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My 8-inch RFT - Some Things Old & New

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#1 Rustler46

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Posted 05 November 2021 - 10:28 PM

My home-made 8-inch reflector has been with me for some 54 years. It was a labor of love grinding, polishing and figuring its fast (for the 1960s) f/4.8 mirror. I spent more than 200 hours just in figuring. It was meant to be a wide, rich-field telescope (RFT), with short focal length optics. With an old war-surplus 32mm Erfle eyepiece it gave around 1.8° FOV - not bad for a 1-1/4 inch format.

 

Here's the RFT on its original mount back in 1967.

 

8-inch RFT-1.jpg

The mount shown is an early iteration of GEM that was featured in recent thread:

In the above photo the mount was just a basic polar axis with pillow-block bearings and declination axis with babbit bearing. At this stage it was not motorized nor adjustable for latitude. The telescope has a fiberglass tube made by a friend. It is heavy but functional.

 

The finder is an old military surplus M-17 tank sight, with a manufacture date of 1943. That 8X50 RACI finder is the oldest piece of the entire setup, beating my own 75 years. But it cost 16 big 1967 dollars from Edmund Scientific. Back then that company was the source for many ATM supplies like mirror-grinding kits. With such a kit they even supplied a set of lenses, for those wanting to fashion their own Ramsden eyepiece.

 

Now in late 2021 the primary & secondary mirrors just came back from getting new Beral coatings. The Clausing family has served in that capacity for the life of my RFT. While my 10-inch reflector has its mirror out for re-coating, I have been using the 8-inch RFT as my grab-n-go telescope. Well, it's not exactly quick setup. But is a different experience compared to my pier mounted Losmandy G-11 with SCT/APO rig or 10-inch push-to reflector. As I get older I really appreciate a go-to or push-to (DSC) setup. I have considered adding encoders on the RFT for a DSC setup. But that seems a bit out of character for a 1967 vintage telescope.

 

So what to do? Even with that old RACI finder, I don't relish the thought of  bending down to sight along one of its straight edges to point at the area of interest in the night sky. So here comes my latest addition - a new green laser. This was strapped along side of the elbow telescope with some wire ties and a block of wood.

 

8-inch RFT-02606.jpg

 

When I first tried out this arrangement, it worked fine - but only for a while. The cool nighttime temperature quickly lowered the battery voltage, causing a weak laser beam. This made it essentially unusable. My solution was to strap a dew heater strip around laser and finder tube.

 

Also I have been working on improving the thermal performance of my reflectors. The RFT will initially be using a small 40 mm fan to help with cool-down and boundary layer dispersion. This will require 12-volts to power both the fan and the dew-heater controller. 

 

But here is what I've come up with for powering the telescope. The loads are:

  • Old Lumicon Drive corrector to supply 110VAC to power the synchronous RA drive motor
  • Ventilation fan - 12 VDC
  • Dew-heater controller - 12 VDC

The drive corrector can be powered by a GFI mains electrical outlet at my garden observing site. But I would like to avoid an electrical cord under foot to trip over. In the past I've placed a small rubber-backed rug over the cord. Another option would be a small battery pack power supply. One that I have used on my 10-inch Dob is a TalentCell 12V LiFePO4 Battery Pack. This Lithium-Iron-Phosphate battery chemistry is reputed to be of longer cycle life than a regular lithium battery and much lighter than lead-acid batteries. It holds between 12.5 and 13.0 volts for 80% of its discharge capacity. The 12- and 5-volt outputs of the battery pack are handy. On cold nights the latter can keep my iPad Mini running SkySafari.

 

Screen Shot 2021-11-05 at 7.40.54 PM.png

 

The battery pack's 12-volt output can power the drive corrector via its 12-volt input. A single 12-volt power lead running up the mount to the telescope can power the fan and dew heater controller. So the battery pack and drive corrector can reside at the base of the mount. The dew heater controller is light enough that it can reside on the telescope itself. This will avoid having the controller down below with a second cable running up to the telescope.

 

8-inch RFT-02607.jpg

 

The above photo shows the fan, drive corrector and dew heater controller. This arrangement will allow for using my old/new 8-inch RFT both at home and at a remote site.

 

8%22 RFT-EQ-02375.jpg

Old & New 8-inch RFT - 1967 to 2021

 

Some recent viewing of Jupiter with new mirror coatings reminds me of the excellent optics of my old RFT. The transparency was terrible with thickening clouds. But the seeing was excellent, with observations captured using a digital voice recorder.

 

October 18, 2021, Ocean Observatory, Coos Bay, Oregon:

 

220X - 11mm Nagler T6 + 2-1/2X Powermate

  • Seeing is quite good now, transparency is poor and getting worse, this view is just spectacular!, two moons on each side, there is a shadow in transit (Io's), this is within the equatorial zone close to the dimmer SEB; I got my new observing chair to have a more comfortable extended view, @ 220X this is pretty darn good seeing, SEB is dimmer than the NEB and narrower, the moon shadow is just N of the SEB approaching the central meridian, in the E Zone there is another thin belt adjacent to the NEB, in other words the NEB is split (the belt inside the EZ is dimmer), there is another belt further N from the NEB with a vague gray gap before reaching the gray polar zone, something similar to that is between the SEB and the polar zone, but this is less distinct, this is quite the spectacular view, by now the moon shadow has moved almost to the central meridian, this has to be one of the nicest views I've had of Jupiter in a long time, this little 8-inch telescope is a real performer, the NEB might have a little lumpiness along its darker part, the vague split is toward the equator, with naked eye it is apparent there is a thin layer of clouds in the sky in front of Jupiter, its general color  is kind of grey-brown, with the brown being prominent in the eqatorial region, the brightest part of the disc is the light zone that is adjacent to the SEB on its S side, the EZ is lighter next to the SB compared to the area next to the NEB, colors are pretty subdued due to the cloud cover, it is really nice watching the moon shadow move towards transit, now I'm seeing a little structure in the SEB, despite Jupiter getting dimmer as cloud cover increases the seeing is really solid

 

Clear Skies,

Russ


Edited by Rustler46, 06 November 2021 - 08:02 PM.

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#2 John Rogers

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Posted 05 November 2021 - 10:39 PM

Always great to see your setup evolving Russ!



#3 Rustler46

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Posted 05 November 2021 - 11:52 PM

Always great to see your setup evolving Russ!

Thanks for the kind comment, John. Some old things can still perform well. Here is the old Erfle eyepiece referred to in the original post.

 

Erfle Military -01539.jpg

 

Erfle Military -01540.jpg

 

While its edge of field performance is poor, I still use it occasionally. It's what we had for wide field back in the day. The field stop is the inside of the adapter - a bit over 30 mm. But my 24 mm Panoptic gives higher magnification and much better edge of field with only slightly smaller true field (1.7° versus 1.8° for the old Erfle). Thus the advancement of modern optics.

 

We now live in a golden age of amateur astronomy. In 2021 the real price of some fine telescopes has come way down. For those willing to spend big bucks you can get very large aperture optics that one could only dream of in the 1960s.

 

Best Regards,

Russ


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#4 John Rogers

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Posted 06 November 2021 - 07:09 AM

Ah, the classic Jaegers.  I recall it being a workhorse in the 60s.  

1966_Jaegers 1E2670_32mm.jpg

 

The Edmund version of the same eyepiece was their 5160.

1962_Edmund_Pg23.jpg

 

Research using the part numbers found on the eyepiece assembly, I determined that it was used on the M16C Periscope.

M16C_Periscope.jpg

 

The lenses from this eyepiece were the basis for the elusive Edmund 32mm RKE eyepiece.

 

I agree that it won't compete with some of the modern eyepieces.  I had my 1960 Cave 8" f7 telescope out a few weeks ago using some of the Televue eyepieces.  The view with a 13mm Ethos was breathtaking.


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#5 Rustler46

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Posted 07 November 2021 - 01:02 AM

Ah, the classic Jaegers.  I recall it being a workhorse in the 60s.  

attachicon.gif1966_Jaegers 1E2670_32mm.jpg

 

The Edmund version of the same eyepiece was their 5160.

attachicon.gif1962_Edmund_Pg23.jpg

 

Research using the part numbers found on the eyepiece assembly, I determined that it was used on the M16C Periscope.

attachicon.gifM16C_Periscope.jpg

 

The lenses from this eyepiece were the basis for the elusive Edmund 32mm RKE eyepiece.

 

I agree that it won't compete with some of the modern eyepieces.  I had my 1960 Cave 8" f7 telescope out a few weeks ago using some of the Televue eyepieces.  The view with a 13mm Ethos was breathtaking.

Thanks for the interesting research, John. Those old Sky and Telescope magazines had lots of advertisements, vying for our hard-earned money. They were a lot thicker with more editorial content than nowadays. Research is expensive to produce. 

 

As I recall my Erfle was purchased from Edmunds. But I do remember those Jaeger adds. There are likely quite a number of home made achromats featuring Jaegers objectives.

 

Russ


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#6 Rustler46

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Posted 09 November 2021 - 08:33 PM

Progress is being made on getting my old 8-inch RFT up and running. That last time I used it I discovered that the drive corrector was not able to completely compensate for the slight mis-gearing on my home-made German equatorial mount. In post #44 of the link, the gear ratio was too low by some 8%. The correct gear ratio between 1/2 RPM synchronous motor and the worm-gear set should be 3.25:1. My machinist used a chain drive giving 3.50:1 - close, but not exactly correct. He was a excellent machinist, but didn't understand why the ratio needed to exactly match the supplied 65:20 gears. Since I lived a hundred miles away, without telephone service, he couldn't just call me to ask if it mattered.

 

So nearly 40 years later I'm dealing with the consequences. My drive corrector is really just a variable frequency oscillator producing 110 volts alternating current. The user manual is a masterpiece in describing the device - "Lumicon Dual Star Drive". It gives operating instructions, circuit diagram and parts list. It even has a detailed description of how the circuit functions, component by component. It gave directions for adjusting the center frequency of the drive, which should be 60 Hertz (cycles per second). With my trusty multimeter, the center frequency was measured as 58 Hertz plus change. The fastest drive rate was around 64-1/2 Hertz. This was not quite fast enough to track the stars. So I adjusted the center frequency to 60 Hertz, which gave a highest drive rate of 67-1/2 Hertz. This should be enough to get correct tracking.

 

What I found amazing about the Lumicon drive corrector manual was its total lack of the usual page or two of lawyer/safety warnings. These are meant to free the manufacturer from liability for injury caused by unwise use of their product. The directions for adjusting center frequency just said with the cover off while adjusting resister R10, don't touch anything else. A prudent person would avoid coming in contact with 110 volts AC. In 2021 we are a living in a far different world than in 1985 when the drive corrector was manufactured. Nowadays some people are quick to sue for damages, if they think they can get a settlement from a business.

 

The measured current draw when tracking is less than I/2 amp DC (0.44 amp). This is good news since I'll be using a LiFePO4 battery of just 6.5 amp-hours capacity. Added to the drive load will be 0.18 amp for the ventilation fan and 0.35 amp for the dew heater. So it will be a bit less than 1 amp with all things running.  This is less than 0.2 C - that is 2/10 of 6.5 amps (1.3 amps).

 

I like the performance of the Lithium-iron-phosphate battery. Here is the discharge curve under that circumstance (0.2 C, blue line).

 

LiFePo4 Discharge at 2:10 C.jpg

So the voltage under load stays pretty high.

 

Now that performance will be degraded at lower temperatures.

 

LiFePO4 Performance at Temp.jpg

 

In my warm maritime climate, it is uncommon for my observing to take place at 0° C (freezing - 32° F). A common nighttime temperature is 50°F (10° C). At that temperature I would expect voltage to stay above 12.0 volts for 75% of its capacity (between the light green & darker green lines).

 

The life-cycle of this battery chemistry is supposed to be good as well.

 

LiFePO4 Life Cycle vs DOD.jpg

 

Running the battery clear down still promises 2000 cycles. But when treated more kindly, the cycle life can be a as high as 6000 cycles. At least that is what is claimed.

 

Now I'm waiting for some electrical supplies to be delivered. Along with the new power supply, some 14 gauge, two-conductor zipline will be used to direct 12 volts DC up to the telescope for the ventilation fan and dew heater. I also needed to replenish some of my powerpole hardware from Powerwerx. So when all the parts come in, I can finish up the 2021 version of my old 8-inch RFT.

 

Clear Skies,

Russ


Edited by Rustler46, 10 November 2021 - 08:26 PM.

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#7 Rustler46

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Posted 11 November 2021 - 04:47 PM

Progress is being made on getting my old 8-inch RFT up and running. That last time I used it I discovered that the drive corrector was not able to completely compensate for the slight mis-gearing on my home-made German equatorial mount. .... (see #44).

 

My drive corrector is really just a variable frequency oscillator producing 110 volts alternating current. The user manual is a masterpiece in describing the device - "Lumicon Dual Star Drive". It gives operating instructions, circuit diagram and parts list. It even has a detailed description of how the circuit functions, component by component. It gave directions for adjusting the center frequency of the drive, which should be 60 Hertz (cycles per second). With my trusty multimeter, the center frequency was measured as 58 Hertz plus change. The fastest drive rate was around 64-1/2 Hertz. This was not quite fast enough to track the stars. So I adjusted the center frequency to 60 Hertz, which gave a highest drive rate of 67 Hertz. This should be enough to get correct tracking.

The existing chain drive has a ratio at the worm of 3.5:1 - sprockets of 35 and 10 teeth. The gears supplied with the Thomas Mathis worm-gear set were 20 teeth on the motor and 65 teeth on the worm. This gave a higher ratio of 3.25:1 - that is 65 ÷ 20 = 3.25. To compensate for that drive gear/chain error I would need to turn the synchronous motor faster by the ratio of the two - that is 3.5 ÷ 3.25 = 1.08. Since the worm-gear and synchronous motor were designed to operate at 60 Hertz, it must be sped up by a factor of 1.08 to correctly track. So for that the frequency of the drive corrector must be:

  • 64.6 Hertz = 60 Hertz X 1.08

That drive rate is within the adjustment range available when the center (zero correction) frequency is set to 60 Hertz. I found that a setting of +5 gives the exact drive rate. There is still some adjustment above that if necessary, since it will give 66.8 Hertz at full +7 adjustment. This is all interesting to me as I await receipt of electrical components on order.

 

Another small detail that needed to be addressed was that all 4 rubber feet under the drive corrector were not in contact with the shelf on the mount. Two of the feet were beyond the edge of the shelf. So I found 4 stick-on rubber feet that were applied to the bottom of the drive corrector at a spacing to be in contact with the shelf. These new feet were considerably thicker than the originals, giving improved cooling via convection. This was just another detail that was taken care of to get the 8-inch RFT up and running. 

 

Russ


Edited by Rustler46, 11 November 2021 - 08:28 PM.

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#8 Rustler46

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Posted 14 November 2021 - 01:40 AM

My electrical accessories showed up yesterday:

  • Lithium-Iron-Phosphate battery, 12 volt nominal, with charger, outputs of 5-, 9- & 12-volts
  • Various PowerPole hardware
  • 14 gauge , dual red/black conductor zipline

Today I had an opportunity to put it together, so the telescope is self contained, semi portable. Here are some photos of the progress at this stage.

 

Power to Accessories-02609.jpg

The Li-Fe-PO4 battery lays on the aluminum C-channel below the drive motor. The 12-volt output is directed via a PowerPole splitter to the drive corrector below and the telescope tube above.

 

Power to Accessories-02610.jpg

The drive corrector power comes in through a female/male cigarette lighter socket/plug down to the 12-volt input. The 110 VAC output is fed via the orange cable to the drive motor.

 

Power to Accessories-02611.jpg

 

The Thousand Oaks Optical dew heater controller is held to the telescope tube with HD Velcro. A second PowerPole splitter is attached to the wooden yoke with some screws. Additional support is with a long wire tie around through and under the yoke. There is enough slack under the wire tie for the zip-line power lead to pass through, providing some strain-relief. The splitter on the yoke has two outlet cables - one for the dew heater controller and the other for a ventilation fan that will be installed later. The power lead is wrapped loosely around the polar axle to give enough slack for all positions of the telescope tube, including meridian flip. With dew heater and drive corrector running the voltage measured at the fan power lead was 13.10 volts.

 

When the telescope is to be removed from the mount, the power lead will be disconnected from the splitter on the yoke. The dew heater and controller will stay with the tube. The battery can be unplugged from the mount and charged at a convenient location. Next task will be installing the ventilation fan. 

 

So that's where I'm at with this old telescope for now. At home I could have just powered the drive corrector with a GFI mains outlet at my garden observing site. But I would still need a 12-volt battery or supply for the dew heater. The dew heater is key for the green laser on the finder to function at cool temperatures. I could pretty much do away with the drive corrector by replacing the existing 10 tooth and 35 tooth sprockets on the drive with ones giving a closer match to the 3.25:1 design.

Drive Chain Ratios.jpg

 

For portable use at a dark site the present setup will work fine. It has been fun spending some cloudy days and nights working on my 8-inch RFT. It will be ready to go on the next clear night opportunity.

 

Best Regards,

Russ


Edited by Rustler46, 14 November 2021 - 03:25 PM.

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#9 Rustler46

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Posted 15 November 2021 - 12:13 AM

After getting everything to work electrically, I decided give attention to placement of cables for the long term survival of the setup. So I moved all the cables and the PowerPole splitter so that they reside inside the aluminum C-channel. This will prevent the telescope yoke from running into these causing damage.

 

Power to Accessories-02614.jpg

 

The splitter is seen inside the left side. Wire ties are used to hold cables in secure locations. The orange 110 VAC power cord now exits the south side of the mount. The cigarette lighter socket feeding power to the drive corrector is seen wire-tied to the inside of the right side.

 

Another change was in providing more counter weight to balance the telescope. Rather than hanging dead weight junk from the end of the counterweight group. I realized there was room inside the hollow shaft to add weight there. So 3 pieces of 3/4 inch galvanized pipe fit nicely inside the 1-1/4 inch water pipe serving as counterweight shaft. This was enough additional weight to balance the load. More "steam-punk" solutions.

 

Power to Accessories-02611-2.jpg

So the piece of dead weight shown tied to the end of the shaft is not longer there. 

 

Today Oregon is being hosed by an atmospheric river. But tomorrow night is supposed to be clear. So after two weeks of rain, I'll be setting up the 8-inch RFT in my garden observing site.

 

EQ Mount-02379.jpg

On the right is my pier-mounted Losmandy G-11 under the plastic garbage can. While that setup is a joy to use with my 8- and 11-inch SCTs and 4-1/2 inch APO, now my old RFT has my attention. A friend asked today if I would be taking any photos of this week's partial lunar eclipse. My first thought was that I wouldn't. But I don't think I have ever used the old reflector for astrophotography. So that would be a good opportunity to gather some photons with old glass.

 

So I dug around in my adapters box and found a 1-1/4 inch setup I could used with my APS-C Sony NEX-7. I doubt that it will work at the prime focus. But I do have any eyepiece projection setup that might just come to focus. The lowest magnification would be provided with my very first eyepiece - a Brandon 32mm. So I'll try that. If it encompasses the entire lunar disc, that would be great. If not maybe an afocal setup (camera to eyepiece) might work. 

 

Russ


Edited by Rustler46, 15 November 2021 - 06:05 PM.

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#10 Rustler46

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Posted 01 December 2021 - 09:17 PM

I'm making progress installing a ventilation fan on the bottom end of the tube. The fan blows towards the mirror in its cell, up the inside the tube and then directed over the mirror by a plywood ring just above the mirror surface.

 

That ring is a remnant of how the fiberglass tube was fabricated by a friend by in the early 1960s. Several plywood annuli were covered with sheet metal, then several layers of fiberglass. This ended up being the tube now employed for my RFT. The rings remain, one of which happened to be just above the mirror surface.

 

The fan is suspended behind the mirror by 3 small elastic "hair ties" donated to the project by my dear wife. To form a shroud to ensure all the airflow goes up towards the mirror, I used some left over scraps of rubber sheet. This had been used as roofing material for an old pickup camper. The scraps needed to be glued together to make a circular sheet around 18 inches in diameter. This would allow for the shroud to wrap up around the outside of the tube. This was then sealed around the tube with a cord tightened around the shroud. The photos show how it all came together.

 

8-inch RFT Fan-02642.jpg

Here is how I chose to seal the rubber sheet around the tube. 

 

8-inch RFT Fan-02643.jpg

Here's the shape of the sheet.

 

8-inch RFT Fan-02644.jpg

This shows how I added more rubber sheet along the edge. Contact cement works great for this.

 

8-inch RFT Fan-02645.jpg

I'm not pleased with the method for sealing the rubber shroud to the tube. It is quite ugly even for my "stem-punk" mount. But I guess I could say a telescope in made to look through not to look at. It should work for improved cool down and boundary layer scrubbing.


Edited by Rustler46, 01 December 2021 - 09:19 PM.

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#11 Rustler46

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Posted 02 December 2021 - 04:04 PM

I've come up with an acceptable (less ugly) method of securing the fan shroud to the tube. That is an old strap with clip that secures its capture length. I think it was made to secure a heavy lead-acid battery to its hold-down clips. Whatever, it serves to capture the shroud in a way that doesn't add much to the ugliness. In the dark it will work just fine.

 

8-inch RFT Fan-02647.jpg

 

A side note:

 

That old Husqvarna chain saw still runs just fine after 43 years. It's a bit of a brute to start. My youthful energy of bygone years has subsided substantially. When I had it serviced by the local saw shop, the technician said that old saw is older than he is - a real museum piece. I'm just happy it still ran after 20 years of hanging on a nail in my garage. Nowadays I buy all my firewood.


Edited by Rustler46, 02 December 2021 - 04:06 PM.

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#12 Rustler46

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Posted 15 December 2021 - 03:37 AM

One update in the new category is that I'm proceeding with installing digital setting circles on my old German equatorial mount. I already have the Nexus II wireless controller being used on my 10-inch Dob. It can serve with either telescope. Having DSCs on the 8-inch will add the luxury of a tracking mount. The parts are on order:

  • 100-tooth timing sprocket X 2 for the RA and Dec axes
    These will need to be bored out to fit the 43 mm and 38 mm of the axes. I have a machinist all lined up, who is looking forward to working on my old steampunk mount.
  • 30-tooth sprocket X 2 for the encoders, 6 mm bore
  • 2000 pulse per rotation encoders X 2 - these were recommended by Serge at AstroDevices (maker of the Nexus II). With the 3.333 sprocket ratio (100 ÷ 30) this will give almost 6,700 pulses per revolution on each axis.

These parts are coming from China, with the sprockets already shipped. After the large sprockets are installed, I'll need to fashion a way to mount the encoders on each axis. Once this is done I'll know the centerline spacing between 30- and 100-tooth sprockets, and can order the timing belts. These will be around 116 teeth, GT2 (round tooth), around 348 mm length, 9-10 mm in width.

 

Then it will be a matter of wiring the encoders to a cable suitable for attachment to the Nexus II.

 

Hopefully before Winter is over, I'll have my old/new, home made 8-inch RFT ready to go.

 

Clear Skies,

Russ


Edited by Rustler46, 15 December 2021 - 05:11 AM.


#13 Jon Isaacs

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Posted 15 December 2021 - 04:27 AM

Thanks for the kind comment, John. Some old things can still perform well. Here is the old Erfle eyepiece referred to in the original post.

 

 

While its edge of field performance is poor, I still use it occasionally. It's what we had for wide field back in the day. The field stop is the inside of the adapter - a bit over 30 mm. But my 24 mm Panoptic gives higher magnification and much better edge of field with only slightly smaller true field (1.7° versus 1.8° for the old Erfle). Thus the advancement of modern optics.

 

We now live in a golden age of amateur astronomy. In 2021 the real price of some fine telescopes has come way down. For those willing to spend big bucks you can get very large aperture optics that one could only dream of in the 1960s.

 

Best Regards,

Russ

 

goodjob.gif

 

Russ:

 

This is some real good stuff.. I love the historical perspective.. 

 

So often I read that people saying "You need" or "you must have" the expensive, sharp to the edge eyepieces to use an F/5 Newtonian..   And I think and sometimes write, "OK, so just what did people do 40-50-60 years ago when those eyepieces didn't exist and the best thing out there was a Erfle?"  

 

This is what people did.. 

 

Jon


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#14 Rustler46

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Posted 20 December 2021 - 10:36 PM

goodjob.gif

 

Russ:

 

This is some real good stuff.. I love the historical perspective.. 

 

So often I read that people saying "You need" or "you must have" the expensive, sharp to the edge eyepieces to use an F/5 Newtonian..   And I think and sometimes write, "OK, so just what did people do 40-50-60 years ago when those eyepieces didn't exist and the best thing out there was a Erfle?"  

 

This is what people did.. 

 

Jon

I agree with your thoughts, Jon. So much of the discourse among amateurs, particular new ones is obsessing over equipment features that don't matter that much - at least from this old-timer's perspective. While there is some junk offered for sale to the new ones, with some care one can get a fine telescope at low cost.

 

We are truly living in a golden age of amateur astronomy. The real cost of getting into the hobby is low. In the 1960's a 6-inch reflector on a simple mount (equatorial, non-driven) was around $200. In 2021 dollars that equates to $1765! Nowadays a 6-inch on Dob mount is $420, which is $48 in 1965 dollars.

 

My advice to the new ones is get a simple (inexpensive) telescope and get on with observing. Online "analysis paralysis" is fun on a cloudy night. But on the next clear night I'm out with my old home made reflector. Well, I must confess to upgrading it with digital setting circles. But before the parts arrive it's back to star atlas and star hopping, with fresh Beral mirror coatings. If that's too much of a pain in the neck, next time will be the 10-inch Dob with DSCs. - something old and something new.

 

Russ


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#15 Rustler46

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Posted 21 December 2021 - 04:08 AM

Ah, the classic Jaegers.  I recall it being a workhorse in the 60s.  

attachicon.gif1966_Jaegers 1E2670_32mm.jpg

 

The Edmund version of the same eyepiece was their 5160.

attachicon.gif1962_Edmund_Pg23.jpg

 

Research using the part numbers found on the eyepiece assembly, I determined that it was used on the M16C Periscope.

attachicon.gifM16C_Periscope.jpg

 

The lenses from this eyepiece were the basis for the elusive Edmund 32mm RKE eyepiece.

 

I agree that it won't compete with some of the modern eyepieces.  I had my 1960 Cave 8" f7 telescope out a few weeks ago using some of the Televue eyepieces.  The view with a 13mm Ethos was breathtaking.

Does your Cave 8" f/7 have those beautiful rotation rings on the tube? Those were one of the handiest features of those great old telescopes. The college I went to had several of these Cave 8-inchers.

 

Russ



#16 John Rogers

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Posted 22 December 2021 - 06:23 PM

Yes it does Russ.  It was a local Craigslist pickup, described as 1970s vintage.   I almost passed on it but the paint scheme suggested to me that it was earlier than that.   I had the seller pull the mirror to check for a date that revealed it was a 1960 model.   I've had the mirror and diagonal freshly coated and I can tell you it is a fine instrument! 

 

The rotating rings need some work.  There are a couple of rough spots, but I suspect that is caused by the 60 year old grease that has hardened.  The clock drive and clutch are still pristine.  A big bonus was finding a color photo of the model in the Cave 1960 catalog.

 

1960_Cave_ModelB_Deluxe_1.jpeg 1960_Cave_ModelB_Deluxe_Catalog_Back-Cover.jpg

 

 


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#17 Rustler46

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Posted 22 December 2021 - 06:30 PM

Yes it does Russ.  It was a local Craigslist pickup, described as 1970s vintage.   I almost passed on it but the paint scheme suggested to me that it was earlier than that.   I had the seller pull the mirror to check for a date that revealed it was a 1960 model.   I've had the mirror and diagonal freshly coated and I can tell you it is a fine instrument! 

 

The rotating rings need some work.  There are a couple of rough spots, but I suspect that is caused by the 60 year old grease that has hardened.  The clock drive and clutch are still pristine.  A big bonus was finding a color photo of the model in the Cave 1960 catalog.

 

attachicon.gif1960_Cave_ModelB_Deluxe_1.jpegattachicon.gif1960_Cave_ModelB_Deluxe_Catalog_Back-Cover.jpg

Why-oh-why?  If they could do this at a profit back in the 1960s, why can't some manufacturer do the same now? I suspect it has to do with there being very few 8-inch class reflectors being sold on equatorial mounts. But that rotating ring arrangement made those old classics a joy to use. 

 

Thanks for sharing your excellent recent acquisition, John! That looks like f/6 or slower - a real gem. If you could adapt some DSCs, that would make it easy, even for an oldster to use. But before that, I'm sure you will restore that old Cave reflector to its original glory.

 

Russ


Edited by Rustler46, 22 December 2021 - 09:28 PM.

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#18 Rustler46

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Posted 31 January 2022 - 02:49 AM

One update in the new category is that I'm proceeding with installing digital setting circles on my old German equatorial mount. I already have the Nexus II wireless controller being used on my 10-inch Dob. It can serve with either telescope. Having DSCs on the 8-inch will add the luxury of a tracking mount. The parts are on order:

  • 100-tooth timing sprocket X 2 for the RA and Dec axes
    These will need to be bored out to fit the 43 mm and 38 mm of the axes. I have a machinist all lined up, who is looking forward to working on my old steampunk mount.
  • 30-tooth sprocket X 2 for the encoders, 6 mm bore
  • 2000 pulse per rotation encoders X 2 - these were recommended by Serge at AstroDevices (maker of the Nexus II). With the 3.333 sprocket ratio (100 ÷ 30) this will give almost 6,700 pulses per revolution on each axis.

These parts are coming from China, with the sprockets already shipped. After the large sprockets are installed, I'll need to fashion a way to mount the encoders on each axis. Once this is done I'll know the centerline spacing between 30- and 100-tooth sprockets, and can order the timing belts. These will be around 116 teeth, GT2 (round tooth), around 348 mm length, 9-10 mm in width.

 

Then it will be a matter of wiring the encoders to a cable suitable for attachment to the Nexus II.

 

Hopefully before Winter is over, I'll have my old/new, home made 8-inch RFT ready to go.

Slow but sure, I'm making progress getting the DSCs working on my old RFT.

  • The 100-tooth brockets have arrived and are now at a local machinist getting bored to fit on the RA and Dec axes. These will have a slip fit and setscrew to hold in place.
  • The encoders have also arrived and have been connected electrically to an old Cat-5 computer cable, that mates with the Nexus-II DSC/WiFi module. 
  • This electrical connection has been tested with the Nexus and SkySafari duo - all works as expected.
  • I'm gathering some aluminum scrap metal for fashioning the mechanical placement of the encoders on the mount. But since the mount is currently at the machine shop, there's only so much that can be done at this stage.
  • Once the encoders are mounted, I'll know the spacing between large and small sprocket. Then suitable toothed belts can be ordered. Likely this will be from a domestic supplier. While the price will be higher, shipping will be quicker.

Here's a photo showing how the electrical test was done.

 

8-inch DSC-2700-2.jpg

 

The iPad mini running SkySafari is wirelessly connected to the Nexus-II wifi network. The wiring diagram showed how to connect the 8 colored wires of the Cat-5 cable to the appropriate wires on each of the encoders. Red tape identifies the RA encoder and its cable. Turning the encoders causes the telescope FOV on SkySafari to move in RA and declination. I can do a mock align on Arcturus and Polaris. Then a push-to the Orion nebula works in principle - great fun to play with on a cloudy night. I just need to get the encoders and the telescope on the mount, under the stars.

 

But progress is being made on teaching the old RFT new tricks. smile.gif

 

Clear Skies,

Russ


Edited by Rustler46, 31 January 2022 - 03:11 AM.

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#19 John Rogers

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Posted 31 January 2022 - 09:34 AM

That looks great Russ.  I always look forward to your progress reports.

 

There is something special about a vintage telescope.  Especially when it is uniquely crafted with one's own hands and imagination.



#20 Rustler46

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Posted 31 January 2022 - 05:45 PM

That looks great Russ.  I always look forward to your progress reports.

 

There is something special about a vintage telescope.  Especially when it is uniquely crafted with one's own hands and imagination.

Thanks, John. Yes, progress is being made. I may give a call to Greg my machinist to see where he's at on my machining job. I did tell him there was no rush. But really there is. 

 

You are quite right - there is something special about the result of one own's handiwork. While I have a variety of different telescopes to use (see below my signature), my current favorite is the old RFT. Thus the DSC project.

 

Best Regards,

Russ


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#21 Rustler46

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Posted 01 February 2022 - 11:38 PM

Today I went shopping for some hardware to enable attaching the encoders on the mount. 

 

First I found a milling machine bit that will help cut some slots in the mounting plates. I chose a 2-flute, 1/4 inch diameter, 3/8 inch depth cutter that will be used with my drill press to cut the slots. These slots will be in the encoder mounting plates with the attachment bolts riding in those slots. This will allow adjusting the spacing between the timing sprockets for tightening the timing belt. The mounting plates will be 1/4-inch aluminum.

 

Now I know that a drill press is not a milling machine. But it should work well enough for milling a soft metal like aluminum. Previously I would have drilled a series of holes along the slot and finished with a lot of hand filing. But the $7 spent on this cutter should make the process much easier.

 

Also purchased were some M3 X 12 mm screws with washers for attaching the encoders to their mounting plates. I chose to use spring washers rather than regular lock washers to avoid damaging the soft aluminum plate. One small problem was encountered with the threaded holes in the encoders. One of the 6 holes (3 per encoder) was not threaded to the full 7 mm depth. So that screw will not go in as far as the other 5. Likely it will be necessary to cut that screw a little shorter so it won't bottom out.

 

The idea for the adjustable attachment came from forum member DAVIDG. See photos at #36 on this thread.

 

When I get some of the attachment hardware fabricated, there'll be some photos forthcoming.

 

Edit:

 

I've hatched a plan to use an old iPad-1, that I won in a contest in 2011. Yes this old tablet is the original, full sized iPad with 16 GB internal storage. While it cannot be updated past its present iOS 5.1.1, it still has an older copy of SkySafari Pro 3.8.5, that can interact with a DSC, push-to equatorial mount. So this "ancient" museum piece tablet is in keeping with the earlier era, homemade telescope I have. And its generous full-sized screen will be nice out under the stars.


Edited by Rustler46, 02 February 2022 - 05:58 PM.


#22 Rustler46

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Posted 05 February 2022 - 01:58 AM

I made a full scale drawing of the encoder mounting plate today. This shows the layout of the encoder and its 3 mounting screws, as well as the adjustment slots for attaching that plate to its support. This will allow for tensioning the drive belt. The first mounting plate has been cut - 2 X 4 X 1/4 inches. The bearing boss on the encoder is 20 mm (0.79 inches). Since the largest drill bit I have is 1/2 inch, I'll need to enlarge the hole by using the milling bit recently purchased. This can also be used to shape the slots. The bottom inch of the plate (below the dashed line) may be cut off if it ends up being not needed. It may work out that the slots need to be lower down in that bottom inch. Until I get the mount back from the machinist, the exact configuration is uncertain.

 

8 Inch RFT Encoder Mounting-02702.jpg



#23 Rustler46

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Posted 05 February 2022 - 08:42 PM

First encoder on its mounting plate:

 

8 Inch RFT Encoder Mounting-02704.jpg

 

Most everything went real quick. Drilling the holes with my cheap drill press was fast once I marked on the plate the locations. What took the most time was enlarging the encoder boss hole from 1/2 inch to just over 3/4 inch. I didn't like how the milling bit felt while working against the inside of the hole, likely from the two cutter flutes. In any case I used a large rat-tailed file to open up the hole. Lots of sweat and chips later, the encoder fit inside. I may try using less than a full depth cut to see if that will work smoother on the second mounting plate.

 

Next there was the issue of one of the threaded holes in the encoder not being as deep as the others. So I cut off ~1/4 inch on one of the M3 screws, so it would tighten on the plate before bottoming out. So progress is being made on the home front, while waiting for the machining to be done. Now that I know what works, the second mounting plate will be easy.

 

I used a hacksaw to cut the 2 X 4 inch plate. Before doing that I went to the local Oregon Tool store to buy a quality hacksaw blade. Talking to the knowledgable salesman, he explained the better hacksaws are those that tension the blade the highest. My old hacksaw is at least 40 years old and of simple, low tension design. They offered a range of saws from 15,000 to 50,000 pounds per square inch tension. So I purchased their best hacksaw that tensioned the blade to 50,000 PSI. I must admit that the salesman was right. The $35 hacksaw made for the easiest cutting I've ever experienced. It cut fast, straight and was easy to make corrections in cutting direction as needed. I also learned the blades will last longer with higher tension

 

My old hacksaw will now have an honored place hanging on a nail on the garage wall. And most usual was that the new hacksaw was made in the USA, including blades. This had a lot to do with its expense. It has storage in the handle for 5 extra blades. My saw now has two blades of 18- or 24-teeth per inch, depending on the job. But I'm quite pleased with the purchase.

 

Clear Skies,

Russ


Edited by Rustler46, 06 February 2022 - 03:47 PM.

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#24 Rustler46

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Posted 07 February 2022 - 10:08 PM

More progress - both encoders now have their mounting plates. Fashioning each plate takes considerable time for all of the steps:

  1. Cutting and truing the 2 X 4 X 1/4 inch aluminum plate - using hacksaw and large coarse file, this goes fairly fast. 
  2. Marking the 4 holes for encoder and the M3 mounting screws - goes fast using pencil on the plate setting atop the full-scale drawing.
  3. Center-punching the 4 locations to drill - goes fast, but is frustrating trying to get the punch marks exactly in the marked location
  4. Drilling the 4 holes with cheap drill press goes fast.
  5. Enlarging the encoder hole from 1/2 inch (my largest bit) to a little over 20mm (0.79 inch) takes a lot of time. I tried using a milling bit on a drill press. This is not a good idea as it puts undue lateral stress on the drill press bearings - something it was never designed to withstand. Best success came from using a large rat-tailed file, followed with a rotary file on handheld drill. Once the encoder can fit in its hole, one more step is necessary.
  6. Shaping the three attachment screw holes is necessary so that all 3 holes allow screw passage to the threaded holes in the encoder. Due to errors in center-punching (step 3), one or more of the holes do not line up correctly. To remedy this I could have just enlarged all the holes with a larger drill bit. But I chose to use a tiny round file, borrowed from my wife's jewelry making tools. Some judicious enlarging toward an oval shape does the job.

All told, each mounting plate takes several hours to fashion. If I was making a dozen of these, I'm sure there would be ways to reduce the time per plate. My tools and skills are a bit primitive. But they get the job done eventually.

 

Opening up the adjustment slots on each alignment plate will wait until I get the mount back from machining. When I determine more about the mount brackets, the slots can be cut, inter-sprocket spacing will be measured and appropriate timing belt ordered. Things are slowly coming together. I'm excited, but trying to be patient as necessary. In the meantime, I'm relying on my 10-inch reflector with DSCs.

 

Best Regards,

Russ

 

8-inch RFT Encoders-02710.jpg

 

8-inch RFT Encoders-02711.jpg


Edited by Rustler46, 08 February 2022 - 12:55 AM.

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#25 Rustler46

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Posted 08 February 2022 - 01:35 AM

Before taking the mount in for machine work, I dealt with a very stiff declination bearing. Under the stars hand movement in RA was smooth and easy, adjustable via the large clutch hand nut on the axle. But the Babbit declination bearing wasn't easy at all. It required a considerable amount of force applied to the large lever arm at the upper end of the telescope tube. So ease of use under the stars was compromised.

 

To remedy that situation, I removed the declination shaft from its bearing. With the bearing housing positioned over a plastic catch-basin I used some mineral spirits to wash away the 50 year old wheel bearing grease. An application of some light white lithium-based grease made for a smooth movement on that axis.

 

Russ




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