Help me understand the macro ratio.... you know 1:1, 1:1.5 etc

When they talk about a 1:1 ratio they say that means true to size 1cm = 1cm right?

But the pictures come out to be way bigger then real life. I mean I don't have a true macro... I use extension tubes and therefore not anywhere as good as a true macro. I took a pic of ants and they were waaay bigger then true life size.

But I guess that is the question, 1:1 viewed how? at the native ratio of your pixel ratio?

Wouldn't say a 100mm 2.8 macro taken with a 10 mp camera at a 3888x2592 pixel ratio, or taken with an 18mp with a 5760 x 3240 pixel ratio..... have a different macro ratio?

Then there is full frame and crop sensors, they change the size of the ratio right? an 18mp full frame sensor ,would change the size compared to an 18mp crop sensor. You could use the same situation from above and get different pictures, therefore a different size with the same lens , at the same distance..... but still with the same amount of pixels

So where are they getting the ratio from? what is the benchmark? The standard of which they take their calculations from?

The magnification ratios refer to the size of the image projected by the lens onto the sensor.

So at 1:1 a 1cm subject gives 1cm of image on the sensor, at 2:1 a 5mm subject gives a 1cm image on the sensor.
You will hopefully see from this that magnification ratio is not affected by the sensor size or the pixel density of the sensor.

Brian v.

Ok but that still makes my scenario with higher MP cameras to be true. That a 18mp camera will take a bigger picture, then a 10. It will still fill the same frame, but technically is bigger in the higher Mp pic.

Crimzon wrote in post #12683413
Ok but that still makes my scenario with higher MP cameras to be true. That a 18mp camera will take a bigger picture, then a 10. It will still fill the same frame, but technically is bigger in the higher Mp pic.

Yes, of course. But that has nothing to do with the macro ratio. If you have a higher pixel density, then that 1 cm long bug projected across 1 cm of your sensor (at 1:1 ratio) will cover more pixels.

The 1:1 ratio is simply the size of the image projected by the lens is the same as the actual subject (imagine the bug sitting on your sensor, that is the size your image of it will be).

How much you can then enlarge that image by is a totally different matter. When a lens is described with a macro ratio it cannot be a number that depends on the sensor size, number of pixels, what size you are going to make the final print etc. It is purely a function of the lens.

Crimzon wrote in post #12683413
Ok but that still makes my scenario with higher MP cameras to be true. That a 18mp camera will take a bigger picture, then a 10. It will still fill the same frame, but technically is bigger in the higher Mp pic.

If by "bigger picture" you mean you will be able to enlarge it more with less degradation of IQ then yes. However it doesn't matter if you have a 2mp sensor or a 21mp sensor. If both sensors are the same size then object will be rendered on each as the same size.

As far as which "standard" is used, well as with most digital photography the standards is how something would be rendered on 35mm film or a full frame sensor

If you step back to a film camera..... With a true macro lens that is 1:1, you will be able to take a picture of a 1cm ant. Develop the film. Then be able to place that ant on the film and the ant in the image will be the exact same size as the real ant. Does not mater if it is a 35mm, 4X5, 8X10, or any other format. A 1cm ant in real life will be 1cm on the film.What size you make the resulting print is completely non-relivent to weather a lens is macro, or what ratio of macro. Only the subject size to latent image size.

gremlin75 wrote in post #12685608
If by "bigger picture" you mean you will be able to enlarge it more with less degradation of IQ then yes. However it doesn't matter if you have a 2mp sensor or a 21mp sensor. If both sensors are the same size then object will be rendered on each as the same size.

As far as which "standard" is used, well as with most digital photography the standards is how something would be rendered on 35mm film or a full frame sensor

There is no "standard" for macro ratios with regards to sensor size, it doesn't matter what size the sensor is. They could be completely different sizes, even a tiny compact sensor and a FF sensor (or larger), the object will be the same size on the sensor. If you are using a lens with 1:1 macro, a 1cm long bug will take up 1cm of your sensor.

A 1:1 macro lens projects an image, at life size, on your sensor. It really is that simple, there is no need to try and complicate it by worrying about sensor sizes, number of megapixels, viewing size on the monitor, or anything else that has been mentioned - none of that matters. If you held a sheet of A4 paper behind your lens, at the same distance your sensor would normally be, the lens would still project a life size image on the paper.

OK, I think that clears everything up.

Thanks to all who answered my question.