Just some info on the 44 and 66mm asfheric lens from dx ...I purchased both for a single XML canister light build.so I took the 66mm lens to a eye glass place to se if thay could grind it done....that was a no go but thay did read the lens to se what power it was the 44mm was at +14 power and the 66 was at +16 power....don't know if this info will help anybody but fig I would share.. the 66mm defocused to the same size as the 44mm simply just blows it away...but with a much longer focal length.
asfherical lens
- Thread starter tharg
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Interesting!
For all you people wondering what this +14 and +16 means in regards of the focal length, this is the power of the lens in diopter, or the reciprocal of the focal length in meters.
This means:
44mm DX lens has a focal length of 71.4mm
66mm DX lens has a focal length of 62.5mm
Be aware that this is NOT the back focal length, so this is NOT the distance between the back side of the lens and the focal point.
This is however very useful to compare the lenses with other lenses with known properties.
E.g. if you want to find the lens that will capture most of the light of the LED, you'll need a lens with the lowest focal length to diameter ratio.
Tharg, could you give us the diameter of the actual lens, so not including the flat edge? That way we can compare the lens properly with other lenses.
It would also be interesting to get this measurement of the optical power of the Ahorton lens, since the focal lenght of this lens is not exactly known.
Looking at these numbers, it makes sense that the 66mm lens will work better than the 44mm lens regarding efficiency to capture the LED light.
Johan
For all you people wondering what this +14 and +16 means in regards of the focal length, this is the power of the lens in diopter, or the reciprocal of the focal length in meters.
This means:
44mm DX lens has a focal length of 71.4mm
66mm DX lens has a focal length of 62.5mm
Be aware that this is NOT the back focal length, so this is NOT the distance between the back side of the lens and the focal point.
This is however very useful to compare the lenses with other lenses with known properties.
E.g. if you want to find the lens that will capture most of the light of the LED, you'll need a lens with the lowest focal length to diameter ratio.
Tharg, could you give us the diameter of the actual lens, so not including the flat edge? That way we can compare the lens properly with other lenses.
It would also be interesting to get this measurement of the optical power of the Ahorton lens, since the focal lenght of this lens is not exactly known.
Looking at these numbers, it makes sense that the 66mm lens will work better than the 44mm lens regarding efficiency to capture the LED light.
Johan
Thanks, that's the info I was looking for.
So with the 44mm DX lens, the part that is actually acting as a lens is 39mm with focal length 71.4mm (F/# 1.8) and for the 66mm lens we get a 61mm lens with a 62.5mm focal length (F/# 1).
I think these focal lengths are still not very accurate, since the power of the lens was given as an integer number, but at least we have an idea now.
If you're interested in such lenses, you may also be interested in the fresnel lenses that I have (signature). Their focal length is quite a lot smaller than the diameter, so will capture even more light. Due to the flat shape they are also easier to use in dive lights. PM me for more info.
Johan
So with the 44mm DX lens, the part that is actually acting as a lens is 39mm with focal length 71.4mm (F/# 1.8) and for the 66mm lens we get a 61mm lens with a 62.5mm focal length (F/# 1).
I think these focal lengths are still not very accurate, since the power of the lens was given as an integer number, but at least we have an idea now.
If you're interested in such lenses, you may also be interested in the fresnel lenses that I have (signature). Their focal length is quite a lot smaller than the diameter, so will capture even more light. Due to the flat shape they are also easier to use in dive lights. PM me for more info.
Johan
