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Old Jun 12, 2008, 7:36 AM   #1
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I already made my first post under "Camera for Astrophotography", and I may have stumped a lot of people, as I did not receive any responses.

So maybe I need to ask my question a different way. We are looking to possibly purchase a camera for our son who is 15 years old. He is very talented with cameras. He currently has a Canon S1 IS. He has pretty much mastered this camera, so one thing we are looking to do, is get him something that will challenge him more, and allow him to do more with it. Another thing that he is interested in trying to mess around with, is astrophotography, or hooking up his camera to his telescope, to take pictures of the various planets, star clusters, etc. The type of telescope he has, does not lend itself readily to this type of photography, however, he is quite clever, and even with his current camera, has gotten some pretty good moon shots.

The one thing that is absolutely necessary in astrophotgraphy, is being able to keep the shutter open for as long as possible, when photographing things in space. He is not able to do that for more than 30 seconds with his Canon S1 IS. Admittedly, he is learning about this aspect of photography, but would like to know what camera can be recommended that has this capability, and what is the best way to achieve it.

We would really love to get him the Canon D40, but the price is completely out of our ball park, even if it is for a Christmas/ 16th birthday. We have seen it recommended for astrophotography, but as I say, it would be more than we have to spend. I think we are looking more in the $500.00 to $600.00 range.

Thanks for all your help, and I hope that I am making myself a little more clear, as to what it is we are looking for!

Carol





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Old Jun 12, 2008, 7:52 AM   #2
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Most non-dSLR models are not going to do very well at longer shutter speeds because of noise and hot pixels (multi-colored dots scattered throughout an image). The longer the exposure, the less likely a photosite will be linear in it's reponse. So, you end up with pixels that reach maximum brightness too soon, scattered throughout the image.

It's not uncommon to see hundreds of hot pixels on some newer camera models with exposures much longer than a second or two with noise reduction turned off, and it gets worse from there as exposures get longer. It tends to be more problematic as photosite sizes get smaller (higher resolution within the same size sensor will mean that each photosite must be smaller in order to fit more in). Higher resolution is not always better. ;-)

Most newer cameras have a built in dark frame subtraction noise reduction system now (that's the purpose of the noise reduction menu choice you'll see in these camera models). Some models engage it automatically on longer exposures (you can't turn it off), and some models don't have the feature.

It works by taking two photos when exposures are longer than about 1 second. The second (shutter closed) photo is designed to simulate a lens cap on exposure, using the same settings for shutter speed and ISO speed as the first exposure. So, if you take a 30 second shot, the camera needs another 30 seconds to take a dark frame shot.

The reason it works that way is because since both photos are taken at approximately the same time, at the same temperature (which will impact noise and hot pixels), using the same settings, the hot pixels are likely to show up in the same place in both images.

Then, the camera's processing maps out the same pixel locations in the actual exposure that it found hot pixels in the dark frame exposure (since these are the only pixels that would be much brighter in the dark frame). Basically, it replaces these pixel locations in the actual exposure with values interpolated from adjacent pixels so that you don't see them anymore. This process is known a dark frame subtraction, and the longer the exposure, the more degraded the image, and the more likely you're going to have hot pixels that are missed by this dark frame subtraction process (because the actual and dark frame exposure may not have always hot pixels in the same place, once you get a lot of them).

One way to get longer exposures is to take multiple images and then combine them together to simulate a single long exposure. Here is one software package designed for that purpose (and you'll see your problem discussed, with the description mentioning combining multiple 30 second exposures to simulate a longer exposure):

http://www.tawbaware.com/imgstack.htm

You may have better luck getting useful responses in our Digiscoping/Digital Photomicroscopy Forum. We normally ask that "What Camera Should I Buy" questions be asked in the What Camera Should I Buy forum only. I'll make an exception in this case, since you have a specialized application. So, I'll move this thread now (leaving a pointer to it in this forum).

For one thing, you'll need to make sure you get a camera that is suitable for attaching to a telescope (not all will work well that way), if that's a desirable goal.

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Old Jun 12, 2008, 8:08 AM   #3
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I completely apologize for not putting this in the "What Camera Should I Buy" forum. For some weird reason, I thought I had. Honestly, my vision isn't what it should be, and I should have waited until my son could have helped me with this, since I have trouble reading posts on the black background, but while he does know we are kind of looking at cameras, he really doesn't know we are looking at one for a combo Christmas/16th birthday present. Again, I apologize for not being sure of where I was placing my post. I will be more careful in the future.

You are correct about the camera being able to connect to the telescope. We have been told that Canons are the best in this respect, so I think we would likely stick with the Canon line of cameras. And to be honest, we really do like them. I have a Canon S5 IS, and I like it a lot. Again, our son has taught me a lot about the various features of it - oh well, it keeps me humble I guess!

Thanks again,
Carol
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Old Jun 12, 2008, 8:10 AM   #4
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You did post in the correct forum. I just moved it to the Digiscoping/Digital Photomicroscopy forum for you, so you'd be more likely to get some responses from members more familiar with Astrophotography.

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Old Jun 12, 2008, 8:34 AM   #5
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CoffeeRoaster wrote:
Quote:
You are correct about the camera being able to connect to the telescope. We have been told that Canons are the best in this respect, so I think we would likely stick with the Canon line of cameras. And to be honest, we really do like them. I have a Canon S5 IS, and I like it a lot. Again, our son has taught me a lot about the various features of it - oh well, it keeps me humble I guess!
It's my understanding that the Super Zoom cameras like those Canon models are *not* well suited for Digiscoping (i.e., attaching them to a telescope) because of their objective size (the lens must be able to see through the telescope's eyepiece via an adapter). But, I know very little about this type of application.

So, hopefully, some of our members more familiar with this type of use will see this thread and offer some suggestions.

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Old Jun 12, 2008, 9:12 AM   #6
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I'd also let members know what type of telescope he has (brand/model). That may help in finding out if there is a suitable way to mount a given camera.

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Old Jun 12, 2008, 10:32 AM   #7
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Hi,

Jim has pretty well covered the dSLR aspect of your question - the real question is what does you son "really" want to do?

If he is really interested in deep space photography (planets, stars, etc.,) then a dSLR really isn't the way to go at all. What he really needs is a "decent" telescope and a dedicated CCD camera made for this purpose such as:

http://www.meade.com/dsi/index.html

http://www.meade.com/dsi/overview.html

http://cameras.pricegrabber.com/othe...skd=1/st=query

CCD cameras which have cooling built in can be purchased for really low prices (cheaper than a dSLR) and are magnitudes better for this purpose than any dSLR.

Call Meade and find out what their least expensive telescope with AutoStar controller is and look for a good used one. The CCD camera itself is under $300 so you may stay in your budget range if you shop around.

As far as a dSLR goes - a used Canon 350D can be had cheaply. You would then also need a telescope with a dedicated camera port and what is called a "T" adapter for the scope and a standard "T" connector to connect the scope's "T" adapter to the camera body so that the telescope replaces the lens. All the old Meade ETX-90 and most Celestron telescopes have a dedicated port for photography and have "T" adapters available. A new "T" adapter is about $65 and a "T" connector for the camera body about $30. This would allow about a 30 second exposure with any Canon dSLR body, but seriously, the dedicated CCD camera is "much, much" better for this purpose.

Best regards,

Lin
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Old Jun 12, 2008, 2:12 PM   #8
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Our son, Joel, has an Orion, XT10i dob, which, due to its size, does not easily lend itself to astrophotography. Please keep in mind that he is 15 years old, and does not make much in the way of allowance, and we are not rich either. Since he is pretty clever, and has already been able to get some good moon shots, but due to the limitations of his Canon S1 IS in shutter speeds, he was thinking that perhaps he would like to look at the possibilities of getting something a little more advanced in the way of a camera to do some more photography. He can get what he needs to hook up the camera in the way of a t-ring and an adapter from a telescope store, that is made for a specific make and model of camera.

Another thing he is thinkig of, is maybe having he and his Dad build an equatorial mount for his scope, and that would go a long way in helping him also with his photography, but he still would likely end up needing something beefier than the Canon S1 IS. I was kind of wondering about the Canon Rebel, and what others thought about it as a replacement for his Canon S1 IS? Would it be a step up in the way of a camera for everyday use, and would it also be able to be used for astrophotography?

All thoughts on this are appreciated.

Carol
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Old Jun 12, 2008, 3:37 PM   #9
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Hi,

Yes, actually the 350D I recommended is the European designation name for the Canon Rebel. The newer Canon Rebels are fine cameras and would represent a major step up for general photography.

As I said earlier, the downside of using a dSLR for astrophotography is that you can only shoot about 30 seconds of exposure before noise begins to become a major problem because of sensor heating. The dedicated CCD camera I suggested can take 1 hour exposures so there is a major difference.

If his interest is more in photography than astrophotography the Digital Rebel would be a fine choice. Whether or not the Orion has provisions for a "T" adapter would be something I can't comment on, I just don't know. It must have a dedicated camera port for this to work. But even if you can't make the Orion work, you can usually find an older Meade ETX-90 which has a nice battery driven tracking mount for under $200. This would work well with the Canon but probably not with the CCD camera which would require a newer scope with the computerized base. The optics on the older ETX-90 models and the new ones are identical - the only difference is the automated tracking which lets you simply orient the scope by compass then it automatically "finds" stars, nebulae, clusters, galaxies, etc.

Best regards,

Lin
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Old Jun 22, 2008, 12:47 PM   #10
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Check out my recently posted shot of the moon, also my post "Quality Digiscoping". The picture was taken with a Celestron 10 inch Dob. mount, so the scope must be about identical to your XT-10 Orion. The moon is bright, so no special tracking mount is required. This image was digiscoped with my Canon A-550, which is not as sharp as my later A-720 nor the current 12 meg. A-650. A 40mm eyepiece was used.

Of course your scope also has the 2 inch focuser. I strongly recommend the 2 inch tube mount for the eyepiece and bayonet camera body attachment on the A-650. See attachment of 2 inch tube detached from an A-720 camera. The total length of the tube plus adapter is 6 inches.

I know, some people get bird I.D. pictures with hand held support, camera clamping and camera tripod mount attachments. I want my eyepiece and camera mounted precisely. As I have said in the other post, I cannot get as sharp an image using a dSLR camera in the direct or prime focus mode (without an eyepiece or camera lens), as I can get by digiscoping.

There is a lot be seen on the moon. Goggle out the "Lunar 100" and you will see Clavius listed, which is seen in the center left of my image. This crater is distinguished by smaller craters inside of decreasing size in a perfect arc pattern.


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