ollypenrice

2 minutes ago, Elp said:

Other than the better optical corrections on the RASA, isn't HS a similar concept?

I agree on the speed thing, I've found aperture makes a greater difference all things being equal.

Yes, it's a very similar concept and I share Curtis' enthusiasm for fast F ratios.

The RASA is designed from the ground up to work at F2 and seems to have more happy owners than the Hyperstar (just based on reading the forums). The RASA focuser, for instance, is - to my astonishment- capable of holding focus at F2 for long periods of changing temeperature. Some people get the Hyperstar collimated happily but some don't. Then again, there was a problem batch of RASAs so I don't know where we are with that.

Olly

Many (or maybe all) of these issues have been extensively discussed on here and I think you are reiterating a number of mistakes in your video. The most obvious is 'The F ratio myth.' Your Hyperstar does not speed up capture by 25x.  It does not speed up capture at all.  Please bear with me. Exposure time does reduce as the square of the F ratio, as you say, when the F ratio is reduced by increasing the aperture. That's why 'F ratio' and 'aperture' are used as equivalents in daytime photography but note that, in this case, the focal length of the lens has remained the same and the iris has been opened to let in more light. You are not doing this. You are lowering the F ratio by reducing the focal length. 

If you point your scope at a small galaxy which will fit on the chip at F10 and F2, you are getting exactly the same number of photons from the object either way. What changes is the number of pixels you put them on. The Hyperstar puts them on fewer pixels so those pixels 'fill' faster. However, you would get exactly the same result from using larger pixels, or binned pixels. Professional telescopes often have slow F ratios but they have cameras with huge pixels and they are, therefore, incredibly fast. However you go about it, putting your object photons onto fewer pixels simply trades resolution for speed. In an over-sampled system this trade-off may come at no cost in terms of final, real, resolution.

You don't need to convince me that imaging at F2 is great. I love it and do so with two rigs. My point is that the 8 inch F2 RASA I use cannot be compared with with an 8 inch F10 SCT because it has a focal length of 400mm. I'm not going to compare it with an 8 inch SCT with a focal length of 2000 mm. They don't take the same pictures. I'll compare it with a Takahashi Baby Q, though, with a FL of 450mm because they do take comparable pictures - and the RASA is way faster.

I strongly object to Hyperstar hype because it suggests that you can take 'the same photo' 25x faster when, very obviously, you can't.  The manufacturer is perfectly well aware of this deception and may one day fall foul of European trading standards legislation.

Olly

Another with Paul Kummer. 3 panel RASA 8 mosaic taking in these objects and their dusty surroundings. As usual, Paul ran capture and pre-processing and I post-processed. The Ghost and the Iris are gently enhanced with TEC 140 data.

It's a very big image so best seen in a larger format. 

https://ollypenrice.smugmug.com/Other/DUSTY-DARK-AND-MILKY-WAY-TARGETS/i-GWFqWts/A

Olly

11 hours ago, gorann said:

Oh yes, it is amazing what you can do with the data once you get rid of the stars Olly! I imaged the same area with my RASA8 rig a few month ago, but it was full moon so I used NBZ filter for Ha and Oiii. Interestingly, the result is quite different from your RGB, showing that RGB is great in catching faint dust. However, the NB image revealed that there is also a SNR there.

Cheers, Göran

 

That's very interesting! The line of the SNR's arc is just visible in our image as well. I overlapped a screen grab of yours onto it because I wasn't sure how they lined up. Also interesting (and reassuring) is that some reds show through our dust where your image shows the Ha to be strongest. I was a little concerned that my processing might have invented this but your images shows that I didn't.

Thanks,

Olly

It be best just to post a stretched JPEG directly on here. Not everyone has fast internet and some folks don't like downloading for security reasons.

I've made flats from dozens of instruments over the years and I don't recall ever getting perfectly symmetrical vignetting.

Olly

3 hours ago, petevasey said:

I had a quick play on the noise - hope you don't mind : )

Simon

Thanks Simon.  It's a fine line between noise and detail, but I've smoothed the background a little more for the final image on my web site.  The full size is also posted there.

Cheers,

Peter

I like the final one best. Have you tried Noise Xterminator, Peter? I find it reduces noise without significantly impacting on detail. I always apply it as a top layer so I can erase any bright parts which contain detail and don't need the NR but, usually, it's not worth erasing them. My favourite sharpening tool, rather bizarrely, has become Topaz Denoise AI.

Olly

Just going back to your original B-mask image, I'd call it a significant way out. The central spike is clearly on the high side in the orientation below. When using a B-mask I want it to be strictly central. In reality I usually feel with mine that one central spike is slightly offset relative to the other so I compromise with one a tad high and the other a tad low. I never know whether this is an illusion but, when I do it this way, I find I have the best FWHM as measured in camera software.

When I split the channels in your image above and pasted the red onto the blue in Layers, I could erase a section of the top layer's central spike to see how it aligned with the bottom. Red and blue were almost identical with an error only a fraction of the visible error in focus (ie the high central spike.) I certainly think that being more precise with the mask will make a difference.

Olly

1 minute ago, vlaiv said:

And just like that (phrase that sounds familiar for some reason?) we jumped from focusing to this:

https://en.wikipedia.org/wiki/B-theory_of_time

 

Homework!  That's tomorrow taken care of, then. Oh no, wait,, I don't yet know if I'm a B-theorist or not so tomorrow may be an illusion...

lly

1 minute ago, vlaiv said:

And that was before I even saw that you edited your post

  It's not remarkable if you don't believe in the tensed theory of time (past, moving present, future.) And who could belive in a theory as naive as that one???

Olly

2 minutes ago, vlaiv said:

Further you are from the axis of rotation - smaller angle for the same linear motion. So you can make fine adjustments with lever much more easily.

You even matched my red in your image, Vlad! Pure genius, as ever!!

lly

3 minutes ago, shropshire lad said:

Sorry excuse my ignorance .... a lever on what and how.

 

Here's a link to a lever with push-pull micro asjusters. I had one. It's not bad.

https://www.teleskop-express.de/shop/product_info.php/language/en/info/p3286_TS-Optics-Microfocuser-for-your-camera-lens-up-to-135-mm-Diameter.html

Olly

3 minutes ago, shropshire lad said:

How do you mean an improvised lever ?

 

Well, all you need is a lever attached to the focus ring, sticking out from it like a bicycle spoke, if you like. If the focus ring is the O the lever would stick out like this:  O----   The long lever lets you make smaller adustments.

Olly

19 hours ago, windjammer said:

spectacular as usual - but a bit pink ?

Simon

Thanks, Simon. I'm inclined to agree. Tweaks in progress!

lly

My (limited) experience with camera lenses says that you need a micro-focus to avoid going mad. Mechanical ones are available from Telescope Service. Alacant's point above makes sense, though.

Just putting an improvised lever on a lens or focuser can also help with micro-adjustment.

Olly

Here's a crop from an ongoing large mosaic but this part framed up nicely so we offer it as part one. Paul Kummer did the capture and preprocessing, I did the post processing.  One shot colour from AS12600MC Pro and RASA 8.

It's a big image so the full size is here. Again, honestly, it's hard to fault the RASA on resolving nebular detail. (I can say this because it isn't mine! ) If you look at the fullsize, check out the small, whitish nebula near the middle. Interesting.

https://ollypenrice.smugmug.com/Other/Emission-Nebulae/i-rKmnJKp/A

Olly

8 hours ago, Blauvista said:

Very nice results - both the close-up and widefield view - I am always amazed what a RASA will pick-up if you put it under a relatively dark sky ...  and you are right, NGC2179 is a very nice little nebula.  Is the TEC140 data narrowband or RGB?

Thanks. The TEC data are LRGB.

Olly

2 hours ago, tomato said:

I remember a thread on this topic, if I recall correctly a bad batch of drive belts were the culprit. However, wouldn’t Olly hear the motor running if just the belt had failed?

Yes, I think I would. It just is totally dead, as in no current.

Olly

1 hour ago, tomato said:

That’s a great job on the data. I think the modern processing tools are a real win-win. In expert hands they can reveal so much with deep data sets, but beginners with much shorter integration time sets can get a great image without too much work which can only boost their motivation to progress further with AP.

BTW, what happened to the Avalon, if you don’t mind me asking?

The Avalon stopped slewing or tracking one night. I changed from PC control to handset control and when I ran through the setup process it got to the point where the handset said slewing...  but it wasn't. It was as silent as the grave. I tried another handset and another mother board but nothing changed. Just once, during this fiddling, it slewed briefly in Dec and sounded as healthy as usual, so I suspect a loss of current to the motors from a loose connection. I need to work out how to open it up but I haven't found any explanation on that, so far on the net.  

Olly

15 minutes ago, JOC said:

It looks like it has uploaded twice.  Click the three little dots in the top right of the posting in question and click edit from the drop down then check the files uploaded with the posting.  You should be able to click the dustbin or X in the uploaded files list on the file itself and delete the second file if it's uploaded twice.   If not then I don't know.

Thanks. That worked.

Olly

I can't get rid of the duplicate image at the bottom.  Any ideas?

Olly

By anybody's standards, NGC2179 ia a gorgeous little nebula. This old image is at about 0.9"PP with a TEC140:

How about in widefield?  Honestly... not all that promising. This is a basic log stretch of a good recent run in the RASA 8/ASI2600/NEQ6 (because the Avalon Linear has gone belly-up for now.)  Inspiring? Maybe not.

I was wrong!  Given lots of TLC and modern processing, there was an awful lot more to this dataset than met the eye. I've never been so surprised. Don't underestimate your data! The image below is the one above, with no 'painting.'

Capture and stacking by Paul Kummer, my post precessing.

Edit: The triangular open cluster, NGC7142, is interesting because it's heavily reddened by surrounding dust, but also because it has a large number of 'blue stragglers' which I discovered while checking up on the cluster's colour. 

Olly

Location, location, location.  At the risk of being damned annoying, I'll just tell you the truth. I moved to the south east of France.

Olly

Imaged with Paul Kummer who drove the telescope (remotely for him) at my place and did the stacking and calibrating. My post processing.

This is all one shot colour with no additional Ha. We tried using some old Ha but preferred the natural balance between emission nebulosity and dust.  109 x 3 min subs. (5.45 hours.)  TS 2600 camera, ancient EQ6 (because the Avalon has packed up!), RASA 8.

Full size is here. I think the RASA has resolved fine nebular detail very well. See what you think.

https://ollypenrice.smugmug.com/Other/Emission-Nebulae/i-ZkSpWbz/A

Olly

There's theory and there's focus. I prefer focus. 

Olly

When you say it gives a poorer result, are you looking at the picture or at some numbers on a spreadsheet?

Olly