USING THIS PART FIVE, YOU WILL KNOW IF WHAT YOU ARE LOOKING AT IS ANY GOOD.THE CHECK LIST ASSESSES NOT WHAT YOU SEE BUT HOW WELL YOU SEE IT.

Print the check list because you will need to keep a score.

The check list deals only with the basic essentials. Have the listing on your monitor and what you should find out by asking the seller a question.

Give every relevant aspect of the listing a star rating as below and then follow the instructions here to get an overall star rating to produce a verdict along the lines:

minus star rating = don't even think about it.  

0* to 3*  =  a complete waste of good money. Leave it alone.

3.1* to 6*  =  not the worst of scopes but please don't expect miracles from it.

6.1* to 8* =   not bad quality at all and you will probably enjoy using it until you decide to upgrade.

8.1* to 10* = now you are talking about a real telescope that will give you pleasure.

Note:  3.2* = bordering on a waste of money  and      

5.9* = bordering on not bad quality. 

FIND OUT AS MUCH ABOUT THE TELESCOPE AND MOUNTING AS POSSIBLE AND THEN RATE IT item by item according to:-

Sales blurb.                                  Ignore completely .

Refractor or reflector                 Either will be OK

Dawes limit, star magnitudes and number of stars you can see    Ignore for the moment.

'huge' and 'professional'.           Ignore for the moment. 

MAKER

Meade, Celestron, Skywatcher, old Fullerscopes etc.    10*

Chinese Phenix refractors imported and sold by skies_unlimited    8*

Other Chinese reflectors and refractors    0*

Odd scopes with Chinese and Japanese sounding names or no makers name or unknown name     0*     

Other makes           5*

Home made Refractor:  minus 100 stars unless maker is a telescope engineer. 

Home made reflector:  assess on the optics and mounting.

APERTURE : REFRACTORS

a)   less than 60mm  (2.3 inches)             minus 45 stars        

b)   60mm                                 1*

c)   80mm (3.1 inches)             5*

d)   90mm (3.5 inches)            7*                 

e)   4 + inches                         10*

APERTURE : REFLECTORS

a)  Less than 4 inches             minus 60 stars   unless it is an old 3.5 inch Questar with superb optics. Price will be at least $1000

b)  4 inches                              2*

c)  114mm (4.4 inches)           4*

d)  128mm (5 inches)             4*

e)  153mm (6 inches)              9*

f)  204mm (8 inches) plus     10* 

TYPE OF MAIN MIRROR

a)   spherical only

      f/ = 6 or less                       minus 150 stars

      f/ = 6.1 to 8                         minus  50 stars

      f/ = 8.1 to 9                         minus  20 stars

      f/ = 9.1 to 9.9                      0*

      f/ = 10                                 5*             

      f/ = 11                                 3*

      f/ = 12                                 2*

      f/ = 13 or more                  0*              

b)  parabolic                                                     5*

c)  parabolic and diffraction limited            10*

d)  Strehl ratio OF PARABOLIC MIRROR  (Strehl ratio is explained in a later Guide so just ask the seller what the Strehl is)

      0.980  to  0.989              10*    

      0.970 to 0.979                  9*

      0.960 to 0.969                  8*

      0.950 to 0.959                  7*

      0.900  to   0.949             minus 10 stars     

      0.800  to  0.899              minus 75 stars    

      less than 0.800               minus 125* stars

e)   no-one can say parabolic or spherical      minus 10 stars

f)    no-one can say what the strehl is              minus 15 stars         

g)   mirror is made from float (window) glass   5*

h)   mirror made from Pyrex glass                   10*   

 THICKNESS RATIO OF MAIN MIRROR (parabolic or spherical)

a)   1:9 , 1:8, 1:7, 1:6 etc             10*

b)   1:10                                          6*

c)   1:11                                          4*

c)   1:12, 1:13                                 0*

d)   1:14, 1:15, 1:16 etc                 minus 50 stars

e)   no-one knows                          minus 10 stars

 APERTURE RATIO of refractors and the parabolic mirror in the reflector (f/ number)

Refractors:  less than f/5        minus 60 stars unless costing £1000+ new. If so and from a reputable manufacturer, 10*

Refractors: between f/3 and f/8 supplied with Huyghens (H) eyepieces only,    minus 20*

Parabolic Reflectors:   Less than f/4.5      minus 60 stars unless from a very reputable maker. If so, 10*

f/4.5                          10* (wide field with long focal length eyepiece)

f/5 to f/6                   10* (short focal length)

f/7 to f/8                   10* (medium focal length)

f/9 to f/10                 10* (longish focal length)

f/11 to f/12                 8* (takes the highest magnification but image will be dim - depends what you want). Before selling it on Ebay, I had a mirror 6 inches aperture, one-sixteenth wavefront and 72 inches focal length only for lunar observation.

f/13 to f/15                 0*

f/16 and more          minus 15 stars   (image far too dim)

 TYPE OF MAIN LENS of a refractor

a)    Made of plastic                               minus 600 stars

       Made of optical grade plastic        minus 400 stars

b)    Single convex lens (glass)              minus 350 stars

c)    Cemented or air spaced achromatic glass doublet or triplet and no information about its correction          minus 15 stars

d)    Cemented or air spaced glass doublet or triplet very slightly under or over corrected           5*

e)     Fully corrected main glass lens, doublet or triplet, cemented or air spaced          10*

 EYEPIECES  Meade, Celestron, Skywatcher (sometimes called lenses or oculars by Ebay listers), that is, only good makes

a)    0.96 inches                                         2*

b)    1 1/4 inches (32mm)                        10*

c)    2 inches                                            10*

d)   Erfle, Orthoscopic, Plossl               10*

e)   Kellner   (K)                                       6*

f)    Ramsden, modified Ramsden   (R, MR, SR)        2*

g)   Huyghens  (H)                                   0*

For, unbranded eyepieces or eyepieces sporting an odd sounding name, reduce star ratings for eyepiece types above by 5*.

Suppose that there are various types of eyepieces in the listing. You will need to average the overall eyepiece rating as shown in the example at the end.

 MAGNIFICATION.  

Take the aperture in inches then multiply that by 30 and get an answer.

a)    if the listing states the maximum magnification as that figure you got or a bit less or a bit more with or without a Barlow lens              10*

b)   if the listing states the maximum magnification as substantially more with or without a Barlow lens            0*

[ this aspect attempts to check whether what is written in the listing is a complete 'con' on performance and quality ]

Some Ebay sellers say that the aperture in inches should be multiplied by a number higher than 30 to get maximum magnification.

An 80mm  f = 400mm  Skywatcher is a 3.1 inch. Multiply that by 30 and the maximum magnification is 93.

A 4mm Lanthanum glass Orthoscopic eyepiece without a fringe killer in very good seeing conditions gives a nice image at x100. If a Celeston x2 Barlow (silver red dot) is used, the image is degraded at x200.

For a 10 inch Orion mirror with a focal length of 47.4 inches, a strehl of 0.989 and an accuracy of 1/9.6 wavefront and the secondary mirror flat to better than 1/10 wavefront, the maximum magnification is 10 x 30 = 300. With a Lanthanum 4mm the image is fine at x303. With the x2 Celestron Barlow, the image is fuzzy and broken up.

It's all sales talk unless you live in a desert with no lights within 100 miles, when 60 times the aperture in inches is fine with top quality excellent optics. With the average Ebay scope, no chance.

ACCURACY OF FLAT MIRROR AND main parabolic mirror (not for spherical mirrors) in wavefronts of light

 a)    3 or more wavefronts      minus 200 stars    

       2 wavefronts             minus 70 stars

       1 wavefront              minus 35 stars    

b)    1/2                            minus 20 stars

c)    1/4                             8*

d)    1/6                            8*

e)    1/8                            9*

f)    1/10                         10*

g)   1/16                         10*

g)   no-one knows         minus 10 stars

If the accuracy of the flat mirror is not the same or better than the main mirror, deduct 8*.

FOCUSER : REFRACTORS:

a)   Plastic draw tubes (the type of focusing used when the ship’s captain spots the pirates)  - any fitting eyepiece   minus 200 stars

b)   Metal draw tubes – any fitting eyepiece         minus   20 stars

REFRACTORS AND REFLECTORS:

c)   Plastic rack and plastic pinion with plastic eyepiece holder – any fitting eyepiece                                              minus 100 stars

d)   Plastic rack and metal pinion with plastic eyepiece holder any fitting eyepiece                                               minus 150 stars

e)   All metal construction taking only 0.96 inch eyepieces             0*

f)    All metal construction taking only 1 ¼ inch eyepiece               8*

g)   All metal construction taking 2 inch eyepiece and with a reducer for 1 ¼ inch eyepiece – rack and pinion or helical           10*

h)    All metal Crayford focuser          10*

i)     Motor driven focuser                   10* 

NEWTONIAN TUBE – mounted equatorially

a)   compressed cardboard of the ‘Sonotube’ type        minus 100 stars

b)   metal                   6*

c)   unventilated hard plastic (pvc)          8*

d)   for a tube of diameter 10 inches plus and 42 inches plus long, metal or plastic with at least three wooden rings firmly stuck or screwed to the inside for support and vibration deaden    10*

e)   ventilated            10*

f)   any tube not painted dead black on its inside – you should strip out the optics and buy spray cans of black primer and dead (photographic) black paint  -    ignored for star rating

g)   outside of tube of a colour other than silver or white will absorb heat and should be repainted if tube currents are evident  -  ignored for star rating

NEWTONIAN TUBE – Dobsonian mounting

a)   Manufacturers compressed cardboard tube       6*

b)   The same star ratings as in the previous paragraph for all other tubes.

 MOUNTING

Dobsonian. OK if you do not wish to image

a)    if the bearings are low friction ptfe to shiny formica with no impressed pattern on its surface                                  10*

b)    if the bearings are ptfe to ptfe (it sticks)                0*

c)    if the bearings are metal to metal (it sticks)           0*

d)   if the bearings are polished metal to ptfe                7*

 Alt-Azimuth. OK if you do not wish to image                5*

 Equatorial (German and fork)

a)    with no setting circles and no pole star scope and no slow motion drive    6*        

b)    with setting circles and no pole star scope but with slow motion drives    8*

c)    with setting circles, slow motion drives and pole star scope    10*

d)    with setting circles, slow motion drives, pole star scope AND drive AND/OR GoTo    10*

e)    for the German, if no counterweights supplied or are an optional extra, deduct 4*

 Tripod and pier:

a)    More than two section telescopic legs      0*

b)    Two section telescopic legs                        9*

c)    Telescopic legs are thin-walled (like 1mm or less)         1*

d)    Telescopic legs are thick-walled (like  2mm or more)   8*

e)    no-one willing to comment on wall thickness     0*

e)    Telescopic legs are not braced        minus 5 stars

f)    Telescopic legs are braced even by an accessory tray    6*

g)   Telescopic legs are aluminium (aluminum)       5*

h)   Telescopic legs are stainless steel      10*

i)    A pier with steel tube and three feet        10*     

h)   Table tripod               minus 5 stars

 ADD UP THE NUMBER OF STARS AND DIVIDE BY THE NUMBER OF ITEMS YOU PUT THE STAR RATING AGAINST. THAT WILL GIVE YOU AN AVERAGE STAR RATING THAT MAY NOW NEED TO BE ADJUSTED.

It goes without saying that the star rating given is from my personal opinion and others may well disagree. However, any sort of assessment is better than nothing for those who lack the experience of what these sort of advertised things will do and how well they do it.

 Having now got your average, make an adjustment like this

a)      the listing is for a reflecting scope with an aperture of 10 inches or less but it is stated to be 'HUGE'. Deduct 1* from your result because it is likely that the seller is overstating everything.

b)      for a 18 inch aperture or less, the listing calls the scope 'PROFESSIONAL'. Deduct 2* from your result for the same reason. A 36 + INCH SCOPE IS A 'PROFESSIONAL'. An observatory may have an odd 18 or 24 inch kicking around for quick and convenient use before programming the big one.

c)      for an aperture of 20 inches or less, the listing says 'HUGE' and 'PROFESSIONAL'. Deduct 3* from your rating.

d)      mention of Dawes limit, star magnitudes and the number of stars you see, deduct another 1* from your rating.

The reason for this last adjustment is that it pads out the listing and if the seller has anything good to say about the quality of the scope, it should not be about something that is common to all scopes of the same aperture.

e)    If the listing states that this scope is ideal for say, seeing the planet Saturn (and it is a refractor with an aperture less than 100 inches or a reflector with an aperture less than 500 inches) and in the listing is a NASA photograph of Saturn and its rings in very great detail, beware. The photograph is likely to have been taken by a Voyager probe and sent back to Earth. There is no way such a photograph could be imaged through an Ebay telescope unless you need a flatbed truck and heavy lifting equipment to transport it. Deduct 4 stars.

 Now set  your final rating against what it means near the start of this chapter to produce a verdict.

 TAKING A VIEW

IF THE OPTICS PRODUCE A LOW STAR RATING, LEAVE IT ALONE. IF, FOR EXAMPLE, THE TRIPOD PRODUCES THE LOW STAR RATING, IT IS ALWAYS POSSIBLE FOR YOU TO BUY THE KIT AND REPLACE THE TRIPOD WITH A GOOD ONE. THE SAME FOR EYEPIECES, ETC.

If there is no way the Ebay shop seller can give you or is willing to give you the strehl, wavefront accuracy, etc., search the net for reviews of that scope.

If there are no reviews, assume the worst. After all, if the optics were good, quality would be very high in the listing.

AN EXAMPLE OF RATING A TELESCOPE FROM THE LISTING IS GIVEN AT THE START OF PART SIX.