Some people experience astigmatism that comes in varying amounts and orientation. Eyeglasses correct astigmatism, but other factors can cause problems for star viewers:
- Eyeglass correction for near or far-sightedness is not necessary for telescopes.
- Multi-focal (progressive / bifocal / trifocal) eyeglasses cannot focus a wide field.
- Bi-focal or Tri-focal eyeglasses cannot show a wide vertical field in uniform focus
- Many eyeglasses have uncoated lenses, causing brightness and contrast loss
- Most eyeglasses are plastic for safety and are more easily scratched or scuffed
- Frame styles may limit fields and eye positions at the eyepiece
The visual experience in astronomy is maximized by stripping away limitations:
- The limitations of the observing location (dark skies and steady seeing)
- The limitations of the telescope (aperture, field, resolution and contrast)
- The limitations of the eyepiece (field, resolution and contrast)
- The limitations of our eyesight (e.g., astigmatism)
Tele Vue has historically been dedicated to overcoming the first three of these limitations:
- with wide angle, flat field telescopes easily portable for traveling to great observing locations
- matching ultra-wide angle eyepieces with full field image quality to generate a spacewalk type viewing
- a variety of long eye relief eyepieces to allow eyeglass wearers to enjoy the maximum visual experience
To overcome astigmatism, TeleVue has developed a corrector which fits directly onto the eyepiece. Just as Dobsonian owners could not fully appreciate the performance of Teleview eyepieces until installing the Paracorr to compensate for mirror coma, the majority of the population (which has some eyesight limitations due to astigmatism) had no way to correct for this except by wearing eyeglasses.
That is, until now.
Introducing Tele Vue DIOPTRX Astigmatism Correcting Lenses, which extracts the maximum visual performance from matching eyesight to eyepiece. Tele Vue DIOPTRX Lenses attach to the top of all long eye-relief Tele Vue eyepieces to compensate for eyesight astigmatism and are available in 1/4 diopter steps, from 1/4 diopter up to 2 1/2 diopters. Observers do not need eyeglasses to compensate for near or far-sightedness, since telescopes can focus out these limitations. Further, other eyeglass characteristics, such as bi-focal, tri-focal, or vari-focal (progressive) designs are severely detrimental when trying to view a large field at infinity. In the past, it was recommended to get a special pair of astronomy-only eyeglasses that only has your astigmatism correction and multi-coatings. However, frame styles may still limit field sizes, and be uncomfortable in certain telescope orientations. Note, however, that large exit pupils are typical for viewing with large aperture instruments, such as Dobsonians, and for wide angle viewing with small refractors.
Through experimentation, Televue has found that 2 diopters of eyesight astigmatism is detectable down to a 1mm exit pupil, and 1 diopter is detectable at a 2mm exit pupil. DIOPTRX lenses, therefore, obviate the need for a dedicated "astronomical
eyeglass", but are there any other benefits, aside from eliminating frame or comfort problems? The primary benefit is the potential of optimized correction in the amount and orientation of astigmatism for eyesight in astronomical viewing. The ability to compensate for both orientation and astigmatism, as our eyesight changes, is another advantage. With multi-coated high quality lenses accurately aligned to the eyepiece, the serious enthusiast now has another tool to maximize the potential in seeing the faintest stars over wide fields, subtlest small planetary details, and the satisfaction of knowing they have the very best visual experience possible with their prized telescope and eyepieces.
What is the procedure in choosing a Tele View DIOPTRX lens?
- First, look at your eye prescription for any astigmatism in your dominant eye (the one you primarily use for observing)
- Second, note the longer focal length Teleview eyepieces that apply and obtain a DIOPTRX lens for that value of astigmatism on the prescription.
HOW TO CHOOSE DIOPTRX MODELS
Your prescription may look like this, with different numbers:
Ignore spherical and axis values and ignore all ± signs. Simply choose DIOPTRX to match the cylinder (astigmatism) value of your preferred viewing eye. In the example above, you would choose 0.5 diopter model for your right eye and 1.5 diopter model for your left eye. DIOPTRX lenses will apply to all Tele Vue eyepieces recommended for digiscoping (because of their long eye relief):
- 31mm Nagler type 5
- 26mm Nagler type 5
- 41mm Panoptic
- 35mm Panoptic
- 27mm Panoptic
- 55mm Plossl
- 40mm Plossl
- 32mm Plossl
- All Radians (18mm, 14mm, 12mm, 10mm, 8mm, 6mm, 5mm, 4mm, 3mm)
- All Nagler type 4 (22mm, 17mm, 12mm)
How to install Dioptrx?
- Remove the rubber Eyeguard from the eyepiece
- Hold Dioptrx rubber Eyeguard with one hand and unscrew lower half of Dioptrx until the bottom opening is large enough to slip over the eyepiece top lid.
- Retighten Dioptrx until it firmly grips the eyepiece lip, but is still free to rotate.