ollypenrice

When I opened my astro guest house I was purely visual. It soon became clear that I wasn't going to get enough customers from amongst the visual observers because most (maybe two thirds) of our guests were imagers bringing their own kit to use at our dark site. More because I felt I had to than because I wanted to, I decided to get involved and sought the best expert advice available at that time. It came (and still does come) from Ian King and I repeat the same advice to newcomers to this day. A big thanks to Ian and all the best for his new venture with FLO. I had next to no IT competence at all at that time so the process was very intimidating and I wasn't fully embedded in the internet culture, nor was I on SGL. However, once I got going I absolutely loved it and, as I hope is obvious, still do. I don't draw too many conclusions from the fact that imagers outnumber visual observers for me here. It may be to do with the trek to southern France not appealing or to some other factor and I'm delighted that FLO don't see the same trend in their business. I'd hate to see visual observing decline and I can imagine retiring into it myself, one day. I'm glad to say that our visual scope does still have its devotees, as do our lounge chairs and binoculars. Olly Edit: There's an old saying in the motorcycle world: 'When there only two bikes left running on the Earth, one of them will have a sidecar on it.' I suspect that when there are only two scopes left on the Earth one of them will have an eyepiece in it. Then again, it might be both...

I'd be inclined to guide more frequently, at least to see if it worked. I haven't used our EQ sixes myself recently, I just have them to lend to guests, but I think I used to go as low as 0.5 seconds. As Ole says, your RMS needs to about half your pixel scale. Regarding the flex in OAGs, I made a strap to hold this one solid. It worked fine. I must admit that I use our Lodestars in Bin 1, having been entirely unaware that this was supposed to be an issue. I'm using one in a 400mm guidescope to image at 0.9"PP. In the setup above we were also using Bin1 at just over 0.6"PP. Olly

If you're talking about an object which fits on the chip with or without reducer (as I guess you are with small galaxies) you can forget about F ratio and simply concentrate on aperture. You are in the dreaded 'F ratio myth' territory here and this has been done to death (largely by me!) on SGL and elsewhere. The key point is that reducers, in this scenario, don't bring in any new photons. A camera lens is faster at F5 than F10 because the lens is letting more light in. Using a focal reducer to go from F10 to F5 does not let any more light in. They are not equivalent. The other concern is resolution in arcseconds per pixel. To image usefully at 1"PP (a nice scale for galaxies) your guide RMS needs to be no greater than 0.5 arcsecs. This is possible but not guaranteed with an HEQ5. And you also need seeing which is stable enough to make this possible. I find that sometimes we have it and sometimes we don't, in which case we shoot colour and leave luminance to a night of better seeing. Olly

No telescope will produce views which resemble astrophotos but an 8 inch Newtonian, properly collimated, is a serious and rewarding instrument to use. Olly

Where do we check for this disabling of power save? Olly

I think both images are heavily black clipped. This happens when you bring the black point slider in too far the the right. It can be tempting to do this to remove LP gradients - but resist that temptation! This image is black clipped. The histogram peak has no flat line to the left and the sky is jet black. This one is healthy. There is a flat line to the left of the histogram peak. The sky is fairly light and the faint outer parts of the galaxies have not been discarded. Olly

The best kind. I'm told...

I'm obliged to use my present design because, if the village gets uppety, I use our south flaps to lob the odd decaying horse carcass in their direction to remind them that the plague is worse than turning out their lights... (This aspect of my foreign policy has been temporarily suspended during my application for dual nationality.) Now I need to find out what a linear acuator is. lly

I simply followed AstroArt's instructions regarding the making of a BPM. I took my master dark and used Arithmetic-Clip and clipped 2000 ADU off the black point. This is a fair point but I tried the 'bias as dark plus bad pixel map' method on my 11 meg camera to start with just out of curiosity when I first read about it. I found it gave cleaner results than using proper darks. (I'm careful in doing darks. I do it off-scope with the metal chip cover on and the right temperature. I also shoot a reasonable number, at least 20 even if they are half hour subs. A while ago I did a new set of darks for this camera to make sure my bias method was still an advantage and I found it was. The specific issue I found with darks was the appearance of scattered hot pixels in the stack. These did not correspond with hot pixels on the defect map, they were an artifact of stacking with darks and disappeared when I used a bias instead. I've no explanation for this and it didn't happen every time but with bias-as-dark it never happens. On the other hand I'll be using darks from now on with Atik 460. Olly

No, I don't use bias at all if using darks. It's contained within the dark already. (I do calibrate my flats using bias as a dark for flats but this only works with CCD, not CMOS.) That's great and does offer an explanation. Many thanks. Don't put me down as anti-science, I'm far from that! I just suspect that, in imaging, there are many hidden variables which make a mess of the best laid theoretical plans. Olly

I just pass this on because I found it interesting. For a long time I've used bias-as-dark and bad pixel map rather than darks. In the Atik 11000 I found it better and easier. In the Atik 460 I found it easier and it made no difference. But... we have just shot a respectable 48x15 minutes luminance on VDB141, the very faint dust nebula, and the result was lamentable. Not a patch on a similar run I did years ago using an Atik 4000 in the same scope. Noise was worse and delicious little structural details just brighter than the background sky simply weren't there at all. My collaborators suggested going back to darks, so I shot some and the data is transformed, not only in reduced noise but in what is clearly resolved just above the background. Why has 'bias as dark' stopped working in this camera? I don't know, but it is very hot here at the moment and the 460 is only making around -8C. Could it be that 'bias as dark' only works when the thermal noise is held down by the cooler? It normally runs between -15 and -20. (Meanwhile one of our regular guests has emailed me from the UK to say that he can't stop his darks from introducing vast amounts of noise, so should he try bias-as-dark?) Which only goes to show that astrophotography is a funny business... lly

That's a great image. When seen like this I feel that there are new large-scale 'objects' on view. I'd call them objects because they clearly have coherent large scale structure. Loud applause! Olly

Could this be the 'B' side of, 'They have a bad policy of introducing new products too quickly and having to sort them out later?' To answer Steve FLO's question, my purely personal feeling is one of nervousness at the frequency with which new models appear. However, the CEMs have been well reviewed by owners on here, many of whom have posted impressive guide graphs. If looking to replace our EQ sixes I'd certainly be looking at the CEMs. Olly

I agree that it's surprising more work hasn't been done. It might be the catalyst to a more general discovery, perhaps. Vaguely related, this is a fascinating book about research into the Aurora: https://www.amazon.com/Northern-Lights-Unlocked-Secrets-Borealis/dp/0375708820 Olly

Your drawing is pretty good! We run a dual TEC140 here, one side with an Atik 460, EFW2 and TEC field flattener. I make the length 1245 mm, so 10mm more than your drawing. You need to allow for the cables to exit the rear of the camera on top of that. Olly

Brilliant, thanks guys. Olly

Folks, I use SkyMap Pro for my planning etc but I'm working on an article about planning imaging projects and would like to mention a range of such programs, especially the free ones. The feature I use most is the one allowing me to test frame a particular chip size and focal length on an object. Which do you use and which would you recommend? Any supporting comments would be most welcome. Thanks in advance, Olly

Nice to see you in Technicolor again, Pieter! That's a great image with tiny stars. Olly

This all looks like hard work to me.

Such a useful accessory and, for me, the simple ones like this are far less hassle than the over-engineered capstan wheel rotators. Olly

If you've never felt the need for it forget it! lly

The absolute definition of IT in the real world, in my view! Olly

Yes, the light cone has a steeper angle as in a capital X where the left hand half of the letter is the incoming beam and focus is at the point of crossover in the middle. Because pixels have a finite size you have a little tolerance each side of the point of crossover but the steeper the light cone the less is that tolerance (or depth of field). Smaller pixels also give you less tolerance. Your motivation seems to be to reach F4. If this is to make imaging faster a reducer may not do this. For the F ratio rule to work you would have to fix the focal length and add more aperture.* Reducing the focal length at the same aperture is not equivalent. The sound reason for using a reducer is to increase the field of view and if you actually want all that is in the new field you will get to an acceptable S/N ratio faster but at lower resolution. Olly * This is what happens in camera lenses and explains why the F ratio rule does work in this context.

Well, as a remote imaging host I've come to suspect that not guiding is a lot more trouble than guiding... Olly

That's not going to do much for the next customer's PA... Not being into IT, I'm following this thread with a mixture of awe and dread! Hope you get it sorted. Remote imaging is the hardest kind, I think, in the early stages at least. Olly