I got the camera last December, and have only gotten to image a small number of targets due to weather conditions. The images that I have gotten of deep space objects, have been very nice. I am still quite the amateur, but wanted to try to use flats mainly to remove a dust mote that appears to be on the glass in front of the sensor. That is when I first ran into this issue. Short (a couple to 10 seconds) exposures exhibit a problem with slightly curved streaks of varying brightness running pretty parallel and vertically oriented through the frame. I have also recently taken images of the moon, that exhibit this problem in the background sky. When I have tested this with trying to take flats, the scope that it was attached to did not seem to matter, nor did the orientation of the camera. The streaks look to occur in the same locations in every frame. I have not seen these show up in much longer exposures. I am guessing that they are not related to imperfections in the sensor chip. Since they do not seem to show up in the long exposures, even if I stretch them pretty hard. They also do not show up in either dark frames or bias frames. The effect in the long exposures is either absent, or dimmer than the nebula details I am trying to bring out. I tried to upload a couple jpeg files so people could see what I am getting, but I am not sure if they made it or not. One is a short exposure of the moon, stretched to show the streaks in the relatively dark sky background. The other is a single image of the Eastern Veil, 600 sec exposure, and stretched quite a bit. I do not see any evidence of the streaks in the nebula image. Any advise on what this is and how to correct it would be appreciated. Thanks
Use the Upload a File button down below the text entry box that you type the reply in, and make sure to hit Thumbnail or Image buttons. You might also want to upload a FITS image. If its too big, crop it in MaxIm (or whatever your favourite program is), as examining the FITS image might help diagnose what's going on. Also, a screen shot of your driver version and firmware version, as well as details of what programs and versions you used to acquire the images.
OK, for some reason the "Upload a File" is telling me the files are all too large, they are all less than the 19.5 meg. Even when I tried the "Upload a File" on my original post and it didn't say the jpg images were too large, I never saw an option to show the files I had uploaded, the image button just wants a link to an image. Well, I have a google drive, I may as well make use of it. This is a crop of the Eastern Veil image (fit format) This is a stretch of the Eastern Veil, I have not seen any streaking in this (jpeg format) This is a crop of the moon image, with streaks showing on the left side pretty easily (fit format) This is a stretched moon image, shows the streaking pretty well (jpeg format) For acquiring the images, I am using Nebulosity 4.0 running on my MacbookPro. I did install the "Universal driver", but I am not sure how to track down what version of it is installed. I will have to do some research to find out how to get to this. I don't have the camera handy at the moment to check its firmware version.
That didn't work. Can you either post the URLs for the google drive or attach smaller (cropped) FITS ?
Odd, on Safari here, I get these question mark boxes rather than any images, even for the jpegs, but I can right click and choose to open the image, or download, etc. Here are the links though. This is a crop of the Eastern Veil image (fit format): https://drive.google.com/open?id=0B0JWuCPyMSG1T1ZmdHBrRlJRTmc This is a stretch of the Eastern Veil, I have not seen any streaking in this (jpeg format): https://drive.google.com/open?id=0B0JWuCPyMSG1c21jc09kekQ5OFk This is a crop of the moon image, with streaks showing on the left side pretty easily (fit format): https://drive.google.com/open?id=0B0JWuCPyMSG1c0dmbGNROVZuOUE This is a stretched moon image, shows the streaking pretty well (jpeg format): https://drive.google.com/open?id=0B0JWuCPyMSG1VEl1clpZNkpYRk0
Ok, that worked. Agreed, the veil image is fine. Wondering if the moon image is showing streaks due to internal reflection? Or it could be something else. Do you have a star field with a few bright stars like M44 and maybe a cluster like M13/M92? Do you have RBI on ? How about a luminance or clear filter in the path? Also, what's the optical train (e.g. scope, focuser, reducer, filters, etc.)?
Anything as bright as the moon will have some reflections in the optical train. Black Cork in the metal adapter tubes, flocking paper, longer dew shield, blackening the inside of the tube probably won't stop reflections from the moon. If you have a field flattener or focal reducer will show more reflections. Keep in mind your deep sky images look good. The moon will be very unforgiving.
Thanks to both of you. I have used various filters, and on one telescope, I use a flattener, and the other has field flattening built into its optics. The streaking is in a very consistent location and orientation on the field, so am pretty certain that it has to be something within the camera, otherwise I would expect it to rotate and/or scale with the different setups and camera orientations. I have not seen any indication that this camera had RBI. But I have not tried the SBIG software in Windows. I looked back at images of M42 and M45, with no evidence of the streaking. I looked at flats, and I have flats that I took that have a dust mote in the center of the field, and no streaks, then I have flats I took the next day, that have a dust mote over along one edge and the streaks. I think I tried to clean the glass in the camera, and must have left some residue. The M42 and M45 were both taken before the streaks showed up in the flats. So they or other fields with bright stars may be enough to have the streaks show up now. I find myself wondering whether to try to clean the glass again, or see if flats will work. I am worried the streaking that shows up in the flats, will be too pronounced and overcorrect when applied to the dim nebula images, since I haven't seen the streaking show up in those. This week isn't looking good, but maybe the next time I get out, and can shoot the moon, I should shoot it, and some matching flats, and try for some area with some bright stars and nebula, and try to putting the nebula in the streak area in some frames, and the bright star in the streak area in others, and see if the flats will work correctly.
My mistake on the RBI - its the STF vs STT. The streaks look like segments of symmetrical rings to me, the kind of thing expected when a ridiculously bright source like the moon is bouncing off everything inside. Rotation of the camera may not make them move if its internal reflection off tube walls. Now, moving the scope 1/4 degree or so either side of the moon would change the pattern. How did you do the flats? Using a panel, t-shirt method, ??? What happens if you put the camera on the workbench, and try different levels of light getting in, e.g. layer a dozen sheets of white paper over the front of the camera, illuminated with overhead lights ? e.g. indoor flats with everything out of the way. When you say you cleaned the glass, what glass and how did you clean it, with what?
Trying some testing tonight. I have a thunderstorm rumbling outside, so just as well to do some camera testing inside The sets of flats that I had taken early this year, were using a t-shirt, and an iPad as light source, and using velum and the iPad I believe. Tonight, I am setup with the camera in the hall, mounted on my WO Star71. Short enough focal length, that focusing in 30 feet or so, is quite easy. I took some flats, with a sheet of velum across the front of the scope, and am waiting for it to get dark enough to be able to take some images of a test chart, with long enough exposures to give a good test. Probably an artificial star would be a good choice, but I'll try this first. The glass I was referring to is the window on the front of the chamber, behind the shutter. I used a cleaner for camera sensors. I tried blowing the dust off first, and it didn't move. Being right in the center of the field, and on the glass right in front of the sensor, it was pretty pronounced. I probably should have just taken flats and used them to compensate.
All right, finally got all the testing I wanted to do, done. I tested with my Explore Scientific telescope. I had done some imaging with it outside, and locked down the focus, and brought it inside, so should still be focussed pretty close to infinity, and used that to do some flat frames. The streaks showed up pretty easily, I tried cleaning the glass window and saw no change in the streaks. I also tried rotating the camera 90 degrees with respect to the whole imaging train. The pattern remained the same. That suggested to me, that whatever was causing the streaks, must be within the camera. I then took just the camera and set paper sheets on top of it, and added paper until I could get what looked like a sensible flat exposure, with a 3 second exposure. After stacking 100 images, this is what I got: https://drive.google.com/open?id=0B0JWuCPyMSG1UDd3VmhranNOTVk That definitely eliminates anything outside the camera as causing the streaks. Since the actual difference between the bright and dark streaks was pretty small on the flats, it occurred to me, that the reason I hadn't seen it on the narrow band images of nebula or darks, might be that it was simply dim enough in those exposures, so that I had not brought it above the noise level. I experimented with longer dark frames, and started to be able to pick up the streaks, so I raised the temperature on the camera to allow the sensor to have more signal to work with for the darks. This is what a stack of 10 300 second darks, taken at 15 degrees Celsius and stretched looks like: https://drive.google.com/open?id=0B0JWuCPyMSG1YWxDazdwWER2VEE It is definitely proportional to the total amount of light exposure, but is not from optical train aberrations s far as I can see. So it does not seem to me that either dark frames, or flats can be used to compensate for what I am seeing here. Is this something that is just expected? Do I have a bat sensor? I don't recall seeing anyone talk about this sort of thing being normal. Can it be properly calibrated out?
