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05-06-2015, 08:45 PM   #1
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Variable ND Filter and FA31 Limited

I'm looking to get ND filters for my FA31 Limited to better enable fill-in for my flash. I've got a Variable ND filter for my Sigma 18-35 but I've almost never used it. Few questions:
1) I read that variable ND filters can destroy bokeh and do strange things to highlights. Is that right?

2) How does the FA31 play with variable ND filters? There's not a lot of room there and the one I have for my Sigma (72mm) is 77mm on the outside. Looking at the available variable ND filters, there aren't many I'm sure will fit within the built-in hood.

3) I hear fabulous things about the Singh-Ray variable ND filter. But yikes is it expensive. Is it *really* worth it? I'm afraid that the construction of the FA31 may limit me to only a few brands; I'm not sure the B+W one will fit.

---------- Post added 05-06-15 at 09:51 PM ----------

And yes, I know about the X pattern that can happen at the highest settings. I don't think I'll be using it near the max, probably no more than half max.

Perhaps I'm better making my own with 2 polarizers?


Last edited by MadMathMind; 05-06-2015 at 09:01 PM.
05-06-2015, 10:25 PM   #2
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Why not just use a regular set of ND filters? Better yet, get a flash you have more control over.
05-07-2015, 05:35 AM   #3
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QuoteOriginally posted by AquaDome Quote
Why not just use a regular set of ND filters?
Looked into it. It's fine but I switching in the field isn't going to work all that well. I'm shooting people and will be moving around during shoots. With changing angles and positions often, the light can change a lot and make what I've got on insufficient. Switching filters every few shots isn't going to work. I'm entertaining a variable ND to make my life easier. I'm not sure it will work, though.

QuoteQuote:
Better yet, get a flash you have more control over.
I have total control over the flash. What I don't have control over is the daylight sun. I'm going to be using these while I am shooting in bright sun at f/2 or so. At the lowest ISOs, shutter speeds still can hit 1/2000 or higher. The guide number is too small at high shutters and my fill-in is mostly lost. Too much ND is also bad; shooting people at less than 1/125 often results in slight motion blur. I want to keep it over that.
05-07-2015, 05:47 AM   #4
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IMHO, variable ND work *best* on lenses 50mm (35mm equivalent) or higher.
Wide angle lenses generally show "banding" when used at vari-ND *darker* settings.
I've never experienced any issues with bokeh when a vari-ND is used.

YMMV

Michael


Last edited by MJSfoto1956; 05-07-2015 at 07:13 AM.
05-07-2015, 06:43 AM   #5
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It's not universal for them to show banding, it doesn't only show up at wide angles (unless you're talking about ultrawides and the sky, but that's because they're really a pair of polarizing filters stacked), and the 31mm isn't a wide angle anyway, unless it's being used on film.

Making your own might cause vignetting but probably not since it's a ff lens. Just get a cheap one and try it out, and if you don't like it, you're only out $15 or so.

I don't use mine very often. Mostly on really bright days, and especially if i'm using a wide aperture lens (one pretty much lived on my 55/1.2 til the filter glass came loose. I haven't replaced it yet, but now that it's warm enough that I'm taking photos outside more, I need to) and/or using fill flash.

I'm pretty sure I used one on most of the shots in this album, because it was a ridiculously bright day and we were on a lake, so there was a lot of glare, too.
05-15-2015, 04:20 PM   #6
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After looking at a video review which showed the size of the front element clearly, I decided to try the Hoya:
Hoya 58mm Variable Neutral Density Filter A-58VDY B&H Photo

It fits! Downside is no front filter threads, but I guess I will have to live with that. I haven't had a chance to try it out, but at least I have something that works physically.
05-15-2015, 04:51 PM   #7
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I think you will find it works very well on Pentax lenses 35mm and up. I assume you'll be using a step up ring?
Note: as your lenses get wider, it is very likely for you to experience some banding as you increase the density of the variable ND.

Michael

05-15-2015, 05:36 PM   #8
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I have an admittedly cheap variable ND filter for my 35mm Samyang. I bought it specifically for when I may want to be out and about in the daylight with the thing wide open or close to it. I haven't played with it much, but for what little I paid its surprisingly good.

I even did a pano. You can see the stitching of course, but I knew that was going to be an issue going into taking the shot.



From what I've noticed with it, it behaves admirably except for when its really cranked in which case you get a big reverse-X vignette in your shots (best way to describe it). I'm sure a better quality/more expensive filter would probably do the same thing, since it seems a trait of how the filter works more than anything to do with the quality of it.

FWIW, the pano and this shot (only ones I've uploaded as I haven't really used the filter much) were taken with a 77mm filter, as the Sammy 35mm is ginormous. I'm sure a smalelr, better quality filter would fare better than this (and I have zero complaints about mine).

05-17-2015, 03:58 PM   #9
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QuoteOriginally posted by MJSfoto1956 Quote
I think you will find it works very well on Pentax lenses 35mm and up. I assume you'll be using a step up ring?
Note: as your lenses get wider, it is very likely for you to experience some banding as you increase the density of the variable ND.
I may get a 49-->58 ring to use on my FA50 and FA77.

I have a 72mm NDX for my Sigma 18-35 but have never really used it.
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