[philmorley]

I had a friend who is a professional astronomer (tracks asteroids to see if likely to hit earth), unfortunately lost contact over the years but when I had a nice new ds, his telescope (which has own building etc) had a 16mp camera. size of about 2 shoeboxes the electronics were liquid nitrogen cooled to cut down the noise

[JayLawson]

Hi Jocko
Here are the details for the photo:

Comet SWAN C/2006 M4 on Oct 27, 2006 at about 8 PM Pacific Time.

Telescope: Meade 10" LX50, used for guiding
Camera: Pentax ist DL, with Pentax SMC 300mm f/4 telephoto lens
Guiding: None, normal telescope track rate

18 exposures, 30 seconds each at 800 ISO

Processed with Images Plus, aligned on centroid of comet nucleus.

The star trails are due to the software aligning frames on the head of the
comet and the comet moving across the background stars. The gap in the star
trails is when I had to change batteries in my camera and realign.

Jay

[jocko_nc]

Thanks, Jay.

Cool. I have seen those Meades around. The software fixes the images based upon an alignment point that you define. I see that. Then, are the star tracks from the motion of the comet relative to the stars? That is cool. Do I read that you DID use a clock drive? Curious, the tracks seem to be circular like I would expect from the Earth's rotation. The stars are "fixed", I would expect to see a "straight" line from a tiny slice of a huge orbit. ???. I do not follow what you mean by "normal track rate."

I'm not even sure how telescope mounts work anymore, with micro-stepper and servo motor drives as prevalent as they are. Do they still align an equatorial axis to the North and move only the secondary axis? That is how it was done in the past. All you need is a synchronous motor running into a gearbox timed for 1/24 of a revolution per hour. An easy DIY. Do they now use a computer to calculate a trajectory of two axes simultaneously? I don't see why it wouldn't be easier now.

Thanks for the information. As you can see, I am really curious about this: A huge hobby of mine before I found interest in football, girls, and booze.

[LeoTaylor]

What software do you used for compiling the various images? I see what you describe but have no idea how would be done.

My last time playing around with telescopes was probably in the early 80's. Obviously, any kind of digital processing that existed back then would been used by the military. I saw the film camera kits but never tried it. Very cumbersome for the unfamiliar. It was various eyepieces and probably a ladder to get up to them.

If one "permanently" mounted a digital body at the top of a large Newtonian, could someone plug in a laptop and control the action from down at the ground? Wow, that would be something.

Is SCT mean the design, Schmitt - Cassegrain?

I got wonderful images from the old Newtonian mirror design. They are just such a PITA. 8 inches in an F10 (I think I had) means you are 80 inches to the focal length. Ouch. I made the tube from old fiberglass water heater cores.

What do you use for a clock drive? Did you build or are they reasonably available?

That moon shot was 1000mm into a .75 crop, 1500mm. Being nearly full, the light was quite bright and the exposure was fairly short. It was early in the night, about 45 degrees to the horizon. I think some distortion and color was due to that.

Yes, I used to love 1/4 moons and such for the crater detail, especially around the poles. My old telescope was so sharp, even at very high magnification.

--------------------------

Hi Jocko,

You did not say who you were asking all those questions. Jay answered some of them and he and I have some things in common.

He used a Meade Schmidt Cassegrain Telescope 10 inch LX50, I used a Meade SCT 8 inch LX3. Both scopes have motor drives. We both used Images Plus which supports Pentax RAW files (partially thanks to me).

I use external power for the camera thus don't have to change batteries mid session. I DID have a gap when doing star trails with a 19mm Vivitar lens last week. The power cable fell out and about 10 minutes later the batteries went dead. They don't last long at 100% duty cycle (NR turned off)! I lost over 50% of my planned hour of 30 second exposures. I need another dark sky opportunity to do this over with much longer arcs. This was processed with a free program from www.Startrails.de-Home .

http://pages.cthome.net/astroleo/northstar2.jpg

BTW: This is something non-telescope owners can do. Aim a wide angle lens North and take a succession of 30 second exposures.

Digital processing WAS being done by non military people in '78. I have an email friend who did digital astrophotography of galaxies with autoguiding:

Cloudbait Observatory History

I built my first home computer kit in 1976.

Your using 1000mm lens at .75 crop does not make the focal length 1500. At that rate my SBIG camera would make my telescope 10,000 mm and my Webcam would make my telescope 20,000 mm! It is still only 2000mm no matter what camera I attach, just the FOV changes.

Computer control of astro cameras has been popular for years. My SBIG camera can't do anything without a computer connected. Pentax is not very well supported by astro software, for example Images Plus does camera control only for the "Big Two" DSLRs.

I think I've covered all your questions.

[jocko_nc]

Thanks...

(other words to make a valid post)

[JayLawson]

Hey Jocko
Leo Taylor answered most of the questions, but let me see if I can fill in some of the gaps. I did use a clock drive (standard with this telescope) and it was polar aligned and tracking at the normal sidereal rate, meaning if all things were normal, the telescope would have tracked the stars. By doing this and taking 30 second exposures, the relative motion of the comet against the background stars in 30 seconds is minimal. When I processed the images in the software and told it to align on the comet nucleus, the background stars seem streaked. I always assumed the circular arc to the streaks were due to the fact the comet orbit shows as an arc on the sky instead of a normal polar motion circle. Hope that doesn't raise more questions than it answered.

What I meant to say by normal tracking rate was that I was not using an auto guider to take the photo. This is the practice of using second optical path and camera tied to a computer and software that makes minor corrections in your tracking to keep the object perfectly aligned.

Your description of the telescope mount is exactly how mine works. And you are right that some of the new ones move both axes using a computer to stay on track. That causes other problems that I don't like dealing with and I prefer to use polar aligned equatorial mounts.

I have other astrophotos taken with my istDL at my flickr page at
Astronomy - a set on Flickr

[Jonson PL]

Wim did this one, with the K20 :
Damaraland (Namibia): star trails (1 img): Pentax SLR Talk Forum: Digital Photography Review


Martin Zalba has done a lot of astrophotography with the K10 :
Re: Do you agree with this comparison of the 20D and nikon 700D?: Pentax SLR Talk Forum: Digital Photography Review

Here is his midblowing Nocturnas series :
Nocturnas - a set on Flickr

[jocko_nc]

Wow, those are fabulous.

[LeoTaylor]

There are some great star trail photos on the links Jonson PL provided!

I was wondering about the two nebulas in the first photo. Then I noticed that Polaris was missing. Then I realized Nambia is South of the equator and this was the Southern Sky.....

It seems those of us in semi-urban locations are always looking for a site with an unobstructed horizon. These astro-imagers have a low horizon but intentionally include the Earth or buildings in their images. My wife does the same thing with her star trails and keeps telling me I should do the same.

The Nambia shot was 30 minutes non stop, something impossible from Connecticut. Fortunately the StarTrails software from Germany can create all night stacks of 30 second images for us darkeness-deprived people.

I noticed in the discussion of the Nambia image he mentioned using Noise Reduction. He fell asleep while the NR was still processing! I noticed the discussion in another of the links said the K20D with CMOS sensor was noisier than Pentax CCD cameras. This may be the reason they don't allow NR to be turned off on long exposures.

[RiceHigh]

I bought a K20D this summer after using my istDL for general photographic use and also for some astrophotography. My problem is that the K20D will not let me turn off noise reduction for long astrophotos. I would take multiple 2 to 5 minute photos and do a dark frame subtraction. The istDL would allow me to turn off the noise reduction, but the K20D will not. Any ideas?

How would I make a suggestion to Pentax about including this in a software upgrade. I love the K20D, but noise reduction makes it nearly useless for astrophotography.

It is not possible, just because the Samsung sensor used in the K20D is too hot and noisy. The firmware is *intentionally* to force long time dark frame subtraction all the time and thus there is no option to "disable" it. In fact, firmware and software can just do nothing for an in-born hardware problem. For more details on what have been reported and found, see:

RiceHigh's Pentax Blog: K20D is Still "Hot" with Firmware 1.01

RiceHigh's Pentax Blog: Issue of Hot/Dead Pixels of the K20D