Prime + TC = Same Resolving quality as Zoom?

ScottMcLeod

We all know that primes are superior to zooms... (as in, would this combination have less resolving power than a 70-200 Sigma, for instance?)

I was wondering the other day...

85mm f/1.8 + 2x Teleconv = 170mm f/2.8

(272mm equivalent)

Has anyone tried this stunt before?

Bob Bell

ScottMcLeod wrote:

We all know that primes are superior to zooms... (as in, would this combination have less resolving power than a 70-200 Sigma, for instance?)

I was wondering the other day...

85mm f/1.8 + 2x Teleconv = 170mm f/2.8

(272mm equivalent)

Has anyone tried this stunt before?

Scott, you are using generalities as a definition. There are zoom lenses with higher resolving power than primes. Take the example of a 70-200 IS vs 85/1.8. The 70-200 is approx 1% higher lw/ph at their peak apertures. Did you know a 28-70L has a higher lw/ph across the all focal lengths than the 85/1.8.

Resolving power is more than just resolution its contrast as well with a big pinch of lighting conditions.

In your example, you can't use Canon TC so you are using a 3rd party. I am not aware of any MTF tests on TC's. I would expect since prime and zoom lenses tend to be close to each other in MTF test resolution, that any TC would be a large impact, reducing the MTF of a prime to well below a zoom. The application of this outside a lab enviroment, might reveal that in reality its not significant.

Again these are lab style tests, applied to nature you could achieve better results with either tests. The other thing is, I belive natively the lenses resolve greater than the sensitivity of sensors (I might not be reading it right), so its possible, which is the case with Canon Tele's and Super Tele's that a 1.4x TC doesn't have a significant affect on the resolution of the lens below what the sensor can "see".

ScottMcLeod

Bob Bell wrote:

Scott, you are using generalities as a definition. There are zoom lenses with higher resolving power than primes. Take the example of a 70-200 IS vs 85/1.8. The 70-200 is approx 1% higher lw/ph at their peak apertures. Did you know a 28-70L has a higher lw/ph across the all focal lengths than the 85/1.8.

Resolving power is more than just resolution its contrast as well with a big pinch of lighting conditions.

In your example, you can't use Canon TC so you are using a 3rd party. I am not aware of any MTF tests on TC's. I would expect since prime and zoom lenses tend to be close to each other in MTF test resolution, that any TC would be a large impact, reducing the MTF of a prime to well below a zoom. The application of this outside a lab enviroment, might reveal that in reality its not significant.

Again these are lab style tests, applied to nature you could achieve better results with either tests. The other thing is, I belive natively the lenses resolve greater than the sensitivity of sensors (I might not be reading it right), so its possible, which is the case with Canon Tele's and Super Tele's that a 1.4x TC doesn't have a significant affect on the resolution of the lens below what the sensor can "see".

Cool, thankyeh.

I'm gonna go try it out at the store tomorrow.

Manfr3d

ScottMcLeod wrote:

We all know that primes are superior to zooms... (as in, would this combination have less resolving power than a 70-200 Sigma, for instance?)

I was wondering the other day...

85mm f/1.8 + 2x Teleconv = 170mm f/2.8

(272mm equivalent)

Has anyone tried this stunt before?

Keep in mind, that Canon advises the use of TC's
only for L lenses with 135mm and up. So I'd guess
that this combination doesn't measure up with
current L zooms or even a native 200mm/2.8 L.

mercphoto

ScottMcLeod wrote:

85mm f/1.8 + 2x Teleconv = 170mm f/2.8

A 1.8 is awfully close to f/2, closer to that than it is to f/1.4, so we'll use that. Your combination is actually closer to an f/4, not an f/2.8. Its probably roughly an f/3.5. It also won't work as you can't put a tele on a Canon 85mm lens.