Going H-alpha: T-S 2.6x GPC and low profile, helical focuser.

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Friday pm: The 2.6x T-S binoviewer GPC arrived in the post along with a compact T2-T2 helical focuser.  The new GPC is much shorter than the 1.6x and also the correct 31.8mm diameter. Not only does the binoviewer nose-piece go much deeper into any 1.25" fitting but it can be safely clamped. This was a major difficulty with the 1.6x GPC. Which was both very long and undersized at 31mm Ø. The 2.6x also has a much larger, clear aperture.

The helical focuser is smooth and consumes very little light path. Ideal for my  H-alpha converted 6" refractor. The focuser screws between the 2"-T2 adapter and the T2-1.25 15mm extender. It provides about 8mm of focusing range. No more than this should be necessary with parfocal eyepieces in the binoviewer.

The 2.6x GPC is supposed to neutralize the focus foreshortening effect of the binoviewer. Though at the expense of considerably increased magnification. The 2.6x increase is only nominal and will probably be amplified further by its distance from the binoviewer's eyepieces. The glass is almost flush with the end of its cell. So great care must be taken when fitting and handling the 2.6x GPC.

I shall report my results as soon as I have had a chance to try out the new combination on the Sun. The total weight and moment [leverage] of the complete H-alpha filtration and binoviewer set-up will test any focuser. It will be important to check the tightness of all screw fittings before use.

A sudden inversion will seriously unbalance the telescope with the potential for considerable damage. I can't even imagine having this lot hanging from a small telescope and mounting! Even without the two low powered eyepieces the entire assembly weighs 3lbs or 1.5kg!

Well, that was disappointing! The T-S 2.6x GPC does not fully compensate for the T-S binoviewer using Meade 4000s. With the single Cemax in the PST eyepiece holder I could use the helical focuser to good effect. It was nice being finally able to find the perfect focus with the 12mm Cemax. There were two active regions though neither qualified as a true "spot."

Changing to the binoviewer with the 2.6x GPC in the binoviewer nose-piece I could no longer reach focus. I had to remove the helical focuser and then had only about 3mm of the 2" visible barrel to spare after reaching focus. I moved my attention to the binoviewer's diopter focus rings for fine focusing. The surface texture then snapped into view and was far easier to study than with the single eye.

The Sun through the 26mm was easier to observe than with the 32mm Meade Plossls. I don't have a proper match in the 32mm due to different origins. One EP is physically longer than the other.

The magnification with both Meade EPs was ridiculous but revealed amazing detail at first. I kept swapping back and forth between the 32mm and 26mm until thin, high cloud stole my sharpness. The cloud increased until the sky was more thin, white cloud than blue sky with more to come. So I gave up and tidied everything away. The advantage of a fixed set-up, under the shelter of a dome, needs no better confirmation than this trial.

Carrying a large and heavy, flat tub full of drive electronics and telescope optics carefully down the steep stairs to the ground is difficult to say the least. Carrying the nose heavy, 6" f/8 refractor gets easier with practice. I have a solid D-shaped, drawer handle fixed near the objective end without which I would not risk the climb and descent. The 6" tube is simply too large to grip safely even with the clingiest, sponge rubber, industrial gloves. This, despite my size 12 hands. [XXXL!]

I hook the tailpiece of the OTA over the crook of the arm which is holding the handrail.  With the objective downwards for comfortable balance. The aluminium stores ladder has been an absolute godsend since its arrival. Had I used a normal ladder I doubt I'd have survived to tell the tale. Ladder rungs provide absolutely no feedback through the soles as do my wide stair treads. The tubular handrails are worth their weight in gold for repetitive climbs.

In summary: Compared to the single Cemax I have still lost about 25mm of focus using the 2.6x GPC with Meade LP Plossls in the T-S binoviewer.

The binoviewer takes some personal adaptation from scratch but is far more relaxing to use than  a single eyepiece on the Sun.

The PST etalon is now precisely placed at 200mm inside focus. Changing its position might just get me enough focus to use the helical focuser. Would it be worth the effort? Fortunately I was able to easily return to T2-T2 without the helical focuser in the optical chain.

The T-S helical focuser had cost me about €70 + P&P. So not the hundreds which some Borg helical focusers cost. The T-S GPCs both cost €39 each. The 1.6x GPC would need a non-standard shortening of the OTA and PST etalon position setting to reach focus. The 2.6x is better but pushes the magnification very high and still does NOT fully compensate for the binoviewer. It needs a clear sky to make the most of the Sun's incredible detail at such high powers.

Now I need to try the binoviewer in the 90mm f/11 Vixen to confirm the actual glass path compensation of the T-S  2.6x GPC in white light. 

Click on any image for an enlargement.

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