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Giles

Extenders, Diopters & Wet Lenses

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Ok so here's what I know.

 

Extenders - make objects appear closer to you, some light lost and image quality deteriorated. Not cheap eiteher. But they will turn an 100mm into a 160 or 200mm quite easily and they also mount at the lense base so will fit all lenses and bodies !!

 

Diopters - makes you able to get closer to objects by lowering minimum focal distance, not bad on quality loss as long as you pay a bit extra for a good one, also fairly small and light weight most fit in existing ports and can travel easily.

 

Wet Lenses - great if all you are concerned about it underwater and a bit of flexibility while diving on your set up. Yes some are better than others again you get what you pay for.

 

I will be wanting to use mine on land too .. so I am looking mostly at a diopter, the thing is .. i can't work out why someone would use an extender, it is obviously not for macro work in my mind. It is obviously to double up your zoom power?

 

Anyone else got a reason why you would want a extender over a whole new lens? are they any good for macro ? I am guessing they wont get into a housing easily??

 

any experiences or information? I am looking to be able to use on land and water and mostly only for macro. Diopters are the way to go?

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Giles,

 

There are really 3 ways to increase the magnification.

 

Extension Tubes, Teleconverters and Diopters.

 

- Extension tubes and Diopters give you more magnification by letting you focus closer.

- Teleconverters give you more magnification by increasing the focal length.

 

The big difference is working distance.

 

with a 100mm lens at 1:1 the focus distance is ~12 inches

 

Low lets assume that you want 2:1 magnification.

 

If you use a 2x teleconverter to get to 2:1 magnification the focus distance is still 12 inches.

Or if you use extension tubes or diopters to achieve the same magnification, the focus distance will be much less, perhaps 6 inches.

 

The shorter working distance makes it more difficult to sneak up on the subject, and makes it more difficult to light.

 

So then on to extension tubes vs diopters. They both do pretty much the same thing, they increase magnification by decreasing the minimum focus distance. The bigest functional difference between the two is which lens they work best on. Diopters work best on long focal lengh lenses, while extension tubes work best on sort focal length lenses.

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Another fun way to increase magnification above water is a reversing ring. Take a ~100mm macro lens, add a reversing ring, place a 24mm lens on backwards. The 24mm has to be wide open. You can use other focal lengths as well but the reversed lens gives closer focusing and more magnification if its a wide angle lens.

You need a tripod and a non-moving subject. A remote cable release is useful for this as well, as was mirror lock up when using film.

Probably not much application underwater but it can be a lot of fun for not much money if you use lenses you already own.

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Take a look at the pinned thread "Getting more than 1:1 macro from 1:1 lenses".

 

I have used reversed lenses as diopters and I'll tell you the magnification is tremendous. This is great for microsocopy but I think its waaay too much for most underwater applications. DOF is virtually non-existant. I think it would be very difficult to control for moving, 3-D subjects especially without a tripod. For someone properly motivated by the right subject, using a tripod, with the proper ports, very negative bouyancy and much more patience than I have it is possible.

 

But definately try it on land. Reversing rings are very cheap and its loads of fun.

 

You can also reverse mount any lens by itself with the proper adapter ring. That way your $100 50mm 1.8 makes a great manual macro lens. This may have an application underwater if you preset focus and exposure and shot from a preset distance.

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Another fun way to increase magnification above water is a reversing ring. Take a ~100mm macro lens, add a reversing ring, place a 24mm lens on backwards.

 

This is not "another" way. It is just using a reversed 24mm lens as a large/expensive diopter/close up filter.

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Quality is your biggest concern with diopters. Purple fringing or chromatic aberration can be a problem.

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Yes .. this is what I was worried about as I am now buying for a full frame camera as well as a 1.6 crop.

 

I am sure the problems will be more obvious on a full frame but I want to have good results with both.

I was wondering if the more expensive diopters would have better results or at least less problems.

 

The extenders or teleconverters if you prefer seem great until i figure in their size and the fact maybe not ideal for inside a housing.

I am not too fussed about a stop of lost light.

 

Wet lenses are out of the question as they don't do anything for me on land.

I am thinking a good diopter could be the best choice.

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Note that with macro photography, DOF is based purely on magnification and effective aperture. It won't really matter what method you use to achieve the magnification, as the DOF will be the same for a given effective aperture. i.e. if you get to 2:1 with a tube, dipoter or TC, the DOF will be the same for a given effective aperture. (Of course, determining effective aperture might be tricky.)

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Yes .. this is what I was worried about as I am now buying for a full frame camera as well as a 1.6 crop.

 

I am sure the problems will be more obvious on a full frame but I want to have good results with both.

I was wondering if the more expensive diopters would have better results or at least less problems.

 

I assume you are talking about fringing.

 

The dual lens diopters like the Nikon 5T and 6T will not exhibit much of a fringing problem. I have both of these but it takes some digging to locate them for a reasonable price as they are discontinued. These are specifically designed to reduce this effect. Sure there is always a degradation in quality with any added lens but these are very good and if used properly the increased magnification will yield a dramatically different composition that will swamp any pixel peeping technical details.

 

I'd spend my time worrying about the skills required to execute a photo like this instead of the technical. DOF will be sliver thin. Getting close without spooking the critter, disturbing the bottom/subject with the port and getting the lights up close enough will be the key challenges. I'd recommend setting for close focus and leave it on manual. Put the strobe right up to the port and ratio the lights. Then focus by rocking back and forth until the focus light appears then snap. There is also a technique called "Trap Focus" that you can try. This is not easy. Getting this right and an interesting subject are oodles more important (and harder) than what gear you use.

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I assume you are talking about fringing.

 

The dual lens diopters like the Nikon 5T and 6T will not exhibit much of a fringing problem. I have both of these but it takes some digging to locate them for a reasonable price as they are discontinued. These are specifically designed to reduce this effect. Sure there is always a degradation in quality with any added lens but these are very good and if used properly the increased magnification will yield a dramatically different composition that will swamp any pixel peeping technical details.

 

I'd spend my time worrying about the skills required to execute a photo like this instead of the technical. DOF will be sliver thin. Getting close without spooking the critter, disturbing the bottom/subject with the port and getting the lights up close enough will be the key challenges. I'd recommend setting for close focus and leave it on manual. Put the strobe right up to the port and ratio the lights. Then focus by rocking back and forth until the focus light appears then snap. There is also a technique called "Trap Focus" that you can try. This is not easy. Getting this right and an interesting subject are oodles more important (and harder) than what gear you use.

The Nikon versions are hard to find, but the Equivalent canon and Marumi versions are pretty easily available.

Bill

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