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Message: <blockquote data-quote="billb9430" data-source="post: 3332100" data-attributes="member: 98032">I gave one of the little Bresser scopes to each of my two sons and their families. With 4 grandkids and the eldest just 9, I thought the low cost, rugged scope should be ideal for beginners. I also bought one with the idea that it could ride in my car permanently, so as to be available whenever needed. I would not do that with a better scope, but for $40, there's not much risk. Here are some things learned about the three scopes I had:1.I took out the eyepiece and held a bright flashlight at an angle in front of the eyepiece field lens (this works best at the 15x setting). All three eyepieces had varying degrees of "specks" visible inside. Whether it is dust between the lenses, small bubbles in the cementing, or coating imperfections I cannot tell. One scope had very little of this, but the other two had more. In no case was this visible during normal daytime viewing. I have not tried the scope on a bright star - that might show something. l gave the two best scopes as gifts. 2. Now some good news. I've been able to make two adapters to increase scope utility. The first adapter is to convert the zoom to use in 1.25" standard focusers. The threading on the bottom ring of the eyepiece is metric, 0.75 mm pitch. Attached to this adapter, the zoom will come to focus at infinity (though just barely) in my Pentax PF65EDiia and gives a decent image throughout the power range. It also works in my astro-refractors, but I have little use for a zoom there. The OTHER adapter is much more useful and interesting, since it allows several wider field 1.25" fixed FL eyepieces to be used with the spotter. Similar to the adaptation of 26mm 2" eyepieces to Pentax scopes, on this one, several 1.25" eyepieces have lower barrels that can be removed and present a short, male threaded section a little over 28 mm in diameter, threaded metric, 0.60 mm pitch. Some eyepieces like this I've found are the 20 mm SWA (from Agena and Garrett), the Agena 15 mm SWA, and "Flat Field" eyepieces of 27mm, 19 mm, 16 mm, and 12 mm, branded variously Smart Astronomy and BST. All of these give a much larger AFOV than the zoom at any setting. The views through these eyepieces are pretty nice and since the focus in this scope moves part of the objective, no focusing problems arise. This of course eliminates any problems that might come up with the zoom lens imperfections mentioned above. I made the adapter by knurling the outside of a 2" diameter disk  1/2" thick. The top is bored and threaded to take the eyepiece bottom threading and the bottom of the disk bored and threaded to fit on the scope eyepiece port. See three attached photos of this adapter. 3. Now for some not-so-good news. Since the zoom is labeled with power rather than eyepiece focal length, it cannot be easily used to measure objective focal length using the idea that scope magnification is the ratio of the entrance and exit pupils AND ALSO the ratio of objective focal length to eyepiece focal length. But now with some known FL eyepieces usable with the adapter, this method should work. My first measurement with the 16 mm FF yielded a 2.2 mm exit pupil and using the 27 mm FF the measurement was 3.7 mm. I used 60 mm as the entrance pupil (objective diameter) and so calculated the objective focal length to be 436 and 438, respectively.  With two place precision measurements, F = 440 mm. Unfortunately, a glance at the scope and a meter stick confirms that this measurement is not even close to being correct! Based on the physical length of the scope, the objective FL must be more than 300 mm but cannot be over 400 mm! What's going on?Peering through the empty eyepiece port, I discovered that the whole of the objective is NOT visible from the eyepiece position. There is apparently a stop that limits the aperture of the scope to less than its 60 mm objective lens diameter. I recalled the "flashlight test" for aperture that was developed and used a lot on the Binocular forum of Cloudy Nights website, so tried that. Using that test, the effective aperture at which the scope operates is 44 mm! Plugging that back into the entrance-exit pupil relationship and recalculating gives objective FL of 320 and 321 mm respectively. Based on the claimed scope power, the corresponding zoom FL would be 21 mm  to 7 mm. There may be some variation among scopes, so you might want to recheck with your scope, but my three were all pretty close. If these measurements and observations are correct, the little Bresser scope still turns out to be a good bargain for the money - for a knockabout or beginner's scope - but perhaps not the absolute STEAL that it first appeared to be. I hope to take apart the zoom eyepiece to see just what caused the "speckling" and whether it can be cleaned up or fixed - or not. Doesn't look like a fun task since it is obviously not designed to be taken apart by the user. If you were lucky enough to buy one of these scopes at the closeout sale price, I hope you enjoy it, despite the few shortcomings listed above. I'm pretty happy with mine, as are my grandkids. - Bill</blockquote>

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