andrew s

At least you can save on ink and just use gray scale 😀 Regards Andrew

I am sure you know this but doublets have a right and wrong way round. Normally the strongest outside curve is the side for the collimated, parallel, light. Regards Andrew

Well I got a full run last night on V833 Tau trying to capture a spectra of it flaring. I managed some 1283 exposures of which about 1260 were low resolution spectra. Some at the end were of the roof as it closed on high humidity. Just need to look through them now... ... well actually I will use astroimagej to do photometry on batches of images looking for a change. Regards Andrew

That is the correct diffraction pattern for almost monochromatic light. Look at HST images and you can see coloured "dots". In RGB they get washed out. Regards Andrew Yes it is analogous to how a diffraction grating creates a spectrum.

Like it or not your image is competing to catch the eye of the editor or his team . Maybe not exactly the same but both are about seeking recognition for your efforts. Regards Andrew

Do the SGL competitions have UK and other competitor categories? Regards Andrew

What do you think most people buy the mag for? I suspect hard core imagers are a small proportion of the readership. Regards Andrew

Yes as countless images on SGL testify. Having a permanent set up reduces the problems considerably, having a less cloudy than typical UK skies reduces the issues further still. Regards Andrew

The saucer now landing at alph centauri is for... Regards Andrew

It's the focal ratio that counts and the collimator .ens should match the focal ratio of the feed telescope. The camera lens needs to be faster to catch the divergent Ray's of the spectrum. The SIMSPEC design software gives the details. Regards Andrew

But do you have to dress as C-3PO to use it? Regards Andrew

As a non imager, I full support those who wish to try their hand under the skies they have with the equipment they can afford including the processing tools. I see how the challenge can be rewarding and worth while. Personally, looking at yet another Mxyz or ICabcd of almost any quality is a been there seen it before experience. Which is why I went into spectroscopy. I suspect most magazine readers are non imagers and are looking to be impressed with images and artist's impressions. Impact over content seems to be the order of the day in both text and visuals. Go to any gallery or concert hall and they seek to display the best. Can you condem a popular magazine for following suit. You may (should) delight in your children's nativity play but it won't get to the west end. But, it is nonetheless worth while. Regards Andrew

Apochromatic objective, expensive but... Another possibility is a well corrected camera lens often available second hand at reasonable cost. Regards Andrew

If you plan a full range visible Littrow then I strongly suspect an achromat will not allow you to focus well across the spectrum. Regards Andrew

Shelyak sell slits intended for their spectrographs but you can buy them separately. Regards Andrew

Your image @vlaiv is more akin to the classical wave model. In variation approaches you start by pinning the beginning and end and the do the variation over all simple (no loops, touching) paths between them. Regards Andrew

The book goes into the details. What is happening is that they are using Feynman's path integral approach to give a picture of what is happening. As with classical variation methods all paths are considered and in this case all are traversed at the speed of light c. I don't really like it as an image as people tend to believe it is real rather than a mathematical tool. Regards Andrew

No it is just a beam splitter, 4% of the light goes to a guider 92% to a non reflective slit. Used before reflective slits became readily available. Regards Andrew

If you want to know more Richard Feynman's book QED The StrangeTheory of light and matter is still good read even though published in 1990. Like the video it leaves out the polarisation of light. Regards Andrew

I fully agree, we have very effective theories that each have a range of applicability. Regards Andrew

I built one using an echelle grating and a Borg 55mm refractor. I introduced the light using an off-axis guider. A scaled down version of this http://www.astrosurf.com/buil/vhires/test.htm. I have pondered using off-axis paraboloids but could not find suitable ones. I also gather they are hard to collimate so I would not try moving it to focus. There is all the other stuff on Christian Buil's site including the LHIRES III Good luck. Regards Andrew

@Tiki I agree Gravity is a force in Newtons theory but not in GR. Regards Andrew

Not many people take the trouble to measure their system. Also the differences are small as is the error introduced. It is probably just one of several issues that lead to the anecdotal comments on some cameras being easier to process than others. It has been discussed before, I finally remembered I had discussed this with Andy Wilson (who raised it) on the BAA forum here https://britastro.org/node/12121 . Regards Andrew

You use quantum tunnelling every time you turn on a switch. The inevitable oxide on the contacts is an insulator and electrons tunnel through it. Regards Andrew

It is the same issue as getting a quantum theory of gravity. Namely the treatment of time. QT requires a well defined time coordinate but you don't have one in a curved space time. Regards Andrew