Fake star DIY for focusing

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maceemiller
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Fake star DIY for focusing

#1

Post by maceemiller »


Hi all.

Not sure if this is the right place to post this but im sure it will be moved if needed.

I love attempting astrophotography.......as hard as it is the whole challenge is amazing yet I suffer from a classic amateur issue......focusing!

I use a Canon DSLR 100d (unmodified) and a Sky-watcher star adventurer mini that I have rigged up to my smartphone.
My usual way of focusing is to point my camera at a bright star and visually try to focus the lens until it looks as sharp as I can tell on my phone screen which at night is quite difficult to get right.......well it is for me :)

It works fine yet I was wondering if I could do anything to make focusing better......and I think ive found a way which may help a few people here.....

Ive read about using a street light in the distance to practice with yet that is not an option where I live as there are none to use so I came up with the idea of using my phones torch as a fake star, yet it was too bright to work with.

So......I cut a small rectangle of cardboard from a cereal packet and coloured it black.
20210805_201940.jpg
I then used a sewing needle to put a small hole in it and sellotaped it over my phones light, yet I offsetted it to keep the light dim....



received_217160743542447.jpeg
I placed my phone about 10 feet away and used APT (astro photography tools) on my laptop and used the focus aid tool......

It worked like a dream and i feel very confident that, when I have a clear night ill be able to focus correctly.


I hope this will help someone or at least get them thinking.....

Thankyou for reading :)

Carl
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JayTee United States of America
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Re: Fake star DIY for focusing

#2

Post by JayTee »


Carl,

I believe that ten feet away is not far enough to give you infinity Focus. The light rays at that distance are still diverging since it's not a true point source of light. Tonight, place your light source 50 feet away or further, if you can get away with it, to more closely approximates infinity distance.

Cheers
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Re: Fake star DIY for focusing

#3

Post by SparWeb »


Experiment with increasing distances until it works.

While you have your scissors and sellotape out, look for some red film to make a red light filter.
You can use your phone's light to spot things in the dark, but it's hard on the eyes after they've adjusted to the dark.
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Re: Fake star DIY for focusing

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Post by Graeme1858 »


maceemiller wrote: Thu Aug 05, 2021 10:11 pm Not sure if this is the right place to post this but im sure it will be moved if needed.

How about the DIY Corner?

Regards

Graeme
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Re: Fake star DIY for focusing

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Post by maceemiller »


JayTee wrote: Fri Aug 06, 2021 1:18 am Carl,

I believe that ten feet away is not far enough to give you infinity Focus. The light rays at that distance are still diverging since it's not a true point source of light. Tonight, place your light source 50 feet away or further, if you can get away with it, to more closely approximates infinity distance.

Cheers
Oh I agree....this was just a test to practise with APT. As for infinity I tried it on the Moon late last night and managed quite a sharp focus
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