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I've seen a few threads on DJI Goggles / Moverio BT-300, etc. branch out into discussions about issues with vision correction. I responded to a few of the issues raised, but I thought it may be useful to summarize what has been discussed so far, and a little that has been overlooked, and give this discussion its own thread:
1) Bi-focal (varifocal, etc) prescription lenses : In general, these prescriptions will not work in head-mounted displays because they rely on slightly tilting the head up or down to look out at the world through different parts of the lenses for focussing at different distances. Wearers of varifocals will drop their head slightly and peer out through the top of the lens to focus at a distance, and will raise their head slightly and look through the bottom half of the lenses to read, or do close-up work. Since tilting the head also moves the head mounted display you are always looking at top of the display through the 'far focus' part of the lenses and at the bottom of the display through the 'near focus' part of the lenses. Depending on your prescription strength, and the range of diffent focal lengths in your prescription, this will likely result in only part of the display being in focus. In my case, my varifocals gave me crisp focus in the bottom half of my BT-300s, gradually becoming blurry toward the top (to the point where I could not read text at the top of the display).
If you have this type of prescription and don't want the expense of getting a new single-focal length prescription you can just buy a pair of cheap reading glasses from the pharmacy. I recommend taking your BT-300 or DJI Goggles to the parmacy and trying on glasses till you find exactly the right strength, as a lens that works well for reading a book, or computer display may not be quite right for your BT-300 or Goggles.
2: Different prescription per eye: (This will not be an issue for most drone pilots, but useful to know if your are one of the affected)
Since I had had a post-vitrectomy cataract surgery on one eye I could not simply replace my varifocal prescription with a pair of cheap reading glasses as the lens implant in my right eye is not able to change focal length, and I had opted to have the implant 'tuned' to 20/20 distance vision, which means I require much stronger correction in my right eye for near focus than in my left eye. To overcome this I bought two pairs of cheap reading glasses, one which when tried on with the BT-300, gave me perfect focus using only my left eye, and the other which gave perfect focus using only my right eye. My intention was to swap two the two right lenses and end up with a pair that works perfectly for both eyes. However, I found that using the special nose-bridge clip that comes with the BT-300 for glasses-weares put the BT-300 in an uncomforable position on my nose; a little too far away from my eyes, and also made the BT-300 prone to slip down my nose while using them. So I did the following:
2: Rochester prescription inserts : Using the Rochester prescriotion insert is far better than wearing glasses with the BT-300 (I found). I did not want the expense of getting my optician to fit a new prescription into the Rochester frames, and I was not really confident that a regular 'reading glasses' prescription would even be ideal, since the BT-300s appear to require a different focal length than reading a book, or using a computer screen. So I just took the lenses out of my cheap pharmacy frames and cut them to shape to fit the Rochester frames! The lenses in those cheap reading glasses are plastic, not glass, and can easily be cut with a Dremmel tool or similar. Just stick painter's tape on the lenses and draw the correct shape using the inside of the Rochester frames as a guide.
3: BT-300 vs Goggles - Different glasses strength required: A few months after buying the BT-300s I got my DJI Goggles. I had planned to make a way to attach my customized Rochester frames into the Goggles but when tried the Rochester frames using a temporay fixture (blue tack
I found that they did not focus correctly in the Goggles, no matter how I positioned them. It was obvious that the Goggles require a different corrective lens than the BT-300 (probably have a different apparent focal length to the display). So it was back to the pharmacy for me, this time armed with my DJI Goggles, to find two new pairs of cheap reading glasses to cobble together (Note: you get a lot more strange looks and comments when trying on reading glasses with the Goggles in a crowded pharmacy than you do with the BT-300
Whebn I found the two best pairs I again swapped out the right lenses and built a new custom pair which worked perfectly, as far as correcting my funky vision for the Goggles display was concenerned, but wearing glasses with the Goggles raised its own issue, which brings me to ... :
4: Light leakage in the DJI Googles when wearing glasses. At one point, when I was experimenting with the different options discussed above in my DJI Goggles, I had bright sunlight streaming in the window behind me. I discovered that when wearing the glasses, the frames distorted the rubber face cushion and created a lot of light leakage. this despite the fact that the cushion has a 'cutout' for glasses which I made sure was aligned with my temples. When trying the temporarily inserted Rochester frames, although they did not quite focus correctly, there was no light-leakage at all. So I just cut the temples off my new, customized reading glasses and I'm now working on a way to clip the remaining frames into the Goggles. I want to make it easily removable so friends can use the Goggles when I'm piloting the drone. I'll post an update when I have the final design for that.
1) Bi-focal (varifocal, etc) prescription lenses : In general, these prescriptions will not work in head-mounted displays because they rely on slightly tilting the head up or down to look out at the world through different parts of the lenses for focussing at different distances. Wearers of varifocals will drop their head slightly and peer out through the top of the lens to focus at a distance, and will raise their head slightly and look through the bottom half of the lenses to read, or do close-up work. Since tilting the head also moves the head mounted display you are always looking at top of the display through the 'far focus' part of the lenses and at the bottom of the display through the 'near focus' part of the lenses. Depending on your prescription strength, and the range of diffent focal lengths in your prescription, this will likely result in only part of the display being in focus. In my case, my varifocals gave me crisp focus in the bottom half of my BT-300s, gradually becoming blurry toward the top (to the point where I could not read text at the top of the display).
If you have this type of prescription and don't want the expense of getting a new single-focal length prescription you can just buy a pair of cheap reading glasses from the pharmacy. I recommend taking your BT-300 or DJI Goggles to the parmacy and trying on glasses till you find exactly the right strength, as a lens that works well for reading a book, or computer display may not be quite right for your BT-300 or Goggles.
2: Different prescription per eye: (This will not be an issue for most drone pilots, but useful to know if your are one of the affected)
Since I had had a post-vitrectomy cataract surgery on one eye I could not simply replace my varifocal prescription with a pair of cheap reading glasses as the lens implant in my right eye is not able to change focal length, and I had opted to have the implant 'tuned' to 20/20 distance vision, which means I require much stronger correction in my right eye for near focus than in my left eye. To overcome this I bought two pairs of cheap reading glasses, one which when tried on with the BT-300, gave me perfect focus using only my left eye, and the other which gave perfect focus using only my right eye. My intention was to swap two the two right lenses and end up with a pair that works perfectly for both eyes. However, I found that using the special nose-bridge clip that comes with the BT-300 for glasses-weares put the BT-300 in an uncomforable position on my nose; a little too far away from my eyes, and also made the BT-300 prone to slip down my nose while using them. So I did the following:
2: Rochester prescription inserts : Using the Rochester prescriotion insert is far better than wearing glasses with the BT-300 (I found). I did not want the expense of getting my optician to fit a new prescription into the Rochester frames, and I was not really confident that a regular 'reading glasses' prescription would even be ideal, since the BT-300s appear to require a different focal length than reading a book, or using a computer screen. So I just took the lenses out of my cheap pharmacy frames and cut them to shape to fit the Rochester frames! The lenses in those cheap reading glasses are plastic, not glass, and can easily be cut with a Dremmel tool or similar. Just stick painter's tape on the lenses and draw the correct shape using the inside of the Rochester frames as a guide.
3: BT-300 vs Goggles - Different glasses strength required: A few months after buying the BT-300s I got my DJI Goggles. I had planned to make a way to attach my customized Rochester frames into the Goggles but when tried the Rochester frames using a temporay fixture (blue tack
I found that they did not focus correctly in the Goggles, no matter how I positioned them. It was obvious that the Goggles require a different corrective lens than the BT-300 (probably have a different apparent focal length to the display). So it was back to the pharmacy for me, this time armed with my DJI Goggles, to find two new pairs of cheap reading glasses to cobble together (Note: you get a lot more strange looks and comments when trying on reading glasses with the Goggles in a crowded pharmacy than you do with the BT-300 Whebn I found the two best pairs I again swapped out the right lenses and built a new custom pair which worked perfectly, as far as correcting my funky vision for the Goggles display was concenerned, but wearing glasses with the Goggles raised its own issue, which brings me to ... :
4: Light leakage in the DJI Googles when wearing glasses. At one point, when I was experimenting with the different options discussed above in my DJI Goggles, I had bright sunlight streaming in the window behind me. I discovered that when wearing the glasses, the frames distorted the rubber face cushion and created a lot of light leakage. this despite the fact that the cushion has a 'cutout' for glasses which I made sure was aligned with my temples. When trying the temporarily inserted Rochester frames, although they did not quite focus correctly, there was no light-leakage at all. So I just cut the temples off my new, customized reading glasses and I'm now working on a way to clip the remaining frames into the Goggles. I want to make it easily removable so friends can use the Goggles when I'm piloting the drone. I'll post an update when I have the final design for that.
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