Can Anyone Explain This ???

[mongo]

Can anyone explain this?? Mongo was testing a ring flash for macro work and noticed the following:-

Same flower taken minutes apart.
First flower (with arrow and marked centre of flower) was taken with the ring flash.
Second flower taken using natural light (no flash).
Through the viewfinder, the centre of the flower appears as in the second flower i.e.
the centre of the flower has defined compartments – unlike the first flower (flashed) where the centre of the flower appears fused together.
All variables were the same but for flash – v - no flash. Even tried different angles etc. Several dozen photos later - still the same!

If it is only the behaviour of the light when delivered though a flash, then Mongo is in trouble for future flash photos as the non-flash ones are far more accurate.

As a great physics teacher once said, Why is it so ???

[Kym]

Angle of incidence? I.e. the angle the flash light is being returned to the sensors vs the natural ambient light.

[MarkChap]

Mongo hasn't included the EXIF for the 2 shots

If "all variables were the same", there has to be adifference as the exposure would be different with the flash versus with out

The flash version looks very flat, like the flash has provided a light source that is too even across the front of the flower, can you vary the power of one side or other of your ring flash ??

[I @ M]

Can we have some more detail on camera settings please?
Shutter, aperture and white balance used as well as the metering mode.

[Bill44]

To my eye there is a slight difference in the focus point of the two shots. In the first shot the petals seem more in focus, in the second shot the centre of the flower seems to be the focus point.

Also, in the first shot the flash has removed a lot of the shadow that was giving form to the centre of the flower.


If the second shot had been the bad one I would have suspected that Mongo had breathed on it.

[dbax]

It would be good to see the EXIF, but as Kym said the angle of light from a ring flash will be illuminating the outer areas of the inner part of the flower( if that makes sense) from various angles hence tending to flatten the detail.
If possible vary the intensity of the ring flash to say 50%-25% and see if that makes a difference

[arthurking83]

I think Kym is on the right track about the angle of incidence of the main source of light.

light in general comes from 'all directions' and produces shadows where appropriate. The petals in the first(flashed) shot have no shadow detail.

had Mongo used a speedlight/SB type of flash in bounce/remote mode off camera, #1 may have looked more like the second image.

[oldfart]

The depth of field is greater with the natural light than with flash
I'd assume camera selected a higher F Stop value with the natural light.

[old dog]

very interesting Mongo. I might have learned a few things from the troops as well. I don`t have a ring flash....yet.

[arthurking83]

Mongo said:

.....
All variables were the same but for flash – v - no flash. Even tried different angles etc. Several dozen photos later - still the same!....

DOF will be the same regardless of the light source.

the illusion of DOF may be different because of the way the light falls on different parts of the subject.

the illusion is easy to see if you have a flash that can bounce the light output.

shoot with the flash head directly at the subject and then bounce it of a reflective surface and the depth of the image changes.. but not the actual DOF(as long as the variables of distance to subject, focused distance and lens values are the same of course).

One of the reasons I hate flash photography, and would rather use higher ISO values for natural light.

[mongo]

Thank you all for your input and ideas. After seeing Kym’s initial message, Mongo went off and played ring flashes again (sorry, that was not meant to sound that way).

This time he held the ring flash (off lens) at differing angles to the subject and found the results were almost as per the second flower image above which was pretty pleasing. So Mongo thinks Kym had the right idea. If the light is too directly in front and bounces straight back into the lens AND if the light is too even there will effectively be little to no modelling effect and the subject will appear “flatter”.

Moral of the story :-

First, ask your comrades in camera at AP for advice;

Secondly, vary the intensity/output of the light from the flash as between one side of the flash and the other if possible. If not possible within the flash unit itself, then, partly obscure the light coming from one side of the flash to create that difference OR have an additional light source from at least one side to give you that differential in light striking the subject.

Thirdly, share what you may have learned with those good enough to have tried to assist you and your AP comrades generally.

Again thanks to all and hope this has been useful.

[zollo]

very interesting and useful info, thanks for sharing. As far as the images go though, I actually prefer the flatter first image (with flash) To me it looks more "professional" (sorry dont know how to explain better)