Hi, I want to buy a 2 inch eyepiece for an Orion Xt10 Dob for Nebula and other dso's etc. What do you recommend is the best all around starter 2" eyepiece for the first upgrade?
best 2" eyepiece for DSO's
Started by flydudehsv, 10/02/2007 08:28AM
Posted 10/02/2007 08:28AM
Opening Post
Posted 10/02/2007 04:35PM
#1
I use Pentax XWs, XFs and XLs in my 12.5 Dob. In my experience they are a hair better than anything else I've tried for sharpness and light throughput.
I'm particularly fond of the XW 20, XL 14.5, although for less money the XF 12 is also very good for Galaxies. Excellent throughput for the price.
They are as good as orthos for sharpness and offer a much wider field of view, which is needed with an undriven Dob.
I also have a Nagler 22 which is an outstanding eyepiece with a large FOV, but for faint fuzzies I go to the Pentaxes.
I'm particularly fond of the XW 20, XL 14.5, although for less money the XF 12 is also very good for Galaxies. Excellent throughput for the price.
They are as good as orthos for sharpness and offer a much wider field of view, which is needed with an undriven Dob.
I also have a Nagler 22 which is an outstanding eyepiece with a large FOV, but for faint fuzzies I go to the Pentaxes.
Posted 10/02/2007 05:22PM
| Edited 10/03/2007 02:22PM
#2
Assuming XT10 has a focal length of 49.4 inch (1,255mm) (f/4.9) and assuming you want to use a 4mm exit pupil for nebula and using
exit pupil for telescope = focal length of eyepiece / focal ratio of telescope
Solve for Exit Pupil:
Exit Pupil= Ocular focal length / 4.9
So, for a desired 4mm exit pupil:
Ocular focal length =4mm*4.9 = 19.6mm
So, a 20mm eyepiece of some sort will work. If you have the money, a 20mm Nagler is as good as it gets (I've read the type 5 are better suited for f/5 and faster scopes than type 4 Naglers - the 22mm Nagler T4 is said to show a bit of coma in scopes as fast as yours, and it's much heavier than the 20mm T5). A 22mm Orion/Vixen LVW, 19mm or 22mm Panoptics may work too, or the Pentax 20mm XW.
Sometimes you may want to decrease the exit pupil to 2mm for deep sky objects. If so (for desired 2mm exit pupil);
Ocular focal length = 2mm*4.9 = 9.8mm.
So an eyepiece around 10mm is what you'd need. A 9 or 11 mm Nagler will work, or a 10mm Pentax XW or 9 or 13 Orion/Vixen LVW (I really like the 13mm LVW).
I don't know how well these eyepieces work for a f/4.9 scope, though. You may need a paracorr if you want pinpoint stars to the edge of your field of view. I do know that my f/5.4 11" newt works very well with all my Naglers (22 T4, 17 T4, 12 T4) and Panoptics. On my f/4.5 16" newt, I usually use a paracorr, though it's not really necessary - how much coma you want to put up with is a matter of taste.
Try before you buy, if you can. If not, used high end eyepieces on astromart can usually be resold for close to what you bought them for used if they are in good shape.
See
An Eyepiece Primer ‑ by Al Nagler
http://www.skyandtelescope.com/equipment/basics/3311076.html
Exit pupils Article at
http://www.astronomics.com/main/category.asp/catalog_name/Astronomics/category_name/J34KLLT872239NV4HBW7FSRMB1/Page/1
or http://tinyurl.com/yv6c96
exit pupil for telescope = focal length of eyepiece / focal ratio of telescope
Solve for Exit Pupil:
Exit Pupil= Ocular focal length / 4.9
So, for a desired 4mm exit pupil:
Ocular focal length =4mm*4.9 = 19.6mm
So, a 20mm eyepiece of some sort will work. If you have the money, a 20mm Nagler is as good as it gets (I've read the type 5 are better suited for f/5 and faster scopes than type 4 Naglers - the 22mm Nagler T4 is said to show a bit of coma in scopes as fast as yours, and it's much heavier than the 20mm T5). A 22mm Orion/Vixen LVW, 19mm or 22mm Panoptics may work too, or the Pentax 20mm XW.
Sometimes you may want to decrease the exit pupil to 2mm for deep sky objects. If so (for desired 2mm exit pupil);
Ocular focal length = 2mm*4.9 = 9.8mm.
So an eyepiece around 10mm is what you'd need. A 9 or 11 mm Nagler will work, or a 10mm Pentax XW or 9 or 13 Orion/Vixen LVW (I really like the 13mm LVW).
I don't know how well these eyepieces work for a f/4.9 scope, though. You may need a paracorr if you want pinpoint stars to the edge of your field of view. I do know that my f/5.4 11" newt works very well with all my Naglers (22 T4, 17 T4, 12 T4) and Panoptics. On my f/4.5 16" newt, I usually use a paracorr, though it's not really necessary - how much coma you want to put up with is a matter of taste.
Try before you buy, if you can. If not, used high end eyepieces on astromart can usually be resold for close to what you bought them for used if they are in good shape.
See
An Eyepiece Primer ‑ by Al Nagler
http://www.skyandtelescope.com/equipment/basics/3311076.html
Exit pupils Article at
http://www.astronomics.com/main/category.asp/catalog_name/Astronomics/category_name/J34KLLT872239NV4HBW7FSRMB1/Page/1
or http://tinyurl.com/yv6c96
Harry Vanderburg said:
Hi, I want to buy a 2 inch eyepiece for an Orion Xt10 Dob for Nebula and other dso's etc. What do you recommend is the best all around starter 2" eyepiece for the first upgrade?
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