Ocular Diopter - controversial advice alert

[adamg]

I'm going to be controversial here with some advice.

From hanging around scopes rifles and their owners, I am going to say that 80% of you have the ocular diopter set wrong.

Here is a spec sheet for the diopter setting on an example scope. I tried to find this same specification for other brands but it is surprisingly absent. I'd appreciate it if anyone finds more spec sheets that list this, to reply with it here.



Note that one end of the adjustment range is a large negative value, and the opposite end is a large positive number. This suggests, if you think about it, that a setting in the middle of the adjustment is a neutral setting.

Just because your scope arrived from new with the diopter adjustment maxed out in the 'in-most' position, doesn't mean this is the baseline or normal setting. In fact you are using the extreme setting in one direction.

So what's the upshot here? What's the problem I want to help with?

When you leave the diopter set at max-in position, your reticle is optically very close to your eye. To see a sharp reticle, you have to focus your eye very close - roughly 1 foot from your eye.

You are looking at your scoped rifle target off in the distance, whether it be 50 yards or 1500 yards. You get behind your scope and you want to align the reticle on the target. Except you have to focus your eye down from that far distance to 1' to see it clearly. That's slow and bad.

Wouldn't it be better if your reticle was optically farther away - closer to your target - so you didn't have to focus your eye so close?

I set my diopter somewhere near the middle of the adjustment range. This puts the reticle at roughly 20 yards from my eye. This requires less eye focus change when I look through the scope after looking at my target. Plus, now my other eye is focused closer to the target and has better situational awareness.

 

[zupermann]

All I know for sure is that I hate doing the reticle focus thing on a new scope (if Im understanding you correctly)
Im never sure if its correct as I find it so subjective as the eye quickly adjusts to make the reticle clear.

 

[adamg]

All I know for sure is that I hate doing the reticle focus thing on a new scope (if Im understanding you correctly)
Im never sure if its correct as I find it so subjective as the eye quickly adjusts to make the reticle clear.

In my research for this post, I did read the manuals from various vendors. They all recommend a similar technique, like what you mention.

This technique is trash, IMO. It assumes the user is able to set their eye focus distance at the "right" distance, and hold it steady while they move the diopter until the reticle looks sharp.

Two MASSIVE problems:
1. The user cannot hold their focus steady during this process.
2. The user has no idea what distance they are focusing at, much less whether it is the "right" distance.

I am suggesting an alternative:
Step 1. Set your adjustment near the middle of its travel.
Step 2. If you are an advanced user, capable of seeing out of both eyes at the same time, slightly tweak the adjustment to achieve the optical focus distance you want to achieve on the reticle. For me, this is roughly 20 yards - but anything from 5 yards to 50 yards is good for me.

 

[Buck1950]

When adjusting the ocular focus, it is advised to look at the reticle in brief glances so your eye doesn't 'self-adjust' to accomodate the close reticle. I just look for 2-3 seconds, then look away for 5-10 seconds; after 2-3 cycles I'm able to get a clear view ( not fuzzy) of the reticle. I've had cataract surgery on both eyes so my vision does fall within the mid-range of the ocular, but I find a bit of '+' is still needed. As well, about half my scopes have parallax adjustments which adjusts the 'view' of the target, but does Not change the 'view' of the reticle.
I don't really understand your point about a "20-yard" focus distance. When setting the ocular one is to 'aim' at a blank wall or ceiling and adjust the focus to get the 'most clear' view of the reticle itself. Distance is NOT a factor in this in my understanding of the process.

JMO, maybe someone with actual optical education can help clarify this. Are ALL Optical manufacturers giving "trash" instructions on how to set up the ocular ? ?

 

[steve-o1979]

When adjusting the ocular focus, it is advised to look at the reticle in brief glances so your eye doesn't 'self-adjust' to accomodate the close reticle. I just look for 2-3 seconds, then look away for 5-10 seconds; after 2-3 cycles I'm able to get a clear view ( not fuzzy) of the reticle. I've had cataract surgery on both eyes so my vision does fall within the mid-range of the ocular, but I find a bit of '+' is still needed. As well, about half my scopes have parallax adjustments which adjusts the 'view' of the target, but does Not change the 'view' of the reticle.
I don't really understand your point about a "20-yard" focus distance. When setting the ocular one is to 'aim' at a blank wall or ceiling and adjust the focus to get the 'most clear' view of the reticle itself. Distance is NOT a factor in this in my understanding of the process.

JMO, maybe someone with actual optical education can help clarify this. Are ALL Optical manufacturers giving "trash" instructions on how to set up the ocular ? ?

I doubt the manufacturer is giving trash instructions.

 

[bigHUN]

I had many scopes and optics in my hand.
I made a while back a fixture (a piece of pic rail mounted on arca pad), and fix it on my very decent stability photography tripod. This where I mount the scopes I want to set to my eyes.
I can sit at my rear deck, and the tripod in front of me.



Move the scope power to a max and distance to a max, pointing up in a neutral direction, let say to the empty blue sky. So no distance focusing at this point.
With a diopter adjuster turn it there and back from zero until I see the reticle the crisp sharpest.
Now the trick.... never look through the scope more then 5=five seconds, but in intervals look aside to relax your eye focus.
Getting the diopter adjusted to your eyes doesn't need to be a 30 second job, take your time, half an hour if you really need that much.
When you finally get it right, you also got the best parallax as well.
The graduation on the diopter ring also the distance ring doesn't need to be opticians accurately marked, pretty much "who cares" where are the marks or what those mean. It is just for your "reference point" where or how your turning L-R.

 

[Back Country Hunter]

The advice above is spot on for a SFP scope. However the picture shows a FFP scope. With a FFP scope you are better to adjust the diopter with the magnification set at the lowest power as this is where the lack of reticle "sharpness" becomes the most apparent.