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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!

7: A second try at the observatory

A bit disappointed from the last visit at the observatory I moved out once more a couple of days later.

Equipment and weight:

Pentax 645 300 mm ED f/4 lens for astrophoto

This is what I bring with me: A PC Windows computer, power fuse box, dovetail with its two lenses and guide camera HUB, Canon 6D camera, router, lot of cables and a laptop.

Pentax 645 300 mm ED f/4 lens for astrophoto

It weights in at 12.3 kg included the laptop. Not bad, but later when the Raspberry built system I can reduce this weight a lot. And even more if I replace the guide telescope with an off-axis guider.

In the observatory:

Pentax 645 300 mm ED f/4 lens for astrophoto

Connect the cables, set the battery on charge, wait a couple of hours and then power up the computer.

Pentax 645 300 mm ED f/4 lens for astrophoto

Connect the cables to the mount and dovetail with its equipment. Normally I have the router in the house, connect it to the astroserver by a LAN cable. The laptop is connected to the router through WIFI. With the later Raspberry server when it's finished I will setup it as a hot spot and then no need for a router. I can of course do that with the Windows machine too if I want.

Pentax 645 300 mm ED f/4 lens for astrophoto

Even if I don't use the Raspberry computer I let it sit on the dovetail, it's so small that you don't noticed it. And later when both the windows and the Linux system work the other can be a backup.

After this I try to connect my control software, everything worked without the connection to the EQDirect cable and the mount. Later I took a deeper look at the EQDirect cable.

If I thought about to get me another hobby ? Maybe.

From the balcony I got this astrophoto: M39. Now it feels better again.

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