PDA

View Full Version : Unanswered questions for astrophotography



Hatan
2007-Apr-22, 04:56 PM
Hello,

I've been reading a lot about type of astrophotography and accessories, but I have some unanswered questions. So if you can give me some advises I would greatly appreciate it.

So far, my astrophotography has been based on Afocal and I might consider moving to something more advanced - prime focal (wich also mean new telescope, mount, guiding and of course new camera).

So my first easy question is, what is the difference between a CCD and DSRL cameras. Some people seem to consider them the same thing, other consider them as 2 different categories.

Second question a bit harder. A lot of people are talking about video cam(Phillips toucam or the StarShoot Solar System Color Imager II etc) and they say they take GREAT planet pictures, but how can these be better than a 10 megapixel Camera (considering both of them supporting prime focal)? The webcams are around 150-200$ and you can now have a 8-10 mega pixels for 250-400$. The webcams are around 0.3 - 1.2 mega pixels which basically mean the 10 mega pixels have rougly 3-5 zoom bonus right there (because of the precision).

Third question, How can a webcam: this one in particular: "DSI PRO II w/CCD color filters" be SO expensive (700$) and only supportig a max resolution of 752 x 582. What is so great about it compared to the other 150-200$ webcams?

And fourth questions, this same webcam is called "DSI" for DEEP SKY Imaging". I thought that webcams were only good for planets and you absolutly needed a CCD for deep sky imaging? How can this webcam succeed in taking deep sky objects?

So that's it, thanks in advance :)

Siguy
2007-Apr-22, 05:44 PM
1.) A CCD camera is something that's MEANT for deep sky imaging, it connects your telescope and computer so that they work together. A Digital SLR camera is high resolution and works without graininess but it works on it's own. If you want to see what a standard Canon EOS 350D can do for astrophotography, go here. This guy is amazing. http://octane2.deviantart.com/

2.) Telescope webcams are crap. They are only for you if you just want to go cheap and only get pictures of the Moon. They give very blurry images of planets. You need a high quality imager like a Meade DSI if you want to go that way.

3.) It isn't like other webcams. It is meant for deep sky CCD imaging. It isn't about resolution.

4.) DSI is a CCD camera. It isn't really a webcam.

Siguy
2007-Apr-22, 06:40 PM
I also want to add that with the Meade DSI, you can get more for your money if you buy it coupled with a good Meade telescope for $130 (B&W) or $228 (Colour). Much more professional deep sky CCD imagers that cost much more are worth the cost, but low resolution ones like the DSI aren't worth it as much if you buy them alone.

Just don't forget to buy a telescope on a sturdy equatorial mount. ;)

Kaptain K
2007-Apr-22, 08:05 PM
The secret of webcams is that you don't take just one image, but tens, hundreds, or even thousands of very short images and combine the best of them with a program like Registax (freeware). By combining only the best images, image quality and resolution can approach the theoretical limits of your optics. Amateurs with modest scopes (8-12 inches) and webcams are getting better images than the pros with unlimited equipment were able to do a generation ago!

ozark1
2007-Apr-23, 05:48 AM
Hello,
So my first easy question is, what is the difference between a CCD and DSRL cameras. Some people seem to consider them the same thing, other consider them as 2 different categories.

The primary difference is that the astro CCD has very low noise compared to the DSLR. The astro CCD is also more sensitive to light/ has bigger pixels.


Second question a bit harder. A lot of people are talking about video cam(Phillips toucam or the StarShoot Solar System Color Imager II etc) and they say they take GREAT planet pictures, but how can these be better than a 10 megapixel Camera (considering both of them supporting prime focal)? The webcams are around 150-200$ and you can now have a 8-10 mega pixels for 250-400$. The webcams are around 0.3 - 1.2 mega pixels which basically mean the 10 mega pixels have rougly 3-5 zoom bonus right there (because of the precision).

As has already been said, 1 long exposure is easily beaten by a stack of the best of 10000 pictures. It is to do with the (lack of) atmospheric stability.


Third question, How can a webcam: this one in particular: "DSI PRO II w/CCD color filters" be SO expensive (700$) and only supportig a max resolution of 752 x 582. What is so great about it compared to the other 150-200$ webcams?

The DSI PRO II is extremely sensitive to light. Part of the reason is big sensors. On a small chip = lack of resolution. However it gets 6 magnitudes below naked eye on a 10 sec image! One other good astro feature - it's black and white - try selling a black and white dslr.


And fourth questions, this same webcam is called "DSI" for DEEP SKY Imaging". I thought that webcams were only good for planets and you absolutly needed a CCD for deep sky imaging? How can this webcam succeed in taking deep sky objects?

The DSI is easily good enough to mag 17-18 on a 5" telescope. How Deep Sky do you want?

Dave Mitsky
2007-Apr-23, 11:51 AM
2.) Telescope webcams are crap. They are only for you if you just want to go cheap and only get pictures of the Moon. They give very blurry images of planets. You need a high quality imager like a Meade DSI if you want to go that way.

I wouldn't exactly call webcam planetary images like these crap.

http://www.astroshow.com/mars/ccdmars.html

http://www.astrophoto.fr/jupiter.html

http://geogdata.csun.edu/~voltaire/saturn1.html

For more on the topic, see http://www.astrophoto.fr/ccd_video.html

Dave Mitsky

Hatan
2007-Apr-23, 05:11 PM
Thanks a lot for your answers, this is very much appreciated. You answers actually bring up some more questions :)

Assuming money is not an issue, I guess the DSI from meade would be much better for planet and moon imaging than the StarShoot Solar System Color Imager II from Orion?

What about Deep sky objects, which one would create better results, the DSI from meade or some other CCD for the same price range?

And, according ozark1, it looks like that B&W ccd are better than color? Why? I prefer to have my planets in color than B&W usually :) I guess it has to do with the fact most DSO will not have color anyway and you need to have the filters to create them?

Thanks again.

Siguy
2007-Apr-23, 09:17 PM
I have seen planetary pictures from Meade DSI cameras, and they look about the same as pictures from normal webcams, but they are mainly used for deep sky.

I don't know of any other CCD for the same price as the DSI.

Most CCDs for deep sky imaging are black and white for some reason, and all professional ones, including the ones NASA uses, are black and white. I forget why, but it's good just to get the filters.

Peter Wilson
2007-Apr-24, 10:28 PM
Basically, in a color camera, you are recording 3 different colors at once. This reduces the effective sensitivity by a factor of 3. This lost sensitivity doesn't matter for daylight cameras, but for astrophotography...

Bryan817
2015-Feb-04, 08:45 PM
Does anyone following this thread happen to have a Meade DSI II color camera? I need help with mine.

RickJ
2015-Feb-05, 05:51 AM
Different types of imaging have different needs and solutions to those needs. I suggest you go to forums for the type of imaging you want to do and see what the best there are using since you say money isn't a big object.

DSLR cameras are CMOS based while CCD cameras are, well, CCD based. These are two different technologies. I see CMOS developing faster than CCD right now. If that keeps up the differences may favor CMOS. In result the main difference between the two is that DSLRs are not cooled. For long exposure work this means you can subtract out dark current and get a better image. BUT there are now excellent techniques for DSLRs that reduces this difference to where it is small. Still since they are different technologies some of the techniques differ so learning on a DSLR can make the transition to CCD more difficult than you might suspect. Least some in our club I know have found that the case. Still it is the best way to get into deep sky imaging. If it doesn't work out you still have a very good camera for normal pictures.

For planetary imaging while the cameras noted above will work the serious imagers use video cameras made for this purpose by companies like Point Gray ZWO and others. The ASI120 by ZWO color or mono is inexpensive and very good for the bucks. These cameras don't work well for deep sky work and vise versa.

Mono vs color cameras are another matter. Color cameras were never designed for astro work. They put half the pixels in green which is the least important color in astro imaging. They use dye filters which are inefficient and can play havoc with color of emission line nebula as they weren't designed for that purpose. Still for some they are the best choice. Don't fall for them being faster since you take all colors at the same time while a mono camera needs to take them individually. For similar signal to noise ratio they take more time not less. But they are far cheaper since there are no filters or filter wheel to buy. This also makes their use simpler. Of course all DSLRs are color. Mono is only in CCD's for now.

For planetary work color does increase exposure time as the filters block some light but you take far fewer images so here they are faster. Important with Jupiter that rotates enough to blur detail in only a couple minutes. You want a thousand frames or more to work with for high res work. This means a good camera and large aperture to bring in the light for fast exposures (60th of a second if you have the light). Still as with deep sky imaging the top imagers use mono cameras but average Joe's with color cameras can do very well. Again, color greatly reduces the cost and planets aren't emission sources so the dye filters are a good match since everything they see is lit by the sun which the filters were designed for. Most use barlows to extend the focal ratio to about f/30 or so to get optimum image scale. Depends some on the pixel size of the camera.

Deep sky imaging requires a very good mount and and is much more difficult to learn. Best to start with a short focal length system (700mm or so, certainly not over 1000mm). You will need a guide camera and guide scope or Off Axis Guider. Only mounts costing over $6,000 with the needed software can track such a system without guiding. Most cost well into 5 figures. But with a guider and guide camera even a $1500 mount can be made to work but expect a learning curve and TLC for the mount to keep it working. Higher cost mounts usually are better and needed for longer focal length. Here you use prime focus or even a reducer to fit a wider field onto the chip. Many scopes have trouble providing a good prime focus image across a full size DSLR chip (same size as 35mm film) Those with the smaller chips aren't so demanding and most flatteners will cover them (and will be needed). Small CCDs can sometimes get by without a flattener as they see too little of the field to be bothered by the curvature.

One last point. For deep sky work a mono camera can be used under most all conditions from severe light pollution and full moon (thanks to narrow band filters) and under the darkest skies. You can use them for photometric work besides pretty pictures. Due to speed they are good for hunting near earth asteroids and super nova compared to color cameras. Since I use mono I can work every clear night and thanks to automation I do. Even though it is full moon tonight it is collecting photometric data on some AGN's for a project a professional has recruited some amateurs to help with. With a color camera that wouldn't be possible. I get far more use out of my gear because of being mono. But little of it is at the beginner level of course.

Also keep in mind that no matter the gear the most important piece is the person behind the system! After doing this for 60 years I can get a pretty good image out of any gear. Some makes me work harder at it is all. But also for a beginner start simple and build slowly. I see too many try the equivalent of swimming the English Channel for their first swim and wonder why they fail. Too many start with great gear but no knowledge of how to use it expecting the expensive gear to make it easy. It just makes it all the more complicated! In our club it has happened several times. Most of my gear came from fire sales these "90 day wonders" held after being disillusioned by their failure to do it all first try. I got some great deals but at what cost to the hobby. These folks left it very embittered.

One other note on DSLRs. On a simple tripod they take very good short exposure images of the sky you can stack and make into very nice wide field images that show amazing detail. Simple, nearly foolproof under dark skies and will impress most anyone. In fact that's how I started but with fast film. Then I added a barn door drive (manual turning a screw to track the stars) since digital stacking wasn't available in 1955! Now it is which simplifies thing greatly.

If your club has imagers look them up and get first hand information. They know how to deal with your skies and can solve problems quickly. And problems you will have!

Rick