How do I choose coupling rings for reverse-macro with my 30mm, 50mm and 75-300mm lenses?
Asked 2/1/2020
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I want to try reverse-lens macro using two lenses coupled together. My lenses are 30mm (62mm filter thread), 50mm (49mm), and 75-300mm (55mm). I’m considering a coupler and step rings, but I’m confused about which sizes I need and which lens combinations make practical sense. How are step-up and step-down rings defined for this setup, and is coupling these lenses worth doing compared with other macro options?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
6y ago
2 Answers
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The magnification will be the focal length of the forward-pointing lens divided by the focal length of the reversed lens when both are set to focus infinity. If you do actual macro, you'd use the tele lens as forward lens. Combining it with the 30mm lens would have the result start at 2.5×, a rather strong magnification, with a maximum of 10×. The depth of field you are going to be working with is going to be very narrow. Combining tele and 50mm will give you 1.5× to 6×.
There may be a point in other combinations, including coupling your primes for 0.6× and 1.67× (though that is part of the 50mm+tele range): while you may end up not making use of all combinations, it is a bit of a lottery just which combinations will end up pleasing you most.
Originally by user95069. Source · Licensed CC BY-SA 4.0
user95069
5y ago
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Generated from our catalog & community — verify before relying on it.
Reverse-coupled macro can work, but the results vary a lot by focal-length pairing. A useful rule is that magnification is roughly the focal length of the forward-facing lens divided by the focal length of the reversed lens, assuming both are focused near infinity.
That means:
- 75-300mm + reversed 30mm gives about 2.5x to 10x
- 75-300mm + reversed 50mm gives about 1.5x to 6x
- 50mm + reversed 30mm gives about 1.67x
- 30mm + reversed 50mm gives about 0.6x
Higher magnification also means extremely shallow depth of field and a harder-to-use setup. The 75-300mm combinations may be possible, but they can get unwieldy quickly.
For ring sizes: step rings are named from the lens’s front thread size to the accessory size. So a 49-58 ring is a step-up ring; a 62-58 ring is a step-down ring.
In general, stepping up is common; stepping down to a smaller accessory is usually less desirable because it can cause vignetting. Also, reverse coupling leaves the rear element of the reversed lens exposed. If you mainly want practical macro, extension tubes are often the easier and safer option.
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AI6y ago
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