Merlin66

A blatant plug....my book “Astronomical Spectroscopy for Amateurs” covers most of the design bases. Some very helpful links also on the Webpage (see below).

Ok. The distance from the collimator to the grating is non critical, has no impact on the collimator focal length.

Louise, The collimator lens focal length is designed to match the physical distance between the slit and the collimator lens. Not sure how much allowance Paul has designed into the arrangement.

Louise, Sounds like things are progressing...if you consider the finder objectives, just check the focal length..... Keep it going!

Yeah, It seems to be in Spanish = sin

https://www.bbc.com/future/article/20191031-hilda-geiringer-mathematician-who-fled-the-nazis Look at the main image, the formula on the board.......... Something odd?? What's "sen"

Bombs me out, here in Australia......bumma!

This is due to the "encoder" ring positions used by EQMod to read the mount position. Remember that all RA angles end up at the pole.......Once you Park/ Unpark the RA quickly re-sets to match your target and CdC.

Andy, You really need to use a Planetarium program to get the most out of EQMod. You can set-up EQMod through the Planetarium (I used Cartes du Ciel) as your "connect to telescope" If the Comms are OK you end up with a pop-up control panel which replaces (and more!) the Handcontroller. Once set-up you can click a star in the Planetarium and get the mount to GOTO it. You can sync on the star (and others) to improve the GOTO. The help manual downloads with the EQMod software.

Yes, set the "on Camera" for the mount, and "EQMod Ascom HEQ5/6" for the Auxiliary. See photo.

If you add to the Auxiliary mount option in PHD2, it obtains the mount position and uses that.

You can re-use your previous PHD2 calibration without using pulse guiding - I do it most of the time.......using an ST-4 connection.

look forward to hearing about the solution.....

AR 2750 and AR 2751 are now noted on Raben and show on the current GONG images....

Hmmmm, That’s interesting. I use a ATiK 314L for image (spectrograph) acquisition, a Lodestar for guiding, JMI focuser and PHD2 guiding all under ASCOM. with CdC and EQMod - never seen an ASCOM error message !!!!

Michael, 1 arc sec is 1 second of arc. A degree of arc has 60 min of arc, or 60 x 60 =3600 sec of arc. So you could say, 1 arc sec is 1/3600 of a degree = 0.000277 degree.

Alternatives: You still need a camera control and image acquisition software - a cost effective solution is AstroArt http://www.msb-astroart.com/ A complete software for astrophotography: image processing, astrometry, photometry, camera and telescope control. All major cameras, telescopes, filter wheels and focusers are supported by Astroart. Updated plugins are released for free. For tweaking the images PaintShopPro https://www.paintshoppro.com/en/ has all the features of PS and most of the Plug-ins.

Ben, May give you some flexibility over the final spacing when using an OAG.

Ben, Yes that's probably the way to go......

Ben, On SCT's where the focal length is very long and there's a possibility of the main mirror moving (slop...) during a lengthy exposure, it's very common to use an Off axis guider (OAG) set-up. This is positioned in the optical path, close to the imaging camera and diverts some of the incoming light to a fixed guide camera, hence any movement of the telescope optics can be compensated and achieve good guide results. Mounting a separate guide scope and camera relies on a good rigid mechanical mounting with no slack or sag during operation, and unfortunately may not fully compensate for any eventual mirror slop in the SCT. I use a reflective slit which acts like an OAG on my C11 @ f10 for guiding. I can effectively guide for as long as necessary - no issues, no drama. Hope this helps. https://www.firstlightoptics.com/blog/blog-53.html The above review of the OVL OAG is well worth reading.

Louise, For the Spectra-L200 and others I've built, I got my mirrors from Knight Optical https://www.knightoptical.com/ The stainless screws came from Model Fixings http://www.modelfixings.co.uk/fixings.htm My springs we made for me by Airedale springs https://www.airedalesprings.co.uk/

I use the same Carton 100 f13 objective on the digital spectroheliograph. Impressive performer.

Nigella, Yeah, I agree. Soft and flowing is the look to strive for. You'll find ImgPPG is very capable....practise, practise........

Onwards and Upwards....

Louise, OVIO are the local French supplier, Jeulin sells their product outside Paris and France.