Author Topic: Which focal length  (Read 337 times)

yesman85

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Which focal length
« on: July 25, 2017, 01:28:37 PM »
Hi guys,

I'm converting some toy guns for my kids, and the barrel is 22mm in diameter, so it will be mostly very short range.

I want to use the TSAL6100 LED, with an around 22mm lens, when I calculate I should get a focal length of around 62mm to get the least amount of loss.

But I can't find a 62mm focal length 22mm lense, but I can find these from here http://www.surplusshed.com/lens.cfm:
  • 21.5mm lens with 64 focal length, coated
  • 21mm lens with 66mm focal length, uncoated

Which one would be a better bet? Coated apparently means anti-reflection but I'm worried it will affect performance.

Thanks guys!



berk

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Re: Which focal length
« Reply #1 on: July 25, 2017, 05:58:56 PM »
The 21.5 mm lens gives you 95% efficiency.
The 20mm lens gives 89.2%
Anything greater than 90% will give excellent range at short to medium (<100m) range.
Check cmalton's calculator at http://hosting.cmalton.me.uk/chrism/lasertag/lenscalc.html
Tony

yesman85

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Re: Which focal length
« Reply #2 on: July 28, 2017, 11:28:01 PM »
Thanks Tony,

I made a spreadsheet with all plano-convex and double-convex lenses from Surples Shed.

Basically the following items are all within acceptable 10% range:

Stock#TypeDiameterFocalCoatedPriceBeamWidthError
L8177PCX928Y$4.509.87-9.71%
L4444PCX1340N$4.5014.11-8.51%
L7254DCX8.827Y$4.509.52-8.20%
L4367PCX9.529N$4.5010.23-7.65%
L5879DCX2267Y$4.5023.63-7.40%
L8149DCX1545N$4.5015.87-5.80%
L5902DCX21.564Y$4.5022.57-4.98%
L8666PCX2162N$4.5021.86-4.12%
L4433DCX10.531Y$4.5010.93-4.12%
L11191PCX2059N$4.5020.81-4.03%
L5686DCX21.764Y$4.5022.57-4.01%
L10971DCX42.4125N$4.5044.08-3.97%
L5417DCX1544N$4.5015.52-3.45%
L5913DCX1544Y$4.5015.52-3.45%
L11382DCX1544N$4.5015.52-3.45%
L10953PCX3396N$4.5033.85-2.59%
L13821DCX17.952N$4.5018.34-2.45%
L13865PCX9.728N$4.509.87-1.80%
L14533DCX3395N$4.5033.50-1.52%
L11375DCX1543N$4.5015.16-1.09%
L5865PCX12.535N$4.5012.341.26%
L5883PCX12.535Y$4.5012.341.26%
L7377DCX2570N$4.5024.691.26%
L14078PCX12.635Y$4.5012.342.04%
L4316DCX2158Y$4.5020.452.60%
L13082PCX2055N$4.5019.403.02%
L12219DCX5.515N$4.505.293.82%
L13894PCX13.336N$4.5012.704.54%
L11383PCX1746N$4.5016.224.58%
L14072DCX61.8167Y$5.0058.894.70%
L2071PCX1335N$4.5012.345.05%
L14149DCX1335Y$4.5012.345.05%
L14371DCX1643N$4.5015.165.22%
L13524PCX16.945N$4.5015.876.10%
L11425DCX58154N$4.5054.316.36%
L4647PCX22.359N$4.5020.816.70%
L5062PCX26.570Y$4.5024.696.85%
L4331PCX9.525N$4.508.827.20%
L14525PCX9.525Y$4.508.827.20%
PL1182PCX2360Y$8.0021.168.00%
L13767PCX9.625N$4.508.828.16%
L13855DCX40.5105N$4.5037.038.57%
L13749DCX1436Y$4.5012.709.32%
L6593DCX21.956Y$4.5019.759.82%
L12113PCX14.136N$4.5012.709.96%

berk

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Re: Which focal length
« Reply #3 on: July 30, 2017, 05:36:03 AM »
Pick anything that is convex/ plano convex then. Don't forget that SS is OK for the odd lens or two but you will find that in 6 months time you will be unable to get the same lens again.

Good luck!