Xilman

9 minutes ago, Elp said:

When I first saw it I thought it was a post it note. Definitely not Baader film or any solar film I've had (Seymour film is black), unless you've imaged it at an angle to some reflection.

Always follow the wise adage, measure twice, cut once.

The version I know is measure with a micrometer, mark with chalk, cut with an axe.

54 minutes ago, MarkOw said:

Hi,

Wondered if anyone had any knowledge of how precise bhatinov masks need to be to work well. 

I was going to 3D print a few for my camera lenses and scopes but two possible issues.

1. My old 3D printer isn't the highest resolution, so the mask will not have perfectly sharp edges.

2. There seem to be different patterns available, some with more slits (harder to print accurately) and some with fewer slits (easier to print but does this make them less precise on focusing?)

Any experience on this would be useful, or should I just buy a set of commercially made masks instead (although seems less fun!) 

Thanks

 

Given that I used a craft knife to cut one out of a sheet of corrugated cardboard which was part of the packaging of a replacement washing machine, I would say that it doesn't have to be very precise at all.

It worked perfectly for months but started getting a bit tatty. It's replacement is 1mm thick stainless steel which should last essentially forever.

I confess that I had never thought that I would rule a fully functional diffraction grating with a craft knife. It is a shame that I don't have any pictures of it to show you.

27 minutes ago, MalcolmM said:

That's a good idea. I wasn't going to bring binoculars but I think maybe I should! I'm going to have to sacrifice some clothes

Clothes are over-rated. As long as you have enough to be decent and a change of underwear, everything else can either be laundered or purchased on-site. One tip is to wear far too much clothing when boarding the aircraft (3 or 4 pairs of undies and a similar number of t-shirts, for instance) and then transfer them to your carry-on baggage when you are airborne.

My experience, and that of several friends, anyway.

6 minutes ago, MalcolmM said:

Some good advice here. The few times I've been in truly dark skies, the sheer number of stars has left me utterly lost! To say nothing of the familiar ones being the wrong way round

Very envious of you hopefully getting to Starbase! Have a great trip.

Malcolm 

Same here from La Palma, which though northern hemisphere is far enough south to see Achernar and 𝜔 Cen. The stars, and the MW in particular, are easily bright enough to let me walk around the estate without any other lighting.

Although I have spent a couple of weeks in Oz at a conference where I took 15x80 binoculars with me, I am far from being an expert on the far southern sky. The two big globulars and both Nebuculae are well worth a look. The galactic centre, which is well placed from La Palma and further south though not from most of Europe is glorious. 𝛼 Cen is reputably an exceedingly good double but I've never seen it myself. It just about climbs above the horizon from El Roque but only because of the 2km altitude depresses the horizon and atmospheric refraction permits visibility below the theoretical horizon. I guess Proxima is worth tracking down if you have a small telescope or largish binoculars. Not impressive, other than its fame for being so close to us. You will need a decent finder chart because of its faintness.

I could also point you at some impressive galaxies, other than SMC and LMC, and other GCs but they probably don't meet your specs.

8 minutes ago, bingevader said:

Not sure how we'd have got it down from Macclesfield!

I note the smiling face, but do you really have that little imagination?  Renting a van is really not very expensive, especially in comparison with the cost of a fair-sized telescope.

27 minutes ago, PeterStudz said:

At home we are limited to the planets (which actually go down really well) and a few bright DSO. With this limitation enthusiasm can quickly dwindle. And a really a massive Dob in a light polluted sky isn’t really going to help. 

I am going to go out on a limb here and make a possibly unpopular comment which may get people mad at me.

Big Dobsonians can make very good imaging telescopes.

As an existence proof, I give Martin Lewis who uses an 18" Dob from a suburban back yard near St. Albans. He takes superb images of planets, many of which have won awards.. He's imaged the surface of Venus, for instance, through narrow band IR filters. He has picked up the brightest  ring of Uranus. He resolves details on the surface of the Galillean satelites of Jupiter. Any search engine will turn up examples of his work.

Martin uses an equatorial platform and a video camera. I claim that for some work the equatorial platform is not essential, albeit desirable, but the high frame rate camera is required to take decent images. Yes, the object of interest drifts across the FOV but a fair number of frames can be taken before the OTA needs to be moved in position for another set of subs.

Moral: don't write off anything until you have tried it for yourself, especially if others have succeeded.

Back in the day I had an 18" Dob from Beacon Hill Telescopes. Bad spherical aberration but I didn't much care because I wanted a light bucket for VS observing. It sat in a trolley and lived in a small converted shed on my back yard. Setting up was a five minute or less task. Did very good work from a light polluted site and was eventually sold to a group at RAL who wanted to build a lidar system.

I now have a 10" Dob here in the UK. I would like a large Dob (45-80cm say) over in La Palma but I need to get the rest of the kit out there in better shape first.

Is the (relatively) intact one still available? I'm pretty sure that if advertised here on SGL it would quickly find a good home.  I may even be interested in it myself.

Sad to hear this news.

Does anyone else make EQ platforms in the UK now that David Lukehurst no longer does.

Welcome aboard.

I should warn you, though, that we experience occasional outbreaks of sanity.

1 minute ago, TiffsAndAstro said:

I never of this, but after a quick Google I need to try myself. Even if it's tiny in my fov, just the idea of imaging an amazing example of gravitational lensing from my back garden is ridiculous

Good luck.

It is non-trivial but well within range of amateur equipment. Anyway, who is interested in trivial achievments? Depending on the size of your telescope, you may need to take subs over several nights. I managed it in under two hours.  Evidence at https://britastro.org/observations/observation.php?id=20230225_235430_a0cc7592c8804113

Perhaps I should take some more subs to improve the image.

15 minutes ago, bosun21 said:

I do like galaxy season and galaxies in general. I enjoy them in the eyepiece despite being underwhelming to a lot of observers. I also like them as EAA targets watching the image develop after each subsequent frame is stacked.

I also like some galaxies.  The Cosmic Horseshoe is a prime example --- two galaxies, one in front of the other.

28 minutes ago, Saganite said:

I would heartily recommend  a dome, and you know where I am so you must pop over and see how you feel about using one.

I am also in Cambs at the moment.  Please DM me your address and I'll likely drop by when convenient for you. I'd send you my address but don't actually do any observing in the UK. That said, if you fancy coming over for a pie and a pint ...

Paul

My experience is that a dome will give very good wind protection. It also keeps down stray light.

No experience, yet, with a ROR but intend to find out within the next year.

Asteroids are available all year round.  Ditto variable stars and double stars.

As are galaxies, for that matter.

The aurora was seen from as far south as La Palma! Pretty impressive from a geographical latitude of  29N and even more so when you realise that the geomagnetic north pole is over in North America.

https://tvlapalma.com/not/31479/espectaculares-imagenes-aurora-boreal-captada-anoche-desde/

We do these things not because they are easy but because they are hard.  JFK.

Easy is boring, IMAO.

Things what don't move are nowhere near as hard as things which do.  The CH, HVGC-1, and the like can be imaged for as many hours as it takes, on as many nights as it takes.  I've seen folk here bosting about collecting photons from a single object for tens of hours. That effort will easily pick up sub-20th magnitude objects with a 15cm aperture telescope. Indeed, I've seen on SGL a pretty picture of M31 taken with a 75mm refractor which showed stars and GCs in the galaxy down to somewhere about mag 18.

Much harder are objects which move significantly from night to night. Four hours on a 20cm will let you locate TNOs, asteroids, or satellites in the outer solar system down to below 20th magnitude or so, as long as you stack subs on the predicted motion of the object.

1 minute ago, Paul M said:

I've engaged in a few projects suggested by Paul (Xilman) and they have all been DEEP! But that suits my imaging and processing style. Not good a extended objects but I can eek out tiny, exotic subjects.

Exotic is good, IMAO.  I mean, who really wants to take the 13,572nd image of M31 or M42?  Show a bit of initiative and individuality, please!

44 minutes ago, Paul M said:

P.S. Don't listen to @Xilman, your imaging life will never be the same again! 

What on earth do you mean? 🤨

41 minutes ago, Taman said:

Interesting that the study involved taking several hundred short 30s exposures of M81, presumably to reduce the blurring effects from seeing. 

Actually because the autoguiding has never worked very well. This approach allowed me to dump the trailed subs.

Thoughts you want?  How about processing for faint stellar objects, possibly in grey-scale?  You should then pick up dozens of globular clusters.  I can tell you now that you already have several.

See https://britastro.org/observations/observation.php?id=20190311_020000_9a2c47fcf9f3ee97 for more information. I can provide a catalogue of GC positions and magnitudes on request.

It's taken a long time to get a round tuit but here is an image showing (208996) 2003 AZ84. It is a Kuiper Belt Object 44 AU away at the time of observation. Its magnitude was 20.3V.

Technical details: 0.4m Dilworth, unfiltered SX 814 camera, 3690s exposure in 123 30s subs median stacked on the motion of the KBO, start of observation 2023-03-14T21:00Z

On 2024-02-16 I read that the moon was lying close to the Pleiades. I already know that bright stars are easily visible through a telescope as long as they are bright enough and their position known.

Although my scope doesn't have absolute positioning the moon was easily visible through the finder and MaximDL would tell me its position at that time of day --- 13:30 local solar time. A 50ms exposure through a Sloan i' filter (to darken the sky background) showed nice craters. Syncing the mount to the lunar position told the telescope where it was pointing to around 10' or so.

Slewing to Alcyone showed nothing, which was not too surprising given that the field of view is only about 13'. Lots of slewing around at random produced some images containing stars. All contained a bright sky and lots of dust donuts. The starless images were stacked to produce a master flat.

Identifying the stars was not easy. Luckily one contained a double star. I know the image scale (0.6"/px) and the camera orientation (-177o) and so could estimate the separation at 9.6" and the PA at about 225o. I also knew the approximate image centre, to within 10' or so.

Lots of rummaging around in the DSS2 images, SIMBAD and the Washington Double Star catalogturned up HD23964 where the AB components are too close to be resolved with the seeing and the relatively poor focusing, but the AC pair has a seperation of 10.4" in PA 235o. Their I magnitudes are 6.74 and about 9.3 (estimated from R=9.71 and J=8.93). A very satisfactory match!

Another star in another image was somewhat brighter than the pair. 26 Tau, at V=6.46 and J=5.68, lay well within an arc minute of the predicted position. I am reasonably confident of this identification.

Here is HD23964AC

and here is 26 Tauri

You can see how well the impromptu flats have worked.

Given how easy it is to pick up 9th magnitude objects in the near infra-red with an exposure where the sky almost but not quite saturates the CCD, I think I’ll try to find some more Messier objects in daylight. Call me crazy if you wish.

Just now, vlaiv said:

Well, people do have good opinions on telescopes like Maksutov Newtonian and Schmidt Newtonian. Granted, those are full aperture correctors and not sub aperture correctors, but can be quite fast systems as well- often F/4-F/5.

Good point.  I was thinking of post-primary correctors rather than pre-primaries such as Schmidt and Maksutov correctors.

Note what I said about a meniscus lens. It describes  the important characteristic of a Maksutov corrector. Wikipedia has a good article on this topic, including the existence of sub-aperture correctors.

4 minutes ago, vlaiv said:

For newtonian with single curved mirror - it is true that spherical aberration increases rapidly with faster optics.

https://www.telescope-optics.net/reflecting.htm

For paraboloid - it's equal to 0 but for spherical with K=0, we can see that it is inverse of third power of F/ratio, so telescope has to be really slow, or have small diameter.

I don't doubt it. That's why I mentioned corrective elements. A Newtonian can be, but rarely is, corrected for SA with lenses in the same way as its coma (absent in a spherical mirror) can be and usually is in fast systems.  On the same site as my Dilworth is a 0.5m f/3.5 Newtonian astrograph which absolutely requires a coma correcting refractive element.