Ringed Saturn Visible All Night

[davefoc]

Bit of a bummer here. I got my brother's telescope all set up today and functioning. I did experiments with my camera to compare the resolution of my brother's fancy Celestron NexStar with my Caon T5i attached and my SX1 camera. (The Celestron won) I also looked at using RAW images versus JPEG images as far as maximizing resolution (I couldn't see any advantage to the RAW images).

So I was looking forward to the night sky to see what I could see, but the clouds have rolled in and I can barely make out a bright moon through them. Nothing else is visible.

 

[Southwind17]

Bit of a bummer here. I got my brother's telescope all set up today and functioning. I did experiments with my camera to compare the resolution of my brother's fancy Celestron NexStar with my Caon T5i attached and my SX1 camera. (The Celestron won) I also looked at using RAW images versus JPEG images as far as maximizing resolution (I couldn't see any advantage to the RAW images).

Did you study the information in the website that I posted previously (see hereunder)?

Hi davefoc. To avoid further frustration and disappointment it's probably worth investing a couple of hours of your time reading up on telescopes, and understanding what the limiting factors are to even seeing celestial bodies well, let alone photographing them.

I've found this a particularly interesting and readable reference. There's stacks more on the technicalities of telescopes and viewing the night skies - just go to the home page and start there.

Much of what is written about the characteristics of telescopes can be interpolated and applied to cameras. Accordingly, you'll soon realise the limitations of a regular DSLR camera (even with a zoom lens) in photographing planets and their moons. <snip>

Here's a pertinent extract:

It can be seen that the larger the telescope aperture, the smaller will be the Airy disk and the greater the resolution. As an example, the resolution of an 8" telescope is 0.68 arcseconds. A 12" telescope has a resolution of 0.45 arcseconds. For reference, Jupiter is about 45 arcseconds in diameter.

Perhaps you'd care to calculate the resolution of your camera lens to explain your disappointment!

Interesting thought, though, what takes precedence with a camera when it comes to resolution - the lens diameter or the number of pixels? Will the 'natural' resolution, i.e. by reference to the Airy disc, always trump that determined by the pixellation of the CCD? At what point does more pixels become counterproductive?

 

[davefoc]

Did you study the information in the website that I posted previously (see hereunder)?

Study would be too strong a word. It was written clearly but there was a lot of details there that were a little beyond my interest level. One thing I found interesting was the fact that when the telescope's magnification factor increases the planets get dimmer but the stars stay the same. It isn't unexpected when one thinks about the fact that a planet's image keeps getting bigger with greater magnification but a star remains a point source but I had never thought about it.

Here's a pertinent extract:


Perhaps you'd care to calculate the resolution of your camera lens to explain your disappointment!

It would be an interesting thing to do. Perhaps somebody else would like to take a shot at that, my nerd neurons are at a low ebb right now after learning how to mount the telescope use the telescope, the finder, the registax software, post the images and fit in a bit of the rest of my life in the last couple of days

Interesting thought, though, what takes precedence with a camera when it comes to resolution - the lens diameter or the number of pixels? Will the 'natural' resolution, i.e. by reference to the Airy disc, always trump that determined by the pixellation of the CCD? At what point does more pixels become counterproductive?

I don't know the answer but it seems like there is a limiting resolution for both the telescope and for the sensor and improving the resolution of one above the other would not improve image quality.

Any way, I posted the results of my experiments here:
https://plus.google.com/u/0/photos/109328117361721097794/albums/6024160183536733713

There were a few disappointments. Apparently Saturn was in the sky last night, at least the telescope would slew to where it was supposed to be. The sky might not have been clear enough or it was too close to the moon or my alignment procedure on the telescope was too far off for me to find it. I did find Mars and the Moon with it, although the alignment was off enough that it didn't actually point exactly to Mars. I had to figure out how to use the little finder gadget to home in on Mars and I left it on so now I need to buy a new battery.

The moon picture came out amazingly good I thought. I had never looked at an image of the moon very carefully and those craters with the giant streaks of ejected material are pretty amazing.

I took a movie of mars and it might have been interesting to see what registrax would do to it. One thing I had to work through was that registrax seems to be able to work with MPG files but it didn't work with the ones I created and I didn't realize that because I didn't know what it was supposed to look like when it was working. Eventually I converted the mpg files to avi and that worked. Unfortunately I didn't shoot the movies in high def video so the comparison of the moon image taken as a high definition single image and the moon image created by registax from 720 px movie wasn't a very good one.

One thing I particularly liked in the moon image is that you can see the roughness of the terrain along the edge of the moon especially in the top left side of the image.

 

[Soapy Sam]

Summertime stargazing in Scotland is tricksy.
First, it doesn't get dark till about 23:00.
Then it starts getting light again by 03:00.
And it actually rains more than in winter.

I did glimpse the moon a couple of nights ago, but a sighting of Saturn in mid June would require planning and luck.

 

[Southwind17]

Here you go davefoc ... this certainly makes the point about size being king!

Extract:

One of the most challenging aspects will be to create and install the telescope's 39m-wide (130ft) primary mirror.

This will be made from 798 smaller hexagonal mirrors, each 1.4m-wide (4.6ft) and less than 50mm (2in) thick. Prototypes are currently being created by OpTIC Glyndwr Ltd, which is linked to Glyndwr University in Wales.

This technology will allow the telescope to capture 15 times more light than any other optical telescope and it will create images that are 16 times sharper than even the Hubble Space Telescope, which orbits high above the Earth.

Dr Verma said: "This telescope will be so powerful that it will collect enough light to look to the observable limit of the Universe - soon after the Big Bang when the first stars and galaxies formed.

"We'll be able to see when the Universe switched on."

She said that it could also provide a detailed view of exoplanets - other worlds outside of the Solar System.

"Well be able to look at the planets directly, look at their atmosphere and potentially look for signs of life," Dr Verma added.

 

[davefoc]

Here you go davefoc ... this certainly makes the point about size being king!

Extract:

Thanks gor the link, its interesting that thry went with the single giant telescope approach instead of the dual telescope approach to maximize resolution which is a feature of a lotbof the newly desigbed trlescopes. Im on a tablet right now and the internet is a little tedious for me. Butid like to see if ican find out why they went this way,

 

[Beelzebuddy]

Interesting thought, though, what takes precedence with a camera when it comes to resolution - the lens diameter or the number of pixels? Will the 'natural' resolution, i.e. by reference to the Airy disc, always trump that determined by the pixellation of the CCD? At what point does more pixels become counterproductive?

Well, my area of expertise is microscopy, but the principle is the same. You want your pixel width to be no more than half your resolution. That's the Shannon limit. Anything beyond that is gravy - you're making pretty pictures, not detecting events, so a little empty magnification will only make things better.

For a quick-and-dirty check if your pixel density is a limiting factor, grab any picture and look at a few stars. Are they single pixels, or tiny clumps 2-3 pixels wide, with a bright peak in the middle? If the former, getting a better CCD will probably make a difference.

 

[MG1962]

Thanks gor the link, its interesting that thry went with the single giant telescope approach instead of the dual telescope approach to maximize resolution which is a feature of a lotbof the newly desigbed trlescopes. Im on a tablet right now and the internet is a little tedious for me. Butid like to see if ican find out why they went this way,

But it is not a single chunk of glass. It will be made with 80 segments, tied together with adaptive optics

 

[edd]

But it is not a single chunk of glass. It will be made with 80 segments, tied together with adaptive optics

I believe davefoc is referring to the optical interferometry approaches that let you synthesise a larger aperture telescope from smaller ones - as used by the Large Binocular Telescope and the Very Large Telescope. The E-ELT may be 80 segments, but they're still functioning as basically one mirror - they all focus to the same point.

This doesn't gain you anything in collecting area for the same amount of glass, which is one major reason for building such big telescopes. It does mean you have to build more mounts for the telescope, which may or may not have an impact on the cost, depending on the relative cost of smaller and larger mounts.

Interferometry is still challenging. The VLT was built with it in mind and it still took a good couple of years between the individual telescope commissionings and getting the interferometry working. Even then, for many projects the VLT is used for it's just not useful, especially given the difficulty using it. The VLT does also gain in flexibility by being able to treat the four component telescopes as individual units to do four different things at once of course.

If you're wanting your giant telescope simply because it is a giant light bucket and therefore very sensitive, I can see good arguments for making it a single dish as a simpler easier to manage and possibly cheaper design.

Also once you've got that much glass and adaptive optics you're already well in to the territory of superb resolution without having the extra fiddling of interferometry.

It's a complicated business weighing up the two and I can't find documents about the E-ELT design process that covers it, but I might run into someone next week I can bother about it over a drink...

http://en.wikipedia.org/wiki/Astronomical_interferometer

 

[Southwind17]

Here's a shot I grabbed on Saturday morning using the video function of a Nikon D3300 and a still generated with Registax. Well worth getting up at 4.00 in the morning for!