CONGRATULATIONS. YOU WON A TELESCOPE AND HAVE DONE SOME OBSERVING. THING IS, YOU WOULD LIKE TO MAKE THINGS EASIER ON YOURSELF, SEE SOMETHING BETTER  OR WHATEVER.

This PART explains the use of common accessories. After studying it, you will be able to decide on which to spend your money, if at all.

You want to extend the use of your telescope and mounting. What is available, how much will these things cost, are they worth it and what will they do?

What follows is a list of accessories, but there is no order of importance because your choice is individual and the list is not exhaustive.

REFRACTORS

1.      Your scope will come with a STAR DIAGONAL. This is a right-angle 'viewfinder' that plugs into the focusing tube and then you put your eyepiece into the diagonal so that you look down into the eyepiece at all times - more comfortable when the scope is pointing upwards. If the scope is a good make but you have no diagonal or the diagonal you have is under suspicion as to quality, there are two designs of diagonal you can buy.

One has a surface silvered mirror to turn the light path through 45 degrees (good for terrestrial use) or 90 degrees (good for astronomical use) and the other has a prism to do that.

Which you buy depends on personal preference and prices. If you are an avid Moon observer, there is plenty of light available, so it does not really matter if you lose light by absorption when it passes into a thick glass prism. If your passion is deep sky objects, you may prefer the surface silvered mirror because the reflectance of it should be in the order of 86 percent (ordinary silvering) or 97 percent (HiLux coating) with no absorption.

Anything on Ebay for £12.50 to £25 is likely to have a prism in it. Be careful of diagonals where the postage costs more than the thing itself. A mirror diagonal should have its mirror ground to an accuracy at least that of the main front lens, say one-quarter wavefront or better, otherwise, what is the point?

An ERECTING PRISM put into the eyepiece end of the scope converts the telescope into a terrestrial by turning the image the right way up. The cost of these on Ebay should be something like £25 for a good make, used and in good optical condition.

2.      The BARLOW LENS is a tube with a lens combination in it. It goes into the focuser and then, you put your eyepiece into the end of the Barlow.

The effect is to increase the magnification by the factor printed on the barrel of the Barlow, either x2 or x3. So, a scope working at x60 will work at x120 using the same eyepiece with a x2 Barlow lens.

The big 'BUT' is that if the scope is working at f/10 at the lower magnification, it will work at f20 using a x2 Barlow or f/30 with a x3 Barlow lens, something that sellers accidentally forget to tell you.

Be prepared to spend up to £40 for a good make in good used condition. Why have nice optics in the scope and eyepiece and then rubbish the system with cheap lumps of glass?

At f/30, your observations will be confined to the Moon and not planets. Whilst it might be nice to have a x3 Barlow, you won’t be using it as much as you would use a x2. In turn, the x2 will not be frequently used especially if you plan the focal lengths of your eyepieces to give sensible magnifications.

3.      The most common FILTER is the Moon filter. That screws into the threaded one and a quarter or two inch eyepiece and reduces light from the Moon and increases the contrast between the light and dark areas you see. The cost of a new Meade one and a quarter inch Moon filter is about £18. Celestron Moon filters are a bit less expensive and Baader filters look good as well.

A word of warning. The Moon reflects light from the Sun. In fact, all planets and their moons do that which is the reason why we can see them. A Full Moon reflects a lot of sunlight and you should use something a bit darker than an ordinary Moon filter, not only to see features but to prevent any damage to your eye. I’d suggest adjustable cross polarizing filters.

Coloured filters that screw into eyepieces are advertised as individual filters or a boxed set of filters. Just make sure you are not paying £40 for the aluminium case and £5 for six filters. Read a book and get to know what these filters do and decide how important they are to you. Please do not confuse these filters with a filter wheel to be used with a CCD imager because they are definitely not the same things.

Light pollution filters remove yellow street lighting 'fog' in the sky and new ones cost in the region of £85 upwards but on Ebay, you should be able to pick one up for around £40. These do cut down the total amount of light reaching your eye as do all filters.

For the Sun, BE VERY AFRAID of screw into the eyepiece black filters or much worse, the black filter supplied with some Russian telescopes (notably the TAL) that slips over the end of the eyepiece a few mm from your eye. Heat build up on the filter will likely give you an eyeful of shattered filter material and a retinal burn. It was designed by a total idiot and those who have one should immediately destroy it.

If you decide on a refractor, it may need a minus violet filter screwed into the eyepiece for some objects. Don't panic. Unless you are willing to pay $3000 + for the same thing from Astro-Physics, Televue or Vixen, you will get colour fringes to some extent or other.

Many sellers, private and shops, innocently and mistakenly think that fringe killers turn your achromat refractor  into a 'semi-APO' scope. Never mind what APO means, just say that it is an excellent feature. That is not the case but these will definitely improve the image but sometimes with a slight yellow cast that is very easy to live with.

The specialised solar and nebula filters DO NOT keep the light and heat of the Sun away from your eye. They go by the names 'Hydrogen alpha, Oxygen III' and others. These filters screen out all wavelengths of light except what they allow to pass through them. If you are considering these filters, buy a good make and they will not be cheap.

Polarising filters can be purchased as singles or doubles in a barrel. Meade made a good one where one can be rotated and the other is fixed to get cross polarisation. These filters improve contrast but cut down the amount of light reaching your eye.

4.      Even small telescopes have a FINDER. The trouble with finderscopes is that though they have a magnification of around 4 to 6, at night, it is almost impossible to see the black cross-hairs against a black background. It would not be worthwhile to take the finderscope to pieces to try to introduce a light that would illuminate the cross-hairs, trust me, I've been there.

A good and more efficient and much easier thing to use is a red-dot finder. This is a small device you attach to the telescope tube that projects a red dot onto a piece of glass or good quality plastic. You adjust the thing itself just like you would a finderscope. Then, what you see in the sky through the piece of glass having a dot of red light over it should be exactly what the main scope will pick up.

Those who use a red dot will tell you that without any magnification that narrows the field of view, placing the red dot on a star doesn’t necessarily mean that what you aim at is what you will see. What you aim at will probably not be in the eyepiece of the actual scope but will be near. The  red dot finder has a magnification of x1 and the field of view is not narrowed down as with a finderscope.

The best finding mechanism is a finderscope with a magnification of x4 to x6 with either illuminated cross-hairs or a finderscope that takes a one and a quarter inch eyepiece that has cross-hairs built into it that are illuminated. One of these will cost and is probably not a justifiable expense for a beginner who should stick with a red dot.

Prices vary, but buy what seems to be good quality and inexpensive. You do not need excellent optical qualities as long as the thing itself has full adjustment. On ebay, pay up to £20. With luck, you can use the same screw holes in the main scope tube to attach the red-dot finder mounting bracket in place of the finderscope.

 REFLECTORS

You will not need a star diagonal.

For Barlow lens, filters and the red-dot finder, the same applies.

In a previous guide, collimating a Newtonian reflector was mentioned. An easy way to do this is by buying a LASER COLLIMATOR that fits into the scope instead of an eyepiece. It projects laser light from the focussing tube, off the secondary mirror, down to the main mirror, back up to the secondary mirror and onto the screen of the collimator. All you do is turn the scope adjusting screws until both beams line up. Keep a spare set of batteries. They do not last long and messing about with the laser the first time will quickly exhaust them. DON'T LOOK DIRECTLY INTO THE LASER LIGHT OR YOU WILL GET A SPLITTING HEADACHE.

Thing is, your collimator has to be correctly adjusted. That involves adjusting its three small hexagonal bolts so that when you have your laser collimator in a V-block and you rotate it, the laser spot 7 meters away does not rotate in a circle more than 10mm diameter. The price of new laser collimators on Ebay is around $40 and in the UK, around £57.

MOTOR FOCUS is having a focuser that racks the eyepiece in and out using an electric motor.  Normally, you have to buy a focuser with a motor already built in, although converting a manual focuser is not difficult.

You will need a motorised focuser if you are imaging, otherwise, twisting the focusing knob with two fingers is the done thing if you have eyeball to eyepiece.

A good motorised focuser will cost anything from £85 upwards, but more like £200 or so new, especially one very accurate American make.

With the help of Beacon Hill, I have fitted an old reversible geared motor from a broken photocopier to my Orion focuser running from one AA battery. It engages and disengages by hand using the rack and pinion from a photographic bellows unit. Cost? Very reasonable. The direction of focusing is controlled by a DPDT marine switch bought on ebay for $6.35. The gearing you will need turns the focusing knob one revolution in something like 1 to 2 minutes or the speed can be controlled using voltage.

A HARTMAN MASK is no more than an mdf or metal disc that covers the whole aperture where the light enters the tube. There are several designs and these masks are used for accurate focusing. The mask has two holes in it or two holes and a triangle cut out of it, or some other combination. The holes (about 1 to 2 inches diameter) produce two images. When you focus, these images come together and then overlap. Once overlapping occurs, the scope is focused. I have seen only one Hartmann listed on ebay for a 12 inch tube and at a starting price of £40. I got a 6mm thick mdf disc turned and two holes and a triangle cut and was charged £10. All that it needed was a coat of primer paint and then a couple of coats of matt black.

ALT-AZ AND DOBSONIAN MOUNTS

To be honest, I would not try to improve on an alt-az mounting because they do not lend themselves to any purpose other than going round and round as well as up and down. Celestron make a 60mm refractor on a computer controlled alt-az mounting and you will never get your alt-az to do anything like that. In fact, if that is what you want, it will be far cheaper to buy that Celestron rather than trying to convert such a mounting.

For Dobsonian mountings, on the market are two things. One is computer control that tracks an object in the sky. You still get eyepiece image rotation. The other device converts a Dobsonian into an equatorial mounting. These are the electrically driven platforms on which you stand the Dobsonian. They go by various names including the 'Poncet platform'. These can be very expensive and it is probably much cheaper to buy a good equatorial mounting.

 EQUATORIAL MOUNTING

Unless your equatorial already has motor drives, a dedicated DRIVE for both axes by the manufacturer of the mounting you have is useful provided that your mounting is a good one. Please try to avoid the temptation of buying an equatorial drive unit and then try to make it fit your mounting unless you have access to a well-equipped machine shop.

If the manufacturer has not provided a POLAR TELESCOPE for your mounting but offers one at as an optional extra, that is worthwhile provided that your mounting has the facility to fit it. That telescope is a low power scope that goes inside the polar shaft of your mounting. You use it to get the polar axis accurately lined up with the North Celestial Pole because the Pole Star is not at the North Pole but about the width of the Full Moon away from it. Just follow the instructions and all should be well.

PHOTOGRAPHING THROUGH THE TELESCOPE

Prime focus photography is replacing the eyepiece with an SLR camera body loaded with fast film and focusing until you see a focused image in the viewfinder. Then, click the cable release.

For this, you will need an adapter to join the eyepiece holder to the camera body. You may need a T-mount for your camera.

With practically all SLR bodies, you will find it difficult to focus because of a very dim deep sky image. Barry at Beacon Hill has a service where he will grind a section of your camera pentaprism to make images clearer.

Eyepiece projection photography involves using an attachment that first takes an eyepiece and then the camera body, the whole lot then being shoved into the focusing tube. The light hits the eyepiece that then focuses a much enlarged image onto the film plane.

If you ever see a 'cold camera' advertised on ebay, give it a miss unless you collect antiques.

Photographic film has the feature that there comes a point where you pour even more light on it and nothing further happens. That rejoices in the name of 'reciprocity failure'. This feature can be reduced if the film has been treated (gas hypersensitized) or is cold (around  minus 15 degrees Celsius). A cold camera takes a load of one frame of film (do it in a light bag) and a compartment of it is filled with dry ice (solid carbon dioxide) that you must handle using thick, insulated gloves - provided that you know where to buy dry ice. You really don't need the hastle.

DIGITAL IMAGING THROUGH A TELESCOPE

This can be done in a few ways. The easiest and cheapest is to hold your digital camera against the focusing tube or put in an eyepiece and do similar whilst looking at the camera LCD screen.

The next step up is to use a custom made or universal attachment so that your digital camera fits into the scope much the same as a SLR camera body.

Up a notch is a CCD imaging camera. There are many on the market and some of the best and reasonably priced are made by Meade - the planetary imager and the Deep Sky Imager. These plug into your pc and store overlaid images ready for printing. The DSI will produce colour images whilst the planetary imager is a monochrome camera.

If you want to film what the scope is 'looking at' in real time and record it as well, there are astro video cameras that are ultra-sensitive (0.01 lux). Brand new, be prepared to pay £500 for a reliable piece of equipment that is not just a glorified CCTV camera.

EYEPIECES

For the different types of eyepieces, how to recognise them and which are worthwhile, please see previously.

Whether you are replacing not very good eyepieces or adding to your range of focal lengths (and therefore magnifications), do buy a good make and not a make that no-one has heard of sporting a fancy technical sounding name.

As you already know, eyepieces are sold by type and focal length. Please do not buy an eyepiece 'less' than a Kellner. As to focal length of the eyepiece, decide on what magnification you want and then divide the focal length of the mirror or lens by the magnification you want. That will give you the eyepiece focal length to buy.

Zoom eyepieces are on sale on ebay. These are not usually advisable for astro observations as they have too many glass lenses each of which will absorb light. For terrestrial use, zoom eyepieces are exceedingly convenient. If you must have a zoom eyepiece for astro use, buy one of the good makes that brand new costs in the region of £200 to £350.

On Ebay there are electronic eyepieces for sale and I have no experience with these other than a Meade Deep Sky Imager that plugs into a pc. These things plug into a TV and look like a very affordable 'scaled down' version of the much more expensive real time video cameras but with less pixels and therefore less resolution. They should be OK for views of the Moon but don't expect to record deep sky objects.

Binocular eyepiece holders plug into the focuser and take two perfectly matched identical focal length eyepieces. You use the binocular just like binoculars, viewing with both eyes. Of course, you will need double the number of eyepieces and good binocular eyepiece holders can run at something like £250 to £450.

FOCAL REDUCER

Take a telescope working at f10 and put a x0.5 focal reducer into the system and it will now work at f5. It works opposite to a Barlow lens. Which should you buy, an f5 scope and a x2 Barlow or an f10 scope and a x0.5 reducer?

The Barlow will narrow the field of view. The reducer widens the field of view. I have seen reducers that widen the field to the extent that when you put in an eyepiece, you see a smaller circular image of the sky because you are also looking at the blackened inside of the tube which is out of focus, all because of the wide field. That is called vignetting and you will not get that with a Barlow.

The plus point to all of this is that if you buy or already have one of the good makes where the maker sells a reducer designed and made for that particular telescope, you will get no or very little vignetting. That sort of quality of optical design comes at a price.

SOMETHING TO THINK ABOUT

Let us suppose you go to a shop (ebay or High Street) wanting a Froligit. There are several made by different manufacturers. The cheapest is £12.50, the next is £30, the next is £90 and the top of the range is £140. You avoid the cheapest one and go for a 3 inch Super Froligit for £30. Now take some reasonable figures.

The retailer has a mark-up of 30% and so the retailer buys in the Froligit for £20.

He gets that from the wholesaler who has a mark-up of 20%, so the wholesaler buys in from the UK distrubutor or manufacturer for £16.

The manufacturer needs his profit after all manufacturing expenses paid, so let's call that 45%. Then, the actual cost of the parts, the glass, the lenses, the focuser and everything else is £8.80.

I am not saying that these people do not deserve their profits. What I am asking is what do you expect from a piece of equipment whose parts, cost of labour and overheads cost just £8.80 which is about the cost of a cup of coffee and two packs of sandwiches at a motorway (freeway) service station?

PART ELEVEN TALKS ABOUT UPGRADING.