Playing with Ringflash.

[JohnP]

How am I going to wait until spring when the bugs start to appear again? I've been trying out my new toy so don't pull me to pieces with this tin opener shot. I'm just trying to get a feel for using an external flash as I've never used one of any kind before.

Canon EOS 60D, Canon EF 100mm f/2.8L Macro IS USM

1/160s f/32.0 at 100.0mm iso400. Sigma Ringflash.

Edited December 5, 2012 by JohnP

[Leon]

thats uncanny, certainly bRINGS a new LIGHT to the situation!!

:)

[Guest Salvatore]

Ring flashes in my day was called mooning ;)

[JohnP]

My macro lens set at f32 seems to give pretty good DOF, I wonder how this will work on when taking insects.

[Guest DaveW]

Depends if you use extension on the lens John. f32 will be reasonably accurate on your lens until you put extension tubes on it since it is only the relative aperture at higher magnifications, not the effective aperture which is smaller and you may run into diffraction problems. Your camera and the lens may still show you are working at f32, but the effective aperture will then be less. Only Nikon DSLR's as far as I know show the effective aperture on the camera read out, other makes simply show the aperture marked on the lens at all extensions. I have had my Nikon macro lens set to it's smallest aperture f32, yet my D200 told me I was working at f64 due to the extension I had on. Other makes would have told me I was still working at f32 as marked on the lens, which would have been incorrect.

Most photographers are unaware that the aperture marked on the lens (relative aperture) is only true at infinity. As you focus closer the marked aperture diverges more from the effective aperture you are working at. At normal photographic distances the change is so minor it can be ignored, but the differences increases rapidly at close up and macro distances. In the past, when using separate hand held light meters you had to apply an exposure correction factor close up to allow for the loss of light as the effective aperture decreased, therefore the difference was apparent. With TTL metering however the camera now does that automatically so most modern photographers are unaware of this effective aperture change.

"In order for a camera lens to focus progressively closer, the lens apparatus has to move further from the camera's sensor (called "extension"). For low magnifications, the extension is tiny, so the lens is always at the expected distance of roughly one focal length away from the sensor. However, once one approaches 0.25-0.5X or greater magnifications, the lens becomes so far from the sensor that it actually behaves as if it had a longer focal length. At 1:1 magnification, the lens moves all the way out to twice the focal length from the camera's sensor. The most important consequence is that the lens's effective f-stop increases*. This has all the usual characteristics, including an increase in the depth of field, a longer exposure time and a greater susceptibility to diffraction. In fact, the only reason "effective" is even used is because many cameras still show the uncompensated f-stop setting (as it would appear at low magnification). In all other respects though, the f-stop really has changed."

http://www.cambridge...acro-lenses.htm

http://fstoppers.com...-on-dslr-camera

As I understand it the video above gets it wrong that it is the angle of the light at small apertures hitting the sensor that causes the fuzziness. It is the scattering of light passing the edge of the aperture blades. The reason this is greater at smaller apertures is there is proportionately more edge to clear centre of the hole in smaller apertures, so the edge effect (diffraction) is more pronounced.

Also which f-stop you use can depend on the final reproduction of the image. For images posted on Forums like this which are to be viewed on computer monitors that are comparatively low resolution, diffraction at f32 on a macro lens at 1:1 will probably not be apparent, so you can use the smallest apertures. If you make reasonably large prints of the same image it may be however. Once you start going beyond 1:1 or life size on the sensor by using extension tubes, as Fuji does, then you may have to use larger relative apertures on the lens to actually produce effective apertures of f22 or similar, and at greater magnifications diffraction is such a problem relative apertures like f8 may need to be used, plus focus stacking to gain enough depth of field. A macro lens is different to conventional lenses in that its much longer focusing travel is in fact the equivalent of a built in extension tube, so it's f-stop behaves exactly as if you had used a conventional lens on an extension tube at close distances.

http://www.ophryspho...diffraction.htm

http://dpnow.com/7644.html

DaveW

Edited December 6, 2012 by DaveW