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03-10-2011, 03:01 AM   #1
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Longest matching hood for lens

I read in somewhere in the articles that adding the hood really improves the contrast and colour and sharpness of the image.
Since then I am wondering which would be a longest possible matching hood (not the standard one for it) for Pentax DA 35mm F2.4 AL.
This question comes being a newbie I am not sure about a hood that will match its 49mm and also that will not come into its FOV.
Someone please suggest.

thanks

03-10-2011, 03:31 AM   #2
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I use a Cokin type system for the hoods on all my lenses, and as you can see by my signature, I have a few lenses.



You get one holder, the correct ring(s) for your lens(es), and stick on as many hood modules as you can without it coming into your field of view. Scroll down here to see what I'm talking about the multiple modules:

NEW Square Lens Hood Filter Hood for Cokin P series - eBay (item 270704920710 end time Mar-12-11 20:58:10 PST)

Not only is this dirt cheap, it really protects your lenses. And as you may know, this also holds filters.
03-10-2011, 03:44 AM   #3
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there is an other tread running for the "optimum hood" within that thread is a spreadsheet with a hood length calculator which is based upoon format and diameter of the hood.
03-10-2011, 09:01 AM   #4
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I'm on the same quest right now - looking for a better hood for both my newly aquired Sigma 50mm F1.4 and the older Sigma 70-200. Hoods are way to short for both lenses. I can even rotate the 70-200's lens hood on the 50mm lens and still get no vignetting!

So anyway I tried to find something helpful in that optimum hood depth calculator thread but none of it really helped.
To calculate you either need the hood's depth or its front diameter - both things I have to find out not to just fill in.

What I'd need info for cylindrical hoods. How long can they be for any given FL until they vignette.

03-10-2011, 06:56 PM   #5
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QuoteOriginally posted by Egg Salad Quote
I'm on the same quest right now - looking for a better hood for both my newly aquired Sigma 50mm F1.4 and the older Sigma 70-200. Hoods are way to short for both lenses. I can even rotate the 70-200's lens hood on the 50mm lens and still get no vignetting!

So anyway I tried to find something helpful in that optimum hood depth calculator thread but none of it really helped.
To calculate you either need the hood's depth or its front diameter - both things I have to find out not to just fill in.

What I'd need info for cylindrical hoods. How long can they be for any given FL until they vignette.
You need to be careful because every lens is different due to the actual element diameter and setback from the front of the filter screw threads
03-10-2011, 09:24 PM   #6
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Don't make this harder than it is. For a cylindrical hood just wrap a piece of black construction paper around the lens. Secure it with a rubber band or tape.

Adjust the length until it begins to vignette on the sides. Mark that length and continue extending until it vignettes on the top/bottom. That's the max length for that lens. Cut back the sides by the difference in the two measured lengths until it doesn't vignette.

Won't be pretty or perfect but it'll get the job OK done if the inside's flat black.

https://www.pentaxforums.com/forums/do-yourself/135542-diy-lens-hoods-no-math-required.html

H2
03-11-2011, 04:03 AM   #7
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The hood depth depends on its diameter, lens' f-number (diameter), and focal length. Here's a simple design:


The larger the cylinder diameter, the deeper the hood can be, therefore the more unwanted light blocked.

Pacerr's DIY experimental method is a good one.

Last edited by newarts; 03-11-2011 at 04:21 AM.
03-11-2011, 10:23 AM   #8
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Quick hood

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 both math AND have to build a field-expedient hood on the same day too.

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.

Now if they'd just make black, Styrofoam coffee cups . . .

H2





03-11-2011, 11:02 AM   #9
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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 both math AND have to build a field-expedient hood on the same day too...............
Thanks for the complement!

In the final analysis what matters is if the thing works. Your experimental method comes up with things that work & by no means am I trying to knock that result!

There's way too much nonsense covered up by impressive looking mathematics. Still, I'll keep trying - it is kind of a hobby & I think it is useful to identify directions and the existence of optima etc.

I just the other day saw:
The pessimist says the glass is half empty.
The optimist says the glass is half full.
The engineer says the glass is the wrong size.
03-11-2011, 05:15 PM   #10
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pacerr,
you are totally right.
I somehow forgot I could just try different hoods.
Only problem I really ran into is that I don't have thicker paper laying around here - let alone something black. Found something orange instead.

I like the idea of just building my own hood but I have demand in regards to quality I can't fulfill with DIY.

Even making your own petal shaped hood is a great idea but like I said I wouldn't like the result unless I had the means to do it on a CNC rotary cutter...

Either I'm too stupid to find fitting stuff that is already laying around somewhere or I really don't have anything that qualifies - because I couldn't even find anything with ~77mm diameter.

Also, I prefer my Leatherman whaich also has a scissor that is actually very nifty.

newarts,
I just tested the maths-approach with my Takumar hood.
Real diameter: 60mm, theoretical minimum diameter: 55,7mm. Very close.
Trying to verify this with the same hood and the SMC Pentax 50mm F1.4 I got that the hood's diameter had to be 66mm. So either the lens isn't really F1.4 or it's longer than 50mm because the hood doesn't vignette.

But what confuses me is the Sigma's 50mm F1.4 hood. It is designed for full frame so it is too short for APS-C. Nothing new. To get the optimum hood length/depth for APS-C I just have to make it 1,54x longer.

But its shallowest part is just 28mm away from the front element.
Calculations say it could be 64mm. That's a huge difference.
Does this lens - given the fact that it is a IF design lose so much focal lengt when focusing closer? (apparently not)

Anyway, calculations say a lens hood with 77mm diameter (filter thread size) could be ~96mm deep. That's huge.
No idea what Sigma did there because testing this with a self-made paper hood shows that I can put a hood 80mm deep and some more than 70mm diameter on it and get no vignetting - at no focus distance.

So I'll probably buy this hood Quality 77mm 77 Tele Telephoto Lens Hood Shade Metal bei eBay.de: Lens Hoods (endet 18.03.11 23:30:37 MEZ)

What would the cup be in my case?

If everything works out I'm engineer to be but I'm also a pessimist - so does this make the glass half empty and the wrong size?

Nice to see the internet is good for more than porn...
03-11-2011, 07:47 PM   #11
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QuoteOriginally posted by Egg Salad Quote
....
newarts, ...

...calculations say a lens hood with 77mm diameter (filter thread size) could be ~96mm deep. That's huge.
No idea what Sigma did there because testing this with a self-made paper hood shows that I can put a hood 80mm deep and some more than 70mm diameter on it and get no vignetting - at no focus distance.

So I'll probably buy this hood Quality 77mm 77 Tele Telephoto Lens Hood Shade Metal bei eBay.de: Lens Hoods (endet 18.03.11 23:30:37 MEZ)

.......
I calculate that the ebay.de 77mm diameter 74mm deep hood will probably vignette on a 50mm f:1.4 lens for a 30mm diameter (ASP-C) sensor. I think it should be 69mm deep (measured to the lens front element) to avoid vignetting.

But when I do actual tests I find the hoods can be a bit deeper than I calculate.
03-11-2011, 10:42 PM   #12
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QuoteOriginally posted by newarts Quote
I calculate that the. . .74mm deep hood will probably vignette . . .
"The perfect is the enemy of the good." Voltaire

Ahh, just grind off what gets in the way with a Dremel tool.

I've probably max'ed out the efficiency of a lens hood about as often as I've over-rev'ed an engine beyond its max rated RPM -- very rarely and then only by accident.

H2
03-12-2011, 03:41 AM   #13
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Since I tested with a both longer and narrower hood without vignetting this one should be totally "safe".
Also, I was calculating with a sensor diameter of 28.2mm. 30mm is more generous.

Theoretically I still had to search for a matching hood for the telezoom but at 70something mm depth there should be no chance of any unwanted stray light.

It's like always: the closer you want to get to perfect, the more you have to invest.
If it's worth it dedication and work is something everyone has to answer for himself (or herself).

I'm a perfectionist - but with a hood that is 85% perfect I guess I can just call it a day...
03-12-2011, 09:10 AM   #14
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With the understanding that ANY hood suited to the widest FL of a zoom lens will be less than optimum for its longer FL's, having a (few) tighter, disposable hood(s) along for critical situations at the long end makes some sense. Especially considering that the most use of a super zoom seems to be at the long end anyway.

Ideally, I'd put a tight hood on the long zoom and serendipitously discover I've selected a shorter lens that just happens to be "hood compatible" at the shorter FL's.

H2
03-12-2011, 11:25 AM   #15
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QuoteOriginally posted by sany Quote
I read in somewhere in the articles that adding the hood really improves the contrast and colour and sharpness of the image.
Since then I am wondering which would be a longest possible matching hood (not the standard one for it) for Pentax DA 35mm F2.4 AL.
This question comes being a newbie I am not sure about a hood that will match its 49mm and also that will not come into its FOV.
Someone please suggest.

thanks
There is no standard hood for that lens because it doesn't come with one. I went with the exact same setup as what is pictured in the thread linked below and it works perfectly on this lens.

https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/127299-da-35mm-f2-4-al-lens-my-hood-cap-solution.html
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