Borg 77ED ll

[alan potts]

Some time last year I used the Borg 77ED which is about F4.3 I think. In everything I read it said back focus was 55mm, fairly standard.  However I could never get the 183MC to focus and some kind member pointed out that the spacing needed to be 37mm I think it was to reach focus due the chip being set back in the camera. Now I may have this wrong but it did not work at 55mm and never looked anywhere near it. I have now mounted this with my other scopes and would like to have a play

Can anyone help with some advice?

Alan

[andrew s]

The back focus is measured from the metal back of the scope to the chip not the front of the camera. What is defined as the metal back of the scope depends on the scope and or reducer.

Regards Andrew 

[alan potts]

5 hours ago, andrew s said:

The back focus is measured from the metal back of the scope to the chip not the front of the camera. What is defined as the metal back of the scope depends on the scope and or reducer.

Regards Andrew 

Thanks Andrew it is an odd one as I knew this and put 55mm into the mix accounting for the recessed chip, the correct spacers come with the two Zwo cameras I have but for what ever reason it don't work with this. I have checked on line, not that there is much info on these scopes and it states 55mm. As said a member I think said it needed to be 37mm, I was rather hoping he would see this. I should have written it down, if I have a bit of time later maybe I will use the search engine to see if I can dig it out.

Alan 

[andrew s]

Just a thought, given the Borg scopes are modular I wonder if the 55mm refers to a specific configuration? Regards Andrew

[alan potts]

10 hours ago, andrew s said:

Just a thought, given the Borg scopes are modular I wonder if the 55mm refers to a specific configuration? Regards Andrew

This is the trouble with Borg, a million parts and ways to put them together. I found something last night where he had excellent results using 38.3mm on a specific camera. I know I bought a 20mm spacer for this to get a certain distance and a 0.3mm and 0.5mm spacer. I wish I had written down what I did. I must have a play and try things out, it is clear tonight and the moon is a bit too big so ideal time really to mess.

Thanks for you input,  Alan

[wxsatuser]

Your camera has a back focus of 6.5mm if I'm correct.

If the Borg reducer has a distance of 55mm you need spacers of 48.5mm

https://www.sciencecenter.net/hutech/borg/techdocs/7704.pdf

Edited October 27, 2020 by wxsatuser

[alan potts]

On 27/10/2020 at 12:33, wxsatuser said:

Your camera has a back focus of 6.5mm if I'm correct.

If the Borg reducer has a distance of 55mm you need spacers of 48.5mm

https://www.sciencecenter.net/hutech/borg/techdocs/7704.pdf

I am past worry with Borg, reading about them drives me mad. I banged in the 20mm spacer and a 4mm Borg spacer as well as the first piece on the camera which is 11mm, so as you said the chip is recessed 6.5mm.  I think the 4mm spacer brings the mounting ring level with the back edge of the last element of the reducer.  All in all I have about 36.5mm which seems to bang on the money, I have 0.3 and 0.5mm shims to fine tune but it looks OK.  I may well have mis-read the 55mm back focus at some point in the past. Someone on site told me it should be 37mm and it appear he was correct.

Many thanks,  Alan