I have myopia of 5.25dioptre. I am able to do AF easily without glasses on text which was around 20 - 25 cm away from my eyes .I have been trying to do AF with differentials(4d) but I am not able to do it since a lot of time. The same goes with reduced prescription for distant vision. I just am not able to do it for these. Why is it so?, How is AF for distant vision different from AF for near vision? How can I do it?Help…
Maybe you’re trying to reduce too much?
20cm focus is 1/5m = -5D.
25cm focus is 1/4m = -4D.
If your current prescription is not a big over-correction then you might try starting with tiny under-corrections until it’s pretty easy for you. Remember you want just a little bit of challenge, not “too much challenge”.
Good luck with it!
I would suggest this is something you shouldn’t do much of, the eyes work much harder at this close proximity plus the added convergence strain. Keep trying for the Af at the appropriate distances for your corrections, it will come. Maybe this will help: A little help with Active Focus - YouTube
This is a reoccurring question, so here is my take on it:
Most people find AF without glasses or with differentials first, but struggle to AF with normalised. I think it is because people seem to forget that AF is for the edge of blur. And they simply overestimate their visual acuity at distance.
If your full prescription or your normalised give you enough clarity to read the subtitles on the TV screen at 2.5 metres or the 20/20 line on a 3m Snellen, but with the same glasses you cannot read even 20/25 on a 6m Snellen, and if so then most probably you cannot read street names or house numbers on the opposite side of the road - even if those are your strongest glasses - then you are trying to clear something well outside your distance to blur. You cannot clear something that is simply way over your blur horizon. You may get clear flashes but you cannot do sustainable tiny blur clearance at it.
So put on your distance glasses. Can you read 20/20 at 3 metres? If not walk closer until you can easily read it maybe with a tiny blur and note the distance (Warning for high achievers: yes it may be as little as 1m or 1.5m). It means you simply haven’t trained your eyes to see clearly over the monitor distance yet. If you can read 20/20 at 3 metres, start walking away from the chart keeping your eye on the 20/40 line until it starts getting slightly blurry. Note the distance. If that is less than 6 metres than you simply haven’t yet trained your eyes to see clearly over 3 metres.
Now take the distance you noted, stand there and enjoy the sharp edges of the letters for a while, and then make a step backwards. 5cm? 10cm? Did you manage to hold the clarity? Did it go blurry for a fraction of a second and then clear up? Does it go away when you blink? Or you can hold it?
Stay at that distance for a while and repeat this every day or a few times a week. Or a few times a day. Any frequency can be OK as long as it feels comfortable and you are not pushing your eyes too much.
It’s the same with differentials. Increase your distance to where the tiny blur comes in. Stop there. Then push another 2 to 5 cms. If you can maintain the same clarity, stay at that distance. You are actually AFing in that position! but if you add yet another 2 to 5 cms then you might be simply sitting in blur and what’s the point of that?
So in short with rough numbers: with moderate myopia you can find an AFable distance without glasses somewhere between 20 and 50cms, with differentials somewhere between 50 cms and 1m, with normalised over 1m but preferably between 3 and 6m, with full opto prescription between 6 and 20 metres.
Everybody can AF at any distances but not everyone can select the right distance for the given glasses or the right glasses for the given distance.