Filter Box for DSLR by Astro Hutech / Borg

Filter Box for DSLR astro hutech borg

This is to share with DSLR users who are seeking for the solution with new F3.9 scope systems along with a filter box.

I wished to use my lovely noise-free cooled 6D with IDAS NB2 and NB3 last time. But no room to add one more filter box in front of a camera. So I was forced to use a mirrorless camera like SONY A7.

Now I tried to figure out the solution for coming new moon opportunity. Here is my answer for DSLR users.

  • Remove M57 rotator (7352)

  • Replace 7000 with 7923

Astro Hutch Borg

This gives us 18mm new room. Yes, unfortunately we lose a camera rotator. So inconvenient for the time being. But just temporary. Don’t worry, I start preparing the large rotator indicated the above.

BTW, new rotator is large enough for 55mm diagonal sensor such as GFX or Pentax 645 camera.

As described yesterday, IDAS filter makes light path 0.85mm shorter. To meet the correct back focus requirement of BORG, we need to “mechanically extend” 0.85mm to “offset”.

2 x 7879(2mm) is the answer. I’m glad it was much simpler than what I expected.

BORG BF is 80.00mm as designed. 80.85mm with IDAS filter(=80.00mm light path thru a filter)

80.85 – 55(44 as Canon + 11=5005) – 15(7519) – 7(7507) – 4(2×7879) = – 0.15mm

0.15mm is too long. But I’m sure it should be within the tolerance. And from the viewpoint of general BORG optical behavior I experienced before, longer looks relatively better than shorter.

And once a new rotator will come up, you can simply replace a current rear unit with it without changing other parts configuration. Then, you can orient a camera body while using a filter box.

Astro Hutech Borg

Nikon DSLR is same thing. Just replace above 5005 with 5003. That’s it.

If your camera has IR blocker inside body, you can use NB2 and 3 alone. No extra filter needed. My 6D has a clear filter inside body. So I need to have 2 filters. I hope not to be confused.

For more info, please click here.

Current BORG Availability & 72FL

I summarize current BORG availability for new orders as follows. (This is not for the ones already ordered)

(Objective lenses)

  • 107FL : May

  • 90FL : June

  • 89ED : June

  • 55FL : June or later? (I need more carefully check)

  • And 72FL : Prototype stage

(Rear lenses)

  • 7108/7215/7214/7872 : in stock

  • 7880 : May

  • 7770(=ED reducer for 107FL)/7771(=ED reducer for 90FL) in stock

Sorry for the inconvenience to you. Still way behind the schedule, especially 55FL. But getting slightly better. Thanks for your continuous patience.

I was told 72FL was refined for best matching with 0.72x super reducer. I will try to take some shots before NEAF if allowed or after. This is 72mm fluorite at F4 with total 6 elements configuration.


I will try to figure out best possible configuration as the double-duty scope for imaging as well as guiding.