Magnification - 46x?

If my math is right (and it seldom is so please check me), then by reversing a 17mm lens I'm getting around 46x magnification. I shot a ruler, and 6 millimeters just fit horizontally in my 8mp Canon 20D image. That image is roughly 11x8 at 300dpi, or about 280mm by 200 mm. 280mm divided by 6mm is 46 and change. I had read that if an object is 1mm in lifesize, and it shows up as 10mm when you shoot it, thats 10x. So 6mm x 46 = 280mm. This seems too good to be true, 46x? Then again, each line on the ruler is incredibly thin, and at 17mm, it's huge, like I said, only 6 bars fit into the image. So whats up?

mag= sensor mm/mm across pic. So in this case it would be approx 22.5/6= 3.75:1.
Assume you are reversing onto the camera body ?
Brian V.

22.5? How so? My sensor is 280mm across (roughly 11x8 inches), 6mm across in pic = 46x.

This was done with a 17-40mm reversed at 17mm, nothing else or any other tricks.

Your sensor is 22.2 by 14.8 not 228mm across. If 6mm fills the frame, its about 4:1

gjl711 wrote in post #7494975
Your sensor is 22.2 by 14.8 not 228mm across. If 6mm fills the frame, its about 4:1

Ah, now I got it. I was measuring the final image size, 8x11, not the sensor size! I knew 46x was way too good to be true. So 4x eh? Not bad for a reversed lens. That's almost on par with the MP-E 65. Thanks, guys.

gregpphoto wrote in post #7495133
Ah, now I got it. I was measuring the final image size, 8x11, not the sensor size! I knew 46x was way too good to be true. So 4x eh? Not bad for a reversed lens. That's almost on par with the MP-E 65. Thanks, guys.

From a print perspective, it is about 46x, but that's not how to measure as the same sensor data is used if you print 8x11 or 16x22.

As john commented- it's normal to mention the lens magnification (ie the magnification onto the sensor) not the final print magnification.
Brian V.

Totally. I was saying to myself, 46x? That's powerful enough to see sperm cells!

gregpphoto wrote in post #7495633
Totally. I was saying to myself, 46x? That's powerful enough to see sperm cells!

I'm not sure why you would want to and also i wouldn't like to be there when you do...

Randy McBum. wrote in post #7496448
I'm not sure why you would want to and also i wouldn't like to be there when you do...

I pretty much only shoot natural things with macro, so I wouldn't be averse to it, from a purely aesthetic and biologic standpoint.

hey Greg, did you just get a bunch of step down rings and a body reversing adapter? or how did you get it all to attach? I'm interested. I have the 17-40 and am wanting to try some macro, and the budget won't let me get the 100 until at least summer I was thinking of picking up a cheap fast manual 35 or 28 and a reversing ring, I hadn't thought of using the 17-40 reversed until I read your success here LOL.

PiRho wrote in post #7587335
hey Greg, did you just get a bunch of step down rings and a body reversing adapter? or how did you get it all to attach? I'm interested. I have the 17-40 and am wanting to try some macro, and the budget won't let me get the 100 until at least summer I was thinking of picking up a cheap fast manual 35 or 28 and a reversing ring, I hadn't thought of using the 17-40 reversed until I read your success here LOL.

No I just handhold against the camera. I did just yesterday receive a reversing to camera ring, so I can mount the 17-40 in front of the ext tubes and now not have to worry about how its aligned, or give my hand the cramps from holding that sucker tight. But all my work thus far has been 100% handheld.

At 40mm reversed, you're already closer than what the 100mm 2.8 macro will give you, and at 17mm, you're near microscopic. Without tubes, just the lens reversed at 17mm is gonna give you 3.7x mag.