Yesterday evening I meet Robert. Robert wrote his own report of that evening.
We stood for a few hours at my terrace and compared his brand new ASCENT 102ED f/11 refractor with my 105 mm f/6.2 TMB Apo. My TMB sits in a diy tube. I bought it from the widow of my astronomical friend Ralf, which passed away much too early in 2014 – with only 54. Ralf has a very fine understanding of astronomy and optica, but never too much money. I was not surprised to detect that the TMB lens has a slight vice - a slight amount of spherical aberration, SA. I have a protocol to the instrument, which measured 90% Strehl. Nevertheless it is a real good scope.
SA acts not the same amount as measured. If you measure, you use the central focus. With SA you focus slightly to the "sharp" side - the on where you have a prominent sharp ring. This leads to around half that error in fact.
I was curious how both scopes compare. In short: Nearly identical.
We looked at some double stars, nothing else was in the sky suitable for instrument testing. We started with Castor. The optical quality in the scopes was nearly identical. However, the view seemed slightly different, more a different feeling than a real difference in resolution. The Starwave showed nearly no aberrations: A very slight amount of SA (less than my TMB) and a tiny amount of blue blue light around the Castor A - just detectable with concentrated viewing. Of course, we used magnifications which were nearly identical.
We switched to zeta Canci, a not so easy triple. The closest double we could detect (but not split) was STF 1426 in Leo. Again a triple: 8" and 0.9".
I have my instrument at a Berlebach report tripod and use a syktee mount. I extend the legs of the report only slightly, Robert uses a UNI and a medium heavy Giro type mount, extended fully. As you might guess, we love azimutal and manual driven mounts. Both instruments had the same amount of stability with this setup. A moderate kick against the focuser was dampened in around a second.
We tried what happens if we set the Ascent at my tripod and mount. We had to extend the Report to full degree. This combination can be used – in case of need. But the kick against the focuser lead to a large amplitude of swinging which needed 8 seconds to quieten. Nothing you want to use regularly.
I get very good images with a 5x Televue powermate barlow lens and orthoscopic eyepieces. Robert can use normal wide angle eyepieces, TeleVue DeLiteI think.In both combinations the stars were sharp from edge to edge. Real sharp, down to the shape of the Airy disc. The DeLite have a much wider FOV,of course.
The conclusion: You can change the huge amount of money you need for a real good but short Apo against a fraction of the money for a real good f/11 ED Apo (which works Apo like). You have to pay for it with a larger tripod and mount and a longer scope. You get payed back less problems with the eyepieces, but again pay with the largest FOV (4° with my Apo and slightly more than 2° with the Starwave).
The Starwave is a very good instrument for sun, moodn, planets and double stars. It resolves what the stability of air delivers in most nights. The image is very pleasing. Colors of the stars are distinct: Something you sacrifice if you have false color to an amount more than neglectable.
At our next telescope meeting end of the month we have the chance to compare 4 4 inch scopes. I hink somebody of us writes a few words here afterwards.
