Bahtinov filter

[Roy Easto]

Hi all,

Has anyone tried a Bahtinov filter for focussing whilst imaging? I see
you can buy small cardboard ones from Amazon for a few quid. I thought I
might try one out but does anyone here have any experience of them? I am
looking to use them to focus my Nikon camera and the Atik camera at Kenley.

Roy

[Kevin Phillips]

Hi Roy

I use then all the time. When I do meridian flip I always use the mask to make sure the focus is smack on. I don't use it whilst imaging but I certainly use it when I am changing filters from L enhance to oxygen 3 filter they pretty accurate. 

Regards Kevin

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From: 'Roy Easto' via croydonastro <croydo...@googlegroups.com>
Sent: Friday, December 12, 2025 3:29:14 PM
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Subject: [croydonastro - 8139] Bahtinov filter

 

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[drja...@aol.com]

Roy

I have tried but maybe not competently.   I found it hard to judge when the central bar was really 'in the middle'.  Seeing less than good didn't help either.  There is a specific app that helps with this but never tried it and don't recall its name

NINA however has a Bhatinov routine, is free and is an astro program widely used.  It's an all in one for controlling every piece of equipment used to image and may be overkill. 

Sharpcap is simpler and has a number of focusing tools and I found them useful.   Not sure if they are in the free version or if you need the premium.   The premium upgrade is an annual subscription but not much, given all the other included capabilities such as accurate polar alignment, on top of the standard camera settings support and the imaging sequences facility in the free option.  (Firecapture may have similar. )

I personally found the most effective focusing for a dslr and its general control, with a shallow learning curve, is Backyard Canon/Nikon.

James

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[Graham Cluer (CAS)]

It is the standard way to focus the original Unistellar smart scopes. 
They even build one into the lens cap.  I find them wonderful

Graham Cluer

[Roy Easto]

Thank you Kevin, James and Graham for the feedback,

I'll go for a cheap cardboard one and upgrade to metal if it works out.

Cheers,

Roy

[Kevin Phillips]

Hi Roy 

I was going to mention the metal ones to you. 

They are a better option. 

Need to be sure t8 get the right diameter 

Kevin

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From: 'Roy Easto' via croydonastro <croydo...@googlegroups.com>

Sent: Friday, December 12, 2025 4:05:47 PM
To: croydo...@googlegroups.com <croydo...@googlegroups.com>
Subject: Re: [croydonastro - 8143] Bahtinov filter

 

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[Kevin Phillips]

Ho Roy this what it should look like when you use the mask.

Regards Kevin

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From: Kevin Phillips <Thewelsha...@hotmail.com>
Sent: Friday, December 12, 2025 3:33:35 PM
To: croydo...@googlegroups.com <croydo...@googlegroups.com>
Subject: Re: [croydonastro - 8139] Bahtinov filter

 

[trevsie7]

I have used them on my C9.25 SCT. They do give a good focus but they have to be used on a star. If there isn't a suitable start in frame, it means moving the scope to focus then reframing to what you want to image. I now use an electronic focusser with SGPro (NINA and APT have similar functionality) and automatically focus on every filter change or every half an hour or so to allow for temperature changes. I find that much more convenient. I believe it is possible to adapt an electronic focusser to a DSLR lens.

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[tcos...@gmail.com]

I also use a Bhatinov mask for initial focussing – as Trev says it needs to be on a relatively bright star. I start my imaging routine focussing on a bright star near the target and then move the scope for framing/image composition of the target and subsequent imaging. TBh I don’t bother re-focussing for imaging when changing colour filters.

@Trev I’d be interested to see how electronic focussing works with SG Pro.

Regards

Tim C

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[Trev S]

Hi Tim,

SGPro automatic focussing is quite comprehensive. It's probably best explained in this Youtube video.

https://www.youtube.com/watch?v=s8xc1DBbHT0

I usually set it up to autofocus on filter change or every half hour whichever is the sooner. Once set up in an equipment profile it doesn't need changing and that profile can be used for every sequence that uses that set of equipment.  I haven't had any real issues with it and use it with my Lakeside focusser as well as my home made one which is based on Robert Brown's MyFocuserPro2.

[tcos...@gmail.com]

Thanks very much for sharing Trev. I’ll look into it – although have been a bit distracted with my trusty QSI CCD camera playing up at the moment!

Tim C

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