Posts Tagged ‘20X60 Pentax’

Binoculars set up in Observing Shelter awaiting darkness for testing with doubles - and really testing me more than the binoculars. Unitron is there to check seeing conditions and acts as control of sorts - so to the Sparrow Hawk. (Click image for larger view.)

Until the past week I have never seen really sharp stars in binoculars – and what’s more, I assumed that was normal – that what I wasn’t seeing, others were not seeing.


Maybe decades worth of wrong. How many decades?  I’m not sure simply because it’s been relatively recently that I made a serious attempt to see double stars with binoculars and splitting close doubles is the most demanding resolution task of both the instrument and the observer.

From my experience I’ve developed some basic guidelines for splitting doubles with binoculars.  They are:

1. Wear your glasses if you have astigmatism – otherwise do without

2. Sit down – or better, lie back in a lawn chair – you must be comfortable

3. Hold the binoculars steady – even 7X50s will benefit from being on a tripod, or parallelogram mount unless, of course, they are image stabilized types

4. Focus carefully – very carefully –  first the left eye with center focus, then do the diopter adjustment for the right eye while keeping the left eye closed

5. Spend time on target – Look for at least one solid minute – don’t expect instant success.

6. Relax your eyes – let them focus at a distance and get used to it

7. And if all else fails, maybe you have a problem similar to mine – back off from the eyepieces an inch or two, move your head about some – find the correct head position – the one that works and yields sharp stars.

What follows is all about my own special case of “if all else fails” – because believe me, points one through six didn’t make a difference for me until I could settle the issue of point 7 and right now I’m not sure how many others have a similar problem, but I think it’s relatively few.

OK – the point is, I have been happily using binoculars for years without realizing I wasn’t getting the most out of these instruments – not even close to the most. Oh, I’ve seen galaxies out to  50 million light years or more – and I’ve gotten all sorts of expansive views of star clusters and nebulae. But I suspect what I discovered a few days ago may actually enhance  viewing of those objects as well.  What did I discover? That binoculars can, indeed, deliver “refractor-like” images of double stars. Let me be as clear as I can about this.

Double stars should look like the stars in the images to the right. That is, they should look like nice round discs with clean edges. Now any star that is low in the sky is  likely to throw out spikes of light, change colors, and dance about in any instrument just because in that instance you are looking through an awful lot of moving air.

But, if they are overhead or roughy 45 degrees or higher – and the air is average steady, then you should see nice sharp images when your instrument – binocular or telescope – is properly focused.

I do with telescopes – I don’t with binoculars – or didn’t up until recently and still don’t unless I am especially careful.  Is this my special problem? It may be. I have evidence there are some others who share it, but I suspect most people see the sharp stars they should, assuming their binoculars are held very steady – or are of the image stabilized variety – and they have been focused well.

Now let me emphasize that telescopes give me no problem – I can always see sharp, clean images with telescopes when seeing conditions are good. And while I am most likely to see the best images of doubles with either a long focal length refractor, or an apocromatic refractor, I get good, clean star images with any well-adjusted telescope of any design. Not so with binoculars. There the images have been consistently poor for me and I’m still not sure why. but lately I’ve come to suspect that my head simply isn’t screwed on straight – something critics have been telling me for years 😉

Determining what to expect with binoculars – that is, which doubles will split with binoculars  –  is much different than with telescopes. Double star fans know that all doubles aren’t created equal – and that the main problem is how far apart they are in angular measure – usually stated in seconds of arc.  A typical binocular has a field of view of between 2 and 8 degrees depending on how powerful it is. A typical binocular double is separated by less than one minute of arc. So when we are talking about stars separated by, say 30 seconds of arc, we’re talking about a distance that is just 1/120th of a degree. If your binoculars show a six degree field, then this pair of stars is taking up  about 1/700th of that field of view. Darned little.

So you also typically put the pair of stars in the middle of your field of view and the middle of the field of view is where even poor quality binoculars tend to perform quite well. Stars half way out to the edges may start to deform and stretch, but in the center they are sharp.  That’s why I say – and my experience confirms – that quite inexpensive binoculars can perform reasonably well when splitting doubles.

That is the first piece of big news I pulled out of my recent Eureka Moment.

The second was a handy rule of thumb I stumbled across when researching this subject trying to figure out what the heck was wrong with me. Telescope resolution – or expectations of resolution – are typically guided by something called the Dawes Limit which is entirely dependent upon the size of the objective  – a bigger objective creates smaller star images (in terms of angular size)  and will thus split stars that are closer together – it’s as simple as that. Now double star observers no it’s not really that simple – that frequently when the pair of stars have one that is much dimmer than the other, this rule crumbles because the dimmer star gets lost in the glare of the brighter one.

But if we are talking about stars that are within a couple of magnitudes of one another in brightness, the Dawes limit is a good starting point for determining how close stars can be and still be split.  The problem is, this rule assumes you are using fairly high magnification – say 30 times your objective diameter in inches. With binoculars you are almost always using much lower magnification. For example, my 10X30 image stabilized binoculars deliver only about eight times the objective diameter in inches. And my 25X100 binoculars have a power just four times the objective diameter in inches.

But Gary Seronik, in his small book “Binocular Highlights” suggests another rule of thumb that applies to binoculars – simply divide the power of your binoculars into 300. The answer is the separation, in seconds of arc, that those binoculars should be able to split. Thus my 10X30 binoculars – or 10X50 – should be able to split two stars that are separated by 30 seconds of arc. Albireo, a very popular double, is separated by 34 seconds of arc, so the 10X glasses should split it. My 25X100 should be able to split  stars that are 12 seconds of arc apart – that means the very popular double Mizar – which is separated by about 14 seconds – should split in the 25X binocular – and, indeed, it does. However, my 20X glasses will probably have problems with it  – 300/20=15 – and they do, though I have been able to split Mizar with those glasses, it’s difficult. So I think this is an excellent – though rough – guide. (The Dawes limit on those 25X100 binoculars, btw, is  barely a second  of arc – but that is a totally unrealistic expectation for binocular performance. Dawes limit = 4.56 Arc Seconds / Objective Diameter (inches) so 4.56/4 = 1.14. In fact, it is rare for a telescope to achieve this resolution on a double, but something like 1.8″ of arc is a reasonable expectation for a 4-inch t eleescope.)

But these numbers have not mattered much to me when using binoculars. I have only split the widest doubles. So, for example, over the years I really needed 15X binoculars to get a good, obvious split of the Dragon’s Eyes – Nu Draconis – a charming pair of 5th magnitude stars a wide 60 seconds of arc apart. Now, the new me finds them simple with just 10X30 binoculars.  Fifteen power glasses should, by this rule, be able to split stars just 20 seconds apart. The Dragon’s eyes should fall to binoculars as low as five power!  What’s more, in the past when I split this pair I didn’t get the kind of clean, “bullet hole”, stars shown in the image – I got dancing stars – bloated, jiggly stars throwing out spokes of light. It’s just that the 15 power binoculars – and the wide split – made it possible for me to see this pair as  two stars – and I assumed everyone was seeing the same thing.

But I was puzzled how observers I respect and admire like Seronik and Ed Zarenski, to mention just two, routinely split stars that were far, far closer together and instead of bragging about their amazing eyes and observing skills, seemed to think that others could routinely do the same. I know I couldn’t.

It must be my eyes. They must have problems I’m not aware of. That was my first train of thought and I’ve been pursuing that one for the better part of a year – without staisfaction. And a recent trip to the eye doctor confirms my practical experience – there’s nothing seriously wrong with my eyes. In fact, I have what the doctor describes as a “slight astigmatism” – so slight that they say that if I get corrective glasses I will barely notice the difference – and though this doctor worked with folks who sold glasses, she didn’t recommend them for me. (I ordered them anyway – there was  a special on where they’ll cost just $50 and this is something i have to see for myself because this whole business is driving me more than a little crazy.)

The Breakthrough

My breakthough came on a morning when I had decided to test five different binoculars –  10X30IS Canons, 15X70 Celestron Skymasters, 20X60 Pentax, 20X80 Celestrons,  and 25X100 Zhummels.  With the exception of the image stabilized Canons, all would be tested mounted on one of two parallogram mounts. The largest of these mounts was on a pier and really too tall for me to use sitting down, so I was using that one standing.  As a way to check the seeing and to make sure I could actually split these particular stars at low power, I had two small refractors set up as well – a 60mm Unitron using a 40mm Kellner eyepiece for roughly 24X and a 50mm Stellarvue Sparrow Hawk that was a lot like a single binocular in that it used a prism diagonal and was of very short focal ratio – F4.1. I used a 20mm eyepiece in this to get 10X, so it was, in many ways, a good match for the Canon 10X30IS.

My targets were the doubles Albireo (34.4″), Zeta  Lyra (44″), Nu Draconis -Dragon’s Eyes–  (62″), and Mizar (14.3″) – all were at a good altitude on this spring morning.

Initial tests

And the notes from my initial test showed nothing went particularly well at first.  This was the old me.

Actually, I started in the early evening with Mintaka – a wide  split at 52.8″ of arc that should be easy with all the binoculars I was testing, except there also is quite a difference in magnitude –  2.4, 6.8. That 4.5 magnitude difference makes Mintaka a bit of a challenge.  But the 25X100s showed it well. The 20X80s gave me a good look, though not quite as good as the larger binoculars. Actually, the best view came with the 20X60s – not sure why, but this is the old me talking.  I’m seeing a split, but the primary is shooting fire. The 10X30IS gave me an occasional glimpse.  The best view came with the Unitron with the 40mm Kellner, so this was roughly comparable to the 20X60 binoculars, but the star images were much better. I assumed that was because it was a long focal length refractor – and that probably was part of the reason, but as I later learned, didn’t account for all the difference.

The point here is that even the old me could split some doubles – just not nearly as well as I later learned was possible.

I moved on to the much more challenging Mizar. The 10X30IS couldn’t split it – no surprise. The separation is too little for those binoculars. Here I drew a quick sketch of what I saw with the 20X60s because the stars were so bloated and dancing so much I couldn’t be sure I was seeing a split, but I thought I was.  When I checked with the 60mmUnitron I was sure – the binocular view was correct – but, there was absolutely no comparing the two views. The Unitron – at roughly the same power- was far, far cleaner than the binoculars. (Remember, at 20X you should barely be able to split  Mizar – the formula says 15″ is  the minimum separation. Mizar is 14.3″ – though the stars are fairly close in magnitude –  2.2    and  3.9.) The 25X100 gave me a certain split, but certainly NOT “refractor-like” stars.

But something strange was starting to happen. As I maneuverd the binoculars on the parallelogram mounts they were sometimes a few inches from my eyes and once in a while I got a glimpse of sharp stars such as I saw in the Unitron. This first happened with the 20X80 Celestrons and it came when I seemed to bend my head back and literally look down my nose from an inch or two behind the eyepieces. I was tired. I was getting cold. And I really didn’t know what was going on, so I went in with the intention of getting four hours sleep and trying again when I was refreshed.

Morning session

Field notes on Albireo - at last, a clear view.

Nothing comes easily to me – especially in terms of binoculars. I wrestle with mounts, I fiddle endlessly with focus, and mostly I have ended end up seeing something like this:

I have a sense of two stars here, of course, but theimages are dancing, the colors swapping sides, and sometimes I think I see the secondary in one place, sometimes in another.

When I should see – and now do see –  this:

What a delight! This is what I'm used to seeing with a telescope and now - with more and more consistency and less and less hassle, can see with binoculars.

In one sense the change was nearly instantaneous – that is, I would go from a terrible image to a perfect one – no inbetween.  But it only happened after a lot of work and a lot of false steps.

What made me put in the extra effort was I justc ouldn’t reconcile the diffferent experience of using two very nice instruments on Albireo. The first was the Stellarvue Sparrow Hawk aka Little Rascal. This is a 50mm finder, essentially, but  it takes standard eyepieces and is easy to focus. But like a binocular it has a very short focal ratio – F4.1 – and it uses a prism to deliver an erect image. And as my notes show, when I pointed it at Albireo on this particular morning with a 20mm eyepiece (10X) I got a “clean and delicate” split just as I would expect with any telescope – though this wasn’t any telescope. this was essentially half a binocular.

Then when I switched to the 10X30IS Canon’s I was back in Blursville with dancing stars.  And then I started to notice something. I noticed it with the large, mounted binos – the 25X100 Zhummel and the 20X60 Pentax, and 20X80 Celestrons. If I backed my eye way off – I’m talking two or three inches from the eyepieces – and tilted my head so I was in effect looking down my nose  there were long moments when the two stars snapped into sharp focus. Crazy? I’m not sure. When Ibrought this up in a Cloudy Nights discussion forum a few people came forward to talk of similar experiences – but on a few.

Believe me , my heart was racing. I have looked at countless double with binoculars and I had never seen them like this.  This was a real breakthrough and I quickly skipped about from Albireo to Zeta Lyre, to the Dragon’s Eyes and then to Mizar. With these kargerf binoculars everything was great – really great with the bright image sof the 25X100,

I couldn’t believe my luck. I hadn’t even brought out the 10X30IS for this session because I had about given up on them. Twilight was starting to grow brighter in the east. I quickly went back to the house, got the 10X30IS, and voila! There was a perfect Albireo – a yellow star with a scrumptious blue pinpoint right next to it.  I simply couldn’t believe it.  It was every bit as good as I had seen in the tiny Sparrow Hawk refractor.  The only question that remains is why the heck did it take me half a century of observing to discover this?

Well, not the only question. Since this breakthrough I have had three more sessions under the stars and I have expanded the variety of stars I’m looking at to include 16 & 17 Draocnis, Regulus, and Psi Draconis.  I have had my eyes examined by a professional and asked her for ane xplanation – why the heck do I have to look down my nose at doubles? And I have discussed it in online forums and with Larry Patriarcha, the guy who makes and sells the best parallelogram mounts  I know of.  Allt hese people had ideas, but no really firm answers.

But here’s the rub. This is getting easier and easier for me to do – that’s good news, but doesn’t solve the puzzle. I am finding with practice I now achieve this state of double star nirvana without half trying. But it still is easiest to reach if I back off form the eypieces, then, once i get it, approach them slowly being careful to maintain my head position.

So I think it does have something to do with head position – after all, with binoculars you look up – with many telescopes using diagonals you look down.  And it may have some tiny thing to do with astigmatism, and it may have to do with stressing my eye muscles by tiltilting my head back and looking down my nose. But two things are clear to me – first, most observers don’t seem to experience this problem. Second, I don’t understand fully why I do, nor do I understand fully the solution because the ground rules seem to be slipping out from under me. There definitely is a groove and I find it easier and easier to get in it. And believe me, I’m not complaining. This opens up a whole new area of especially enjoyable observing for me.

Doubles I love. I always have found a magic in seeing two perect little globes next to one another.  But now I can see them with both eyes open and while leaning back in a comfortable lawn chair and looking up at the sky – and that, for me, really is double star nirvana.



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Oh boy! Been having a discussion on Cloudy Nights about astigmatism, etc. and the last post.  What was bothering me was, among other things, how to separate the impact of power increase from the impact of exit pupil change.

See, in my last experiment, detailed here, what I did was take a 50mm objective and repeatedly change the power.  This resulted in  a smaller exit pupil – good for negating the impact of astigmatism in my eyes – but also a higher power which, of course, makes it easier to split doubles. So the experiment is interesting, but inconclusive. Someone on Cloudy Nights suggested that what I needed to change, of course, was the aperture – not the eyepiece. Keeping the eyepiece – and thus the power – the same, and cutting down the aperture would give me a shrinking exit pupil and a better guide – at least with bright stars – as to the impact of the smaller exit pupil.

So off I went immediately to make a 40mm mask for the 20X60 Pentax binoculars – which I did and the skies cooperated by giving me a cloudless early evening – something that wasn’t predicted, but I was delighted to take.

I used the masked 20X60 Pentax  as is and stopped down to 40mm, first on Albireo, then the Pleiades, Jupiter, M34, and the Rams Eyes. Very interesting – and I’m a happy camper because at last I’m seeing pinpoint stars with binoculars! (You can’t imagine how many excellent pair of binoculars I’ve owned and sold because they did not deliver this – and they all had fairly large (4-5mm) exit pupils!) But there are still a combination of factors involved, the most important one being the relatively small exit pupil which seems to overcome my astigmatism and the second most important, finding the correct head position. I did play some with IPD, but couldn’t see that as an issue.

The most surprising situation came after spending about 20 minutes trying to get a really good view of Albireo. That wasn’t a matter of splitting it, but one of trying to come up with clean, refractor-like stars – bright, round little bullet holes in the night sky – and in this case, showing lots of color.

As I settled on Albireo I kept fooling with head position – the binos were on a p-mount, of course – and focus and just couldn’t get the primary to settle down completely. Then suddenly I accidentally moved the image off center – about half way to the top of the field, and bingo! There were my two perfect stars, bright orange (not gold, as I usually see it) and blue.

This blew my mind and I kept repeating it – bringing the image back to the middle of the field where there was still significant flare on the primary, then moving it up and when I did so, having it clear. I can’t explain this. I don’t think it had anything to do with the binocular. I think it had something to do with my head position. When I moved everything around and went after the stuff in the east later I could not repeat this in any form – in fact, as time went on I was getting good crisp stars throughout the field of view, so it just didn’t matter.

Could it be the binocular cooling down? I doubt that very much for I had left it out for at least an hour before going out to observe.

The stopping down produced obvious and predictable results in all the tests. I got a little less light, but I got sharper star images with it stopped down to 40mm and thus yielding a 2mm exit pupil. I did try 15X70 glasses as a test case and while I could split Albireo with them, the split was very, very sloppy and there was no way I could get it to even remotely look like what I was seeing in the 20X60/40.

Binocular doubles in the Pleiades - modified from SkySafri screen shot.

The Pleiades provided a terrific experience. I’m planning a post on binocular doubles in the Pleiades for the double star blog I share with John Nanson, so I was real pleased to go over several doubles, some of which I had split before – they’re ridiculously easy – and some of which I had never split with binoculars. One thing that revealed itself nicely is that triangle near Alcyone towards the center of the cluster. (See the inset in the above image.) It’s easy enough to get the 6th mag star there, but the other two are fainter and I hadn’t seen them before because of the glare from Alcyone. I could just detect them with the 60mm stopped to 40mm and could see them clearly when using it unmasked. This was the clearest indicator of how much light I was losing by going from 60 to 40mm objective.

But most satisfying was the whole cluster of sharp stars.

Jupiter was certainly better when I stopped down to 40mm. That way I could just pick out Europa which had recently transited and was still quite close to the planet. Ganymede and Callisto were obvious and Io was in eclipse.

Being in the neighborhood I decided to give the Ram’s Eyes a try. There the split is 7.5-seconds and I just couldn’t do it, though with the 40mm masks on I did have a distinctive figure eight that was oriented in the correct north/south direction. Maybe with more practice and a better night . . .

With M36 I could pick up two or three of the pairs that make the body of what I think of as a Klingon War Cruiser.

Bottom line – many thanks to Ed Zarenski for telling me about astigmatism and exit pupil and others here on CN who joined the discussion and have helped me work through this to the point where I can now enjoy binocular astronomy a lot more. It’s good to see sharp stars and it’s good to have some rationale for why low power views have never worked well for me with binoculars or telescopes.

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Ok, I’ll eat my words.

When was it? Last week, perhaps, or the week before? That I tried binoviewing once more and swore that would be my last trip down that road?

See, I have ventured into binoviewing a total of five times now over several years. My most successful experience was with an early Denkmeir and they worked best for me on the 8-inch SCT I had at the time. That was about six or seven years ago. I’m not sure why I stopped using them. Perhaps just too much of a bother to change powers – and they were rather big and awkward and subject to getting knocked about.

Since then I’ve tried the closely related Earthwins and had to return them because – as with the Denks –  found them too large, and awkward, and complicated to use – especially for the kind of public outreach I was doing then. You can’t have people line up for a view and then spend half the  time adjusting the binoviewers for each person. Too bad, because the view can be absolutely stupendous as I found last night when I approached a new, inexpensive pair with an entirely different attitude.

Yes, your approach and expectations matter. In this case I made up my mind that I would treat the binoviewers as if they were a pair of binoculars with fixed eyepieces and that’s all I would use for that observing session. That’s much different  than  the mind-set you have when viewing in cyclops mode and frequently popping in one eyepiece or another with little to do but make a slight focus adjustment.  That approach can’t be taken with binoviewers where they can:

  • radically change the scope balance on a mount
  • the interpupillary distance may need to be changed
  • the focus will change considerably – I mean considerably – from a single eyepiece to a binoviewer
  • the changing focus can mean with a SCT  enough image shift to actually lose sight of your target, or at least require recentering
  • the individual eyepieces may need to be adjusted so they show they both are in focus
  • and, depending on design, you may have to pull the binoviewer out of the diagonal and screw on a barlow lens just to get them to come to focus in a refractor – hey, in my case I also had to change from  a 2-inch diagonal to a 1.25-inch one

Bottom line, that’s a lot of screwing around. Denk, Earthwin – and perhaps others – get around some of these issues by adding lenses that slide in and out in a patented mechanism, thus giving you two or three different powers with minimum hassle – but also adding bulk and weight to the whole set up.

So, my solution? First, i changed my mind set and expectations and it turned out to be a real lesson in how expectations relate to perceived outcomes.  As i say, i decided to treat the binoviewer/scope combination as if it were a fixed-power binocular – with the bonus that with some hassle I really could change powers, but it would be more involved than with a single eyepiece and I shouldn’t do it casually.  This mindset actually complements my observing philosophy where I think too often that I tend to flit around too much and not stay on target long enough.

Second, I bought – new for $179 – a pair of the Chinese imports from Orion – simple, light weight binoviewers, and as it turns out, quite effective in terms of my lower expectations. In these I settled on a pair of 20mm TV Plossls and I decided to use them primarily in the observatory with an 8-inch Meade SCT – a typical alt-az “go to” set up where most of the time I ignore the “go to” part, but take advantage of the tracking. Tracking also encourages time on target and makes using the binoviewer less stressful.

And I loved my initial experience despite really crappy conditions – a nearly full Moon, way too much dew, and high clouds frequently interfering, not to mention abysmal seeing.

The detail on Jupiter was terrific even through a dew-covered corrector plate. The Great Red Spot just jumped out at me – despite the moon being right next door.  And I know it’s just our mind playing tricks on us, but damn, Jupiter looked like a sphere rather than a disc! And the Moon? Hey, it was like taking a helicopter ride over a landscape that was fascinating even though mostly flatly lit. Almach, a favorite double, was pretty darned good as well – and I was transfigured by my view of what I regard as a Klingon Warship – the brighter stars of the open cluster M34.  That cluster has a fascinating set of pairs as well and even though the Moon was washing it out and the binoviewers stealing some of the light the 8-inch mirror was gulping down, I was transfixed. I even liked the view of M31/32, but by this time I was struggling with clouds and quickly gave  up trying to spot M110 in the moonlight and mist – and yes, I did put the 2X nosepiece on and it did give a nice view of Jupiter and the Moon, but I need  more time with it.

So I came in, jotted some notes, then decided there were enough sucker holes to give this thing a try on the TV85 – at least find out if it would come to focus. So I put the LXD75 on the deck, didn’t bother with a battery – just slapped the TV85 on and pointed it manually at the Moon – big blob. Uh huh.  Put on the 2X Barlow – and Orion does warn you that you may need this to reach focus in a refractor. Nope – didn’t do the trick. So I took out the 2-inch diagonal, put in a 1.25-inch diagonal and tried again. This time I could reach focus as long as I used the 2X Barlow. Eh – not bad, but I would have to have real good reason to change things around that much. Binoviewing is nice, but for now I think I;’ll consider that the TV 85 is a clyclops scope – and I really don’t want to try the binoviewer on anything smaller both because  of light loss and weight.

The Orion isn’t the weight of the Denk, but it’s not light. The Denk in the old Big Easy package I had most recently used – no special switches or anything – weights 20 ounces. The Orion is an ounce or two lighter. But add the switching mechanism to the Denk and it really bulks up and the price is much more.  I guess price was a major factor here. I could accept the idea of the binoviewer/scope as a fixed-power binocular at the $170 price of the Orion – not at the $500 price of the Denk Big Easy.

Truth is, the Orion binoviewer, even with an extra Plossl eyepiece counted in is roughly the equivalent of one my Naglers on the used market – so this is a binoviewer I can treat as another eyepiece. Again – frame of mind – it means a lot. 😉

Anyway, somewhere I had read – I think it was in the Denk literature – that you shouldn’t use the binoviewer with a focal reducer on the SCT. Hmmm. I wanted to give the  C6 SCT a turn with the binoviewer through the next sucker hole and there was a focal reducer on it. Certainly would give me a wider field and make finding things easier. Hell – I left it on. And guess what – no obvious problems. I need to investigate this more, but my first impression was” “I love it.” There was the Moon again, looking like a 3D globe with some space around it – 47X in a six inch by my calculations. Now that’s a nice step up from my 20X60 binoculars. Yeah! Lot’s of possibilities there.

I went back in, put up a “wanted” ad for a pair of 15mm TV Plossls and quickly ended up with an offer for some 13mm of the old  Circle “NJ” type. I like those, so I bought them. I also think the 13mm a better choice in terms of powers with the  C6  or the eight inch than the 15mm. SO given the   focal reducer, this is what the two sets of eyepieces – 20 and 13mm Plossls, plus 2X Barlow – wo;; offer me.

In the 8-inch I will then have 100X, 154X, 200X and a mostly unusable 308X – on the C6 with focal reducer the range will be more reasonable:

47X, 73X, 94X, and 146X

Take out the focal reducer and the C6 goes from 75X, 115X, 150X, and 230X – not too shabby.

But, of course, I need to return to my mindset of fixed binocular. Switching this stuff around won’t be that easy. In fact, the only relatively east   switch will be to just change to the Barlow. See, changing the eyepieces means refocusing each eyepiece individually. Something that goes smoothly enough, but. . .. well, I need experience with the system with both sets of eyepieces and I won’t have that second set for about a week. It’s on its way now from Canada.  Then , given the price, maybe I should get another Orion and put the 13mm eyepieces in it, then treat the two binoviewer as if they were individual eyepieces, putting one or the other in the diagonal. Don’t laugh.  If the convenience factor is important enough and I continue to really enjoy binoviewing – and I do like using both eyes – afterall, it’s what most people are born with, so . . . stay tuned.

Oh, and about those new binoculars . .. .

Yeah, there was more going on than binoviewing this evening. I was also putting Ed Zarenski’s advice to the test and finding out that I probably do have some astigmatism and this is what has frustrated me with low power binocular use – especially when trying to split doubles.

The binoviewers arrived yesterday just a few hours after UPS delivered a new pair of Pentax 20X60 binoculars. I put them on the P-mount and in darkening twilight – and a whole lot of moonlight – was able to see all four moons of Jupiter with ease. With the 1030IS I could see three moons – two were close enough together to blend as one. OK – that’s inconclusive. I was also able to split Albireo. That was more encouraging, though it was hard to judge because seeing was so poor.

But later the trees moved enough to give me a quick shot in yet another sucker hole at Mintaka. With the 10X30s I could detect the secondary – with the 20X60 mounted I could see it just as plain as could be.  That’s encouraging. But the important note here is that I have tried repeatedly to see Mintaka with the 15X70s mounted and can’t. Now that might relate to objective quality, but I suspect what it relates to is exit pupil and an undiagnosed problem I think I have with astigmatism. The 15X70s have an exit pupil o f 4.6mm. The larger the exit pupil, as Ed pointed out, the more problem you will have if astigmatism is an issue.  The exit pupil with the 10X30s and 20X60s is the same – 3mm. And with both those binos the primary settles down enough to allow me to see the secondary. The extra power and light grasp of the 20X60s just makes it easier than with the 10X30IS.

Don’t get me wrong. I still love IS and I still want the Canon 18X50IS at some point. The exit pupil would be even smaller – BUT, their cost is prohibitive right now. Maybe after  I sell a few more things 😉

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