Can I use a non-underwater close up lens?

Going on a trip later this week and remembered that I wanted closer-up macro shots than I was getting with my Canon G10 in a Patima housing. I think the best solution would be an Inon UCL-165M67, but I can't find one in stock anywhere.

Can I just grab a "regular" 67mm thread +4 diopter lens, attach it to the port and zoom the lens in on the G10 2x for a similar effect? I know I'll lose some light by zooming in, but this will all be strobe anway. Any other concerns? Is this a dumb idea? It sure would be cheaper!

Going on a trip later this week and remembered that I wanted closer-up macro shots than I was getting with my Canon G10 in a Patima housing. I think the best solution would be an Inon UCL-165M67, but I can't find one in stock anywhere.

 

Can I just grab a "regular" 67mm thread +4 diopter lens, attach it to the port and zoom the lens in on the G10 2x for a similar effect? I know I'll lose some light by zooming in, but this will all be strobe anway. Any other concerns? Is this a dumb idea? It sure would be cheaper!

You can certainly do this, but because the indices of refraction of water and glass are very similar, your +4 diopter lens (250mm focal length) will effectively become a +1.33 diopter lens (approximately 750mm focal length) underwater. So, to achieve the same effect as an Inon UCL 165, you'd have to use a "regular" +18 diopter lens (or a combination that adds to that dioptric strength) to account for the 2/3 loss underwater.

This may sound a bit extreme, but I've seen some folks use stacked +10 and +20 diopter 'dry lenses' on their systems and achieve excellent results.

If you can't find an Inon UCL 165, you might want to take a look at the SubSee. There will be +5 and +10 diopter M67 versions available shortly (not before your trip this week though).

Keri

Zounds! I thought it would be more like 1/3 difference, not 2/3. I didn't really want to stack based on the extra hassle of getting all the air out, but good to know I have that option.

I did find the Olympus PTMC-01 in stock. That looks to be equivalent at 2x mag. I haven't seen much in the way of posts on that thing, not sure if it's Olympus specific in any way. Perhaps I'll get it *and* a cheap +10 diopter lens and see what works?

Thanks for the calc. on air vs. water on the close-up lenses, I'd appreciate any other advice esp on the Oly lens.

You need to be careful when interpreting the "magnification" that many wet lens manufacturers claim (including the PTMC-01). The numbers they use are often misleading, since image magnification depends primarily on the focal length of the camera lens that the wet lens is being used with.

The magnification values that many manufacturers state (2X, 3X, 10X, etc.) are often calculated using the close focus distance of an average human eye as a reference value, which can vary from source to source (somewhere around 220mm-300mm). Depending on the value that they use, different magnifications will result... meaning that a BRAND A "2X" magnifier could be equivalent to a BRAND B "3X" magnifier. Without concrete values like dioptric strength (+2, +5, +10, etc.) or effective focal lengths (500mm, 200mm, 100mm, etc.), it is impossible to accurately compare two lenses without knowing the assumptions the manufacturers have made.

So, while the PTMC-01 might claim to offer 2X magnification, be aware that it might not be equivalent to the Inon UCL 165. But, in any case, since it has a standard thread, I'm sure it can be mounted on your system and will work to the extent it is capable of.