EF 100 F/2? Is it really 100mm or 113 or 116mm

[gaul]

Hello

saw somewhere the EF 100 F/2 is actually giving of longer focal than 100mm?

113 or even 116mm?

is this true that a rounded number painted on the lens is not always what’s implemented in physical in the lens



not that it makes a great difference

looking at the 100 F/2 as it’s small, lightweight, well built and cheap

 

[Sittatunga]

Hello

saw somewhere the EF 100 F/2 is actually giving of longer focal than 100mm?

113 or even 116mm?

is this true that a rounded number painted on the lens is not always what’s implemented in physical in the lens

not that it makes a great difference

looking at the 100 F/2 as it’s small, lightweight, well built and cheap

I've just checked mine against my Pentax-M 100mm macro and they both have almost exactly the same field of view at infinity. (Edit. Within 0.5% of each other as close as I can measure.)

I'd expect prime lenses to be within 5% of their marked focal length. That's one reason why they don't call it a 105mm. Zoom lens markings are notoriously elastic.

I really enjoy mine on full frame, it's a relaxing focal length for portraits and good for concerts. A wee bit of longitudinal colour aberration but DPP4 or DxO PhotoLab usually keep it from being bothersome.

 

[WindwardHaole]

Although leading edge manufacturing practices may allow stricter control, I've read that tolerance is commonly ±5%, although more than 5% is considered acceptable with zoom lenses. The Edmund Optics site shows focal length tolerances from <±1% to ±7%.

 

[BAK]

There is a concept in optical design called focus breathing.

As you focus your lens, the focal length may get a little longer or shorter.

The indicated focal length may not match the focal length determined by an optical bench at some focus distances, but be fine at other focus distances.

BAK

 

[Sittatunga]

There is a concept in optical design called focus breathing.

As you focus your lens, the focal length may get a little longer or shorter.

The indicated focal length may not match the focal length determined by an optical bench at some focus distances, but be fine at other focus distances.

BAK

Basically, if the lens doesn't decrease its angle of view as you focus closer, that's because it's shortening its focal length. A mathematical 'thin' 100mm lens focussed at 900mm from the sensor would be 114.5mm away from it and would have the same angle of view as a 114.5mm lens focussed on infinity. That must mean that a 100mm lens that doesn't breathe as it focusses to 900mm from the sensor becomes an 89mm lens at that distance.

The EF 100mm f/2 focusses internally and does breathe a little, but only about half as much as it would if it kept a constant focal length as it focussed. It has a nearly 7% wider field of view at its minimum focus of 900mm than the unit focussing Pentax-M 100mm macro at the same distance.

 

[gaul]

Thx all for very informed replies

I found the reference (DxO review under Distorsions.. but shows at 105mm..) :

Loading…

www.dxomark.com

Not sure where this poster found the 113mm (he was also mentioning 116mm) référence

apologies for cumbersome post.. but at least I learned . Even if I cannot comprehend all of it

thx!!

 

[gaul]

Thx all for very informed replies

I found the reference (DxO review under Distorsions.. but shows at 105mm..) :

https://www.dxomark.com/Lenses/Canon/Canon-EF-100mm-F2-USM---Measurements

Not sure where this poster found the 113mm (he was also mentioning 116mm) référence

apologies for cumbersome post.. but at least I learned . Even if I cannot comprehend all of it

thx!!

 

[Sittatunga]

Thx all for very informed replies

I found the reference (DxO review under Distorsions.. but shows at 105mm..) :

https://www.dxomark.com/Lenses/Canon/Canon-EF-100mm-F2-USM---Measurements

Not sure where this poster found the 113mm (he was also mentioning 116mm) référence

apologies for cumbersome post.. but at least I learned . Even if I cannot comprehend all of it

thx!!

That's a graph. The red dot on that plot represents both the focal length of the lens and its distortion. You have circled the high end of the x-axis of the plot, which in this case runs from 70mm to 105mm. The red dot is much closer to the 105mm end of the scale than the 70mm end; by my scaling, it corresponds to a focal length of about 101mm.

What we don't know though, is at what focussed distance did they measure the focal length? That changes as an internally focussing lens focusses.

The distortion scales at just under +0.3%, which is a tenth of the distortion from many zoom lenses. It would be helpful if the sign convention were displayed on the graph, so we could tell at a glance whether it was barrel or pincushion distortion. Again, distortion can vary with focussed distance.

The graphs on DxOmark are very pretty though.

 

[Trevor Sowers]

Hello

saw somewhere the EF 100 F/2 is actually giving of longer focal than 100mm?

113 or even 116mm?

is this true that a rounded number painted on the lens is not always what’s implemented in physical in the lens

not that it makes a great difference

looking at the 100 F/2 as it’s small, lightweight, well built and cheap

I've just checked mine against my Pentax-M 100mm macro and they both have almost exactly the same field of view at infinity. (Edit. Within 0.5% of each other as close as I can measure.)

I'd expect prime lenses to be within 5% of their marked focal length. That's one reason why they don't call it a 105mm. Zoom lens markings are notoriously elastic.

I really enjoy mine on full frame, it's a relaxing focal length for portraits and good for concerts. A wee bit of longitudinal colour aberration but DPP4 or DxO PhotoLab usually keep it from being bothersome.

I really enjoy 100mm as a focal length.