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Hi, Can someone let me know the the difference between and pros/cons to Rack & Pinion vs. FeatherTouch focusers? Thanks! |
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| Bringing this back up to the top of the threads... anyone? |
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| I thought the Feathertouch focusers were rack and pinion vs the Crayfords which are not. |
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| Interesting... for example the William Optics FLT 156 comes in two options... rack and pinion then feather touch, which is significantly more expensive. |
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| I can say from experience that the feather touch focusers are very high quality. |
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| Gotcha! Perhaps it’s just a higher quality focuser when it comes to WO scopes. |
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Rack and pinion focusers are the ones that there is a linear geared bar on the focuser tube, and a round gear is attached to the knob. These focusers do not slip but can come from the ultra-cheap plastic quality of Skywatcher 80/400 doublet to the precision of Feathertouch. If this focuser is not constructed properly then it has a lot of backlash between the teeth. The "Crayford" focusers, do not use any gears to move the focuser. They have a flat bar of metal, without any oil or grease on it, on which the axle of the focuser knob is pressed hard, letting the friction do the job of the gear. If constructed properly (eg. Baader Steeltrak or Moonlite) they have minimal slippage (if any) but in cheaper Chinese implementations you fiddle with the screw pressing the axle, just to make it move with a fairly heavy load. In all cases, the technique used inside the focuser does not guarantee quality. It is the mechanical precision, which unfortunately for all of us is also reflected in the price, that distinguishes a good quality focuser from the rest. |
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Thanks for the info! Specific to the William Optics FLT, do you think it’s worth the extra $500 for the feather touch? |
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Feathertouch sells both R/P and Crayford focusers. See their focuser page for the options - the ones with the R/P suffix are rack and pinion: https://starlightinstruments.com/store/index.php?route=product/category&path=37 (hopefully I'm not breaking any rules by posting the link) If you're planning on imaging with the scope, which I assume is the case given that you're here on Astrobin, then I would prefer an R&P focuser. Bear in mind that the FT focuser are not threaded, so if you get a WO flattener and if they are threaded to match the stock focuser (which I believe that they are), then it may not attach properly. You should check with the dealer to make sure before putting money down on the focuser. I have a R&P FT focuser on my Newt and I love it. I am about to set up an AT152EDT where I stayed with the no-name Chinese R&P focuser that came with it, but I haven't tried it yet. The quality seems very good, but the proof will be in the photos. I'm just waiting for a part that is scheduled to arrive next week. Note - you can always choose to go with a FT focuser later if you don't like the performance of the stock focuser. You can order it straight from Starlight Instruments. You'll just give them (Wayne) the dimensions of your telescope tube, or even just the model itself, and they can direct you to the correct model. |
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The originaldesign of the Feather Touch focuser was intended to be used for Newtonian scopes and is basically a modified Crayford type focuser. The intent of the design was to be able to use a coarse and fine focus knob adjustment while focusing. All previous focusers, whether of a standard design or Crayford design did not have this feature, although it was common in the microscope industry. Feather Touch, specifically Starlight Instruments, Inc. (please note the Inc. not to be confused with the LLC) was the original developer and manufacturer of this type of focuser. There was an evolution in the design as is typical with most products, as the needs changed. The focuserwas greatly improved with the reverse Crayford design in that a hardened steel friction plate allowed the driving pinion shaft to press against four small ball bearings that rode against steel rails. This made the design much more robust in that the wear or high-pressure points were now hardened stainless steel unlike less expensive units that pressed against aluminum surfaces. This design change made the focuser very robust and care free and gave it the ability to lift significant loads without slipping.This designproved to be very popular and soon requests were made to use this type of focuser on refractors and SCT’s. For most applications this works without a problem and the 2” models had a limited lifting capacity around 5 pounds. For most applications this works without any difficulty and it is rare that something else is needed. As StarlightInstruments, Inc. further developed its focuser it caught the eye of Yuri Petrunin of Telescope Engineering Co. better known as TEC, the manufacturer of high-quality optics, specifically refractors. Yuri contacted Starlight Instruments, Inc. and requested the development of a 3.5” focuser to be jointly developed for the use on his refractors. The two companies worked very closely and the 3545 focuser was born. Since thefocuser required larger loads to be accommodated, a friction Crayford type design would be unsuitable and it became the obvious choice to go with a rack and pinion design. There are other advantages to this but for the most part it made the design more practical. This is not to say that a friction drive could not be incorporated in a larger focuser but there was a certain comfort level and practicality for going this route. Afterall, the philosophy of Starlight was to make the highest quality focuser possible. The fine focus mechanism on the larger focusers were also made larger to accommodate higher output torque of the pinion by the reduction assembly. In general, the pinion reduction assembly is somewhat proportional to the size of the focuser.Many other designsof the 2” focuser, 3.5” focusers, sizes in between along with micros evolved during the 16 years that Starlight Instruments, Inc was in business. When the owners of Starlight Instruments, Inc. retired in 2007, the business was sold to what is now known as Starlight Instruments, LLC. who over the years has continued to further develop the Feather Touch focuser. So, insummary, for Crayford type applications, a 2” Feather Touch is very useful and practical and a rack and pinion would only make the design more expensive when a simple friction drive will do the job just fine. A rack and pinion design is certainly a greatsolution, but it generally requires grease on the rack which is undesirable. For larger focusers, the preferred option would be a rack and pinion to allow for higher loads like a large camera, filter wheel, etc., that increases the demands of the focuser. However, keep in mind that most applications do not require more than a 5 pound load, so even a 2” will do the job for the vast majority of applications with the exception of some rare circumstances. Both designs, as with most designs have prosand cons. I hope this sheds some light on the topic, but not too much especially at night!Regards,Detlef W.SchmidtDesigner ofthe Feather Touch Focuser and founder of Starlight Instruments, Inc. |
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| Thank you! This is very useful info! |
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You're welcome and all the best, Detlef |
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Do these high-end focusers have a higher tolerance with slop when inserting/locking off a 2" camera/image train? I upgraded my stock focuser to a low-profile Orion so I could achieve focus on my Orion 8" Newt, but the 2" locking mechanism (brass collar) has some slop and requires some finessing to maintain collimation/alignment after rotating the camera for framing purposes. When I insert and lock off, the brass collar pushes against the imaging train slightly causing mis-collimation. My solution is to compensate for that movement when I laser collimate (not very accurate at all). Do these focusers have a better locking mechanism? |
