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Never worked.
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andrea tasselli: So last night after a long time i got a clear night Went for two targets the M5 and the Veil Nebula   The M5 is about 1 hour of integration and the Veil nebula is about 2 Hours of integration Both have the same set of correction frames. The only difference is the moon was closer to the M5 as compared with the Veil. Could that be the reason for the green rings in the M5 cluster Image? Other than that the scope is performing extraordinarily well. Amazed with the results. |
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Hi i have the same problem here. I think is a second mirror shadow but it doesn´t fix by flats . I could try in 3 200/1000 pds scopes and it has similar resaults. Indeed the only one it has flocked. it has more significant shadow or ring pattern. The image is resault of taking flats in different scopes and then i run dbe with 10 tolerance, normalized and substraction. I changed the spider with the same resaults...  This is the first light i stacked and when i found the problem  |
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The dark spot in the center looks more like the result of condensation/frost on the sensor.
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andrea tasselli: Maybe but i did the test whithout cooling and in a room and didn´t see any condensation....any idea? |
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Maybe but i did the test whithout cooling and in a room and didn´t see any condensation....any idea? Condensation could also happen without cooling if the camera is brought inside a warmer place. But the main rule is never take flats inside, at least for open designs such as a newton. Having said that the flats show also significant light leaks so you might want also to address that. Flocking in nearly irrelevant for that but darkening of the secondary side isn't. Also light path from the back end as well as from the focusers are a source of light leaks. Most importantly, try to take flats without direct lighting onto the scope. And use a dew shield. Check with a dark frame of signficant length (in the same conditions you are imaging with) to see whether you are free of those leaks. |
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andrea tasselli:Maybe but i did the test whithout cooling and in a room and didn´t see any condensation....any idea? Hello, I thought that would not happen in flats without cooling...Thanks for the clarification. Yes, the shots you see in the images were taken with the 3d back cover + black cloth on the primary mirror part. The focuser was also covered with black clothes to avoid leak lights, in addition to the fact that the focuser is flocked at the joints with the scope.Maybe i will try with a dlsr? |
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Same shadow with dslr without filters or coma corrector  |
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Anybody who has 200/1000 pds can send me a masterflat from his scope? thanks in advance
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Any luck with this? I've been having the same issue using the TSGPU. I have my whole rig flocked and painted, as well as the CC. About to buy a Paracorr and see if that alleviates the issues.
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David A Pyle: *Before spending your money do the following test: Take a flat with the scope pointed to the zenith, then a flat with the scope pointed to around 35 degrees altitude to the east, same to west, north, south. Then divide any of these flats with any other flat by simple pixel math for example flat_zenith/flat_east. Post an autostretched jpeg of the result here and we will see if you have issues. I suggest this because 95% of the time this ring pattern with newtonians is due to mechanical issues where some optical or mechanical component moves between the lights and flats, making flat calibration impossible. Many possible weak points such as the mirror cell and focuser, but do the test first and lets move on from there. |
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Oskari Nikkinen:David A Pyle: In my case i think that was the problem. With a horn and flats after take lights , fix the problem. Anything happen between take lights and take flats day after that even if you don´t move the camera or something |
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The cause of ring is that the optical structure is not sturdy enough, as during shooting, the primary mirror, secondary mirror, or focuser moved due to gravity. It was fine when using ASI533MM with HyperStar, but the same issue occurred when using ASI2600MC.
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I have just started using my SW 250 pds for imaging. Its always been my visual scope. For flats I use a white plastic garbage bag just tied with some cord. Steer the scope to zenith. Wrinkles are not a problem. On top of the bag a I place a white hazy piece of plastic; from a skylight (similar to that that covers a fluro light). On top is just a large cheap tracing board from Amazon. Flats look nice with little vignetting. I previously tried a large cross stitch wooden loop with white material. They were not the best as I had a dark grey spot in the middle of my flat frame. It looked as if the secondary mirror threw a shadow. Probably more so it would have been condensation as it was a little damp the first time round. Camera is a 2600, FW, OAG-L and 174 mini. CC Televue Parracor |
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Here's a couple images I subtracted. Hopefully I did this right. Zenith from East & North from South. |
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David A Pyle: Just to confirm but you did this with division and not subtraction? But anyway, the test has confirmed my suspicions. I tweaked these screenshots a little bit to make any patterns easier to see, here is the top image:  Does the ring pattern look familiar? Then the bottom image  Here it is less obvious, but we can still see it. To clarify the purpose of this test is to confirm that the telescope has mechanical stability issues, and this is now confirmed. It does not however tell anything about where that mechanical issue will be found and this falls on you to investigate. If this test was successful the flat division test would result in a perfectly flat noisy grey image with no gradient or pattern to be seen, both of your tests here show a gradient and a pattern, which means the 2 flats do not optically match and therefore neither will any of your lights. |
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I fixed this problem with larger 2 inch filters. Suddently the problem was gone. No joke. Had the ZWO 2600mm with 36mm filters before. Changed them and done.
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Oskari Nikkinen: That would be right if: 1. There is no light leak 2. The source is the same Neither can be guranteed by the test. As I said before, it is pointless for small displacements (i.e., few hundredth of mm). Mirrors do shift in the simple 3-points cells used in cheap newtonians, as they are are wont to do under varying gravity vector, otherwise they would be stressed and that is well worse. |
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andrea tasselli:Oskari Nikkinen: *If there is a light leak then this must be solved, the test is still valid and hard to interpret wrong. And in this test there is no light frame involved, so the amount of light leak should be the same as the only variable was the orientation of the tube (leaving only mechanical issues as the source of the different illumination). Not sure what you mean by the second point about the source? About the mirror shifting thing, yes the mirror has to be able to move just a little bit but not under gravity in the typical tube orientations. For the cheapo SW/GSO mirror cells that only support the mirror from the outer part of the mirror and not at all from the center it is complicated. In that case the mirror should be siliconed to the cell to stop gravity based mirror movements. Better cells, such as the 9 point support systems in the ONTC or OOUK mirror cells are easy to adjust in a way to completely negate mirror flop under gravity. |
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Here is my master light (luminance) with and without the flat. I've flocked the entire tube, painted everything with chalkboard paint, flocked my focuser and even around the end of the coma corrector. The tube is a CF tube with a reinforced run along the bottom side, including the focuser to resist flexure. I had a spider machined out of aluminum to make that as solid as possible. The only thing I haven't changed is the primary cell. This is built from a StellaLyra 10" Newtonian (GSO)
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David A Pyle: *Looks good but one question. Which focuser does the scope have? If the factory standard one it probably should go. I have a Diamond steeltrack on both of my newts and it is very good. Im sure there are others that do the trick but this one doesnt cost an arm and a leg and does the job. Do the silicone trick for the cell and see if it fixes your issues first. Costs about 5€ and might be enough to fix stability issues. Place generous blobs of silicone sealant on the cork pads and place the mirror gently on it (do not apply pressure, let the weight of the mirror do the work). Let cure for at least a day. This trick can also go wrong and lead to pinching, in which case you'll need to try again and experiment with the amount of silicone. |
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Oskari Nikkinen:David A Pyle: I have the Pegasus Astro Prodigy Microfocuser. I'll try to silicone the mirror and see if that helps. |
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If it is of any help all my mirrors shift to a degree and none of this has ever affected my flats (or the correction thereof). You have a light leak and you need to sort this out. From the picture I'd say it is more likely from the rear end.
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