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08-02-2020, 11:40 AM - 3 Likes   #1
Pentaxian




Join Date: Jul 2016
Posts: 433
HSS vs ND Filter. Tricks, tests and thoughts

Hello.

After several years with Godox HSS capable equiment, I admit that I barely use HSS (or TTL). When I'm outside, under bright sun and need to take a pic for a family, I just look for a place in the shade, and make my best, mixing ambient and flash light at 50/50. I use my sekonic photometer to get the correct power for the flash, and that's all.

I've been doing test under bright sun to see what flash, diffusers, setups are up to the task. As a general conclusion, I think I need to 'put' the sun on the subject's back (If you have a face partially illuminated by the sun you get 'panda eyes', the pic is usually horrible and need PP), and try to fill the subject with flash the best way possible. So I need a flash with minimal power. But what is that minimum power? In bright sun, usually yo need to expose for 1/160 f/10 or so, so yo need a flash that can give you around f/10 to mix your subject with the background. If the flash gives me less than f/10 I can only fill, with just f/10 I can equate subject and background; with more that f/10 I can get a background darker that the subject.

Ok, this is just an introduction, there are a lot of places with techniques for taking pics with bright sun, and there are a lot of folks here that take great pics outside under full sun.
But I see that maybe 90% of people here use HSS to achive such desired look, that is, a sharp subject with a soft/blurry background, but I didn't see a lot of threads about using the clasical ND filter to get the same. Lately, I've been considering using this filter instead of HSS. I've been thinking on the possible advantages of the ND filter, such us: I still can use my photometer, I can use all the power from my flash (longer flash live), less WB shift.

So in this post:

* I will make a comparison HSS vs ND. Specifically, AD200 HSS vs Haida 8x ND filter.
* SETUP: 65cm, double diffusion layer softbox with AD200. I use the AD-S17 plate to avoid AD200's light spill, this plate can help to squeeze up to 1/3 extra stop from the AD200. The softbox is 1m from the subject.
* 'exceed sync' trick to squeeze 2/3 stops from the flash

I'm inside home during the test, there is hot outside, so I'm puting a doll as a subject, inside, but using the outside under full sun as a background.


So let's start with the basic setup, a doll on foregrund with a bright background. To expose for the background I need 1/160 f/9, so I measure the flash and set it at 1/2 power. This is the result.



A more or less well exposed pic, it can be 1/3 EV off.

No let's try to get a more blurry background by changing the exposure to 1/1250 f/3.2.



As expected, the doll is underexposed, you lose power by using HSS, so I increase flash power by 1 stop and set it to 1/1.



Now it's better, by maybe is still a bit underexposed compared to the first picture.
So now I set my 8x ND filter and set 1/160 f/3.2 (that is 3 stops under f/9). Flash power is set to 1/2.




Ok, so a 'correctly exposed' picture with such blurry background. If I compare this pic with the HSS one I can see some differences:

1. I need half the power on the flash and still I get more more light on the subject, so it's more efficient, I don't need to use the AD200 at full power all the time.
2. HSS pic have some WB shift, it's around 500K warmer. I noticed this issue time ago. I don't notice WB shift when using the ND filter.


I see no issues when I look at the viewfinder with a ND filter if I'm outside on a bright day; so, for me, using the ND have some advantages.

Now lets go to the second part of my post. What If I still need more power from my AD200 ?
I'll show you a kind of device I use to make some tricks with the sync, and get 2/3 stops of light or more against the background (sorry, mobile pic):



So this is my K3-II with the X2TP on top, configured this way:

* channel 8 (any channel that DOES NOT control your flashes)
* no group selected
* HSS sync
* 4.4ms delay

Then I have the XProP stacked on top. The XproP is set on CH 7, the channed that control my flashes.

So when I press my camera shutter, at any speed, the X2TP triggers the XProP. The XproP can't handle HSS, so it just act as a dumb trigger, and fires your flashes using normal pulses (no HSS mode).
So what do I get with such strange setting ? I think I have more than one post about it... If I use speeds up to 1/180 there isn't anything special, that is, you get no difference by using the XProP alone or the stacking device. But when you use speeds like 1/200, 1/250, 1/320 ... you enter HSS mode, but just between camera and X2TP, the X2TP 'gets' the HSS thing and triggers the XproP trigger, which triggers the AD200 in normal mode (no HSS). If you don't set anything more, you'll get just a black pic, but, here comes the X2TP 4.4ms delay. This is a delay to sync the HSS signal with the AD200. Once you set this delay, you get a frame fully illuminated, but you have only few usable speeds: up to 1/250 you get a well illuminated frame, at 1/320 you get a bit of black strip at the bottom, that is more noticeable at 1/400 etc. This black strip is an area only with ambient light, not a really black area. So it's up to you to decide a convenient speed to sync. you can look a David Hobbie article about this here.

The practical result if that you can sync your flash up to 1/250 without compromises, this means 2/3 stops more of 'power' for your AD200. Let me explain...


Let's get the initial setup 1/160 f/9, and let's change camera settings to 1/250 f/7.1. I still get the same exposure for the background but, I need 2/3 EV less from my flash right ? But... I can't sync my camera at 1/250 without HSS right? ... Wrong, you can do it with this setup, you'll sync at 1/250 without HSS and 2/3 less flash power.

So let's take the pic at 1/250 f7.1 and AD200 at 1/4 +0.3 EV



I get the same exposure than pic #1 but I need 2/3 EV less power from the flash.
So let's add now the ND filter. The correct exposure should be now 1/250 f/2.5 but, as my lens can only go up to f2.8, this pic will be 1/3 underexposed. AD200 is set to 1/4 +0.3EV.




So, as a final result, I have a pic that needs near 2 stop less of light compared to HSS one, and without significant WB shift.
Are all advantages? What do you think?

Regards,
Javier.

P.D: I'm, sorry if the post can be a bit confusing at reading. As you know, I'm not English native speaker and, to write long posts is a challenge for me; it is difficult for me to explain things with the necessary precision.

P.P.D: sometimes I'm just bored, I don't see a lot of activity here and just like to write a post. Al least this time I have not uploaded wall pictures .

08-02-2020, 01:46 PM   #2
Pentaxian




Join Date: Sep 2012
Location: NY
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Posts: 4,176
I have seen videos about people using 3 and 6 stop filters to achieve similar background and foreground lighting in images while using flash. It is an effective option. That is one of the reasons I have the 3 and 6 stop ND filters.
08-02-2020, 08:19 PM   #3
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Nice Explanation with samples, Kudos to OP.
08-02-2020, 09:47 PM - 1 Like   #4
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Join Date: May 2015
Location: New Orleans
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Posts: 3,216
It is a great option when all your lens are the same size like 48mm. Buy 1 and done. 2 flashes these days are the cheaper option with more versatility. If you already have one for long exposures you should definitely use it. Both have advantages.

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