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Posts: 1
Registered: ‎03-05-2014

What's the best ND filter to buy to get the most shallow depth of field while taking pictures?

I have a Rebel SL1 by the way.  

Esteemed Contributor
Posts: 3,816
Registered: ‎06-11-2013

Re: What's the best ND filter to buy to get the most shallow depth of field while taking pictures?

This depends on if you're trying to use flash at the same time.

Outdoors in full mid-day sun, the exposure based on a "Sunny 16" rule is f/16 and the shutter speed set to the inverse of the ISO speed. At ISO 100 you'd use 1/100th. But if you dial the aperture open 5 stops to f/2.8 then you can dial the shutter faster by 5 stops to 1/3200 and have an equivalent exposure.

f/2.8 is fairly shallow, but it is not the shallowest... f/2 and f/1.4 are even more shallow. Canon makes 50mm and 85mm f/1.2L (L series lenses) which can create especially shallow depth of field (particularly the 85mm). Canon used to have a 50mm f/1.0 lens but they have not made that in years.

Depending on your subject... there's a point where the depth of field is so shallow that it's not possible to to get your entire subject into acceptable focus. At f/1.4 and f/1.2 the depth of field can get REALLY thin (especially at close focusing distances.)

While most of my lenses can handle f/2.8 or better, I often find I prefer f/4 unless I can control subject placement well enough that f/2.8 (or lower) can still work.

Your SL1 caps out at 1/4000th sec shutter speed. So if you were to shoot in full mid-day sun (a bit of an extreme example) and you wanted to use, say, an f/2 aperture, you could not halve the shutter speed to 1/6400th because your shutter doesn't offer that setting. But you COULD do that with just a single stop ND filter (ND 0.3 -- when represented this way each "0.1" worth of density is equal to 1/3rd of a stop of light. So 0.3 is 3/3rds or 1 full stop.).

I have a 2 stop (ND 0.6), 3 stop (ND 0.9) and 10 stop (ND 3.0) filters in my bag.

If you use flash, this changes things... with flash (which I usually use during the day to fill the deep shadows and soften the light) you are capped at the flash sync speed. For your SL1 that's 1/200th sec (or slower) unless you have a speedlite that supports "high speed sync" mode.

In this situation, you might actually want 4 or 5 stops worth of ND if you are shooting in mid-day sun using fill-flash that doesn't support high-speed sync. You can change the shutter from 1/100th to 1/200th (1 stop) but you'd still have 4 more stops to make up to get from f/16 down to f/2.8... one more stop to get to f/2.

You can "stack" filters, but stacking increases the odds of artifacts from reflections... use high quality anti-reflective coated filters (this is a situation where it doesn't pay to buy budget filters.)

The major caution is that there is a point where the shallow depth of field is "too shallow" for the subject.
Tim Campbell
5D III, 5D IV, 60Da
Reputable Contributor
Posts: 846
Registered: ‎03-06-2013

Re: What's the best ND filter to buy to get the most shallow depth of field while taking pictures?

For most of portrait or street photography, I use 3 stop more. For landscapes, I use 10 stop more. You can buy vari-ND if you have the $ for it.

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Esteemed Contributor
Posts: 3,816
Registered: ‎06-11-2013

Re: What's the best ND filter to buy to get the most shallow depth of field while taking pictures?


@hsbn wrote:

For most of portrait or street photography, I use 3 stop more. For landscapes, I use 10 stop more. You can buy vari-ND if you have the $ for it.


We should probably add... using a 10 stop filter is often to allow for a long enough shutter exposure time to create intentional blur on moving elements in the scene (commonly flowing water.)

 

Tim Campbell
5D III, 5D IV, 60Da
Reputable Contributor
Posts: 780
Registered: ‎06-11-2013

Re: What's the best ND filter to buy to get the most shallow depth of field while taking pictures?

What lens do you have? If you are taking still shots, I'm sort of wondering why you need an ND filter at all.

 

Set ISO 100 on your camera and you should be able to use f2.8 and 1/3200 shutter speed, on the brightest sunny day. If you have one of the kit zooms, about the larget aperture is f3.5 at the wide end, f5.6 at the tele end, and you could use 1/2500 and 1/800 shutter speeds with those, respectively.

 

If shooting video, well, yeah you might need a strong ND filter due to frame rate and ISO limitations.

***********
Alan Myers

San Jose, Calif., USA
"Walk softly and carry a big lens."
GEAR: 5DII, 7D(x2), 50D(x3), some other cameras, various lenses & accessories
FLICKR & PRINTROOM 

 





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