Up until last night, I have only used narrow band filters with my ZWO asi1600mm Pro Monochrome camera, mainly because during the winter months the majority of imaging is of nebulous objects, with the milkyway high overhead there is a vast number of these deep sky targets to choose from – now that the long nights are over, it’s the turn of the galaxies to occupy the imagers time. However narrow band imaging shows little on these distant islands of stars, only Ha really picks out the star forming regions and then only on the closer galaxies, this means that galaxy imaging is done with wideband filters, Red, Green and Blue, I decided to image M51 the Whirlpool galaxy in the constellation of Canes Venatici, below the handle of the Big Dipper, changing from my narrow band filter wheel to my colour filter wheel only took a few minutes, however the focus position was way off – luckily it was outward focus travel that was required as my narrow band filter focus position leaves me with only 2.5mm of inward focuser travel remaining. I managed 45 x 300 second exposures giving me 3.75 hours worth of data with the red filter. I now need to do the same with the green and blue filters and combine the three mono images in Photoshop to create a colour image, I will then use the Ha filter for the star forming regions and add this data to the image followed by a luminance for detail. The forecast looks good again for tonight, when I’ll use the green filter – this is the only disadvantage to using a mono camara, you have to use multiple filters to create a colour image but the result is far better than using a colour camera alone.
It’s been a while since my last post, nearly 4 weeks in fact – a combination of poor weather and other commitments including going away in the campervan to Cornwall when we had that glorious 4 day bank holiday weekend has kept me out of the observatory, I could hardly say to my better half, sorry dearest we’re not going away this bank holiday – the weather is just too good. Anyway I have finally done some imaging, addmitedly over a couple of nights and on a very dim target – PK219 + 31.1 or Abell 31 or Sharpless 290 – this is a very dim and ancient planetary nebula in the constellation of Cancer it is slightly larger than M27 the Dumbell nebula ( mag 7.5 ), though much much dimmer at mag 12.2. The image below is the culmination of two nights imaging, totaling 5 hours exposure time ( 30 x 600 sec ) in Ha, to be honest I think that 2 or 3 times as long is needed, it is brighter in OIII but that will have to wait until there is no moon around.
I also took the opportunity to check if my collimation efforts were any good or not, I centered the telescope on Pollux, β Gemini the brightest star in that constelletion and took a 60 second exposure, thankfully the collimation I did on the 8 inch RC was nearly spot on with only very small adjustment required. the exposure showed that while the stars in the image are round in all four corners, the vignette or uneven illumination was slightly off centered to the left of the image and only very minor adjustments to the secondary mirror is needed, the two bright patches to the right edge of the image is Amp glow from the camera sensor this would normally be removed with dark frame subtraction when processing.
This Uncentered vignette is only a problem if a bright star is in the field of view ( otherwise it is removed by subtracting flat frames ) as there are none around PK219 I’ll leave the final adjustment to a later date, below is the same image with a gradient map applied to make it easier to see, lots of clear skies needed, fingers crossed.
Just typical, I re-collimate my main imaging telescope and ever since then the weather has been typically British for April, clouds and rain. The forecast for the coming week is not good with more of the same unfortunately. The days are getting longer and the period of astronomical darkness ( when the sun is more than 18° below the horizon ) is getting shorter, Orion is pretty much out of view for me now so I’ll have to wait till later in the year to get more data on M42. However I want to get a closer look at the Leo triplet of spiral galaxies M65, M66, and NGC 3628 – at my telescopes native f8 focal length, come on blue skies.
After discovering that my 8 inch RC was out of collimation ( read previous post ) I thought I’d run through the steps needed to re-align the two mirrors. The first thing to do is to dismantle the focuser end of the telescope to gain access to the primary mirror, this was because when I washed the mirror I had to remove the centre light baffle tube – this has a thin rubber O ring that needs to be seated correctly on the baffle, if not then the mirror will not be secured in place properly and will have a certain amount of play.
Remove the top and bottom Losmandy plates and the Radius blocks from the focuser end only, undo the two remaining cross head screws and gently lift of the mirror housing, do not drop and place on a flat surface. Unscrew the centre baffle tube counter clockwise and check the rubber O ring ( do not touch the mirror ), it has to be sat in the groove and not on the threaded portion of the tube. Re-assemble the telescope in reverse order.
The Howie Glatter laser collimator I use is quite expensive costing about £200 with attachments, but it is the only reliable method to collimate these RC scopes because of the two Hyperbolic mirrors, Newtonian telescopes on the other hand have a concave primary and a flat secondary. Now the safety bit, Never look directly at the laser beam or eye damage and blindness may result.
Insert the collimator into the focuser and only just slightly tighten the focuser thumbscrews so that it turns freely in the focuser without being loose. using the tight beam attachment that screws into the end of the laser, get the red laser dot of light onto the secondary mirror centre spot ( it marks the centre of the secondary mirror and is essentialy a paper disc with a hole in the middle just like a ring binder reinforcing ring. do this by adjusting the primary mirror collimation screws ( there are three sets of two screws and work in a push/pull fasion ) only make small adjustments to get the laser on the spot, this can be seen from the front of the telescope and looking at the reflection of the secondary in the primary.
When you have the laser in the centre of the spot or ring, you then look at the reflected laser spot and see where it falls on the white disc at the end of the laser, you will probably see two red dots this indicates the misalignment of the secondary to the primary, move the outer red dot to cover the centre red dot by making small adjustments to the secondary collimation screws arranged in a triangle around a larger centre screw.
When this is done it’s time to change the laser attachment to the Holographic ring projector, this as the name suggests projects a series of concentric rings down the telescope tube to the secondary mirror, these are then reflected back onto the primary and then out of the end of the scope tube and onto a white surface ( a wall or large piece of white card, or in my case the side of my fridge ) this is for fine adjustment to get the rings concentric with the shadow of the secondary in the middle of the rings, the actual proccess will take two or three iterations of the above procedure until finally no adjustment is needed and you can swap between the dot and the circle attachments and the laser spot will be on the secondary centre spot and projected circles will be concentric.
Only fine adjustments are needed and the proccess can be time consuming and also frustrating as these telescopes seem to be on the tipping point of going out of alignment, especialy if you forget where you were in the procedure. Lets hope I got it right, you can only know when you take an image, any remaining misalignment will be instantly obvious as the stars in each corner will be different shapes.
After getting home from work on Monday evening I decided that I had to do some imaging, after all it’s not often that the sky is clear at the same time that the moon is out of the way. I also figured that I could set it all up start imaging and get a good few hours worth of data together before going to bed. So I rolled the observatory roof back to equalise the temperature and cool the telescope down quickly to ambient, while this was going on I got all the software running making sure that the USB connections were ok, USB connectivity in an outdoors enviroment is about the only problem that I have, any issues is usually solved by disconecting and then plugging the USB back in again. When it was dark enough I went through a 1 star alignment ( this is good enough as I plate solve the image and then sync the mount co-ordinates, RA and DEC from the result ) and took a few focusing shots, that’s when I noticed something more problematic than a dodgy USB connection, the star image was clearly wrong and that the telescope was out of collimation by quite a lot – that’s when I started calling myself a few choice names for being such a pillock. The telescope was out of collimation because the week before I took it apart to clean the main ( or primary ) mirror that was quite dirty and when I put it back together again I never checked and re-collimated the optical path, even a small misalignment between the primary and secondary mirror will cause the stars to be mishaped when imaging, it’s even more pronounced in a RC ( Ritchey Chretien ) telescope. So that was that, no imaging until the collimation is done.
I did however take one image a single shot of the star Regulus, Alpha Leonis, this image shows clearly the only issue with the ZWO asi1600mm Pro camera and that is the lack of an Anti-Reflection ( AR ) coating on the cover glass of the camera sensor, made by Philips and used by ZWO in this camera model.
The strange pattern around the star is the reflection between the protective cover glass over the sensor and the micro lenses over each pixel of the camera sensor, come on Philips what were you thinking, AR coatings is pretty well standard on any optical equipment even camera sensors.
Last night, I managed to make it to the March meeting of the Crewkerne and District Astronomical Society, and I’m glad I did. The guest speaker was none other than Dr Carl Murray, who is based at the Queen Mary University of London. In 1990 Carl was selected as a member of the camera team for the NASA/ESA Cassini mission to Saturn. Naturaly enough the talk was about the Cassini-Huygens Spacecraft and its mission to the jewel of the solar system, what can I say other than the talk was fantastic and if your club wants a really good speaker who won’t bore you with fact and figures, then don’t hesitate to book him.
The image of Saturn’s solar eclipse was only made possible when Cassini’s safety systems was bypassed, allowing the camera to be pointed in the direction of the Sun, and yes that little blue dot is Earth.
After Carl had finished, Bob Mizon gave us his object of the month, the star Alpha Hydrae or Alphard, ( the snakes heart ) in the constallation of Hydra. Of particularly interest was Bobs explanation of the mythology behind Hydra and why it has a crow and an urn on its back.
A few club members – including myself, showed our images we have managed to take with the poor weather we have had to suffer recently, My favourite was Bud Martin Budzynski’s lunar images taken with a C11 and a Point Grey, Flea 3 Camera.
I’m looking forward to the next meeting, the talk will be by Bob Mizon – Solar System Alphabet, now that will be good.
Clear night skies, just what the doctor ordered – but I’m still unable to do any imaging, the reason for my lack of imaging is purely down to wind. Gusts of up to 50mph put paid to any chance of setting up the guiding calibration in PHD2 never mind imaging, when it is windy the telescope acts as a sail and gets buffeted about no matter how beefy your mount is and if you forgo the calibration setup in PHD2 and use your previous calibration which is normally ok if your pointing to same area of sky as before, then when the telescope and guidscope gets nudged by the wind PHD2 will try to correct for an error that has nothing to do with guiding and before you know it, you have a series of over corrections that sets up an uncontrollable oscillation in the guiding. The larger the telescope the more surface area it has and the more pronounced the effect of wind is, so it makes sense when it is windy to use a smaller scope, but I have set up the 8 inch RC, all balanced and aligned with the guidscope and I did not want to upset this setup because I want to image the Leo triplet in more detail at the next opportunity, I’ll just have to wait.
Since my last post I’ve not done anything astronomy related, we have had a few nights that would have been good enough for some imaging, but these have been on work nights ( three glorious days during this week with record temperatures for February recorded ) and when the weekend turns up the weather without fail turns to rubbish again ( severe weather warning with storm Freya for the weekend, you dont say ). I have however been doing some work on my camper van, which in a round about sort of way leads to an upgrade for the observatory – I’ll explain. I have recently fitted a 160 watt solar panel on the roof of the camper, this leads to a solar charge controller which converts the 21 volts from the panel into a voltage ( 13.7v ) that can charge and then maintain ( trickle or float charge ) the condition of the 105 Amp hour leisure battery, I also wanted to install ( in Parallel, Positive to Positive and Negative to Negative, like you would jump start a car with starter cables ) a second 105 Ah battery, this would give the same voltage but double the usable Amp Hours – the problem is I did not know the age of the leisure battery that was already in the camper, this is an issue because when you fit two batteries it is highly recommended that both batteries are the same Amp hours, the same age and make, due to the older weaker battery dragging down the stronger newer battery, so in other words – two new identical batteries need to be fitted. I only found out about this little point later on.
The original battery was the grey 12v 105Ah Lucas, and I put in a new Numax 12v 105Ah battery which apart from the colour is identical but obviously not the same age, so I ordered another Numax. This leaves a spare Lucas 12v 105Ah battery, it just so happens that I use a 12v 60Ah car battery to run both my dew heaters and a DC focus motor for my guide scope, this battery is years old and on its last legs and does not hold a charge well, I have taken to charging it up a day ahead of when I need it. so I replaced the old worn out car battery with the not worn out Lucas leisure battery, this is also being charged up during the day by means of a 12v 20w solar panel and a charge controller.
So now my dew heater power needs are sorted, just want a clear Friday or Saturday night.
The image of the Crab nebula I finished on the 3rd did not seem right, I decided to re process the narrowband data – Ha, OIII and SII. As Deepsky Stacker ( DSS ) sends a 32bit unprocessed image to the folder that contained the light frame images in the first place it was fairly simple, I just opened that ” untitled ” image in Photoshop CS5. The program can work on 32bit images – but not all of the resources can be used, instead you have to convert the image to 16bit to unlock all the editing options, again simple just go to image, type select 16bit from the dropdown menu and it will open up HDR Toning, this stretches the image so you go from a black seemingly devoid of detail image to one that shows everything. you then reduce the highlights and the shadows ( both on handy sliders ) until all the whites are not overexposed and the shadows are not totally black. This is a lot easier than trying to preprocess the image in DSS, I did this to the three images then copied and pasted them into their respective colour channels in a new image of the same type and size, Ha into Green, OIII into Blue and SII into Red.
This creates a colour image from three monochrome images, Then using the selective colour adjustment option you adjust the Greens, Yellows and Cyans with the figures in the following image.
This gives what is called the Hubble palette or colour mapped image, coupled with some noise reduction and a bit of subtle sharpening to finish things off – I ended up with a cleaner image than last time. I’m happier with this image.
I have had cloud, light drizzle and now snow. With many roads impassable due to black ice, your heart sinks as this rubbish just keeps going and going – and then, amazingly a sunny day and a whole clear night, frosty but clear; I can live with that. So I decided to change the telescope over to the 8inch RC ( a reflecting telescope ), with a longer focal length. You get more magnification imaging at a focal ratio of f8, let me explain – focal length is the distance light has to travel after going through a lens or bouncing off a mirror before it comes to focus, focal ratio is a function of lens or mirror focal length in mm divided by its aperture in mm, so for my 8 inch RC with a focal length of 1625mm and an aperture of 8 inches you get 1625mm devided by 203mm equals 8 ( called f8 ). My William Optics megrez 72 on the otherhand has a focal length of 430mm and an aperture of 72mm giving f6. This means that the WO72mm has a wider field of view than the 8inch RC, so a lower f ratio has a wider and brighter field of view than a higher f ratio which has a narrower and darker field of view and for my targets last night I wanted a smaller field of view with more magnification.
I got everything set up and running nicely, guiding all good, plate solving just fine and the planetarium software synchronised with the mount, my first target was M1, the Crab nebula in Taurus, this is a supernova remnant that was first observed by chinese astronomers in 1054AD who called it a “guest star”. I captured 30 x 180 second exposures in all three narrowband filters, Ha, OIII and SII for a total of 4.5 hours exposure. I have a 2 inch manual filter wheel at the moment, so I had to rotate the carousel to the next filter each time a run was finished and it was cold -5°C by the time the SII was used. I couldn’t be without a warm room now, even the cat came in and stayed in for the rest of the night.
Then I changed to the Neodymium filter as I wanted to capture 2 galaxies in Ursa Major, M51 the whirlpool galaxy and to get a closer look at M101 the Pinwheel galaxy, again I used 30 x 180 second exposures. This only gives monochrome ( greyscale ) images, however these greyscale images can be used later – added to a colour ( RGB ) image as a luminance layer to give detail to the image.
In my last post, I mention anti-dew heaters and the anti-dew ring on the end of my ZWO asi 1600mm Pro camera,I got this add on heater because my sensor chamber window would every now and then get condensation building up on the outside of the window ( as the sensor is cooled to -20°C this comes as no surprise ), the inside of the chamber is sealed and has 4 desicant tablets inside and does not get condesation, this is a single image to show the effect this has on the captured frames.
It has since turned cloudy again, but for now – I’m happy.