rl

Result! Superb shot.

It's the wavefront. They make the point about the 2:1 ratio on their website somewhere. They also miss out the secondary shadow zone which is fair enough. I don't think the test includes the secondary but I might be wrong on that one. 

This looks superficially like an OO zygo test certificate. All of theirs I have seen have a few extra details though...telling the data and time of the test, and the size and focal length of the mirror, and its serial number, and the wavelength at which the test was done, and the operative (usually R Rogers) The numbers on yours are typical of an OO 1/10 wave mirror. On wavelength, OO use a 632nm HeNe laser so 1/10 wave is more like 1/8 wave at 550nm where the eye is most sensitive. 

Attached is the one for my VX14 for comparison.

Without full details tying the report to a particular mirror, there is no traceability. I would be a bit suspicious...

Thanks @ JeremyS. Don't know why. 

One of the better frames:

Bit of a change of plan last night. Life called off the dark sky / good seeing excursion with the 14" so I set up the 6" refractor in the garden to have a peek at Jupiter and Saturn. Dubhe is unfortunately behind the house. Planets a were not much good due to seeing, so I tool a leaf out of John's book and tried Lambda Cygni instead. It would be good practise since the separation is about the same (0.9 arcsec). The brightness difference between the two components is not so great as Dubhe but it would be a good training target to hone skills and manage expectations. 

Oh the joy of using a decent driven equatorial mount on close doubles! Whereas in the Dob the other night it was a right pain nudging the scope with one hand while trying to damp off the vibrations with the other...the star just sits where you want it with the eyepiece at a convenient height! Much easier to concentrate! Lambda Cygni was resolved as double quite easily if a bit messily using a 4.7mm Ethos (*320). The B component was a very striking blue compared to the white primary. Seeing good for round here but not spectacular. 

Inspired, I put the planetary camera on just to see if I could get an image of the split. To make the scope's resolution the limiting factor rather than the camera I put a *2 Barlow in the system but this resulted in a more than expected increase in focal length since the spacing is not as intended. The focuser had to be racked right out and the whole camera setup was clinging on by its fingernails...I'm not sure the optical axes are properly coaxial which explains some slightly oval star shapes not seen visually. The blue colour of the secondary was even more apparent on the monitor at night; it's not so obvious viewed in daylight. 

Video clip attached; this is 105 images taken with 1 second exposures on a 6" f/10 triplet,  Barlow stretched to officially f/20 but probably f/30 or f/40 in reality. No filters. 

I had rather dismissed the refractor for Dubhe as just a bit light on resolving power. But based on this it's worth a try. It's certainly going to be harder just down to the magnitude difference. A blue filter might help.

I noticed this post in early May and have been trying to split Dubhe on a few good nights since. I've been using my 14" Dob but seeing has usually been awful with the star just a splodge at *230. But last night was tantalisingly close...after an hour of cooling, occasional diffraction rings were visible over an hour around midnight. There were hints of doubleness (duplicity?) with the secondary looking suspiciously like the same colour as the primary. However I can't claim it yet. With the forecast looking good this week I might take the scope out away from the buildings on the housing estate where I live and give it its best shot..

I've got a 6" refractor but I think the close separation, while being on the Dawes Limit will be too close given the difference in magnitude. 

I had exactly the same issue:

You can get a red dot finder that clips on to the hotshoe on the camera. I only found this out in a reply to my own review..worth its weight in gold.

6 minutes ago, nephilim said:

I ended up wasting a lot of time & money trying to get into AP with the wrong type of equipment (I didn't listen to all the 'buy cheap, buy twice' advice from people on here who definitely knew a lot more about it than I) & it put me off trying again for around 6/7yrs. I think there should be a pinned post on here along the lines of 'What it really takes & costs to begin a journey into AP' 😬 It would maybe save some people a lot of disappointment & money.

Even though I now have what I would call a fairly decent set up i'm fully aware of the frustrations that will be heading my way, the weather, technical issues, learning processing (Thats the other 50% of the hobby) further spending (theres always going to be 'something else' i'll need 😂), the inevitable days at work where i've had little or no sleep the night before (I'm way past been able to successfully pull off all nighters 😴

I have to stay positive though as each step will be a step forward (and probably three backwards) & as many mention, AP is very, very addictive & when you get even the smallest thing right its also very very rewarding 🙂.

Steve
 

This is word for word my own experience...

It's difficult to add much to Nephilim's excellent answer but I would stress it's not just a cash investment here. It takes a lot of time and frustration learning all the software to process the images and to guide the mount; It's worthwhile getting kit that will produce good quality subs in the first place just to keep you motivated. 

Th Star Adventurer/ DSLR route is a good place to start and will always be useful for holidays/ portable operation. Above all it's simple. If you get the bug, you will outgrow it fairly quickly and the next step up is where the spending really starts...

A few notes attached...

nova_herculis_june2021.docx

Quote

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Posted 11 hours ago (edited)

  12 hours ago, rl said:

No idea how valid a result this is..did anyone else get a spectrum?

Looks good. Here are spectra by Hugh Allen and David Boyd at around the same time from the BAA spectroscopy database

https://britastro.org/specdb/data_graph.php?obs_id=9977%2C9978&multi=yes&mix_flux=yes

There are two clear broad lines with P Cygni profiles. H alpha with emission at 6563A   and another line with emission at ~6350A  (Si II ?) both with absorption at about 80A /3700km/s to the blue (P Cygni shape profiles)

The features to  the red of H alpha are mainly telluric absorption bands from O2 and H2O in our atmosphere

(Note the dramatic change   just 2 days later in my spectrum up the thread)

Robin, Jeremy, I'm going to do a proper writeup on this with all the details in. 

RL

After a lot of faffing about learning how to use Vspec I got this spectrum from my data taken around midnight on the 12th - 13th June when it was at its short-lived brightest (X-axis in angstroms calibrated with a neon lamp):

No idea how valid a result this is..did anyone else get a spectrum? Seems to ba a symmetrical dip and peak either sie of the Hydrogen Balmer line at 6563, plus other wide absorption lines. Six 10-minute exposures all gave the same result. 

Both are brilliant shots, better than I ever achieve regardless of the scope. I would agree the Mewlon has the edge. But it should do with a 50% advantage on resolving power, assuming the pixel size is correctly matched.. I wonder what the result would be if the exposures were balanced...the refractor shots look a little darker to me, possibly down to the slightly slower f ratio. For me it's something of a moral victory for the SW.

Heard about this nova on this thread early this evening after a long, long day. Was in two minds whether to get the kit out or not...in the end  I made the effort. 

I managed to get some spectra subs taken on my 8" Newt with an Elliott Instruments CCDSPEC. I've had the thing for years..this will be the first time it's been used in anger. 

One raw sub shown below; hope I got the right star on the slit!

I got about 60 min of data in total; Hopefully there might be enough to drag a few lines out of the noise and work out the expansion velocity once I've got the spectrometer calibrated in the morning. 

If you're prepared to go secondhand the 24mm Maxvision 68 degree can be a good option. I bought mine secondhand on ABS 7-8 years ago for about £50 and it has never been a source of disappointment, even in fast scopes. It's comfortable to look through with an adjustable eye guard. Aberrations are not zero but very well controlled. I'm always impressed by just how bad it isn't when compared to much more expensive tackle. It has survived many an eyepiece cull over the years. 

Sadly no longer available new, Maxvision were rebadged Meades as a result of some contract mess-up, but I think the same optical design has been cloned several times over and is probably still out there as a badge-engineered new product . Others will be better clued up on the clones than myself. Imitation is the most sincere form of flattery..

2" Barlows definately do have their place. My main objection to Barlows in general is that you're never quite certain what the scale factor really is because it depends on the distance between the Barlow lens to the eyepiece's focal plane, which is all down to the eyepiece metalwork design. A *2 barlow can be anywhere *1.5 to *2.5....

They are very useful in faster scopes for planetary/ lunar photography for matching the pixel size to the focal ratio. 

They make off-axis eyepiece aberrations less obvious in my experience. YMMV. 

They can be very useful in "extracting" the focal plane further out if your scope does not have enough in-travel on the focuser for some accessories.  The focal plane moves more than the real linear mechanical movement on the focuser as you turn the knob. The increased focal length can be either a problem or a blessing depending on context; but at least you have options. 

I have a spectroscope which is quoted as being suitable for f/5 to f/30 scopes; adding a *2 2" Barlow optimizes the optical path for a f/4 Newtonian while allowing a tight and strong mechanical connection. 

I followed this star during the 1980s with a 5" achromatic refractor until it got too close to split..somewhere roundabout 1992 I recall. I remember it appearing as a figure-of-eight with a waist at that time at about 0.9 arcseconds. It's one of only a handful of doubles where I've seen a change in my observing career. If someone can split it now with a 20" Newt that would be testament to both the scope and the observing site!

If by "transparent" you mean "least light lost" then the Plossls would have to be in with a shout. Less glass is usually better in this respect. This assumes the coatings are the same as the more expensive offerings which may or may not be true. I'm guessing the shorter focal lengths in any given range would have thinner lenses which may convey a slight advantage. 

Having minimum glass in the eyepiece used to be big thing for many observers just to cut down the light lost, but modern glasses and coatings have made possible transmissions in complicated eyepieces which are not that far behind the minimum glass offerings, and future improvements will only make the gap smaller. But it's mathematically true that, for given glass types and coatings, the simpler design should transmit more light. 

Whether it's worth bothering about is a different matter. More basic considerations like magnification aberrations, and FOV would normally determine your eyepiece choice. It's probably more important comparing the same focal length from different manufacturers. Zeiss orthoscopics seem to have the best reputation in this regard.

A more relevant point might be what happens to the lost light. If you lose 5% of the light absorbed in the glass or scattered out of the field of view , that's not too bad. No-one will notice a 5% loss. if it comes back into the field of view as a ghost then it can be really very annoying. 

The mount needs a clean source of DC from 12 to 14 volts, called a power supply. You need to choose its current rating; add up all the 12 loads like the mount (use the slew current..it's a lot higher than the tracking current), dew heaters, cameras, whatever else. 10-12 amps is a typical total number if you don't have access to all the individual numbers. If in doubt, go higher. Then you're in a position to buy the power supply from someone like Nevada. 

The power supply needs 12v connectors to suit. The car cigarette lighter plugs have become standard..personally I hate them because they can come loose easily

I use a Farnell 0 to 30v supply but I'm not sure I'd recommend it just in case a spot of finger trouble in the dark turns the voltage up. A specialist 12v supply or 13.8v supply is better. A modified 12v 10 amp laptop power supply is another option; they are small, don't generate much heat and are cheaply available on ebay. But you need to be certain what you're doing changing the 12v connector so possibly not the best bet if you have no electrical experience. 

Battery chargers are not a good idea since the output 12v is not always clean. 

You can get mains to USB chargers that should be ok for the quark. 

If you add up all the bills buying proper new stuff you might find the costs are not that far short of a new battery...

Yes, it's fine but common sense applies..

I power all my gear off the mains when doing photography at home. Everything is powered through one extension lead which has a safety Residual Current Detector (RCD) plug. This will trip automatically if the current in the live is not the same as the current in the neutral because current is leaking out to ground (potentially through you!).

You want all the exposed metalwork either grounded or double insulated. Commercial stuff that comes with 2-pin mains connections should already be double insulated. 

I can't see how even a big setup will take more than a couple of amps at 240v (500 watts) unless you're using a hairdryer for dew prevention. 

There may be a "time of life" element to this discussion. It's one of the great ironies of the hobby that by the time a lot of us can afford the best, our eyes are on the wane and less able to use the optical quality. I've seen huge magnifications quoted in this thread..for me even *50 per inch shows up a lot of floaters..an exit pupil of 1mm is about the smallest I can go without having to continually move my eye to dodge the dreaded diffraction patterns produced the detritus in my eyeball. A magnification of *200 produced on a 14" is much more satisfying for me personally than on a 4" refractor. however good the quality!

Perhaps it's dual function. Can you turn it around and use it as the objective with one of their HR series to make a complete mini-scope?

If you're going to drop 500 quid then a few more details might help. What do you expect to improve by changing the scope? What other accessories are you using and can they be carried over to your new scope? For example, are you using a coma corrector and off-axis guider? These would go with a bigger Newt, but will the mount then be adequate? Personally I don't see a massive gain in going to a 8" f/5 Newt, or possibly even an 8"f/4. Would you be better off improving the camera or the guiding?

An ED refractor in this price range will have a shorter focal length and larger field (and no diffraction spikes) so is better suited to a different class of objects. But you will also need the matching flattener and may need to change your guiding arrangements. 

Would a better mount allow longer exposures with your existing scope?

Specific recommendations if changing the scope really is the way forward; I've owned a ZS61 which is just about in budget secondhand with the flattener and is fairly undemanding on your mount, and gives good results, and makes a useful travel scope . If you are lucky you might get a secondhand TS65Q which has the flattener built in and makes a really good solid well-built dedicated imaging scope. I paid #380 for mine on ABS. Some of the early ones had pinched optics in cold weather but the issue is easily fixed, and it works visually only with a 1.25" diagonal. As to Newts. I'm using a CT8 f/4.5 which is a beautiful scope but secondhand ones are rare as rocking horse manure and tend to come in at #600 plus. But a "wanted" ad on ABS costs nothing...

Both mine are several years old. Both have the OO Crayford. They are manageable but could be better. One works fine providing you don't rack in too far (wherupon it falls apart). ..The other is either stiff and lumpy or too loose to be useful ..there is no really happy mean. I've tried a couple of the new ones and both have been beautiful..smooth and tight at the same time.

I currently have both in my possession, both bought secondhand at prices far below the new rate. I'm currently pondering which one to keep. Nice problem to have..

The VX14  gives you the choice of mirror accuracy. I have the 1/10 wave and it makes a superb dob. It's the largest thing I can reasonably lift. Having said that, the tradeoff is that the tubes on the VX series are a little thin and prone to dents if you aren't careful. 

The CT12 comes as 1/10 wave as standard. I have the f/4 option. It is more rigid than the VX and less prone to dents.  It holds collimation better if you're going to be carrying it around., not that the VX is bad in this respect but, as previously stated, the tube is more flexible. The CT12 also seems quite a lot lighter due to the smaller aperture and shorter length..I don't recognise the 22kg number but I might be wrong on this. Note..the lovely carbon fibre finish is easily scratched and very prone to dewing up on the outside, (but not on the inside where it matters). The improved rigidity and smaller coefficient of thermal expansion will be plusses for astrophotography. One annoyance of the CT12 is that you can't stand it on end without sitting it on the collimation bolts risking the adjustment. Not a problem one it's on the mount. I fitted some some spacers to get around this niggle. 

Both mirrors are superb, but to be honest on 98% of nights the atmosphere is the limiting factor unless you're on top of the Pyranees. Both are capable of really good results on planets even with the central obstruction.

The mirror cells on both are well made and easily adjusted, especially if you disassemble them and grease the bolts. The CT12 seems better made but the VX is easier to adjust having thumbscrews rather than Allen bolts. 

The VX14 cell has 2 mounting options about 30mm apart giving you the choice of setting the focal plane in the most convenient place. I'm not sure if this was an intentional feature but it is useful. The 3 metal blocks on the edge of the cell have 2 sets of holes. 

A lot of the CT12 metalwork is machined from aluminium plate. The end rings on the VX14 are pressed out of thin sheet and feel a little flimsy if you take the whole scope to pieces. I generally have no conscience about drilling holes in Newts for accessories but I make an exceptIon for both these scopes, especially the CT12. 

On balance I think the CT12 is the better all-rounder. It's almost the same aperture, more portable, better adapted to photography. But in my case, the VX14 mirror is exceptionally good according to the zygo report, having a 99.1 Strehl and virtually zero astigmatism. 

The newer focusers (Baader Steeltrack?) are a big improvement on the older OO home grown offering on both my scopes. They are the only Crayford types I have any confidence in. 

A lot of the choice may come down to the mount.  The CT12 is just about useable visually on an AZ-EQ6 with extra counterweights and an extension bar. The VX14 really gets you into EQ8 territory. I had an EQ8 once and bitterly regret selling it....

One costs a small fortune new, the other costs a large one, but this is the inevitable result of UK manufacturing costs and lack of economy of scale. Both have the potential to be a scope for life. Both are much better value secondhand but make sure you get the Zygo certificate. 

The OO customer experience can be "interesting" . Personally I've not had too many issues but you will find alternative viewpoints on this site. 

Hope this helps. 

RL