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peterclark

Trying to understand diopters / wet lenses

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I currently shoot with a Canon 60mm macro lens.  I keep reading and hearing about people recommending various diopter wet lenses for use in underwater macro photography, but I keep reading conflicting things about them.  Some say they allow you to get physically closer to the subject and still be able to focus, others say it does that AND ALSO increases the size of the of the subject as if you were zoomed in more.  I also hear some say it reduces the working range a ton making it hard to work with.  Most of what I read seems to apply to lenses that are not already macro lenses though, so I have a feeling most of the benefit won't be there for my lens.

So my my main question is, is there any benefit to using a diopter with the Canon 60mm macro?  Since the lens is already a macro lens, would there be any real change?  Would it increase the size of the subject, kind of like a teleconverter would increase the zoom?

 

Thank you!

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Hi 

Yes they allow you to get physically closer to the subject and still be able to focus, AND they ALSO increases the size of the of the subject as if you were zoomed in more. They reduce the working range a ton making it hard to work with.  

These are the benefits / problems to using a diopter with the Canon 60mm macro.  It would it increase the size of the subject, kind of like a teleconverter, and since your closer the object would be larger, and since you are focusing closer the depth of field will be shorter and it will be harder to focus and you probably will not get the complete item in focus. You may also have problems lighting the subject due to the distance from the lens / diopter and the lens diopter may be in the way of your lights. 

The only option that I see is more megapixels and cropping the picture. 

 

You did a great job on your research. 

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Thank you!  Luckily on my next trip I'll be using my new Canon M6 Mark II, so a lot of extra megapixels compared to the 10 year old 7D I've been using.

For 99.9% of what I shoot, it does sound unneeded.  I know on my next trip there is a chance fo pygmy seahorses which I have never seen, but the cropping idea is probably still best.

Thank you!

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Hey Peter

Exciting on the Pygmy seahorses. They are very cool little guys. Little being the operative word.

Figure they are about 1/2” in length. Might be worth, at home, seeing how that looks with a 60mm lens and how close you need to get for a good balance between proximity to a very shy creature and serious cropping. 

The classic shot is head on but, as I’m sure you’ll discover, it takes no time at all for a Pygmy to look away and turn its back to you. So the closer you get, the bigger that problem. 

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Being too close to the subject is a big issue with shy critters like pigmy seahorses.

This is why using a 105 mm macro is often recommended over using a 60 mm macro.

Worth considering if you have the ability  to get one.

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Diopters reduce working distance they do not magnify anything. The magnification comes from getting closer and is only controlled by the camera field of view and focus distance.

You do not say if you use a DX of FX camera in any case it is preferable to work at 100mm+ equivalent for macro so that you have some working distance for the strobes this also helps with skittish subjects. Obviously if visibility is not a major issue

 

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I shoot with a Canon M6 Mark II (formerly shot with Canon 7D), which is an APS-C (crop sensor) camera.  So the 60mm Macro comes out to be 96mm equivalent.

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I also shoot with an APS-C camera (D7500), but still using the 105mm macro.

When I see some photographers with their port literally in the sand trying to shoot some small critter, I'm glad of the distance provided by this longer lens, especially when I add a diopter. So even for APS-C recommending the 105 mm ...

 

 

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1 hour ago, Algwyn said:

I also shoot with an APS-C camera (D7500), but still using the 105mm macro.

Me too. D500 with a 105mm. 

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Diopters increase possible magnification for a subject by allowing you to focus more closely. 

For most cases, the longer the focal length of your lens the more magnification you can get with a given diopter.

For example with a 100 mm macro lens (1:1) and a +10 diopter you can expect to see a 2.1 to 1 meaning for a full frame setup without the diopter you can shoot a 35 mm subject full frame, while with the diopter you can shoot a 16.6 mm subject full frame. 

Similarly with the 60 macro lens (1:1) and a + 10 you will see a magnification of about 1.5 to one so you now will be able to shoot a 24 mm critter full frame.

For a +5 diopter with the 100 you get about 1.5 to 1 and with the 60 you get about 1.2 to 1. 

All of this comes of course with working distance and DOF considerations as well as lighting issues. 

 

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I shoot with a Canon M6 Mark II (formerly shot with Canon 7D), which is an APS-C (crop sensor) camera.  So the 60mm Macro comes out to be 96mm equivalent.

I would get a longer lens as priority then add a close up lens for further magnification
This will also help compressing the background behind the subject


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Diopters increase possible magnification for a subject by allowing you to focus more closely. 
For most cases, the longer the focal length of your lens the more magnification you can get with a given diopter.
For example with a 100 mm macro lens (1:1) and a +10 diopter you can expect to see a 2.1 to 1 meaning for a full frame setup without the diopter you can shoot a 35 mm subject full frame, while with the diopter you can shoot a 16.6 mm subject full frame. 
Similarly with the 60 macro lens (1:1) and a + 10 you will see a magnification of about 1.5 to one so you now will be able to shoot a 24 mm critter full frame.
For a +5 diopter with the 100 you get about 1.5 to 1 and with the 60 you get about 1.2 to 1. 
All of this comes of course with working distance and DOF considerations as well as lighting issues. 
 

What Bill says is theoretical
Practically you need to see what is the lens working distance in water and then see how the close up lens improves it
I found all those calculations to be incorrect
Sometimes a lens focusses so close that a wet lens has zero benefit despite the formula


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Keep in mind that many macro lenses lose focal length as they focus close in. The general rule is that 1:1 magnification is achieved at a distance (from sensor plane) exactly four times that of the focal length, so the minimum focus distance of 200mm specified for Canon 60mm macro lens means that it drops to 50mm focal length when focused to 1:1.

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The theoretical point that matters is that using a diopter to increase magnification depends intimately on the focal length of the lens. Working distance underwater will depend on the index of the glass in the lens but in general is larger by the water index 1.33.  Unlike Interceptor, I think that my testing on land translates pretty well to both the theoretical model and to how a diopter behaves UW.

The Olympus 30 mm is in fact one of those that a diopter doesn't help in any way except that you can use a diopter not for magnification but rather for Bokeh considerations. 

Bill

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Fascinating discussion!

I have not shot the Canon 60mm, but have used its Nikon equivalent with the D500 (cropped sensor) and find that it is an ideal solution. It's close focusing ability more than makes up for its lack of focal length. In terms of getting close to subjects, this takes patience, but is often possible.

By happy coincidence (?) the Nauticam SMC-1 is a great combination with it. As others have mentioned above, using a diopter/macro conversion lens reduces the minimum focusing distance of the lens. With lenses that inherently focus very close, this advantage can be lost, but the SMC-1 seems to be an excellent performer.

Apologies for distracting with information about Nikon rather than Canon.

 

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