While I'm trying to get my AO-8A unit functioning, I figured that I could build my Calibration library. I take a couple of sample shots to try to get the exposure time somewhat close. My sample shots of the O3 filter shows something I've never seen before. What is this & what do I do to eliminate it? I also posted a Flat from my S2 and this is basically what all the other filters show.
Wow... never seen anything like it! Maybe you better pop that filter out of the wheel and inspect it. See if it's either very dirty or damaged somehow. If it looks okay then put it back in, with a different orientation, and then do the flat again. If the pattern rotates then it would have to be the filter. If it's the filter we'll send you a replacement, but we'll want to get the original sent back so we can inspect it.
Very good thought... it hadn't occurred to me that the filter might have frosted up on its own, not due to the camera cooler. If it were exposed for a long time in cold conditions, radiating heat into the sky (through the telescope optics), it could have dropped below the dew point and frosted over. In that case I will revise my suggestion... try it again. If the frost has since evaporated it should work properly again.
Okay, I just did a sample flat of the O3 without the cooler on. Even with some ambient light coming into the Observatory casting a partial shadow on my Flat screen, this looks fine. I will try again tonight when I can control the source light better. Seeing that the filters are not inside the cooling chamber, It didn't occurred to me that this could have been a frost issue.
I suspect it's frosted up not because of the cooled sensor, but because the glass got cold simply being exposed to cold air and losing heat via IR.
Well, it looks like tomorrow I need to inspect the O3 filter. This evening, I took another sample shot w/o the cooler & I got the same thing as last night.
Okay, please have a look at the OIII filter and let us know what you see. If it's obviously dirty then just clean it. If it's damaged we'll replace it. Try getting some cell phone photos - reflected light front and back, reflected light at a sharp angle, transmitted light (e.g. from your flat fielder or similar).
I just got done inspecting the O3 filter. I could see zero flaws on either sides. It was cleaner that expected due to the fact that it spent the last year in my Observatory only 75 feet form a corn field. I rotated the filter approx 45° and reassembled everything. I will test it out tonight.
NO joy. for the O-3 filter, I did test images @ 60, 180, 300 sec & all shown the same thing. I followed up with an HA & S2 image @ 300 sec and they seemed to be normal. I then returned to the O-3 and moved my scope a bit to see if the O-3 was actually imaging my Flat field light. The shadows and streaks on that image didn't move. Strange, the images from the other six filters are pretty mush what one would expect. Being new to Color & NB imaging, I'm at a total loss.
Strange. I don't understand why it would only appear in the OIII image, but isn't affected by rotating the filter. Maybe you should try recharging the desiccant.
Just a suggestion. Try repeating your OIII flats using sky-flats and not panel flats and see if that is significantly different. Many LED panels do not output light in a continuous spectrum but have notches or holes in the spectrum, it is possible that the bandpass of your OIII filter is slightly offset from one of these notches creating an extremely narrow pass wavelength and this is accentuating pre-existing water or fabrication marks on the sensor. You tried rotating the filter and with cooler on and off and this produced identical flats, therefore filter orientation and condensation on the sensor can be discounted since there would be some differences between them, even if very slight, and yet all your images are the same. Also noticeable in your OIII images are the very strong diagonal stripes, these are wafer polishing marks, created during the sensor fabrication process and are normally only visible when using virtually monochromatic light with extremely narrow bandwidth. It might be possible that your OIII filter has slipped through production and testing with an extremely narrow OIII band-pass and this is allowing these sensor marks to be revealed, one way to prove or discount this would be to try a different OIII filter but try Sky Flats first to eliminate the panel as a reason. When I looked at your images the first time they reminded me more of extremely narrow IR pass filtered images, used for surface defect analysis on optical flats from an optical bench, rather than OIII filtered images. A very simple double-check of the filter bandpass would be to point it at a strong OIII object, take an image and see if it is captured, if not, that is another indication that the filters OIII bandpass is incorrect. If you have not tried Sky Flats before, point the telescope just after Sunset, or just before dawn, to approx 30 degree elevation in the sky quadrant directly opposite the Suns current location. IOW before dawn point the telescope to the West with ~30 deg elevation, after Sunset point the telescope East with ~30 deg elevation turn off mount tracking and take some flats with a stationary mount. Adjust the exposure time to produce ~50% ADU through the OIII filter and then examine the flats. Do these still show the marks? If yes, try a different OIII filter. HTH. William.
William, I think you hit it on the head. I left the Flat Box light off, I turned on the Observatory interior light & took some sample shots. NO streaking, They look like the other filters. Thank You William, take two attaboys out of petty cash. What is IOW?
Those latest OIII flats look just as expected but if you look very carefully at the new OIII flats and previous SII flats you can see what looks like very faint water marks, top centre, about a quarter way down the frame, and bottom right, about a quarter way up the frame. Most likely you had some condensation or ice on the sensor previously, or condensation on the camera window, and that has left some traces behind. Good flats should compensate for those, but if you do have any problems calibrating those marks out of your final images then the camera might need a service to get those marks cleaned away thoroughly. Once you get imaging, review your first calibrated images to evaluate how well the flats handle those remaining marks and then take it from there. William.
