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Showing results for tags 'flats'.
Found 18 results
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Hi All, I have recently converted from an old Canon DSLR to a ZWO ASI1600MC-Pro. The individual subs look great with the new camera, but I am having seemingly insoluble problems processing, so I need the assembled wisdom here! The first image shows a single sub on the left (auto-stretched), and the result of stacking some 25 subs on the right, combined with flats. The flats have corrected quite nicely for the dust doughnuts, but given me inverted vignetting. (I should say that I have tried processing with darks and bias as well, but the basic problem of the reversed vignetting remains. Processing was done in Deep Sky Stacker, although I get the same results using PI and the BPP script). I initially thought this was down to using the wrong ADU values for the flats, so I've tried various from 5,000 up to 30,000 in 5,000 increments, but nothing improves - the higher the ADU the worse the effect seems to get. I've also tried different techniques for taking the flats - grey skies (easy at the moment) with t-shirt layers in front, or a tablet screen on white. Flats are seemingly ok - here is an individual sub on the left and master flat on the right. OK, they are rather brownish, but apart from that they look ok to my (DSLR-attuned) eye. Different ADU values seem to fail to correct for the dust doughnuts, as well as making the vignetting worse. I have one further thought / problem to add. The over-corrected centre of that processed image (top, right-hand side) shows some odd details. Here's a zoomed version. There are fairly broad swirly lines showing up in there. Actually the lines are across the whole image, but most visible in the centre where the vignetting shows it up. My only thoughts are that this could be condensation or similar? Might this account for the flats not correcting properly? As I said I'm using the ASI1600MC-Pro, and have it set to cool to -20C for all lights, darks and flats. I've not encountered a problem like this with flats failing to work so miserably, so I'm after any and all knowledge at this point. To a fair extent I can take out the vignetting with ABE/DBE, but that then leaves me the dust doughnuts. I really don't want to have to 'edit' my pictures to that extent, and feel that the flats should take care of the vignetting. Thanks for looking. Phil
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Hi All, I am posting what I suspect is a newbie mistake question but hoping that someone can assist with the issue of flats. Although I have been fumbling around the sky, taking snaps at leisure, recently I became serious. I have read up about the different calibration files (flats, darks, bias) and they seemed to make sense; different ways to capture the image defects and extract those from the image of the sky. After a few weeks (months) of further fumbling I went back to the very first target to receive my attention, M42 Orion Nebula. In short, I took 20x 30s exposures in LRGB and ran these along with 20x LRGB each of darks, bias and flats. To obtain the flats I used a diffuse sheet of perspex (lightbox material) and an LED video lamp that has 180 white LEDs, turned to its lowest setting. Attached below is the stacked Luminance flat and the light image. In the lights I am getting very strong marks from dust and I had thought that the flats would subtract this but looking at the flats the marks are completely different shapes and do nothing to remove them from the lights. The attached has been further stretched to show the issue. Now, I am obviously doing something wrong but I have no idea what, any pointers from the vast pool of knowledge will be much appreciated. Thanks, Anthony
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Does anyone seen the new Ikea LED lighting lineup ? They have launched a new LED product, FLOALT, which is some sort of light box and it comes in three different sizes, from which one is really interesting: FLOALT 30cm. Does anyone already acquired it, would this work as a flat box ?
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Hi All, I have just made myself a light box for doing Flats which on my first play with it last night, seemed to work okay, but I am not sure what brightness / exposure level I should be aiming for? Attached are a few screen shots taken at different exposures (0.2 seconds up to 1.0 second), all taken at the same brightness level. Now, rather than changing the exposure, I can make the lightbox darker or brighter, but I will see similar images to those below. So my questions is, which one of these exposure times is the 'best'? I have included the histogram in each screen shot, as I understand that this is the important thing, or is it the number in the White / Black box which is important? Hope someone can offer some advice here 0.2 Second Exposure 0.4Second Exposure 0.6 Second Exposure 0.8 Second Exposure 1.0 Second Exposure -
Hi all While I've been largely locked under clouds for a couple of months, I thought I'd write some software that I've been meaning to get around to for a while. I use a standard LCD computer monitor for taking flats. I plug it in to my imaging laptop. I started off using a blank HTML page in a full-screen browser window to provide the uniform grey colour on the display but I needed to vary the brightness of the display for different filters. So, I wrote some software that does it. The software is called Second Monitor Lightbox and is available free of charge from my site (paw-print.com). If you use a CCD with filter wheel, it'll link to the filter wheel via the ASCOM driver so that, once you've set the perfect brightness for each filter, it will change brightness automatically as the filter changes. It also has a 'preset' mode for non-ASCOM set ups so that you can just re-call a pre-determined brightness to match a certain configuration (filter, binning, etc). There's a tutorial based around using SGP Pro on the site, so if you want to try it have a look through that. When you install it, Windows will warn you that it's from an Unknown Publisher. This is just because I don't pay Microsoft an annual fee for a developer's certificate. Just tell Windows to install it anyway - you may need to click 'More information' to get the option to go ahead. Let me know what you think. I hope some of you will find it useful. I know it saves me a load of hassle at the end of a long session trying to get the right brightness level to give decent flats for each filter. You can get it from here: http://paw-print.com Steve -
I've had continual problems with reflections in my flats. I have an Atik 383L, an Atik EFW2, and I use 36mm unmounted Baader filters. It seems that when using the camera and wheel 'as intended' I get reflections. I see these especially in my flats, but I think they are there in the images too. They do not calibrate out - I am left with lines in my images and I either have to crop them heavily or use blunderbuss processing techniques, which inevitably leads to some degradation in image quality (and my images are already quite degraded enough). I have posted about this problem before: https://stargazerslounge.com/topic/260450-horizontal-lines-in-flats/ and https://stargazerslounge.com/topic/269119-does-atik-efw2-work-with-atik-383l/ There is a solution, but it is not ideal. I thought that I would provide an update as to my progress and post my solution. If anyone has any other ideas I would consider trying them out. I am struggling to believe that I am the only person having this problem. First off, here is the issue - it appears to me to be a reflection of either the optical window edges or the sensor itself (I've pushed the contrast a bit to make the issue obvious in a reduced size JPEG): The issue is most obvious in the NB filters, but it is there in the RGB too - perhaps worse in the blue filter. I have tried the set up on 4 separate scopes - 3 x refractors and 1 x SCT - there is no difference I have tried two different 383L cameras - they both cause this problem I have tried 2 different sets of Baader LRGB filters (thanks to FLO for supplying the second set) and a set of Baader NBs - no difference I have tried reversing the orientation of the filters in the carousel (suggested by the chap from Baader) - no difference I have tried a different filter - a Chroma Green kindly supplied by Bern at Modern Astronomy - no difference (indeed maybe the reflections were a little more obvious - I've posted the Chroma version) I have tried 3 different methods of taking flats: an LED panel; a Gerd Neumann EL panel; and sky flats with a pillowcase I had one camera back to Atik who tried blackening the optical window edges. The chap from Baader also suggested putting a spacer between the camera and the wheel. This started to work. As I added spacers, the lines moved to the outside of the frame. Eventually they went away altogether. I was able to lose the lines at 7mm of spacing on one 383L. I needed 7.5mm of spacing with the other. The spacing does not seem to make the vignetting any significantly worse, so this is a 'fix'. On the other hand if you are considering using an OAG, then being forced to add that 7.5mm could be significant. Am I really the only one having this problem?
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As this is my first go at doing flats, I am going to go into a bit of detail, as almost any step I have taken in this could be the cause of the weird result I got. I purchased a 10cm circular white ELP (sticky back) which I attached to a circular piece of card. I covered this with a piece of plane white paper (to diffuse the light) and attached a ring of card so that it would sit over my small refractor or camera lens. It is powered through the mains cable. After completion of my lights, I moved the axes of the mount so that the camera lens was pointing vertically, placed the mounted ELP over the lens hood (having made no alteration to the settings) and switched it on. I switched the camera from manual to Av (it is a canon 1000D) and went into EOSutils, adjusted the aperture to f/4 (the aperture I had been using to take the lights) and took 10 subs. The screen advised me that it was taking 1.3s subs. I then rotated the ELP through 90 deg and took another 10 subs. Upon loading the subs into DSS to produce a masterflat - the description file produced by DSS is attached. MasterFlat_ISO800.Description.txt My first surprise was that it was telling me that it was only stacking 17 out of the 20 flats loaded. Now I do have it set to only stack the best 80% lights - is it automatically doing the same for flats? It also told me that the exposure time was 1/32s, compared to the 1.3s I was advised when taking them. These two surpises, however, paled into insignificance compared with what it produced. Firstly, a jpg of one single sub (20%). Secondly, a jpg of the masterflat produced by DSS (20%). To me it looks incredibly dark compared to the single sub. And finally a closeup of the masterflat (500%) - this is only a small bit of it, but it looks the same all over. Now, I am no expert on flats, but I have seen a fair number on SGL over the years, and I have never seen one that looks anything like this. And, on the basis that it is far more likely that I have done something wrong than that the entire astro-community has been doing something wrong all these years, I am guessing that this one should not look anything like this either. So my question is: what have I done wrong? And (even more important): how do I not do it wrong next time? Thanks. -
From the album: LightBox 90mm refractor
© SabinFotafotografie
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I need to get/adapt an ELD for use with my Explore Scientific 80ED and Mak 127 to make Flats. What is the current thinking on the best choice of panels to base one on (uk) and any advise on power supply. Many thanks David
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So after Carole helped me to realise that I was taking my flats wrong, I've reprocessed this image and finally the funny rings have vanished. Original thread TL;DR - I was underexposing my flats, which resulted in failure of calibration to remove vignetting, as well as it introducing weird red concentric oval rings. Last night was supposed to be clear, so I set up in the garden. Cue the Irish weather. I only managed to get PA and focus (you know, the most fun bits) and then the clouds rolled in. Anyway, so instead of imaging, I took a bunch of calibration frames. The setup was slightly different to the lights - 1) temp 4 C instead of -1.5 C (no big deal) 2) camera at different angle to telescope (can't correct dust motes) 3) new camera angle adjuster in path (different vignetting and internal reflections) so I didn't hold out much hope that it would correct the problem. But it did! I used the new bias and darks to correct the new flats, and then the old bias and old darks and new flats to correct the lights. I'm so pleased I've finally figured out what was going on as it's ruined many images for me over the past year+. Thanks again Carole, Barry
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I have been generally pleased with my Moravian camera and filter wheel. However, I noticed I was getting some very odd results when trying to calculate filter offsets for my autofocus routine. I found that the wheel was not rotating to the filter requested - indeed it seemed random. Of course it was not random .... I have a 10 position filter wheel. However, it seemed that the Moravian Ascom driver was convinced I had a 12 position wheel. To get the Moravian wheel correctly configured, you have to run a configuration program. It tells you to do this in the manual. I just hadn't read the manual. As you can imagine, this led to erratic results. If I shot filters in sequence, things would go OK. However, if I tried to go back to a filter I had shot before then it would not work. Now, I shoot the flats from my 7 filters all in one go, BUT I test out the required exposure times first which means a cycle through all 7. So when I come to shoot the actual flats, I am shooting through the wrong filter or (sometimes) through no filter at all. I was never all that happy with the M31 I did back in early December 2016. There seemed an odd gradient on the left side of the image: https://stargazerslounge.com/topic/282827-m31-revisit/ So, having got the wheel correctly configured, I redid the flats and recalibrated the data. Lo and behold, the bright patch on the left disappeared. Data: Baader Blue 36 mm: 16x300" Baader Green 36 mm: 16x300" Baader Luminance 36 mm: 61x300" Baader Red 36 mm: 16x300" Chroma Ha 3nm: 6x1200"
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Note sure what to make of this. I was watching a video on improving flats for my WO Star 71 and using CCD Inspector to help with this. I downloaded the free trial and performed a Flat analysis on one of my Flat frames. I was fairly alarmed by the results because when I looked at them in SGP they looked fine. CCD Inspector appears to show at least two issues. One is the centre of optical illumination is quite a way out from the centre of the CCD chip (KAF8300) Also not sure if the high percentages around the image are an issue? Though they seem to be fairly consistent though. When I perform a high stretch on a Light frame the image in SGP does seem to follow the off centre illumination issue. I have looked at other settings on CCD Inspector but have to say I am not too sure on whether the results I get back are good or not. How or do I need to adjust the optical illumination train to be more central? Is this a massive issue? Basically I have the CCD camera fixed with extension tubes to allow me good focus with not much drawer tube extension (11mm). It is a good fit with no slack. I have included a picture of one of the flats. Thanks
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Can anybody suggest what might be wrong with my flats calibration process? I created a master flat from 40 images taken by placing an ipad over the end of the scope displaying a photo of a featureless wall (maybe not the best method?) A stretched image of the master flat shows a number of very faint dark circles which I think are grease spots on the objective lens of the scope. I can see these clearly when the lens is starting to dew up after an imaging session. Anyway after using these flats in DSS or Atik Dawn, these artifacts start to come through on the processed image, see M81 image below. Any suggestions or thoughts would be much appreciated. Steve
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From the album: LightBox 90mm refractor
© SabinFotafotografie
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Hi again! I posted a query about flats a while back, but have now run into a more specific issue so starting a new thread for this. I had a decent clear night couple of days back and a chance to give the ASI1600 a bit more informed testing. Still finding some oddities with flats generally though, so hoping for some further thoughts please. In the past when doing flats with the DSLR, I've pointed the scope at an evenly illuminated area of the ceiling and run off a number of exposures sort of mid-gray middling histo no problems - always worked very nicely. With the ASI1600MM a couple of oddities though. First, opinions seem to vary on what gain to use - some say a low gain, some say the same gain as the lights. Same gain as the lights seems sensible, so thats what I went with. But with quite high gain (300 in this case) the flats only need very short exposures. This seems to cause horizontal banding, possibly due to flickering in the source light, and if I cover the scope (T shirt method) to reduce the light and extend the exposure to say 60 seconds, same as the lights, I get a lot of noise - I guess this is shot noise. So I settled for just doing lots of flats and hoping the noise would even out - I settled for 100 - though subsequently I see some folk use more, maybe for this very reason. Superficially the master flat looks OK, but at high mag it still looks noisy. See below and magnified section 300%. So what is the solution? Even more flats? Or maybe reduce the gain - all I need is the flat to replicate the vignetting. The mid gray/mid-histo used for flats isnt really the same light level as used in the lights anyway, so does the gain matter? With the DSLR I always set the ISO to 100 for flats and that worked just fine. Grateful as ever for any thoughts and advice!
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Hi all, Last week I made some photos using my canon 500d on fixed tripod, with also the darks and bias. The results were not bad, but no milky way really visible, and I've been trying a little bit to fiddle with DSS parameters, or ACDSee, but no luck. I thought maybe the lack of flats was partially the cause of this, so I made some, yesterday. But probably I haven't understood flats at all, because instead of cancelling the vignetting, it added bright vignetting...... So my question is, if my lights are 30 20sec subs, 1600 ISO, f/4.5 at 18 mm, what should my flats be like? I did 30 subs at 1600 ISO, f/4.5 18 mm, but left the exposure automatic, which meant 1/320sec... (I used a tablet screen using a flashlight app). The flats show vignetting. If I had kept the 20sec exposure, they would obviously be completely white, overexposed... I attach two photos, one with, and one without the flats... NB: the one with bright vignetting is the one WITH the flats... :-/ thanks for any help!! Gerhard.
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Folloing on from a post I made in early November :- http://stargazerslounge.com/topic/198663-is-this-acceptable-or-only-30-mins-of-data/ I am finding myself frustrated by lack of time and the clouds.... (set up three times last week, clear skies, but by the time it was dark the good ole clouds had rolled in and put paid to another night.. So with the limited time I set myself a challenge to see what I could achieve with only 30 mins of subs, I have included three images of what I have so far. I would be interested to see what others could achieve with the same limitations, so are you up for a "30 Minute Challenge" ? Not too many rules :- Only 30 mins total of Subs (1 x 30m, 2 x 15m, 15 x 2m, 30 x 1m, you get the idea...),(Be Honest) Unlimited dark's, flats, bias etc. Include some capture information with any image submitted. Thats about it.. So heres my attempts :- all taken with a SW200P, HEQ5 Pro unguided, Canon 1000D at ISO800 M31 15 x 2m Lights 10 X 2m Darks 10 x Flats 10 x Bias M45 12 x 90s Lights 10 X 90s Darks 10 x Flats 10 x Bias M81 20 x 90s Lights 10 X 90s Darks 10 x Flats 10 x Bias Any One Else Up for It ????
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What sort of exposure length do people use for their flats? In particular with a flat field panel. I'm concerned my Gerd Neumann panel is too bright. He now sells grey filters to cut the light level. I use Skyflats4 to ctually take the flats. My exposures are around 0.03 seconds for LRGB. Is this too short? I'm using a SXVH694. Thanks Anne
