Effects of Astigmatism
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Canopus Lim
- Posts: 1144
- Joined: Fri Jun 03, 2005 12:46 pm
- Location: Macpherson
There are solutions:
1. Use a long eye relief eyepiece (eye relief >=17). Actually the more eye relief is required for eyepieces that has huge apparent field of view like Naglers. For plossls, I think 16mm is probably enough.
For such:
a) Wear spectacles that is well corrected for astigmatism. Well corrected as in given FULL CORRECTION and not less as some opticians recommend because giving full correction may make the person feel giddy. If it causes a person to feel giddy, then this spectacles should be only used in astronomy.
Note that the spectacles have to be multicoated especially when every loss of light is big in astronomy. Imagine if you buy all the high quality optics but your own spectacles is not of that standard....
b) Buy eyepieces that can fit Dioptrix (for people who do not like to observe with spectacles). Eg. BO/TMB, TV eyepieces that are stated to allow Dioptrix, Hyperion (I think it can). Perhaps there are more eyepieces that allows it. However, you would need to have your eye check to know what Cylinder value your astigmatic eye (observing eye) is.
2. Wear toric contact lens. However, if I am not wrong, you can only choose either to have your astigmatism corrected OR your spherical (short sightedness or long sightedness) corrected for contact lens. Either one. So if you have short sightedness, you will have a problem looking at the stars when putting on the contact lens without spectacles. Unless somehow if you wear spectacles corrected for short sightedness but not corrected for astigmatism and put them together, it does have the advantage of looking at stars sharp with naked eye, and taking out the spectacles to observe through the eyepiece with the astigmatism corrected by the contact lens.
The big advantage with the toric contact lens is that even with short eye relief eyepieces like Plossls and orthos it can be used.
3. Alternatively, buy your eyepieces wisely. From the test procedures that I stated earlier, test your eyesight on your eyepieces and know which range you can observe stars without astigmatism seen. Some eyepieces especially for higher magnification, you can live without spectacles while lower magnification it becomes necessary. Hence those lower magnification eyepieces must have long eye relief.
1. Use a long eye relief eyepiece (eye relief >=17). Actually the more eye relief is required for eyepieces that has huge apparent field of view like Naglers. For plossls, I think 16mm is probably enough.
For such:
a) Wear spectacles that is well corrected for astigmatism. Well corrected as in given FULL CORRECTION and not less as some opticians recommend because giving full correction may make the person feel giddy. If it causes a person to feel giddy, then this spectacles should be only used in astronomy.
Note that the spectacles have to be multicoated especially when every loss of light is big in astronomy. Imagine if you buy all the high quality optics but your own spectacles is not of that standard....
b) Buy eyepieces that can fit Dioptrix (for people who do not like to observe with spectacles). Eg. BO/TMB, TV eyepieces that are stated to allow Dioptrix, Hyperion (I think it can). Perhaps there are more eyepieces that allows it. However, you would need to have your eye check to know what Cylinder value your astigmatic eye (observing eye) is.
2. Wear toric contact lens. However, if I am not wrong, you can only choose either to have your astigmatism corrected OR your spherical (short sightedness or long sightedness) corrected for contact lens. Either one. So if you have short sightedness, you will have a problem looking at the stars when putting on the contact lens without spectacles. Unless somehow if you wear spectacles corrected for short sightedness but not corrected for astigmatism and put them together, it does have the advantage of looking at stars sharp with naked eye, and taking out the spectacles to observe through the eyepiece with the astigmatism corrected by the contact lens.
The big advantage with the toric contact lens is that even with short eye relief eyepieces like Plossls and orthos it can be used.
3. Alternatively, buy your eyepieces wisely. From the test procedures that I stated earlier, test your eyesight on your eyepieces and know which range you can observe stars without astigmatism seen. Some eyepieces especially for higher magnification, you can live without spectacles while lower magnification it becomes necessary. Hence those lower magnification eyepieces must have long eye relief.
AstroDuck