1:1 and focal length question

Hello,
Im not quite sure how to go about searching on this topic, but I suspect the answer is in plain sight and I have tunnel vision. I understand true macro lenses have a 1:1 ratio. I understand this means the subject will be represented on the film/sensor in true size. My question is at what point does a macro lens reach 1:1? Is it at minimum focal distance? Is it safe to say that up until minimum focal distance, a macro lens reacts pretty much the same as any other lens would? If a normal non macro lens was able to focus at a shorter distance, would they effectively be macro's as well?

second part of the question, is that if the focal distance is what designates a lens as macro, do longer macro lenses reach 1:1 from a further distance?


I apologize in advance, I suspect these questions are pretty basic and could be answered with a proper search, but I just cannot seem to pinpoint the answers.
Thanks

A macro lens is just a lens that can focus very closely. For example, I have the 100mm macro and it works nicely as a portrait lens at normal shooting distances. Should I need to shoot "macro", I just get closer to the subject. It achieves 1:1 at its minimum focusing distance which is much closer than a non-macro lens like the 100mm f/2.

Yes, longer macro lenses like the 180mm macro are 1:1 at their minimum focusing distance which is farther out. This is good if you need more distance from the subject but still want 1:1.

The fact that a macro lens has such a short MFD is what allows it to hit 1:1 magnification.

And yes, the longer the focal length of the macro, the longer the MFD and 1:1 focus distance.

thank you guys. kind of what I suspected, just couldnt really confirm.

1. Yes there is a difference between an ordinary lens with say extension tubes and a macro lens at the same magnification. The macro lens will be designed for closeup work and will have much better control of aberrations and will also be designed for a flat focus field in closeup. The trade off is macro lenses tend to be a stop slower, larger and heavier than their non-macro counterparts.

2. Yes max magnification is at closest focus. However, magnification vs subject distance is not always a straight forward relationship with internal focus lenses; I found this to be the case for the 180L. This does not realy impact you for normal use.

3. Yes the reason for using a longer macro lens is partly that the subject is further away which may help with aproaching live subjects, help with not shading natural light. A longer lens also gives a tighter perspective helping to remove background clutter. A longer lens can be better for tripod use. Downside is a longer lens is heavier, more difficult to handhold, can be more of a problem in long grass, can mean you have to backup too much for larger subjects like flowers.

Lester Wareham wrote in post #16290156
... However, magnification vs subject distance is not always a straight forward relationship with internal focus lenses; I found this to be the case for the 180L....

This internal focus systems (IF) have the drawback that focal lenght is changed during focussing. Because of this macro lenses with IF have at 1:1 a shorter focal length than at infinity.
The Canon EF 100/2.8 Macro seems to have ~78mm focal length at 1:1. But I am not sure about that - pure calculations depending on working distance are not necessary correct. And only few people do actually measure the focal length.

Simple (older) macros with only helicoid or bellows focussing don´t have this issue.
But for example the old Nikon 55mm/2.8 micro has something special, it has not IF, but clsoe up correction (floating elements) and this changes focal length too. Its focal length gets a bit longer at 1:1.

But all this is not documented in lens manuals or such. So exact calculations are hard.

ZoneV wrote in post #16305879
This internal focus systems (IF) have the drawback that focal lenght is changed during focussing. Because of this macro lenses with IF have at 1:1 a shorter focal length than at infinity.

Correct. You can estimate this effect using equations from the Eyes of EOS book and a bit of guestimation, the Canon tubes include some tables to help.

I had a go at this here http://www.zen20934.ze​n.co.uk …ent.htm#Extensi​on%20Tubes
it is probably not super accurate.

Internal focus is quite a useful feature operationally however.

Lester Wareham wrote in post #16306403
Correct. You can estimate this effect using equations from the Eyes of EOS book and a bit of guestimation, the Canon tubes include some tables to help...

Yes, but I would like to know the focal length. Guessing without knowing the probably moving principal planes it very rough guessing.
I remember asking a very good lens manufacturer (no details here) about a extension tube and macro lens. He could not calculate it, and need to test it with the lens, camera and tubes. Cause support there did not know real focal length for close up settings.
I thought they had tables, or could perhaps ask an optics designer.

Lester Wareham wrote in post #16306403
Internal focus is quite a useful feature operationally however.

I love it for long focal length lenses like my 300mm/2.8 and longer.
But for macro I see nothing good for me. But I have to admit, with some kind of floating element for near field correction focal length change would bother me too, but I would be happy with the correction.

ZoneV wrote in post #16306811
Yes, but I would like to know the focal length. Guessing without knowing the probably moving principal planes it very rough guessing.
.

Well can work it out reasonably well using simultaneous equations and the published values but it is a while since i did this. Typicaly it seems widly understood that the focal length at 1:1 is about 70% that at infinity. I understand even a conventional lens can have a 10% tollerances on focal length.