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Archive for November, 2011

 

OK – I’ve decided this before, but I have to learn a lesson at least three times before it takes hold: Binoviewing is not for me. Oh – and the Denkmeir “Big Easy” is big, but it’s not easy.

Alright, in fairness to Denk, when they said “Big Easy” I think what they meant is that we’ll sell a beginner package that will come to focus in all the major types of scopes – no need to break out the hack saw and shorten the tube 0f that 100mm APO.  And they did – and it does. But it’s not easy.  As you use this package and attempt to change powers using the various attachments you may find, as I did, that fumbling with these various screw-in thingees in the dark and the cold isn’t that much fun. What’s more, achieving focus isn’t all that straight forward and may call for really major adjustments.

For example, in switching to high power mode in a refractor – 2.5X normal power –  I had to back the focus way out and when I did that – given the weight of the binoviewer – the scope went out of balance so I had to change its position in the clamshell. So changing power in this case meant:

  • removing two eyepieces and replacing them with two others
  • removing the binoviewer from the diagonal and replacing the “nosepiece” with a different, screw-in “nosepiece”
  • loosening the clamshell, sliding the scope forward, tightening the clamshell (repeat until it balances)

Right – and in mono mode you would simply swap one eyepiece for another.

Just call me Cyclopian!

That’s a big price in what Pooh would call “bother” to pay for being able to use two eyes instead of one.  Makes me feel a lot more comfortable with the habitual, one-eye approach.

But what if I limit the use? What if I say I’ll just use this one with the TV85 at  relatively low power and treat the combination like a super sharp binocular? In this mode I simply go with the low power view using the 25mm Plossls.

Well, the field’s pretty small for a binocular, but I can live with that and if I really like this idea, I could put a couple 24mm Pans in there for another $200 or so. That would give me a wider field – but . . .

What about the old business reported by many that the binoviewer cuts the light in half? You know what? It does!  OK – I know this is controversial, so breathe through your nose all you binoviewer fans. I can’t speak for anyone else, but I spent a whole lot of time this evening with the Pleiades – particularly a little segment between Alcyone and the center of the cluster – well – that little arrow asterism near the center.  Right here:

Click image for larger version - prepare from SkySafari screen grab.

There’s a triangle of  twelth magnitude stars near there and guess what – I could see them while in binoviewer mode with the TV85.  (M45 was near the meridian and transparency was average – maybe a bit better.) That’s good – except, I could see them just as easily with the 60mm Unitron set up next to it!  (I could not see the 13.57 star noted in either scope.) Bottom line – as near as I could tell there wasn’t any difference in the light reach of the 60mm  Unitron and the 85mm Televue.

This, by the way, is exactly what the math shows. Figure the area of the 85mm lens. (Just square the radius – you don’t need to throw pi in there.)  Now divide by two and take the square root of your answer. That give you the radius of an objective that would produce half the light gathering area of the 85. Or in math-speak: 42.5 squared is 1,806 – divided by two is 903 and the square root of that is 30.05 – times two and you have a 60mm objective. Don’t you love it when the geeky math actually shows you the same thing as your eyes and common sense!

Downsizing the TV 85

So by putting binoviewers on my TV85 I was turning it into a TV60 – as far as light grasp goes. I should hasten to add – and this was obvious on Jupiter – that the added resolution of the 85mm is still there despite the binoviewer, so Jupiter certainly looks better in binoviewer mode in the TV85 than it does in the Unitron at a similar power. Which is why the common wisdom is that binoviewers are really great on the Moon and planets, giving you a sense of 3D even though at astronomical distances that really isn’t the case.

So – why not just limit binoviewing to the Moon and bright planets – and bright doubles?

Maybe. It’s tempting. The binoviewers do a good job on bright objects – but I did run into some unexpected CA problems which I can only attribute to the binoviewer – or maybe my difficulty in reaching precise focus with them. I must admit, at high power I actually had to ease the binoviewer out of the  diagonal a bit, then clamp it tight, in order to reach focus  in the TV85. Different eyepieces might have solved this problem. But that’s really no way to hold the system together and I had no remaining outfocus, so let’s ignore that CA business.  It wasn’t there, for example, with the 25mm Plossls – just with the 17mm Plossls.  But whatever the cause it was irritating.  And by that time my patience was wearing thin. See, when it’s clear I like to observe – not screw with equipment.

And really – I am neither a planetary or lunar observer. I look from time to time and enjoy both activities, but I don’t think that is reason enough to have $400-plus  invested in binoviewer and eyepieces.

Oh – a few other notes from this observing session – which was really three sessions starting at  about 9 and ending after 2 am with significant breaks between as clouds came through.

  • I could not split  Polaris with the 60mm Unitron or the TV85 in high-powered binoviewer mode. I could split it with the TV85 in cyclops mode.
  • I could not split Mintaka – frustrating – with the 10X30IS Canons, or the 15X70 Celestrons handheld. (The mount for the Celestrons was in a shed 100 feet away and I was too tired at that point to go get it.)
  • I could split Mintaka with a 50mm F4 and a 50mm F12 on a double mount – but what I was really trying to do was to get a handle on the linear size of the star image   – something that the optical experts says is controlled strictly by the focal ratio of the telescope.  But I had a brain freeze about this time – it really w as time to go to bed – and I just couldn’t make good sense of what I was seeing or even remember what I thought I saw when I went to making notes.
  • Still, the last thing I did was a quick tour of familiar sights with the 10X30IS binos – I do like them – and I meandered long enough to get some idea of their lingering magnitude -in the neighborhood of 9. I was checking what I think of as the “house” in the Hyades – what Daphene calls the “bell.”  Here are the test stars.

Screenshot from SkySafari on my Ipad showing the 8th and 9th magnitude stars I was able to note with the 10X30IS binoculars. Less tired and more patient I'm sure I could go deeper with these. Click image for larger view.

Actually the number I’m getting are pretty fantastic – enought o make me wonder about whether SkySfari is giving me the right magnitudes. Of course,t here are various opeinions on limiting magnitudes for different size instruments. Here’s what respected observer Clay serrod has to say about it on his web site:

 

There are formulae available in all the books that I will not bore you with; from that formulae, I have prepared a MEAN value, an average of sorts, of all of them and offer the list below. My 32 years in astronomy has shown me that this list is, indeed, VERY close to actual performance.

Under the darkest conditions (see below)

            HUMAN EYE             - 6.5            5.0"         - 12.8
            2.5"                 - 10.5            6.0"         - 13.2          
            3.5"                 - 11.4            7.0"         - 13.6
            4.0"                 - 11.7            8.0"         - 13.9

Hmmm . . . 30mm is about 1.2 inches and if 10.5 is the limiting magnitude for 2.5-inches  I have to think 8.7 is a respectable figure for 1.2 inch binoculars. Of course there are two of them, so let’s multiply 30mm by 1.3 – that gives me 39mm – more like 1.5 inches. well, 8.7 is good there too.  (That 1.3 multiplier is another compromise – binoculars increase the light grasp over a single scope by a factor of 1.2-1.4 accoridng to conventional wisdom.)

What I’m more surprised at is my 60mm (and the 85 inmbinoviewer mode) delivering a magnitude 12 star when Dr. Sherrod’s compromise chart above would set the limit at more like 10.5 – that’s a huge difference.  And Starry Nights Pro has the same, or slightly lower magnitudes for those three stars.

So what’s going on? i think there’s just too many variables and so this limiting magnitude business is all over the charts. For example, according to another web site with a very sophisticated looking formula I should see significantly deeper – and yet another one has me seeing deeper than I  should.  None of which matters for what I was trying to learn with the binoviewers. The simple truth is they made the 85 perform like a 60 – no matter what the absolute values involved, this was a side-by-side test.

 

 

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, , , for example, I dressed as if it was going to be below freezing – way below freezing – and I stuck a pair of chemical handwarmers into an extra pair of gloves on my pockets – and the temperature went from 36 at  3:30 am to 39 at 5:45 am when I came in, which is just the opposite of what I expected. Good!

But my enthusiasm for binoviewers on the LT-8 in the observatory dininished, not because of the light loss – I had anticipated that and really, it just doesn’t seem that bad – but because of several things I didn’t anticipate, such as:

To change powers you screw in different nose pieces which is:

  • more time-consuming than changing eyepieces
  • more difficult to do with gloved hands than, say, changing eyepieces

In fact, removing, then placing back in the whole binoviewer is the equivalent of changing eyepieces, so the fooling with threaded nosepieces is all extra work. (This, I should add, is why Denkmeir sells a sliding switch that does the same thing in a no hassle way – but at a significant cost, of course.)

And perhaps as important, in the crowded, six-foot diameter space of the observatory, having 4-5 inches of binoviewer projecting from the diagonal really does cramp your style and just sits there as something begging to be bumped into with an elbow or shoulder.

Plus that added length in the diagonal does change the height of the eyepieces significantly. For exmaple, my first target was the Orion Nebula and it was just above my house at about 30-degrees altitude and that put the eyepieces  so high that I had to put a thick boat cushion on top of my pneumatic draftsman stool which was already raised to its highest level. Yet on a high altitude object – I went to M67 next – the stool was too high at its lowest setting and so I had to shove it aside – and there is not much “aside” room in this little space – and use the lower setting on a normal office chair.

This problem of space has haunted me since I built the observatory  twenty years ago. (Well, had it built – I designed it, though, so the space issue is on my shoulders.) It works OK with  an 8-inch SCT in alt-az mode. But that’s it. Nothing larger. I once had an 11-inch SCT in there – no way.  And I’ve tried all sorts of other scopes on all sorts of mounts and they just are too cumbersome with the exception of small refractors on the UA T-Mount – that tends to work.

Hmmm . . .  maybe I need to try the UA T-Mount with TV85 in binoviewer mode?

Oh – that reminds me  – I did try the TV85 straight through in binoviewer mode. Interesting, but not really successful.  Maybe I need to give it another chance. It just seemed unusually awkward.  I was using the T-Mount on the pier in the Observering Shellter. This was something suggested by the previous owner. You discard the diagonal and put the binoviewer in the scope with nothing but the hollow nosepiece on it – same as you do for medium power in the SCT. It couldn’t quite come to focus when I first tried it, so I switched to  a very low profile 1.25-inch adapter  and it worked fine.  But the views didn’t knock my socks off – probably because there was a lot of high clouds and nothing resenbling either average seeing or transparency – in fact both sucked to the point that when I started about the only thing visible to the naked eye was Jupiter with a haze halo around it.

Which reminds me – this experiment was done on Thanksgiving  night around 8:20-9 pm – six hours before the experiments in the Observatory with the LT-8. And before those I had been at Sarah’s house in Rochester and invited my granddaughter, Amanda, out to take a look at Jupiter through the 10X30 IS Canons. Great!  We both could easily see three of the Gallilean Moons using those little binoculars. Now I have seen them with binoculars of similar size, but none as small as 30mm and with the image stabilazation I saw them more clear than with any handheld binocular – and so did Amanda.  So that was an unmitigated success and once again speaks well for the little binos as a keeper.

But this straight through business with the TV85 needs a better trial, I think.  What I like is it gives me a nice step up in power, at least, from the 15X70 binos.  If you do the math the light grasp of the two instruments should come out very similar. That is, being a binocular the 15X70s should act like something closer to an 80mm scope. And given the light loss in the binoviewer the 85mm probably acts like something closer to a 75mm scope. But in term of power, when used straight through witht he 25mm Plossls the 85 is probably delivering about 25X – and doing so through a superb 85mm  lens, so it really should give me the best, high-power binocular view available.

Sidenote: Actually, if you do the math according to the way some figure, the 85 in binoviewer mode is equivalent to a 60mm scope. See, the binoviewer splits the light from 80mm lens in half. So if you take the area of the 80mm lens, divide it by two, then take the square root of that and multiply by two you come up with a 60mm objective.  Now I’m going to have to try it side by side with a 60mm to see if this is true.  It sure doesn’t seem like the light has been cut that much.  But. . . there’s another line of thought that says you are getting two eyes worth of light and your brain recombines this.  I like that idea – except – and this is a big except –  I’ve done some very casual testing where I close one eye and look through just one side of the binoviewer and the image doesn’t seem to dim.  So this really does need exploring.

Bottom line – I’ll experiment some more with it on that mount in daylight and see if I can get around the apprent awkwardness I found last night  – afterall I was tired, rushed, and conditions were terrible.

That said, this morning I was neither tired , nor rushed, and conditions were not so terrible – though transparency was poor and I couldn’t believe how dew attacked all glass surfaces the second they were exposed – even though they had been sitting in the cold of the observatory all night! Remove the lens caps and instant dew problems. That was unexpected and so my first problem was to remove the dew. And it kept coming back. For example, when I looked at Castor I was puzzled by the fact that I could barely see the third star in this easy triple. I took that as evidence that the binoviewer was eating up more light than I thought. Looked like a 60mm cyclops view, really. So I switched to cyclops mode using the same 25mm eyepiece. Oops – no third star this way – or a very faint one. Time to clean the dew off the objective again! Yep – there’s the third star – easily seen whether in cyclops or binoviewer mode.

Bottom line. I’ll give this some time. I’ll try it with different instruments. But last night and this morning things did not go as expected in binoviewer town, so stay tuned. And yes, I am not using them yet in the one area where I am sure they will shine – the Moon and bright planets.

Addendum: I fooled around in daylight this morning and after trying different mounts and chairs I came up with a configuration that works. Having done that, however, I’m now really thinking “so what?”  Why am I so bent on using this thing straight through when it is so much more comfortable to use in a diagonal?

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Also, a new observing routine: I have decided to halt my public programs and focus on my own observing projects – something i haven’t done for five years or more. As part of that change, I’ll try to keep a record here since I think it’s always good to reflect on what you’ve done.

True to the CSC, it cleared early this morning, though  just along the coast, and so I got out in freexing temps with terrible seeing at about 4 am.  I had two basic goals.

  1. Assess the performance of the new (used, of course) Canon 10X30IS binoculars.
  2. Make a preliminary estimate of the light loss caused by the new (used, of course) Denk Big Easy  binoviewers when using them on the Televue 85.

I met both goals in about 90 minutes and ended up with very cold hands despite several trips from the deck to a warm, red-lit library.

First, the 10X30.  I had just tried a pair of 10X42IS Canon’s and was unimpressed – that is, unimpressed in terms of their perforamnce relative to their price, so I owned them for less than a week.  The 10X30s are quite different, first in cost – used $245 vs. $770.  Second, in light grasp  42 vs 30 is 1,384 vs 706 square millimeters of light gathering lens – or put another way, using my 5mm dark-adapted pupil as a measure (19.6 sq. mm), that’s 71 eyes vs 36 eyes.  Of course I didn’t do a side-by-side test, but the bottom line is this – I didn’t miss the extra eyes, I didn’t miss the extra quality, and the dollar savings gave me enough to buy the Denks and a couple Plossls!

Truth is, Sky and Telescope binocular guru Gary Seronik says of the 10X30 IS : “I own a pair of these and find I use them more often than any other binocular in my collection. ”

Yep – I can understand why. First, the ergonomics are simply better – they feel right in your hand. Second, they don’t weigh nearly as much: 1.4 pouunds – nearly a pound less than the 10X42s.  Third, you need to hold the IS button continuously – a supposed disadvantage – but I found the placement of the button on the larger binoculars – it’s to one side – awkward and on the 10X30s (just in front of the center focus) intuitive.  With the bigger ones I did a lot of searching when wearing gloves for that button and then wasn’t sure I had hit it, so I would take the binoculars down from my eyes and look to see if the green light was on.  With the smaller ones it just worked naturally and I guess it’s a little noisier or more obvious when it kicks in because I always knew when it was on.

Of course, the big question I think most amateur astronomers have on their mind is can you see anything with the 10X30s? I mean, that’s barely more than an inch of objective – well , a bit more because it’s a binocular, but still darned little. And the answer is yes. Seronik describes it this way in his online review: ” the 10× magnification, image stabilization, and superb optics more than make up for the smaller aperture.”

To confirm this I did a very quick survey of some obvious binocular targets – the Pleiades (30 stars without any effort to see the faint stuff) ; Hyades – really beautiful and easily picking up stars of magnitude 9 and on the bright side of magnitude 10; the “enagement ring” around Polaris; Orion Nebula – really impressive; the three gorgeous clusters in  Auriga – M37, M36, and M38 with no sweat at all; M81 and M82 with no sweat; M51 (Whirpool Galazy) with a little sweat; M65 and M66 with a serious effort. (The cold was already getting to me, so no sweat there, but they weren’t easy 😉

What that means is I can easily use these to aid in star hppping and enjoy quick views and that’s all I expect of them – though I intend to also use them in a binocular double star program.

OK – what about my TV85 as a binocular?  This is interesting. Binoviewers cut the light in half, sending half to each eye. The brain does some recombining. And as near as I can tell no one knows quite what to make of this, nor is there agreement on anything except that there is some light loss – not sure how much.

Well, I really like the idea of observing with two eyes – it feels right and it makes sense. I did it before, but cut it out when I switched into public mode – some people have toruble getting the images together in abinoviewer and everyone  needs to adjust them for interpupilary distance and maybe make a diopeter adjustment as well, so they are too much of a hassle for public sessions. Private viewing is naother thing. the jury is still out, but I want to give them a serious try this time around. Afterall, we were born with two eyes and most of us are fortunate enough to be able to use both all the time. So why not use two eyes while observing? The answer is it’s either prohibitively expensive – though there are such things as binocular telescopes – or there are a host of quality-cutting compromises.

With typical binoculars the compromise comes in making two telescopes work together as one – to do that you need to make the two telescopes “fast” – that is with focal ratios in the neighborhood of F4 – and to sell them you need to make them cheap.  Fast and cheap just don’t go together, so binoculars invariably sacrific quality and can be used only at relatively low powers.  I have a devil of a time getting even moderately bright stars to be pinpoints with even the best binoculars I’ve used.  Use an inexpensive, achromatic, long focus telescope and it’s a piece of cake to get nice, sharp stars.  Use an inexpensive, short focal length binocular and you just can’t seem to get there from here – or I can’t.

Enter the binoviewer. You can use it on any telescope, but there are two big quibbles:

1. You introduce a lot of extra glass into the light path and that creates potential issues with reflections, collimation, and light loss.

2.  You are splitting the light beam in half sending 50 percent to each eye – so some feel you’re cutting the light grasp in half.

I can’t do anything about point one except to use quality binoviewers which the Denks are.  (They make a higher quality one than these which I haven’t yet felt compelled to get.)

I just don’t know what to make of the second point and in the final analysis I guess it comes down to the fact that there will be some light loss and you have to decide if that is important to your observing experience. There’s a trade off here – some light loss for the privledge of using two eyes. So my question is, how much light loss?

There’s actually a third problem I’ll deal with it after the light loss question.

To determine light loss I simply honed in on the Pleiades – they were just above my tree line in the west – and particularly on the stars around Alcyone. I didn’t care about actual magnitudes. All I wanted to do was to find some faint stars with the binoviewers, then examine them in cyclops mode at a similar power and with a similar quality eyepiece.  I was using 25mm plossls in the binoviewers, so my comparison eyepiece was a 17mm Plossl in cyclops mode. (That gave me 33X in the binoviewer and 35X in cyclops mode.)

I located a triangle of roughly 11th magnitude stars and my assessment was simple. I could see them in the binoviewer – though the faintest needed a little averted vision. I could see them more easily in cyclops mode. How much easier? I don’t have a clue. My rough guess is we’re dealing with no more than half a magnitude light loss and probably about half that – but that’s just guessing. Whatever the numbers, it wasn’t enough to disturb me. The view was still wonderful and using two eyes was relaxing.

Thatw as the only real test I did. I did look at M51 and enjoyed the view – but I did not do a comparison. Why? well, that’s the third issue. See  to get the binoviewer to come to focus in the TV85 you have to put another piece of glass in front of the diagonal. That means to go to cyclops mode you have to remove the binoviewers, remove the diagonal, take this piece out of the diagonal, return the diagonal, put in a single eyepiece, AND rebalance the scope – in this case slide it a bit forward on the mount.  Not a real big hassle but on a cold morning I wasn’t enthusiastic about doing that repeatedly.

But that leads to point three – in the TV 85 the binoviewer  delivers either 1.4X or 2.5X the normal magnification.  So a 25mm Plossl in cyclops mode will normally deliver  24X and thus a nearly two degree fov – very nice for the Pleiades, for example. In binoviewer mode that same eyepiece is delivering 33X and something closer to a 1.5-degree fov which really crowds the Pleiades. The guy who sold me this said I can use a 32mm or even 40mm Plossl with it and urged me to do so. I did try the single 32mm Plossl i have and it did give me a wider field. But there’s something bugging me where I thought the size of the prism in the binoviewer limited the low end of eyepieces – but it may not. I need to explore that.

But – if a 40mm Plossl works in it, it should deliver about 20X and a 2.1° true field.   That may be worth it. (The gain in true field isn’t as large as you might think because the apparent field of view on the 40mm Plossl is typically about 44° as opposed to 52° on most Plossls. )  In cylops mode I’m used to the 24mm Panoptic and a 2.8° field of view.  What i found this morning  is not having that extra field is important in finding stuff. The 24mm panoptic made finding things fairly easy – you could point the scope by intuition alone and usually find what you want in the eyepiece. Not so with the smaller fov in the binoviewers with the 25mm pair. So this is something I need to explore if I want to use the binoviewers seriously on the TV85.  And I may.  I was frustrated this morning because I have a red dot finder on that scope, but I almost never use it and it was way off and my fingers were getting too damned cold to fix it, though I tried for a while.

One last note on the TV85 – the guy I bought it from suggested trying it in straight through mode. I think I will – especially since I could put it on the  UA Tmount and use it while sitting down. Could be real cool.

So at this point I’m real happy with the 10X30 IS Canon binoculars – they’re a keeper.  And I feel I have a lot of experimenting to do with the TV85 and other scopes before I will be convinced to go the binoviewer route in a serious way. If I do go that route, then the changes it will generate will sort of travel through my equipment list as if they were dominoes and result in a lot of buying and selling – something I’m addicted to anyway, but I’m not convinced the addiction is healthy.

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