Originally Posted By M4_man_223:
I just got that scope. It's marked 4, 5.3, 8, 16.

It's a nice scope but the marked values are odd....  5.3??

Originally Posted By BigWaylon:
Found this nugget on sniper central talking about a different Vortex scope:

Originally Posted By VortexSam:
Yes, that's correct. This is a SFP scope and with all SFP scopes the reticle must be calibrated to be accurate at one magnification. In the case of the 4-16x we calibrated the reticle at 16x.

So, this is what happens: Your reticle has hash marks on it that are used for measuring objects, to estimate distance, or for measuring hold over. However, in a SFP scope when you change magnification the reticle doesn't change size relative to your eye, but it does change size relative to the image of your target.

Think of the reticle as a ruler. Say you had a projector and you projected an image of a scene (or target) on a wall. Then you held a ruler up against that wall and measured objects in the scene with the ruler. That's basically the same thing you are doing with your scope reticle. However, if you increase the size of the image on the wall, your ruler doesn't change size. So now if you measure the same objects in the scene on the wall with your ruler you are going to get different measurements.

Now, say you took that projector and set the magnification so that it was such that your ruler accurately measured everything in the scene on the wall again. Then say you decreased the magnification by 2. Your ruler would measure everything in the scene twice as large as it really was. So you could easily do a quick mental conversion, say if you measured something that was 1in, you would know that it's really 2in. Then you decreased the magnification from the original setting by 3. Now a 1in measurement would really be 3in, and so on.

It's the same thing with your scope. Since the reticle is calibrated at 16x, if you decrease the magnification by 2 (8x), your reticle will now measure things only half of what they really are. So a 1MOA or 1mrad measurement is really 2MOA or 2MRAD. Now take 16x and divide by 3 (5.3x), your reticle will measure things 1/3 of what they really are, and finally at 4x it will measure things only 1/4 of what they really are. Hence the 16x, 8x, 5.3x, and 4x markings on the magnification ring.

Basically, it's a handy way of being able to estimate object size or hold over with your reticle at magnifications other than what the reticle is calibrated for in a SFP scope. Hope this helps. Let me know if you have any other questions.