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DIY Lens Hoods - no math required
Posted By: pacerr, 03-04-2011, 11:54 AM

The ultimate purpose of a lens hood is to prevent unwanted light from impinging on the front element of your lens and it doesn't have to look pretty or cost a lot to achieve that goal.

It helps if the hood's cheap, light weight, folds to take up almost no room in your kit bag.and is somewhat adjustable in length.

Here's a step-by-step description of making one such hood -- no math required. This one's made from a file folder to show the layout and it can't get much cheaper. This took all of about 30 minutes to complete including the decision to do it and processing the photos.

1. Materials: use your own judgment as to what will work and how much you want to spend. Heavy-weight file folders are a good place to start but I've made 'em from poster board as thick as that used for the back of writing tablets. Start with something dark or spray paint the end product with flat black paint for best results.

2. Layout: there's no particular advantage to using other than a square shade which avoids having to design origami-type fold lines. As you can see, unequal sides simulate the tulip-shaped hoods and can be custom trimmed to any degree of precision you wish. The width of the "box" should equal the diameter of the lens barrel at the point of attachment. You can make it a tapered cone but that just complicates things and necessitates that origami trick to fold it. A good starting length is also equal to the diameter of the lens and this can be "trimmed" by moving the hood forward or back on the lens.



A filter ring MAY be a good aid in laying out the dimensions but be sure it's the same diameter as the lens barrel.

A smaller hood might be laid out so as to have only one glue seam if the material is large enough. I suppose you could go for an octagon pattern rather than square if you wanted to get closer to a round hood but still have it easy to fold.

Why not just trace the outline of one of the tulip hoods? Well, you could do that, but remember, a primary goal is to have a collapsible hood and round or tapered designs present fold problems.

3. Assembly: Glue, tape, rubber bands -- I assume you'll sort that out in the layout. Note the fit of this pictured hood is a little "sloppy". Two reasons: there's a ridge on the lens barrel that adds about 3mm to the diameter ahead of the rubber band, and the mounting tabs are just a little wider than necessary - they're clipped in the corners here but could be trimmed to a better fit as well.



Even if you already have a hood for your lens(es) you may want to make one like this as a space and weight saving solution for the trail. This hood's 120mm inside diameter! Which one of these would you rather carry?



I don't even want to think about the priceof a replacement hood for the Tamron SP 300/2.8 shown here even if I could find one. But more inportantly, this demo model won't go to waste; it'll be painted and tucked in the kit bag for a 'sunny day' afield.

(As a side note, here's a mod I've made to my tripod legs over the years. One fixed brace is disconnected and replaced with light-weight chain and a hook so that one leg can be adjusted independently. Works quite well in tight spaces or against a wall and the brace can be reattached if desired.)


Did ya notice I can twist that hood around the barrel to catch a stray light source and slide it back an' forth to adjust the length and vignetting? Even make it oversized or cut it up or bend a corner to compensate for the lack of a perfect tulip pattern while on site.

Oh, yeah, the metal Tamron hood weighs 3/4 pound where as the cardboard one comes in at 3/4 ounce (with the rubber band)!. An' the tabs are long enough it'll fit the SP 180 and SP 80-200 as well.

I'm a lifelong fan of pragmatic, field expedient solutions that I can afford an' I'd have to take out a mortgage if I had to replace the hood for that SP 300/2.8.

Besides, it's fun to watch the guys with $$$$'s-worth of gear go dumpster-divin' after the ones you throw away when they don't have anything with 'em in the field.
H2

Last edited by pacerr; 03-08-2011 at 02:49 PM.
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11-18-2011, 03:12 PM   #16
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QuoteOriginally posted by newarts Quote
Hood.diameter=Lens.diameter(Hood.depth/focal.length +1)
I just bought a 49 mm lens hood and wanted to check with this formula if I can use this hood for my F 28 mm f/2.8. The lens has a diameter of 30 mm and the hood has a depth of 21 mm. When I use this values I end up with a allowed diameter which is smaller than the lens diameter. Is this correct?
I checked the math: for every case hood.depth<focal.length+1 the allowed hood diameter is smaller than the lens diameter. Is this possible? I'm really no expert on this...
Another question: Does it make a difference if I use the lens on APS-C or film?

09-01-2012, 07:11 AM - 1 Like   #17
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QuoteOriginally posted by Davidw0815 Quote
I checked the math: Does it make a difference if I use the lens on APS-C or film?
Be pragmatic, not mathematic ! Unless you're going into the hood manufacturing business, the only mathematical equation that helps shade a lens is one scribbled on the hood itself.

In keeping with the original title of this thread there's really only two critical tests that count and fortunately (for me anyway) neither of 'em require math.

* Availability -- do you have the hood/shade with you and does it fit securely on the lens so it doesn't become a distraction?

* Efficiency -- does it protect the the front element of the lens from unwanted light without vignetting?

Everything else is either a personal cosmetic preference or related to availability, durability, price and convenience.

Make a tube out of dark paper. Attach it to the lens with a rubber band. Adjust it until it satisfies the two critical points above and let the size and shape of the results determine the suitability of any other device you might acquire or fabricate.

No math or batteries required.

H2

Shades do count!
09-01-2012, 10:23 AM - 1 Like   #18
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QuoteOriginally posted by Davidw0815 Quote
I just bought a 49 mm lens hood and wanted to check with this formula if I can use this hood for my F 28 mm f/2.8. The lens has a diameter of 30 mm and the hood has a depth of 21 mm. When I use this values I end up with a allowed diameter which is smaller than the lens diameter. Is this correct?
I checked the math: for every case hood.depth<focal.length+1 the allowed hood diameter is smaller than the lens diameter. Is this possible? I'm really no expert on this...
Another question: Does it make a difference if I use the lens on APS-C or film?
In the equation Hood.diameter=Lens.diameter(Hood.depth/focal.length +1) the term in the parentheses must be bigger than 1 (because 1 is added to another positive number, so hood diameter must be greater than lens diameter - probably you used (hood.depth/(focal.length+1)) instead of
(hood.depth/(focal.length)+1).

Here's a better equation and a description of where it came from.


using your numbers and the above equation

Hood diameter > Hood.depth*sensor.width/focal.length + lens diameter = 21*24/28+20 =38

With film, sensor.width is 36, not 24 so the hood diameter should be greater than 21*36/28+20=47, so I'd expect vignetting at the corners.

Dave in Iowa

Last edited by newarts; 09-01-2012 at 10:34 AM.
09-01-2012, 02:19 PM   #19
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DAMN! I LOVE it when you show 'pitchures' an' talk dirty like that, Dave. Sends shivers down m' spine, lad.

H2

09-01-2012, 04:06 PM   #20
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QuoteOriginally posted by pacerr Quote
DAMN! I LOVE it when you show 'pitchures' an' talk dirty like that, Dave. Sends shivers down m' spine, lad.

H2
Awwwww, thanks [Blush].

Actually, you only need to put a tube /box on the lens & cut it back 'till it doesn't show any more. (As you point out!)

Dave in Iowa

Last edited by newarts; 09-01-2012 at 04:18 PM.
09-02-2012, 06:15 AM   #21
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I'll be darned.

Someone should actually market a version of this lens shade design; or at the very least have it patentened (is that a word??).
09-02-2012, 10:02 AM - 1 Like   #22
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QuoteOriginally posted by newarts Quote
. . . put a tube /box on the lens & cut it back* 'till it doesn't show any more.
Yeah, my usual approach goes sumthun like this:

"Jus' keep addin' cardboard or (beer can) 'til she starts a gittin' dark in them corners, Bubba.

An' a l'il a thet mud on the inside'll kill the glare, too!"


H2

* Heck, just slide it forward 'til it shows dark at the top -- mark it -- slide some more 'til it shows at the sides -- mark it again -- an' ya don't even need a ruler (or a math equation!) to adjust the length.


Last edited by pacerr; 05-09-2013 at 09:10 PM.
05-14-2013, 06:46 AM   #23
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QuoteOriginally posted by pacerr Quote
Much as I'm enjoyin' Dave's math-based approach to this (an' yeah, I've run the numbers) I'm just too pragmatic (or lazy?) to do math AND have to build a field-expedient hood on the same day.

Here's a fruit cup container that needs only a squirt of black spray paint or a Magic Marker to become a Prized Lens Accessory of the finest kind -- a really, really cheap one! It literally took longer to set up the shot and transfer it to the computer than it did to trim the container -- or eat the contents which counts as extra benefit points.

Certainly neither precise nor optimum, but it does work for everything from my M 35mm up that has a 49mm filter ring and could be easily trimmed shorter for a wider FoV and/or larger diameter lens barrel. And I bet I'd have to search long and hard to find a scene that this hood wouldn't handle as effectively as the most expensive hood available. Plus more extra points for re-cycling?

And now you have an excuse to carry that Swiss Army knife with the neat little scissors you've never used. If they'd just make black, Styrofoam coffee cups . . .




As an interim, or ultimate, (depends on how you see it!) solution remove the glass from cheap 49mm filters and stack 'em until you begin to see vignetting -- then remove one. A little flat or semi-gloss black, spray lacquer makes 'em look nicer.

Filter rings generally absorb a lot more abuse than thin aluminum hoods and if the rim gets dinged, just replace the outer ring. Add or remove rings to suit various focal lengths for true versatility. Use a stepping ring and larger filters to build a conical hood.

You could wrap a cylinder of paper around the lens or just stack filters to determine the final length in advance if you have to find some filters.

H2
Thats a great idea! With the taper, and flexabilty you just cut to fit, and paint it black and I bet 90+% of the people would not know it from top end gear!!

05-14-2013, 06:51 AM   #24
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Well pacerr, that is simple and effective ... not too mention foldable .

But is it WR!?
05-15-2013, 02:50 PM   #25
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If I give you a spread sheet where you do no math, just enter numbers like the diameter of the hood, length of hood, diameter of front element and front element recess I can tell you whether itis beyond or below the limit for vignetting, is that good enough. P.s. I have already uploaded such a spreadsheet. It's called hoodcalc
06-07-2013, 03:22 PM   #26
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QuoteOriginally posted by newarts Quote
In the equation Hood.diameter=Lens.diameter(Hood.depth/focal.length +1) the term in the parentheses must be bigger than 1 (because 1 is added to another positive number, so hood diameter must be greater than lens diameter - probably you used (hood.depth/(focal.length+1)) instead of
(hood.depth/(focal.length)+1).

Here's a better equation and a description of where it came from.


using your numbers and the above equation

Hood diameter > Hood.depth*sensor.width/focal.length + lens diameter = 21*24/28+20 =38

With film, sensor.width is 36, not 24 so the hood diameter should be greater than 21*36/28+20=47, so I'd expect vignetting at the corners.

Dave in Iowa

I would like to point that this calculation will be correct for the rectangular hood. For the circular hood S (Sensor width) should be equal to sensor's diagonal dimension.

Cheers

Last edited by pavpen; 06-08-2013 at 09:56 PM. Reason: corrected spelling
02-03-2014, 08:17 AM   #27
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QuoteOriginally posted by mikeSF Quote
i didnt want to reveal my best hood making tip, but here goes...

...if you use bright yellow cardstock for the hood, you WILL attract butterflies and bees. If you are shooting close focus flowers, they will come toward you and then find the closest flowers.


my yellow hood got me these:


Neat trick! I love it....
02-03-2014, 08:49 AM   #28
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QuoteOriginally posted by mikeSF Quote
i didnt want to reveal my best hood making tip, but here goes...

...if you use bright yellow cardstock for the hood, you WILL attract butterflies and bees. If you are shooting close focus flowers, they will come toward you and then find the closest flowers.


my yellow hood got me these:


If this summer I will see a lot of people wearing yellow while doing macro photography, I will know who's fault is that

Great idea, that's for sure .
02-03-2014, 02:18 PM   #29
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QuoteOriginally posted by mrNewt Quote
If this summer I will see a lot of people wearing yellow while doing macro photography, I will know who's fault is that

Great idea, that's for sure .
ha, I still have my yellow cardstock hood and waiting for spring...
04-14-2014, 08:02 PM   #30
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I recently have done a LOT of shooting of aircraft using Runway 02 (generally pointing toward a compass bearing of 200 degrees mag) and into the low, afternoon winter sun. While the sun was usually not actually in the frame, it was often within 70 degrees of the lens axis. The cameras were the Kx, K200D and K5. Lenses were the DA 55-300, DA* 300, DA 18-135 and Tamron SP AF 24-135.

In those few days when I DID NOT use a hood for some reason there was a noticeable reduction in contrast if the sun, or even just bright hazy light, struck the front surface of the lens. It's easy to notice flare spots when the sun's within the frame, it's a much more subtle effect when the sun isn't in the frame but it's there.

When using a hood, ANY hood whose length was at least as long as the lens diameter provided flare protection that wasn't noticeably less than the manufacturer's dedicated tulip-type hoods intended for that specific lens.

Considering the cropped image circle associated with APS-C and the hoods provided to prevent vignetting of zoom lenses at the widest FL, I've reduced my working hood inventory to a few circular designs of a length that don't vignette at the widest FL with the intent that if a specific, noticeable flare situation arises I can always find and use a make-shift shade by many means.

The ubiquitous circular rubber hoods and a black paper wrap that can be positioned and fixed to the lens with a rubber band are regaining a favored place in my bag. Light, cheap, versatile, easy to carry and effective if you take the time to assure shade protection for the face of the lens.

[ The most expensive and least effective lens shade/hood I've ever used was a hyper-critical, sort'a voice activated, self-propelled human female holding sumthun. Try to re-sell one of those (in used condition) in the PF Marketplace if ya don't like it after a trial period! ]
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