$400/$500 eyepiece challenge for 12" DobPosted By Mike Ratcliff |
Hi Dan, congratulations on the new scope. I can give you some suggestions, but I am more used to the Tele Vue line of eyepieces that would exceed your budget if bought new. There are several other lines that are similar to Televues at lower costs. If you talk to a dealer and ask what eyepieces they have that are similar to a certain Tele Vue eyepiece, they will be able to immediately give you an answer. Or you may be able to find a Tele Vue eyepiece in the used market here.
You would most benefit from a wider apparent field of view compared to the plossls that came with your scope. The plossl have about a 50 degree field of view. Going to a 68 degree or an 80 degree field would give you a wider view for the same magnification. This adds to the wow factor and also makes finding objects easier. I used a 26 mm plossl for several years with my first scope, and going to a 19mm Televue Panoptic with a 68 degree field was amazing.
For a low magnification eyepiece that shows a lot of sky (true field of view), I would recommend one of several Tele Vues:
35mm or 27mm Panoptic (68 degree)
31mm or 26mm Nagler (82 degree)
The clone versions of these could cost $200+.
I usually jump down by a factor of 2 in focal length to get a medium magnification, since you are going for 2 or 3 eyepieces + barlow. This would be
14 mm or 12mm Delos (70 degree) or 12mm Nagler (82 degree)
A final eyepiece would be roughly 1.5x smaller than medium
8mm Delos or 7mm Nagler (about 200x magnification)
With a barlow that gives you 400x that can be used on the great nights.
Some rules of thumb, you can calculate the "exit pupil" of the eyepiece by dividing the eyepiece size by the telescope focal ratio (4.9 for your scope). The exit pupils to use would be no larger than 7 and no smaller than 0.5. For example a 35mm Panoptic would be about 7 (35mm divided by 4.9).
You can calculate magnification by dividing the focal length (1500mm) by the eyepiece size. So the 35mm Panoptic would be roughly 43x.
You can then calculate the true field of view approximately by dividing the apparent field of view by the magnification, for example 68 degrees for the 35mm Panoptic divided by 43x = 1.6 degrees.
You can set of a spreadsheet for all of your possible choices, but it might drive you crazy too!
You would most benefit from a wider apparent field of view compared to the plossls that came with your scope. The plossl have about a 50 degree field of view. Going to a 68 degree or an 80 degree field would give you a wider view for the same magnification. This adds to the wow factor and also makes finding objects easier. I used a 26 mm plossl for several years with my first scope, and going to a 19mm Televue Panoptic with a 68 degree field was amazing.
For a low magnification eyepiece that shows a lot of sky (true field of view), I would recommend one of several Tele Vues:
35mm or 27mm Panoptic (68 degree)
31mm or 26mm Nagler (82 degree)
The clone versions of these could cost $200+.
I usually jump down by a factor of 2 in focal length to get a medium magnification, since you are going for 2 or 3 eyepieces + barlow. This would be
14 mm or 12mm Delos (70 degree) or 12mm Nagler (82 degree)
A final eyepiece would be roughly 1.5x smaller than medium
8mm Delos or 7mm Nagler (about 200x magnification)
With a barlow that gives you 400x that can be used on the great nights.
Some rules of thumb, you can calculate the "exit pupil" of the eyepiece by dividing the eyepiece size by the telescope focal ratio (4.9 for your scope). The exit pupils to use would be no larger than 7 and no smaller than 0.5. For example a 35mm Panoptic would be about 7 (35mm divided by 4.9).
You can calculate magnification by dividing the focal length (1500mm) by the eyepiece size. So the 35mm Panoptic would be roughly 43x.
You can then calculate the true field of view approximately by dividing the apparent field of view by the magnification, for example 68 degrees for the 35mm Panoptic divided by 43x = 1.6 degrees.
You can set of a spreadsheet for all of your possible choices, but it might drive you crazy too!
