Removing the "Trash" from a Trash Scope - Trash Panda :-)

[Rocket_the_Raccoon]

I bought this Celestron Travelscope 50 for $20CAD, primarily for the two 1.25" eyepiece barrels that I can scavenge for my DIY eyepiece projects. I have seen and used "bad" telescopes before but it was never as bad as this one. Though a 50mm f/7 achromatic objective should show minimal to undetectable chromatic aberrations (CA) according to the 1.22D rule, Celestron still put a ~30mm baffle in the tube and worst, a ~5mm baffle inside the focuser! One can almost call this a CA-phobic scope. To make this "trash scope" usable, first thing to do is of course removing the two baffles. The one in the telescope tube is easy to deal with and I would suggest removing the focuser to get access to this baffle instead of removing the lens cell (to avoid possible mis-collimation). The removal will leave some bare metal marks and they need to be repainted with flat black paint (I uses Tamiya XF-1 acrylic model paint). The focuser baffle seems to be moulded as one piece with the focuser itself but it is not. It is just a very tight fit and can be removed by "force" but one needs to remove the focuser first. This also exposes the roots of the two finder bracket retaining screws and thus serves as a good time for any finder modification. After that, the inside of the focuser barrel MUST be painted flat black as it is unusably shiny. To improve image contrast, the objective lens can be removed then have its edge darkened by a black marker. This can be done by taking out the hood and unscrewing the retaining ring without the need of removing the whole lens cell. As the objective lens is not exactly tight fit (horizontally) inside the cell, a narrow piece of chalkboard sticker can be placed between the lens and the cell wall to fill the gap. Finally, when putting back the objective lens into the cell, the 3 spacers between the two lens elements of the achromatic objective should be aligned with the 3 screws that hold the lens cell and the tube together. At this point, the scope has become much more usable than its stock form but there are other improvements that can be done.

          

The stock finder is basically useless. It is even worse than a 5x24. I have a DIY 21mm achromatic finder but unfortunately the bracket is too tiny to fit it. Given I have an extra Vixen-style dovetail finder bracket, I might just put it on the tube and borrow a finder from my other scopes but I don’t so I simply use a L-shape corner brace (left image above) to make a peep-hole. It is of course far from accurate but it is usable at very low power, with which the 360mm focal length of the scope and my DIY 33mm eyepiece (middle image above) can give. I have two other DIY eyepieces (right image above) and they are both good companions with this little 50mm. One is an 18mm “traditional” Kellner scavenged from an old pair of 10x50 binoculars. I think it is based on the original optical formula because it has pretty tight eye-relief for an 18mm and a relatively narrow field (still way wider than the two stock Huygens, of course). Another one is a 10mm 1-2 König scavenged from a pair of 10x25. I have another post written for this nice little eyepiece here:

With the above additional modifications on finder and eyepieces, the scope has now been improved to a point that any further advancement would require a new purchase. However, I just love the extreme portability of this scope so I might buy a cheap 1.25" star diagonal (as the scope includes a .965"-1.25" adapter, I do not have to buy a hybrid) just for it as I found the stock 45 degree hybrid, though not bad in quality, gives very odd viewing angles for anything 30 degrees above the horizon. Finally, to make an “one and for all” decisive improvement for this scope is to replace its .965” focuser to a 1.25” one. The AFOV of my 33mm eyepiece is not just now limited by the .965” focuser but also the 20mm opening of the hybrid diagonal. Having a 1.25” focuser and a full aperture star diagonal, the 33mm eyepiece would give a spacious 4 degrees of field.

     

As for the "mount", I replaced the included super filmsy tripod with my portable photo tripod. Because the scope is extremely light, the ball head tension can be tightened to point that it gives smooth motions. At 40x, it takes only ~2 seconds for image to stop vibrating. Below is a handheld cellphone photo of the moon taken through this scope using the 10mm 1-2 König.

[cuivenion]

Nice post. Regarding the baffles could it not be on attempt to limit reflections. From my admittedly meagre knowledge of optics the cone of light will narrow as it travels down the tube, so the baffles you mentioned may not be necessarily limiting it's aperture. It would depend on the placement of the baffles of course, and the size of the light cone at the baffle points.

[Rocket_the_Raccoon]

1 hour ago, cuivenion said:

Nice post. Regarding the baffles could it not be on attempt to limit reflections. From my admittedly meagre knowledge of optics the cone of light will narrow as it travels down the tube, so the baffles you mentioned may not be necessarily limiting it's aperture. It would depend on the placement of the baffles of course, and the size of the light cone at the baffle points.

Thank you, Cuivenion. You are right about the baffles. It is just an individual case that the two baffles of this scope has a severe "side effect" of limiting its aperture while not doing a much a job in limiting internal reflections. Of course, to be sure, one needs to do a trace diagram of the objective lens. ?

[Peter Drew]

My first thought as well.