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Lens Hoods and caps

sportback

sportback

Member
I sometimes wonder if I'm in a minority of one on this planet. I seem to have strange ideas about most things - one of them is lens hoods.

I tend to use, well, actually always use a lens hood, for the obvious reasons (Extraneous light, protection of the front element etc) and I've often wondered why it is that Hasselblad/Zeiss don't provide a series of caps that fit the HOOD?

It seems truly amazing to me when I read the Compendium, that with the hundreds of accessories made for the Hasselblad system, that this was never considered important enough. I once wrote to Sweden with this same question - sadly I never received a reply.

Is there anyone else out there as crazy as me?:z04_5769:
 
sportback said:
Is there anyone else out there as crazy as me?:z04_5769:
Click to expand...


Lenscaps for square hoods are a bit difficult.
The good news is there is a third party lens cap availalble for round hoods as used with WA C lenses as well as for the SWC with C lens.
 
I'm sorry but I have to disagree - but then I'm a product of the 'Blue Peter' school of do-it-yourself :)

('Blue Peter' was a BBC TV production for children, and during each programme kids were shown how to build everything from book stands to Inter Continental Ballistic Missiles from wire coat hangers and sticky tape)

I'll post some pictures of my home made plastic caps for SQUARE lens hoods - and the crazy thing is, that one size fits practically all, from 80mm to 250mm.
 
Maybe we can change the name of this thread to "Pet Peeves." I too have a similar peeve I'll share - Mine also concerns the lens hoods, but not the lack of a cap for them, but their shape. It is strictly my opinion, but one which no one will convince me otherwise:
The purpose of a lens hood is to prevent stray light from entering the lens, and finding its way to the film or sensor, thus degrading the image. So it seems to me that the hood would provide better or best protection if it were the shape of that it was protecting - ie, the lens. And lenses are round, not square. So why do major lens manufacturers like Zeiss and Leitz insist on square or rectangular shaped hoods?? They say it better protects the film or sensor which happen to be rectangle or square. But if you stop to think about it, the hood would do a better job of preventing stray light from hitting the film/sensor IF it did a better job of protecting the lens. With a square hood, you have 4 corners which are more susceptible to stray light. With a round hood, the front glass element is more protected. If stray light can get past the front element, you're pretty much SOL.
So, in my humble opinion, these big companies have it all wrong. Hoods should be ROUND, not square.
Michael
 
For a round lens hood, suppose the radius of the smallest circle that would not mechanically vignette is 1. The area of that circle will be pi, approximately 3. The smallest non-vignetting square fits inside the circle with just the corners touching, and the area would be 2. The smaller the area, the smaller the amount of non-image-forming light falling on the front element.
 
Well I don't know about all that, but what I can be sure is that it's a whole lot simpler to have a cap on the hood...whatever shape it is :rofl:

Here's one of mine...
 

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sportback said:
Well I don't know about all that, but what I can be sure is that it's a whole lot simpler to have a cap on the hood...whatever shape it is :rofl:

Here's one of mine...
Click to expand...

Duct tape..

On the C50 and C38 lenshood you can fit an original Hasselblad cap. I had one on my C50 hood, very practical. Unscrewing that bloody hood all the time just does not make sense.

Wilko
 
Yes, duct tape - covering a hand-crafted plastic cap!

When I 'dusted off' my 'blad gear after 25 years in boxes, the three caps I'd made all those years ago were fine - obviously a very superior class of duct tape used all those years ago!!
 
Matthew Runkel said:
For a round lens hood, suppose the radius of the smallest circle that would not mechanically vignette is 1. The area of that circle will be pi, approximately 3. The smallest non-vignetting square fits inside the circle with just the corners touching, and the area would be 2. The smaller the area, the smaller the amount of non-image-forming light falling on the front element.
Click to expand...

But then what would the diagonal of the square be? And you could always make the hood a little longer. Nope - you can't convince me that a square hood on a round lens is better. Sorry.
 
The diagonal of the square is 2. The square is composed of two triangles with height 1 and base 2. Therefore the area of the square is 2 * 1/2 2 * 1 = 2

So the smallest-necessary square shade has a smaller area than the smallest-necessary circular one, and thus admits a smaller amount of non-image-forming light.
 
Let me try it this way -

If you have a lens with a 52mm thread, a hood, whether round or square will have to have a round opening of 52mm in order to screw into the lens, regardless of the length of the hood.
A square hood would have to have the same 52mm circle bored out in order to fit the lens, meaning that the height & width of the square hood would have to be a minimum of 52mm, so as not to block the lens. IF the square has a height & width of 52mm (which of course is the widest of any measured diameter around the circular hood), then the diagonal measurement of the square hood has to be longer than 52mm, thus less effective than a round hood.
Michael
 
Michael, your lens with 52mm threads will require a round lens hood with a larger diameter to prevent vignetting in the corners of the image. You can see for yourself if you stack filters on a wide angle lens. More than one or two frequently results in vignetting.

The solution is to make the lens shade the same shape as the image so that vignetting is not a problem. In the case of a rectangular (or square) image, the smallest hood that will not vignette will always be a rectangle (or square); any other geometry will necessarily be larger.

Mike
 
A square lens hood blocks more stray light than a round hood can.

The only problem with a square hood is that some people cannot put them on straight. The proper technical term for this is an Operator Assisted Failure, as in "the OAF did this" or "the OAF did that".

I hope that this clarifies the reason and use of square lens hoods.

Steve
 
What is wrong with some new expressions from time to time?

Operator Induced Failure sounds ok to me.
 
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