ollypenrice
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Posts posted by ollypenrice
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25 minutes ago, tomato said:
that's why I would chose a RASA11 if I could only have one scope.
As would I. I'm bored by the slow systems I know so well. They were a great adventure for many years and a double FSQ106/Full frame CCD seemed like a wild adventure - and was - till I started working with Paul and the RASA 8-CMOS rig. Vlad may tell me that I'm dealing only in impressions, here, and he may be right - but what I feel is that I'm working with data which are different in kind from any I've worked with before. I can make different pictures from these data. I'm excited! I wasn't exactly a cheapskate on exposure time, either, with the slower systems. 20 hours was routine for a single panel. But when I drop those 0.9"PP 20 hour panels onto 3 hour RASA images to improve resolution, there is nothing there in faint stuff.
We are in this for enjoyment (which can be hard to believe!) and, when it comes to enjoyment, give me the RASA. It's the difference between sitting on a nail and sitting on a sofa.
I was a very reluctant convert but there is no going back.
Olly
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7 hours ago, wimvb said:
Nice images, but if you used any form of sharpening, the comparison isn't relevant anymore.
One caveat, though: the deeper the data the more effectively it can be sharpened.
Olly
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9 hours ago, vlaiv said:
Olly, if you really want to see if RASA can be compared to even 80mm scope - point it to the moon and try to match 80mm in resolution of the image on the moon.
Rather than test the RASA on objects I'm not going to image, I'd rather test it on the objects I am going to image. That's my whole point: used as intended it performs extremely well on nebulosity.
In the two images you post above, I would describe the resolution as very similar, the processing being different. Mine came from a widefield mosaic for which I needed dynamic range at the bottom end, in other parts of the image, leaving me with less to play with around the Bubble. I'm not concerned with comparing aperture with aperture. Its perfectly true that the RASA doesn't resolve as an 8 inch aperture would be able to do. What matters is how it resolves as an instrument with a 400mm focal length. As such, which is how it is intended to be used, I think the resolution is excellent.
Olly
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2 minutes ago, vlaiv said:
But is it as sharp as can be produced by 8" optics at "400mm" of focal length (or rather at that resolution)
That's narrowband! And there is more information in ours everywhere except in the little strand from centre to 4 o'clock. Nope, you're not winning this one so far!
lly
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On 23/08/2023 at 23:57, skybadger said:
This sounds like a reason to do osc on the rasc and mix in mono luminance on the refractor.
Not that I have a spare asi178 cool mono available to try with...
No, if you use luminance from a slower system you will simply darken out the wonderful faint nebulosity which the fast system is so good at finding.
What is worth doing is using high resolution data (probably as luminance) to enhance regions of interest which the RASA cannot resolve to the same level. I find that the best way to do this is to register the high res, with stars, to fit the widefield and then de-star it. It can then be applied as luminance in Ps which allows you to manipulate its curve while it's in situ over the widefield. A seamless blend is possible. When you re-apply the stars, use only the widefield stars so they will be consistent across the image.
Olly
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On 24/08/2023 at 12:08, vlaiv said:
Look at spot diagram for RASA8 to see where the lack of sharpness comes from.
It has nothing to do with additional central obstruction (which impact will be negligible given other factors - it acts on order of magnitude smaller stuff - like for planetary where normal F/ratio is over F/10 not F/2).
Small pixels used with RASA8 are a waste. Ideal pixel size for this scope is about 9-10um if I'm not mistaken. Consult spot diagram for details.
This doesn't square with what I actually find in our RASA data. You and I have debated many times, over the years, you taking the theoretical position and I the empirical one.
No reason to stop doing so now!!
This is a close crop of the Bubble nebula extracted from a RASA 8 widefield. The image comes from a focal length of just 400mm. Pixel size is 3.76 microns in a Bayer Matrix. (I don't know how you feel the Bayer needs to be factored in, if at all.) I think that this Bubble is exceptionally well resolved for a focal length of 400mm. Dammit, it is bloody good for 400mm!
Olly
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Another RASA 8 image with Paul Kummer, who did capture and pre-processing. As well as the dark nebula there's the rather delightful little V1331Cygni with its circumstellar disk.
Olly
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38 minutes ago, saac said:
also what we will never have enough of!
Jim
Oh, I'm not so sure. I adhere to the phrase, 'Enough is enough...'
It would only be a small paraphrase of Einstein to say, 'Time is what our body measures...' 😁
Olly
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2 minutes ago, Dan_Paris said:
Thanks a lot @peter shah, @mackiedlm and @ollypenrice !
Yes, 20km precisely.
Near Marseille ? I guess the Peltier of your cameras have a harsh time these days...
Not too near. I'm in the 05, Hautes Alples, at 900m altitude but, yes, it's hot. 35C today. Dark sky, though, which is why I find your image particularly impressive.
Olly
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Let's think about the word 'before' in the phrase 'Before the Big Bang.'
'Before' requires there to be a point on the timeline, a point which separates before from after on that timeline. (The present is also such a point, but it is constantly moving, whereas the point which separates before from after can be arbitrarily defined and fixed.)
If we consider time to be a dimension which came into being at the big bang, there is no 'before' which can be placed on it because that dimension wasn't there. Accepting this isn't easy, but who wants easy? The idea that time wasn't there doesn't necessarily mean that nothing was there. Existence may have been going on in different dimensions, meaning that there was nothing 'before' the BB but there may have been something 'outside' it.
Also, the idea that there is a past, a moving present and a future is what kind of idea? It is, dear friends, a theory and it is a theory which has taken some heavy knocks from theoretical physicists... I'm convinced we need a more generalized theory of time.
Olly
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It's usual to see this in Ha/OIII/LRGB, OIII being essential for the Squid, of course, without which it just isn't there! However, this is pure broadband using OSC at F2. What's different, here, is the amount of dust overlappng the emission nebulosity.
I'm coming to think of results like this as MDLG images, or More Dust Less Gas.
Well, it makes a change.
Paul Kummer drove the scope and pre-processed while I post-processed. Robotic RASA 8/EQ6/ASI2600MC based at my place.
Bigger one here: Bigger one here https://photos.smugmug.com/Other/Emission-Nebulae/i-3MGGvVn/0/ae7e2d60/X4/SH2_129_OSC FIN 2 WEB-X4.jpg
We also got a result on the Propellor Nebula but it turned out not to be very interesting so here it is as a stocking filler:
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Beautifully done and from near Paris??? Congratulations! (I live not too far from where Stéphan discovered the Quintet.)
Olly
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10 hours ago, josefk said:
Short @ollypenrice panic over. I’m not sticking my finger in to check but the rear element looks a long way away and it looks like there is a balk at the back of the focussed anyway. Phew.
The design may have changed slightly. On mine the rear element was vulnerable, at least from memory. Anyway, better safe than sorry!
Olly
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The 150 wins - on this target - but would it beat a larger RASA?
I often drop old TEC 140 data onto RASA 8 widefields in order to tweak up the resolution in regions of interest, but what I find pretty shocking is how shallow the high res data are. Even in 20 hour TEC runs I have a black background sky while, in the RASA with 3 hours, I have structured faint dust.
Olly
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I did look through my FSQ85 and it was truly remarkable for its aperture. On the other hand, it's heavy and it would be easy to have more aperture for less weight.
Don't scratch the rear element with your diagonal - not that you haven't thought about this.
Olly
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Great stuff. I'm a fan of this target, for sure.
Olly
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The hallmark quality across the board. This is also great in widefield.
Olly
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^^ Dead right about the roof. If it can collide, one day it will collide.
I host six robotic instruments. We've had 10 micron, Avalon Linear, Avalon M Uno, EQ6 and Mesu 200 mounts in residence The Mesu is the very clear winner on reliability. Including mine, there are four of them here now and, touch wood, they never go wrong.
As Andrew says, you need someone competent on site. Remote from an untended site is, in m view, a non-starter and very risky. I'm called up to the sheds several times a week because things just do go wrong, often inexplicably. Mostly it's switching things off and on again, unplugging USBs, putting mounts back on their park positions, etc.
Personally I would avoid all scope-top mini computers. I've replaced quite a few and of various makes. I think the best solution is a desk-top machine with lots of USB ports, so no hubs of any kind. I don't know how fast internet connections are in the rest of the world but it might be worth planning to do your stacking and calibrating on the observatory computer so you only export a final file. We have no choice at my place.
Another very unreliable item is the UPS. They tend to have shortish lives and they don't like getting hot. Reliably clear skies and high daytime temperatures often go together. You do need them but be prepared to replace them regularly. Once a year might be the average.
There are good providers in Spain nowadays. They're not cheap but you'd be surprised by how much work is involved in running a robotic setup.
Olly
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42 minutes ago, michael.h.f.wilkinson said:
Actually, in this comparison, you have to be very careful what you mean. If for a given aperture you image at F/2 and have a smaller chip, so you have the same area on the sky as with F/10 and a 5x bigger chip, all things are essentially equal. However, if you use the same chip in both configurations, you are capturing a larger area on the sky, and therefore capturing more photons. In practice, if I have a 22 mm diagonal chip (matched to the RASA 8 image circle), and use the same chip at normal F/10 focus of a Celestron C8, you are gathering 25x more light on the chip. You are sacrificing resolution to do so, but with modern small pixel devices this might not be an issue. If you have a chip of 48mm (which is pushing the C8 beyond its limits, but could work on bigger SCTs) you gain a factor of 4.76 in area on the sky, but still lag well behind the RASA (by a factor of 5.25). The number of photons for any object fitting in the FOV provided by the chip used only depends on the aperture, not on the speed, of course, but using the same chip, you do gather more photons in total, because you are imaging more objects.
This is certainly the key distinction. We can call the photons 'object photons' or, alternatively, 'wanted photons.' If you don't want them, there is no time gain in capturing them. My thinking is that there is no point in talking about speed until you have decided what picture you want to take, and my beef with Starizona is that they ignore this. And I think they do so intentionally as a piece of marketing hype. I might just as well say, 'I can make your car ten times faster by reducing your journey length by a factor of 10. '
Olly
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On 31/05/2023 at 01:42, licho52 said:
Yes because mosaics are fundamentally and dramatically turning down the speed of your setup. On one hand people fall over themselves to get f/2 and whatever hyperultraspeed setups, on the other they casually mention doing mosaics with them, which are an absolute slog to capture, normalize and process. Mosaics are evil and should be avoided by anyone who has limited time/clear sky which is most people.
To answer OP's question, it should work very well, I'd recommend drizzling 2x because you'll be undersampled.
I think you may be over-simplifying the mosaic versus single panel alternative. Suppose you want field of view 'x.' You can shoot it in low res, fast F ratio, short FL widefield in one go or shoot it in 4 panels in higher res, slower F ratio, longer FL. (Obviously you could also shoot it in super fast F ratio, larger aperture, longer FL, but not for the same approximate price!) If you go for the mosaic, and resample downwards, you do not need 4x the exposure because you can downsample each panel to a quarter of its area, so boosting the S/N ratio of each panel.
The choice really is a complex balancing act and is a very target- and intention- driven one.
An irony which constantly amuses me is that I never mosaic with my longest FL setups and almost always mosaic with my widefield ones.
Besides, until you have spent a week of 8 hour days grappling with a 35 panel mosaic, you haven't lived!!!
Olly
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36 minutes ago, Elp said:
Isn't the 25x blurb used in comparison to the SCT at its native F10? But that's like comparing apples to oranges.
It is, as you suggest, used to make a totally meaningless comparison. Where is the 55.8 mm telescope in this discussion? It needs to be there at F2 in comparing the Hyperstar with something meaningful, or there at F10 comparing the native SCT with something meaningful. Why? Because the 55.8mm scope has a light collecting area 25x less than the C11.
This topic always produces more heat than light, to quote MartinB, and I'm guilty of perpetuating this!
lly
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7 hours ago, tomato said:
The distinction between the dust and the background sky is one of the best I have seen, the bright nebula region has been balanced in perfectly, and there is just no noise at all, superb.
What is the integration time on each panel?
About 55 x 3 mins per panel, Steve. Almost shamefully short!
Olly
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On 02/08/2023 at 08:39, old_eyes said:
Good point!
I had not thought of that explanation. Would make sense of what we see. Generalised low-level emission from large clouds of Hydrogen, with that nice brighter ‘outlining’ of the Veil.
High-res spectroscopy should tell, but that is way beyond me.
However... I'm currently working on a vast mosaic including the Veil, and the line of brown dust rising from the tip of the WItch's Broom seems to carry on for a long way, so the alignment between the broom and the dust may be chance. To be continued...
Olly
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19 hours ago, curtisca17 said:
I think you haven't watched the video because we are saying similar things but coming to different conclusions. I clearly state in the video that the same number of photons from the DSO are entering the camera with or without hyperstar. And I go on to point out that it is the fact that the FOV has changed which means that those photons are concentrated on fewer pixels which is what increases the optical speed of the scope. In a nutshell, I believe that I said exactly what you are saying here. So, indeed, you get a 25X increase in optical speed. But, as you say and I point out in the video, since the FOV is much larger with hyperstar than without, the two images are not the same. Now, as I also say in the video, with the larger sensors typical on cameras these days, one can blow up the image a fair amount without significant impact to resolution since we are very likely oversampling to begin with. You seem to get this later point but apparently did not hear me say it in the video.
As I point out hyperstar also allows one to fit much larger DSOs into the FOV of the frame which is a major advantage as well.
If one wants a dedicated fast SCT type scope the RASA is a great choice, I agree. But an SCT is valued for its versatility in going from f/10 to f/7 (or f/6.3) and f/2. Hyperstar is the tool that gets it to f/2 and I don't consider what I say in the video to be "hype". But you are welcome to disagree with me.
Yes, but my question is, '25x faster than what?'
Edit: With a bit more free time I can now answer that question: it's 25x faster than a telescope with an aperture of 55.8mm and the same FL.
Olly
RASA8 - One imaging scope to rule them all?
in Imaging - Discussion
Posted
Where do you see this? Mostly in stars or in nebulosity? RASA stars are not good, straight from the linear stack, but they can be fixed. (I'm becoming an expert at this!
) If I can fix it I don't mind.
Olly