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DIY find fresnel focal length??

Started Apr 6, 2016 | Discussions thread
Aussibum Forum Member • Posts: 55
Re: DIY find fresnel focal length??

CardBoardBoxProcessor wrote:

I used my better beamer and it was great. So I want to make my own for my sigma 150-600mm S to make up for its poor appeature of 6.3 at 600mm.

Questions:

do I want the focal length to be adjusted for the bulb itself or the front of the flash?

How do I figure out my fresnel's focal length t?

My theory is that I open a window and perfect the image on a wall. Where ever distant objects are most clear is infinity focus. Is that correct?. Refer to image.

Your method is absolutely correct. I use the same method.

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