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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!

6: Move the equipment to the observatory

As you maybe have read on my pages earlier I built an observatory a couples of years ago. Haven't used it for astrophotography more than once. Where I live the light pollution is classed as Bortle class 9 according to the weather app Clear Outside. Class 9 is as worst it can be. At the summer house where I have the observatory it's much better, Bortle class 4, still far from perfect. Bortle Scale is an astronomical scale of the quality of the dark sky.

More about Bortle Scale:

When I use my equipment out at the summer house I must bring with me other equipment. Not a stationary computer but a lap top with its limited screen area. I also have the observatory battery operated in the case of a power failure.


Pentax 645 300 mm ED f/4 lens for astrophoto

Long time since we visited the observatory, just come here a couple of times during the winter. The observatory is still there and the roof is still water proof.

Pentax 645 300 mm ED f/4 lens for astrophoto

My guest pier in the back ground, it's possibly to connect to the local network and to have it powered from the grid.

Installing the equipment in the observatory:

Pentax 645 300 mm ED f/4 lens for astrophoto

I brought the EQ6 mount and installed it on the pier. If I want to reach the horizon I must have a pillar between. The direction where I have the best darkness is from the East to the South. There will not be a clear sky tonight, I only use the time during daytime to get the equipment installed and maybe work.

Pentax 645 300 mm ED f/4 lens for astrophoto

I got a lot of problem, the battery couldn't deliver power enough, I have it always on charging during the observations. But only maintenance charging, 2 Ampere can be delivered to the battery. The equipment take about 2.5 Ampere when the heating band operates. It emptied the battery after only 30 minutes, it's a 45 Amph car battery. After I shut down the heating band I could run the equipment. Very convenient to have the Volt and Ampere meter on the equipment. I can follow exactly what happens when I put load on the battery.

I got problem when connecting the terminal to the astroserver. It has dynamic IP address and I must know the IP addresses to connect it. Through the router I normally can see to what IP addresses the equipment is connected. But this router is old and a bit primitive, I only succeeded once to get a connection. It ended up that I had to bring home all the equipment for more test at home.

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