Ed120 and steeltrack back focus

[Steve Clay]

I've fitted a Baader steel track to my Ed 120. I use a 1.25 inch diagonal with a 2 inch T2 nosepiece

Problem is there isn't enough back focus available to get any of my starguiders to focus. I've put an extension tube onto the Nosepiece which has solved the issue but only have about 5mm to spare

I'm visual only but I'm surprised to have encountered this with the steel track.

Steve 

[Robindonne]

Nice thread.  I was thinking about switching the focuser, and the possible problems that can occur. That steeltrack looks on itself shorter then the original one.  Really interested in this outcome.  

Edited September 10, 2020 by Robindonne

[Steve Clay]

13 minutes ago, Robindonne said:

Nice thread.  I was thinking about switching the focuser, and the possible problems that can occur. That steeltrack looks on itself shorter then the original one.  Really interested in this outcome.  

I've just ordered a Baader 2 inch 18mm fine tune ring which will sort the problem and push the diagonal back. The other is an Ep extension tube. You would have thought Baader would have taken this into account with the Skywatcher adapter ring.

[Robindonne]

Is there no way to extend the connection between the telescope and focuser?

[Steve Clay]

14 minutes ago, Robindonne said:

Is there no way to extend the connection between the telescope and focuser?

Not that I'm aware. As I said you'd have thought Badder would have designed it into the adapter flange. 

[johninderby]

Does the adaptor flange use an M90 thread? In that case you can use a TS M90 extension. 50mm extension available from Teescope Express.

https://www.365astronomy.com/ts-optics-25mm-m90x1-extension-tube-for-6-and-8-rc-focusers.html

 

Edited September 10, 2020 by johninderby

[wornish]

I only do astrophotography, no visual, and have recently bought a C9.25 and a a Baader Steel-Track focuser to help with planetary shots.

The focuser is certainly well made and a quality piece of engineering, but it seems to create more issues than it solves. 

The whole back focus definition seems to be a mine field and is driving me crazy at the moment - what does it actually mean?

The main focus knob on the C9.25 moves the backfous well before and after the so called published distance. I really don't understand what's going on!

I guess that to to achieve the published focal length the back focus is as what is published but that does not mean you can't get focus at different distances. - or does it?

I would really like someone to explain ??

Edited September 10, 2020 by wornish

[Robindonne]

15 minutes ago, wornish said:

I only do astrophotography, no visual, and have recently bought a C9.25 and a a Baader Steel-Track focuser to help with planetary shots.

The focuser is certainly well made and a quality piece of engineering, but it seems to create more issues than it solves. 

The whole back focus definition seems to be a mine field and is driving me crazy at the moment - what does it actually mean?

The main focus knob on the C9.25 moves the backfous well before and after the so called published distance. I really don't understand what's going on!

I guess that to to achieve the published focal length the back focus is as what is published but that does not mean you can't get focus at different distances. - or does it?

I would really like someone to explain ??

Strange, i used one on my c8.  But of all the different types of telescopes, these sc’s are the ones i would have tought to not getting in trouble, using a crayford focuser.  Your Internal mirror focusser should almost always give you extra margin.   Not an expert so i might be wrong.  
I assume you use a reducer/flattener?   The backfocus is probably somewhere between 55 and 100 mm.

in what sort of trouble do you get when your sensor is 55-100 mm from the reducer?

-Backfocus of the reducer is the ideal distance from your reducer to your sensor.-

Edited September 10, 2020 by Robindonne

[John]

It is probably best if this thread deals with @Steve Clay's issues with the Baader Steeltrack in his ED120 scope rather than open up a general discussion on other scopes, definitions etc.

I wish I could help myself but I use a Moonlite focuser with my ED120.

 

 

 

[JamesF]

13 minutes ago, John said:

It is probably best if this thread deals with @Steve Clay's issues with the Baader Steeltrack in his ED120 scope rather than open up a general discussion on other scopes, definitions etc.

Yes, I think we could end up in a maze of twisty-turny postings, never quite sure which telescope the comments apply to.  I believe I may be able to offer some enlightenment, @wornish , so if you want to start a new thread I'll be happy to ramble a  bit in that :)

James

[Adam J]

2 hours ago, Steve Clay said:

I've fitted a Baader steel track to my Ed 120. I use a 1.25 inch diagonal with a 2 inch T2 nosepiece

Problem is there isn't enough back focus available to get any of my starguiders to focus. I've put an extension tube onto the Nosepiece which has solved the issue but only have about 5mm to spare

I'm visual only but I'm surprised to have encountered this with the steel track.

Steve 

A picture would help me to understand the issue.

[wornish]

11 hours ago, JamesF said:

Yes, I think we could end up in a maze of twisty-turny postings, never quite sure which telescope the comments apply to.  I believe I may be able to offer some enlightenment, @wornish , so if you want to start a new thread I'll be happy to ramble a  bit in that

James

Didn't mean to mess up this topic sorry. Seperate thread started.  

[johnturley]

15 hours ago, Steve Clay said:

I've fitted a Baader steel track to my Ed 120. I use a 1.25 inch diagonal with a 2 inch T2 nosepiece

Problem is there isn't enough back focus available to get any of my starguiders to focus. I've put an extension tube onto the Nosepiece which has solved the issue but only have about 5mm to spare

I'm visual only but I'm surprised to have encountered this with the steel track.

Steve 

You say back focus, but do you actually mean out focus.

I think that most focusers designed for refractors these days are designed to be used with 2in star diagonals, which have a longer light path (typically 100-120mm) compared to 1.25in diagonals (typically 50 -70mm), so it is not surprising that you might need an extension tube of around 50mm to reach focus with a 1.25in diagonal. 

John 

Edited September 11, 2020 by johnturley

[Steve Clay]

1 hour ago, johnturley said:

You say back focus, but do you actually mean out focus.

I think that most focusers designed for refractors these days are designed to be used with 2in star diagonals, which have a longer light path (typically 100-120mm) compared to 1.25in diagonals (typically 50 -70mm), so it is not surprising that you might need an extension tube of around 50mm to reach focus with a 1.25in diagonal. 

John 

Great thanks for that John its given me the numbers between to 2 diagonals. Yes I mean out focus. I've now solved the issue with a Baader fine tune tube that connects to the diagonal Nosepiece with filter thread. It gives an extra 18mm so now have a bit to spare.

Cheers

Steve

[jetstream]

14 hours ago, John said:

I wish I could help myself but I use a Moonlite focuser with my ED120

Me too- did I copy you again John?😁

From what I've seen the SW120ED scopes need help with in focus, which the Moonlight provides and also a very stable focuser platform.