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Longer exposures

John Barry

John Barry

pfm Member
I've never tried long exposures to smooth out water, cloud movement etc and would like to give it a try. I have a compact camera, so although it can shoot in manual it's never going to compete with a DSLR. I also have a suitable tripod from my film days

So a couple of questions, as I don't want to get too complicated (or expensive):
One ND filter? If so what rating for general use, or would a variable Hoya be more useful? Do you need to focus manually which would be a bit of a handicap?

There's plenty on the web, but any help from the experts here would be really appreciated

Thanks
 
John,

I've dabbled with a bit of long exposure (example image of mine included below), but Mr P. is the real expert. To achieve the sort of exposure times you are looking for, you will need an ND filter. If you are looking to take long exposures in full daylight, I would recommend a 10 stop filter. I started out with a cheapish Tiffen filter for around £40, but have recently moved onto a Formatt Hitech Firecrest. The difference is that the more expensive filter is much more neutral. (The cheaper filters give a colour cast which can be troublesome to remove).

In terms of focus, it depends on if your camera is able to focus through the ND filter. My Nikon D610 couldn't, so I had to focus manually and then attach the filter hoping that I didn't disturb the focus setting. My current Fuji X-T2 is able to focus through the ND filter.

Hope this helps and best of luck! I look forward to seeing the results :)



Cala Xarraca - Ibiza by Amar Sood, on Flickr

Nikon D610 / Sigma 35mm f1.4 ART

Lefty
 
John

According to Lefty I'm the resident expert, not sure I am but here goes (I have run several long exposure workshops for a local camera store, so I seen all sorts if cameras and filters)

Firstly don't bother with the variable filters, in my experience they are really nasty, and definitely not worth the money.

I agree with Lefty that a 10 stop is a good place to start, as most live views will allow you to focus through it, and in reasonable light at around F8-F11 you will get exposure times in the 5 sec to 30 sec bracket depending on the amount of light. The pictures I posted of West Kirby marina last week were using 13 and 16 stoppers, live view struggles to focus through 16 stops so you have to resort to manual focus. Each stop doubles the exposure time, and the 16 stopper was exposed for about 320 secs. There are plenty of long exposure calculators available for smart phones which can help.

But anyway with a 10 stopper a lot if the time the camera will work it out for you. Most cameras cope up to 30 seconds before you need Bulb mode, though some Panasonics will go up to 60 seconds

A 10 stop filter will not be exactly 10 stops, but a useful pointer is to take a non filtered shot and note the histogram, then you can check with your LE shot whether it under or over exposes. The original image is useful to try and get the colours right of your LE image in post production, many filters have a colour cast.

Now filters, in essence you get what you pay for (no colour cast is what you are aiming for along with no degradation in IQ), I have tried loads and seen many more, these would be my recommendations:-

For a cheap starter Xsource screw in from Amazon, will cost about £10

Next level up Hoya Pro ND, £30-£50 ish depending on screw in size, very little colour cast

Top End, Hitech Firecrest but you are looking at £70 plus, no real colour cast, available as screw in and slide (slot) systems.

I'm sure I can provide a load more information, just ask away, at be at my desk most of tomorrow so it easier to reply with links/pictures etc rather than tapping away on an iPad
 
Mr Perceptive said:
John

According to Lefty I'm the resident expert, not sure I am but here goes (I have run several long exposure workshops for a local camera store, so I seen all sorts if cameras and filters)

Firstly don't bother with the variable filters, in my experience they are really nasty, and definitely not worth the money.

I agree with Lefty that a 10 stop is a good place to start, as most live views will allow you to focus through it, and in reasonable light at around F8-F11 you will get exposure times in the 5 sec to 30 sec bracket depending on the amount of light. The pictures I posted of West Kirby marina last week were using 13 and 16 stoppers, live view struggles to focus through 16 stops so you have to resort to manual focus. Each stop doubles the exposure time, and the 16 stopper was exposed for about 320 secs. There are plenty of long exposure calculators available for smart phones which can help.

But anyway with a 10 stopper a lot if the time the camera will work it out for you. Most cameras cope up to 30 seconds before you need Bulb mode, though some Panasonics will go up to 60 seconds

A 10 stop filter will not be exactly 10 stops, but a useful pointer is to take a non filtered shot and note the histogram, then you can check with your LE shot whether it under or over exposes. The original image is useful to try and get the colours right of your LE image in post production, many filters have a colour cast.

Now filters, in essence you get what you pay for (no colour cast is what you are aiming for along with no degradation in IQ), I have tried loads and seen many more, these would be my recommendations:-

For a cheap starter Xsource screw in from Amazon, will cost about £10

Next level up Hoya Pro ND, £30-£50 ish depending on screw in size, very little colour cast

Top End, Hitech Firecrest but you are looking at £70 plus, no real colour cast, available as screw in and slide (slot) systems.

I'm sure I can provide a load more information, just ask away, at be at my desk most of tomorrow so it easier to reply with links/pictures etc rather than tapping away on an iPad
Click to expand...

Nice reply
 
Thanks both, that's a big help. I have a Fuji X10 which I'm very comfortable with using. I can't get RAW processing to be any better than the camera jpegs because of the sensor, but I'm happy with post processing. We're off to the Dorset coast near Lulworth in March & I just fancied trying something a bit different from normal

I will order a 10 stop Hoya, & hope that the weather is kind

Not strictly a long exposure, but I am optimistic:

31446048384_6290da84ee_b.jpg
 
Order the Hoya Pro ND1000. - Camera King are usually cost effective on Hoya filters

Have a practise before you go!!
 
if you already have a polarizer - just get a second one - then you've got your own variable ND filter. As you rotate them 90 degrees against each other they approximate near infinite density....
 
A polariser is typically 1-3 stops depending on orientation, a pair of stacked polarisers would only give you 6 stops max, added to the fact that polarisers are usually quite thick, a pair of them may vignette at wide angles.

My preference is to have the right tool for the job.
 
Nice suggestions, Mr.P.

The other thing I would urge the OP - just go ahead and try it, and play, play, play.

I take quite a lot of long-exposures: mostly native B&W , and at night.

But as an example of ...just playing at it, here is (a rare colour) one I've posted before - Fuji X100, cheapo 10-stop ND where the colour cast contributes positively to warming the result, Manfrotto Pixi tripod; a system that fits in any coat pocket. wasn't really paying attention / was pottering in a dinghy at the time. (nb this is a straight/ unfinessed reduction from camera, only a bit of foreground dross cropped)

DSCF4156_2-1_1024px.jpg


Lyme dream.
 
in theory - no light whatsoever should be transmitted since crossed polarizers
would not permit ANY light to pass. Though it's impossible to make a perfect polarizer - I'd suspect you'd get a good deal more than six stops blockage! More like 12-15.

if nothing else it's a good experiment to play around with physics....

http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/polcross.html


Mr Perceptive said:
A polariser is typically 1-3 stops depending on orientation, a pair of stacked polarisers would only give you 6 stops max, added to the fact that polarisers are usually quite thick, a pair of them may vignette at wide angles.

My preference is to have the right tool for the job.
Click to expand...
 
Ok I see where you are coming from, and yes you could have an experiment, and it's something I could try as I have suitable polarisers and even polarising film, but it would certainly take some experimentation to determine exactly how long to expose for, most cameras as I mentioned previously will only auto calculate exposure up to 30 seconds, after that you are into bulb mode and done form of remote release. Also it would be interesting to see the effect on colour.
 
Jonathan said:
yes - just run tests and mark the positions.This is precisely how variable ND filters are made.
Click to expand...

Not quite!!!

We are both right!!!

I've just run some tests here using the following, two polarisers (one Hoya, one Hitech Firecrest) and some Linear Polarising film. I have only looked at light transmission and not resultant image quality.

If I use the two circular polarisers (polariser -step ring - polariser), then I get as I described a maximum of 6 stops, in effect an variable ND filter of 2-6 stops. This is because both polarisers are in the same directional orientation.

If I reverse the second polariser, I get the effect that you describe, creating a variable ND filter of 2-x stops where x is probably at least 10.

If I use a linear polariser and a circular polariser, I again get a variable ND filter of 2-x stops where x is probably at least 10. This is how variable ND filters are made. I haven't tried stacking two linear polasiers, as I dont want to cut my film, unless I have to!, but this would give the same effect.

But these points should also be taken into account, with regard to stacking polarisers:-

Polarisers are often more expensive than ND filters and you need two of them.

  1. Stacking two filters can cause vignetting with wide lenses.
  2. You have an extra glass surface with two polarisers which can cause flare and potentially loss of contrast/sharpness.
  3. Extreme wide angle lenses will exhibit uneven darkening due to the difference in incidence angle across the polarizers
  4. A polariser will reduce reflections, while a Neutral Density filter will not. You might want to include reflections in your images.

And this is before we start discussing colour shift (which will vary according to the scene), etc, a high quality ND filter will be neutral, and shouldn't alter the colour of the resultant image.

I stand by my comment that Variable ND filters are nasty, all the ones I've seen with students on my courses have been, though they may have just been very cheap ones!!!
 
yes indeed... stacking standard filter housings and multiple layers of glass CAN caertainly cause vignetting. and all the usual provisos apply in terms of glass quality. Thats why many back in the day would use gelatin filters without glass. But i would certainly stand by my contention that variable ND filters are made using two linear polarizers.

as for 'circular' polarizers, it won't work. a standard linear polarizer is a field of very finely spaced parallel lines. two of these stacked and 'in phase' will pass any light that is oriented along the axis of the array. turning them ninety degrees to eachother will filter out all light not oriented to the first layer and then filter out any light that isnt oriented to the second... leaving no light passing through. whereas a circular polarizer is sort of a 'cheat' ... something that has avery limited polarizing effect but only radially, and made for consumer grade autofocus camera systems. linear polarizers are generally far more effective. just turn off your autofocus if you want to use one. anyway.... this is the reason why you will also find that manufacturers of variable nd filters will specify that autofocus cannot be used with them.

mostly its really a gimmick though. if i need an ND filter... i would just use a specific density filter made for the purpose. but if you wanna have some fun with a variable nd filter (or two polarizers) then get a piece of cellophane or other clear plastic and stretch it out a bit and stick it in between the two polarizers... you will see something very interesting... a wild cacaphony of colour gradients where the stress patterns of the plastic have distorted the polarization in a very interesting way...
 
you shouldnt be able to get full blockage using one circular and one linear pola filter though... you really need two of them to get the effect.
 
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