28 replies to this topic

[akdwivedi]

a C5/C6 sct is currently my best. I do have a skywatcher 120ed doublte that I use with a 1.8x gpc, and I agree with the refractor team. I am seriously tempted by the askars 120/140 APOs both of which are bino friendly without a gpc.. but I must hold the temptation.

[GGK]

How about correcting for the aberrations introduced by the BV? I read that GPCs are mainly for correcting those, and that the magnification and lengthening of focus are side-effects only. Do you really need a GPC or are the aberrations introduced in a refractor by a BV not that much anyway?

The Glasspath corrector moves the focus point outward, enabling focus with the longer light path binoviewer.  It also minimizes the color aberrations caused by the binoviewer prisms at fast focal ratios (which are refractors). I use either a Prism or BBHS mirror Baader T2 diagonal with a heavy duty Quick Changer between the diagonal and binoviewer.  The GPC is convenient because it fits within that assembly and requires zero extra physical length.

 

I use my binoviewer with my SCT mainly for higher powers using a 2.6X Baader GPC to reposition the primary mirror back close to the optimum position for best image contrast.

 

I also us the binoviewer in three of my refractors -- TV-85 and AT60ED with a 1.25X GPC, which is needed to reach focus, and the A-P Traveler which reaches focus with no GPC.  The Traveler has an f/5.8 focal ratio and I see slight color fringing from the binoviewer when observing the moon, so will usually use the GPC that best works with the desired magnification and eyepiece.

 

Since my binoviewer eyepiece clamps are 1-1/4 inch, true field size is limited compared to 2" eyepieces.  Field size also shrinks when a GPC is required to reach focus.

 

Gary

[faackanders2]

The one you have

[Victor Martinez]

Do you need the GPC with a refractor though?

The TS 125 has a built-in extension with M95x1 connection thread and 60 mm length. If it is removed, the working distance increases from 150 mm to 210 mm, for example for binoviewers or reducers