2 replies to this topic

[MT4]

My left eye probably suffers from a moderate case of irregular astigmatism and as such it's typically very hard to achieve best focus.  I've resorted to using a Bahtinov mask on a bright star or a planet in order to focus for my left eye.

 

Japan is currently in the middle of the rainy season.   Based on past experiences, it might be months before I see clear, blue skies again.

 

How am I focusing my binoculars in the absence of any stars or planets?    Read on to find out and have a good chuckle 

 

-------

 

After looking at the Shibuya cityscape for months in many of my instruments, sometime in the past couple of weeks I suddenly had a flash of inspiration.  Why not use distant building lights as substitutes for the stars?  By the way, those buildings are some 5km away from where I am.

 

The idea seems both plausible and crazy at the same time but it does work.  I can also use a Bahtinov mask on those building lights to get a sense of how close I am to achieving optimal focus.  When the instrument is in near-perfect focus, those distant lights show up tight and with few spikes.

 

When I get to see the stars again, I most likely will need to tweak the focus slightly, but at least having used distant building lights as my "artificial" stars I have gotten the focus about right for distant targets.  The crazy idea turns out to not be so crazy after all 

 

Here's a pic taken off my Tak Astronomer 22x60's eyepiece.   You can see that those lights at the top of the building under construction are round in shape.  Everything looks "tak sharp" in the Tak!

Attached Thumbnails

• 

Edited by MT4, 30 May 2023 - 06:53 AM.

[Rich V.]

Distant lights ought to be just fine if planets work with that focusing mask.   I look around the valley at night and lights about five miles across the valley from me focus very similar to brighter stars.  I use them from time to time as collimation targets as well.  I like that they stay put instead of moving out of the FOV like stars.  

[MT4]

Distant lights ought to be just fine if planets work with that focusing mask.   I look around the valley at night and lights about five miles across the valley from me focus very similar to brighter stars.  I use them from time to time as collimation targets as well.  I like that they stay put instead of moving out of the FOV like stars.  

 

That's reassuring to know.  Thank you for the confirmation Rich.

 

In my case, with my poor weather and annual months-long rainy season, being able to use distant lights as focusing targets means a great deal to me.   Best thing is these targets are right across from my bedroom.  I could sit for hours watching the night cityscape and once in a while check if my binos are still in focus using the "magical" Bahtinov mask.