unsure of focal length and power.

[jarrod lineberry]

I just bought a redsail x700. I thought it has a standard 55mm lens, but I don't know. My focus spot seems to be about 1/2 inch from the nose cone. 55mm is a little over 2in. I don't think my lens is much more than an inch from the nose cone. That's seems shorter than 55mm. Is there another common length. It does seem pretty picky about the table height. If it's more than 1/8" up or down it doesn't want to cut as fast. My cut speed also isn't as good as I had hoped. I am cutting 1/8" acrylic at 100% and 15mm/s
It is 50watt and I checked with a power meter and it is outputting 62w at the head and 34w out the lens. This seems like a lot of loss. Is that normal?

[Kev Williams]

Sounds like your beam may be misaligned, hitting part of one of the mirror frames rather than hitting the mirror near the center. Have you done the 'tape test' to find out where the laser's actually hitting? Also, try cutting without the nose cone. I found mine was causing power loss even with a well aligned beam.

There's a simple way to test your lens's focal length-- remove it from the housing, so you can hold it between your fingers. Find some small print on a medicine bottle or box of Pop Tarts or whatever. Take the lens and move it until it's in focus where you can read the small print easily. The distance between the lens and the print will be your focal length. (I have 1.5", 2", 3" and 4" lenses, and that's how I tell them apart)..

If you have a 1.5" lens, it might be a little tough to tell the difference between it and a 2". If possible you have a helper actually measure the distance while you're holding it...

As for your "more than 1/8" up or down it won't cut as fast", that's normal for a 2" lens, you really need it focused at the surface of what you're cutting, and 1/8" plus or minus is too much variance. You want to keep it at less than half that amount...

[Jerome Stanek]

on mine the lens is about 1 inch up in the nose cone plus the 1 inch from the nose con to the material. that makes it 55 mm focal length.

[Keith Winter]

Great tips for identifying the focal length of the lens Kev!

[jarrod lineberry]

I used fedex thermal labels to line it up. The beam was hitting near the bottom of the first mirror but not into the frame. I adjusted closer to middle of the rest. The rest seem pretty clean, but maybe not clean enough.

[jarrod lineberry]

Ok. The lens I have it strange. I tried to read print through it and the coating wouldn't let me see through it. I thought maybe I could shine a flashlight through it, but the light would not make it through. And it is a very bright led light. Any thoughts on what I have?

[Mike Troncalli]

Try using the ramp test.. Start with a long thin strip of wood.. On the far left have the wood sitting below what would be a reasonable focal distance, and on the right side have the wood raised up to just under the head (so that nothing hits it). Create a thin line drawing the length of the wood and run it.. You will be able to determine the point at which the line is the thinnest.. Manually move your head over to that spot and measure the distance.. Then you will have the exact focal length from the head to the material.

[Richard Rumancik]

Ok. The lens I have it strange. I tried to read print through it and the coating wouldn't let me see through it. I thought maybe I could shine a flashlight through it, but the light would not make it through. And it is a very bright led light. Any thoughts on what I have?

It would seem that the lens has become extremely fogged up with some kind of residue. It should transmit visible light very well. Perhaps something you were cutting has deposited on the lens. You might be able to clean it off without damaging the lens. No need to do any testing until you get the lens cleaned. It might be a good idea to get a new lens on order as you should always have a backup option.

There is a tolerance on focal length on lenses. Even if a lens is sold as 55mm or 2" focal length you still need to do the test. I have a 2" lens that seems to be closer to a 1.9" focal length. It is a Chinese lens, perhaps they did not hold the manufacturing tolerances that well. Not a problem for me as I use a dedicated probe for each lens I have.

[jarrod lineberry]

I will do the slope test. The lens appears clean. Coating is intact and not scratched it just doesn't let light through.

[Dave Sheldrake]

Gallium Arsenide lens (GaAs) don't pass visible light. To the eye they look a strange metallic silver colour and are used on some machines as they are more resistant to wear and damage than Zinc Selenides (ZnSe)

[Roy Sanders]

This thread was very helpful for me. I wonder if anyone has a YouTube link or is willing to create a video to demonstrate this. Like someone else stated, "my skill is not natural, I have a steep learning curve.

Thank you

[Bill Carruthers]

Gallium Arsenide lens (GaAs) don't pass visible light. To the eye they look a strange metallic silver colour and are used on some machines as they are more resistant to wear and damage than Zinc Selenides (ZnSe)

I wish I had known that a couple of years ago Dave when I received a GaAs lens from China when I had ordered a regular ZnSE lens and was convinced it could NOT be a lens but was instead a mirror- albeit a poor one. When they told me to give it a try anyway, I found that it did work and am still using it today. Liv'n'lurn....