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MT 24 EX Diffuser Test Shots

TOC

Introduction

White Balance Check

100mm f2.8 Macro USM at Life Size

MP-E 65mm f2.8 1X-5X Macrophoto at Life Size

MP-E 65mm f2.8 1X-5X Macrophoto at Twice Life Size

Conclusions

Introduction

On this page there are some comparative lighting shots using the MT-24EX with Stofen diffusers fitted or not. In all cases the flash heads are mounted 180 degrees apart to the left and right of the frame. Unless otherwise stated the exposures are are all auto flash exposure with the camera (20D) set to 1/250, f11, manual,  with zero FEC and using the "As Shot" (i.e. flash supplied) white balance with capture to RAW and conversion using ACR.

Due to the reflective nature of some of the subjects some variation was seen in exposure and sometimes colour balance. The uncorrected frames are shown first, the the digitally corrected files are shown in each section.

White Balance Check

This is a simple comparative test to see if the diffusers introduce any colour cast. The lighting ratio was 1:1 and FEC of +1 stop was used. The test was done at a magnification of 1:1 using the 100mm f2.8 Macro USM. The target is a rawworkflow WhiBal card sitting on a gray card background to reduce any reflected colour cast.

So there seems to be a measurable difference, but in practice no discernable colour balance is introduced.

100mm f2.8 Macro USM at Life Size

In these tests small buttons have been used as test subjects. One smooth,  shiny, round and darkish rather like a beetle may be, the other metallic but with raised detail. Tests are conducted with and without the diffuser and at a lighting ratio of 1:1 and 4:1 in each case.

There seems to be a spurious exposure and colour balance issue on some shots. This is compensated for in ACR below.

There seems to be very little affect with the rough button, but the highlights on the round button are noticeably softened.

Looking at 100% crops of the rough button with 1:1 lighting ratio the highlight distribution seems unaffected.

And 100% crops of the smooth button, the effect seems confined to the highlights.

MP-E 65mm f2.8 1X-5X Macrophoto at Life Size

Again there some exposure and colour balance variations, equalizing these in ACR gives.

MP-E 65mm f2.8 1X-5X Macrophoto at Twice Life Size

Again correcting and harmonizing the exposures in ACR. The smooth stone was under exposed and a nominal 1.5 stop adjustment was made.

The effect of the diffuser is not obvious with the detailed button. However with the smooth round shiny button the flash highlights are very obvious and are noticeably softened by using the diffuser, this also smoothes the tonal graduations around the highlights.

Looking at the rough button at 100% for the 1:1 lighting ratio below. The issue is slightly confused by a small change in the plane of focus. However the level of fine detail seems to be no better with the diffuser than without. There is perhaps some broadening of the specula highlights.

Repeating the 100% crop with the smooth, round button below. It can be seen that the specula highlight is larger and more diffused. There is an indication of more graduation in tonal variations away from the highlight with the diffuser but this is still relatively local.

Conclusions

The diffusers do not seem to provide any more detail that the unaided flash. Specula highlights on smooth, shiny round object, typical of many insects, are more finally graduated at the boundary, but larger. The effect is more obvious at higher magnifications but is probably also dependent on the radius of curvature of the object.

In all, the diffusers may provide slight less artificial highlights but the effect is subtle. It seems that to do much better would require a very large reflector approaching a light tent.

Last Updated 05/06/2008

All Content © 2005-09 Lester Wareham All Rights Reserved     

All material is supplied  as is and without warranty, use at your own risk.  

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