cutting Fresnel?

[David Lyga]

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]

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]

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

 

[Rick A]

They can be sanded or filed David.

 

[benjiboy]

Modern fresnel screens are laser cut.

 

[paul ron]

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]

Painter's tape over the section to be retained?

 

[paul ron]

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]

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]

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]

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]

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]

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]

Modern fresnel screens are laser cut.

Not laser-cut but injection-moulded.

 

[AgX]

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]

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