles:

L/D = F/d

so:

L = F x D / d

Gerald, what that calculates is simply the maximum length of hood before vignetting occurs. It has no relationship to the direction of
direct or reflected light rays that might cause flare or loss of contrast, and it doesn't take into account any amount that the front
element is recessed.

I once had a Jupiter 21M that flared badly due to internal reflections, and I experimented with various cardboard lens hoods up to
300mm long to see if I could overcome it. I didn't succeed but a hood certainly improved things a lot, however only up to about
75mm long. Longer lengths than that made no difference.

I presume you sometimes shade your eyes with your hand when you are looking towards the sun? Even if you can't directly hide the
sun, you can cut out a lot of reflected light from the sky and other surfaces. Shading any lens in the same way can make a huge
difference, not just to the amount of flare and haze but also to improve contrast and to prevent the meter from underexposing. I
don't see how you can argue differently.


PostPosted: Tue Jan 12, 2016 7:16 am    Post subject: Reply with quote
peterqd wrote:
Gerald wrote:
meanwhile wrote:
Quote:

L = F x D / d

where:

L = lens hood length
F = focal length
D - lens hood diameter
D = image sensor diagonal


It's an interesting formula, where did it come from?
It seems to presume the use of round lens hoods?


Consider the diagram below:


I used the relation for similar triangles:

L/D = F/d

so:

L = F x D / d

Gerald, what that calculates is simply the maximum length of hood before vignetting occurs. It has no relationship to the direction of
direct or reflected light rays that might cause flare or loss of contrast, and it doesn't take into account any amount that the front
element is recessed.
...


Even worse, with this formula you create hoods that work for object side telecentric lenses. For normal photo taking lenses (endocentric on object side, object may be larger than lens diameter) there is vignetting.


PostPosted: Tue Jan 12, 2016 8:25 am    Post subject: Reply with quote
Totally ridiculous, sorry.

The Sun effects a good portion of the compass on any given day, considerably more than 1%. Nearly every high end prime modern prime either comes with a shade, or there is a special one made for it. Why?

Because they are very useful. Smile


I was silly enough to believe a thread where many said such a shade was not necessary with this lens. I learned immediately it was. I should have kept the shots that were ruined. LOL

s.[/quote]

My Summicron R 90 has a 2 tier sliding hood. It doesn't prevent flair and would collapse if dropped so won't function as lrns protection either. Perhaps it's not "high end" enough for you?

( insert meaningless picture of costly gear here).
Like Dog


PostPosted: Tue Jan 12, 2016 8:39 am    Post subject: Reply with quote


Taken with a lens hood.
Laugh 1


Hmmm, are those....hoods?!?







Leica APO-Telyt-R 1:5.6/1600mm


And let us not leave out these big pricey ones as well..

http://petapixel.com/2015/04/28/bh-is-selling-a-used-canon-1200mm-f5-6l-lens-for-just-180000/

http://petapixel.com/2015/09/19/this-is-what-a-200mm-f1-0-lens-looks-like/
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