Getting Rid Of People

[OpenC]

I'm interested in using neutral density filters to take long exposures and remove moving people from shots of static stuff; architecture, or whatever. I've got a couple of questions which I haven't been able to find the answers to with a search of this place.

First, and most important: how dark a filter do I need for this technique, assuming that people/cars/etc will be fairly fast-moving wherever I'm shooting? Will x8 be enough, or should I be looking to find a darker one?

Secondly: will the camera still be able to meter/focus/determine shutter speed/etc through the lens in aperture priority, or will I have to do everything in manual? I'm guessing that focus won't be too important as the exposure should be long enough to bring most things into focus; it'd be nice if the camera could give me a hand with shutter speed, though.

Any advice gratefully received :)

[TeeJay]

Sorry, can't help with the filter question, but I would have thought that if a subject is out-of-focus, then no amount of exposure will correct it.

[SkipD]

I'm interested in using neutral density filters to take long exposures and remove moving people from shots of static stuff; architecture, or whatever. I've got a couple of questions which I haven't been able to find the answers to with a search of this place.

First, and most important: how dark a filter do I need for this technique, assuming that people/cars/etc will be fairly fast-moving wherever I'm shooting? Will x8 be enough, or should I be looking to find a darker one?

Secondly: will the camera still be able to meter/focus/determine shutter speed/etc through the lens in aperture priority, or will I have to do everything in manual? I'm guessing that focus won't be too important as the exposure should be long enough to bring most things into focus; it'd be nice if the camera could give me a hand with shutter speed, though.

Any advice gratefully received :)With a really dense ND filter on the camera, auto focus may have a hard time functioning properly. Manual focus would be the solution. Focus without the filter, then apply the filter.

The camera's metering system should handle the task, though. If it doesn't, measure the light and determine settings without the filter applied. Use M (as in Manual) exposure mode and dial in the settings but with the necessary change(s) dictated by the exposure compensation value for the filter.

[OpenC]

Thank you TeeJay: my post was very badly phrased but what I meant was, I imagine that I don't need to worry about focusing to within six inches if my subject is at, or near, infinity anyway (which it generally will be with this kind of shot) and my exposure time is going to potentially be tens of seconds. So, when I say 'badly phrased' I mean 'missing important information which will allow people to answer my question properly'. My apologies.

And SkipD: thank you also. I'm hoping the 30D can do it for me; I don't fear manual, but most of the time I'd rather let the camera have a go at something first if it feels up to it, and only turn to M if I need to.

So, any idea how dense a filter I would need for this kind of work? I've been assuming x8 means equivalent to eight stops; is that right, or do I have another set of rules to remember when I start using these things?

[PacAce]

What you need to determine first is how long an exposure you'll need so that most normally moving people do not show up in the picture. One second? Five? You'll then need to see what Tv your camera gives you for the aperture you have selected to get the proper exposure. The difference, in stops, between this Tv and the exposure time you really want will determine what kind of ND you'll need and how many to stack if more than three stops.

[OpenC]

OK, that makes sense. I think. Thank you.

So if the difference is 10 stops, I'll need a x8 and a x2?

[Scottes]

A few tips - that is, learn from my mistakes...

Go dark. Very dark. It's easy to add a lot of exposure time - at the possible loss of image quality - by going to F/22. So a 2x or even a 4x is not so worthwhile in my opinion. I got a 2x and 4x, and on my first shoot I wished that I had gone 6x and 10x.

SkipD's comment on AF is right on - focus, attach filter, shoot.

Consider the very expensive but very useful Singh-Ray variable ND filter. Sweet!

If you have a polarizing filter then you have an ND that's approximately 2x.

Note that adding tons of filters can lower image quality. So a 2x + 4x + Polarizer means there's a lot of extra glass in front of that lens....

Buy a watch with a second hand or one of those nifty timer remote shutter releases (TC-80N3). You'll often want to go over 30 seconds....

...and if you do you'll want a very stable tripod....

...and a remote shutter release. The timer is great for 30-second exposures or less, but if you go to Bulb you will need a remote.

Enabling mirror lock-up cuts the timer down to 2 seconds rather than 10. Nice if you forget your remote. (DAMHIKT!)

There's nothing worse than taking a 3-minute exposure and finding out you underexposed by a stop. So remove all filters, open up to f/2.8 or the widest, and take some test shots to get the exposure correct. Then do the math to get your exposure time for your desired f-stop with filters. f/2.8 to 4.0 to 5.6 to 8.0 to 11 + 4x ND + 8x ND means you'll take that original shutter speed and multiply it by 128 to get the final shutter speed. (Did I do the math right? Another lesson - figure this out before going shooting!) :-)

[PacAce]

OK, that makes sense. I think. Thank you.

So if the difference is 10 stops, I'll need a x8 and a x2?
An 8x filter gives you 3 stops, a 4x, 2 stops and a 2x, 1 stop. So, to get a 10 stop difference, you'll need three 8x and one 2x filters.

[Scottes]

Leo's post makes me realize that I didn't do the math right on my example....

[PacAce]

A few tips - that is, learn from my mistakes...

Go dark. Very dark. It's easy to add a lot of exposure time - at the possible loss of image quality - by going to F/22. So a 2x or even a 4x is not so worthwhile in my opinion. I got a 2x and 4x, and on my first shoot I wished that I had gone 6x and 10x.

SkipD's comment on AF is right on - focus, attach filter, shoot.

Consider the very expensive but very useful Singh-Ray variable ND filter. Sweet!

If you have a polarizing filter then you have an ND that's approximately 2x.

Note that adding tons of filters can lower image quality. So a 2x + 4x + Polarizer means there's a lot of extra glass in front of that lens....

Buy a watch with a second hand or one of those nifty timer remote shutter releases (TC-80N3). You'll often want to go over 30 seconds....

...and if you do you'll want a very stable tripod....

...and a remote shutter release. The timer is great for 30-second exposures or less, but if you go to Bulb you will need a remote.

Enabling mirror lock-up cuts the timer down to 2 seconds rather than 10. Nice if you forget your remote. (DAMHIKT!)

There's nothing worse than taking a 3-minute exposure and finding out you underexposed by a stop. So remove all filters, open up to f/2.8 or the widest, and take some test shots to get the exposure correct. Then do the math to get your exposure time for your desired f-stop with filters. f/2.8 to 4.0 to 5.6 to 8.0 to 11 + 4x ND + 8x ND means you'll take that original shutter speed and multiply it by 128 to get the final shutter speed. (Did I do the math right? Another lesson - figure this out before going shooting!) :-)

Hey! Scott, welcome back. We missed cha! :)

[Scottes]

Hey! Scott, welcome back. We missed cha! :)
Well, I was gonna go shooting, but had to look something up on POTN, and got caught up - just like the old days, where I did nothing but get caught up in POTN conversations.

I'm not gonna make it shooting today, I don't think... But I'm all set for tomorrow.

[OpenC]

Heh heh, this sounds like the most complicated thing in the world. I can't wait to try it :) Thank you for your help, all...

[Scottes]

Heh heh, this sounds like the most complicated thing in the world.
It's not complicated at all. It's just that you learn something every time you make a mistake. And obviously I've made a few... :-)