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DIY find fresnel focal length??

Started Apr 6, 2016 | Discussions thread
AustinMN Contributing Member • Posts: 674
Re: DIY find fresnel focal length??

To accurately determine FL for a fresnel, I would use the moon.  The sun is too hot and will start a fire.  Make sure the paper or other stock is parallel to the moon (a perpendicular line would point directly at the moon).  The fresnel needs to be parallel to the focus paper as well.

For your other question, I'm really not sure if you want to focus the front of the flash or the bulb.  If you use the front of the flash, then you probably don't want to focus it sharply.  If you do, thou will just end up projecting the pattern of the front of the flash with it's lines and patterns onto the subject.

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