Canon 6D modified with Baader filter images out of focus when HA filter is installed.

[Oliver2278]

So I have just had my Canon 6D modified to make it more sensitive to HA. I also thought I would buy the Astronomik 12 nm filter to take advantage of the mod and do some HA imaging.  I knew it would be hard to get good focus with a Bahtinov Mask while the HA was in place so I decided to focus the Samyang 135 lens without the filter installed in the camera and then tap off the lens so focus did not move, once that was done I would and then place the HA filter back into the camera. My issue is that looking at the images taken they all seem to be out of focus. Perfect focus on my Samyang 135 with the Bahtinov mask is right at the point where it stop turning. Is there something  I am doing wrong?  The two images I have attached are one with the HA filter in and one without, both images were taken with the lens focused in the same place to infinity right where i am unable to turn the lens anymore.  I was a little scared of placing the filter in the camera, its a tight fit and the mirror lockup I was convinced I was going to break the camera! . Just to note that when I took the HA filter out the images was in focus, please see images attached. Any tips or advise would be most welcome. From looking at the blurred picture I think I caught the Lagoon Nebula Thanks Oliver 

[bottletopburly]

You need to focus with filter in place as this will alter focus point .

[fifeskies]

Rule of thumb is that focus will change by 1/3 the thickness of the filter , so a typical 3mm filter will add 1mm.

It is because the refractive index of glass is not the same as just air.

 

To focus with Ha filter and Bahtinov , just push camera to high ISO , just remember to lower it again before imaging.

[Oliver2278]

Thanks for all of your replies,  I will implement all your wisdom when next the cloud part!  Thanks again.!

[Oliver2278]

Thanks for all of your replies,  I will implement all your wisdom when next the cloud part!  One other thing, when I place the HA filter in with the mirror on lockup will this effect the working of the camera in anyway, or was the camera designed to have such a filter put in place?  Thanks again.!

[michael8554]

15 hours ago, Oliver2278 said:

Perfect focus on my Samyang 135 with the Bahtinov mask is right at the point where it stop turning.

In which case you may not be able to get good focus with the filter in place.

Michael

[david_taurus83]

10 hours ago, Oliver2278 said:

Thanks for all of your replies,  I will implement all your wisdom when next the cloud part!  One other thing, when I place the HA filter in with the mirror on lockup will this effect the working of the camera in anyway, or was the camera designed to have such a filter put in place?  Thanks again.!

Perfectly fine to use a clip in filter and hold up the mirror. I use a LP filter myself in this way. Who done the mod? They should have also shimmed the sensor a little to compensate the fact the IR filter has been removed. As Michael above has mentioned, this is usually done so you can focus properly with camera lenses. If using on a telescope, then it's not necessary but the 2 main camera modifiers in the UK always do it anyway.

[newbie alert]

Focus point on ha and broadband are different .. you have to focus with what you're going to use.. up the iso and exposure time using your bahtinov mask

[Oliver2278]

I used cheapastrophotography.com, I had noted that other people had used him before and that he does a good job. this is what his quotes "In my camera astro modifications I will re-shim the optical train so the camera will maintain the autofocus capability. It will also be able to achieve focus to infinity with any lens." So I am hoping everything will be OK. I know it maybe a little trial and error at the beginning. Thanks for all you comments, I really appricate it.

[newbie alert]

Juan did my camera a good few years ago now... Still going strong 

[Oliver2278]

On 04/07/2022 at 18:03, newbie alert said:

Juan did my camera a good few years ago now... Still going strong 

He is a top guy, he was very helpful an knowledgeable and pointed me in the right path toward the mod that I eventually ended up with. 

[Oliver2278]

Just to say a big thanks to all of you guys, I have managed to get my lens in focus using the moon and using a high iso. The focus definitely shifted with the filter in. Now I just have to wait for some clear skies!