rl

I have to confess I'm struggling a bit to identify features for certain.  Are these single exposures; would stacking help improve the signal-to-noise?

What are the y-axis units? ADC counts?

The Castor trace on your last plot (blue line) shows most clearly what are probably the H-beta and H-gamma lines. The Planck curves do sort of follow the expected pattern based on temperature.

Having owned many Newtonians I've never been really bothered about diffraction spikes that much visually. I find them more annoying in photography.

The JWST sports some of the worst diffraction spikes I've ever seen...nobody seems to mind!

Personally I think that's quite a good advert for the ODK...

About a year ago I offered -free- three Dob mirrors on this site, collection only.  All three would have made a good Dob project. The only one to go was a 14" f/5.7 by AE optics. One is a 18.5" by Oldham Optics which I thought would have been snapped up but the relatively long focal length probably put people off; you needed a ladder to reach the eyepiece when pointed at the zenith. I did make a scope with this mirror and it was indeed optically wonderful, but the operational risk to life and limb made it hard to justify its place in the garage...it cured me of aperture fever. I'm down to 14" now and I may sell that one in the near future. 

Dobs have always been the classic DIY scope, and DIY scopes generally seem to be on the wane. Looking at the quality and price of some of the imports you can see why.

I think more and more people are primarily interested in photography now, the visual attraction of full-colour high-res pictures which you can get published will for many outweigh the more arcane satisfaction of star-hopping from one fuzzy blob to the next. Not a judgment; I do both, and neither particularly well!

The UK weather probably holds a veto on many people's ambitions now. It's easier (and less controversial) to justify keeping something that breaks down into small pieces easily and unobtrusively stored than have a massive scope lying idle for weeks on end in the house. 

I have a secondhand Mk1 GT81 and it has one of the best corrected OG I have seen on any scope regardless of manufacturer. 

I believe it's still the same lens even though much else has been updated which probably says something.

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Impressive looking scope for an impressive price !

I sometimes wonder if these whopping refractors are designed to attract the crowds at astro shows, as much as anything else 🙄

Yep...my John Owen 6" f/10 triplet purchased for circa 3% secondhand of the WO cost always gets a crowd, 

7 elements!...Es Reid will have a job for life tweaking those!

I seem to recall a WO 71mm 5-element astrograph that went out of production quite quickly to be replaced with a simpler design..more is not always better?

Not working for me at 12:40. Comes back with a Cloudflare fault.

It's not unusual to have difficulty connecting to ABS...

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One thing's for sure: I would not try to sell any image which did not contain something new, something not seen in any existing images. Over the last fifteen years that might leave me with about five images which meet this requirement, so not many!

Better make that 6!

Brilliant work...

50 minutes ago, Flame Nebula said:

Hi rl, 

I had heard it was OK when in Az mode. Did you have problems even in this mode? 

I'm wondering if carrying it on a trolley, then connecting to the az-eq6 mount is an option that would make it easier to handle. 

Is it the length of the tube that you think caused it to be on the limit, because weight wise it is well within the load capacity that the mount is supposed to be capable of. 

Thanks 

Mark 

I used it as an equatorial. Never tried the alt-az mode. I would willingly defer to the experience of others on that one, but sooner or later you will want to try out your 12" for astrophotography on deep sky stuff for which it should excel if you don't mind the diffraction spikes

The OTA on its own is certainly well within the mount's stated capability ( I forget exactly, 20kg for visual?)

But you normally take a half to 2/3 of that number for photography. Add on a camera and a filter wheel, OAG and second camera for guiding and you are getting close.

I suppose there is no absolute right or wrong here as long as you are inside the 20kg limit but:

• It's not just weight but bending moment that comes into play here. The extra diameter of the 12" increases the weight* distance moment which calls for extra counterweights, or the same counterweights placed further out. I remember ending up with 4 by 5kg weights. Balance becomes more critical. the motors did track ok provided there was no wind but I always felt fast slewing was stressing things.
• The 12" scope is a bit of a sail. Not an issue maybe if you have an observatory (I don't). 
• The mirror and cell are quite heavy which pushes the OTA centre of gravity well down the tube. This results in the eyepiece end sitting quite high. I needed a ladder to reach the eyepiece at the Zenith. Less of a problem if you are using a camera; the camera can be permanently situated on the inside.
• It's a serious lump to take on and off the mount in the dark on a regular basis. Manageability is an important factor in how often the kit gets used. 
• Turning said lump in the cradles to get a better eyepiece position is possible but clumsy. Definatley a plus for refractors, or ALT-AZ mode.

It did work after a fashion but I found the AZ-EQ6 mount was a whole lot happier with an 8" scope plus full astrophotography kit. A 10" might be a reasonable compromise; there is one for sale on ABS at the moment.

I had an EQ8 mount for a while which was perfect for the 12" with full AP suite....but it was an absolutely backbreaking job to set it up and take it down each session.

Going back to your original point; I have always found the optical performance of OOUK 1/10 wave Newts to be excellent over several examples, and I don't regret paying the premium just to be sure that any optical issues will be down to other causes. Much better value secondhand.  It's the other factors that will make or break the success of your setup, in terms of what inconvenience you can live with.

Just one man's opinion..not sure it helps much! 

42 minutes ago, Space Hopper said:

 

 

43 minutes ago, Space Hopper said:

A VX12 F4 would be too much of a handful on an EQ mount, and i think you'd soon tire of it.

14kg may not sound that much, but you have to take into account the volume and sheer bulk of the thing.

I've owned my own VX 12 short tube a few years ago now, but on a dob mount. It was a big old scope. Not for the feint of heart in solid tube configuration.

It excelled at low power, rich field, wide angle views with good quality eyepieces. This was what i used it for.  I never used a CC.

And I never considered it a planetary scope as such. The VX had quite a big secondary, and with that aperture, was always too fussy with seeing conditions. My 5.5" refractor is a much better planetary performer,

and despite sometimes missing the aperture when looking at those fainter Messiers, i don't miss its bulk and humping it about.

If you do go down the road of imaging planets with a big newt, then i take my hat off to you. 

 

I would have to agree with much of Spacehopper's  comments. I had a VX12 (and later a CT12) on an AZ-EQ6 and for me it just did'nt work. Extra counterweights and the extension bar were needed to achieve balance. The mount would slew but it always felt on the edge. The eyepiece can end up in some funky positions requiring the flexible talents of a contortionist and possibly a ladder..not conducive to the relaxed posture needed for concentrated study of fine detail. They do work better as dobs.

Where I might disagree is that I found the f/4 was no real hinderance to good planetary observations, in spite of the secondary obstruction. My scopes all had the 1/10 option and the detail they could resolve on a night of good seeing was remarkable. I've seen more detail compared to refractors of 5"-6" even if the image was not as "pretty" in terms of contrast

The 1/10 spec is a bit of an advertising thing...the check is done with a helium/neon laser source with a wavelength of 632 nanometres and as such is perfectly true. But your eyes are most sensitive at about 550 nanometres which equates more to 1/8 wavelength. They are still excellent mirrors though...I've had several.

A 200P plus all the gizmos might be a bit heavy for an HEQ5 (others might disagree on this) but maybe it's worth checking the balance; it should be slightly off balance, just enough to take out the mechanical ambiguity of the backlash. The reflector has more than twice the focal length of the frac so all the sources of mechanical drift have to be beefed up in proportion. An OAG is virtually de rigeur with Newtonians in my experience. Much better guiding at the cost of far fewer guide stars which can be an issue when you're looking out of the plane of the milky way (but you only need one).

Which coma corrector are you using? I use the Skywatcher 4-element aplanatic jobbie which turns out a decent image with a 8" f/4.5 Newt and an APS-C sensor. Some of the simpler, cheaper ones are not as good. 

How about your polar alignment? Using a polemaster (or similar setup using the finder) can really cut down on the amount of work PHD2 has to do.

If you want an easy life, go the frac route. But it's very expensive compared to a secondhand 200P for the same scale factor and speed!

No future in losing the will to live!...how does the main subject in the middle of the frame look when examined at a normal distance? Sometimes we all lose the plot obsessing over the corners....or maybe I've been doing AP long enough to have the last vestiges of perfectionism beaten out of me!

I have a CT12 at f/4...I have tried it on my azeq6. It required extra weights plus an extensiom bar. I regard it as a step too far for the mount, and the eyepiece was virtually unreachable at some angles. The centre of gravity lies towards the mirror end of the ota which puts the eyepiece quite high. Not a good combo lmho....

RL

My CT8 Newtonian. Not the best at any one aspect but a close second at virtually everything. Light enough to be easily carried (admittedly not Ryanair friendly) and a useful light-grasp on DSOs. Fast enough for photography.

Work of art..love the colour rendition

Those don't look too bad. I think a gentle clean with the Wonderfluid will do the trick. If there is a lot of gunge then try a wash under a running tap with tepid water before going to the Wonderfluid; This may stop you rubbing in any sharp dirt, but to be honest they look basically ok.

I don't remember anything like a waterproof seal on Skywatcher OGs before...I think it's all there.

There may be residual marks on the convex front element which will help you keep the correct orientation on reassembly.

Send us some photos when you can.

A 2-lens achromat is not too difficult to clean and service. I've taken several to pieces and managed to realign them ok. 

Try and remove the 2 elements together over something soft....

The important thing is to mark with a pencil on the edge an alignment point for reassembly; ideally it would make no difference if one element rotated with respect to the other but sometimes there is an optimum angle that minimises astigmatism. Most people use a "V" that points towards the front surface. This also helps in not accidentally reversing one element. The curves are not generally the same on the convex crown glass (usually at the front)

Cleaning; Baader Wonderfluid and the correct cloth will work wonders. Well worth the few pounds invested to make sure you don't scratch the coatings. 

On reassembly I generally put 3 short lengths of tape around the edge (over the tinfoil bits). try and feel with your fingers all the way around the circumference to make sure the optical axis passes through the centre of both component lenses before you put the tape on. 

Don't overtighten on reassembly; just enough to stop the lenses rattling. Else you risk deforming the glass and ruining the diffraction patterns, by pinching down on the tinfoil spacers. If the cell is too tight, the metal will shrink around the glass in cold weather causing further deformation. Commercial manufacturers have been guilty of this problem. 

A small amount of coating degradation is not the end of the world provided the affected area is only a small percentage. 

Triplets are a different matter altogether...

I've owned both 12" and 14" Dobs made by OOUK. Both have been excellent optically and the OO mounts have been expensive but well-made. They are possibly not the smoothest, but certainly smooth enough. The mount components are all milled from solid plate and would last a lifetime. The friction brake works well but needs the occasional adjustment. Personally I've had no problems tracking planets at *200 and above, but I use widefield eyepieces which helps. It's a bit more difficult with an orthoscopic in the focuser but not a showstopper.

Using a cats-perch astro chair helps a lot; you can adjust the height to suit the eyepiece and it's much easier sat down to concentrate on the planet and to tweak the scope's position. 

I've never tried a platform or go-to with a Dob. Something about it gets away from the beautiful simplicity of the Dob concept for me...

I too am an electronics/computer engineer...and fully sympathise with the OP.

One of the beauties of visual astronomy is the complete lack of technology..just you, the scope and the stars. No broken wires, no unexpected windows updates, no flat batteries, no USB lockups...

Tico

What do you want to do with double stars?

If you just want to look then any steady mount that is good for planets will work. Equatorial is always more convenient but a solid Alt-Az will be ok. You will be using high magnification on close doubles, looking at the Airy discs and diffraction patterns which will be on the telescope's limit.

If you are trying to do useful science by making accurate measurements of separation and position angle, a solid and permanent equatorial mount is essential; it will need to be stable from one year to the next!

Aperture is king. At least up to the point where the atmosphere starts to interfere. Doubling your aperture halves the size of the smallest lunar feature you can see; a 5" scope will resolve about 1 arcsecond which translates to just under 1 mile on the moon. (the wavelength of light also enters into the calculation; these numbers are for green light). Shadow effects can make the minimum visible feature even smaller. Doubling your aperture while keeping the focal length the same has the additional advantage of cutting down the exposure time by 3/4 (see below)

Seeing in the UK puts a limit of 0.5 to 2 arcseconds due to atmospheric turbulence implying that there is no point in having more than 10" of aperture on most occasions for detail. This is generally true for visual observations; very occasionally you can do better but it's single digit number of night in a year where I live.

But there is a trick for astrophotography of bright solar system objects called lucky imaging. If there is enough light that the exposures can be kept short (meaning a few milliseconds) then you can shoot a video of thousands of frames in a few seconds. Some of those frames will coincide with instants where the atmosphere behaved itself and will be unusually clear. There is free software available that will analyse the file and pick out just the good frames..say the best 20%..and add them up into a single more detailed image, throwing away the rubbish ones.  Virtually all the brilliant results you will see on this site are done this way. It's a result of modern PC hardware being able to move, store and process vast quantities of data quickly.

Generally speaking, virtually all amateur astrophotography relies on adding up multiple frames (called subs). The real detail adds up in proportion to the number of exposures, while the random noise adds up more slowly (technically as the square root of the number of subs) so you get an improvement in the contrast.

It will be fine for showing people planets. On a good night you will see Cassini's division and the GRS, plus shadow transits on Jupiter (look them up first)

It's worth remembering that the maximum useful magnification in the UK is often about 200 times regardless of whether you're using a 4" or a 14" just down to conditions. Don't know about Spain.

I find it's worth managing expectations before taking people to the telescope. I hold a 5p/ 5 cent piece at arm's length and ask people to read the writing...it's useful in setting the context.

ED is the important bit. Just choose your eyepieces appropriate to the OG focal length.

Very slow scopes like f/11 or f/12 allow the use of cheaper flint glass for similar levels of chromatic aberration, and possibly cheaper eyepieces for the same off-axis aberrations. The views can be excellent; the tradeoff is cost for  compactness and the mount. The ED scopes with shorter focal length will do both high magnification for solar system and wide field for deep sky, but the OTA will be more expensive, as might the eyepieces if you go as low as f/5

In my book a halfway decent 10" Dob will beat any 4" refractor providing all four "C"s are met at the same time; Conditions, Collimation, Cooling, Coatings.

But they are bulkier and more temperamental...which is why you raised the post!

Nagler 3-6 zoom?

Some interesting comments by several contributors.

I went to the first Astrofest in 1992 when I was an impecunious postgrad student. At the time I was more interested in seeing the trade stands and ogling the dreamland Pentax and Tak scopes! I've been to most of then since and have always enjoyed the trip. In fact, the first weekend in February is a date now held sacrosanct in our household where I can do my own thing with the rest of the anoraks!

Over time I've learnt to take more interest in the talks. Of the 16 talks over two days I generally enjoy most of them. There are always a few that are pitched too simple but you have to include something for the newbies and the intrigued walk-ins. It can be an effort to hear sometimes; the PA system is less effective in some parts of the auditorium and, for many speakers, english is not their first language. I always come away having learnt something and with a revived astro-mojo.

I would agree that this year, the trade stands were a bit substandard. This is probably a bit shortsighted on their part...looking around me now a lot of my more expensive kit has been bought or ordered at Astrofest. In 2015 I bought a CT8 off OO. Normally there is no way I would have dropped something north of £1k on an 8" Newtonian, but the chance to see it in the flesh, blag a mirror upgrade to 1/12 wavelength, and get a discount swung the deal.  On the train home I was starting to have buyer's remorse but I still have that scope and it will probably go in the coffin with me. That humble 8" actually ticks the most boxes for me of any scope I've ever owned, but I had to see it to appreciate that fact before purchase (no remorse now!). I've done more varied astronomy with that instrument than anything else...AP, visual, spectroscopy, portable. Same story with my CCDSPEC spectroscope, and many eyepieces. I'm contemplating a Pulsar dome..the chance to see it and talk to the makers does inspire confidence. Currently the only holdup is negotiating a discreet space in the garden, and it will have to be green...Last year there was a guy doing some brilliant run-off sheds..where was he now I'm looking?!

On the upper deck there was a sad empty space that used to be filled by Jodrell Bank. In 2002 I signed up at Astrofest for their distance learning certificate on radio astronomy, which I completed and really enjoyed. There was a field weekend at the end where you actually got to use one of the smaller dishes to look at the neutral hydrogen emission from M33. Would I have done that without the first contact at Astrofest? Probably not. 

Every year I'm tempted by the University of Lancaster BSc course. Coming up to retirement I might just do it...just hope I get to actually finish it before I croak!

So yes, maybe this year some aspects fell a bit short. But looking back I've had many brilliant weekends spent at Kensington town hall. I really hope it continues, along with the other events in the year.

And a massive, massive thanks to Profs Lucie Green and Stewart Clark for organizing it.

RL

The 6" Newtonian has always been the value-for-money entry into "serious" telescope territory for visual.  It's available in several flavours; f/8 is more bulky but best on solar system due to small obstruction, f/5 better for wide-field and a bit more compact, f/6 in the middle. But you can do it all with any of the options. Just match your eyepieces accordingly...with a top whack of *150 you would want a 8mm on the f/8 and a 5mm on the F/5 option. Bottom end *30 maybe, you're looking at 40mm at F/8 and 25mm at f/5. I'd get one with a 2" focuser just to optimize the wide-field views and finding objects, but if your main interest is planets then the smaller 1.25" will serve just as well.

The other standard choice is an 80mm ED refractor but that might not be a big enough step up on your 70mm (is it an ED?)