Lens diffraction

siejones

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I was out Sunday taking some pics of Pistyll Rhaeadr. A stunning waterfall near Snowdonia.

In the daytime light I had to stop down to get my shutter speed down to give that smooth flowing water common with this type of photo.

I am aware of how diffraction works and know that some lenses deal with it better than others by maybe a stop of aperture. I am using a canon17-40L which is pretty standard in it's diffraction fall off.

Anyway to get a decent slow shutter speed I was stopping down to F22 which I knew was bad for diffraction but all I could do to slow it down enough. Besides I have noticed many waterfall shots in the past using this aperture and presumed it was a pretty standard thing to do. It also caters for the great depth of field needed for shots taken in such close proximity as waterfall shots demand and therefore right across the focus range of the camera.

Anyway when home and having a quick look at the pics I find myself dissapointed. I knew the focus wouldn't be sharp but the diffraction level made unacceptably soft images. I was using tripod and remote. I am pretty confident of no camera shake and certainly not for all 20 odd shots.

I am using a 350D and I realise this is only a small sensor in terms of DSLR's and with bigger to FF sensors that diffration at these apertures is dealt with a lot better due to the bigger pixel area.

So my quesiton is what do you guys use for waterfall shots of this nature. Do you:

- Stop down the aperture and accept the poor IQ?

- Wait till it's dusk or dawn and therefore dark enough to not have to stop down quite as much?

- Use ND filters to knock the light down a few stops again not having to stop down so much?

- Have a shiny FF and not worry so much or do you still suffer to a certain degree even with the larger sensor?

Ta

Sie
 
1 method i plan to use, but havent yet, so dont know for sure it will work well...

Firstly assuming your using a decent tripod, setup and take a shot at a nice high shutter speed (~1/250th F4) so you have a sharp image, then retake the shot at your preferred shutter speed (~2seconds f22) and use Photoshop layers and masks to merge the two images to get the best out of both.
 
Dreeder touches on a useful method of getting a longer exposure:

Take 4 shots with the same settings on a tripod.
Place as layers on top of each other.
Set opacity from base layer upwards as follows - 100%, 50%, 33%, 25%

Helps recreate the effect of extending the overall time/exposure as well as sharpening those items that are stationary. A very good tutorial is here

HTH :wave:

Gary
 
DreederUK and Himupnorth: Thanks for replys. It's amazing how many tricks of the trade there in photography :) Makes perfect sence. Really want to try this out now.

Just out of curiousity what aperture would you tend to use considering the DOF needed for this kind of shot.

Oh and that link points to the site I used to get my better understanding of diffraction. His tutorials and explanations are excellent.
 
The important factor for me would be to get the length of exposure I thought necessary and would move other variables (aperature, ISO, ND filters) around this.

An understanding of hyperfocal distances to ensure a correct DOF is all that is really required here.

:thumbs:
 
A pureist (which I'm not) would cart a tripod a cokin adapter and umpteen filters down
to the waterfall.
Set the Camera on its lowest ISO (100 most probably) and add filters to create the desired effect

Me I've been known to give my sunglases a bit of a clean and hang them on the front of the lens. Does the trick...
 
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