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06-13-2015, 03:04 AM   #1
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Alternative lens hood for DA21

As you know, DA21 comes with a complicated lens hood that is attached to the lens with special locks. So if you want to put a filter to it, you need to have a 43mm one.

I'm wondering if there any alternative hood that could be crewed to the lens' when a 49mm filter is already on it. Have you seen any?

06-13-2015, 03:14 AM   #2
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Any of the standard 49mm lens hoods screws into the 49mm filters but you lose the pancake factor. I take it you would like a similarly designed hood to the one it comes with in the box. Haven't seen one of those.
06-13-2015, 03:17 AM - 1 Like   #3
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This older thread might have some answers:
https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/135789-da-2...necessary.html

Basically, you can add a filter and then a step down ring on top of the filter. Just beware, if the step down ring gets too small, it can act as an aperture, essentially slowing down the lens. You would have to test it in Av mode at lowest f-number, to see if step down ring is too small (if it causes vignetting or makes the camera choose a longer exposure)
But you can use any 49mm screw-on hood. You probably want a wide angle one. You can find some really cheap on the ebays from China, but the shipping can be slow.
06-13-2015, 05:01 AM   #4
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QuoteOriginally posted by Na Horuk Quote
Basically, you can add a filter and then a step down ring on top of the filter. Just beware, if the step down ring gets too small, it can act as an aperture, essentially slowing down the lens. You would have to test it in Av mode at lowest f-number, to see if step down ring is too small (if it causes vignetting or makes the camera choose a longer exposure) But you can use any 49mm screw-on hood. You probably want a wide angle one. You can find some really cheap on the ebays from China, but the shipping can be slow

Can you please explain how the step-ring acts as an aperture? As I understand it hoods are designed to block light that comes from sources that aren't in the photograph. If you take off the hood and your images are brighter, does that mean you're getting light from sources outside of the composition?


I've got this hood for my 35mm: B+W 49mm Screw-In Metal Lens Hood #950 65-041210 B&H Photo Video It is designed for 50mm on full-frame, which is close to 35mm on a crop sensor. Just tried it on my 21mm + a filter and surprisingly it worked fine. Was expecting some vignetting but nada. B+W also make a wide-angle version of the hood - they aren't cheap but look better than plastic ones and thread on nicely.

06-13-2015, 06:32 AM - 1 Like   #5
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QuoteOriginally posted by trevorg Quote
Can you please explain how the step-ring acts as an aperture? As I understand it hoods are designed to block light that comes from sources that aren't in the photograph. If you take off the hood and your images are brighter, does that mean you're getting light from sources outside of the composition?
This is a special case. If the inner diameter of the step-down ring is less than the "entrance pupil" (usually the lens iris diameter), then the step-down ring has effectively taken over as the aperture, like a Waterhouse stop at the front of the lens. The step-down ring diameter becomes the entrance pupil diameter. Since the f-number of the lens is calculated as the focal length divided by the entrance pupil diameter, the f-number of the lens increases.

PS: It's not really an issue on the DA 21, since the entrance pupil at f/3.2 is only 6.5mm. Not a lot of 49mm-5mm step rings out there. This usually comes up when using step-down rings as hoods on 50/1.4 lenses.

Last edited by THoog; 06-13-2015 at 06:37 AM.
06-13-2015, 03:25 PM   #6
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Yeah, THoog explained it very well. For most cases you only have to worry about vignetting. And apparently the DA 21mm is not super demanding in that respect, either.
06-14-2015, 12:34 AM   #7
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I'm currently using a 49-37mm step-down ring + a 37mm empty ring. The latter is a cheapo 37mm UV filter with the glass removed. There's no vignetting whatsoever.

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