Nereus
Enlightened
I finished my aspherical Mag (see this thread) some time ago and I have been very satisfied with it. However, there is one weakness in it, the protruding glass lense which is very fragile:
In principle aspherical lense can be substituted with a flat fresnel lense and of course I had to try that...
I found a suitable fresnel lense in the Rolyn Optics catalog, namely this product. Here you can see a photo of it:
The diameter of the actual lense is some 5 cm so it is perfect for a D size mag. Focal length is 32 mm. Here I hold the lense in my hand for a size reference:
It is indeed perfectly flat:
Next I had to cut the square edges away, otherways it will not fit in the Mag head. Intact lense on the left, cut-down on the right (yes, I bought two of them... ):
Here is a closer look on the cut-down lense. Acryl is surprisingly hard and brittle. That's why the edges are quite rough but you can't see them after the installation.
Here you can see the fresnel lense installed - perfectly flat lense guarded by the bezel
Glo-powder glows through the fresnel...
Here is a close distance beamshot with as narrow beam as possible:
The beam at its widest (you can see my kitchen ceiling here... ):
The beam projected by fresnel lense is very similar to the beam projected by aspherical lense - based on the beam profile, you can not tell which optics is used.
So far this fresnel lense experiment has been a success story - all the benefits of an aspherical lense without its vulnerability. However... when I measured center beam brightness (narrow beam) I noticed that aspherical lense performs slightly better: 57 600 lux @ 1m for aspherical and 40 000 lux @ 1m for the fresnel lense.
So, to answer my own question in the topic of this thread: yes, the aspherical lense can be substituted with a fresnel lense but there is a trade-off here between robustness and performance of the flashlight.
On the other hand this was my first fresnel lense experiment and the performance might be improved with slight changes in the fresnel lense specs. I guess I have to order a few more... :thinking:
Thanks for looking!
-N
In principle aspherical lense can be substituted with a flat fresnel lense and of course I had to try that...
I found a suitable fresnel lense in the Rolyn Optics catalog, namely this product. Here you can see a photo of it:
The diameter of the actual lense is some 5 cm so it is perfect for a D size mag. Focal length is 32 mm. Here I hold the lense in my hand for a size reference:
It is indeed perfectly flat:
Next I had to cut the square edges away, otherways it will not fit in the Mag head. Intact lense on the left, cut-down on the right (yes, I bought two of them... ):
Here is a closer look on the cut-down lense. Acryl is surprisingly hard and brittle. That's why the edges are quite rough but you can't see them after the installation.
Here you can see the fresnel lense installed - perfectly flat lense guarded by the bezel
Glo-powder glows through the fresnel...
Here is a close distance beamshot with as narrow beam as possible:
The beam at its widest (you can see my kitchen ceiling here... ):
The beam projected by fresnel lense is very similar to the beam projected by aspherical lense - based on the beam profile, you can not tell which optics is used.
So far this fresnel lense experiment has been a success story - all the benefits of an aspherical lense without its vulnerability. However... when I measured center beam brightness (narrow beam) I noticed that aspherical lense performs slightly better: 57 600 lux @ 1m for aspherical and 40 000 lux @ 1m for the fresnel lense.
So, to answer my own question in the topic of this thread: yes, the aspherical lense can be substituted with a fresnel lense but there is a trade-off here between robustness and performance of the flashlight.
On the other hand this was my first fresnel lense experiment and the performance might be improved with slight changes in the fresnel lense specs. I guess I have to order a few more... :thinking:
Thanks for looking!
-N
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