Understanding lens reproduction ratio charts

[Craig]

I'm looking at a Rodenstock Gerogon lens guide and they have published this chart that is supposed to show the relationship between focal length and image size. There is no explanation of how to use the chart and I can't figure it out.

If I have an 8x10" original and a 210 mm lens, what do I do to determine the size of enlargement I can make? The relevant page is attached.

 

[ic-racer]

Looks like x-axis is reproduction ratio and the y-axis is image circle (inches and mm on left ) and practical covering power (image sizes on right).

 

[ic-racer]

If you have the APO-GEROGON 210/9, that is pretty amazing lens according to the chart and will cover 8x10 up to 50" across enlargement. Is that the lens you have?

 

[Craig]

Are you sure about the 50"? I didn't see the Y axis going any further than 42". My reading was at a 1:5 enlargement, the biggest a 210 would do is a 16" image circle.

That's the lens I'm considering buying. It's quite a wide angle lens which I need for my enlarger, as I don't have a lot of ceiling height.

Further up in the brochure ( which I didn't include) it said it was optimized for 1:1 reproduction of 16x20" originals.

 

[ic-racer]

The y-axis is the covering power; how big the negative.
5:1 enlargement of 8x10 negative will be 50" across.

Yes, at 1:1 lenses have a lot of covering power. I use my Componon-S 210mm for 1:1 enlargements of 8x10. Much more control of contrast, dust, exposure and flatness than trying to contact print.