December 12, 2014 – Upgrading the Mak, Part 3 – 8mm TeleVue Plossl, filter

Well after 9 days of clouds, I finally got to go out and use my brand new eyepiece, an 8mm TeleVue Plossl that I picked up for just 50 bucks on eBay – which is one helluva bargain, almost half-price.  The clouds didn’t start clearing until late in the night, so I wasn’t able to see anything from the roof until 11:30.  But the conditions were excellent.  Jupiter was fairly high in the sky by this time.  The clouds made the seeing very transparent.  It was very dark as well because by this time all the roof lights were turned off, not to mention that the lights from the building next to where I observe were also off because people had gone to sleep already.  Oh, don’t get me wrong, this is still Manhattan, and there’s still tons of light pollution around.  But at least my site was nice and damn dark for a welcome change.

TL; DR:  the TeleVue did not disappoint.  On the other hand, it did not impress, either.  Obviously, one brief half-hour observing session isn’t enough, but at this point I’d have to say that I didn’t see any further detail on Jupiter or the moon when comparing the TeleVue to my good old standard Meade Plossl.

Through both EPs I was able to see 4 bands on Jupiter:  the two main equatorial bands were clear, and I could see some detail in them.  I also saw a third band and fourth band to either side of the main pair, with the third being more apparent than the fourth.  It’s possible that I saw a little more detail in the equatorial bands with the TeleVue, but it is difficult to say.  The Great Red Spot wasn’t quite in position for viewing when I looked.

As for the waning gibbous 62% moon, both EPs showed nice detail along the terminator, but again, it was just another quick 10 minute peek, and not a full-blown observing session.  In that 10 minutes, I really couldn’t tell if there was any difference at all.  Maybe – just maybe – the views through the TeleVue were a little sharper.  But it could also be that they looked better simply because they were bigger in the 8mm at 193x than in the 9.7 at 159x.

Obviously, since it’s late, it was just a quick 10 minute peek, and that’s not enough to judge.  I need more time, to really sit and look comfortably at both objects to make a fair comparison.  However, I’m not going to get another chance to see the moon again for another 10 days because until then, it will be rising too late at night.  As for Jupiter, it is supposed to be clear again all night long on Sunday, so I will have another chance soon.

As with much in astronomy, the problem here – in determining which EP is better – might have absolutely nothing to do with the equipment at all.  The limiting factor might very well be the atmosphere.  Because it is constantly roiling, constantly rising, falling, moving sideways, carrying moisture around, it places an upper limit on what you’re able to observe.  This is called the “seeing”.  Usually, under fairly standard good conditions, getting to 200x is not a problem; meaning, that you can observe at this high of a power and expect there to be more detail shown than when observing, say, at 150x.  And usually, when it’s partially cloudy, like it was when I was observing, the clouds actually help, because they’ve grabbed the moisture and concentrated it into one spot, leaving the rest of the atmosphere drier than usual.  But the limit in the atmosphere could very well be 150x, so that no matter how much more magnification you use, you won’t see any more detail – the object will simply look larger.

But then again, it could just be that the TeleVue Plossl really isn’t that much better than the rest.  We’ll see.

So, for those of you not in the know, what is the big deal about TeleVue, and why was I expecting so much from this EP?  TeleVue is the leader in the wide-angle EP revolution.  Back in the day, meaning in the late seventies and early eighties when I was observing as a teenager, there weren’t that many types of mainstream EPs.  There were Kelners, which were 3-elements, with a relatively narrow 40-45-degree field of view.  A nice step up from Kelners were Orthoscopics, which had the same FOV, but were supposed to be much sharper.  In the eighties, we got our first Plossl, and it was a revelation.  I think it was a 20mm EP.  It was a wide-field EP to us at 50 degrees, and it was really sharp and clear.  Then there was the Erfle, which were super wide-field EPs, around 65 degrees, but only around in low-powered versions, around 25-30mm.  And that was it.  There just wasn’t much else in EPs that came up in our astronomizing back then, 30 years ago.

TeleVue came along around then, and changed all that.  Their main EP designer, Al Nagler, practically invented the wide-field revolution single-handedly.  And he did it by improving the performance of the EPs that his company was making over what was out there.  Wide-field Erfles suffer from a loss of focus as you get out to the edge of the FOV – the image just isn’t as sharp as it is in the center of the field.  Not TeleVues.  The rep on TV is that whatever the design of the EP, whether it’s a humble Plossl, like I now have, or a Panoptic, or a Nagler, or a Delos, or an Ethos, they are all sharp, sharp, sharp, right to the edge of the field.  And TeleVue EPs are available in 68 degrees, 82 degrees, even 100 degrees.  Other manufacturers copied the designs, with greater and lesser degrees of success, so that now there are many wide-field EPs available with all different fields of view at many price points from various vendors.

TeleVue is still the pinnacle of performance for an EP.  Beyond being the innovator, one other reason is because of the coatings on each of the individual lens elements in a TV EP.  Oh, sure, all EPs are “fully multi-coated”, but coated with what?  TV has mastered not only the manufacturing of the elements themselves to a level of perfection, but has somehow figured out what to coat them with so that they give maximum light transmission.

Of course, with this kind of performance, one TV wide-field EP costs almost as much as my entire scope.  Which is why the half-price TV Plossl I snagged was such a bargain.  So, further testing will ensue as the clouds permit. I need to sit there for a good hour, switching back and forth between the EPs, really observe for a while.  Which I’m more than happy to do, because Jupiter is my favorite.

Meanwhile, there is one other upgrade I’m interested in:  a blue #80A filter for Jupiter, but which is supposed to work well for all the planets.  Colored filters, such as blue, red, and yellow, are supposed to increase the contrast on planets so that you can see more detail.  They screw directly onto the bottom of the EP, or on the telescope side of the diagnonal.  Seeing detail is all about contrast – if everything is the same brightness, you can’t see much of any difference.  One way they increase contrast is to decrease the amount of light, and therefore glare, you see from the planets.  Since planets are pretty bright anyway, losing some light isn’t much of a problem, if it’s any problem at all.  The blue filter, the 80A, has been deemed to work best on Jupiter, the red one best on Mars, the yellow one best on Saturn.  But the blue one is more of the jack-of-all-trades and is supposed to work on Mars and Saturn as well as on Jupiter.

On the other hand, some people say that they don’t really get much of a benefit at all from these filters, so that buying them should not be a priority, and those that do buy them end up seeing them put way in the back of the EP case.  These filters cost about $10-12 each, which is very reasonable in the world of astronomy.  I just want to try the blue one first, see if that makes any difference.

Next time, a full report on the TeleVue Plossl!


2 thoughts on “December 12, 2014 – Upgrading the Mak, Part 3 – 8mm TeleVue Plossl, filter

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