ollypenrice

Why would FL matter? Surely the issue is resolution. I don't know your resolution in arcsecs per pixel, nor do I know at what point it becomes a problem, but I do know that a dual rig works for me painlessly at 3.5"PP and not at 1.1. (Or 0.9 on one side and 1.1 on the other.) Maybe tube length and bending moment come into it but I suspect it's resolution. I know of others who've found two high res instruments problematic. Of course, short CMOS sub lengths would be a big help. I see a considerable difference in trailing on the slave scope between 10 min and 15 min subs. 3 minutes would be great! Olly

There's no tendency for mirror flop in TEC 140s either but it still doesn't work... Olly

Beware of dual rigs (ie on one mount) at high resolution. Most who try it find it is difficult/impossible without recourse to Peter Goodhew's solution of an AO unit on the slave scope. We found it worked sweetly at 3.5"PP but is a pain at 0.9. Olly

Our first automated sheds used cycle-chain-drive electric garage door openers. They worked reasonably well but the electronics didn't like the cold and they became increasingly suspect. We converted the big 4-scope shed to a rack and pinion garden gate opener, which worked fine. The toothed rack was screwed onto a horizontal wooden beam on the roof. It worked fine and still does. However, when we converted the next two automated observatories to this system it proved difficult to get a consistent mesh at the rack and pinion because of warpage on the rack-carrying beam. Seasonal changes kept causing the mesh to be too tight or slack. I've just rebuilt the garden gate mechanism on one of the sheds so that a hefty single length of angle steel (4.5cm per side) now sits on top of the original wooden beam and the toothed rack bolts to that. This has cured the warping problem, it would seem. If you're aiming to use this system I would suggest using a steel support for the rack. It is also much easier to set up. Firstly I attached the rack to the steel and then put a single screw half way along the steel to attach it to the roof beam. I could then pivot it horizontally on that screw to get both ends of the rack (and the middle) the right distance from the motor. That's to say precisely parallel with the rails. Adjusting the rack up and down was easy because I had open access to the nuts on the bolts fixing rack to steel. Ignore the white arrow! That was for the owner of the system inside. In the finished version none of those bolts is missing. The last job was just to put 60mm of ply under the motor to lift it to the new height of the rack. Olly

If you'd asked me whether this picture could have been taken at a FL of 400mm I'd have said, 'Not a chance,' and been totally wrong. I'm a great believer in the power of small telescopes with small pixel cameras (and wrote an Astronomy Now article on the matter) but, even so, this amazes me. The problem of how one might combine a NB-filtered OSC image with an unfiltered one has been ticking over in my head (because I'm thinking about a CMOS OSC for here depending on how the pandemic evolves.) If the idea were simply to add star colour then I'd be inclined to try the unfiltered image as a bottom layer and erase the top layer's stars. This would let the colour through while preserving the small size of the NB stars. Alternatively the unfiltered layer on top in Blend Mode Colour might work. While the full image is mighty impressive, I do feel it has that slightly two-dimensional colour seen in HOO images. What looks like a strong OIII presence in the crop makes that that region look richer from a colour point of view. But maybe the impression just arises from a lack of star colour. One thing's for sure: the game has changed. Olly

Lovely resolution. They're 11 lightyears long, so I'm told! Olly

Very fine image with spectacular contrast letting the Tadpoles show so much detail. Most impressive. Have you considered trying a blend of the dual band filtered data with unfiltered to get the star colour? Olly

Here's a recording of a phone call I made with my CCD camera: 😁lly

TeleVue Ethos 13mm. I say this not because a 13mm is my favourite FL: it's a bit short in the SCT. But for sheer quality the view is impeccable. Sharp to the edge (and the edge needs you to move your head to find, which I like.) Stunning contrast and a strange sensation of the glass being invisible. I'd like a longer FL Ethos as well but have a 26 Nagler so I've no excuse to buy one... Olly

They must do. The focal length of the lens is a constant. I'm sure you'd be able to source an extension tube if you were really worried, even if you had to get it made by Precise Parts or another machine shop. But surely something will already exist. FLO and Telescope Service may have something. I used to use one on my TEC140 before fitting the flattener which ate up some of the distance Olly

Before fixing it I'd certainly want to be sure it was broke! As suggested, first check for tilt. Olly

I agree. The balbearing is still used by optical professionals. Simple and very effective. Olly

You could probably find a TEC 140 on the used market for that. However, the Esprits are not just good value, they're very good scopes. I'd personally go for them over WO. Two things to consider: what FOV do you want? With modern small-pixel cameras a one metre FL gets you right into the small galaxies. This is the TEC at 1015mm FL with an Atik 460. https://www.astrobin.com/full/393219/0/ But you might prefer something to cover more sky without a mosaic. The other thing is the size of the corrected circle. If you ever intend to use a full frame camera you'll need a corrected circle of at least 44mm with flattener. I would check this out and also confirm that it really does work by looking at posted images. Tak claim the Baby Q will cover full frame. It won't. Olly

Steve Richards outlines the star masking method I use in Ps in his book Dark Art... But I rather agree with AKB that Starnet offers a better solution than masking, which I no longer use. When I did use masks I used them on the linear image and very gingerly for a soft initial stretch or two. After that I discarded them. I outline my Starnet method here if it's of interest: Field stars (as opposed to stars placed over nebulosity) can be controlled using two stretches, a hard one for the galaxies and a soft one for the stars. If you get the background sky to exactly the same brightness in both stretches (this is vital) it is a simple matter to place the soft 'star' stretch over the hard 'galaxy' stretch and erase the top layer wherever it covers a galaxy or faint fuzzy. This, I think, gives the best result by far but only on images with few stars placed over nebulosity. Here are two examples of this method. https://www.astrobin.com/335042/?image_list_page=2&nc=&nce= https://www.astrobin.com/419975/?nc=user Olly

The 35 panel Orion which Tom and I did was eyeballed on framing. No plate solving - so you don't need it though it's no doubt convenient. I would strongly suggest 20% overlap for a beginner. Less than that and it can get difficult. Olly

I'm told that this is no longer what's recommended for PHD2. It was certainly what Craig Stark said for earlier versions but I gather that sharp focus is now preferred. (For all that, I haven't touched my guide scope focus literally in years and it seems fine!) Olly

That makes a lot of sense to me. At least with LP unfiltered you're going to get a smooth gradient. Once it has steps in it ('chunks' as you say) you're going to be faced with the massive task of removing those 'chunks' in post processing, which first means defining their boundaries. Give me a smooth gradient to remove any day. This isn't based on experience of LP so it may be flawed. Olly

Given the cost of the gear, a potent gradient removal tool punches well above its price weight but you mention not wanting to pay for things online. I wonder if any of the options would be available by cheque. Olly

That's very good, Alan. Flat background and tight stars. (Always the hardest parts!) You could bring in the black point a tad, too, maybe. My own feeling on playing with the data was that the scope had done a decent job. Stars were consistent across the frame which is the main thing. With the present post-processing tricks now available, having inherently tiny stars is no longer such an imperative. There are two things I'd want to understand better: 1) Colour. What's the camera? Unfortunately I have zero experience with LP filters so can't be of any help but maybe those used to using them could chip in. 2) The data seems to me to cut off rather dramatically around the outer part of the galaxy. There is faint galaxy to be had beyond what we are seeing here but I couldn't find it in the data. Maybe it just isn't getting through the filter, in which case more subs/longer subs might find it. (In the end I prefer your stretch to mine because you haven't chased that outer signal and I've chased it too hard.) Olly

Colour was tricky, with rather overbearing greens in the galaxy and very red stars. There isn't a lot of colour differentiation to work with either, but that's usually a matter of integration time. I felt it was beginning to go in the right direction by the end so more data would help. PI dealt with the background sky nicely (DBE, not too many markers) and SCNR green helped with the colour. Stars removed in Starnet++ and then replaced in Photoshop with a soft stretch used in blend mode lighten. Olly

Not so sure. I found the OIII very interesting on the Jellyfish: it produces a distinctive outer shell rather like the outer shell of OIII around the Crescent. It was after seeing it in NB images that I decided to see what it would give to my HaLRGB image of the target. It picks out the outer edges of the Jellyfish feature quite distinctly and, visually, helps lift it forward of the background nebula. It's rarely seen in broadband renditions but I think it was well worth the effort. Olly

There is also the visual 'wobble' caused by unsteady seeing, turbulence in the atmosphere disrupting the incoming beam of light from the object. There is nothing you can do about this other than come back another night. Generally the lower the object is in the sky the more likely it is that poor seeing will affect you. The real question about magnification is this: at what point does it stop being worth increasing the magnification? If the seeing, the mount or the optics will only yet you increase the size of the projected image while not letting you detect any more detail in it, then is it worth it? Imagine using a telescope to read a distant sign. You cannot make out the individual letters. You increase the magnification and you still cannot make out the letters. So the increase in image size has produced no new information. This is exactly what happens in planetary observation. Olly

Yes, Vlaiv is right to point out the big difference between NB and broadband with regard to the optics. You can refocus a less-corrected doublet between NB filters. A purist might argue that, to combine them into a single image, you would really want not just to co-register them to the selected reference image but also to resize them to it because the focal change has a small effect on the image scale. Registar would do this and I think it's also possible in PI and APP if you know how. There are some very well corrected doublets out there, though. One of our guests gets great broadband results with a TeleVue 85. Olly

It won't solve the problem. My guidescopes aren't aligned at all yet I shoot 15 minute subs at high res and 30 minute subs, on occasion, in widefield. I have no problem with either. Adjustable guide rings were not invented to let you align your guidescope. They were invented for precisely the opposite reason - to allow you to search off-axis for a guide star when that was necessary (for manual guiding or with old, insensitive guide cams.) Because they are a source of flexure I don't use them, preferring to bolt the guide scope down hard while pointing in more or less the right direction. I am always suspicious of the claims of software, so I wouldn't be prepared to believe what Sharpcap says about your PA without testing it. A drift test would soon confirm or refute your PA's claimed accuracy. Olly

Tiny pixel CMOS cameras, great camera lenses and sophisticated portable mounts... The compact imaging rig is going from strength to strength... Olly