almcl

Interesting. The figures in my list above are the APT reported temperatures, I've just checked to see whether Exiflog gives the same answer and, perhaps not surprisingly, it does, which doesn't get us any further forward, sorry!

Using a different Canon (700d) I just checked my dark library for ISO 1600, 180 seconds and found every temperature from 1°C to 32°C, no gaps, although this may not be very helpful as it's a different sensor and processor. What software are you using to extract the EXIF data? Might this have a bearing on the figures?

That would explain it! Glad you got it sorted.

A little while since I saw this issue, but think it was using the 32 bit version of DSS and it was an indication DSS was running out of memory. There was a work around that enabled it to use more of the available RAM (sorry, can't find a reference to that just now and it may have been for Win 7) but the long term solution was a 64 bit operating system and then to use the 64 bit version of DSS (presently using version 4.2.4 Beta, which seems pretty stable). Another possible cause may have been attempting to use drizzle, discovered that this was definitely not worth doing with my data. @perdrix who is a member here is now the guru for DSS and can probably explain all in much more details and with much more authority!

If the same line is present in several subs in the same place, it may be something out of frame causing a reflection. Bright stars can cause this (Alnitak in Orion is a favourite) but can also result from inconvenient street lights, neighbouring (in)security lights, or even equipment LEDs showing up in the wrong place. In the case of your night1 image, the line points straight back at Deneb in Cygnus: I haven't processed the other images but my guess is they will show a similar origin for the line. Not sure what the solution is, maybe someone else will comment?

I think the one Andy is referring to is about a quarter of the way down the page here: I am interested because a Ritchey Chretien (for imaging smaller galaxies and planetaries) may be in my future too, but worries about collimation (amongst other things) are holding me back.

Well done! And the adventure is just beginning....!

I use a SW 200p and the improvement in star shapes when I switched to guiding with an OAG was dramatic. Prior to this I used an ST80, initially with a QHY 5l ii mono until the USB connector on that broke and then switched to an ASI120 mini mono. The ST80's focuser was very floppy and that coupled with mirror movement was probably at the root cause of the poor guiding. As to whether a 50 mm guide scope (likely focal length about 180 mm?) will do rather depends on your imaging scale. I use a suitably adapted SW finderscope with the ASI 120 to guide my EQ5 with Canon + 200mm lens and it usually achieves just over 1" guiding. As the 200 mm lens is imaging at a little over 4"per pixel, this is fine but when imaging with the 200p (.85" per pixel) on an Alt Az EQ6 it wouldn't (and didn't) do. With the OAG the guiding is usually somewhere between .6" and .7" and on rare occasions drops below .5". This gives nice round stars. I use the dedicated Canon OAG and it certainly saves weight compared with the ST80. Another benefit is that I no longer need a dew strip for the guidescope: the ST80 was an absolute dew magnet - an OAG doesn't need heating. I've never had a problem finding a guide star with either camera (both mono) in any of the configurations, although focusing the guide camera is slightly more time consuming to start with.

Yes, in DSS the box is usually checked:

Adam, just thinking about that, the third image was taken without a Coma corrector yet it still has colour separation (admittedly in a different orientation to the other two) - so given that the only things in the image train are the two mirrors and the DSLR sensor, could it be something on the sensor, Bayer matrix or Baader filter, perhaps?

Thanks, Adam. I feel an upgrade of some sort may be on the way!

I can identify with that one ! Hadn't thought of that, thanks! Will give it a try during the light nights. I've changed the mirror cell mounting arrangements on my 200p (longer mounting bolts, stronger springs). This helped with mirror flop/guider flexure but at the same time I also switched to an OAG so whether this stopped mirror movement or just concealed it isn't clear. I've not heard any movement - but am fairly deaf (and don't usually wear my hearing aids when out with the scope) . I do find the scope needs both primary and secondary tweaking every time it gets mounted and put this down to the tube flexing.

Thanks for running that through CCD inspector, Skipper Billy. I have often suspected that while I can visually collimate through the eyepiece (Cheshire, Concenter &c) hanging nearly a kilo of camera, home-made TEC cooler, coma corrector &c off of the slightly modified Skywatcher focuser probably undoes at least some of this at least as regards focuser tilt. Although the CCDI tilt measurements don't look too bad? Does anyone know of a way to collimate with the camera in situ? I've seen a couple of ideas somewhere but they were a bit vague on what to adjust if the out-of-focus star in the center of the field of view doesn't have the secondary circle in the middle (and having read Suter's Star Testing Astronomical Telescopes, am not sure that merely racking the focuser out a random amount is a completely valid test.)

For a while now I have been concerned about multi-coloured stars turning up in my final, processed image. Here's one such image (heavily downsampled) : and here's one of the stars from the upper left part: At first I thought this was just down to a lack of processing skills on my part, but then I noticed that individual raw subs also had some colour separation: and wondered if this was a feature of the SW Coma Corrector which I use with my slightly modified SW200P. So last night as it wasn't going to get fully dark, I removed the coma corrector and attempted to image with just the camera sensor and main and diagonal mirror in the light path. The results (which were tricky to obtain - the OAG really picks up the coma stars big time) surprised me: there are still odd coloured fringes to the stars: So what's causing these coloured fringes? Is it chromatic aberration and if so, where's it coming from? Or is it a characteristic of the astro modded Canon 700 (with the Baader filter that Juan at Cheap Astro Photography supplies)? Any thoughts on what the cause might be and how to mitigate it would be most welcome.

You've got some nice colour there, but as Toothdragon says, the flats haven't worked - they should eliminate the dust bunnies. Here's a crop of the central area, very quickly (<5min) processed in StarTools. Just a stretch, wipe, decon and colour: definitely one to persist with, it took me ages to get that much detail!

If you're using APT, why not use its histogram function?

Once you put some files (bias frames would be a good choice) in the Main Group, a new tab will become available, 1st Group, if you put your lights and flats in this group a further group tab should open. However, you may find stacking different length and ISO subs altogether doesn't produce a very good result and it may be better to stack the short subs and long subs separately and then selectively combine them in your image processing software, maybe using layers and an eraser tool.

I think leaving the UHC filter aside for now is probably wise. My Canon specific OAG came from TSS: this one. Not sure if there's a Nikon specific one but if not the prism is 7mm wide and sits well outside the of the sensor's field of view

Sorry, that's gone way beyond my knowledge level! There's a thread about colour gamuts and spaces (I think) here: and some more here: There isn't universal agreement about all the statements made in the two threads. I use sRGB.

If you decide to try StarTools, the Release Candidate versions (RC) are stable and have all the latest bells and whistles. You can do everything a paid-for version does, except save (but you can take screen grabs). There is a bit of a learning curve but several SGLers use it rather successfully.

The only stacking program I use (DSS) doesn't use the term demosaic, so not absolutely sure about this, but if it's synonymous with debayering, and you are using a DSLR then, yes it has to be done. DSS will do this automatically with RAW files but the correct Bayer pattern needs to be selected (for the ones I've encountered it's RGGB). The FITS planes in Fits Liberator are, as you say, Red, Green and Blue. Your latest image has got colour, although it's quite hard to see until it's been stretched (image below is a crop of your central area which I stretched and colour balanced in StarTools). As expected from the UHC filter, you've got blue/green and red, but of course no yellow. Nice round stars and several of the smaller faint fuzzies, too.

Visual through the polarscope. Gets me within 10' almost always and within 5' (which is enough for PHD2) most of the time.

Forgive me if you already know this, but FITS Lib treats each channel separately and you have to stretch and then save them separately and then combine them in other software. Confusingly it refers to them as plane1, plane2 &c. Your image looks as if you may only have one of the channels?

Yes, flexure is the term. My rig suffered from it quite badly (had a thread about it somewhere but can't find it at the moment). I switched to a Canon specific OAG and the improvement in star shape was dramatic. Originally I used a QHY 5Lii m but the USB socket on the back wasn't strong enough for the heavy and inflexible QHY supplied cable and it became unreliable and eventually broke (there's a thread about that somewhere, too). I then switched to the ASI 120 mini and found it to be very similar to the QHY. It has never failed to find a guide star (YMMV) in the two years I have been using it. If your QHY is OK, I think it would work well with an OAG. Yes, my Newtonian is (or was) an F5. I have since mucked it about a bit (shortened the focus tube to stop it intruding in the light path, moved the mirror cell when a Baader click lock was added to better centre the Coma Corrector, baffled the main mirror to remove the mirror clips from view, added a bottom fan to stop the main mirror dewing up, replaced the single speed focus knob with a Lacerta 10:1 geared version &c &c). Opinions vary a bit on how big a dither to use, some say big (>20 pixels) others say 5 or 6. Getting your capture program and PHD2 to co-operate is the trick. I am currently using between 5 and 12, but again YMMV. I think I left DSS at the defaults (Kappa 2, iterations 5) but Vlaiv had a thread in which he suggested other values (with convincing mathematical arguments) but they didn't work as well for me so I reverted. By the way, your latest stack is beginning to look quite nice - hours of processing fun to had during the light nights of the summer :-)

Good luck with those, Steve - quite a bit of work. The moving artefact may be caused by mirror or guidescope movement ( a few microns is all it takes), but dithering and a Sigma clip stacking routine may help.