Re: Mount recommendation for TEC 180FL with FLI 16803 + FW #Mach2GTO


Bill Long
 

Why would you not consider the dew shield in the length? For critical imaging application a single *cable* and its location is something considered (not only for snag purposes) so a heavier piece of metal on the front of the scope is important not to forget as well. 

There is no free lunch in imaging at all. Consider everything, double check everything, dot all your i's and cross all your t's... etc etc. 


From: main@ap-gto.groups.io <main@ap-gto.groups.io> on behalf of Terri Zittritsch <theresamarie11@...>
Sent: Wednesday, May 20, 2020 4:17 AM
To: main@ap-gto.groups.io <main@ap-gto.groups.io>
Subject: Re: [ap-gto] Mount recommendation for TEC 180FL with FLI 16803 + FW #Mach2GTO
 
On Tue, May 19, 2020 at 06:11 PM, uncarollo2 <chris1011@...> wrote:
I am guiding and doing unguided imaging with an AP160 scope (27lb tube) which has 1200mm focal length. The scope is quite robust with a heavy 4" focuser. Overall system length with extended dewcap and camera is 58", weight I'm guessing at around 48 lb (which includes the camera and dovetail system). The scope is balanced with 64lb worth of counterweight and counterweight bar. The mount is on a very light weight Losmandy tripod, which is definitely not recommended for serious imaging, but it works for me in the observatory. I have measured damping times of between 1.5 to 2 seconds, depending on where the scope is pointed. Most of that is because of the tripod which torques and twists pretty easily. The mount guides this setup quite easily and doesn't really tax anything. The weak link is of course my tripod. If this setup were mounted on a concrete pillar, the damping times would most likely be less than a second.
 
I have not seen a TEC 180, don't know the dimensions and weighs involved. I suppose if it is used with a robust tripod or pier, the mount would have no problem slewing it around. The bearings are heavy enough to hold any kind of weight, and normal tracking doesn't really stress the gear teeth. I would lower the max slew speed to 1000x, down from 1800x. If the mount doesn't catch a lot of wind, it would most likely guide very accurately. I've imaged in gusty wind conditions with the 160 and had no problem guiding.
 
Just make sure there are no dangling wires off the back of the scope because that represents quite a bit of force at the gearwheel. Every ounce of cable drag is multiplied 10x at the gear teeth. A disturbance of 1 arc sec at the gears is only 0.4 microns of  gear wheel motion at the teeth.
Yes Roland, understand.  I did go out and measure the length of my own setup and estimated a 180mm at focus.  I don't think it's fair to include the dew shield in a length calculation of weight unless it was overly heavy, and the TEC ones I don't think are.   The lens cell is where the weight is on one end.    And I use lightweight CMOS cameras, not the FLI/SBIG monsters that I see some use.    But agree and suspect 50" is optimistic and maybe more like 52-54" for the 180mm (not including dew shield extension).
Maybe the 180 is more appropriate for a permanent installation anyway. 

Terri



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