4 replies to this topic

[Mlad]

Hello Everyone,

I ordered Astrosolar Film 5.0 from Baader Planetarium to build an off-axis filter for my Explore Scientific 12" UL Dobsonian (305/1525).

From my measurements, the diameter of the filter itself (film) can be a maximum of 4".

 

Please advise what diameter of off-axis filter to make, 3" or 4"? Or maybe 2 or 4 smaller pieces in one mask (bypassing the spider and secondary mirror)?

 

If I counted correctly, with a 3" filter the focal length will be f/20, and with a 4" filter f/15...

 

Best regards,

Edited by Mlad, 22 April 2025 - 04:49 AM.

[Mlad]

Hello Everyone,
Over 80 views in less than 24 hours but the lack of suggestions from you leads me to the conclusion that I asked an infantile question.

 

I asked my questions from the first post seriously and I really care about your opinions and I count on your help.

 

Best regards,

[Kerste]

Do not use two filter holes in one mask – the result would be a Scheiner Mask (similar to a Bahtinov) which is perfekt for focussing as you will see two suns when it is out of focus. I did this years ago wit a C8, didn't work too god.

 

I'd make the single hole for the filter as large as possible - but I don't know if an oval or semi-circle would be of disadvantage.

Edited by Kerste, 23 April 2025 - 02:09 AM.

[C0rs4ir_]

I think many dont understand the question, since you can simply choose the size of the mask. So what stops you from using the maximum possible?

[rigel123]

I’m with Dennis, go for the 4”.