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Focuser all the way in tube with 55mm back focus problem

Astrophotography Beginner Equipment Optics Orion
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#1 davidmalanick

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Posted 20 June 2021 - 07:00 PM

Didn't know whether to put this in Equipment or Refractor's forum, figure somebody with  refractor might had the same problem.

 

I have a perplexing problem trying to reach 55 mm of back focus with my telescope. As you can see in the picture, between the MAIN camera sensor and the back of the Orion reducer/flattener the distance is 52 mm. With that set up it leaves approximately 3 mm of space before the focus is all the way up against the tube. My stars are little elongated in the corners so I know I need to get that up to 55 mm of backspace. I also have a UV/IR filter inside the reducer/flattener so I really probably need an extra .5 mm. When I put 3 mm worth of spacing in between the sensor and flattener, to bring it to 55 mm, focuser is all the way in the draw tube with no more movement possible. And the stars are just quite not in focus. If the focuser tube was a few millimeters longer, the stars would be in focus. I do have a added adapter between the telescope and the reducer/flattener that adds 1 mm. It is the new Orion flattener/reducer made for this telescope. However, I had to add the adapter because the reducer/flattener only fits the models made in the last year. The reducer/flattener requires 55 mm of backspace. I really have no solution for this, kind perplexing that the focus or would be all the way in the tube with such a standard set up as this. Any ideas or suggestions?

55mmproblem

 

Any help or ideas would be very much appreciated.

Thank You


Edited by davidmalanick, 20 June 2021 - 09:06 PM.


#2 rgsalinger

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Posted 20 June 2021 - 08:08 PM

Why can't you just put a 3mm spacer between the OAG and the main camera? Then just move the guide camera out a bit to compensate. Then you would have both par focal and at 55mm. 



#3 davidmalanick

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Posted 20 June 2021 - 09:03 PM

Why can't you just put a 3mm spacer between the OAG and the main camera? Then just move the guide camera out a bit to compensate. Then you would have both par focal and at 55mm. 

It's not the about the guide camera, it's the main camera image train that will not work with 55mm between the MAIN camera sensor and the back of the reducer.

At 55mm the focuser is all the way in and the stars are out of focus.  If I take out 3mm of spacing and go to 52mm of backspace, the stars are elongated showing I need more backspace.

At 52mm of backspace, there is just about 3mm of travel left in the focuser. 

At 55mm of Backspace the focuser is in all the way and can't focus that last little bit needed.

Can't set 55mm of backspace AND get the stars good.



#4 rgsalinger

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Posted 21 June 2021 - 12:50 AM

I found this on the Orion website which says that perhaps you are wrong in the BF requirement for the reducer (if this is the right one).

 

Orion 3" Field Flattener for EON 115/130 EDT Refractors

 

"The 3" Field Flattener has a backfocus, or flange focal distance, of 51.5mm, though it is known to be effective at up to 5mm on either side (46.5mm - 56.5mm). It adds 88.8mm of mechanical length to an imaging train.

 

If the flattener is really 3.5" long, then the focuser is going to have to be racked pretty much all the way in. Sounds like a terrible design to me. 

 

Rgrds-Ross


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#5 davidmalanick

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Posted 21 June 2021 - 03:58 AM

I found this on the Orion website which says that perhaps you are wrong in the BF requirement for the reducer (if this is the right one).

 

Orion 3" Field Flattener for EON 115/130 EDT Refractors

 

"The 3" Field Flattener has a backfocus, or flange focal distance, of 51.5mm, though it is known to be effective at up to 5mm on either side (46.5mm - 56.5mm). It adds 88.8mm of mechanical length to an imaging train.

 

If the flattener is really 3.5" long, then the focuser is going to have to be racked pretty much all the way in. Sounds like a terrible design to me. 

 

Rgrds-Ross

It's not the big 3" flattener that's giving me problems, I also have that, it's a flattener only.  It's their NEW 0.8 flattener/reducer for  the EON 115/130. They just came out with it.  Needs 55mm backspace. I agree, that it's a bad design.

Have a Feather Touch focuser coming in the mail that I bought used here on CN.  Hopefully it works better.




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