ollypenrice

Your stars dilemma, either too bright and sharp or too dull and lifeless, is dead easy to resolve in any layers-based program. You simply paste one onto the other as a different layer and adjust the opacity of the top layer till you get what you want. This is the mainstay of my Photoshop processing but can be done in the free GIMP as well, I expect. If it's only the stars you want to blend, there's a MartinB tutorial on the Imaging Tricks and Techniques part of this forum which tells you how to isolate stars. (Alternatively you can use Noel's Actions in Ps to select brighter stars. It's now sold as Pro Digital Astronomy Tools. Nice image. No question. Olly

Well, I got there in the end but I'm not really sure how. I tried to make one change at once but somehow lost track when I decided to follow an internet tutorial on Photoshop for photography. (What else is it for? ) I switched to Adobe RGB colourspace everywhere I could find, ditching N. America General Purpose 2 which one expert dismissed as 'pretty useless' and went for Custom-Adobe RGB. In View, I also went for Proof Setup- Custom-Adobe RGB again. Proof Colours is unchecked. I'm convinced I'd tried all this before and still had pinkish-red for white but now I have good agreement with my copy of CS3. I also received a Datacolor SpiderX (miraculously delivered next day, which is good for where I live) and calibrated my screen. It was clearly about right before because it didn't change by much, but it may affect printing more dramatically. I'm dithering over a good photoprinter now that the ink-tank printers don't hold you to ransom over cartridge prices.) Thanks Tom, Alan and Ciaran for your input. Olly

I think the three key numbers are 1) the height of the space swept by the highest part of the scope in all positions. At no point should it be able to contact the dome because, if it can, it one day will. Maybe allow for the possibility of a longer OTA in case you ever change, and don't forget the dew shield. This number is more likely to be an issue with roll-offs than domes but bear it in mind. 2) access to the lowest objects you are ever likely to want to image or observe. This number may be horizon-limited anyway, depending on your site. The scope needs to be able to see over the bottom of the slit. 3) neither end of the scope should be able to hit the floor. You might say to yourself, 'This only applies to the back of the scope' but that would assume that nothing will ever go wrong - and it will! I host a number of robotic scopes and fairly regularly find them in positions of cable-tugging contortion... All these numbers are specific to individual setups. Mount heights vary, as do scope lengths and horizons. This probably won't apply to you with the DDM but anyone wanting to track well past the meridian, as I do, will need to raise the pier because the OTA gets progressively lower after the meridian. This applies even more strongly with dual or side-by-side rigs. I suppose the failsafe rule would be 'as high as possible,' consistent with not hitting the roof. Olly

It is certainly a reflection nebula. Many renditions - even most - don't have a dedicated Ha input at all but your Ha is very well worth having because Barnard's Loop, which is bright on the east side of Orion, is still there on the west side though somewhat 'pushed in' by some kind of shock front or particle wind. My second attempt at the Witch was much enhanced, I thought, by Ha. A band of Ha intersects with the Witch almost at right angles. https://www.astrobin.com/full/383965/0/ The Witch is very faint so avoiding the moon is pretty important and it can also be plagued by Geostationaries (which, being stationary relative to the Earth move across the sky.) The only defense against them is to take a lot of subs and use a sigma clip stacking routine. AstroArt did a great hob of this for me. Olly

Thanks Tom. The plot thickens after following you pointers. If I set the settings in View, Proof Setup and View, Proof Colours to the same in both CS3 and CC I get totally different colours. My CS3 settings are: Proof setup, working CMYK (which is probably wrong but that's where it's always been.) And Proof colours is checked. If I apply these settings in CC the images look awful. But why are they different?? I get the best results in CC with Proof Setup set to Monitor RGB and Proof Setup unchecked. There must be some other parameter in CC which is causing the difference but I don't know where it might be. Olly

My point is really that any star-sized dot in the blue channel could be adjusted to give the right level of blue. Couldn't you do this just as easily with Ha as with H beta which traces the same gasses but with lower signal? Olly

I would only put RGB stars into a NB image that was replicating, fairly closely, an RGB image. I guess that would be HOO. Then we need to think about why blue stars are blue. Are they blue because they produce more H beta emission? Not so far as I know, but I'm not a physicist. Wien's Displacement Law links the colour of blackbody radiation to temperature so all its radiation is displaced towards blue as its temperature increases. This makes me doubt that the proportion of H beta emission is causing the blueness of blue stars. I'll happily stand corrected. Olly

Despite, to the best of my ability, setting the colour settings in Ps CC to those of my old CS3, these two editions of Ps give very different colours. Here we have both CC and CS3 values on one screen. This screen grab is from CC with a screen grab of the colour settings dialogue box of CS3 open (in CC) on the right. I've also tried unchecking the CC option Blend Text Colours using gamma, for what it's worth, and I've closed and re-opened CC asking it to restore defaults. As you can see, the screen grab of the CS3 settings box on the right has a pinkish background in CC but it looks white in CS3. It looks pink on here and my pictures, processed in CS3, look right on SGL and elsewhere, so CS3 seems to be the 'right' one for net publication. I cannot see why these versions of Ps give different colours. What am I missing? Another thing: I get the warm pinkish-whites thing going on in Lightroom's 'Library' page but I get my CS3-like colours when I open the same photo in the 'Develop' page. So Lightroom's Library page seems to agree with PsCC while Lightroom's Devlop page agrees with PsCS3. Help! lly Edit: Here is the dialogue box from CS3 on the left with a version of itself copied, opened and saved in CC over the right hand side.

You don't mention autoguiding but this is a game-changer in astrophotography. Nothing will add so much value as that. If you are guiding then 30 second subs are rather short, I'd have thought, and wont let the signal swamp the noise. For many years I've used a mixture of handset and camera to find and frame objects but I'm also involved with a fully automated rig which plate solves. With the handset method I align on one star, which is good enough with a permanent polar alignment, and refine the star alignment by centering the star on the camera's image of it. I then send the scope to the target using the handset's catalogue of objects or, if it's something obscure, using the RA and Dec values shown on the handset. I then take a test sub and frame up the target to my liking, looking at the star patterns around it, and so on, to get an attractive framing. I wouldn't rely on plate solving to frame a target unless it had a lot of empty sky round it and I was aiming to crop anyway. I realize that the small scope-top computers which control everything are attractive but I also know that, as a remote imaging host, I've replaced rather a lot of them! (To be fair this does not include the Altair which none of my clients has tried.) My co-conspirator and I elected to use a desktop with lots of USB ports for our remote setup. This, however is an 'observatory solution.' Olly

I don't find this with EQ6 or Avalons running EQ6 electronics. However, I guide in ST4 and sometimes use much shorter exposures, down to 0.5 seconds. I do use longer guide subs (4 secs) with the accurate Mesu mounts. It's odd that our findings differ. Olly

You can, in my view, calculate till you are blue in the face but, until you've tried all the options, you will (quite rightly) wonder if you fed everything necessary into you equations. Experiment! Some of my own experimental results disagree with the relevant arguments from calculation. Olly

Dutch members of SGL will sympathize. The Netherlands is traumatized by these light-blazing greenhouses which many of my guests come to escape for a while. I once asked if they had any dinnertime dislikes and was told, with a dry smile, 'Tomatoes.' When I asked Why tomatoes? one of the group slid his laptop over so I could see a picture of those monstrous orange-glowing fruit sheds... Olly

You'll simplify your imaging life if you set your camera to have its edges aligned with RA and Dec. This makes adding data from subsequent nights easy and simplifies mosaics. The orientation can be landscape (long side along RA) or portrait (long side along Dec) but I use one or the other. Quite honestly I'd rather shoot two panels than rotate the camera to fit a target into a single frame, though this hardly ever arises. It also makes guiding troubleshooting much easier because you know which axis is which. To set the camera this way just eyeball it relative to dovetail or counterweight arm then shoot a 10 second sub while slewing slowly on one axis. This will produce star trails but are they parallel with the chip? Rotate the camera and repeat until they are. You'll be very glad you did this, believe me. Olly

Having copied and pasted the JPEG onto an equalized version of the California image I did finally concur that the bunnies often correlate with the dark arcs. However, there are some dark arcs without correlating bunnies and I did have to offset the flat a good way to the left to line up arcs with bunnies. (The equalize adjustment in Ps is really a diagnostic tool for greatly exaggerating local contrasts and made the arcs jump out.) This offsetting to the left sets a mental alarm bell ringing when I also remember that you use a filter drawer. If the bunnies are caused by dust on the filter and the filter was offset slightly to one side when the flats were taken, then this offsetting of the bunnies between flats and lights would be exactly what we would expect. Here's a screen grab showing the extent to which the flats had to be offset to get the bunnies aligned with the arcs. An offset filter draw when the flats were shot seems to me to be a good fit with what we're seeing... It's not a perfect fit but these things rarely are. Olly

Something dark in the calibrated image will be created by something light in the flats, if the flats are the cause. I can't download large files with our rural French internet connection but it would be good if you could post a JPEG of a stretched flat. I'm wondering whether the bright light source used for the flats has created a reflection from, say, the edge of the filter and that this is being shunted around back and forth as an internal reflection. The artifacts seem to be segments of a consistently sized circumference. Olly

The orientation of the spikes relative to the sky is the same on both images. That means that the OTA has not rotated in the tube rings so presumably the camera has rotated. I think the split may be caused by a twist in the vanes but I'm not well up on Newt imaging. Olly PS Somewhere along the line, green has replaced blue in this processing. This means your blue is somehow being suppressed, either at capture or in processing.

I've only used the 2600 so can't compare them. Olly

OK, my pessimism about the moon seems to be misplaced! Olly

The Flame is a very good test of colour and this passes muster with full marks in my view. Olly

Agreed. An exchange of opinions doesn't have to be an attempt at persuasion. Olly

Are you comparing OSC with mono here? OSC will be very hard-hit by the moon. The fairly recent dual- or tri-band filters would open up the sky to your OSC CMOS. I've just dipped my toes in the waters of CMOS and think it's fine, though there are other big variables when I compare results from both. Most obviously the CMOS is in an F2 system as opposed to F5 and F7 with my CCDs. Give it a go without the moon, I'd say. Olly

Choice of camera is significant because you need to be sure the chosen scope can cover its chip, which is to say that it should provide a clean image into the corners without elongated stars or other distortion. You might need a field flattener with this but they are available. The mount is probably quite marginal for AP in terms of payload and tracking accuracy. Aiming for a lower resolution by going for a shorter focal length camera lens might make life easier, as Stu suggests. Prime lenses are the best bet. Olly Edit, your post above came in while I was typing, so you already know what the lenses can offer. A focal length of around 400mm is not really a 'galaxy' FL though it will give a reasonable-ish scale on the visually large ones, M31, M33, M101 and IC342. After that they are going to look very small at much less than a metre or so. This will also bump up your resolution, meaning you'll need much higher tracking accuracy. This really means a new mount if we're honest. Olly

Agreed. There hasn't been any real innovation at TV for a long time where scopes are concerned. Indeed that's why I'm a bit mystified by the idea that the 'is' scopes are some kind of betrayal or hybridization of the originals. As far as I'm concerned they are almost, but not quite, identical and, if I wanted a 4 inch astrograph, I'd go for an FSQ - as indeed I did. I still have a TV Pronto for visual and would love another Genesis or TV85. Actually the 85 is a seriously under-rated imaging scope, the only person I know using one for that purpose being Frans Kroon, who does great things with his. There is something very nice about the build and feel of TV scopes in the modern age because modern they are not, at least in the way they're built. Olly

For me a hybrid instrument is a combination of two designs, such as an SCT with a Hyperstar conversion, a Maksutov-Newtonian, an Optimized Dall-Kirkham or even just a fast corrected Newt. In these cases the hybridization changes the purpose of the instrument and renders it unsuitable or sub-optimal for its original purpose. However, if you went observing with a TV is you would find it absolutely identical to its non-is counterpart and this is why I don't regard it as a hybrid. In the end we are just using terms differently, I suppose. Olly An ironic afterthought: Arguably the first Genesis was a hybrid in the sense that the Petzval was designed as a photographic portrait lens and first came into astronomy in the role of astrograph. (E.E. Barnard, etc). Historically, if it's a hybrid it's a camera lens hybridized into a visual scope. The 'is' bit just takes it a step closer to its roots. This is interesting. https://en.wikipedia.org/wiki/Petzval_lens The article seems unaware of TV's use of the design in a visual instrument and of its various incarnations in astro-photographic optics.

Why do you call it a hybrid? It's not a blend of two designs, it is the same very fast F ratio Petzval that it always was, allowing the observer to choose between what is effectively a binocular field of view and a high power planetary one. Very few instruments can do this. The design has simply been modified to add imaging potential without affecting its visual performance at all. The design has not been hybridized or compromised, it has simply been extended. Is that marketing? Obviously it is: TV are looking for a wider customer base for this scope. They have not, however, turned it into an astrograph like the Takahashi FSQ106. It remains what it always was, plus a bit. I don't presume to know your mind but does your hostility to the new TVis range spring from a hostility towards imaging? Do you perhaps prefer a telescope which carries a banner, as it were, saying, 'Only for visual observers?' Olly