Is there a technical reason why TC’s are 1.4 and 2.0x?
p.1 #1Is there a technical reason why TC’s are 1.4 and 2.0x?
Just curious if there’s a technical reason why teleconverters are 1.4 and 2.0x? Particularly the 1.4x
Why not 1.5x?
A new 400 f2.8 GM II with built in 1.5x TC has a nice ring to it! Making it a 400f2.8/600f4
I believe Nikon also used to have a 1.7x TC. Just curious if there’s a technical reason for these numbers
Why not 1.5x?
A new 400 f2.8 GM II with built in 1.5x TC has a nice ring to it! Making it a 400f2.8/600f4
I believe Nikon also used to have a 1.7x TC. Just curious if there’s a technical reason for these numbers
Jan 27, 2026 at 02:35 PM
p.1 #2Is there a technical reason why TC’s are 1.4 and 2.0x?
1.4x loses one stop and 2x loses 2.
Jan 27, 2026 at 02:50 PM
p.1 #3Is there a technical reason why TC’s are 1.4 and 2.0x?
1.4 squared is 2 and 2 squared is 4. A 1.5x would be 1.17 stops darker rather than one stop with the 1.4x. Humans like round numbers. 
Nikon made a 1.7x. It would be nice to have more options, but there are fewer in the MILS era.
EBH
Nikon made a 1.7x. It would be nice to have more options, but there are fewer in the MILS era.
EBH
Jan 27, 2026 at 03:12 PM
p.1 #4Is there a technical reason why TC’s are 1.4 and 2.0x?
gdanmitchell wrote:
1.4x loses one stop and 2x loses 2.
Ahh…makes sense!
Thanks!
1.4x loses one stop and 2x loses 2.
Ahh…makes sense!
Thanks!
Jan 27, 2026 at 06:27 PM
p.1 #5Is there a technical reason why TC’s are 1.4 and 2.0x?
Nikon made 1.5X and 1.7X TCs.
Olympus has 1.25X built in TC in their 150-400 Pro lens.
Kenko and Vivitar make 3X TCs.
I'm sure there are others.
So 1.4 and 2X are by far the most common but others exist.
Round numbers sounds like a reasonable explanation.
Olympus has 1.25X built in TC in their 150-400 Pro lens.
Kenko and Vivitar make 3X TCs.
I'm sure there are others.
So 1.4 and 2X are by far the most common but others exist.
Round numbers sounds like a reasonable explanation.
Jan 27, 2026 at 06:35 PM
p.1 #6Is there a technical reason why TC’s are 1.4 and 2.0x?
I have an off-brand 1.7x a-mount tc tucked away somewhere in one of my drawers of never-seen-again photo gear.
Jan 27, 2026 at 07:31 PM
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p.1 #7Is there a technical reason why TC’s are 1.4 and 2.0x?
Choderboy wrote:
Nikon made 1.5X and 1.7X TCs.
Olympus has 1.25X built in TC in their 150-400 Pro lens.
Kenko and Vivitar make 3X TCs.
I'm sure there are others.
So 1.4 and 2X are by far the most common but others exist.
Round numbers sounds like a reasonable explanation.
I recall the TC16A at 1.6x, but the only "TC" I found in 1.5x was a front mounted setup for an all in one. Is that what you mean or is there an SLR 1.5x TC?
EBH
Nikon made 1.5X and 1.7X TCs.
Olympus has 1.25X built in TC in their 150-400 Pro lens.
Kenko and Vivitar make 3X TCs.
I'm sure there are others.
So 1.4 and 2X are by far the most common but others exist.
Round numbers sounds like a reasonable explanation.
I recall the TC16A at 1.6x, but the only "TC" I found in 1.5x was a front mounted setup for an all in one. Is that what you mean or is there an SLR 1.5x TC?
EBH
Jan 27, 2026 at 07:54 PM
p.1 #8Is there a technical reason why TC’s are 1.4 and 2.0x?
Many seem rounded up a noticeable amount. The Kenko 1.4X and 1.5X Tele Plus MC4s use the same optics and are more like 1.3X. I know I had 1.7x once. I still have a Kenko 3x.
Jan 27, 2026 at 08:02 PM
p.1 #9Is there a technical reason why TC’s are 1.4 and 2.0x?
Choderboy wrote:
Nikon made 1.5X and 1.7X TCs.
Olympus has 1.25X built in TC in their 150-400 Pro lens.
Kenko and Vivitar make 3X TCs.
I'm sure there are others.
So 1.4 and 2X are by far the most common but others exist.
Round numbers sounds like a reasonable explanation.
Actually, a 1.7X TC is half-way between a 1.4X and a 2X TC and results in a stop and a half loss of light. The 1.7 is probably 1.67 or the square root of 2.8, just like a 1.4X TC is probably 1.41 or the square root of two. Just think of the math as following the square root of the typical apertures. The square root of 2 is 1.4X and that results in a one stop loss of light. The square root of 4 is of course 2 and a 2X TC results in a 2 stop loss of light.
Olympus' 1.25X TC doesn't follow this pattern and the light loss isn't an even number in the same way as it results in a little less than 2/3rds of a stop, and a 3X TC would of course be the square root of 9 and would result in the loss of 3 and third stops of light.
Having the TCs result in an easily understood loss of light was important for getting exposure right back in the film days, but is probably less of an issue with digital. The typical TCs, however, are of course carry overs from the film days.
Nikon made 1.5X and 1.7X TCs.
Olympus has 1.25X built in TC in their 150-400 Pro lens.
Kenko and Vivitar make 3X TCs.
I'm sure there are others.
So 1.4 and 2X are by far the most common but others exist.
Round numbers sounds like a reasonable explanation.
Actually, a 1.7X TC is half-way between a 1.4X and a 2X TC and results in a stop and a half loss of light. The 1.7 is probably 1.67 or the square root of 2.8, just like a 1.4X TC is probably 1.41 or the square root of two. Just think of the math as following the square root of the typical apertures. The square root of 2 is 1.4X and that results in a one stop loss of light. The square root of 4 is of course 2 and a 2X TC results in a 2 stop loss of light.
Olympus' 1.25X TC doesn't follow this pattern and the light loss isn't an even number in the same way as it results in a little less than 2/3rds of a stop, and a 3X TC would of course be the square root of 9 and would result in the loss of 3 and third stops of light.
Having the TCs result in an easily understood loss of light was important for getting exposure right back in the film days, but is probably less of an issue with digital. The typical TCs, however, are of course carry overs from the film days.
Jan 27, 2026 at 08:46 PM
p.1 #10Is there a technical reason why TC’s are 1.4 and 2.0x?
I meant a 'standard' TC between camera and lens but my googling was less than thorough.
Nikon do make a front mount 1.5x but the standard type was actually a Kenko.
EB-1 wrote:
Olympus has 1.25X built in TC in their 150-400 Pro lens.
Kenko and Vivitar make 3X TCs.
I'm sure there are others.
So 1.4 and 2X are by far the most common but others exist.
Round numbers sounds like a reasonable explanation.I recall the TC16A at 1.6x, but the only "TC" I found in 1.5x was a front mounted setup for an all in one. Is that what you mean or is there an SLR 1.5x TC?
EBH
Nikon do make a front mount 1.5x but the standard type was actually a Kenko.
EB-1 wrote:
Choderboy wrote
Nikon made 1.5X and 1.7X TCs.Olympus has 1.25X built in TC in their 150-400 Pro lens.
Kenko and Vivitar make 3X TCs.
I'm sure there are others.
So 1.4 and 2X are by far the most common but others exist.
Round numbers sounds like a reasonable explanation.
EBH
Jan 27, 2026 at 08:50 PM
p.1 #11Is there a technical reason why TC’s are 1.4 and 2.0x?
robert614 wrote:
Just curious if there’s a technical reason why teleconverters are 1.4 and 2.0x? Particularly the 1.4x
Why not 1.5x?
A new 400 f2.8 GM II with built in 1.5x TC has a nice ring to it! Making it a 400f2.8/600f4
I believe Nikon also used to have a 1.7x TC. Just curious if there’s a technical reason for these numbers
They made a 2x, and the 1.4x is in the middle of 1x and 2x.
sqrt(2) * sqrt(2) = 2.
sqrt(2) ~= 1.4
Just curious if there’s a technical reason why teleconverters are 1.4 and 2.0x? Particularly the 1.4x
Why not 1.5x?
A new 400 f2.8 GM II with built in 1.5x TC has a nice ring to it! Making it a 400f2.8/600f4
I believe Nikon also used to have a 1.7x TC. Just curious if there’s a technical reason for these numbers
They made a 2x, and the 1.4x is in the middle of 1x and 2x.
sqrt(2) * sqrt(2) = 2.
sqrt(2) ~= 1.4
Jan 28, 2026 at 12:18 AM
p.1 #12Is there a technical reason why TC’s are 1.4 and 2.0x?
In the past, the differentiation between a bad tc and good one was how much glass was in the optics. 4 was bad, and 7 was good.
Jan 28, 2026 at 05:53 AM