elpajare
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Post by elpajare on Feb 7, 2019 15:44:16 GMT
In the post-processing of these photos with Startools I have always respected the original colors of the object. I have only used the Color tool to increase the saturation, sometimes never to modify the color balance.
NGC 3675 :The galaxy features two ring structures, with diametre 1.62 and 2.42 arcminutes. The spiral arms are tightly wound and form an inner pseudoring and they continue for one revolution outside the ring. The outer arms are very patchy and filamentary.
SKW Quattro+IMX224+Risingsky software 15x18" +DFC+Startools
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elpajare
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Post by elpajare on Feb 8, 2019 7:55:04 GMT
NGC 3726 is a spiral galaxy with a small bar, seen with medium inclination. The bar is 1.38 arcseconds across and it ends at an inner ring with 1.50 arcseconds diametre. The bluest regions of star formation are located at the ring. Three arms emmanate from the ring. The southern is the brightest and the north is the best defined. The third arm emmantes from the east side of the ring, moves towards NNW and then bends sharply to the southwest. The spiral arms are thick and well defined and can be traced for half a revolution. The arms then branch into fragments. The spiral pattern of the galaxy is a bit disturbed and asymmetrical. Numerous bright HII regions are present in the galaxy. The galaxy has a massive dark matter halo. The nucleus of the galaxy hosts a supermassive black hole with mass 106.5 (3 million) M☉, based on Ks bulge luminosity.(Wikipedia) SKW Quattro+IMX224+Risingsky software 15x18" +DFC+Startools
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Post by Deleted on Feb 8, 2019 11:51:57 GMT
Carlos, Great work as usual I would be interested to see what detail you would get using your IMX294 on those images. I understand the FOV would be much greater and the image much smaller. The question is, would the resolution be better? cheers Paul
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elpajare
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Post by elpajare on Feb 8, 2019 14:35:07 GMT
Although the IMX924 chip has more pixels / mm being larger than the IMX224 chip and having the higher pixel size does not give more resolution. The tests I have done give the IMX224 winner.
My practical result is subjective, of course, but I find the SKW Quattro + IMX224 combination for this kind of objects is better.
Tanks for yor support!
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elpajare
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Post by elpajare on Feb 8, 2019 16:07:18 GMT
NGC 3877 is a type Sc spiral galaxy that was discovered by William Herschel on February 5, 1788. It is located below the magnitude 3.7 star Chi Ursae Majoris in Ursa Major.(Wikipedia) SKW Quattro+IMX224+Risingsky software 15x18" +DFC+Startools
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elpajare
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Post by elpajare on Feb 8, 2019 16:23:02 GMT
NGC 3893 is a grand design spiral galaxy. It has two main arms, with high surface brightness and numerous HII regions. A faint spiral arm extends from the south to the north side making an arc on the east side of NGC 3893. The galaxy is categorised as SAB in NED, but Hernández-Toledo and Puerari didn't detect a bar in their observations. The stellar disk of NGC 3893 is estimated to have a mass of 2.3x1010 M☉ and dominates gas dynamics in the optical radius. The star formation rate in NGC 3893 is about 5.62 M☉/year.SKW Quattro+IMX224+Risingsky software 15x18" +DFC+Startools
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Post by Deleted on Feb 8, 2019 23:36:56 GMT
Hello Carlos My RASA8 is all boxed up and ready for its US holiday trip to Celestron for collimation. That makes my 200f/4 newtonian as my main imaging scope at home in the pod so I have a few questions if you dont mind. I note that most of your small galaxies are 18 sec exposures and the stack is 15. Do you find there is much difference if you stack x 10 ? When you use your 294, do you use similar exposures and stacks? Because the newt is fixed in position, you said you do a 1 star align. Do you have much trouble getting the image in the the field of view with the 224 as the FOV is a quite small? One last question. How often do you need to collimate the 200f/4? Thanks Paul
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elpajare
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Post by elpajare on Feb 9, 2019 8:21:10 GMT
I will gladly try to clarify the things that concern you. I hope to overcome the difficulties of translation I know that there is a rule that regulates the SNR / stack ratio and that from a certain number of stacks the SNR improvement is minimal. For the type of photos I make (Videoast./EAA) it seems to me that with 15-20 stacks I can have acceptable photos. You can choose yourself the number you prefer.. The sensitivity of the IMX294 is a bit lower than that of the IMX224 but since the FOV is higher, in practice I serve almost the same exposure. The aiming of the align star is one of the things that delays me the most before starting a session. The choice of the finder is of the utmost importance. For the Nerwton I make serve one subject with 6 adjustable screws and it is illuminated. And every night I exactly readjust it to the star when I have it focused on the camera. www.astroshop.eu/optical-finders/bresser-messier-8x50-finder/p,25184 The SKW collimation I do with laser every afternoon, with light, before starting the night session. I keep the OTA in a plastic garden box next to the pillar. I take it very carefully and I avoid blows. Anyway collating a newton is very easy when you take custom www.astroshop.eu/laser-pointers/hotech-1-25-2-sca-laser-collimator-crosshair-laser/p,22957 I hope I have helped you, do not hesitate to ask more and if I can help you I will be delighted
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Post by Deleted on Feb 9, 2019 9:02:41 GMT
Thanks Carlos You have answered my questions. I have a skywatcher wifi but do a 2 star alignment and polar alignment each time. It appears I dont need to do this if I dont move my scope after each session. My aim with videoastronomy is to keep the total exposure to 3 minutes and then see what the best image I can do in that time. 10x 18 secs is 3 minutes and that was the reason for the question. My ultimate aim is to get decent images of dim DSO's with 1 minute total exposure . I will have to wait for the RASA to achieve that. I find that I need to collimate the newtonian quite often. The f/4 is quite demanding.
I appreciate your input cheers Paul
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elpajare
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Post by elpajare on Feb 9, 2019 11:10:57 GMT
More important than the total exposure time is the number of stacks of each exposure, IMO Spinning fine, each chip has its particularities and I apply different treatments. The IMX224 has amp-glow and high background noise, at least 15 stacks are needed for the stack to increase the SNR and the photo is fine. The IMX294 has no amp-glow and less background noise, with 10 stacks you could pass. These are all minimums. It does not matter if the stack is 1 " or 30", the fact of stacking is to reduce the noise and you need a 10-15 stack to do the job
I make 1 star align because I withdraw the OTA every night. When I put it back there is always some mismatch and that is why I do a realignment to 1 star. Each OTA needs a specific realignment (SKW / Omegon / TSoptics)
What is always fixed is the base of the mount and the motors.
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elpajare
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Post by elpajare on Feb 9, 2019 11:51:28 GMT
NGC 3938 is an unbarred spiral galaxy in the Ursa Major constellation. It was discovered on 6 February 1788 by William Herschel. It is one of the brightest spiral galaxies in the Ursa Major South galaxy group, and is roughly 67,000 light years in diameter. It is approximately 43 million light years away from Earth. NGC 3938 is classified as type Sc under the Hubble sequence, a loosely wound spiral galaxy with a smaller and dimmer bulge. The spiral arms of the galaxy contain many areas of ionized atomic hydrogen gas, more so towards the center.(Wikipedia) SKW Quattro+IMX224+Risingsky software 15x18" +DFC+Startools
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Post by Deleted on Feb 9, 2019 13:31:16 GMT
Carlos Got the 200f/4 newtonian out tonight. NGC 1365 ZWO 294 and 45s x 4 stack with .6 FR. Astrometry.net gets it at about F2.9. There was severe vignetting which I cropped out. I welcome any of your comments on how to improve the image cheers Paul
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elpajare
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Post by elpajare on Feb 10, 2019 9:43:15 GMT
This is a very beautiful galaxy that I can not see, it is too low on the horizon. The detail is good but you can feel the wind in the shape of the stars. The 15 "exposure is the same as I do with the IMX224 with a smaller FOV, which is what I told you before, the lower sensitivity of the IMX294 compensates with a higher FOV (+ light) Disadvantages of a large chip with the Newton f4 to photograph small galaxies, globular clusters and planetary nebulae: Elongated stars on the edges and some vignetting. Missing detail in the main subject
For this I make serve a smaller chip like the IMX224 .... IMO
This is a picture of NGC 2392 with SKW Quattro+IMX294 that better explains what I'm trying to tell you:
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Post by Deleted on Feb 10, 2019 11:57:05 GMT
Yes Carlos ,I understand what you are telling me. I will give the 224 a go next observing night. Meanwhile this evening I did a 20" x 15 on the same galaxy ngc 1365 with the 294 with bin 2. Sharpcap automatically saves at 1,3 ,5,7.....etc minutes so I did 20x15. The extra stacks did not reduce the noise in this case. Also I am making the vignetting worse with the FR .6. In fact ,it looks terrible. Will add this to my collection of bad images
Also here is the horsehead 20" x 15 .I will have to stop using the focal reducer. cheers Paul
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elpajare
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Post by elpajare on Feb 10, 2019 12:14:25 GMT
I understand you perfectly. The reducer worsens the vignetting.
The 200 f4 + IMX224 will give you good results, there are no vignetting or stars drowned.
Remember to collimate before...haha
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elpajare
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Post by elpajare on Feb 10, 2019 12:19:33 GMT
For the big bright nebula I use the combination TSOptics 72/432 f6 +IMX294+UHC filter: THis is a 10x30" stacking
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Post by howie1 on Feb 11, 2019 1:09:38 GMT
Just remember that flats take very little time to make and will cure that vignetting. SharpCap has a tool which guides you through it. Very bright light is used to create flats at some typical gain/ISO ... so the exposures are super fast! Daylight, scope pointed to Zenith with white T shirt over objective is perfect in fact! SC will create the master flat in just seconds using 10 super fast sub-second frames.
You can shoot them at different gains with even ten cameras in no time at all during daytime. Save the master flats named like ASI294gain100, ASI294gain150, ASI294gain200 and ASI224gain100 ASI224gain150 and so on, then at night on some object if you find the ASI294 gets a good stackable image at gain of 230 then just select the flat called ASI294gain250 ... it will be close enough and work fine! Very quick solution.
Purists and AP folk always poo-poo the above telling you to shoot flats darks bias all at night under the conditions at that time and the camera at temperature yada yada ... but for EAA it works fine and very quick and easy to do without buying light panels and fiddling at night. The old ... EAA is not about getting NASA Photo Of The Day images!
Second option to fix vignetting .... in the past before SC had the "flats tool", many got SC to produce the single frames, but they used AstroToaster to stretch and process those single frames from the SC folder. Why? Because AT has a built in anti vignette tool called Lens Grad. So you could do that (process all the SC frames in AT).
OR, you could do it all in SC then save the final SC processed image just like you did to post up all your nice SC EAA images in this forum. But out in the dark you could drag and drop the saved image from the SC folder into the AT folder and bingo ... adjust the lens gradient tool and ... bingo no vignette.
Lasers for collimation ... just beware that being made in China the quality is once again totally suspect and in fact ... many lasers need to be collimated before being used! On placing mine exactly 5 metres from a wall, and in a ST80 minus the objective (so I could rotate in 45 degree increments) with someone marking a spot on the wall where the laser "dot" appeared after each rotation .... the laser scribed a circle a full 9.5cm in diameter! I repeated this a couple of times, including in a aluminium jig I made to 'rule out' the ST80 focus tube itself being the problem. Same result.
IE Over the 1000mm length of the newtonian the laser dot was nearly 2cm out! Ie focus that laser dot smack bang in the newts primary mirror doughnut with the bullseye target facing the primary mirror for that adjustment ... meant it was out by 1 cm from being properly collimated! IE the true collimated point was still outside the doughnut!
You can collimate a laser by picking out the rubber compound you'll see in 3 places around the edge of the laser unit. I did this but just touch a screw and the distant (5 m away) laser 'dot' on the wall will move some crazy amount. After a full day of tweaking and failing to fix it, the whole laser ended up in the bin in disgust.
Stacking number vs time to reduce noise below ...
Stack of 4 frames halves the noise in the final stacked image. IE 50% noise reduction after 4 frames. Stack of 9 frames reduces the noise in the final stacked image to one third of the original noise in one frame. IE 66% noise reduction after 9 frames. Stack of 16 frames reduces the noise in the final stacked image to one quarter of the original noise in one frame. IE 75% noise reduction after 16 frames. See the sequence here?
So if you are happy with the image after 9 frames (66% reduction in noise), then to get 75% reduction in noise you have to wait almost twice as long. As so on. The problem is that along with noise reduction, the more frames you shoot the more chance you have of getting a few photons of extra faint stuff and details appearing as signal in some of the frames. So gradually you are able to tease out better quality images. So you have to determine with your particular camera's gain/noise ratio what best length of stacking "works" for your style of EAA. Your ASI224 at gain N may well be the shortest wait for some object at X seconds and Y stacked, with the ASI294 totally different. For you that is! While I may look at both of your "best" settings for each and it won't be my "taste" and use totally different settings.
By the way ... I've read many authors who claim signal (IE the data in the frame) does NOT increase with stacking. It only increases with the length of each individual exposure frame. I do not agree with this. Stars twinkle due to atmosphere dust/thickness/heat/breeze etc. Thats direct evidence of the 'seeing' of the DSO you are shooting is being shot through the same conditions. DSS and other (SC/AT) software shows 'rating' of every frame in the stack and each varies according to focus, brightness, FWHM etc pixel by pixel analysis of every frame. Planetary lucky imaging clearly shows this effect with many/most frames in the video being discounted for the 'good ones' to make the final image. Sensors 'efficiency' is a statistical average of a test sensor results for converting photons of light into eVolts. IE they change from second to second in efficiency with a statistically calculated average being posted as the value for the sensor. But out there using it in the dark, the eVolts in a single frame are just for that duration of shot. And it will change with every shot eventually reaching the best possible overall efficiency possible at some point many exposures averaged. All of this dictates a single image will never contain the same exact signal as another frame even at the same gain and exposure time. It varies. And there are posts on DSLR-Astronomy and others where the 200% cropped images between all areas of every frame in a stack are examined using software for noise and signal ... and the result is the Signal increases steadily as you stack more. It takes a while. It doesnt double in N frames ... I don't even think it ever doubled even after 200 frames! But it does slightly go up as more are stacked.
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Post by howie1 on Feb 11, 2019 1:17:01 GMT
Carlos Got the 200f/4 newtonian out tonight. NGC 1365 ZWO 294 and 45s x 4 stack with .6 FR. Astrometry.net gets it at about F2.9. There was severe vignetting which I cropped out. I welcome any of your comments on how to improve the image cheers Paul Paul, great shot! Especially considering you cropped it. I clicked on the image to see full size and there isn't much noise there. I've heard the NSN blokes say the 294 is low noise. Donboy is usually using it over the past month I've caught one of his broadcasts. Of course he pretty much does AP rather than EAA ... but his fav gain 300 and exp times from 30sec to 60 seconds he notes are low noise. Of course he uses cooled cameras too.
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Post by Deleted on Feb 11, 2019 4:50:43 GMT
Thanks very much for that Howie. I have been doing VA long enough now to stop producing so many crappy images. Occasionally I get it right though. I need to get onto flats particularly when I use the FR's so often. I will try the daytime master flats method What about darks Howie? Do I need to do dark subtraction as well? I understand the theory of the noise reduction but I must admit I find it hard to believe with the 224 and 294. I never seem to get any improvement after 4 or 5 stacks.That stack of 15 of ngc 1365 was just awful.
On another point, the synscan wifi has been working well. The last 2 nights I didnt align the NEQ6 and it slewed very accurately each time. ..And no crashes with the software. As Ken said, laptop bootup was the most time consuming part of the setup. cheers Paul
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Post by howie1 on Feb 11, 2019 6:17:09 GMT
What about darks Howie? Do I need to do dark subtraction as well? I understand the theory of the noise reduction but I must admit I find it hard to believe with the 224 and 294. I never seem to get any improvement after 4 or 5 stacks.That stack of 15 of ngc 1365 was just awful. Paul, Re no noise improvement with your cameras after 4-5 stacked frames ... then like I said ... Great as you've found the sweet spot for your gear and tastes! That's all that matters. Darks will help if you see warm RGB pixels and amp glow appearing. Again, some folk don't care about such stuff and just want to see the objects details ... who cares about the background sky? Darks can be done during daytime if your camera is cooled .... but unwise to do in the daytime if uncooled. The hot daytime temp cause the sensor to show far more warm pixels and amp glow at some gain and exp time when it's 30C ambient temp, compared to the same gain and exp time at nightime at 22C ambient or cooler. If you do decide to still do darks in the daytime with your uncooled camera then dont forget .... there's no need to put the camera into the actual scope! Just cap the nosepiece of the camera and start setting gain and exp time and take your darks minus any setup of your gear! I've actually read on some forum a bloke stuck his uncooled camera in the fridge with the cable coming out the closed fridge door ... to create his 'proper' nighttime gain/exp time master darks at nightime temps. Yeah Paul, flats are good! Easy to do in the day so give it a crack. ChrisV in Sydney pointed out to me the benefits about 12 months or so ago when I was slowly "turning towards AP". My Canon DSLR being APS/C (big 23mm sensor) suffers from vignetting in my big newt. When doing EAA I found the AT "Sky Gradient" tool flattens it very nicely so no need for flats. But AP is a different animal and flats are what gets rid of vignetting for AP. And, of course, flats get rid of vignetting when using ZWO type camera's using SC for EAA. For interest .... Darks and Canon DSLR's made after 2012 .... are not necessary! ClarkVision website (an award winning AP as well as award winning Nature photographer). Canon DSLR model's which came out from 2012 onwards can remap the bad pixel/amp glow maps on the fly. So what you do is shoot until you see some frames showing one or two warm pixels or amp glow, then without turning off the camera, using the menu button on the back, navigate to the "sensor clean" option. It remaps the sensor factory "map" to the exif 'bad-data' contained in the RAW data files of the photos. Thus it gets rid of noise and bad pixels for the images by subtracting the 'new' map internally. Pretty neat. As soon as you turn it off, it remaps back to the standard factory bad pixel map. So just press 'sensor clean' in the menu but dont turn it off so it applies the newly created map out there in the dark! It's what I did to get rid of any hot pixels and glow when producing these AT nine x one minute stacked RAW frames out in one of my last EAA sessions (link below). For anti-vignetting, you'll also see the desktop captures show the AT Lens Gradient slider moved over - IE thats what I used instead of shooting flats at that session. Howies last EAA stacking session 10 months ago! Sigh!
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