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djdulux
01-21-2016, 11:26
Hi,

I am just trying to understand how a pair of cylindrical lenses work, I have struggled to find info on this, maybe because its so simple!

https://farm2.staticflickr.com/1688/24157354169_9aba24bc6d_c.jpg (https://flic.kr/p/CNGKLn)Cylinder Lenes (https://flic.kr/p/CNGKLn) by Simon Redfearn (https://www.flickr.com/photos/av-candy/), on Flickr

Look right, on the left is most common here, by using a concave lens you reduce the space required. Magnification given by FL2/FL1.

Thanks,

Dupe...

NobleGas
01-21-2016, 11:58
The image on the bottom left illustrates it, the beam incoming from the left is expanded when it leaves the lens on the right whilst remaining collimated; the lenses, being cylindrical, don't affect the beam in the other axis (the axis coming out of the page / screen as you view it), so that axis isn't expanded; the net result is that an oval beam becomes circular if the focal lengths of the lenses are correctly selected.

djdulux
01-22-2016, 01:09
The image on the bottom left illustrates it, the beam incoming from the left is expanded when it leaves the lens on the right whilst remaining collimated; the lenses, being cylindrical, don't affect the beam in the other axis (the axis coming out of the page / screen as you view it), so that axis isn't expanded; the net result is that an oval beam becomes circular if the focal lengths of the lenses are correctly selected.

Thanks for the reply, I am pretty happy with the concept now, the last I would like clarifying is the addition of focal lengths to get the approximate space needed for the correction?

Thanks,

Dupe...

Shadow
01-22-2016, 01:49
Thanks for the reply, I am pretty happy with the concept now, the last I would like clarifying is the addition of focal lengths to get the approximate space needed for the correction?

Thanks,

Dupe...

Well you want the laser beam focused as close to "infinity" as you can. The space between the corrective optics I have heard is 34mm. But I'm not certain.

djdulux
01-22-2016, 06:22
Well you want the laser beam focused as close to "infinity" as you can. The space between the corrective optics I have heard is 34mm. But I'm not certain.

I had assumed that the spacing was related to the focal lengths of the 2 lenses and the thickness of the glass etc?

Also, are 12mm by 10mm lenses big enough, with focal lengths ranging from around 10 to 40mm?

Dupe...

Shadow
01-22-2016, 13:04
I had assumed that the spacing was related to the focal lengths of the 2 lenses and the thickness of the glass etc?

Also, are 12mm by 10mm lenses big enough, with focal lengths ranging from around 10 to 40mm?

Dupe...

I don't remember where I got it but I believe it may be from drlava, when he was selling them.

49344

kecked
06-19-2016, 07:11
old thread but found this while searching.

isn't the first lens backwards from how everyone else uses it? I always thought the curved surface faced the diode? Much more convient the way he shows it for alignment since I can flush up the collimator of the diode with the first lens surface.

planters
06-19-2016, 17:01
Yes, it is "backwards", but as I explained elsewhere, that orientation would be optimized for a collimated source that has no spherical aberration. You may want to introduce some negative spherical aberation. It would be best if you mount the lenses so that you can flip each to optimize the far field spot. Also, a 3x cylinder pair will have approx twice the divergence IN THAT AXIS as a 6x cylinder pair.