How to find a matching lens hood?

[timo832000]

I still need hoods for two of my lenses.

1. SMC Pentax - M 2.0/28 (49mm filter thread)
2. SMC Pentax - M 1.7/50 (49mm filter thread)

Both lenses are used on Pentax K-r (Crop 1.5).

How can I calculate the dimensions of the perfect hood?
I would prefer to buy a simple metal hood for each lens, how long should they be?


Thanks for your advice.


Timo


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[Attila]

normal lens is easy any hood okay I think, wide is different , do you sure do you really need hood ?
I never use hoods , most lens works well without hood.

[timo832000]

Yes I think so, I got some images with low contrast or lens flare caused by bright lateral light. On the other hand a hood will also protect the front elemet from unwanted touch.

I even got the feeling that a bright light source which shines into the lens but can`t be seen in the view finder because of the crop factor of my camera nevertheless can bother my image.

[Attila]

On 49mm filter thread my suggestion is take an East German rubber hood very practical, 20mm I have really no idea , I have factory hoods for some 20mm lenses they are usually nothing just a little ring. Try to make a DIY one from card board and look which size is okay .

[TimHar]

A good read http://toothwalker.org/optics/lenshood.html

[luisalegria]

For 28mm on crop almost any "normal" metal hood will be fine. This is like a 42mm on crop, so there usually isn't a vignetting problem.
If you are concerned, get a plastic "flower" hood.
As Attila says, the ordinary rubber hoods are good also. I use one with my 24mm Pentax on crop (36mm equivalent).

Just be careful with filters, filter+hood could cause vignetting. On DSLR there is rarely a reason to use a filter, except sometimes a polarizer.

Another way, if you are concerned with vignetting, is to get a normal metal hood one or two sizes larger - say 52-55mm for 49mm, and use it with a step-up adapter. I would certainly do this with a polarizer.

Look in ebay, there are plenty of normal hoods from China for $3, plastic or metal.
Step up adapters are $2-3

The cheap 'wide angle' metal hoods they sell are usually too large and don't look good on a little lens, and I think they aren't such good protection.

I always use a hood, no matter what lens. Its better protection than a filter, and it improves results, often surprising by how much.

[gmonkman1]

I always prefer to use a hood on all my lenses too. With 1.5 sensor it is easier
to find lens hoods because you are only using most of the centre part of the
lens. Since I no longer use alot of my old film filters , I remove the glass part
and just use the rings as hoods. My pentax 50mm 1.7 uses four rings
(thickness may vary) so use 3 or 5. Makes a perfect hood.
Once you have them on...turn lens to smallest aperture (highest f number)...
aim at bright wall or blue sky...press aperture stop down button to check in
view finder to see if vignetting and adjust accordingly.Works for any lens.

[Lightshow]

On 1.5x, I typically just go to the next longer hood, so far so good, just look for vignetting in live view.
24->28
28->35
35->50
50->85

[tao]

When I was new to m4/3 I simple made a long paper hood for each lens and cut it down until I did not see any vignette before go on hunting on eBay. Now I have so many hoods I don't have to do that any more.

[Orio]

[timo832000]

Thanks Orio, this is really simple. Very good Idea, I will do that.

Timo