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  1. #1
    justmike's Avatar
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    Default CCD advice needed



    Hi, I'm looking for some "Newbie| advice. I recently purchased a Celestron NexImage and have been pretty happy with it and the software it came with. I also have and older Canon S1 (3.2M) digital camera and was wondering if it would produce better images then the NexImage. In movie mode the Canon also records in 640X480 AVI (same as NexImage) so I'm not sure it will be any better. The Pixel size of the NexIage is 5.6X5.6 and all I could find on the Canon was that it Zoom is from 5.8-58. If the Canon is going to be better, then I'll pick up the hood and t-mount for the eyepieces, but I don't want to bother and find that it is similar to what I already have.
    Thanks!
    Mike
    oh, I'm using a 8" SkyWatcher SCT and EQ5 with synscan

  2. #2
    AustinPSD's Avatar
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    The Canon S1 IS uses a 1/2" format sensor, 5.2mm x 3.96mm. The NexImage uses a smaller Sony HAD sensor in 1/4" format, 3.6mm x 2.7mm. The individual pixels on the Canon S1 sensor are 2.57um square, while the NexImage uses 5.6um square pixels.

    The Canon sensor is higher performance, but there is more "in the way" with regard to using it in direct objective mode. The autofocus and stabilization will be in your way, and you'll have to use the camera in manual focus mode. The longest exposure you'll be able to take is 15 sec., there is no "bulb" mode on this camera.

    Point-and-shoot cameras are not great choices for astrophotography in direct objective mode - they can be OK for afocal use (i.e. through the eyepiece), but otherwise are lacking. The NexImage, although having an inferior sensor is probably going to work better than the S1 IS in direct objective mode.
    Last edited by AustinPSD; 10-19-2009 at 11:49 PM. Reason: spelling

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  4. #3
    justmike's Avatar
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    Thanks for the info. If I was going to use it afocal use, would it be better then the NexImage? If not that's fine, I just don't acquire the hood. step down ring and afocal eyepiece ring and have the same performance I have with the NexImage

  5. #4
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    I've never used the Neximage, but the larger pixel sizes will collect more photons and probably be a better fit for most scopes......the smaller pixels are great for camera lenses but pretty impractical for most telescopes unless very fast wide fov's. Also, the HAD sony chips have very little noise. I don't know if it is possible to add a cooler to the Neximage, but for the dollars it seems to be a pretty nice little camera.

    best regards,

    bud guinn
    Bud's astro

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    Quote Originally Posted by justmike View Post
    Thanks for the info. If I was going to use it afocal use, would it be better then the NexImage? If not that's fine, I just don't acquire the hood. step down ring and afocal eyepiece ring and have the same performance I have with the NexImage
    You can't really use the NexImage in afocal mode, as it has no lens, and no means of affixing it to an eyepiece. It is a direct objective imager.

    Apologies if this is redundant, but we may have a terminology mix-up here:

    - direct objective, aka prime focus imaging involves the use of a camera or imager in place of an eyepiece, usually with the imager installed in the focuser tube directly or via an adapter tube. With DSLR cameras, the connection is made with a T-ring (sometimes called T-adapter) with a camera-specific bayonet on the outboard end, and a threaded (T) ring on the inboard end. This in turn mates to a T-ring tube adapter, with threads on its outboard end, and a plain tube sized to mate with the telescope's focuser on its inboard end. In effect you are using the telescope as the camera/imager's prime lens.

    - in afocal mode, the camera is either hand-held some distance away from the eyepiece or an adapter rail/bar are used to hold the camera a fixed distance from the eyepiece. You are taking a picture through the camera's objective lens through the eyepiece.

    You can use the S1 IS in afocal mode through the scope's eyepiece, and it will image whatever is in focus/in view - the quality of the image will be affected by the distance from the eyepiece, the secondary focus (how well you've focused the camera), and any vibration (for example hand-holding the camera).

    Unfortunately Canon, and for the owners of some of the earlier point-and-shoot cameras like the S1 are affected by "pixel-itis". As "budguinn" points out the Sony HAD sensors are relatively low noise, and use relatively large pixels. Smaller pixels = more noise... that's the simple semiconductor physics of a sensor. Canon, in an effort to claim a large pixel count crammed more, smaller pixels on this particular sensor, which in turn lead to more noise. That's one of the reasons the maximum exposure is limited to 15 sec. on this camera.

    You're probably going to get better overall results from the NexImage.

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  9. #6
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    Thanks for the advice! I will just use the NexImage for now (with a focal reducer) and forgo the Canon S1. The earlier "afocal" question was in regard to the Canon S1.

 

 

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