6 hours ago, jefdriesen said:
Yes, that was actually the reason for asking my question. There is quite some information out there on those newer lenses, but it's rather difficult to compare with those older Inons because there are no direct comparisons. According to the Inon specifications, the UCL-330 and UCL-165 are respectively +3 and +6 diopters. Is that on land, or also in water? I have no idea.
How do they compare for example to a Subsee +5 or +10? Or even the much more expensive Nauticam SMC-1?
It is difficult to compare the different diopters for two reasons:
#1.: Some companies give the refractive power of the diopter only in air, not in water. There is no simple formula to convert the power of diffraction in air to the one in water, since the change in refractive power depends also on the refractive index of the optical glass that is used for making the diopter (the refractive index of optical glass, depending on the type of glass is variable between approx. 1.4 and 1.9 - so one cannot just mulitply by a factor). As far as I understand the Inon descriptions, they give the refractive power in water, so this seems to be solved.
In case the diffraction power in water is not known, you can empirically measure the refractive power of the lens under the watery, using paralell light beams (=e.g.: sunlight): the distance to a projection area (e.g. the bottom of a swimming pool), required to give the smallest bright point of the light, is measured. The reciprocal of this distance (in meters(!)) gives the dioptries. E.g.: the distance, where the sunlight is focused to a single point would be 10 cm (closer or further away gives a disc instead of a small point). Then the refractive power is 1/0.1 (10 cm = 0.1meters), i.e. +10 Dioptries.
#2.: In geometrical optics one can just add the refractive power of lenses (e.g.: the Nikon 100mm has +10 dioptries and an additional +10 diopter would add to +20 dioptries in total). The bad news is that this works only for very thin lenses (i.e.: thickness of the entire lens assembly is small in relation to the focus distance). Our lenses are very far away from beeing thin in comparison to the focus distance, often the focus distance is shorter then the entire lens is (therefore lens construction is an entire engineering science by its own and not covered by experimental physics)...
Still you can ESTIMATE the magnification by tools like these here (but deviations are no surprise, because of the two points described above: It is certainly more accurate to measure magnification empirically, as e.g. Masssimo (=Interceptor121) did in a former post here for several lens/diopter combinations): https://www.cambridgeincolour.com/tutorials/macro-extension-tubes-closeup.htm
Accordingly, the magnification with the 105mm Nikor would be 2.02x with the +3 diopter and 2.75x with the +6 diopter, instead of the 1.3x that the lens alone provides (1x in air, but 1.3x because of the refractive index of water (="diving mask" magnification effect of a planport))...
Wolfgang
