I hope I can banish mirror flop for ever....what I plan

[pyrasanth]

All Celestron SC telescopes suffer from mirror flop- even the Edge designs with mirror locks were meant to mitigate this but I can tell you that if your moving the mirror you get weird issues that can only be explained by the mirror moving or having a requirement to move.

The Edge 11" has been away for the last few months being repaired as the focuser developed an issue- it jammed solid so needed some serious TLC. I decided on a serious upgrade. The mirror will be locked & will never again be used to focus the telescope. I've had installed the Optec secondary mirror focusing system which moves the secondary mirror & not the primary to achieve focus in 200 micro steps. It is fully ASCOM compatible & supports all the popular focusing software methods. I plan to use the innovations foresight ONAG & in conjunction with a modified version of Sharplock again offered by Optec I should be able to keep focus for an entire session being fully automated & dynamic.

I will let you know how I get on and post some pictures of the new upgrade if it ever gets out of customs!

Clear skies to you all

[Owmuchonomy]

Excellent suggestion. I have always wondered why folk 'upgrade' their SCT focusers to more expensive dual speed ones when it does nothing I know of to stop a floppy mirror. Perhaps that explains why there are plenty in the FLO sale. I'm happy to be corrected though.

[Stu]

Should be interesting.  Which position has the mirror been locked in? I guess allowing you maximum back focus? 

[pyrasanth]

The mirror has not been locked yet. I will use the normal focus to achieve rough infinity with the Optec SMFS set at 50% maximum travel. I can then lock the SC mirror & use the SMFS to achieve any required focus. This gives an almost unlimited back focus as there is an amplification of x5 from the smaller secondary mirror. This is mounted on a very precise parallel rail to fine tune its motion.

[Stu]

15 minutes ago, Owmuchonomy said:

Excellent suggestion. I have always wondered why folk 'upgrade' their SCT focusers to more expensive dual speed ones when it does nothing I know of to stop a floppy mirror. Perhaps that explains why there are plenty in the FLO sale. I'm happy to be corrected though.

The EdgeHD I had had a locking mechanism which I used after fitting a Baader SteelTrack focuser. I didn't like the image shift and imprecise focusing by using the mirror focuser, but it was excellent after fitting the SteelTrack, no shift and precise focusing (motorised too with a SteelDrive unit)

[nmoushon]

With fitting a secondary focuser would there not be wires and thus creating star spikes? Unless its a wireless control I guess. Is there a link to the secondary focuser? Would be interested in reading up on it. 

Also wouldn't doing the same thing (with perma locking the primary) and then added crayford style focuser on the back do the exact same thing? Except that there is no movement in any of the mirrors, primary or secondary. 

[pyrasanth]

This is the link https://optecinc.com/astronomy/catalog/fastfocus/index.htm

There can be secondary spikes but it can be mitigated by using a split Ethernet wiring system which spreads the diffraction pattern like a spider. Whilst you could lock both the mirror & use a secondary focuser the issue would not be a complete solution for imagers as this would invariably soak up a lot of the available back focus somewhat limiting what accessories could be attached. The SMFS compliments the back focus.

[Davey-T]

Sounds like an expensive upgrade, hope it all works out.
I looked into the ONAG once but I believe at the time the guiding was behind the filter so not good for NB not sure if it still applies.

Dave

[pyrasanth]

16 hours ago, Davey-T said:

Sounds like an expensive upgrade, hope it all works out.
I looked into the ONAG once but I believe at the time the guiding was behind the filter so not good for NB not sure if it still applies.

Dave

This is a common interpretation mistake for the ONAG. The guide camera sits at the back of the ONAG so gets the full parallel light path of IR radiation which the beam splitter filters to the guide camera which are very sensitive to IR- The IR simply passes through the mirror. When the light beam hits the beam splitter mirror the light is directed at 45 degrees to the imaging camera. This path would contain your narrow band filters or RGB filters as well as any light pollution filters with the imaging camera as the last device in the chain. This means the ONAG never "sees" any of any filters & thus is not affected by them. The mirror is so precise that there is no image degradation but you can get some ghosting on very bright stars.

However you don't want to put a UV/CUT filter anywhere in the path to the guide camera as this would remove the IR radiation which is required to guide by.

[pyrasanth]

16 hours ago, Davey-T said:

Sounds like an expensive upgrade, hope it all works out.
I looked into the ONAG once but I believe at the time the guiding was behind the filter so not good for NB not sure if it still applies.

Dave

This is a common interpretation mistake for the ONAG. The guide camera sits at the back of the ONAG so gets the full parallel light path of IR radiation which the beam splitter filters to the guide camera which are very sensitive to IR- The IR simply passes through the mirror. When the light beam hits the beam splitter mirror the light is directed at 45 degrees to the imaging camera. This path would contain your narrow band filters or RGB filters as well as any light pollution filters with the imaging camera as the last device in the chain. This means the ONAG never "sees" any of any filters & thus is not affected by them. The mirror is so precise that there is no image degradation but you can get some ghosting on very bright stars.

However you don't want to put a UV/CUT filter anywhere in the path to the guide camera as this would remove the IR radiation which is required to guide by.

[Owmuchonomy]

18 hours ago, Stu said:

The EdgeHD I had had a locking mechanism which I used after fitting a Baader SteelTrack focuser. I didn't like the image shift and imprecise focusing by using the mirror focuser, but it was excellent after fitting the SteelTrack, no shift and precise focusing (motorised too with a SteelDrive unit)

Yes I understand that option for the Edge. Mine is the standard SCT. I did try the Borg helical  focuser but without the lock it was a bit superfluous.