Over the years my favoured eye has developed astigmatism. As a Televue user I have purchased an appropriate value Dioptrix filter/lens that will attach to a number of the wider angle eyepieces. I find that it improves my viewing experience significantly.
However, it can become tedious moving the filter to alternative lenses, especially in the dark.
I also have some Nagler type 6 lenses that I use throughout the night. While TV do make an adapter that will fit the Dioptrix to the Type 6 eyepieces, it is still fiddly, and not inexpensive.
To address these issues I have come up with the idea to fabricate an aluminium sleeve that will fit over the narrower eyepieces and hold an optical astigmatism lens used for eyeglasses on top of them.
The astigmatism correction lenses that I sourced are 36mm diameter.
Now I can just lift off or on the correction lens to any of my narrower eyepieces effortlessly. Simply rotate the whole assembly to achieve best clarity. The lower retaining flange sits on top of the rubber cup and rotates on it. The arrangement may restrict the available viewing angle in the case of the Naglers, but there is still a reasonable area that can be seen.
This concept can fit any of a number of eyepieces. It would also facilitate some one carrying this adaptor with them and just drop onto a colleagues eyepiece when group viewing without disturbing the setup.
I’ve made my sleeve to accept 43mm outer diameter eyepieces, and (now) without eyeglasses, there is plenty of eye relief.
Fabrication is relatively simple if you can access a lathe and get a bolt of aluminium. Some of the plastics would also be suitable, I happened to have some aluminium already.
I believe you can give your lens holder to your optometrist. They can send that holder away and have a lens cut to that shape and even anti-reflection coated for less than the TV product cost. The lens machines cut the plastic to follow/match the profile of the frames.
I have not tried this. I worked it out years ago but then found that my astigmatism was mild and didn't need correction at the telescope. Mine was caused by an eye accident, many lacerations that changed the lens shape just once so the correction has not changed and remained small enough that I have not needed it at the telescope even with wide exit pupils. The astigmatism has not progressed to stronger corrections over the past 10 years and because of my age, I don't use any eyepieces that result in an exit pupil(EP) wider than 5.5mm. At those EP's, I don't have a problem.
If you have optical health insurance, you probably get two pairs of new glasses every year. Those glasses have the astigmatic correction built in. You could make your own less attractive correctors by using those lenses in a holder.
That's a clever idea!
I was playing with a camera I was given just last week and I found the camera focused at the same point as the removed 12mm Vixen Lanthanum eyepiece Id been viewing through. Problem is my focal point vs my sons focal points are very different, it even looked somewhat focused on the laptop screen, again, according to my eyes.
I was somewhat disappointed with my end results of M42. I have to learn to take stronger reading glasses out for this hobby.
In saying that I haven't had my eyes checked for years, I wear cheap reject shop reading glasses because I have a constant habit of bending over to put something in my car (or remove it), step away and wonder what the crunching sound was underfoot, it's usually my glasses which have fallen from my shirt pocket. Maybe if I just wore them all of the time it wouldn't happen but it probably would.
My last pair of expensive prescription glasses were placed right in the very corner of a Dojo when I was training (when I was younger) and a clumsy friend who was observing stepped right on the things. That was it for prescription glasses for me.
Yes, I'm aware I'm probably doing more harm than good with the cheap things but they seem to work.
The bare lenses from the optometrist are circular. I made the lens holder to fit the diameter of the bare lens, which adjust for astigmatism only. No other corrections. This way there is no need to cut the lens. With the the astigmatism corrected, the other corrections usually made in spectacles can be made by adjusting the telescope focus. Simple!
