Eyepiece Focus: FFP Precision Scopes
This is another subject that comes up with reasonable regularity. I did a couple of videos on focusing riflescope eyepieces a while back, but a bunch of people complained that it was too long and too technical. They were looking for something simple and to the point.
Simple and uncomplicated is not something I do well, so I figured I should try to put together a through the scope video that demonstrates the point. That turned out to be a little bit involved, but I think I've got a reasonable way of doing it. In the meantime, here are some general guidelines and the reason why this is a bit different with FFP scopes compared to SFP.
Do note that is a little different with LPVOs. Not very different, but still this applies to FFP scopes that do NOT go down to 1x. The video I am trying to put together to demonstrate this is ZCO 4-20x50.
1) Mount the scope on something steady. Do not do this handheld. If you've seen me do it handheld at SHOT or something like that, please pretend it never happened. I have adjusted hundreds, if not more, scopes over the years and developed a feel of sorts. Still, for my guns I do this on a steady platform of some sort.
2) Start out doing this with fairly bright lighting conditions.
3) Point the scope at something uniform and light colored (sky, wall, etc). The reticle should be the most prominent thing in your sight picture, so you eye focuses on it.
4) Set the magnification to something fairly high and slowly adjust the eyepiece focus to make the reticle perfectly sharp. Frequently look away from the scope at something distant. When you look through the scope the reticle should be immediately sharp without any time allowed for accommodation.
5) Once you converge on a reasonable setting, lower magnification to some setting where the reticle is clearly visible, but thin. Basically the lowest magnification where the reticle is still easily visible, but small. Repeat the adjustment process. This is finetuning, so go slow and give your eyes time to rest.
6) Repeat step 5 in somewhat lower light when your eye pupil is dilated half way or so. You will likely end up on somewhat higher magnification than step 5. This is more finetuning, so go even slower.
You should be done, but it is not a bad idea to check the setting in good light again at some future point. For most people, the eyepiece setting you converge on in step 6, should work across the board, but everyone's eye differ and sometimes you can end up with daylight setting and night time setting. I can always mark the two spots just in case if you need to switch, like you would if there were two users to the scope.
Lastly, with FFP scopes, the reticle is between the erector and the objective, so as you rack through the magnification range, with some high erector ratio designs, it is possible to have a spot where for one specific magnification, the reticle goes out of focus slightly. Make sure that in steps 5 and 6, are not sitting on one of those magnifications.
