use of flash extender


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denniskee

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Oct 26, 2003
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#1
very much appreciate if those who used it (mine bought from konota) can shed some light into the set up.

the spec. states should be used for 300mm and above, inorder for the angle of illumination to cover the angle of view.

tried with friend's d30 + 550ex + 70-200. base on the instruction sheet, it should be use with TTL, but all Canon's Digi cam works only with ETTL.

when mounted normal and took a shot @100 (100x1.6=160mm) pointing @ a wall @ 4-5m away, the flash falls on the top half of the photo.

will the flash falls back to centre as the distant between cam & subject increases? if so, what is the min. dist.?
 

Darren

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#2
Its very important that the fresnel lens is aligned and perpendicular with the front of the flash. As the fresnel lens is essentially "focusing" the light from the flash, any slight angle will divert the resulting "hot-spot" from the centre (which is where you have aimed your lens).

By your description, the placement of your fresnel lens suggests that the light is being "focused" and diverted upwards. Adjust the extender downwards.

Also, need to note the zoom position of the flash (eg if your flash can compensate for zoom ranges eg from 24-80mm) - you can see that the front of the flash is itself a fresnel lens to "focus" the beam, thus having two "concentrators" will reduce the resulting hotspot to a very small spot.

Most extenders recommend the flash zoom position to be set to less than 50mm, but you may need to experiment with your setup to determine the best settings.

So, basically, you make sure that:-
1) Flash zoom position set to 50mm or less
2) Flash extender's fresnel lens is perpendicular to flash

And you may need to experiment with different flash zoom settings to see how big or small the resultant spot of light will be for a given distance.
 

TME

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#3
Sorry to hijack this thread but could Darren or Dennis post a pic of the flash extender? I haven't had the opportunity to see one. Thanks!
 

denniskee

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Darren said:
Its very important that the fresnel lens is aligned and perpendicular with the front of the flash. As the fresnel lens is essentially "focusing" the light from the flash, any slight angle will divert the resulting "hot-spot" from the centre (which is where you have aimed your lens).

By your description, the placement of your fresnel lens suggests that the light is being "focused" and diverted upwards. Adjust the extender downwards.

Also, need to note the zoom position of the flash (eg if your flash can compensate for zoom ranges eg from 24-80mm) - you can see that the front of the flash is itself a fresnel lens to "focus" the beam, thus having two "concentrators" will reduce the resulting hotspot to a very small spot.

Most extenders recommend the flash zoom position to be set to less than 50mm, but you may need to experiment with your setup to determine the best settings.

So, basically, you make sure that:-
1) Flash zoom position set to 50mm or less
2) Flash extender's fresnel lens is perpendicular to flash

And you may need to experiment with different flash zoom settings to see how big or small the resultant spot of light will be for a given distance.
Hi Darren, I have tried adjusting the flash head to -7deg during the same trial, the flash landed at the bottom half of the frame.

My question is, with flash head set at normal positiion and the sheet of fresnel lens mounted normally onto its bracket, will the flash falls into the centre as the distant increases, at what distant does that happen? beyond that distant range, will the flash falls below the frame?

I dont own a DSLR, so testing on film is expensive. If there is anybody who is interested in the flash extender and has a canon DSLR, we can arrange a time to go do some experiment. Any assitant is most appreciated.
 

sulhan

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May 11, 2002
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#5
Hiee...


Some flash....with the addrd weight of the extender causes slight droop..while the flash on the shoe...on the camera hotshoe......hence.....causing the illuminated area to the bottom.....

Therefore......those people who use the external holders.....have more room to adjust.....for vertical errors (angle of elevation).

regards,
Sulhan
 

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