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DIY find fresnel focal length??

Started Apr 6, 2016 | Discussions thread
ibiza123 Regular Member • Posts: 280
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.

You could also focus the Sun light on the sheet of paper and find the distance between  the lens and the paper while the image of the Sun is smallest. But be careful not to burn the house!

 ibiza123's gear list:ibiza123's gear list
Fujifilm FinePix HS10 Sony Cyber-shot DSC-HX90V Panasonic Lumix DMC-GX7 Panasonic Lumix G Vario 14-140mm F3.5-5.6 O.I.S Panasonic 20mm F1.7 II
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