[sibyrnes]

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In the review of the DFA100 macro here at the forum, a step down ring 49mm to 28mm is suggested as a substitute for the lens hood. Where can I obtain such a device? So far I have not found one at the usual sources.

[photoptimist]

Hmmm.... 28mm seems a bit small and will certainly cause vignetting.

If you can find (or have) an unneeded 49 mm filter, you can usually easily unscrew or pop-out the retaining ring, remove the glass, and reassembly the filter with a black paper or cardstock donut with what ever size hole you care to make.

[PKMike]

I'm not sure what that is exactly in reference to, but I have used the hood from the DA 40mm lens and found it quite handy. It is a little steep price wise (about $50 maybe?). If you already have one (I did) you could give it a try.

[dms]

You can do it with two step down rings--e.g., a 49-37mm and a 37-28mm.

[Na Horuk]

I think the lens is already slightly recessed in the DFA 100mm and it has good lens coatings, so you might not need 28mm. You have to be careful if the step down ring goes too far, it will cause vignetting. Or worse yet, it can act as an aperture, which can limit your lens (so f2.8 can be chosen in camera, but due to the small aperture of the ring it would actually behave as.. f3.5 or whatever). Honestly, I would not go smaller than 35mm..

You can also buy online "universal" screw in lens hoods, which are probably much cheaper. You can just get a rubber one.

The original hood is probably not super affordable, but its quite nice. It goes on the bayonet, so your filter threads remain free. Maybe someone makes a knockoff. You can find a lot of clone hoods online, just search for the lens hood code (PH-RBE 49mm). JJC or JinFinance or some others (that end up getting sold under various names) can be found.

[PKMike]

BTW I checked vignetting on a white wall with and without DA 40 hood @ both minimum and maximum focus distance. I could not detect any vignetting.

[UncleVanya]

In theory focal length / aperture. In reality the apparent opening can vary from actual but for simplicity:

100mm / 28mm = 3.57 so you will be losing almost a full stop.

The smallest opening you should use is at least 36mm.

[PKMike]

In theory focal length / aperture. In reality the apparent opening can vary from actual but for simplicity:

100mm / 28mm = 3.57 so you will be losing almost a full stop.

The smallest opening you should use is at least 36mm.

This made me curious. So I took 2 shots with no hood and 2 with the DA40 hood all @ same aperture, shutter speed, ISO and controlled light condition. Again using a white wall as subject (metered @ 18% gray) and 2 different focus distances. I can not discern with my (aging) eye any difference in the shots. Certainly not a full stop. I do believe the DA 40 hood has a 30mm opening though rather than a 28mm opening. So it is somewhat closer to the theoretical 3.57. Or 100/30 = 3.33... Interesting.

[UncleVanya]

The difference between 3.3 and 2.8 is rather small - and I don't know that I can see a 1/2 stop difference myself. As for metering. I think a 1/2 stop might fall either way depending on how you set your stops up (1/3, 1/2, etc).

The best way may be to use a constant light source, take two pictures in "f/2.8" on M mode with iso and shutter held constant and then look at them side by side in post. But then again - apparent size and actual size optically aren't the same precisely so it may not even matter.

[clickclick]

I get this hit on eBay:

49mm-28mm Step Down Ring 49-28 DSLR Camera / 49mm Lens to 28mm Filter Cap Hood | eBay

For a $1.50, not much risk.

[Na Horuk]

The vignetting of an added aperture might only be visible at certain focus distances and if you set the aperture to wide open. It should affect vignetting, overall EV, and also DoF and bokeh. Yes, the difference might be very small. I can't tell the difference between f2.8 and f3.5 in 99% of photos. But if I'm using a lens, I'd prefer to be able to use all of its range instead of limiting it mechanically

[Bophoto]

The front glass is quite far in, so a lens hood is not that important.
Are you using an APS camera or a K1?

[sibyrnes]

Here is the review where the alternate lens hood idea is brought up:


Pentax-D FA 100mm F2.8 Macro WR Review - Construction and Handling | PentaxForums.com Reviews

[jumbleview]

Here is one thread regrding this topic:
https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/323124-49-...-macro-wr.html

I first tried hood from 40mm limited, then bought dedicated Lens Hood replaces PENTAX MH-RC 49MM - JJC
On Pentax K5IIs I did not see any vignetting.

[sibyrnes]

Here is one thread regrding this topic:
49 to 28mm step down adapter for SMC-D FA 100mm Macro WR? - PentaxForums.com

I first tried hood from 40mm limited, then bought dedicated Lens Hood replaces PENTAX MH-RC 49MM - JJC
On Pentax K5IIs I did not see any vignetting.

Thanks for the info.