Going H-alpha: Binoviewer [partial] success.

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Easter Monday: Sunny periods with large lumps of Cumulus cloud. Today I managed to get the binoviewers working in H-alpha using "straight through" viewing and a 40mm x 2" extension. The 1.6x T-S GPC was used but there was still no room for a diagonal in the light path. 

I tried pairs of 26, 20 and 10mm Meade Plossl eyepieces. Hard on the neck bending backwards to try and align my eyes on axis! Tilting the head relative to the binoviewer blacks out the images.

I then returned to a single eyepiece and took a few snaps with my Canon short zoom digital camera. It was simply held up to a 20mm Plossl eyepiece. The cropped image shows fairly even surface texture and a large prominence shaped like a dog or wolf. The prominence is visible but not very distinct, I'm afraid. Though I could blame today's softer seeing conditions, I am definitely making progress.

The sky became progressively more misty so I gave up on H-Alpha and tried some of my refractors for terrestrial use. Just to get a feel for their capabilities. The 90mm f/11 was quite happy at 40x & even at 50x. The 70mm f/10 was better below 40x. I even removed and gave the 70mm lens a clean with lens fluid and a microfiber cloth but it made no real difference to clarity.

I have just realised that I have no idea of the native magnification of my T-S binoviewer. It does seem to increase magnification even when used without the GPC. A quick bit of online research suggests the long glass path of the binoviewer prisms is the cause of the amplification. The mass of glass effectively increases the focal length of the primary objective. As does the PST etalon. It is also the cause of running out of enough light path for inserting [vital] diagonals without shortening the OTA's main tube. Glass path correction lenses can help with this but these introduce their own power. Even more so, when spaced further from the eyepiece.

Click on any image for an enlargement.

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