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Howie Glatter TuBLUG-2" Newtonian Collimator
The TuBLUG (Tube + Barlow + Plug) is Howie Glatter's Barlowed laser collimation accessory for adjusting the primary mirror of a Newtonian, made by Starlight Instruments. This version is for 2" laser collimators. It is used with a regular laser collimator in single-beam mode on closed tube reflectors.
How Barlowed collimation works
The TuBLUG goes in the focuser and the laser collimator inserts into the other side of it. Its built-in anti-reflection coated Barlow lens, mounted in a central axial hole, diverges the beam, so the beam reaching the primary is large and defocused and easily covers the primary's center marker.
After reflection from the primary, the shadow of the center marker returns to the TuBLUG's white screen. You adjust the primary until the shadow is centered on the screen's central hole. If the center marker is of a certain size, a small red ring of light appears outside the central hole and inside the marker's shadow; making that ring even in thickness helps the adjustment.
The screen
The TuBLUG has a matte-white 45° face. It is easily visible from the primary adjustment position, and the TuBLUG can be turned 180° to face the front; it has a cut-out. The screen sits outside the focuser, so it can be seen when collimating the primary from below, and the shadow is more easily seen in twilight or darkness than on a sunny afternoon.
If you cannot see the screen from below the primary, use a simple 5-6x close-focusing monocular; on smaller scopes you can sit between the bottom of the scope and the focuser and lean one way to turn a knob and the other to see the screen.
Step by step
- Insert the TuBLUG in the focuser and tighten the focuser binder against it. Aim the window toward the primary mirror if you will watch the screen from below the primary.
- Remove the aperture stop from the laser if it has one (you want a large beam) and insert the laser fully into the TuBLUG; nylon screws hold it without marring.
- Adjust the primary until the shadow of the center marker is centered on the central hole.
TuBLUG-2" or TuBLUG-1.25"
Howie makes the TuBLUG for 1.25" and 2" lasers. Choose this 2" version for a 2" laser collimator.
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Why is Barlowed collimation with the TuBLUG-2" more accurate than a standard laser?
With the TuBLUG, the beam reaching the primary is large and defocused, and after reflection the shadow of the primary's center marker is returned to the white screen. You adjust the primary until that shadow is centered on the central hole, rather than judging a single return spot.
Can I use the Howie Glatter TuBLUG-2" with a 1.25" laser collimator?
No. Howie makes the TuBLUG in 1.25" and 2" versions for 1.25" and 2" lasers; use the TuBLUG-1.25" with a 1.25" laser.
What's the best way to see the TuBLUG-2" screen when adjusting the primary on my 12" f/5 Dobsonian?
If you cannot see the shadow on the screen from below the primary end, use a simple 5-6x close-focusing monocular from there.
I have a closed-tube 8" Newtonian. Is the TuBLUG-2" the right tool for primary alignment?
The TuBLUG is for Barlowed primary mirror alignment on closed tube reflectors. Check that your focuser takes it: the TuBLUG goes in the focuser and is held by the focuser binder.
Do I need to remove the aperture stop from my laser to use the TuBLUG-2"?
Yes. For the Barlowed method to work correctly, you need a large, defocused beam to illuminate the primary mirror's center mark. If your laser collimator has a removable single-hole aperture stop, you must take it off before inserting the laser into the TuBLUG-2".
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| Type |
Barlowed laser collimation accessory (Tube + Barlow + Plug) for Newtonians |
| For |
2" laser collimators |
| Fits |
Focuser drawtube (tightened by the focuser binder) |
| Screen |
Large white screen visible outside the focuser |
| Lens |
Built-in anti-reflection coated Barlow lens |
| Laser Retention |
Nylon screws (non-marring) |
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Howie Glatter Warranty
