Hi David, I've just bought the Baader Steeltrack for my Meade 127mm triplet and struggled to find a video covering how to install an EAF (Gemini), thanks for a very well explained tutorial , clear skies, Keith ( UK)
Thanks for the question - I'm doing some deep sky imaging with this setup tonight, though not with the OAG. I'm getting as low as .4 arcsec total RMS without the use of a guider in the observatory - the CEM120 is behaving very nicely at the moment. However, I see no reason why you could not use an OAG and filter wheel. It will just need to be added in your backspace calculation. This is more critical if you have a reducer in the mix as well. I am not using a reducer, but I have been targeting 151mm backspacing to meet the guidance published by Celestron for optimal performance. I have to say, I was a little skeptical about using this RIG for DSO work, but the quick grabs I'm getting tonight on some globs and a planetary nebula are really nice - even at the level of oversampling my planetary camera is delivering. Cheers!
@AstroDNAObservatory that's impressive. I have a 9.25 mounted on AM5, I do get good results with oag, but focusing is always a challenge. I really like your idea of a Crayford focusser with the mirrors locked in place. Hopefully, I will finally see the illusive V curve. I get all kinds of strange shapes, not quite V lol.
If you go the crayford route, which I like, you'll just have to spend the time to determine the backlash setting for your setup. Once you lock that in, you'll get your curve! Cheers!
I agree. Very much enjoying this product. It has about a 30mm travel, so I make sure to get in rough focus while the Baader is set around 15mm. This gives me equal play inward and outward. I also always make sure my final turn on the rough focus knob is couter-clockwise - pushing on the primary mirror minimizing shifts during the session. Cheers!
what about thermal expansion of the telescope? It's much more than the focuser backlash. Let's say an increase of 1 degree Celsius with my C8 changes its focal length by 190 microns. Things get worse with Barlow. I'm wondering what to do if the telescope changes focal length to get the best focus each time. Should we adjust the primary position or should we accept that the size of the planet may change during the night because the focuser can only find the best focus without any focal length control? Why not install a focuser moving the secondary mirror to avoid touching the primary subject to tilt with certain telescope positions and loss of collimation as a bonus? This solution gives free access to the rear of the telescope, making it possible to install a reducer which will be focused by the secondary mirror. Collimation can be performed and the secondary configuration can be fully aligned to the center of the baffle axis regardless of the focal length. the dilation can be compensated in order to maintain the focal length. Additionally, the secondary can be replaced with a hyperstar when necessary. May be this will improve the spot because the Schmidt blade primary mirrror is always the same and this has a impact of optical abberation like Coma.
I'm going to need to pause and read your comment more carefully. You are raising a number of points and asking about mechanisms that I am not sure exist (secondary mirror focusing). I can answer part of this now - the part relating to the effects of thermal expansion - I generally run a trigger on HFR increase (5%) to refocus. This is helpful for DSO imaging. With planetary, I generally use contrast detection to obtain as sharp a focus as a possible - given the stacks are usually a couple of minutes long, I don't concern myself with the potential of thermal expansion in that short burst. The discussion around secondary mirror movement is odd to me at the moment, as the secondary of the SCT is fixed in a housing within the corrector plate - also fixed at the end of the OTA. Having said all that, I will re-read your post tomorrow! Cheers.
