wulfrun

6 minutes ago, ashm4n said:

I know the focal length is measured only when extended. However usually the focal length corresponds with the depth at which the mirror is located in the tube and hence the maximum angle at which light can enter. Therefore bigger focal length results in a narrowed angle and hence smaller FOV. So if we do not cover the extended part, while focal length is 650, the mirror is in the bottom of a smaller 40ish cm tube, so doesn't that result in a larger angle and therefore larger FOV?

I might be wrong, I'm just stating my reasoning for you guys to correct my mistake if I am.

No, wrong, sorry. Take the mirror out of the tube altogether if you want, the focal length is not changed. Any light reaching it from wider angles will simply not reach the focal point. Indeed, any such light will be only a nuisance.

25 minutes ago, ashm4n said:

Sidequestion.

The collapsible Heritage can retract and extend the focal point. However the sides of the extender are empty, so does that mean it has a focal length of 650, but the field that you see is as if the focal length was ~400 (or however long the tube is) since that's the actual depth at which the mirror is located under the entrance of the tube, and the real restriction regarding the maximum angle at which light can enter?

No, the focal length of the 130 Heritage is indeed 650mm, f/5, it's determined by the mirror curve and nothing else. If you don't fully extend the upper part you would simply push the focal point so far beyond the focuser* you would not get an eyepiece anywhere near in-focus. Likewise the Heritage 150 is a 750mm, f/5.

They are simply collapsible for storage, so they are half tube (roughly) and half open in use. A shroud is easily made and very advisable, to enclose the extending part when in use.

* and simultaneously lose a lot of light since the secondary mirror is now too small for the light-cone

2 hours ago, ashm4n said:

I understand the difference between the 90/900's f/10 and the 90/660's f/7-ish.

I've been reading up on Barlow lenses and Focal Reducers, of which I see the former being much more prevalent.
Correct me if I'm wrong, but a 2x Barlow would effectively make the 90/660 into a 90/1320 of sorts. In that case would the 660 have more versatility with just that extra Barlow?
Also, does the Barlow lens hinder the quality in a way? For example would a 90/500 with a 2x Barlow be inferior to a 90/1000? If so, in what way? Color? Resolution?

Your calculations are correct on the Barlow use. But (there's always a but!) a 90/900 would have lower chromatic aberration, assuming equal quality. So the Barlow would not correct for that. A good Barlow should be "invisible" in the sense that you shouldn't notice it besides the increased magnification. There's more glass involved, so a loss is inevitable but it's slight.

With a small budget, I agree that you'll get more for your money with a dobsonian reflector, as mentioned above. Don't let collimation scare you, it's intimidating when you read all the stuff about it but the reality is that its not scary at all after a couple of times. Anyway, if your scope doesn't get knocked about it'll never be more than a small tweak and often nothing required.

If you're dead set on a refractor, you might find one second-hand?

Oh and welcome to SGL, keep asking the questions.

Another vote for the 150 over the 130. It gathers about 1/3 more light but takes up barely any more storage space, if you can afford the difference it's the better choice. They are highly capable scopes that will show you a great deal. (Yes, I do have one so I could be biased).

2 hours ago, Gonzo0 said:

Cheers mate, thanks for your input on this post.

Oh yes, that's another can of worms ready to be opened I'm sure when the time comes 😅

As for the finder, that right angled one looks good and I can see it'd be a lot handier to use. But the problem I have with my finder isn't really anything to do with having to crouch down to get a look through it if, say, I'm trying to find something in at the zenith. It's more an issue of it being too magnified, sort of acting like it's own mini scope which can sometimes make it hard to know where exactly I'm at especially as I am trying to learn the constellations at the same time. I think something like a telrad might be better suited for me as when looking into a red dot kind of sight it doesn't black out your peripherial vision, which I think will help in aiming at the right target as I can use it just like aiming a gun or something along those lines. The circles within the telrad will also be a big help too I'm sure. 

If you get a Telrad or equivalent, leave the finder on too. A lot of folk (myself included) prefer both. Swing around till the Telrad gets you close, then the finder gets you pretty much bang on target.

1 hour ago, Mandy D said:

BTW, that is a small transformer. 😁

It's a case of context, no? It's tiny compared to (say) a power substation transformer. In a domestic appliance setting, it's getting pretty big (probably 400VA ish?). Small, in terms of a thermal fuse being the only option for safety, is somewhere up to around 15-20VA. A properly designed setting using a 400VA transformer shouldn't require a thermal fuse and I'd be mightily miffed if the designer cheaped-out by using one (of the buried-in-windings, non-replaceable type).

1 hour ago, Mandy D said:

Don't count on it. Because this is an integral part of the transformer, it might not be shown on a schematic.

Unlikely in a transformer of that size. Besides, if it were there and it tripped it'd be a dead transformer now. They are put into small transformers because it's not feasible to protect them with a normal current-fuse. A large transformer can and should be protected with a normal fuse.

16 minutes ago, Clarkey said:

Fair enough. I shall bow to the superior knowledge of @Carbon Brushand @wulfrun.

As a chemist I shall crawl back in my hole🤣

I'll let you into a 'secret'...I was an industrial chemist in a previous career, so my qualifications are in chemistry too! Electronics though, has been a 50-odd year hobby so I've studied that (non-academically) probably more than I ever did for my chemistry qualifications. No need to crawl back in any hole, you probably have knowledge in areas that would baffle me.

46 minutes ago, Clarkey said:

I appreciate that it is not steady state current, but to draw more than 5 amps even at start up still seems excessive. Without any other demand the mount takes very little and I'm not sure what would take it above 5A. Having said this, the quality of SW soldering leaves a lot to be desired so who knows what "special" load they have added😂

Wouldn't surprise me one bit. A single moderate-value (470uf) electrolytic capacitor has an ESR in the tenth of an Ohm range and that's all that limits the 'surge' at switch-on, other than wiring and pcb-track resistances. It would therefore like to draw about 12/0.1=120 amps, albeit very briefly. Admittedly, pcb & wiring will add resistance so it'll not be anywhere near in reality. However, a sprinkling of decoupling capacitors dotted around a board (highly likely) means that a lot of electronic gear, even low-voltage gear, can have inrush currents in the tens of amps. Enough to blow a quick-blow fuse for sure.

7 minutes ago, Mr_Smith said:

F5AL250V

It's a quick-blow fuse. I was about to ask what was on it but beaten by @Carbon Brush

The F means fast, so it blows quickly on any surge/overload. I'd get a slow-blow/anti-surge type, it'll be marked T5A not F5A.

EDIT: we may have found the problem!

Ah OK, that adds to the confusion then! If the mains power supply works fine, then the mount must be OK with no power shorts. No need to start messing there. In that case, logically the 5A fuse is inadequate. It's not unusual for electronics to have a current-surge at power-on but I'd be very wary of just upping the fuse rating.

What exact type of fuse is the one that blew? Is it definitely the recommended fuse?

OK, kind of not unexpected. Next step is to get at the power leads inside the mount and trace back then. Once inside I'd expect an obvious short somewhere since you know the mount works. Sadly, it's not my area of knowledge and you'll have to wait for someone else to guide you on it. Before doing so, just double-check if the fault is present with mount switched OFF as well as ON. If it's still there with the mount OFF it pretty much narrows it down to the mount's power socket itself.

If you power it from mains, are you still using the same 12V socket on the mount? Just realised that that would be puzzling if it works OK that way.

Next step would be to take meter readings on the mount then (no power applied). Use the Ohms range and test both ways with the meter leads. If you can't easily get at the mount socket terminals, use your lead and test the cigar-end. Just to repeat...the powerpack is NOT used or connected at all for this bit.

22 minutes ago, Mr_Smith said:

So I’m guessing the 10amp output was too much. I always thought that the mount would only draw the amount of amps that it needed though. Or am I completely wrong? 

No, you're completely right, the mount draws what it needs (provided there's an edequate supply).

9 minutes ago, Mr_Smith said:

Thank you, I do have a multimeter. The fuse blew as soon as I turned the power pack on. The fuse that blew was 5amp 

OK, so everything was connected up before switching on at the powerpack? I'm not familiar with the mount, it'll have a rating marked on it...is a 5A fuse enough (I'm guessing it's plenty)?

Use your test meter to check the lead first of all then. Continuity along both conductors, the polarity can be verified and no short between the conductors. If that checks OK, replace the fuse, plug the lead in and don't connect the other end to the mount. Switch the powerpack on and the fuse shouldn't blow. If all's well up to then, the fault is in the mount as some disassembly will be needed but let's see.

First off, do you have or have access to a multimeter? It'll be pretty indispensable to have one and you don't need an expensive, all-singing one.

Are you sure the lead delivers the correct polarity? When exactly did the fuse blow? Was it when you plugged it into the power pack, when you plugged the other end into the mount or only when you switched the mount on? What's the rating marked on the blown fuse? (Not what it should be, but what it actually is).

You need to troubleshoot methodically to find the fault and the first thing to note is NOT to keep replacing the fuse and blowing it again, you may well do (more) damage.

1 hour ago, DaveS said:

I should have been clearer. My mild scepticism was about the practicality rather than the principle of MHD.

Well founded scepticism, I suspect. One problem would appear to be generating enough electrical power, which got no mention. I'm not convinced it'll work in space on "virtual particles" either. The video seemed very fanciful with too much dreamy music and too many cgi, futuristic-looking ships and no demonstrations of any working reality.

1 hour ago, DaveS said:

To get this back on track

Anyone with better physics than me @Macavity? want to take this apart and debunk it?

MHD is a thing, it's been been known about for a long time. Nowt wrong with that aspect from a science point of view. Whether it's useful & practical in this application is a different matter.

Seems to me that all our ideas so far involve throwing "stuff" out of the back, at as high a velocity as possible. I'm aware that we don't know of any alternatives but it's a severe limitation since you have to take said "stuff" with you (on a practical basis and at least to start off). Perhaps this is where the next leap will be, with either new physics knowledge or lateral thinking. I can't see how serious speeds can be attained without a new concept, which means we're stuck at the not-yet-practical stage for covering astronomical scales of distance.

2 hours ago, Mandy D said:

I was honestly surprised when I looked at who had posted that silly response and saw it was you! 🙃 I'm sure I'll post something just as silly before too long. The comment is now immortalised ...

Guilty as charged...one of those instances of engaging fingers before brain!

1 minute ago, Mandy D said:

Sorry!

No problem, I'll go hang my head in shame 🙂 Even more so as I also use a full-aperture filter!

Just now, Mandy D said:

Newts are absolutely fine for solar. I use a 250 mm one for solar observing. You just have to place the filter at the opening of the tube so the mirrors only get a factor 10E-5 of the light and heat.

Yes, I realised what I'd put and removed it. Too late, you quoted too quickly!

Erroneous post, please ignore

I spent best part of three hours looking (mostly) at Saturn and Jupiter, I got the best views so far this year. I had the 150PL out.

Started on Saturn since it was further south, higher and nearest towards disappearing behind the neighbour's roof. I used a 9mm to start with, in which I could just make out Cassini and what looked like the ring-shadow or banding, not sure which. Titan was easy and at least 4 other moons were visible, either directly or with averted vision and at least some of the time. I upped the mag with a 6mm planetary EP, which pretty much lost me the smaller moons but made the Cassini division a doddle, if a little wobbly, though it took the power pretty well (x200).

Moved on to Jupiter and went back to the 9mm, which just got me all 4 of the galilean moons in the FOV with some spare framing. Banding was obvious but no sharp detail and no GRS around, sadly.I did try the 6mm but the view got worse so I stuck to the 9mm. I noticed one moon getting (visually) closer to the planet, assumed it was Io but nope, checked later and it was Europa. Carried on watching and eventually was rewarded by what I thought was a black dot on Jupiter, the moon's shadow, around 12.30am. By 1.30am it was unmistakable, maybe 1/3 of the way across and Europa was about to be swallowed by Jupiter's glare.

Getting a bit late so I thought of packing up but then realised Mars was well over the rooftops so I had to look. Sadly it was still in the "mush" zone so not really anything to see beyond a red blob. I fancied the colour wasn't even north/south but that might well just be atmospheric effects. I consoled myself with a quick look at the Pleiades and Hyades, above and below Mars and then packed up.

Interesting that they've gone for AAA batteries rather than AA, although the Telrad's AAs last so long there's a risk they'll leak before you actually run them down. Can't say I like the styling (personal opinion) but if it functions well you don't have to see the styling in the dark! How does it compare on price? And does it have built-in flashing mode?

18 minutes ago, globular said:

Thanks for the suggestions.  I have the same thoughts but just can't find appropriate parts in my google searching. I can see this ending up in a 3D printer purchase.... 🙃

Ask @DaveL59 where he got his copper tape for his lens repair, covered in this thread. There may be thicker/wider grades available (what he used is probably too puny for your idea):