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Televue Dioptrx first light


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My Televue Dioptrx finally arrived last Saturday and it had it first light last night. I placed an order with Widescreen Centre in September, but it took a while for Televue to dispatch it from the US. I guess the introduction of the new focal lengths Delos and the hurricane must have affected TV’s shipping schedule.

Televue Dioptrx is designed to correct astigmatism in the eye. Most people know glasses correct for near/far slightness but many are less familiar with astigmatism. Astigmatism is caused by the eye’s lens being slightly elliptical, which causes light from different axis to focus at different point. Astigmatism appears in an optician report under ‘cylinder’ and ‘axis’. Cylinder describes the severity and axis describes the orientation. My cylinder is 1.0, so I ordered the 1.0 Dioptrx.

The most common method to deal with astigmatism is to observe with glasses on. This usually required eyepieces with more than 16mm eye relief. However, glasses have some drawbacks. First the spectacles need to be in good alignment with your telescopes, otherwise it can create a lot of problem. Then specs can be a major source of flare and scatter and this is made worse if the lenses are dirty. Finally, glasses do not work well with ultra wide angle eyepiece. The last problem is the reason why I decided to buy a Dioptrx.

The Televue Dioptrx came in a typical Televue hard cardboard box. Inside the box, there is the Dioptrx, a rear cap and a sheet of instruction. I can’t understand why TV didn’t include a front cap. It doesn’t make any sense to protect the element on one side but not the other.

The Dioptrx is designed to attach onto the rear of a number of TV eyepieces. This aligns the astigmatism corrector with the rest of the telescope’s optics.


The attachment method was a bit of a mystery. I posted a question about this a while ago and the answers ranged from a proprietary thread that only works on TV eyepieces to a simple push fit. I can now confirm it’s neither. The Dioptrx uses a twist lock compression ring fitting. It’s a bit like the ones you found holding your eyepieces in the focuser. The differences are the Dioptrx one is smaller and it uses a twist lock instead of thumb screw.

The Dioptrx itself is made of two parts. The upper part houses the glass and a shallow rubber eye cup, while the lower part houses the twist lock mechanism. Once you insert the Dioptrx, you turn the two parts against each other to lock. The barrel diameter of the Dioptrx is about 44mm. This means the Dioptrx can be attached to any eyepiece with the right dimension and not just Televue’s. As it happens, I don’t own any Televue eyepieces and I will be using my Dioptrx on third party eyepieces.


I tried fitting the Dioptrx on several eyepieces I owned and I can confirm the Dioptrx will attach to Vixen LVW (include LVW42), 5.5mm Meade S5k UWA, and Nikon NAV-HW. None of these are very secured attachment, all will fall off if you attempt to lift the eyepiece by the Dioptrx, but the Dioptrx will not fall off the eyepiece if the eyepiece is turned upside down. The Dioptrx will not attach to Aero ED, Pentax 8-24 zoom or Nikon NAV SW.


Last night’s observation session was quite short. I observed for about an hour before my telescopes dewed up. I was mostly interested in whether the Dioptrx worked. I tested it on the Pleiades with my SV80s and various eyepieces. The eyepiece that benefited the most was my 42 LVW. I inserted the Dioptrx, at first met some ridiculously distorted stars, but as I turned the eyepiece, the stars gradually became tighter and tighter, until they became pin points when the Dioptrx axis cancelled my eye’s axis. I’ve never seen Pleiades like that before. The stars were tighter and looked sharper than when I observed with my glasses on.


Then came the most important test. Would the Dioptrx work with my 102deg NAV-HW? When I observed with my glasses on, it produced an unacceptable amount of lateral colour near the edges. These colour were absent when I observed without my glasses, but stars become distorted by my astigmatism. My spectacles simply can’t cope with me viewing 50deg off axis and this was the reason why I ordered the Dioptrx.

I inserted the Dioptrx, pressed my eye socket against the rubber eye guard and let the Pleiades drift. The stars were pin point up to the field stop.

The Dioptrx has passed its test. :)

That’s all for now, I will test it on other targets another night.

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  • 3 years later...

The Dioptrx is a great idea. I have a little astigmatism but not terrible - only going to get worse as I get older!

I wonder if something like this could be made as a 1.25 or 2 inch filter or if it needs to be at the eyeball end of the optical train??

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  • 2 weeks later...

Very interesting - thanks for posting this it is food for thought.

I thought I only needed my glasses for slight short sightedness and thought as long as I cold focus then viewing without glasses wasn't a problem. However, as I got more experience under my belt I realised I was seeing astigmatism. I spent some time trying to track down which bit of my scope was causing the problem and in the end realised it wasn't the scope it was me!

I really don't like using glasses when observing but I can tell that the older I get the more grumpy I will be about tolerating distortions. This may be the answer.


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  • 5 years later...

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