Seriously, the 1:3.9 is closer to macro (1:1) then the 1:7.7. Basically those numbers represent the size of the image on the "film" compared to the actual object. In other words, in a real macro (1:1), if you placed a dime on top of a negative of a photo of a dime they would be the same size. Following that analogy, the size of the dime on the 1:3.9 negative would be about double the size of the dime on the 1:7.7 negative.
Long story short the smaller the second number the better. :roll:
Now I haven't even tried to figure out how or if the "magnification" factor effects this at all.
1:1 means the size of the object on the sensor can be as large as the actual size of the subject. Only a true macro lens, like the Nikon 60/2.8 micro, can do this. Technically, anything less does not qualify as macro, and falls into the classification of "close-up lens", though the manufacturers may still call it a macro lens.
1:3.9 means the size of the object on the sensor can only be 1/3.9th (or 25.6%) of the actual size of the image at best.
1:7.7 means it can only be 1/7.7th (or 9.7%) the actual size of the subject at best.
So the Tamron 24-75/2.8 is a much better close-up lens than the Nikon 35-70/2.8.
Thanks, for the explaination. I was debating between these two for a portrait lens on my D2H. But since the Tamron goes to 28mm and does a better close up, I might just go Tamron. Part of me though is becoming a Nikon snob, and feel I should buy Nikon regardless!
I hate arithmetic, so I just put the numbers on the lens like this: The first number, 1 is the size of the picture behind the lens - on the sensor, so I say it is 1 centimeter (the sensor is 1.6X2.4 cm so a circle about a centimeter in diameter makes a good subject size.)
Then the object in front of the lens is the second number, in this case 3.9 centimeters, vs 7.7 cm. So with the 1:3.9, I'd take a picture of something about 4 cm but if the thing were 8 cm, a 1:7.7 ratio would be fine.
For me, the trick is remembering what order the numbers are in, so I say it with the camera in front of me pointed away, and say "one" (pointing to the camera), "to three point nine" (pointing to the subject.) I dunno - the visceral part helps me keep it straight.
I understand the Nikon snob part. I drool over some of the Nikon glass. However, I have been using Tamron lenses for a few years and they provide excellent results. The SP lenses from Tamron are especially nice.
I haven't personally used either of them. However, I am seriously considering the Tamron 28-75 f2.8 as a portrait lens. i am currently trying to figure out how to setup a studio in the house (with little or no expense). :wink:
I have used some other 2nd party lenses but I don't feel as strongly about them.