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Thread: D.I.Y. flash Extender

  1. #1
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    Default D.I.Y. flash Extender

    Hi its obvious that flash fill is a useful tool in nature photography and at times flash can be the only light source. Flash extenders use a fresnel lens to project / concentrate your flash beam to give you greater range. Equally importantly perhaps ( as pointed out to me by Chris Ross ) an extender can allow you to power down your flash and still get the same illumination of the subject with positive implications for flash recycling times and conservation of battery power.

    My homemade little extender is simply a 1litre yoghurt container with a hole cut in the back to be a neat fit over your flash head and a piece of fresnel lens reading magnifier stuck on the front, I have also lined the device with some old metallic glossy wrapping sheet as I figure the more light coming out the front the better. I have then covered the extender with black contact so I will possibly look like a photographer and not a complete cheapskate. Forgive the rough and ready, quicky workmanship on this model, I can do better.....really
    Click image for larger version. 

Name:	_MG_6971.jpg 
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ID:	14279 I've tried to incorporate both the extender and the package the fresnel lens came in.

    Performance. Using my 40D,300mmf4+1.4TC combo in Manual mode for fixed exposure and tripod mounted, test target was approximately 10mtrs away ( a painting on canvas /no glass on wall )
    Flash is a Canon 430EX again in manual mode with power set at 1/16th. The flash's zoom setting is at its narrowest 105mm I found this projected the most concentrated beam obviously.
    Histograms are unretouched RAW's from ACR
    Click image for larger version. 

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ID:	14281
    Without Extender

    Click image for larger version. 

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ID:	14283
    With Extender
    I dont know how this performance compares with commercially made flash extenders, there may well be purpose made fresnel lenses that are more efficient. The only variable I didnt experiment with was the length of the unit as I was limited by the container?? I am also very grateful to the 'flash extender thread' on the forum for making me aware of the dangers of these things if left on gear pointed toward the sun, mine also passed the test of making a leaf catch fire fairly quickly when I used the extender to focus sunlight onto it.

    I have also used similar containers to make very effective macro photography flash diffusers using an internal reflector idea so that no direct light from the flash leaves the diffuser, but thats another story.
    Kind regards Trevor.

    Website: www.trevormurrayphotography.com

  2. #2
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    The focal length of the fresnel is important Trevor, the better beamers use a fresnel lens with a 200 mm focal length I believe, It comes to focus about 25mm inside the BB arm length so appears to not be placed right at the focus point. Incidentally BBs are supposed to work best (most range) at about the 50mm setting on most flashes. What would be more instructive and comparable would be to decrease flash output to match the exposure provided by the bare flash. A BB generally should give about a 2 stop improvement. The best way is to shoot an incident flash meter which will give you a direct reading of the light falling on the subject.

    You might want to try placing the fresnel about 25mm beyond the point where you see the flash head come into focus, which may require a different container.
    Chris Ross
    Helensburgh NSW
    www.aus-natural.com
    Instagram: @ausnaturalimages

  3. #3
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    Thanks for that Chris, like most things this will be a work in process. I dont think I have a light meter any more? I read the better beamer info suggesting 50mm setting, yet found brighter histograms at the longer zoom setting. I'll have a play around with the length of the device and with matching histograms at differing flash powers. I forgot to write in the article that the fresnel magnifier cost $10.
    Kind regards Trevor.

    Website: www.trevormurrayphotography.com

  4. #4
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    This particular fresnel lens is suggested to be held about 10cms above the page in its intended use. The histogram was slightly brighter with the extender pushed as far onto the flash as possible so thats convenient for firmness of fixing. Adjusting the flash power to obtain the same histogram unit on and off seemed to be close to one fraction multiple ie 1/8th power extender off equaled 1/16th power extender on. Not sure how that equates to f stops. Taking a photo with a wide angle lens unit off and unit one certainly shows how the extender concentrates the flash beam.
    Kind regards Trevor.

    Website: www.trevormurrayphotography.com

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    Cool! Very clever

  6. #6
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    Trevor, the 50mm setting is right for the BB fresnel, not necessarily your one. 1/8 to 1/16 would be a stop brighter. Sounds like yours should be about 130mm from the lens on your flash?
    Chris Ross
    Helensburgh NSW
    www.aus-natural.com
    Instagram: @ausnaturalimages

  7. #7
    Tony Hansford Guest

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    So when will the Yoghurt Beamer be hitting the marketplace?

  8. #8
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    Quote Originally Posted by Tony Hansford View Post
    So when will the Yoghurt Beamer be hitting the marketplace?
    There available right now in the refrigerator at the supermarket and the lens at a newsagent or stationer.
    And yoghurt is yummy and good for you!
    Kind regards Trevor.

    Website: www.trevormurrayphotography.com

  9. #9
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    Hi Trevor, this is a great DIY project but after buying a commercial BB I have a few ideas I reckon would improve it.

    The commercial BB has only two sides, which allows it to flex sideways rather than break or buckle when you lay it down. You could copy this idea using the plastic from an icecream container or similar if the yogurt container material is a bit thin. You can hold the thing together with sticky tape or sticky velcro as per the BB.

    I'm pretty sure the foil on the inside of the yogurt beamer adds no additional light in the direction you want it and is not necessary.

    Although other fresnel lenses may have different focal lengths to the BB that should not be a significant issue if they are not too far apart. Shorten the fresnel-head distance to give a wider field coverage (less concentrated light) or increase it to give a narrower coverage (more concentrated light). My BB is specified for full field coverage with lens focal lengths of 300mm and longer. I shortened the arms of my BB by an inch to make it more compatible with my 70-300mm lens and I now get full field coverage at focal lengths of 180mm and greater.

    Cheers
    Richard Jackson
    http://www.owlphotographer.com/
    your comments and suggestions are welcomed

  10. The following user says thank you to Richard Jackson for their reply:

    Trevor Murray (01-02-2012)

  11. #10
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    Default Fresnel lens

    Quote Originally Posted by Trevor Murray View Post
    Hi its obvious that flash fill is a useful tool in nature photography and at times flash can be the only light source. Flash extenders use a fresnel lens to project / concentrate your flash beam to give you greater range. Equally importantly perhaps ( as pointed out to me by Chris Ross ) an extender can allow you to power down your flash and still get the same illumination of the subject with positive implications for flash recycling times and conservation of battery power.

    My homemade little extender is simply a 1litre yoghurt container with a hole cut in the back to be a neat fit over your flash head and a piece of fresnel lens reading magnifier stuck on the front, I have also lined the device with some old metallic glossy wrapping sheet as I figure the more light coming out the front the better. I have then covered the extender with black contact so I will possibly look like a photographer and not a complete cheapskate. Forgive the rough and ready, quicky workmanship on this model, I can do better.....really
    Click image for larger version. 

Name:	_MG_6971.jpg 
Views:	185 
Size:	186.4 KB 
ID:	14279 I've tried to incorporate both the extender and the package the fresnel lens came in.

    Performance. Using my 40D,300mmf4+1.4TC combo in Manual mode for fixed exposure and tripod mounted, test target was approximately 10mtrs away ( a painting on canvas /no glass on wall )
    Flash is a Canon 430EX again in manual mode with power set at 1/16th. The flash's zoom setting is at its narrowest 105mm I found this projected the most concentrated beam obviously.
    Histograms are unretouched RAW's from ACR
    Click image for larger version. 

Name:	beameroff.jpg 
Views:	180 
Size:	43.7 KB 
ID:	14281
    Without Extender

    Click image for larger version. 

Name:	beameron.jpg 
Views:	182 
Size:	45.4 KB 
ID:	14283
    With Extender
    I dont know how this performance compares with commercially made flash extenders, there may well be purpose made fresnel lenses that are more efficient. The only variable I didnt experiment with was the length of the unit as I was limited by the container?? I am also very grateful to the 'flash extender thread' on the forum for making me aware of the dangers of these things if left on gear pointed toward the sun, mine also passed the test of making a leaf catch fire fairly quickly when I used the extender to focus sunlight onto it.

    I have also used similar containers to make very effective macro photography flash diffusers using an internal reflector idea so that no direct light from the flash leaves the diffuser, but thats another story.
    Hi Trevor, which way does the fresnel lens face in your extender...does the smooth side or the rough side face the subject..?
    Cheers,
    Ron.
    It's not so much how fast you drive, but rather, how good you look doing it...

  12. #11
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    Hi Trevor,

    Did much the same years ago but then decided it was easier to buy a BB. I am curious to know where you got the lens. Overflow used to do a pair for $2.50. But not for some years now. DIY lenses are certainly a worthwhile saving, given the $12 or so for imported replacements.

    Cheers,
    Tony

  13. #12
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    Default Finding focal length of a fresnel lens

    This info is fairly obvious, but only if you already know it, may be useful for experimenters. The focal length of a converging lens can easily be measured by focusing the suns rays to a point and measuring the distance from that point to the lens plane.
    Lenses are often described by dioptre number (eg 10x), focal length in mm can be found by dividing 1000 by dioptre, so a 10 dioptre lens has a focal length of 1000/10 = 100mm.

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