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Last night I tried my first long exposure photo of M44 (the beehive cluster). While my exposure time was 60 seconds, my photos came out with a giant ball of light in the center of the photo.

Could this be due to my set up, as I only was using a phone app and putting my phone up to the eyepiece for one minute?

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  • $\begingroup$ Is their a reason for the giant ball of light? $\endgroup$
    – Max K
    Commented May 25, 2020 at 14:13
  • $\begingroup$ Question marks help! :-) It would be great if you included the image itself if possible. Also, do you mean that you held the phone to the eyepiece by hand for 60 seconds, or did you use a firm mounting? What kind of telescope exactly? What focal length eyepiece? Could you see the M44 on the phone's screen before you started? Did you try shorter exposures? Have you had any success photographing other objects this way? Have you tried objects on the horizon during daytime or twilight to make sure you can get it to work with short exposures first? Please include more detail, thanks! $\endgroup$
    – uhoh
    Commented May 25, 2020 at 14:17
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    $\begingroup$ I’m voting to close this question because this will be much better answered on photography.SE $\endgroup$
    – Carl Witthoft
    Commented May 26, 2020 at 17:42
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    $\begingroup$ @CarlWitthoft this would probably be rejected much more quickly in Photography SE than here. Without more information it's not answerable. Needs more information would be the appropriate close reason, not "better asked in a different site". Astrophotography is absolutely on-topic here with 176 questions tagged photography so I think you've got the close reason all wrong! $\endgroup$
    – uhoh
    Commented May 26, 2020 at 18:56
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    $\begingroup$ I vote for "leave open" because 1. if the question is ontopic on both sites, it remains where it is 2. sites should be inclusive, friendly, growing 3. this is a practical astronomy question, that is useful content what we should like. $\endgroup$
    – peterh
    Commented May 26, 2020 at 20:57

2 Answers 2

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It's hard to tell, however the very likely solution of your problem lies in a combination of two or three effects:

  • The image is not focused. Did you focus on bright stars or the moon and not change the phone afterwards? This a common problem and (I personally) find it hard with a phone to get a sharp image through a telescope. On the telescop I have available, I need to hold my phone about 1cm away from the eye piece to get a sharp image. The focus WILL need to be different than for you looking through the telescope with your naked eye. An un-focused image will be just that: bright area where like arrives and black outside, showing vignetting.

  • the image is motion-blurred.

  • you really took too long an exposure with too high an ISO rating. Reduce either and see whether you get better results. At highest ISO rating my DSLR camera yields bright white images after a comparable time (I didn't try my phone but suspect similar sensitivity behaviour). How long exactly depends on how dark your local sky is.

From all these points the most important is: make sure you have your camera-telescope-combination focused. Test that on bright objects, thus a sharp moon or smallest-possible dot for a bright(!) star imaged. You can do the focusing in video mode and highest ISO setting. When that is ensured, then only start to image interesting objects.

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What did the star look like in Live view in the Camera app on the phone? If it looked dim, the phone might be compensating for brightness in post-processing, leaving the image too exposed. If it looked bright in Live view, then that's obviously the reason.

If the reason is not post-processing, I've got suggestions.

  1. Try exposure times of 5s, 10s, 15s and so forth, until the image looks OK.
  2. If you've gotten decent photos at some exposure time, take multiple images and try stacking them together. A number of programs can do that for you, for example the freeware DeepSkyStacker
  3. Try using another camera, it doesn't have to be of the latest or best kind. A good photographer can take excellent photos using cheap gear.

Good luck!

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