Search the Community
Showing results for tags 'bobs knobs'.
Found 2 results
My Celestron 5 Schmidt-Cass has gone out of collimation a few times, whether observing on my own or lending it to club members for astrophoto (I got to chose some targets as payback). That was always annoying, and always at the wrong moment, no matter how important or not the session was, because of the nasty allen collimation screws where you're supposed to put the key while watching something else. The key is easily misplaced in the dark, or forgotten, and it risks scratching the plate. My C5 has 24 knobs and levers but Celestron's designers stopped thinking about them when they decided what collimation means to choose. Bob's Knobs were good news until I read their price; 23 euros for three screws, shipping not included, that always slowed me down. But when they appeared at an 18€ price at First Light Optics, I finally ordered them thanks to a friend who has a PayPal account. Flawless transaction and delivery. First, their thread is made of steel, a magnet pulls them, nice. I wouldn't trust aluminum or plastic here. And their knob is scratch-resistant polymer, nicer to touch than metal when it's cold. They're very well made except for the rough tip. These screws pull with their thread, they don't push with their tip, still I don't like seeing that: After checking them against an original - stainless, nice touch! - Celestron collimation screw to make sure they can be shortened a bit without danger… ...I rectified the tips using the coarsest diamond-plated sharpening tool I own. Took a minute each. At 6€ a pop, I believe they should be presentable, even at the place I won't see. They were still a bit too long, but that's an advantage; they're easier to catch with the fingertips. Bob provides washers (four, the extra one was either a mistake or a backup) to fill the void: Once installed they look and feel good. Bob packed them in a paper bag, and First Light Optics sent them in an adequate lightly padded envelope, but I would find it safer to pin them inside a hard foam block like that: A Wrestlemania dude could stomp that screw from any side without bending it, but the foam adds only a few grams in weight. The leaflet tells all the do's and dont's of changing collimation screws on a single page, and especially to swap screws one by one to avoid letting the mirror fall inside the tube! And now, the result, you ask? After a few minutes to get used to their range of motion, I quickly reached a near-perfect alignment at 127x power... ...that I refined with the same ease at 266x power: That shot was made effortless thanks to Celestron's new NexYZ tri-axis smartphone adapter, and a 5-second delayed trigger. As an extra precaution the phone's sound was cut to prevent blurring caused by vibrations. The screws seem to be plated with a slick self-lubricating coating, they turn without a trace of binding or backlash, firmly but smoothly. I was a little afraid the 15mm head would be too small, but no, it has enough leverage to make very accurate adjustments. If you look closely, you'll notice the central dot is double on the second picture (visually it was like a miniature croissant). That's because the artificial star was a crude pinhole in aluminum foil, good enough for collimation but not for assessing optical quality! Star test and collimation are two different stories, if you use a homemade light source for a star test, unless it sits very, very far, you'll believe your Airy disk looks like an otter or a Ninja Turtle, you'll blame the telescope and maybe the seller and the maker. But my C5's Airy disks are fine, the scope is just resolving the rough pinhole since it's only six meters distant. The pinhole was reasonably round as seen through a magnifier but maybe because of diffraction and reflection on the aluminum, it looks double here. The new knobs don't hit the objective cap, they don't protrude outside the secondary housing, and they don't mismatch the looks of the front end of the scope. Except for their high price and perfectible tip finish, I like everyhing about them, especially how they make that crucial collimation job natural. After years of frustration, it's finally as trouble-free as it should have been all along.
The coming wet weather is the perfect opportunity to treat my baby to some upgrades and mods. My XT10i is to be pampered with: Telrad finder on a 4" riser Primary mirror cooling fan Protostar flocking Bob's Knobs on secondary Moonlite CR2 focuser Fingers crossed it all goes well and my baby will be even more wonderful. :-)