cutting Fresnel?

David Lyga · Oct 10, 2015

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

BrianShaw · Oct 10, 2015

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.

David Lyga · Oct 10, 2015

Thank you Brian. I would imagine that the rough edges can be either sanded or filed. - David Lyga

Rick A · Oct 10, 2015

They can be sanded or filed David.

benjiboy · Oct 10, 2015

Modern fresnel screens are laser cut.

paul ron · Oct 10, 2015

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.

John Koehrer · Oct 10, 2015

Painter's tape over the section to be retained?

paul ron · Oct 10, 2015

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.

ic-racer · Oct 10, 2015

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.

Dr Croubie · Oct 10, 2015

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.

David Lyga · Oct 11, 2015

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

John Koehrer · Oct 11, 2015

Dr Croubie said:
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.

Those a BOTH great thoughts.

Nokton48 · Oct 11, 2015

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.

AgX · Oct 11, 2015

benjiboy said:
Modern fresnel screens are laser cut.

Not laser-cut but injection-moulded.

AgX · Oct 11, 2015

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.

DWThomas · Oct 12, 2015

As to sanding edges, I would use wet-or-dry sandpaper wet. That and a rinse should keep the dust pretty well subdued.

cutting Fresnel?

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