ollypenrice

Agree with Steve, a different and refreshing view.

Olly

41 minutes ago, petevasey said:

Yes indeed, superb!  Of course the Dawes limit for an 8" optic is 0.57 arc-secs, and the resolution of the 2600 at 400 mm fl with its 3.76 micron pixels is 1.94 arc-secs per pixel - I would think easily obtainable at your location.   But I'm not sure how the one-shot colour affects that resolution.  Nevertheless to obtain the detail shown in your image with such a wide field is undoubtedly exceptional.  Your close up is similar to the field of view of my QSI 683 on my RC10.  But at its f8 ratio it would take 16 times as long to collect the same amount of data.  Ouch!  And of course my camera is far too large to go on an 8" RASA - I'd need to lash out on a 2600.  Nevertheless that target is now on my must do list.   Getting a bit late in the year for me now - I'm tied up in early March, but might get a chance under dark skies at Kielder - a weekend on 8th March coming up.  Probably my Sharpstar 140, at f 6.5 only 10 times slower than the RASA 😉

Cheers,  Peter

My feeling is that the debayering algorithms are so good that OSC loses nothing perceptible to mono in DS imaging. I also found this when comparing the OSC and mono versions of the Atik 4000 when I had one of each. I know that the mono is recording real information and the OSC uses interpolation, but at scale of four pixels I really don't think it matters.

Olly

8 minutes ago, Stuart1971 said:

So how do you stand in the age old Mono V OSC discussion…as you certainly seem to have taken to the OSC on the RASA…? Do you not feel that you miss mono imaging, as I know it’s pretty hard with the RASA set up with not being able to use a filter wheel.

I miss mono less than I expected to for three reasons: 1) The RASA pulls is such a vast amount of signal that what is normally 'narrowband or nothing' often, but not always, appears bright and clear in OSC. 2) I have in stock, or can obtain through collaboration, NB where its essential. 3) A dual or triband filter remains an option for the future.

At F2 in both our current rigs (the Samyang 135 being the other) I'm enjoying OSC, but I still think it is too slow for slower systems. Using NB filters is itself a slow business but it is, in practice, a shortcut to getting faint emission signal to show in the final image. The isolated NB can be stretched harder relative to the other reds, which is why it's a shortcut.

I don't think I'd like OSC so much in more normal imaging systems.

Olly

11 hours ago, petevasey said:

Hi, Olly,

Wow that's one heck of a project!  And the image of Sharpless 257, when in the vertical configuration, puts me in mind very much of Dan Dare's arch enemy 'The Mekon', particularly with a colour adjustment.   I wonder if calling it 'The Mekon Nebula' will ever catch on 🤡

Cheers, Peter

When I started processing the crop I had it in a vertical orientation and there was something slightly disconcerting about it. It made me feel distinctly uncomfortable and I think you've identified the reason why.  It was a relief to find that its orientation for us was horizontal. Once rotated, I no longer felt spooked by the darned thing...

I do think that Paul's RASA has performed out of its skin, finding so much detail in a tiny object for a 400mm widefield focal length - and in broadband.  This is my answer to doubters who don't like its numbers on paper. In no small measure its success, here, is down tho the volume of signal it found in 5.8 hours. In the real wold of imaging the relationship between signal and resolution is complex. They cannot, on targets like this, be considered as independent properties.

Olly

28 minutes ago, Stuart1971 said:

Olly, with these superb broadband images you regularly post, and are using a 2600 OSC camera, do you use any filters at all, ie, any light pollution suppression such as an L-Pro or similar…? Or are they totally unfiltered…?

From memory, I think the camera has a cutoff filter built in. We certainly don't use any external LP or narrowband filters. Neither I nor anybody else I can think of has ever used an LP filter here because it isn't necessary. This is a dark site reaching SQM22. I've also used CCD OSC cameras here, again with no additional filtration.

The degree of NB capture we get from the otherwise unfiltered OSC varies. No sign of the Squid, for instance, but Goran showed that the same setup can do a great job on it with a dual band filter.  We got very little signal from Simeis 147 (Spaghetti Nebula) in Ha, either, but many Ha objects come through beautifully.

What I like is that the proportion of dust to gas is swung in favour of the dust on many familiar targets, meaning we get a new look.

Olly

4 minutes ago, Icesheet said:

Quite amazing detail given how close the crop is! I suppose this is pre BlurXT too?

No, that had been through Blur X in Correct Only mode at the linear stage.

One note on ease: the RASA holds focus for much longer than my FSQs did.

Olly

Paul captured and pre-processed this with an eye on using it to enhance our Orion-Monoceros mosaic, which I'll look into later.

Initially I found a very nice starfield and a very small nebula in the data:

However, looking at the nebula at full size, it proved surprisingly interesting so I did a close crop and a more intensive star reduction so as to present it like this:

RASA 8, ASI2600MC, NEQ6. 116x3 minute subs.

Edit: blended into our giant mosaic it looks like this, if you can find it! (Below the Monkey Head nebula.) https://ollypenrice.smugmug.com/Other/Emission-Nebulae/i-G8HJCM3/A

Olly

Nice work. I love this nebula and, like you, am surprised by how rarely it's imaged. Maybe it's just too big to appeal to non-mosaic makers.

Olly

Yes, it does look a bit grumpy!

Great to see these, though. As ever, you find interesting ones.

Olly

A tantalizing galaxy that will never let you rest!

lly

Tip top. Lovely images.

Olly

Today a new dataset fell into my lap, Paul having captured 116x3 minutes on little Sh2-257, mostly to enhance our Orion-Monoceros widefield. It gave me a chance to study RASA resolution rather nicely, though. Here's the full field just given a basic stretch.

Now let's have a look at the Sharpless object itself in a very close crop to see what's there. I hope you'll be able to see this at full size, which is how I've posted it.

Olly

58 minutes ago, Adam J said:

Olly is that image Duel narrow band data? 

No, just OSC.

Olly

42 minutes ago, Icesheet said:

I wasn’t making an argument, I was asking a question. I was curious to know, based on my local conditions what would resolve more detail and provide a sharper image.

 

I certainly do not, and your images as well as your apparent change in stance regarding such scopes is part of the reason they interest me. However, I see the other side too. I am interested in spot diagrams and star shapes. I’m looking for the right balance of going deeper in my limited imaging time but getting the most from the optics in terms of sharpness and star shapes. It’s also about me choosing something that fits my habits. 

The sampling rates and FL of both are fairly similar so maybe there is a quasi-objective answer of what would provide the more pleasing image.

Anyway all good input, don’t know if it’s made a decision any easier for me though 😆

I have changed my view on the RASA, for sure.

When time is limited, my view is that the priority has to be signal. I've come to feel that that's the case when time isn't limited as well. Obviously the signal has to be of a certain quality but in a trade off between slightly better star shapes and four times as much signal, I'll take the signal.

Olly

Edit: I entirely agree about choosing gear which suits your habits and preferences. Same with software. We need to be happy and comfortable.

38 minutes ago, Adam J said:

Vlaiv is correct they are intrinsically connected. 

OP is making an argument that 200mm aperture will resolve more than a 85mm refractor..am not so sure that true, I would say that for most of Europe unless you are at significant elevation both will resolve the same due to atmospherics but if you did take the RASA up the mountain your not going to get close to 0.58 from its optics. 

Image quality is also about Signal to Noise as you cant get details with poor signal to noise to the RASA images will help in this case but the problem is that there is a point when more Signal to noise will no longer gain you detail. 

So it depends on the target. 

Adam 

 

 

I don't say that they are not intrinsically connected, I say that certain optics can perform relatively poorly on stars while performing well on extended objects.  I think the relationship is not simple, that's all. Two instuments come straight to mind, the Meade 10 inch ACF and the RASA.

Resolution in imaging is also intimately connected with signal because, with more signal, you can sharpen more in software.

I would not expect to get O.85" out of the RASA's optics even though I do live on a mountain. I repeat that I don't need to, I need to get respectable resolution for a 400mm FL. 

Unfortunately I cannot compare the resolution of my Tak data with my RASA because the sampling rates are so different, the Tak being under sampled. What I can say is that that I'm delighted by the extended object resolution I find in the RASA. This is a crop of the Pillars of Creation from a single frame RASA image which comfortably framed the Eagle and Swan nebulae together. Let's forget spot diagrams and look at pictures. Do you find anything to reproach in this level of visible detail from an instrument of 400mm focal length? I don't. What does the OP think?

Olly

1 hour ago, Adam J said:

Fitting the filter draw in for a start but yes no filter wheel. But I could also add off diffraction spikes form leads and not being even close to diffraction limited performance to that list. 

I can't see that the diffraction limit has anything to do with this comparison because the OP is looking at common focal lengths, not at common apertures. The RASA can quite possibly out resolve a diffraction limited 85mm mm scope without, itself, being diffraction limited.  The diffraction limit of 85mm is 1.36 arcsecs while that of 200mm is 0.58.   The Epsilon gives good numbers but produces star spikes and, in the case of stars of a certain size, small square stars. You have to be sure you want this on a widefield instrument.

Although I know that Vlaiv does not agree with me, I do not believe that quality of stellar image necessarily equates to quality of extended object image.

5 hours ago, Elp said:

I don't have a RASA but do image at F2 with a Hyperstar and I can say this, once you image at this speed and resolving capacity with the given aperture you likely won't use anything else as often because everything else will seem too slow.

This is my experience.  I imaged for several years with a Baby Q (and a pair of FSQ106 scopes after that.)  I've also been imaging with a RASA 8 for two years. They are all good options, but would I go back to a Baby Q after using a RASA?  Never in a million years.  And bear in mind that I don't lack clear nights. I expect around 250 per year.

A 3 to 4 hour image from the RASA usually shows me things I have never seen before. This is the Pacman in OSC.  This front of dust is new to me, though I can't speak for anyone else. 

Anyone determined to ruin their own astrophotography experience by pixel peeping should probably go for a Baby Q, hoping they'll get a good one. But if you want signal, which is what I do want, go for the RASA.

I could not possibly go back. RASA data are too exciting.

Olly

13 minutes ago, gorann said:

Amazing project Olly! Very promising. If you need a widefield template maybe you could just use DSS2 in Aladin Sky Atlas:

Cheers, Göran

Good idea. Thanks, Goran, I'll try it.

The internet tells me the A7iii raw files weigh in at about 47.3 meg. How did this get to be 800?

52 minutes ago, alacant said:

Hi

Nice shot.
I removed the gradient and gave it a crude stretch. There is colour:)
As you can see, I'm hopeless at balancing it but I'm sure one of the processing gurus will be along soon.

Cheers and HTH

I wouldn't be too sure that there is real colour there. It looks pretty monochromatic, though not greyscale. I don't think differentiated colour will appear just through balancing but can't be sure.

Olly

11 hours ago, Richard_ said:

Is that also with a dew shield fitted or not? I imagine having heat from the camera mounted on the lens helps a lot!

Whilst I don't disagree with what you're saying regarding the RASA being faster, I imagine you need a lot more mount (eg EQ6-R pro) for the RASA unlike these lighter, 60-70mm aperture refractors.

Plus, you need specific narrowband filters for very fast optics right? My Antlia filters are good down to around f/3, so that's one less thing I'd have to consider upgrading if I moved to one of these fast* refractors.

*I mean fast by refractor standards 🙂

Yes, a shot dewsheild to camera height.

You're right about the mount and the RASA is not my idea of portable since it's a vulnerable setup when assembled. It's also fickle and best left alone once sorted. It is also best seen as an OSC instrument in my view, though this makes the tri-band filters an option. Pure narrowband would be an expensive palaver.

Olly

9 hours ago, Paul M said:

Thats's nice. But if I had to criticise, the top left blank box isn't square. The r/h edge isn't vertical.

Pretty much ruins it for me..

Oops, nearly forgot the 🤣🤣

On a serious note, I don't think I've ever seen that set of objects presented quite so spectacularly. Their symbiotic relationship is not generally so clear.

You touch on a serious point, though. There is dramatic field distortion in the top right of the image arising from the fact that I registered the top mosaic to the bottom one. This has concentrated the distortion in the top right.

I'm wondering about a solution. Maybe a very widefield, short FL lens, aimed at the image centre, could be upsampled and used as a template. Distortion is inevitable but coherent distortion would be nice. We have a year to cogitate over this because the missing southern parts are no longer available.

Olly

15 minutes ago, Richard_ said:

When fitted with the reducer, this looks like a much more affordable alternative to the WO Pleiades telescope!

https://www.firstlightoptics.com/william-optics/william-optics-pleiades-68-f38-astrograph.html

I wonder what grade of glass is used as it just says ED.

Regarding water proofness, I would guess that the nitrogen purging and  coatings on the lens elements inside the telescope would be to prevent/stop fungus growing inside the telescope. I think it would still be a good idea to use dew heaters to prevent dew from forming on the outer surface of the lens.

At a first glance, the RASA 8 blows this out of the water. It has a 100mm longer FL but is nominally  3.6 times faster, though rather less given the central obstruction. Even so, it will cover the same FOV in far less time and, I think, with perceptibly better resolution. The RASA is not diffraction limited but it doesn't need to be when considering its competitor refractors of comparable focal length.

The RASA is entirely dew-proof without heaters, in my experience. Camera heat and fan deals with the problem.

Olly

9 minutes ago, Elp said:

"That's a nice mountain"?

Because it was there...

1 hour ago, Elp said:

Doesn't mean you have to...

An interesting theory but what did Hillary say about Everest?

lly

Olly

Question: can one 'gaze' into a telescope?

Olly