1.20
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| Quick question regarding flats. I`m REALLY struggling with mine!!! I currently use an ASI 1600 MM Pro and these scopes...TS65 Quad apo150 PDSThese filters... Optolong L pro and Baader NB filters.I`ve tried various values using APTs flats aid with little to no success. Would anyone care to help with settings / rough exposure times with their 1600??RegardsAlan |
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Nobody can't give you the right exposure time, because it depends on your setup and your 'light source'. You must go with an ADU value, shoot the flat with same cam temperature, filter, gain and offset as your images. For me, I use an ADU of 30k on a scale 0 to 65,000. Some people, will use lower ADU, 20K. It depends on preference. Good luck. the exposure depends on your light source -> half range between 0 and 65k is your flat image range... |
12.30
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I use an Edge HD 8 SCT and the ASI1600mm camera. I purchased the Artesky Flat Field Generator shown here. The brightness is USB controlled so you can set a brightness for each filter from your imaging software to get a perfect exposure and the field is perfectly flat. It is a bit pricy but well worth it in my opinion. Here is my process. I have previously determined the proper brightness for the flat field Generator (FFG) for each filter. This was done by setting the camera for a 5 second exposure and varying the brightness until the mean value of the image was in the center of the range. This was repeated for each filter and the brightness value for each is recorded in the software (I use SGP). When taking flats I point the scope straight up and set the FFG right on the top of the scope. A sequence is created for the appropriate number of flats for each filter, each with a 5 second exposure. SGP sends the correct brightness to the panel via USB and then takes the flat frames. This way I can also take a set of 5 second exposure dark frames and calibrate the flats with flat darks. I do not take bias frames at all. I get perfect flat frames every time with no problems. I know Pegasus Astro has a product called the Flatmaster that does the same thing as the Artesky FFG and the size would be more appropriate for your APO, I think. I hope you find this helpful. If I can answer any questions I am happy to do so. Best and clear skies! Tim |
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1.20
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What sort of exposure lengths do you aim for?? I hear different opinions about too long or too short... Regards Alan |
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12.30
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I don't know that it matters greatly. What is more important (to my knowledge) is that the result is in the linear range of the sensor. 20k - 30k mean values is what I look for. I take 5 second exposures and set the brightness panel to get in that range. The reason that I stick to 5 seconds is so that I don't have to create a new set of flat darks each time. This way, every set of flats for every filter can use the same set of flat darks. Might not be the best solution, but it seems to work well for me. Tim. |
9.90
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Alan Hancox: Hi Alan, I shoot mine at 15K ADU. I have an ASI 1600 and a refractor of 71mm among others. What is the exact problem? Use a histogram and see if the shape is a bell cure symmetrical and most importantly you don't cut the blacks. Sharp Cap pro and Sequence Generator pro have useful software for rapidly determining the right exposure. Some aim for a mean ADU of 30K in the middle, for it looks too strong on the calibrated subs and I think some faint signal may me missing (normally it shouldn't : ) ). CS Bogdan |
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1.20
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They don`t seem to be correcting the background. When i stretch the image in Pix Insight i can see the dust motes and vignetting are still there.. Regards Alan |
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9.90
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Alan Hancox: do you see the dust in the master flat ? |
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1.20
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If you stretch the master in Pix Insight you can but only just. I wish i could post an image... Regards Alan |
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9.90
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| The focus was the same as the one during the lights ? All settings should be the same. Sometimes if you optimisé the darks in pix, it won’t work. |
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1.20
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| I use DSS to calibrate my images....Not got my head around Pix to calibrate images... |
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| What is your f/? |
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1.20
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| I use a TS65 quad apo (420 mm f6.5) and a Skywatcher 150 PDS (675 mm @ f4.5) |
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At F/2 the flats are very forgiven, but at F/6, you must have it right, as any dust on the sensor or lenses will create a problem. i use the t-shirt method and shoot the flats at 8 am, early morning, when the scope is in the shade. now, someone is proposing a flat box at $500. An expensive option that works, but it does not have to be that way. My t-shirt, i think was $25.00. it works for my sct 9.25' or F/6.5. clear skies |
2.71
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Alan, I use an ASI1600MM with both a 90mm apo and 200mm RC. I shoot for 20,000 ADU for my flats, but I don't obsess over it, I take anywhere from 19,000 to 21,000. The idea of a panel that has variable brightness is a good idea to keep exposures all the same length, but seems too pricey just for that. Sky flats work well with a T-shirt as long as you follow the instructions to have the scope in the shade, i.e., no sun on the scope as it will cause bright areas. I've used sky flats before. currently I use an iPad or a tracing pad, also with a T-shirt over the scope, to take flats. both seem to work very well for me. As for exposure time, I've heard that too short is not good, but I routinely use under 0.5 seconds with no issues. Finally, make sure that you touch nothing in the imaging train between the flats and the lights. Also, I do use flat darks, but I'm not sure it is really necessary. Good luck, Ron |
1.51
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How many flats are you taking? I like to take a lot (~60). With Pix you only have to make the master flat once so the extra time isn't too bad. How do you change your filters? If you use a filter wheel check to make sure that it always come to the same position when you change the filters. |
3.21
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Ron: In my experience this is totally necessary, if you calibrate your light with darks. You eradicate noise with this step, and if you would use uncalibrated flats, you would inject noise again. If you don't calibrate your lights with darks, you don't need to calibrate your flats either - but you totally want to use darks, so... :-) |
1.20
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I think Bogdan Borz is right. Did you change the focus between shooting lights and darks? It does look that way with the M81 in your gallery. I used to see exactly the same, because i defocused the telescope when shooting flats. That was before I started using the white T-shirt and just left the focus were it was after shooting lights. Therefore you also have to shoot flats AFTER lights. Otherwise you change the focus once you start shooting lights. Exposure wise, try and keep it around half of max ADU. You "don't need darks" if you use pixel rejection when stacking the flats, but darks is slightly better. |
8.04
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I have helped several people using APT with their flats. It's a great bit of software, but Flat plans just don't seem to give the right length exposure. In each case I have advised to NOT use the flats plan but use "shoot" instead adjusting the length of the exposure until the histogram is 1/3 to just under 1/2 way across from the left. This advice seems to have worked for the 3 people I have helped with this problem. If you have a camera that shows ADU between 23,000 and 26,000 seems to work best for me but I think you can go slightly higher and lower (maximum 30,000). Carole |
1.91
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Hi Alan, I’m a little late on your question, but there’s lots of good stuff here in these replies. My only thought is that PI’s calibration process works really well but it does take some study to get the best result. There is a very good write-up on the website for Light Vortex. Check it out and take your time getting it set up. Also keep in mind that lots of folks get a better result if they Uncheck the Optimize box under the Dark Master section. Best of luck! Bob |
0.00
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| Greetings. I use APT for my imaging sessions and the APT Flat generator tool. I notice the poster a couple above doesn't like the APT flat generator, but I have found it to be of great use. I set the object ADU between 19000 and 21000. I use a light board on a dim setting (it was only like $25 off of Amazon) and APT builds a flats plan for all of my filters. This has worked great for me, is simple, and only takes about 25 mins from start to finish. |
