BAS

Challakere Event

2024-02-26T00:00:00+00:00

Challakere Stargazing event by Bangalore Astronomical Society

As a part of the public outreach, BAS conducted a public outreach program at Sri Venketeshwara Rural High School on 24th February,2024 evening at Challakere,Karnataka. Following are the images from the program. Credits to BAS member Sanjay Purohit for the images.

A brief summary of the event shall follow.

Nsd Iia Event

2024-02-25T00:00:00+00:00

Amrita Event

2024-02-19T00:00:00+00:00

BAS Astrophotography talk at Amrita University,Kasavanahalli

This event was conducted by BAS member Chakravathy. Following are pictures from the event. Following are the images from the program.

Do It Yourself Dew Heater

2015-11-27T00:00:00+00:00

A Do-It-Yourself Dew Heater (Courtesy Sanath)

The Problem

At low temperatures (say, as low as it gets on a winter night at the typical observing site near Bangalore), if the air is humid enough, the moisture condenses on any exposed surface, including mirrors, corrector plates, and objective lenses.

This is the dew problem. Its primary effect is that it can derail your observing session by giving the proceedings a foggy appearance.

That apart, the dew also exposes you to the problem of accumulating sticky dust on your telescope optics - especially if there are trees around your observing site.

Prevention is better than cure, and this is true of dew as well.

Dew Shields

Since dew only forms on exposed surfaces, one solution is to shield them. This can be done by having a long enough shade, or dew shield extending from the objective end of the tube. This applies primarily to Refractors and Maks.

This Sky & Telescope article has more to say about dew shields, including how to make your own. If you’re looking for foam rubber (as mentioned in the article), all that you need to do is to get hold of a Yoga Mat.

Sanath’s article on dew heaters has references to sources for other things you might need, like Velcro strips.

Per a discussion with Sathya, the formula for the length of the dew shield is 1.5 x D + 50mm, where D is the telescope aperture in mm. Sathya also recommends using corrugated cardboard reinforced by a covering of duct-tape instead of a rubber mat.

Dew Heaters

Dew Shields are the first line of defence against dew. Sometimes it is cold enough for dew to form despite dew shields. What you then need is a dew heater. Think of it as a dew shield with a built-in heating mechanism.

Dew Heaters work by maintaining the temperature around the objective (and hence that of the objective as well) above the dew point. While commercial dew heaters are available, it is not too difficult to make your own.

Sanath has written up plans to make your own dew heater. It also comes with vendor/shopping references in Bangalore for the parts involved.

A discussion on the BAS google group might also make for interesting reading.

References

Buying A Telescope

2015-11-27T00:00:00+00:00

Opinionated Guide to Buying Telescopes

Karthik Subramanian, karthik !remove spaces! 301176 !+! bas !AT! gmail !DOT! com

The objective of this article is to provide the first-time telescope buyer with the minimum information needed to ask the right questions before investing in a telescope.

Please note that this article only covers equipment for visual observation. It does not cover equipment for astrophotography.

If you’ve already made up your mind that you want to buy a telescope, then jump straight to the Vendor Information page. If not, read on.

This guide by itself is probably not enough to help you buy a telescope; but it should definitely help you get started. It is necessarily short on many details. Like its title implies, it makes many assertions without proof, or even evidence. If you find that you have questions, please do ask on the BAS google group. In addition, Star Ware is a good resource on this topic.

No originality of content is claimed, except perhaps for the presentation.

Don’t Buy A Telescope …

… not just yet, anyway.

A quality telescope is an expensive instrument. Should you choose to buy a telescope and decide later that amateur astronomy is not for you, you’re stuck with the scope until you find someone who will buy it from you.

Many beginners approach a telescope with very high expectations. No matter how expensive the telescope is, it cannot do certain things.

For one, what you see at the eyepiece will not be anything like the colourful photographs you see taken from the Hubble Space Telescope. In fact, most of what you see at the eyepiece will be images in varying shades of grey. This isn’t really the telescope’s fault; the human eye cannot perceive colour in very dim images. Cameras can, however - but that’s the subject of another discussion.

For another, your telescope will likely not show you the massive images of the planets that you’re used to seeing in photographs. Jupiter will probably appear smaller than a single whole piece of black pepper.

So what can you see through a telescope? This site gives a good idea of what to expect at the eyepiece.

A word of caution: the sketches in the link above show you views that can be achieved with a telescope. The views are real, other people besides the original sketcher(s) have seen them, /and/ documented them. However, please do keep in mind that it takes a lot of practice to actually achieve these views.

Inspired by the sketches, you might take your newly-acquired scope to your rooftop and hunt for say, the Andromeda Galaxy. In all probability, you will see just a grey blob. Many factors affect the view in your telescope - some, like the equipment, and its care, are in our control. Others, like dark skies (or the lack thereof), or the weather, are not entirely so.

Please try and look through a telescope or two, to appreciate what you’re getting into before you put down your money. One way of doing this is to attend star parties. Another is to just sync up with your friendly neighbourhood BAS member, most (if not all) of us will be happy to show you our telescopes.

Binoculars

If you really want to buy something right away, consider buying a good pair of binoculars. Why binoculars?

Binoculars are a useful astronomical instrument in their own right. Most experienced amateurs usually have a pair of binoculars, and with good reason. See Rony de Laet’s page for examples of what is possible with binoculars.
Binoculars are relatively inexpensive as compared to a telescope.
Binoculars are multipurpose. Should you decide that amateur astronomy is not for you, chances are that you will still not regret your binocular purchase, and will continue to use them in other pursuits.

This page has more to say about binoculars.

Buying a Telescope

It is usually a good idea to get familiar with some telescope terms, and what they mean, before buying a telescope. The Telescope Terminology page should help. The rest of this guide assumes that you are familiar with at least some telescope terminology.

Some General Remarks

More aperture is a good thing to have. With more aperture comes more light-gathering capability, brighter images, and the ability to resolve finer details. More aperture also brings with it more bulk and weight.

Longer focal lengths yield a smaller field of view. Shorter focal lengths give a wider field of view. Longer focal lengths also result in a longer telescope, except in the case of Maksutov- and Schmidt-Cassegrain telescopes.

When budgeting for a telescope, keep in mind that you might also need to buy a few accessories. The minimum setup you need is a telescope OTA, a finder scope, a mount, and one or more eyepieces. Depending on the telescope, you might also need a star diagonal. Most beginner telescope packages contain all of the above, in which case you probably do not need to buy anything more.

To Ponder Before Buying

Disclaimers

The prices mentioned below are current as on the time of writing (Nov 2015).
The prices mentioned below are necessarily approximate, and are meant to give the reader a rough idea of the cost. Please contact your vendor for up-to-date and accurate pricing information.
The ultimate buying decision is that of the buyer. Please do not take the recommendations below at face value - instead, use them (and this guide) as an aid to do your homework before arriving at a buying decision.

Budget

If budget is your limiting consideration, then the buckets of your interest are roughly Rs. 13K, and Rs. 23K. If your budget is smaller than Rs. 13K, and you do not already possess a pair of binoculars, you are encouraged to read the binocular page.
A budget of around Rs. 13000 will fetch you a 70mm Equatorially mounted refractor. In the same bucket, you might be able to find a 70mm Alt-Az refractor for a little less, or an 80mm Alt-Az mounted wide-field refractor for a little more.
If you’re willing to stretch your budget roughly twofold, a good “middle path” choice would be a 6” Dobsonian telescope. This should typically set you back by around Rs. 23000.

Size, Weight & Portability

As a rule of thumb, do not buy a refractor with optics sized smaller than 70mm. You will read that any telescope is a worthwhile investment, even if it’s “just” a 50mm refractor. This statement is true. The trouble with smaller (and cheaper) telescopes is that they are usually a marriage of decent optics with useless mounts. Thus, it takes some experience to extract goodness out of these telescopes; this can be a frustrating experience for a beginner.
In a similar vein, avoid reflectors sized smaller than 4.5” (114mm).
The ideal starter scope according to many is a 6” Dob. This is indeed a good recommendation. Before you go ahead and buy a Dob, please try and see one for yourself. A person of typical build should have no trouble in carrying a 6” Dob, in two pieces at the most. However, you should verify that this will indeed work for you before investing in a Dob. If portability is your overarching concern, you might want to consider a small (5” or thereabouts) Mak or SCT.
“Starter” mounts are usually underprovisioned. Buying a well-provisioned mount will let you buy a second (bigger) telescope in the future without having to buy a mount for it. (Assuming that you do not want to use both telescopes simultaneously.) It goes without saying that a good mount will also inflate your budget. It will also be a rather heavy piece of metal.
GoTo mounts are capable of providing some of the conveniences of an equatorial mount, without weighing as much. Most of them work with reasonable accuracy after being aligned. Note that GoTo mounts need power, either in the form of batteries, or AC. Some will not work at all without power.

Use/Interest

All telescopes do not perform equally well on all kinds of targets. Broadly, one could speak of Planetary Observation and Deep-Sky Observation.
Long focal lengths are suited for Planetary targets, since the narrow FOV (and high magnifications) will work well to show details on the Moon and Planets. This is also good on Double Stars.
Short focal lengths give a wide field of view, and are suited for Deep-Sky targets.
Here too, a good “middle path” choice is a 6” Reflector. Most available 6” Dobs seem to be figured at f/8 or thereabouts, making them slightly on the longer side.

Maintenance

Refractors need the least maintenance.
Reflectors need to be collimated fairly often. Collimation is a simple procedure, however, and is nothing to be afraid of. A badly collimated reflector will perform badly.
Short-tube reflectors with spherical mirrors and a corrector (Barlow) built into the focuser (the Bird-Jones or Jones-Bird design) are difficult to collimate. You can recognize them by comparing the stated focal length of the telescope to the physical length of its tube. If the tube length is a lot lesser than the focal length, the scope is a Jones-Bird. Note: There is nothing inherently wrong with the Jones-Bird design; it is just that most low-end scopes using this design are badly done. See References 5 and 6 for more details.
Maks and SCTs usually do not need to be collimated in the field. Collimating a Mak is more difficult than collimating a Newtonian reflector.

Accessories

Collimation Tools

Newtonian reflectors need collimation every now and then. Most reflectors come with a collimation cap, which should be sufficient to perform satisfactory collimation. More expensive collimation tools like Laser Collimators and Barlowed Lasers are available as well.
Cleaning Tools

For most purposes, an air blower (of the photographic kind) and a soft camel-hair brush should do. Do make sure to perform the “cheek test” on the brush - poking at your cheek with the brush should not cause any bristly feeling. If it’s soft enough for your cheek, it’s OK to use it on your mirror as well.

More complicated cleaning might be needed on an infrequent basis. This is detailed elsewhere.

Avoid

Buying “Toy-Store” telescopes which are marketed solely on the basis of their magnification. In other literature, these are also known as “Department-Store Telescopes”.
Trusting reviews that do not explain why (or why not) a telescope is “good” or otherwise.
Telescopes with a focuser barrel size other than 1.25” or 2”. 0.965” Eyepieces are hard to come by.
45-degree diagonals. They’re good for terrestrial viewing, but are uncomfortable for astronomy.

Vendor References

Please consult the Vendor Information page.

Post-Buying Checks

Check the OTA for scratches and dents.
Check to see that the mirror (or lenses, as the case may be) is reasonably clean, and doesn’t have any visible spots or scratches.
Check that the mount is working fine, and slews smoothly.
(This test applies to any tripod-mounted telescope). Focus on any object of your choice. Rap the mount near the OTA (or the tube rings) with your knuckles - not very hard, but with just enough force to make the view in the eyepiece shake. (This shouldn’t be too difficult). Count the seconds until the view in the eyepiece settles down. A settling time of 3-5 seconds is good; anything more than 10 seconds is not. If your scope takes too long to recover from vibrations, you might have to do something to make the mount more steady.
The Star Test The idea behind the star test is to focus the telescope on a bright star using reasonably high magnification. Then, adjust the focus inwards until the star is out of focus - you should see a pattern of concentric rings. Adjust the focus outwards, until the star is out of focus again. You should see exactly the same pattern of concentric rings as before. If not, your scope needs collimation.

The star test is detailed more comprehensively in Star Ware, and also in Gary Seronik’s No-Tools Telescope Collimation.

Freshly-unpacked Refractors and Catadioptrics should not need collimation. The best thing to do in such a case is to return the scope.
If you bought a reflector, and the primary mirror is not centre-dotted, then you might want to do this. Centre-dotted mirrors are easier to collimate than the ones without. A good reference for centre-dotting is 8.

I already have a scope from the “avoid” list

No harm done. If you are satisfied with your purchase, and are able to use it well, skip this section. If not, read on - it might be possible to salvage the situation.

I bought/was gifted a small (50mm/60mm) refractor by a well intentioned friend/relative. It shakes like crazy and I can’t seem to find anything in the sky apart from the moon.

Don’t throw it away!. Not just yet, anyway. Small (and cheap) refractors, as mentioned earlier, are usually not a bad deal, except for the mount. This is especially true of the lower-end Celestrons and the like. Typically, the tripod/mount that these telescopes come with are light and flimsy. In some cases, it is possible to make the tripod/mount more stable by counterweighting the tripod. It is also possible to make use of pieces of teflon sheeting to smoothen the motion of the mount head.

If your refractor shows interesting colours of the rainbow on the moon, and you’re not really able to see the moon except as a blob (albeit a blob with some features) then the optics are probably made of plastic, or low grade glass. This is usually the case with Toy-Store scopes. They are usually a bad deal.
I bought/was gifted a low-end Jones-Bird reflector that doesn’t work well

The most popular Jones-Bird reflector in this location seems to be the Celestron AstroMaster 114.

The primary complaint with a low-end Jones-Bird is usually that the images are “soft”, and it is impossible to bring the instrument to focus. This could be caused by either of two reasons:
- The instrument is out of collimation (and is difficult to collimate), or,
- It refuses to come to focus, regardless of the state of its collimation. This usually happens because of a badly positioned corrector, or a bad corrector.
Another complaint could be that the image is blurry throughout the range of the focuser. For instance, the moon remains a white blob, and it is impossible to resolve any details - even craters - on its surface.

Some background is available in Reference 6.

To troubleshoot:
1. Check that it is possible to unscrew (or otherwise remove) either the corrector alone, or the focuser along with the corrector from the OTA.
  
  Sometimes the corrector is secured by it being glued in place. This could make it impossible to remove the focuser/corrector without risk of damaging either.
  
  If this is the case, the best thing you can do is to try and collimate the scope with the corrector in place. This, as we have already seen, is fairly difficult to do. You might want to try using a laser collimator if you can get hold of one.
2. If it is possible to remove the corrector, please try and remember if you removed the focuser/corrector at any time in the past. If you did so, and inadvertently reversed the corrector, the telescope will not come to focus.
3. Remove the corrector. Check the state of the telescope’s collimation. If it is out of collimation, try and collimate it. See either Star Ware or Gary Seronik’s Beginner’s Guide to Collimation for simple collimation instructions.
4. Replace the corrector, and see if you can now achieve focus. If not, try reversing the corrector and check again. If this works, you are good to go. If it is not possible to reverse the corrector, then your best bet is to return the telescope to the seller.
5. If, after performing all of the above steps, the views in your Jones-Bird are no better than before, then you should return the telescope.

If you still have questions, please feel free to post on the BAS Google Group.

References

Beginning With Binoculars

2015-11-12T00:00:00+00:00

Stargazing with Binoculars

Karthik Subramanian, karthik !remove spaces! 301176 !+! bas !AT! gmail !DOT! com

Binoculars are a relatively inexpensive and often overlooked piece of equipment that can be used to explore the night sky. This article tries to provide a quick overview of binoculars for beginning stargazers. Note that this is not a comprehensive review, and many details have been left out for the sake of brevity and accessibility.

No originality of content is claimed, except perhaps for the presentation.

Why Binoculars

Why use binoculars for stargazing? There are a few good reasons.

Owing to their their wide field of view, it is much easier to locate objects through binoculars than in a telescope. This makes it easier for a beginner to learn their way around the night sky, which is a useful skill for any observer.

Two eyes are better than one, as the adage goes. This is true of binoculars as well. The presence of two light paths as opposed to one results in a brighter image. This is partly due to how the brain processes images that are being looked at by both eyes. The author is not knowledgeable enough to say anything more about the biological processes at work; but can instead recommend the following simple experiment: look at your favourite object in the sky through a pair of binoculars, with both eyes open. Next, look at the same object with one eye shut. Look at the object through both eyes again (this time, you might have to wait for a few seconds for your eyes to reach focus.). The difference between the single-eye image and the two-eye image should speak for itself.

Lastly, if you’re a beginner, binoculars are a relatively inexpensive way to get started in the hobby. They are also multipurpose, and can be used in pursuits other than stargazing. Should you ever decide that stargazing is not for you, you can still use your binoculars otherwise, and they will not be a dead investment. The author does recommend that you not point them at your neighbour’s windows, however.

What can you see with Binoculars?

A lot; but here’s a small list (courtesy Akarsh Simha). The “M” stands for Messier. You can look these objects up in a sky chart like Stellarium, or SkEye.

The Pleiades (M 45)
The Hyades (Collinder 50)
The Orion Nebula (M 42)
The Beehive Cluster (M 44)
Ptolemy’s Cluster (M 7)
The Butterfly Cluster (M 6)
The Double Cluster (NGC 869, NGC 864)
The Andromeda Galaxy (M 32)
The Little Beehive Cluster (M 41)
The Swan Nebula (M 17)
The Sagittarius Star Cloud (M 24)
The Lagoon (M 8) and Trifid (M 8) Nebulae
Open Cluster in Puppis (M 47)
Open Cluster in Perseus (M 34)
The Northern Jewel Box (NGC 6231); also the False Comet
Open Cluster in Cygnus (M 39)
Open Cluster in Andromeda (NGC 752)
Open Cluster in Puppis (M 93)
The Wild Duck Cluster (M 11)
Globular Cluster in Sagittarius (M 22)
Delta-1 and Delta-2 Lyrae
Omega Centauri (NGC 5139)
The Coathanger (Collinder 399)
Open Cluster in Gemini (M 35)
Open Cluster in Casseiopeia (M 103)

Most of these objects should be visible from Bangalore rooftops, as long as your skies in that direction don’t look orange. This, of course, depends upon your location in the city.

If you want more objects to look at, then Ed Zarenski’s list of 100 Binocular Deep-Sky Objects and the Binocular Sky’s Object Search should help.

If you would like a taste of what you can see through binoculars, Rony de Laet’s Binocular Sketches are illuminating, to say the least. Please do note that these observations were mostly done under dark skies, and with mounted binoculars. That said, the sketches give you an idea of what can be achieved with binoculars.

Binocular Specifications

Binoculars are primarily specified in terms of their Magnification and Aperture. A pair of 10x50 binoculars refers to binoculars with 10x Magnification and 50mm of aperture. Typically, more aperture gathers more light - but be aware that with increasing aperture, the weight of the binoculars also goes up (not to mention the expense).

Another important parameter is the Exit Pupil. This is the (minimum) diameter of the tunnel of light that exits the binocular eyepiece. The exit pupil diameter can be calculated by dividing the aperture by the magnification. The exit pupil should ideally match the size of your eye’s pupil.

The Eye Relief is the maximum distance from the eyepiece that you can position your eyes, and still view the entire field. This is of particular importance to observers who wear glasses.

Most (if not all) binoculars use prisms internally to provide the correct focal length within the small frame of the binoculars. The kind of glass used for the prisms is usually either BAK-4 (Barium Crown Glass) or BK-7 (Borosilicate Glass). BK-7 is considered inferior to BAK-4, but for most practical purposes, this should not matter. If you hold your binoculars up to the light, and look at the eyepieces from a foot or so away, the shape you see can tell you what kind of glass has been used for the prisms. BAK-4 prisms show a nice circular shape in the eyepiece. BK-7 prisms show a diamond shape in the eyepiece.

Mention must also be made of ED glass - this is Extra-low Dispersion glass, with virtually no chromatic aberration. It’s very good to have in a pair of binoculars, and also comes at a price.

In order to avoid stray reflections and scattering of light within the light path, binocular glass surfaces are usually protected by anti-reflective coatings. You might come across the terms Multi-Coated and Fully Multi-Coated in this context. Multi-coated binoculars usually have their objectives and oculars coated. The Fully Multi-Coated kind have anti-reflective coatings on all glass-to-air surfaces. FMC binoculars are preferable to the other kind, but are also more expensive.

Avoid binoculars with Ruby (or similar visibly red) coatings. These coatings work by filtering out the red parts of the spectrum, rendering them pretty much useless for astronomical use.

Binoculars come in two broad constructions - Porro-Prism and Roof-Prism. Porro-Prism binoculars are the most common kind. Roof-Prism constructions are supposed to have lower light losses. Between the two, Porro-Prism binoculars are definitely more cost-effective.

Stay away from zoom binoculars. Good zoom binoculars probably do exist - like the Nikon XL series. They are however, very expensive, and not easily available. Cheap zoom binoculars are bad. Stay away from them.

Using Binoculars

Most “beginner’s” binoculars come with centre-focus. In other words, both the optical tubes are focussed by a single knob which lies between them. If not centre-focus, the optical tubes can be focussed individually (Individual Focus). We will not worry about Individual Focus further in this article, since most beginner’s binoculars are centre-focussed.

When you look through a pair of binoculars, you should see one image, preferably crisp. You should also not feel any strain in your eyes whatsoever. In order to achieve this, it is good to try out the binoculars in daylight against a distant target, preferably something like a telephone pole or power line, that has both vertical and horizontal lines.

Adjusting the IPD

If you look through the binoculars and see two disjoint images, or if you can only see one eyepiece, you need to adjust the Inter-Pupillary Distance. Simply put, the distance between the eyepieces needs to match the distance between your eyes.

Binoculars usually have a central “hinge” about which you can “push” or “pull” the two optical tubes. Doing this will reduce or increase the distance between them. The idea is to adjust this distance (the binoculars’ IPD) until it matches your IPD.

How will you know if you’ve adjusted it properly? It’ll feel a lot more comfortable than when not. Ideally, you should also see a single image instead of two disjoint images.

Dioptre Adjustments

One of the downsides of wearing glasses is that it is impossible to look through most binoculars and see the full field while wearing your glasses. Some binoculars provide sufficient eye relief for eyeglass wearers, but most do not.

If this is the case, then the only option is to divest yourself of your glasses, and adjust the binoculars for your eyesight. Most binoculars have an adjustable right ocular for this purpose.

The procedure (best done at night) is as follows:

Look through the binoculars with only your left eye open. Preferably cover your right eye with a patch. If this is not possible, just hold the right eye shut. This is not ideal, but will suffice. Then, adjust the focus until you get a crisp image and pinpoint stars.
Patch/shut your left eye, and look through the binoculars with your right eye open. Twist the right eyepiece and achieve pinpoint stars. Do not turn the eyepiece through a large angle, make small adjustments.
Look through the binoculars with both eyes. If need be, adjust the focus. Do make a note of the position of the right eyepiece.

Collimation

If you’ve adjusted the IPD correctly, and have made the dioptre adjustments, but still feel some kind of eye strain, or see a “cross-eyed” image, then perform the following test, in daylight.

Look at a target that has both vertical and horizontal lines. Check that the horizontal lines are at the same level in both the eyepieces. In other words, you should only see one horizontal line. If you see a broken horizontal line, then your binoculars are out of collimation, and are best returned to the manufacturer. If you’re feeling adventurous and don’t mind voiding your binoculars’ warranty, read References 1 and 2 and proceed further.

Holding Binoculars

The “intuitive” way of holding binoculars is usually not the right way, in the sense that it becomes hard to hold them steady for more than a few seconds.

Holding the binoculars by placing your hands as close to the objectives as possible (without your fingers hanging over them) will provide more stability.

The author’s personal favourite is the “A-Brace” hold, described under a different name in 3.

Mounting Binoculars

Hand-Holding binoculars for more than a few seconds can be cumbersome. It is not much fun to look at stars dancing to form elliptical shapes. The solution lies in mounting the binoculars, so as to hold them steady.

Using a regular camera tripod to hold binoculars is not a good idea; this will result in much strain on the observer’s neck. A better solution is to instead use a monopod, preferably with a trigger-grip ball head.

One of the best binocular-mounting solutions is a Parallelogram Mount. This is probably the best way to mount heavier binoculars. One of the nice things about a parallelogram mount is that it can be hacked out of some plywood by someone with very little carpentry experience.

Reference 4 deals with binocular mounts in some detail.

Looking up through binoculars can be a pain in the neck, no matter the mount. To prevent strain on the back and neck, a (preferably reclining) chair is highly recommended. A chair and a monopod make for good binocular observing companions.

Image-Stabilized Binoculars

If you’re set on binoculars, but prefer hand-holding over mounting them, but do not want shaky images - despair not, there is a solution for you! It’s called Image-Stabilized Binoculars.

The author has no experience with Image-Stabilized binoculars, so what follows is gleaned from other sources - take it with a pinch of salt. This disclaimer will hold true until someone who’s experienced rewrites this section, which should happen sometime soon.

The idea is to internally move the binocular prisms to compensate for the motion of the holder’s arms. The mechanism to do so might be electro-mechanical, or completely mechanical.

Happy owners of Image Stabilized binoculars report that they are life-alteringly good. A small minority of users who are sensitive to motion-sickness, or suffer from borderline vertigo, claim that they are unable to use Image-Stabilized binoculars comfortably. As always, try it before you buy it.

There seem to be a few major vendors selling Image-Stabilized binoculars - among them, Canon, Fujinon, Zeiss, and Nikon. The Zeiss binoculars are mechanically stabilized, and don’t need power. The rest of them are battery powered.

References 5, 6, 7, and 8 cover Image-Stabilized Binoculars.

Big(ger) Binoculars

Binocular owners are not immune to aperture fever. Most are content with 10x50s, but some go on to own big(ger) binoculars. The biggest that can be hand-held, with some effort, (in the author’s experience) are 20x80s.

Bigger models, like 25x100s are also available. These need to be mounted, and cannot be hand-held. As the size increases, it also becomes difficult to synchronize the focusing motion of the two optical tubes. Hence, big binoculars are more likely to be Individual-Focus (IF) as opposed to Centre-Focus (CF). In other words, each optical tube has its own focusing mechanism, independent of the other - not unlike two telescopes mounted next to each other.

Reference 9 shows a few (representative) models of Big Binoculars, with pricing information.

What prevents us from getting hold of two identical telescopes, and making a binocular telescope? Nothing. Reference 10 shows several successful BTs made from pairs of regular telescopes.

What to buy, and how

Firstly, fix your budget. As on this date (circa Oct 25, 2015 in Bangalore), the binocular budget buckets are roughly Rs. 5K, 11K, 15K, Motorbike-class, and Hatchback-class. There is some amount of overlap between the buckets, especially in the last two.

Secondly, decide how big you want your binoculars to be. The best binoculars for hand-holding are probably 8x40s. The biggest binoculars that you can hand-hold for short periods of time are 10x50s. Bigger binoculars, like 20x80s, give you better views (though some would disagree), but are also much heavier, and ideally need mounting. Most amateurs tend to start out with 10x50s.

Thirdly, please avoid ruby coatings and zoom binoculars.

Please note: the recommendations that follow are entirely personal opinions of the author, and may please be taken with a pinch of salt. They are not the gospel truth. If you find a better deal, and judge it to be a good buy, please go for it.

The pricing information below is merely representative, and is not accurate.

Around Rs. 5K: Olympus 8x40 DPS-1, Olympus 10x50 DPS-1
Around Rs. 11K: Pentax 10x50 PCF WP-II
Around Rs. 15K: Celestron SkyMaster 15x70, 20x80
Motorbike: Canon/Fujinon/Nikon Image-Stabilized binoculars, Binocular Telescopes
Hatchback: Zeiss 20x60 T* S Image-Stabilized Binoculars

The Olympus 8x40 is the easiest to hold, and can double as a good pair of birding binoculars. Ditto the Olympus 10x50, except that it’s a little heavier.

The Pentax is probably the best 10x50 for its price.

A word of warning about the 15x70s - please don’t buy them unless you can return them easily. Many people have complained that the binoculars were miscollimated out of the box. It earns mention here because the views through a well-collimated pair are truly amazing, and it’s the most affordable 70mm binocular here.

There are definitely other models available at around the same price points, which are not mentioned here. (Like the Nikon AE series). It was the author’s decision to mention only models which he has personally looked through. It’s not that the others are bad, just that yours truly has no experience with them. The situation is similar with the bigger and IS binoculars.

If your budget is bigger, or you are undecided, please post on the B-A-S list. We’re all too happy to help you spend your money :) All of these binoculars are available locally, except perhaps for the last 3 buckets. If you’re willing to import, or have a friend visiting from elsewhere, then your list of available choices increases dramatically.

As far as possible, buy your binoculars at a place that lets you try them before you put down your money. Sadly, the author is unaware of such a place in Bangalore as on the date of writing. The next option is to buy them at a place with a well-defined return policy, so that you can buy them, unbox and check, and return them if necessary.

Post-Purchase Checks

Check the binoculars for collimation. If they are miscollimated, return them.

If the binoculars say they are BAK-4, but they have BK-7 instead, return them. It’s not that BK-7 is bad - but you didn’t get what you paid for.

If you look at bright objects (like Jupiter or Venus) and see a purple hue around them, don’t worry. This is perfectly normal - unless you plonked down a lot of cash for a pair of ED binoculars. If that is the case, return them.

Look down the objectives (preferably with some lighting below), and check for dust inside the binoculars. If there is dust inside, or you see anything cloudy, return them.

Keeping them clean

DO NOT breathe on the objectives, or spit on them. A small amount of dust on the objectives is OK, and will not hurt. Keep human fingers (yours and others’) away from glass surfaces. DO NOT rub them with your shirt, undervest, or handkerchief.

Disclaimer Please read the manufacturer’s note before attempting to clean your binoculars. The recommendations below are given in good faith, but might not be the best way of cleaning binoculars. BAS and the author are not liable for anything that might go wrong by following this process - proceed at your own risk.

If you go birding with your binoculars, and you get pollen or tree-dust on the objectives, blow it away with a small air blower. A mechanical foot-pump (of the kind used to inflate bicycle or car tyres) works well for this purpose, as long as the nozzle is clean, and free of dust and grease.

To get fingerprints off the objectives, wipe them off very gently using a white soft tissue that has been made damp with distilled water. Do not use pressure. Discard the tissue after using it for two or three wiping motions. Use a sprayer to wet the tissue; if need be, squeeze off excess water so that the tissue is just damp. The process should not leave streaks on your glass. Do not use coloured or perfumed tissues, or tissue that is too stiff.