GH4 Lenses and NDs and SpeedBoost... OH MY!

W

wwjd

Well-known member
Some theory / thoughts for discussion....

Let's say you've done all the research, and discovered your choice lens is sharpest/least vignette/and aberration at f2 - f4 ish. And past 5.6 is starts going into goo-goo land.
Now, add an ND filter in front of it, (no, not a $2000 one, just any simple $150 one with "ok" quality) what is that going to do to your sharpness?

Added the ND because it was too bright at f2.8 outside in the sunlight, but COULD setting it to f8 or 11 actually be CLEANER than f2.8 + ND?

I mentioned speedboost because I am using that also, but because there is nothing you can adjust on it, it is sort of nulified in this situation - except that it makes things brighter and need for more ND comes up.
Can't change F easily without the speedbooster and love the widening it does, so it stays.

AND I am assuming the sharpest point in the lens remains constant even when speedboosting right? So, if f4 is 6 clicks in, you'd still want 6 clicks in using speed boost - even though it is brighter. Yes?
 
wwjd said:
Some theory / thoughts for discussion....

Let's say you've done all the research, and discovered your choice lens is sharpest/least vignette/and aberration at f2 - f4 ish. And past 5.6 is starts going into goo-goo land.
Now, add an ND filter in front of it, (no, not a $2000 one, just any simple $150 one with "ok" quality) what is that going to do to your sharpness?

Added the ND because it was too bright at f2.8 outside in the sunlight, but COULD setting it to f8 or 11 actually be CLEANER than f2.8 + ND?
Click to expand...

First off, I have never encountered a lens which had it's "sweet spot" at f2-f4_ish. Around f5.6 to f8 or so is where I've seen it fall.

Using ND with the lens at about f2.8 may get the exposure close to what's needed but as you surmised you might be better off at around f8. In bright sunlight ND will help you get the aperture to a wider f2.8, going for f8 or so you may still need about .6ND or .9ND (2 and 3 stop reduction) just to keep from being forced to f16 as has happened to me a couple of times.

Of course the speedbooster adds the need for another stop of ND.

Whether ND filtration adversely affects sharpness depends on the quality of filter used. Since Shane Hurlbut states his preference in brands is Tiffen, I've felt reasonably comfortable in purchasing most of my ND filters in that brand. Most of the time when I need ND I find I need LOTS of it, as in around 4 stops of reduction - 1.2ND - and that is the beginning of the range where IR begins to adversely affect color. So my most recent purchase has been Tiffen 1.2ND and IR filter, I made the decision based on one of Tiffen's demo videos. But haven't had a chance to test it myself.

I've had good luck with Tiffen 0.6ND (2 stops), 0.9ND (3 stops), and 1.2ND (4 stops but not the IR version). I've also tried Polaroid veriable ND filters but have seen reports of variable ND filters adversely affecting sharpness of some telephoto zooms. Only potential problem areas I've seen with them on my lenses has been uneven patterns at the darker settings, so for most of my projects I use single strength ND filters.

Hope some of this has been helpful.

wwjd said:
I mentioned speedboost because I am using that also, but because there is nothing you can adjust on it, it is sort of nulified in this situation - except that it makes things brighter and need for more ND comes up.
Can't change F easily without the speedbooster and love the widening it does, so it stays.

AND I am assuming the sharpest point in the lens remains constant even when speedboosting right? So, if f4 is 6 clicks in, you'd still want 6 clicks in using speed boost - even though it is brighter. Yes?
Click to expand...

I believe this is correct. I'm using an RJ copy, a focal reducer that supposedly works just like the Metabones, mine is in Nikon to m4/3 mount. The 1 stop brightness increase is not much to deal with and if you can't get the aperture right at the "sweet spot" point I'd settle for getting it as close as possible.
 
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I agree with Bruce. f4 to f8 is typically the sweet spot of FF lenses. Not just in terms of sharpness but the point where the edge detail is a closer match to the center detail. The Rokinon lenses at f2.8 can still be a bit soft and I generally consider that a bare minimum f stop with those lenses if I can help it. Generally outdoors I will use ND to keep those lenses at f5.6 and would never dream of using f2.8 on them outdoors.

If you have a $150 ND filter I'm not sure I would worry about a loss of detail. While there could be some it is negligible in the scope of anything else you could do to get correct exposure outside of adjusting the shutter speed which is a no-no for video. I also use the Tiffen regular ND filters and I also use a Hot Mirror for the higher ISO levels. Not as good as the Tiffen IR filters but the hot mirror helps the color a lot up to a certain level. Eventually I will be replacing my ND filter set with a Tiffen IR set.

I also refuse to use a variable ND filter. The combination of two polarizing filters do so much more to hurt detail and can eventually add odd artifacts to video. Plus polarizes have a certain affect on reflections and skin that one shouldn't always use. A traditional ND filter is the only 100% pure way to adjust exposure without too many odd artifacts or issues. Variable makes sense in run&gun situations where adjusting exposure quickly has more of an impact but even then you still have to be careful using them and you may not always get the most desired results.
 
Thanks, Bruce and Thomas for the valuable feedback. I've got variables that SEEM decent quality, but I don't know such things. :) I'll look into normal NDs for the future.

Looks like my sharpness stats WERE based on Center only, and I see what you mean about evening it out at 5.6 and maybe even 8. Looks like 8 starts to loose on these two sigmas
https://www.dxomark.com/Lenses/Sigma/Sigma-18-35mm-F18-DC-HSM-A-Canon-mounted-on-Canon-EOS-760D---Measurements__1011
http://www.photozone.de/canon-eos/872-sigma1835f18_canon?start=1

https://www.dxomark.com/Lenses/Sigma/Sigma-50-100mm-F18-DC-HSM-A-Canon-mounted-on-Canon-EOS-7D-Mark-II---Measurements__977

Thanks to you guys, I learned a ton more important info about my lenses that I didn't know I didn't know! :)
 
I took a chance on these filters and glad I did.

http://www.dx.com/p/lipa-filter-pro...E?Utm_rid=91266049&Utm_source=affiliatewindow

They are a knockoff of the Tiffen IRND 4x4 filters. Water white glass. Excellent sharpness. Here's a shot using the ND1.2 stacked with the Polarizer--

malik_desert.jpg
 
Here's a variable ND filter mini shoot-out that I did. I agree that Tiffen IR NDs are the best option, but variable NDs are more versatile and convenient. My SLR Magic Variable ND doesn't appear to affect sharpness at all, and it even has a locking ring that enables you to orient the filter to dial in polarization.
 
Remember - don't use front filters on lenses above 120-135mm. They affect the sharpness severely. That's how we used to stress test front filters- stick them in front of a 200mm lens. With todays high resolution cameras that is even more critical. But maybe filters are a lot flatter these days as well... just be careful
 
Going off topic, why does a filter affect the image when used in front of a long lens? I can think of reasons why it might, but I'd prefer someone to tell me why so I can confirm what I'm thinking.
 
Greg_E said:
Going off topic, why does a filter affect the image when used in front of a long lens? I can think of reasons why it might, but I'd prefer someone to tell me why so I can confirm what I'm thinking.
Click to expand...
Probably because the viewing angle is narrow and any small deviation in incoming rays (filter flatness) affects it more than wide angle lenses with wide viewing angles...
 
Light Craft, that's what I have. They seem to be gone now? SLR MAgic's looks amazing! But looking at Tiffen VND... even though I have a mattbox with filter holders, I have yet to even use all that due to inconvenice. So I'm going screw on again.
 
Imamacuser said:
Here's a variable ND filter mini shoot-out that I did. I agree that Tiffen IR NDs are the best option, but variable NDs are more versatile and convenient. My SLR Magic Variable ND doesn't appear to affect sharpness at all, and it even has a locking ring that enables you to orient the filter to dial in polarization.
Click to expand...

I've had the SLR Variable ND mark 2 for about 2 weeks now and have been testing it mainly on stills and a little bit of video. Using the 100-300 pana lens and I love it at the long end of the lens. Also got a cheap one from RJ and it's horrible. The SLR vari is sharp and if there is any color cast I'm not seeing it, and the polarising adjustment is real handy when shooting at the beach. RJ does sell some cheap but good quality 4x4 nd's that I've previously used for surfing videos, but the SLR Vari ND 2 is far superior and so convenient.
 
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