andrew s

From a pure control engineering perspective a mount with excellent mechanics and firmware with On Axis guiding would be ideal. Closing the loop on the target is always the final cherry on the cake! Regards Andrew

I don't think you would. It's PEC is low and slow and it is stable without them.(Based on reports on here.) Regards Andrew

Yes all mounts with DC or servo motors have encoders built in to the motor control but normally when talking about encoders people mean shaft (RA, Dec) encoders Regards Andrew s

@vlaiv when I chose my last mount the key factors were, in order were: mechanics, firmware, software integration and finally support.. That's why I went for a Paramount (no encoders) Regards Andrew

My last post crossed with @vlaiv. I agree with your points but to a degree it's a matter of choice both work. For some types of mount the encoders are an integral part of the drive system control (direct drive, some friction types) and without them the system is not stable. Regards Andrew

@RayD just to be precise. PEC is a form of feed forward control where a model is used to make a correction before an anticipated error occurs. The same is true of mount/atmospheric models. Shaft encoders are used in feedback control where the correction rate is so much higher than that frequency of errors encountered due to the mechanics of the mount and scope it behaves like a feed forward system. Either can reduce periodic error to very low levels with good quality mounts. Regards Andrew

I have a Paramount ME II with a OO ODK 16 and spectrograph attaced. This is a challenging load as the spectrograph is quite long and assembled from several components. The mount does not have encodes on the axis but you can still use a pointing/tracking model. I don't bother guiding as I take short exposures (10 -25 s) . For interest I measured the drift over 4 hrs 13 min of exposures last night. It drifted 1 arc sec in RA and 85 in Dec so about 0.33 arc sec per min. I suspect the Dec drift is due to the spectrograph and a stiffer imaging rig would be better modeled. Anyway just for interest, it show you can use modeling without encoders. Here is the spectrograph. Regards Andrew

Maybe the Dec axis encoder on the EC2 is about removing backlash when it does have to move. Regards Andrew

Pending a new thread. Taking the definition of empty magnification as making the image scale such that the images highest resolution components are over sampled by the eye (I.e. the eye could fully resolve it at a lower magnification) then if the illumination is high enough and the atmosphere steady enough then there should be no issue. The number was set in an era of lower quality optics, especially eyepiece design, by heuristics based on observation. As with the various resolution limits they are arbitrary. Science does not provide hard and fast numbers only useful ones in specific cases. Regards Andrew

Maybe I misunderstood you. My view is simple, if your equipment doesn't add to the FWHM of your stars beyond that determined by your local seeing then you can't do better. I believe several mount/software technologies can do this, some with some without guiding. It does not matter to me which technology you chose if it works reliably and achieves the goal stated above. Regards Andrew PS Unless you can afford pro level adaptive optics.

No problem, I will refrain from contributing to this thread further. Regards Andrew

Yes it's focal length but I don't know of any fast astronomical telescopes with a "long" focal length. I should have been more precise. Regards Andrew PS I do but they are professional telescopes

Most fast telescopes suffer from field curvature unless they have a built in flattened which is not the norm. Regards Andrew

There is no such thing as perfect polar alignment. The position of the refracted pole varies with where you are pointing in the sky. Without some form of model to compensate for this you will get drift. The best you can do is aim for the mean refracted pole. Regards Andrew

Gary gave a fascinating talk on it at the Chester Astronomical Society last year. Well worth following up his article. Regards Andrew

@Peter Drew I agree for extended objects but for stars I was led to believe a higher magnification darkened the background while leavig the "point source" stars largely unaffected. However, it's so long ago that I looked through a telescope I am relying on hear say. Regards Andrew

Same here

Excellent to my untutored eye. What is the thinking behind the two different Ha bandwidths? Regards Andrew

Just remember astronomical twilight is an arbitrary choice, albeit informed by experience from pre CCD/CMOS days, you can stretch it a bit on either side. Regards Andrew

Oh come @JeremyS it is for a Takahashi after all. Regards Andrew

You do realise it's a psychoactive compound that stops you thinking or behaving rationally with respect to Takahashi products for the rest of your life. Regards Andrew PS I think they have supplied a similar compound to a certain tripod manufacturer.

Very nicely executed. Please don't take this the wrong way but as one who could never produce such a fine rendering do you aim of accuracy or an artistic result or something inbetween? Regards Andrew

I don't think you will find a paper atlas to mag 15 and if you did it would be enormous. I have one to mag 13.5 at it's in 3 large boxes. Regards Andrew

Will you lot stop drooling over Takahashi refractors your dissolving my tablet. Regards Andrew

Hi @saac your scope is looking good. I donhave a spare Thorlabs 50x25mm echelle grating you can have if your current spectrograph is not up to the job. Mind you you will need to build the rest of it. 😛 Regards Andrew