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cutting Fresnel?

David Lyga

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Nov 25, 2007
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3,449
Location
Philadelphia
Format
35mm
If you have a need for a replacement Fresnel (plastic) for under the prism of an SLR that you are working on, and have one from a junk camera that is slightly too long, are you able to cut that Fresnel? How? Done this? - David Lyga
 
I'm no expert but I've done that twice. Once scored deeply with a shap x-acto knife and snapped it apart. Worked ok but the edge wasn't very refined. Next time cut with a razor saw - a very sharp and thin backsaw bought at a hobby store. That worked the best.
 
Thank you Brian. I would imagine that the rough edges can be either sanded or filed. - David Lyga
 
They can be sanded or filed David.
 
Modern fresnel screens are laser cut.
 
ive scored the flat side n snapped it off. i used a utility knife as a scraper.

sanding or filing will create dust that will get trapped in the tiny grooves n you'll never get it clean no matter how hard you try. the dust from sdcraping did leave some stuff in tyhe grooves so if i ever do oit again, ill just leave it alone n maybe flame polish the edges instead.
 
Painter's tape over the section to be retained?
 
that might work but the edges will be filthy. the tape doesnt get in the micro groves at the edge and may leave adhesive behind.

acrylic flame polishes very nicely.
 
I used a fine kerf saw like this to cut a damaged 6x9cm fresnel to 6x6cm for my Rolleicord. Nice that the damage was in the area that was cut off.
 
And in case it's not already obvious, cut each side equidistant from the centre. Nothing worse than having a fresnel with the center halfway to one side.

If it's some kind of acrylic plastic, I'd suggest a Hot Knife (like a soldering-iron attachment). It'll cauterise the edges, but that'll be where it's held in place by the mount anyway.
 
Well, dust might not matter, as I routinely WASH Fresnels very gently with mild dish liquid. It works and comes out quite clean. - David Lyga
 

Those a BOTH great thoughts.
 
I use a motorized grinding wheel. Works just fine for my uses.
Most recently I used it to cut down fresnels i bought from China, to fit my Plaubel Makiflexes.
Came out fine and it was a quick job. Yes I clean them in the sink with dishwashing soap.
Center the fresnel before cutting; I use a fine sharpie marker.
 
Getting particles from filing or sanding off the screen once they got electrostatic charged will be troublesome.

Also keep in mind issues of focal length of the fresnel lens.
 
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