alan4908

My first attempt at NGC3718 which lies at a distance of about 49 million light years from Earth. It's a very unusually looking galaxy, featuring a twisted dust lane in the central region. To the right you can also see the companion galaxy NGC3729 which, occurring to radio measurements, appears to be interacting with its larger partner. At the top of the image, Hickson 56 can be seen, a grouping of five small galaxies that are estimated to be about 390 million light years away. The LRGB image represents just under 16 hours and was taken with my Esprit 150. LIGHTS: L: 35, R:23, G:20, B:16 x 600s, DARKS:30, BIAS:100, FLATS:40 all at -20C.

I use the freeware version of FocusMax in conjunction with Maxim DL and ACP Expert and find it gives excellent results, so I've never had the need to get the paid version. The main reason I suggest using FocusMax is that it works out the focusing from a defocused position, which helps to combat the effects of seeing. To further reduce the impact of seeing, I'd also recommend you choose the FocusMax option of convergence which takes (say) 5 exposures at the defocused position and attempts to pick the best one. Seeing will also be minimized by picking a focus star near the zenith, since this minimizes the amount of atmospheric distortion. If you want to best possible focus then you should also look at the various FocusMax tutorials and select a focus star and exposure that puts you on the linear part of your camera. It is also quite fast, in my system, it takes a total time of about 80s to achieve focus, with the slower but more accurate option of convergence selected. On the downside of the freeware version, I seem to recall there is an issue with using the FocusMax acquire star feature, this doesn't impact me since I use ACP Expert to select the focus star. Alan

SH2-115 is a faint emission nebula in the Cygnus constellation about 7500 light years distant. It is normally imaged in narrowband, however, since I prefer natural looking colours, I went for a LRGB composition with an Ha blend into the red and lum channels. The image below represents about 17 hours and was taken with my Esprit 150. I encountered an interesting challenge in the processing stage of the above image in that I discovered that I had also acquired high levels of scattered light from an out of field star. These rays appeared in all the Lum, Red and Green subframes. Having analysed the likely candidates in the direction of the rays, led me to the conclusion that the most likely cause was the star Deneb, reflecting off some surface in my scope. I occasionally encounter this problem, but this was extreme, presumably due to the very high relative brightness of Deneb compared to the nebula. On the good news side, the scattered light was not evident in the Ha captured by my 3nm filter and was only just visible in the red data. So, after Pixsinsight and PS manipulation, I think I've managed to reduce this effect to acceptable levels. Alan LIGHTS: L:9, R:22, G:11, B:17 x 600s; Ha:14 x 1800s; DARKS:30, BIAS:100, FLATS:40 all at -20C.

Hi Brian Thanks for the comment Yes, I find it amazing how amateur equipment can capture such faint and distant objects in such detail. I guess it is primarily due to the advances in digital cameras and digital signal processing. Alan

Located in the constellation Bootes, approximately 52000 light years from Earth, lies the globular cluster NGC 5466. It is designated as a class XII cluster, meaning that it has relatively non-concentrated stars towards the core compared to a class I cluster. This last fact starting me wondering if my scope would be able to resolve the "gaps" in the central core...... note also the various background galaxies. The LRGB image below was taken with my Esprit 150 and represents just over 9 hours integration time. Alan LIGHTS: L:12, R:17, G:10, B:17 x 600s, DARKS:30, BIAS:100, FLATS:40 all at -20C.

Thanks for your comments Dave. The LRGB image was improved by my first attempt at creation of a super luminescence (a noise weighted result of the individual L, R, G, B stacks - my RGB data is binned 1 x 1 so, it increases SNR without decreasing detail). Thanks Goran Thanks Alan ! - apart from the superlum creation (mentioned above) I was also experimenting with a couple of new PI techniques that I also recently learnt from Adam Block's PI tutorials ( https://adamblockstudios.com/) - the first was to boost nebula contrast via the fuzzy logic script (LocalFuzzyHistogramHyperbolization) and the second to boost the blue contrast in the nebula via a specific Adam Block technique. Alan

Thanks Alan. Yes - it seems a very good target with my field of view, I was also somewhat pleased on the tadpole details. Thanks for the comment Alan

My first attempt at the Tadpole Nebula (IC410). Located in the Auriga constellation, the nebula is about 12000 light years distant and is approx 100 light years across. The red tadpole like objects are believed to be about 10 light years across and consist of dust and gas that have been shaped by stellar winds. The nebula also contains an open cluster (NGC1893) that contains newly born stars that are estimated to be only 4 million years old (in the center of the image and a little to the right). Since I prefer natural looking colours, on the acquisition side, I decided to go for an LRGB image with the details enhanced with some narrowband Ha data. The image was taken with my Esprit 150 and represents 16 hours integration time. Alan LIGHTS: L23, R:19, G:15, B:18 x 600s, Ha: 7 x 1800s, BIAS:100, DARKS:30, FLATS:40 all at -20C.

Thanks for the comment Adam Alan

Thanks Adrian Thanks

The open cluster M37 contains almost 2000 stars and is spread across 20 light years. Most of the stars are young blue/white but it also contains red giant orange suns which provide considerable colour contrast. I first imaged M37 a couple of years ago but I decided to add to the data since I was never entirely happy about the quality of the some of the sub-frames. I also decided to try out some of my newly learnt stellar processing techniques to improve the data which I describe below for anyone that might be interested. Since I often image in non-ideal conditions, I sometimes find that the red stacked channel has a larger FWHM values than the blue or green channels, if I combine this data to obtain an RGB image. the result is a red fringe around the stars. For blue stars, this is particularly apparent and creates magenta halos. This time, I decided to shrink the red channel via a ring mask using PI's erosion filter. The ring mask protects the star core, minimizing damage and core dimming. The main issue is generating a good ring mask which captures the majority of the red fringing. After watching one of the Adam Block's Pixinsight's tutorials ( https://adamblockstudios.com/) on how to de-emphase stars, I decided to apply a technique he recommends. Basically, you first create a star mask which includes all the stars and all the halos. This mask should be white across the star and halo and slightly feathered around the edges. Having done this, you then subtract from this the Red channel lum information to create the ring mask. The reason this creates an accurate ring mask is that the lum data contains accurate information on how the light profile various from the stars center. So, for example, at the stars core, the star mask will be close to 1 (in PI everything is normalised to 1), whilst the lum information will also be close to 1, so if you subtract one from the other you end up with something that is close to 0 (eg black) at the core. Thus, at the core you will be protecting the star's core almost 100%. Outside of the star mask (eg outside of the halos) you will have 0, whilst in the lum channel you might have 0.2 (say representing a non-stellar structure), if you subtract 0.2 from 0 you get 0, since you cannot have negative values in PI, so outside the star mask the ring mask will be 0 eg black. Within the halo, the ring mask will mimic the stars halo hence generating an accurate ring mask. The LRGB image below was taken with my Esprit 150 and represents just over 15 hours integration time. Alan LIGHTS: L:23, R:26, G:23, B:21 x 600s, BIAS:100, DARKS:30, FLATS:40 all at -20C.

I had a look at your data and used Pixinsight and Photoshop to process the result (below). As you can see you've captured quite a lot of detail. On the vignetting issue this seems to be mainly in the RGB data, your Lum data is much flatter. I eliminated both with the use of Pixinsight's DBE function - you can do a similar function in PS but you will require the use of the plug-in Gradient Xterminator. I also noticed that your lum data is very slightly misaligned with the RGB data, so I realigned this to get better stellar profiles. Alan

Hi Vlad I thought you might be interested in seeing the Pixinsight screen show (below) which I've taken with the cursor hovering over part of the green blob located at x= 51 and y = 40. The image is after I've performed DBE but before any PCC. This shows what happens to the linear RGB values as they are put through the non-linear stretching function (called Histogram Transformation in Pixinsight). So, for example, the red value before the stretch is 0.0066 and goes to 0.48 when it is stretched. If you make a table of the values you get: DBE (linear) DBE(non-linear) R 0.0066 0.4800 G 0.0071 0.5678 B 0.0068 0.5221 With R normalized to unity DBE (linear) DBE(non-linear) R 1.00 1.00 G 1.08 1.18 B 1.03 1.09 So, at the linear stage the green blob is 8% more peaky than the red whilst introducing a non-linear stretch makes the Green component 18% more peaky than the red. At this point it looks green. This is without any increase of saturation, application of PCC etc. In subsequent processing I would boost saturation, perform noise reduction etc to create a final image, these steps further increase the differences between the values (in my case the final image as a green component that is 60% more than the red component. My point is that even a very small percentage differences when in the linear stage can lead to very large percentage differences in the non-linear stage. Alan screen shot

Here's some documentation of the Pixinsight Photometeric Color Calibration tool which might help answer your question: https://pixinsight.com/tutorials/PCC/index.html I presumed this was the consequence of the various non-linear operations performed between the linear to the final processed state. Alan

If I look at the data at the stages after Pixinsight's DBE (image is linear), Photometric Colour Calbibration (image is linear) and the Final (LRGB non linear) I get these RGB values: DBE PCC Final R 0.00664 0.00679 0.40200 G 0.00707 0.00727 0.64300 B 0.00683 0.00679 0.62000 RGB ratios with R normalized to unity DBE PCC Final R 1 1 1 G 1.06 1.07 1.60 B 1.03 1.00 1.54 So, this particular green blob has quite a peaky spectrum with respect to the red. Hmm interesting, I don't recall seeing anything green in my M33 images but I shall go back and check ! Alan

Thanks for the response Adam and highlighting more green blobs...However, I'm still somewhat puzzled about what these green blobs actually are. Alan