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Thread: Longer Focal Lenght Lens

  1. #1
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    Longer Focal Lenght Lens

    I have a customer who wants something engraved with my co2 machine and the job has a slightly curved surface, convex. My standard go to lens is the 50.8 mm or 2 inches, will either a 3 or 4 inch let me do up to a .250 or .375 inch rise without going out of focus? Yes I know there might be some distortion but just wondering?
    Retired Guy- Central Iowa.HVAC/R , Cloudray Galvo Fiber , -Windows 10

  2. #2
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    I don't think a 40 watt glass tube would work well with a 4" lens and the 3" may be too long as well. The longer the lens, the larger the spot size, and the larger the spot size, the lower the power density. One way to know for sure is to try it. Cheap lenses on eBay shouldn't be more than $20/$30, worth the chance to test it out.

  3. #3
    With a 3" lens you may be able to muster close to 1/4" rise by focusing at the 1/8" center between the low and high points, but a 3/8" rise is asking a bit much...

    FWIW I Cermark titanium bracelets- the engraving is 13 characters, the engraved length as the crow flies is 1-3/8" long, and the total 'drop' from the center zero point at each end is .145"- Cermark being critical as to focus, I have 6 total focus points programmed:
    0, +.022, +.044, +.074, +.118, +.143
    -- my LS900's table can be programmed to raise or lower by color layer from the initial focus point which makes it all easy and automatic, thankfully...but the point is, just going beyond .03" when doing Cermark with a 2" lens is the difference between it fusing good and not--

    I've found anodized to be the most forgiving when it comes to focus. A bandaid to help with distortion when creeping down the circumference is to condense the width of the edge engraving if possible, to counteract the stretch-
    ========================================
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  4. #4
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    Thanks guys, my only rotary I have now is the one for the Fiber. I might try the 3 inch one.

    BTW I just went through Hell, I let Windows Update download a update with a lot of download time a couple days ago, and thought nothing of it. About 2 1/2 hours ago, (it seems longer) I rebooted and it came back on with Installing Windows Updates do not turn your computer off! It hung on that and every reboot, was same ole thing. Finally got a recovery disk to work and did a restore point, thank the Lord it worked!!
    Retired Guy- Central Iowa.HVAC/R , Cloudray Galvo Fiber , -Windows 10

  5. #5
    Assumptions:

    6mm incident beam
    M^2 = 1

    2 Inch lens = 1.4mm depth of field
    3 Inch lens = 3.1mm depth of field
    4 Inch lens = 5.6mm depth of field
    6 inch lens = 12.6mm depth of field

    When you double the focal length (say 2 to 4 inch) you get double the spot size and four times less power density

    Only way round it is an incident beam expander, the inbound beam is increased in size to get a better DOF at high power density
    You did what !

  6. #6
    Bill, not sure what Windows you're using but I went thru some similar BS with Win7 about 2 months ago- it would hang on updating, so I start doing them one at a time... found a couple that just wouldn't go. And after the updates that DID take, the computer started acting like it was too busy to help me with anything- I did a system restore as far back as it would let me and haven't let it do an update since. And computer life has been grand ever since.

    I really should look into alternative OS's I guess, I hate Windows with a passion, and i-os-anything just doesn't do a thing for me either... good luck with yours!
    ========================================
    ELEVEN - rotary cutter tool machines
    FOUR - CO2 lasers
    THREE- make that FOUR now - fiber lasers
    ONE - vinyl cutter
    CASmate, Corel, Gravostyle


  7. #7
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    Quote Originally Posted by Kev Williams View Post
    Bill, not sure what Windows you're using but I went thru some similar BS with Win7 about 2 months ago- it would hang on updating, so I start doing them one at a time... found a couple that just wouldn't go. And after the updates that DID take, the computer started acting like it was too busy to help me with anything- I did a system restore as far back as it would let me and haven't let it do an update since. And computer life has been grand ever since.

    I really should look into alternative OS's I guess, I hate Windows with a passion, and i-os-anything just doesn't do a thing for me either... good luck with yours!
    I have turned off this morning any automatic updating. or even checking. I never let it before install without permission, now it won't even be able to check. Yes Windows 7 Pro 64 bit


    I have Norton's and it updates daily, the Windows updates that I really need are few and far between. Now I spend 2 hours this morning trying to get Outlook to work right and finally had to do the new Beta to get anything done!!
    I hate Microsoft even more.....

    Thanks guys for the help, I am trying to order a new lens, turns out to be a 15mm which is as rare as hens teeth.
    Last edited by Bill George; 03-21-2018 at 11:13 AM.
    Retired Guy- Central Iowa.HVAC/R , Cloudray Galvo Fiber , -Windows 10

  8. #8
    win-win-mechatronic

    They do all the 15mm stuff
    You did what !

  9. #9
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    If you are using win 7, I'd NEVER let it update again.... Just say'n.. I've stopped win 10 for the 30 days...... Wish it were longer.
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  10. #10
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    Much of what I do (coconut shell, whale's teeth, etc.) is quite curved. I have used a 2.5" lens with great success in both cutting and engraving, using both my 40-45 watt Epilog and my Chinese lasers (80 & 100 watt). I am well aware that part of what I do is beyond the "depth of field" (which is an arbitrary thing anyway). It works well for me and my customers were quite happy with the results.
    Longtai 460 with 100 watt EFR, mostly for fun. More power is good!! And a shop with enough wood working tools to make a lot of sawdust. Ex-owner of Shenhui 460-80 and engraving business with 45 watt Epilog Mini18.

  11. #11
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    Quote Originally Posted by John Noell View Post
    Much of what I do (coconut shell, whale's teeth, etc.) is quite curved. I have used a 2.5" lens with great success in both cutting and engraving, using both my 40-45 watt Epilog and my Chinese lasers (80 & 100 watt). I am well aware that part of what I do is beyond the "depth of field" (which is an arbitrary thing anyway). It works well for me and my customers were quite happy with the results.
    Thank you John that really helped me to decide. It looks like now I have to source from China unless Dave's link takes me else where for a Longer Focal Length (spelled correctly) Lens.
    Retired Guy- Central Iowa.HVAC/R , Cloudray Galvo Fiber , -Windows 10

  12. #12
    Quote Originally Posted by Bill George View Post
    Thank you John that really helped me to decide. It looks like now I have to source from China unless Dave's link takes me else where for a Longer Focal Length (spelled correctly) Lens.
    Drop them a line Bill, WW will get you any focal length you like
    You did what !

  13. #13
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    Quote Originally Posted by Dave Sheldrake View Post
    Drop them a line Bill, WW will get you any focal length you like
    Got one ordered last night and its in the mail.... China mail that is! Thanks again.
    Retired Guy- Central Iowa.HVAC/R , Cloudray Galvo Fiber , -Windows 10

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