Attn to BORG Visual Observers, & Focusing Depth of New BORG Astrographs

1- Believe or not, BORG didn’t (still does’t) have 2″ compression ring type holder in spite of common item in the market. I understand this is a demanded item by the visual observers. So I decided to carry as Hutech. Now it’s in stock.


M57 male at one side. So you can simply replace BORG 7504 or 7508 etc with this. 18mm light path. Slight shorter than them.

New BORG visual scope sets provided through Hutech will include this holder as standard.

2- Recent BORG astrograph – 107FL F3.9, 90FL F3.9 & 55FL F3.6, these scopes’ focusing depth is super shallow. Losing the right distance affects not only the image sharpness but also the quality of star shape at each corner. Inward or outward focuses show sagittal or meridional coma.

Because of that, they are also very sensitive to the temperature change. These are typical behavior in these optics. I realized that after field testing by myself. So they require paying more extra attentions to achieve the fundamental optical performance. But if you do, you get the wonderful rewards. The result is totally sharp entire the frame.

Recently I started using a following WO’s mask to more secure my focusing. (My eyes are getting older and older)


Yes, this comparison is true. Brighter and larger. For manual focusing, this is a highly recommended for super critical focus like recent BORG astrographs.


~ by tedishikawa on January 30, 2019.

2 Responses to “Attn to BORG Visual Observers, & Focusing Depth of New BORG Astrographs”

  1. Hey Ted,

    Will that WO mask fit the 71FL? It should fit the 90FL nicely.



    Perry Holcomb
    North Augusta, SC

  2. Their smaller version should be fine for 71FL.

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