[aoeu]

It's my duty lens. If I drop the camera aluminium might save it.

[stevebrot]

Turns out that the 49-28mm step down ring just works as an aperture ring, reducing the effective f-stop of the lens, meaning you could just stop down this lens.

Ummmm...I would not be so sure. That style of hood is pretty much standard for Voigtlander for their SL II series focal lengths under 50mm. The purpose of a hood is to shade the front element from stray light that is outside the field of view. This can be done a number of ways, but the end effect is the same.

As for the idea that it would constitute a "front iris" (not to be confused with a Packard shutter). I know the thread on this site you are referring too and I believe there is a knowledge gap in regards to lenses that can use that type of iris and the lens that is mounted on your camera. Vignette is not the same as stopping down.

In regards to the OP's request, I use a metal screw-on hood from Heavystar on eBay ("tele" size) with my fast 50s on APS-C. It looks a little deep, but there is no vignette. Likewise, I use the "normal" size hood on my 28s. The nice thing about the metal hood is that it accepts a 58mm pinch cap at the front and does a heck of a job protecting the front element.


Steve

[troika]

Thanks, Steve.

OP still engaged.

[kh1234567890]

Read that thread again.
While this applies to a lens with F/1.4, it does not apply, or it does but to a much lesser extend, to a lens with F/1.7.
50/28 = 1.78, very close to 1.7, probably well within tolerance
In fact, I'm using a 49-28mm stepdown ring for my FA50 F/1.7, and see no effect on exposure setting with or without this "hood."
Of you can stepdown to 30.5 (49-37mm + 37-30.5mm stepdown rings). 50/30/5 = 1.64.

I've got a 49-37mm ring on its way from China and I'll re-do the test with the f1.4 lenses when it arrives.

Even if the effect with the 49-28mm ring is just to stop the f1.4 lens down to f1.8ish, it is worthwhile since setting the aperture at f1.8 manually is a pain, as it is between the f1.4 and f2 detents. As my test shows, there is no exposure effect at f2 and up, so a 49-28mm ring should be perfect for a f1.7 lens.

[kh1234567890]

OK, a proper test of the 49-28mm step-down ring hood on a Pentax-A f1.7 lens.

Left without this hood, right with hood. K-7, tripod, SR off, focus at infinity, M mode, same exposure (f1.7) and post-proc for both.



Lossless centre crops, same :


Lossless bottom right corner crops, same :



SilkyPics meters these as the shot with hood being 0.2 EV darker (i.e. effectively just a touch under f1.8), just about spot on as to what the maths predicts.
To me the one with the hood (right) looks to have better contrast and less fuzzy flare.

One of these days I'll take this lens to bits and set the infinity focus stop properly

[macTak]

Kudos to you for another helpful test. Since the light could have changed a little with the sun behind those clouds, I would caution against reading too much into the 0.2 EV number. Now all we need is a comparison test of these stepping rings against a deep regular hood (which actually blocks more off-axis light then the stepping ring can)...


Edit: P.S. your test also shows how good the 50/1.7 optic is even wide open.

[kh1234567890]

Kudos to you for another helpful test. Since the light could have changed a little with the sun behind those clouds, I would caution against reading too much into the 0.2 EV number. Now all we need is a comparison test of these stepping rings against a deep regular hood (which actually blocks more off-axis light then the stepping ring can)...

Edit: P.S. your test also shows how good the 50/1.7 optic is even wide open.

Those shots were taken less than 30 secs apart. The view is to the north and it was pretty overcast at the time to the south where the sun usually is around here I repeated it a few times and the result was very much the same - a very slight (about 0.2 EV) darkening with the ring on. The ring hood seems to get rid of the hazy flare which stopping the lens down a touch does not. Microcontrast is definitely better. Unfortunately I do not have a really deep narrow hood here.

[EarlVonTapia]

OK, a proper test of the 49-28mm step-down ring hood on a Pentax-A f1.7 lens.

Left without this hood, right with hood. K-7, tripod, SR off, focus at infinity, M mode, same exposure (f1.7) and post-proc for both.



Lossless centre crops, same :


Lossless bottom right corner crops, same :



SilkyPics meters these as the shot with hood being 0.2 EV darker (i.e. effectively just a touch under f1.8), just about spot on as to what the maths predicts.
To me the one with the hood (right) looks to have better contrast and less fuzzy flare.

One of these days I'll take this lens to bits and set the infinity focus stop properly

Good stuff! The step down ring definitely lessens the purple fringing (check those roof edges) and increases the overall contrast.

I still won't use one though. Lens hoods look dumb! Always gotta look cool when shooting . . .

[troika]

My lens came in the mail today. It's virtually indistinguishable form new. I have to work, but took some time to snap a few around the house and in the garden. Colors and contrast are amazing. I need to get used to AF lenses and this is probably a good one to do it with. This photo is not necessarily the best example of those things of the ones I took, but it's the most interesting (believe it or not). I will pick up a hood for it, thanks for the advice,