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Posts Made By: Richard Francis

February 6, 2024 06:58 PM Forum: ASTRONOMY

Cataract surgery

Posted By Richard Francis

This thread is a bit old, but for anybody finding it later on and facing this I can give a few words on my experience. I didn't have cataracts, but had myopia and astigmatism. It wasn't severe but I needed glasses to enjoy the night sky (or to drive for that matter).

My wife, who had much worse vision problems, went for multifocal IOLs in each eye, that was in 2010. The type was called M-Plus (though the manufacturer has now gone bust, for reasons which will become clear). They have the part with a different strength (by 2 dioptres) in a segment, like a pizza slice. She loved them and went on campaign to persuade me to have the same procedure. After 2 years I relented and went for it.

However, there is a particularity with these IOLs: the different strength in a sectors has edges, which cause diffraction spikes, like the spikes around the support of a spider in a reflector telescope. They're not noticeable in daytime, but with bright lights against a dark background, whether it's driving at night, or looking at stars or the Moon, they show up as 2 horn-like projections.

I spoke to the designer (put in contact by the opthalmologist) and he actually advised me not to choose them in my situation, being interested in clean and clear night views. But my wife insisted it was not so bad and it's true that the brain does eventually adapt so that they are scarcely visible. As you might guess, my wife was persuasive and I did take them. The change in my vision was breathtakingly good, and after a time I did find the spikes to be less and less troublesome.

But, after about 9 years, I found my vision was becoming cloudy, just as if I was developing cataracts. It got so bad that I could only see the brightest stars and was unable to see nebulae in the eyepiece. It turned out that the lenses I had, in 2012, had been part of a batch which had been transported in a contaminated liquid, which caused internal crystalisation in about 10% of patients. The only option was to have them replaced. my opthalmologist told me that all costs would be borne by the IOL manufacturer, and sent me to one of only 2 surgeons in The Netherlands who could perform the procedure.

In the end, the company did not pay, because they had gone bust, quite possibly as a result of this. But the surgeon I chose had been able to obtain all thier stocks, so I only had to pay for his work, the replacement also being an M-Plus multifocal IOL.

This time the procedure was more difficult and required going in via the pupil, and not without risks. In fact the surgeon told me he thought he was the only one in Europe who could do it.

So now, almost a year later, the cloudiness has gone, but I'm left with myopia and astigmatism again -- pretty well back where I started -- and have to wear glasses to view the night sky.

February 9, 2024 06:48 PM Forum: Mounts

US digital encoders...S2 or S1?

Posted By Richard Francis

Sorry I'm rather late to this topic (just seen it) and I strongly suspect you've resolved it by now.

I've used many US Digital encoders over the years. Sometimes to replace existing ones (such as in the Meade motor/encoder combination) and sometimes in my own designs. I've found that the ability to specify exactly what you want is invaluable.

For replacements I've always (ie in the Meade case) used exactly the same spec as the one I'm replacing.

For my own designs though I have base it on the associated software (sometimes my own design). In one case I actually switched from a low CPR to a much higher one when it turned out, in correspondence with the hardware/software vendor that it would be advantageous. That's one of the things I like with US Digital -- I only had to order a couple of replacement parts and not the whole thing.

I looked at the spec for the S1 and S2, and at first glance the major difference for a mount application seems to be the available CPR values. That said, they point out that if you want the S2, it's obsolescent and they recommend the S6 instead.

I'm sure I'm too late with this reply, but maybe it could help.


February 9, 2024 07:01 PM Forum: Mounts

Mitty Wedge

Posted By Richard Francis

I bought a Mitty Wedge in may 2004. It was in fact the prototype Euro Wedge (with a higher latitude range).

I may still have some instructions but it will take some finding.

Do you mean assembly or operating instructions? I assume assembly since operation is essentially the same for any wedge.