Long Exposure Advice

t1mm

Hi All,

I've just invested in a set of ND filters for my Canon 600d. I'm using the kit lens, but trying to get to grips with some long exposure shots which I'm quite fond of (over water, sunsets, etc). I have a couple of questions however:

Do you guys have any particular method for calculating the exposure based on a set of values you have without a particular filter? I've tried out some Android applications whereby you plug in the iso,shutter speed of well exposed shot without a filter, then plug in the amount of stops the filter is bringing you down, and it gives you relevant values to plug into the camera after you've attached the filter. They didn't seem to work very well at all however.

I've also seen the notion of multiplying your shutter speed by 1000 given that you're using a 10stop ND filter. I've just tried this indoors and it ended up being very overexposed.

Also, I spent half an hour just testing values etc to take well exposed shots with the 10stop filter, but they didn't appear too crisp, and the colour seemed off, although the brightness seemed okay. Are my filters just cheap crap?

http://www.amazon.co.uk/Neutral-Density-Filters-Canon-1100D/dp/B009GWXX8O/ref=sr_1_10?ie=UTF8&qid=1404428513&sr=8-10&keywords=58mm+filter

I'm using the ND8 and ND2 stacked on top of each other.

Any help would be greatly appreciated!

t1mm

11811

There's a few handy charts that may help you out here http://www.vassilistangoulis.com/gr/?p=4958

Those cheaper filters can leave you with fairly soft images and can leave a purple hue. Stacking them as well can be a bit problematic. Also the cheaper one's ND ratings tend to be a bit inaccurate.

t1mm

Just took another couple of photos indoors with those charts in hand - the purple hue has disappeared and they are pretty much the exact same as photos taken in aperture mode with a fast shutter speed (no waterfalls or moving clouds in the house unfortunately!)

Thank you very much for your reply 11811 I'll see how I get on with them outside tomorrow evening and post back. Cheers!

D.S.

Not sure if there is an Android version but I use an IOS app called Longtime - it's not perfect - sometimes it will under/over expose a little, and you have to compensate manually.

Getting sharp shots on long exposure can be tricky. Some things I find that work are:

1) Have a good / sturdy tripod. Hang a sandbag from it or use something heavy to keep it firmly planted (particularly with any wind).
2) Use exposure delay to help with mirror slap.
3) Get your in camera focusing right before you stick on the filters. Then flick your lens into manual focus mode before sticking on the filters. I also typically use Liveview to focus, where I zoom in as far as possible and sometimes use manual focus to get things where I want them.
4) Think carefully about depth of field (which will vary with the focal length youa re using). I use DOF Master or True DOF sometimes to make sure I have enough DOF for the image I am going after.
5) Contrast/curve adjustments and selective sharpening using layers and masks in PP usually get the sharpness to where it needs to be...I also manage colour casting in post also..
6) If stacking one /more filters, I find colour casts are usually most pronounced depending on how the filters are positioned (for instance if I stack a variable density and ND filter, I get a lot of colour casting when the VD is at stop 8, but little to none at stop 6).


Apologies if you are doing this already - that's what seems to work for me..

D

adox

Print out one of the many exposure charts that are available online or save one to your phone and use it as an approx guide. You can re-adjust your time after taking a shot. Use the histogram to see if you need more or less time.

Only put the filters on when you have everything else done and are ready to dial your exposure time in and press the shutter.

Use live view and manual focus, zoom in as far as you can on the image and fine tune the focus. Use a remote or time delay. Decent tripod or well weighted one is essential.Even if you are happy with the shot maybe take a couple more slightly under and slightly over on your original exposure. It will give you more choice when you get to PP.

Shoot to the right without blowing out the image. It will give you loads more information in the image to work with.

Keep the ISO as low as you can. All you should be concerned about is what your shutter speed is without the filters on and then the recalculation of shutter speed with the filters on.

Shoot RAW, especially with long exposures. You can correct the white balance to get rid of any unwanted colour cast from the filters.

t1mm

Hi Guys,

Thanks for your fantastic advice - I really do appreciate it. The biggest help so far has been using those charts as above, instead of the terrible applications I've found for my phone. If there was a reliable formula for working this stuff out, I'd like to see it - I'd be very interested in developing a proper application for android myself - what do you guys think?

Bit annoyed that I got these screw-on filters now, as it affects the manual focus when putting them on the lens. I've taken to applying them while AF is still enabled, and disabling it immediately afterwards (so the focus ring isn't too loose).

Btw, using Magic Lantern for its Bulb Timer feature.

DaireQuinlan

t1mm wrote: »

If there was a reliable formula for working this stuff out, I'd like to see it - I'd be very interested in developing a proper application for android myself - what do you guys think?

There is. For every stop, double your time. This is complicated shooting film but digital is easy peasy because it doesn't suffer from reciprocity failure.

A 10 stop ND filter should increase your shutter speed by 2^10 or 1024, so 1000 should have been in the right ballpark, so either you'd metered incorrectly or the filter is lying about it's stop value.

D.

t1mm

I think the main issue was that the applications I had provided strange intervals for f-stops which I could not match exactly with those available on my camera.Strange setup really - should be quite easy to include all eventualities when programming a (supposedly) simple formula such as that!

Also, I was incorrectly adding up the values for the stacked filters - the article posted by 11811 above cleared that up however.

In essence,

(2^numberStopsOnFilter) * shutterSpeedInSeconds = newExposureValue? Cheers