Thursday, January 27, 2005

The First Night with the Powermate

Review of the 5x Tele Vue Powermate

First and second nights of observations

I thought that it would be an exception today, since the sky was still sunny in the afternoon - I've received my new Tele Vue 5x Powermate. Cloud began to move in, after 18:00. I tested the Powermate anyway, but not on stars, just some lights and buildings.

My first comparison was 75x, offered by the 6.3mm Celestron Plossl and the Powermate plus 32mm Sirius Plossl. Before the test begins, the first winner would definitely be the Sirius Plossl for the eye-relief. Actually, what I was interested, was the light throughput, and the contrast. In the Powermate system, we have eight elements in four groups; and in the straight plossl, we have four elements in two groups. My target was a cable tower far away, there were no lights nearby. The images produced were nearly identical, the FoV produced were similar as well. I could make out the structure of the cable tower in both setup. Careful examinations reveal that the FoV in the Powermate system was better, and I conclude that it was not due to the slight magnification difference but it was a result of eye-relief. I don't know whether it's a pyschological effect or not, the straight plossl looked slightly brighter. I was not sure though, anyway, it's so similar.

Next I tried the Powermate with the 20mm Tele Vue Plossl. "It's wonderful!", I would say. After centering the view with the 20mm alone, inserting the Powermate immediately gave me a sharp view! Now, I see what's meant by parfocal! The view was bright and the image was so constrasty and nice! Next, I tried to test the 32mm Sirius Plossl with the Powermate and quite disappointed, I found that the Powermate is not parfocal with the 32mm Sirius Plossl; similar result were obtained with the 6.3mm Celestron Plossl, no luck. Tele Vue has successfully attracted me towards a 32mm Tele Vue Plossl as a future upgrade.

I have also tried to use the Powermate before the diagonal, again it couldn't be focused with any of my eyepieces. My last test were the 6.3mm Celestron Plossl with the Powermate, simple calculation told me that it yields 381x, which was too much for such a small scope. I had tried to push the C90 to 317x and the image was already broken. Surprisingly, the 381x image in the Ranger was not bad at all, except it was too dim to be useful, all the detail were still there and I would think this magnification would be useable with brighter objects like the moon, the Jupiter (tested later to be okay, but a bit too dim) or even the Saturn. Great little scope.

Finally, I found that my 6.3mm Celestron Plossl might have negative eye-relief, since I couldn't quite see its whole field even I had pressed my eye to the eye lens. Now, the Powermate with the Sirius Plossl gave me a nice alternative, without real noticeable difference with the straight plossl.

A star test would be performed once the sky is ready.


I was lucky that I've got a chance to test my Powermate again in the next day. The sky was not very clear, but quite a number of stars were visible. When the eyes were a little bit dark-adapted, it was possible to see the whole Orion.

My first target was the bright Jupiter. By using the 32mm with the Powermate, I got 75x which was so nice. The image formed was very nice in that kind of seeing condition. Four cloud belts were visible, though not very clear. You know, I was so happy that since it's so more comfortable than the 6.3mm. Next, I tried to use the 20mm with the Powermate, and it yields 120x. I would say it's the optimal (or something in between 120x and 150x) for the Ranger at high power. Even the power was not as high as the one produced by the 6.3mm in 2x, but the view was absolutely comparable since the image was brighter at 120x.

My next target was the Saturn, which was near the Zenith. Pointing to this kind of bright targets were very easy with the Star Pointer. The images produced by the Powermate with the 32mm and 20mm were 75x and 120x respectively. Being parfocal, the 20mm was one of the most wonderful experiences of using the Powermate in my present eyepiece collection. Cloud belts were suspected, since the view was limited by the poor seeing and transparancies.

I then proceed to get even higher power by stacking the Orion Shorty 2x to the Powermate, yielding 150x and 240x with the Ranger, by using the 32mm and 20mm respectively. The images produced remained so nice in both settings, but bad seeing limited everything. The Cassini division and the GRS (later confirmed that it was out of sight at the time of my observation) were not noted, probably because the environment was so badly light polluted and the seeing condition was just marginal.

I had also tried to use the Powermate with the 6.3mm at the Sirius to check the chromatic abberation of the Ranger (it's 381x), too bad. It was so colorful, but I don't need to get such high power with the Sirius anyway.

Finally, I would say, it was a wonderful experience. After this test, my desire of getting more eyepieces were diminished a lot, since I got a lot from the new Powermate, the existing 2x Barlows and the two eyepieces.

Lastly, I guess I must have tested that 381x on the Jupiter or the Saturn, but I hadn't. Another test should be conducted later when the sky is better.


* It undoubtly transforms my long focal length eyepieces, with their long eye-reliefs, into short focal length eyepieces
* It brings your small focal length scope into a much longer one, even with a 400mm scope, you got a new 2000mm scope with the setup time of several seconds
* It has got a real small aperture, and the light cone is narrow anyway
* I got no chance to compare with short focal length eyepiece, for the long focal length eyepiece and powermate combination, except the 6.3mm Celestron Plossl, which is supposed to be not very good anyway.
* The property of being parfocal is an excellent feature
* This kind of four elements optics should be more profitable than the Plossls, in Tele Vue's point of view
* Stacking barlow is no problem, at least for my eyes
* I guess it is useless for common SCT having more than 1500mm focal length already, but how about the 2.5x Powermate?
* BUT it is a must for short focal length refractors, particularly those from Tele Vue

21,22-Dec-98 Night

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