Contamination on images

hello,

it might be some dust. As it is focused, I would say close to (on the window) or on the sensor.

JF

I agree with Sigga.  This is almost certainly dirt/dust on the sensor.  The cleaning is not too difficult, but do be careful with the sensor and mirror.  If in doubt get it cleaned by a professional.  But make sure they do a good job.

Definitely seems like dust (the circles) and other debris like hair/fuzz (long ones), as the others have alluded to, although I'll admit that my dust/debris usually looks more donut-shaped (lighter in the middle) than disk shaped (even throughout) like yours.

I happen to image with the same camera, but I've had that happen on any of my Nikons, especially after disconnecting something from the imaging train and opening it up to the surroundings. It's crazy how fast it can build up debris that you can't even see. If it's sitting on the sensor, the particles are almost invisibly small, but out of focus there, so they appear large in the images. Here's a recent light frame I took of IC342 that has one (I keep it very clean):



The best solution here is to get a filtered air squeezer (really cheap) and squirt/pump the air into your camera to remove the debris. Hold the camera with the opening facing down once disconnected, and even lock the mirror up for cleaning to get right to the sensor. Blast everything out, and see the results afterwards. If things change, your sensor is fine. If not, you could have a problem, although not likely. Note that material on the aperture of the telescope is very unlikely to be visible like this; it's way too far down the imaging train to come to a close focus at the sensor.

Once cleaned, try not to disassemble the optical train as much as possible. I don't care how hard I try, something always ends up back in there without another cleaning.

Finally, it's amazing how well flat frames will fix this, assuming nothing moves before taking them (dust has a tendency to shift, which can't be fixed), so take the flats right after imaging without moving the scope, and they'll pretty much vanish when you calibrate it, it's pretty surprising.

A few points in response to your message:

~ I don't recommend ever wet-cleaning a DSLR sensor. You risk getting the electronics wet, but more importantly, this type of sensor doesn't seem to get things pasted onto it like a telescope aperture does (and I've only wet-cleaned by 8se's corrector plate 3 times in 3 years). Get a static-charged paint brush with soft bristles (search online), and simply gently drag it across the sensor to dislodge anything that's stuck. We're not scrubbing, but simply dragging, the brush. I've only done this twice in my life. No more pressure than a drag should ever be applied.

~ Yes, don't clean with anything, like cotton, that leaves pieces. You'll end up worse off from where you started.

~ Are you sure all of these were scratches? I'd be very surprised to see dot-like scratches. Perhaps the long, linear ones are, but I just can't picture scratching the sensor producing such small dots. You may have to wet clean it (with something softer) again if you've pasted on some material onto it. Get a super bright light and shine it right on the sensor to see if that's the case. I'm not convinced all of those artifacts are scratches. Definitely don't do away with your camera until you're sure. You still might be able to get away with using it; proper flat frames are likely to help even this.

~ Concerning flats, I'm somewhat nontraditional. I've tried it all, mind you, but I've found, consistently, that even though I image at ISO 200 (which you should be imaging at as well, with this camera), my flats work substantially better when done at the highest ISO possible, 25600. I've tried all types (TV, sky, etc.) with perfect methodology. This may not work for others, but with my setup it is substantially and certainly better to do this. For this reason, and because the brightness of your light source matters, I wouldn't recommend you concern yourself with the exposure time value. Ours will likely differ. Traditional wisdom is to set the ISO to match your lights (if your flats are biased calibrated, I have never heard a good justification for this), and the exposure to make the histogram peak right around the 50% mark. I use the highest ISO and peak the histogram around 95%. I deviate from the usual here, but it always helps my calibration substantially.

~ Some artifacts will be obvious to your eyes in the flats. Others won't. You should measure their success based on how they do in calibrating your lights after they're calibrated and stacked, not how the flats appear alone. You'll know after processing if the flats helped or not.

Sounds good! Be sure to keep the optical train closed once you've cleaned out the material, preferably using a filtered air bulb, to prevent what gets inside. Shoot me a private message if you have flat frame questions.