Robofocus for Tak Mewlon 210 - any feedback or suggestions - thanks.
I am considering a motorised focuser for my Tak Mewlon 210, mainly for astrophotography (Moon & Planets).
I understand that the optimal back focus for the Mewlon 210 is 105mm from the rear cell opening and can extend to 118mm maximum.
Motorised focusers such as units from Moonlite, Feathertouch, JMI, etc. really eat into this back focus, hence I am considering a Robofocus unit which will focus via a belt driving the Tak focus knob.
I would be interested to hear of your experience in using Robofocus, whether on a Tak or other instrument.
The Robofocus website sort of looks a little dated (mentions Windows XP, etc.) and was wondering if they are still relevant today.
My MK91 has similar limited backfocus as it has fixed mirrors. I replaced the focuser with a low profile Baader Steeltrack 50mm UNC one from TeleskopService, though doing this involved having a new backplate adapter machined by TS - which was at a very reasonable price I should add. The focuser has a pinion with clutch for a toothed-belt drive and I have the TS motor drive for mine - though currently not using it.
This gave a focusser travel of 25mm. If interested I’ll add a web link to the unit.
This issue for you to sort out is that these low profile focussers all assume the drawtube (probably 65-70mm outside diameter) can fit inside the backend of the scope anywhere from 15-25mm in order to provide the full travel. In my case 15mm.
This may or may not be possible on the Mewlon and you’ll have to dismantle the back to find out.
If the backfocus is close but not quite enough the other solution is to use the primary mirror adjustments to shift the mirror forward. Shifting the primary forward 0.7mm (1.0 screw turns) will shift the focus out approx 5mm.
Thanks for the replies Andy and Nick, I appreciate it.
I am trying to minimise the length of the optical path once the light cone exits the Mewlon tube at the rear cell, so I can remain faithful to the 105 – 118 mm back focus range as recommended by Takahashi.
105mm = optimal
118mm = maximum recommended
I read that the image circle at the Mewlon 210 native FL is 18mm and using the Tak x0.8 Reducer increases this to 39mm. To benefit from this, I assume you would need to place the sensor in the recommended 105 – 118 mm range.
If I install a motorised focuser at the rear cell, it would eat up over 60mm (even based on a relatively low-profile unit like the JMI Event Horizon) of back focus. Therefore, I am looking at the Robofocus unit that operates on the Tak focus knob and doesn’t introduce any additional components into the optical path.
I occasionally image with my Tak Reducer, Filter Wheel and Atik 414 EX camera and using this combo with a motorised focuser fitted in the optical path at the rear of the mirror cell, would push the imaging chip plane well beyond the 105-118 mm range that Tak advises. (I maintain a 56mm distance between the rear of the Tak Reducer and the Atik imager chip).
I had a Mewlon 210 and used a low profile Moonlite motorised focuser at the back. So not a robofocus but I do remember that I had only 15mm to 20mm of slack to play with within the recommended backfocus to fit everything in. I don't know about the reducer.
I had a Mewlon 210 and used a low profile Moonlite motorised focuser at the back. So not a robofocus but I do remember that I had only 15mm to 20mm of slack to play with within the recommended backfocus to fit everything in. I don't know about the reducer.
Thanks marc, I appreciate your reply.
As a picture is worth 1,000 words, here are 8,000 words showing what I am attempting to achieve.
I can keep within the 105 - 118 mm recommendation using the Tak 2 inch Adapter but if I were to replace it with a motorised focuser, I would breach this immutable law and incur the wrath of all Tak users.
A Robofocus or Pegasus Focuser which operates on the Tak EOM focus know via a belt should bypass this issue.
The only issue I would suggest is that the stock focuser has a little backlash when changing direction.
Thanks and yes - I have noticed a bit of backlash and also mirror movement when using a small chip e.g. ASI 120MM and a x1.6 or x2 Extender, although the target remains on the chip, so its not too severe.
You could clamp your robofocus off the filter wheel body?
Hi Marc
From the Robofocus website it looks like they provide a bracket with double side adhesive, so if I end up going down that path, I will just find an out of the way location on the back of the mirror cell.
I have a robofocuser on my refractor. They are an older design with serial comms etc but they are built like the proverbial tank. Mine has been very reliable and generates very repeatable focus points.
I think you could have made up a simple securing point attached to a circular clamp fitting around the TAK OEM 2” rear adaptor. Nice and secure and not impacting the integrity of the scope.
I have a robofocuser on my refractor. They are an older design with serial comms etc but they are built like the proverbial tank. Mine has been very reliable and generates very repeatable focus points.
I think you could have made up a simple securing point attached to a circular clamp fitting around the TAK OEM 2” rear adaptor. Nice and secure and not impacting the integrity of the scope.
Thanks Steve - that is useful information to help with the decision.
I assume the software stills works under Win 10 OS and that the USB to RS232 Serial connection is stable?
I have the USB/RS232 Serial Adapter provided by Wildcard Innovations (Gary) which drives my mount via The Sky X Pro.
I guess I will need 2 adapters; 1 for the mount, the other for the Robofocus unless I Open/Close Serial Ports as needed.
Hi Dennis,
There is too much mirror shift on my old u-210 to use the stock focuser when imaging or to bother to motorise it. I replaced the visual back adapter with a custom lower profile one and added a low profile Crayford focuser and motorised that. There’s a very long thread on CN that discusses this: https://www.cloudynights.com/topic/5...10-yes/page-15
IMO, that’s the way to go.
Hi Dennis,
There is too much mirror shift on my old u-210 to use the stock focuser when imaging or to bother to motorise it. I replaced the visual back adapter with a custom lower profile one and added a low profile Crayford focuser and motorised that. There’s a very long thread on CN that discusses this: https://www.cloudynights.com/topic/5...10-yes/page-15
IMO, that’s the way to go.
Thanks Jason, all very helpful and thanks for the link to CN, I'll take a peek.
The standard Tak OEM 2" Adapter takes up just over 50mm of back focus and I just removed it and replaced it with my JMI EV Motorised Focuser (from my C9.25) and it takes up some 75mm, which pushes me way beyond the Tak recommendation of 105-118mm with FW and Camera fitted.
Yes, software works well under Win 10 and the USB to RS232 connection is stable. I use the same Keyspan USB to RS232 adaptor supplied by Gary at Wildcard Innovations. Definitely, only use quality adaptors to ensure a stable connection.
I suspect using two adaptors will be a easier solution in your case.
Their website looks as though it has not been updated since launch many many years ago. Their manuals are comprehensive but also very dated.
Steve.
Quote:
Originally Posted by Dennis
Thanks Steve - that is useful information to help with the decision.
I assume the software stills works under Win 10 OS and that the USB to RS232 Serial connection is stable?
I have the USB/RS232 Serial Adapter provided by Wildcard Innovations (Gary) which drives my mount via The Sky X Pro.
I guess I will need 2 adapters; 1 for the mount, the other for the Robofocus unless I Open/Close Serial Ports as needed.
Yes, software works well under Win 10 and the USB to RS232 connection is stable. I use the same Keyspan USB to RS232 adaptor supplied by Gary at Wildcard Innovations. Definitely, only use quality adaptors to ensure a stable connection.
I suspect using two adaptors will be a easier solution in your case.
Their website looks as though it has not been updated since launch many many years ago. Their manuals are comprehensive but also very dated.
Steve.
Thanks Steve, I appreciate those additional details.
It is much as I suspected; a well designed, well-engineered and well-manufactured product can withstand the test of time, even though technology marches relentlessly onwards.
