Televue Nagler 31 vs 17. Focus points

[Kunama]

Could anyone with both the Nagler 31 and Nagler 17 please check if they are parfocal.

If they are not parfocal, could you indicate how much the difference is and which requires the focuser to be racked in further.

At the moment it looks like the N31 will just come to focus at infinity but if the N17 needs to come in further then I will have to cut the poles on the Blunderbuss!


Muchos Gracias,

Matt

[Kunama]

Thanks Glenn and Phil,
Answer found.

When Nagler 31 T5 is set to X, Nagler 17 T4 requires 8.9mm outward movement according to the TV chart.

[tempestwizz]

Does this offset remain the same if using either of the two paracors?

[Kunama]

Can't help you with that one Brian, I don't use Paracorrs, my scope is F5.6 so I can cope without it.

[ausastronomer]

Hi Matt,

Even at F5.6 the 17mm Nagler is improved significantly with the use of a paracorr.

Not only does it tighten up the stars and improve the view off axis, it allows you to see dimmer targets and features off axis.

Cheers,
John B

[Kunama]

Thanks John, I may try to test it out first (before letting the moths out of the wallet). I may have to shorten the poles 10mm to comply with the Naglers' in-focus requirements as I don't want the draw tube intruding into the UTA.

[Don Pensack]

With the Paracorr, set the tunable top for the 31mm Nagler (All the way in, I believe), then remove the 31mm and insert the 17. Refocus using the tunbale top, not the focus knobs.
Look at the setting of the Paracorr. That is the correct setting for the 17mm.
Write it down--you can pre-dial that setting before you insert the 17mm the next time you use it.
Using that technique, you can quickly find the setting for your entire collection of eyepieces of any brand.
And yes, the implication that all your eyepieces will essentially become parfocal as far as the focuser is concerned is correct. Your entire collection of eyepieces will focus within 1mm, maybe 2mm of focuser travel with the Paracorr in place.

[Kunama]

Hello Don,
Thanks very much, I am actually now thinking of getting the SIPS from Wayne at Starlight as it will fit readily with the FTF 2015BCR-LW focuser on my scope.

[Don Pensack]

Just remember that, with the SIPS, your eyepieces will not be parfocal, so the focuser will likely need at least 1.5" or more of travel.

[Kunama]

Thanks Don, looks like the Nagler 31 requires the most inward travel of any eyepiece I am likely to use so I will set the pole lengths based on that eyepiece, then I will have the full 1.5" available to accommodate my other eyepieces. :thumbsup: