Which grade of ND filter for sunny enviromental protraits

I currently have a 24L and 50 1.4 I will soon acquire a 50L.
I have read through the Filter FAQ's and I still can't decide.
I am looking to buy one ND filter in 77mm and a step down ring.
Either a ND 4 or ND8 I am looking for something I can leave on all day.
Is ND 8 too dark for frequent use?

Are you having trouble with shutter speed being too high? An ND4 will cut the light in half. ND8 will cut it in third. You can look at your shots and see what makes sense. If you can live with your exposure times being 3 times as long all the time at a given aperture, then ND8 may be fine.

That's up to you. 2 stops vs. 3. Given your 6D's max shutter speed of 1/4000, then ND8 might be a better bet. With a camera capable of 1/8000, you could counter that extra stop of light with an ND4 with 1 stop faster s/s.

I say use the lens first, then figure if you really need it. I have a 3 stop ND, but rarely shoot in bright sun, so not used too often.

Scrumhalf wrote in post #16634250
Are you having trouble with shutter speed being too high? An ND4 will cut the light in half. ND8 will cut it in third. You can look at your shots and see what makes sense. If you can live with your exposure times being 3 times as long all the time at a given aperture, then ND8 may be fine.

An ND4 is a 2-stop filter, which actually cuts the light to 1/4 of the original, and the ND8 (3-stops), means you will have 1/8 the original light.

You 're correct - brain fade. I meant to say cuts it by two to the second power and third power, which of course is a fourth and an eighth. Sorry about that!

Personally, I use 3 stops. Two just isn't enough difference unless you have the money for both.

I'll add another vote for the 3 stop. If you're at 1/2000 or 1/4000 you aren't going to notice the difference on those lens, however 1/4000 or 1/4000 & overexposed 1 stop you will.

InfiniteDivide wrote in post #16634235
I currently have a 24L and 50 1.4 I will soon acquire a 50L.
I have read through the Filter FAQ's and I still can't decide.
I am looking to buy one ND filter in 77mm and a step down ring.
Either a ND 4 or ND8 I am looking for something I can leave on all day.
Is ND 8 too dark for frequent use?

Heya,

I have a 3 stop that I use. Let's me use that wide aperture in bright day light.

They're super helpful in bright light & with fill flash.

Really, you could do fine with even more stops. The problem though is that as you introduce every stop with the filter, you're affecting your ability to autofocus. If your lens has F2 for example and you stop down 3 stops, your autofocus is going to be working at F5.6 basically (I think?). That's why 3 stops is common to use, because it will retain autofocus for the most part and still work well. As you start to go beyond that, you start to really struggle to focus, and further, outright lose autofocus. You have to then focus before putting on the filter, or, simply find a way to cut through the stops (like boosting ISO temporarily just to get focus, then dropping it for the shot). Depends how many stops you apply via filter.

Very best,

MalVeauX wrote in post #16636098
If your lens has F2 for example and you stop down 3 stops, your autofocus is going to be working at F5.6 basically (I think?).

I dont think so, it just lowers the light input for the lens. F8 wont autofocus (F2 + 1.4x TC + 2x TC), but on a really bright day, F2.8 + 10 stop filter will autofocus.

Charlie wrote in post #16636150
I dont think so, it just lowers the light input for the lens. F8 wont autofocus (F2 + 1.4x TC + 2x TC), but on a really bright day, F2.8 + 10 stop filter will autofocus.

Heya,

Right, I know it doesn't stop down the actual aperture, but perceived light on the sensor is dropped by X number of stops. It can be hard to autofocus depending on how much light is going on. F2.8 with a 10 stop will attempt to autofocus, sure, but it won't be as reliable, depending on the contrast of the frame up. Missing focus on eyes for example would be a pain in the butt. A 3 stop will probably not make a problem for that, at least, mine hasn't. But a 10 stop would be tough.

Very best,

EDIT Sorry, I want to shoot at 1.2-1.4 for the creative DOF. However, I often get blown out highlights even at 4.0
I want to give the images a nice '3D pop' and therefore don't want to step the lens down.
My shutter can be at 1/ 2000 - 1/ 4000 on my 6D, iso 100 I am looking for provide 'shade' to create a much more pleasing picture.
I am not looking to stack filters. It sounds like ND8 may be too much light stopping.
I am not looking to add autofocus issues because I often shoot handheld with a 1 / 4000 shutter speed.
It sounds like ND2 is common is perhaps ND4 will be better. I thank you for your replies.

InfiniteDivide wrote in post #16636751
EDIT Sorry, I want to shoot at 1.4-1.8 for the creative DOF. However I often get blown out highlights even at 4.0
I want to give the images a nice '3D pop' and don't want to step the lens down.
My shutter can be at 2000 - 4000 on my 6D, iso 100 I am looking for provide 'shade' to create a much more pleasing picture.
I am not looking to stack filters. I thank you for your replies. It sounds like ND8 may be too much light stopping.
I am not looking to add autofocus issues because I often shoot handheld with a 1 / 4000 shutter speed.
It sounds like ND3 is common or perhaps ND4 will be better.

You need to be careful about how you define the "ND" number here, and read carefully when you're ordering one. In some cases ND3 means a factor of 3 (2.x stops). In others it means 3 stops, and in still others it means 10^3, which is about 10 stops. I have ND filters of 3 stops and 10^3 (10 stops), and a solar filter which is 10^5 (just over 16 stops).

Do the the math. Sunny 16 rule says sunny conditions = 1/100 @ f16 using ISO 100. From there its simple enough to figure out the strength you want. For example 1\1600 would get you to f4. 3 stops would get you to f1.8.

archer1960 wrote in post #16636772
You need to be careful about how you define the "ND" number here, and read carefully when you're ordering one. In some cases ND3 means a factor of 3 (2.x stops). In others it means 3 stops, and in still others it means 10^3, which is about 10 stops. I have ND filters of 3 stops and 10^3 (10 stops), and a solar filter which is 10^5 (just over 16 stops).

Noted. Thanks. I am sure I do not currently need a +10 stop filter.