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Pentax 645 300 mm ED f/4 lens


  1. Overview
  2. Internal filter holder
  3. Install the lens on the 300 mm rig and setup USB-focus for reverse
  4. Temperature compensating and tilted focus plane
  5. Autofocus with APT and N.I.N.A.
  6. Move the equipment to the observatory
  7. A second try at the observatory
  8. A third try and investigating the FTDI cables
  9. Light leakage
  10. Optical analyze
  11. Fix of tilted sensor
  12. Control of aperture and deformed stars
  13. Update of Ekos auto focus driver
  14. Transport box
  15. To be continued

Related projects:

  1. HEQ5 as portable mount
  2. Pentax 645 300 mm ED IF f/4 lens
  3. KStars / EKOS and Raspberry Pi4

I take no responsibility or liability for what are written here, you use the information on your own risk!

8: A third try and investigating the FTDI cables

I brought the equipment out a third time, this time I didn't manage to get the EQDirect cable to work, nor did the QHY5 camera driver. This was with the Windows 10 system, in the Linux / Ekos I can get the old EQDirect PL2303 cable to work and also the QHY5 camera.

One of the problem is the FTDI cables, the computer connect to the cable but cannot communicate with the mount. I search for information and found that there are faked FTDI chips out on the market. Often they work at the beginning but after a while when Windows and drivers update they failed to work. Do I have EQDirect cables with faked FTDI chips ?

My friend sent me a link how to investigate this:

More problems to solve, but at least I have reduced the weight from 12.3 kg to 11.9 kg.

Investigating the FTDI chip data:

Pentax 645 300 mm ED f/4 lens for astrophoto

I connect all the three EQDirect cables I have. The old PL2303 chip based cable which Windows refused to connect to, my GPS deice also have this old PL2303 chip and cannot be used with Windows. I can install older drivers and it works for a while, but soon or later Windows update the drivers with the latest and the devices stop working.

If you still want to use the old PL2303 EQDirect cables you can try this, a tips I got from Australia:

The two FTDI cables (COM5 and COM11). Right click and choose properties.

Pentax 645 300 mm ED f/4 lens for astrophoto

At the Details I get the information that the COM5 cable has the serial number FTB6SPL3A.

Pentax 645 300 mm ED f/4 lens for astrophoto

And for the COM11 cable I get the information it has the serial number 7&37C645B2&0&2. They are not the same and then maybe they have an original FTDI chip. But what's wrong then ?

Pentax 645 300 mm ED f/4 lens for astrophoto

The driver I use is the FTDI original driver, I have also tried an earlier version, v26. I don't get any of them to work, Windows driver connect to EQDirect cable but refuse to communicate with the serial port of the mount. In Linux it doesn't work at all.

Later this week a new cable will arrive, if that too doesn't work I maybe shall get another hobby.

New FTDI cable:

Pentax 645 300 mm ED f/4 lens for astrophoto

When I ordered this cable I check very carefully that it has a original FTDI chip.

Pentax 645 300 mm ED f/4 lens for astrophoto

It has the correct logo on the contact and it's of the 5 Volt ttl signal standard which is important.

Pentax 645 300 mm ED f/4 lens for astrophoto

I have to cut this connector and only need to connect the: GND, TXD and RXD cable. I shall install a male 9-pol Dsub contact at this end.

Pentax 645 300 mm ED f/4 lens for astrophoto

I cut to the cable to 1 meter and replace the flat contact with a male 9-pol Dsub contact. Solder the black GND cable to pin 4 and 5, the yellow Rx to pin 6, the orange Tx to pin 9.

I followed this instruction how to connect the cable:

Pentax 645 300 mm ED f/4 lens for astrophoto

The Dsub contact attached to EQ6 mount.

I deleted all old drivers I have installed when I tested with the old cables. Insert the USB contact and it started to instal the drivers. But noticed in the device Manager that it wasn't installed correctly, bad ! I did a manual installation of the latest driver from FFTDI and the device manager indicated that it was correctly installed. Now the big question, will it also connect to EQMOD ?

Pentax 645 300 mm ED f/4 lens for astrophoto

I start SkyChart and from that I connect to EQMOD. Surprise, it connect ! First time with Windows 10 and a working EQDirect cable. I have also tested the cable in my Linux system with Astroberry and it work perfect in that system too. I hope this cable will work with later updates of drivers in both Windows and Linux system. Exactly what was wrong with my old cables I'm not 100% sure of, faked chip or some accident.

The new FTDI cable cost 20 Euro, but I have to remade it with a new contact. If you live in Sweden you can by it from Electrokit, the cable come from SparkFun Electronics. Note: you must have the 5-Volts version of Tx/Rx levels for EQ6/HEQ5 mount.

Conclusion, be very sure that you by a cable with the original FTDI chip. All my old cables has once worked with older Windows version, the newer Windows versions are much more critical and block the drivers to work or the drivers itself if there is something wrong. The oldest cable with the PL2303 chip still works in Linux.

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