# Help with calculating resolving power [closed]

I have liked your responses to the MTF questions and wondered if you could help me clear up an issue I have encountered.

I have a Canon 7D with an assortment of EF and EF-S lenses. The current issue of CT Digital Photography Magazine has an article that compares the 7D with a Nikon and Sony. They show that with a Canon EF-S 15-55mm f2.8 lens the resolving power at medium focal length on center axis is 1418 lp/mm. I do the math and get 95.17 lp/mm.

I understand that this value is for the camera system including the sensor and lens. I am finding that the equations for deriving the resolving power for the camera and lens don't seem to work with this value. I know that the 7D sensor has a native resolving power of 116 lp/mm and I know that the system value will be less that the lowest resolving power item.

I would like to be able to determine the value for the lens, but if I use 116 lp/mm and 95.17 lp/mm to solve for the lens, I get an impossible value for the lens. I have the same issue when using measurements in terms of lw/ph. Is there a relationship between the 1418 lp/mm and the 3456 sensor height?

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## closed as unclear what you're asking by mattdm, MikeW♦, Paul Cezanne, AJ Henderson, John Cavan♦Jul 25 '14 at 21:55

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question.If this question can be reworded to fit the rules in the help center, please edit the question.

I think you are mixing magnifications. One measurement is likely based on the image as it is projected on the actual image sensor, the other is likely based on a standard viewing size of 8x10 inches viewed at 10 inches. – Michael Clark Feb 11 '14 at 7:50
Please add all of your calculations to the question. There are too many numbers wandering around to understand what exactly you are asking. – TFuto Feb 14 '14 at 15:10