OTA Diameter

I was at the Orion website looking at the ED120 ota. The tube rings listed for this scope are 116mm ID. This is a 120mm scope shouldn't the ota be at least 120mm in diameter and ideally larger than the 120mm diameter of the objective.

Mark

Mark Nevitt said:
I was at the Orion website looking at the ED120 ota. The tube rings listed for this scope are 116mm ID. This is a 120mm scope shouldn't the ota be at least 120mm in diameter and ideally larger than the 120mm diameter of the objective.

Yes, but the tube rings don't hold the OTA right at the very end, and the OTA is narrower in the middle.

Mark,

I think all the Chinese produced 120mm scopes use a 4.5" tube. While this may not be ideal it is what has been done. I agree that the tube is a little small since there is no room for a baffle in the front section. However with the dew shield in place, there is little chance of glare from this point unless you have the moon in the edge of the field of view.

Orion used a 100mm tube for their 80mmED model and some folks have complained that it feels too big. Compact has become fashionable.

clear skies,
dan