What's the limitating factor as I go up in magnification?

[chiefgibbon]

Hello all,

So I've been playing with my new SW Heritage 130p for a few weeks now (on the rare cloud-free occasions), and the eyepieces and free Barlow that came with it, and getting used to it all!  I'm really pleased with the scope (although it's not quite so universally 'better than binocs' as I'd probably expected - I'm getting used to that too). 

I'm trying to understand what's limiting my views as I use the higher magnifications.  I have a 25mm, 10mm and 2x barlow.  I find that I can't seem to get sharp focus with the 10mm + barlow.  Both EPs on their own produce a fairly crisp image, and the 25mm with barlow seems fine - in terms of clarity it's hard to decide between the 10mm vs 25mm + barlow.  However when I go to 10mm + barlow, even on a bright target like the moon (or during the day looking at a distant building), it's as though I can't get proper focus.  Everything's fuzzy.

I'm not necessarily looking to buy / upgrade anything, really I'm just trying to understand what's the limiting factor.  The highest magnification gives me 130 x I think, which should be within the limitations of the scope size and optics?  Assuming so, from googling around it seems like it could be:

 - seeing conditions

 - eyepiece or barlow optics

 - focuser

 - lack of skill

 - I guess it could be my eyeballs!

And I don't have the experience to decide which!

Can someone offer me any clues?!

regards

[cassiewoofer]

Probably seeing conditons.

In the last year that I've been looking (mainly at Jupiter/Saturn) I've probably only had one great night seeing. I'm fairly close to the city, so there's also lot's of heat from there which must have a large effect.

[Schorhr]

Hello Chiefgibbon,

the Heritage has an aperture ratio of f/5, so collimation is key to get a sharp image at higher magnification. But the problem may be the barlow and the mediocre kit eyepieces, so don't worry :-)

As Cassiewoofer posted, seeing conditions are often the limiting factor, especially if you view out of a window or a balcony or view an object above roof tops, the rising heat will cause aditional air turbulances.

Another issue is the heritage's mirror. On a german forum some have examined theirs with different methods. Overall they are of acceptable quality for the price, not perfectly parabolic though.

10mm with 2x barlow = 150x should be possible though on most if not all Heritage telescopes... And a magnification that should work many nights.

For example I use 200 and even 260x quite often, but when Saturn was low to the horizon, 100x was the most I could use before having similar troubles.

Now the first reflex would be to get a better barlow, but really, all of them decrease contrast a bit. And good barlows can easily cost as much as one or two good eyepieces...

Even the 27gbp 66degree eyepieces will have better results as a cheap ep+barlow combination, though of course not as magnificent as the BST or TMB planetary eyepieces for 40-45gbp.

So for now just try another night, or during the day with something not too far away to limit seeing trouble.

Good luck!

[chiefgibbon]

Thanks Cassiewoofer, Schorhr

So I guess it's most likely either the Barlow + EP, seeing, or both.

Collimation is almost certainly not perfect, but I did buy a laser collimator and have tweaked the collimation so that (1) the red dot appears within the marker on the primary and (2) the red dot dissapears down the hole on the target and also (3) the secondary mirror is centred in the scope pretty well.  So shouldn't be too bad.  I've found the scope actually holds collimation quite well through being opened and closed repeatedly - I confess I didn't expect it to!

I live in Taunton, not exactly a city (!) but a large town, and yes I'm viewing over rooftops.

So if I go out of town on the next reasonably still, clear day (during the day), and view something like trees or a building a few hundred metres away, would that eliminate seeing as the cause?  I.e. over a short distance on a calm clear day would seeing drop out of the equation?

I know I'll end up buying some better EPs one day, but I'm kind of keen not to do it until I've got a much better feel for the performance of the ones I have, what I'd get by upgradging them, and how much it's worth spending (and I understand the SW ones are OK as packaged EPs go). 

As an aside, why are some eyepieces called 'planetary', is there something about them that makes the unsuitable for deep sky targets, or just the magnification category they fit into?

Thanks!

[Schorhr]

Great, sounds like collimation is well then :-)

Yes - it's amazing how well this telescope keeps collimation.

Sounds like roof-top seeing ;-)

You could just point up and view polaris, try if you can get it into focus. Polaris won't move out of sight, and it's (more or less) up high, limiting air turbulances from houses and it's less athmosphere to look through then when looking at something close to the horizon.

Yes, the 25mm eyepiece is Okey, and the 10mm won't make you blind either. But it's really a difference to have a nice wide angle eyepiece... Viewing a full moon completely at higher magnification for example :-)

Eyepieces such as the HR Planetary are called this way, as they offer short focal lengths such as 2.5 or 3.2mm. A 8mm HR Planetary for example will work perfectly for deepsky objects, better then the 10mm Super/SW.

Just don't get any Plössl <10mm. The short eye relief is no fun, at 4mm it's impossible to view through comfortably- making it hard to see anything at all.

Most modern eyepiece designs do include a own barlow element, but compared to cheap-o-barlows the lens design is calculated for the eyepiece. By changing the distance between the barlow element to the eyepice, you can change the magnification by the way (in certain limits of course).

It works with HR Planetaries, the shorter focal length 66degree swa, even hyperion eyepieces, and many more.

It's possible to do this with a barlow and the 25mm SW eyepiece to experiment too, I did this a week ago or so.

This is also how the "Astrozoom" adapter works, or the zoom eyepieces out there.

Usualy a fixed focal length eyepieces has benefits, and you rarely need more then 3-4 magnifications to get started.

It's a good decision that you don't want to spend much right away.

So when you decide to get new eyepieces, don't buy them all at once

[chiefgibbon]

Yes, the 25mm eyepiece is Okey, and the 10mm won't make you blind either. But it's really a difference to have a nice wide angle eyepiece... Viewing a full moon completely at higher magnification for example :-)

I am resisting temptation.  I am resisting temptation!

I'll have a go at getting polaris in focus once the wind and rain has stopped!

Thanks for the info on EPs.  When I do get the upgrade bug I'm likely to do one at a time, replacing the 10mm first.  However right now I have a lot to learn with the EPs I've got, and anyway I think the first thing I'd like to buy is a rigel finder.

Just googled the Sumerian Optics scope from your sig, looks amazing! What does it weigh and how long does it take to set up?  Well out of my price range I'm afraid, just curious;-)

[Schorhr]

Hello,

good choice, the telrad or rigel will make things much easier.

:-)

The 10" Sumerian weighs 9, 9.5kg (depending on the configuration), takes 10-15 minutes to assemble depending on my clumsiness... ;-) But amazing and fair priced... And really my only option if I travel by bike or foot.

[AlexB67]

Hi ChiefGibbon

I would say the red dot finder is quite adequate on the Heritage and easy to use, that coupled with a 25mm is enough to locate things with some practice, I find personally anyway. It may be worthwhile just practicing with it some more before changing it, how to look through it correctly and avoid parallex, but after a while you get the knack.

The telrad I would warn in advance, it will be big and could even upset balance on that scope, you'll be limited to where you can put it on the Heritage, as I found out even on a 10 inch flextube Dob it is not something you can just put where you want. I would say a telrad is not ideal for a small scope such as the Heritage. The Rigel would perhaps fit somewhere where the old RDF would be. I can check that for you as I've got a rigel on order for my bigger scope. I have no intention of using it on the Heritage myself though, but I can see if it could fit somewhere where the old RDF sits normally for you if you like.  such an addon could possibly also go further back on the lower part of the OTA, but that may make it awkward to use, especially if on the ground with the scope as I often found myself using it that way  .  It is handy to have the RDF or whatever finder you use somewhere near the eyepiece however.

[TenBears]

Hello.  My first post...  but, generally speaking...

What's the limitation factor as I go up in magnification?

Use Aperture (mm x 2) or (inches x 50) - as a general rule to calculate your scopes maximum magnification (that you should use).  Ignore what the specs say.

So, 130mm max mag should be at 260x,  a 6" would be 300x.

A lot of variables come into play, but that is just a general guideline.  But, getting close to those maximum numbers requires overall Really GOOD everything.

[TenBears]

And now, I realize that was not what he was asking.  lol, ignore my noob ars.

[brantuk]

On a clear night with good transparency and from a very dark site, I would expect to get around 200x mag out of the Heritage 130P.  With the ten and barlow it should be capable of 130x with no problem using a reasonable quality eyepiece. However the standard 10mm supplied with these scopes isn't the best, and the barlows tend to be not so good either - you'd be pleasantly surprised with the difference a good quality 5mm eyepiece could make with this scope.

Bear in mind that when you magnify an object you also magnify any imperfections in the atmosphere which will make the object appear fainter and grainy. Also consider the amount of atmosphere you are looking through. At elevations near the horizon, the atmosphere is denser, whereas at higher elevations you are looking through thinner atmosphere - and that's quite apart from looking through heat haze off rooftops.

Also think about light pollution - if you're viewing from a built up area, a shroud and a dew shield will help there. And the notion that lower f-ratios (below f-7) become more demanding on the optics - an f-5 scope will be less tolerant of the cheaper eyepieces (of which the supplied10mm is usually a good example). Hth

[Moonshane]

the limiting factor for high power is the weakest element in the optical train and the observing conditions. the optical train consists of the lens or mirror of the telescope, the eyepiece and the observer's eyes. the observing conditions include how clear the sky is (transparency) how steady the air is (seeing) and if there is any local light pollution.

you might have the best scope in the world and top notch eyepieces but if the seeing is poor, high magnification will not be possible. you may have good seeing and good optics but if you are shattered after a hard week at work, you/your eyes won't be on top form. you may be inexperienced and not know 'how' to observe at high power. everything might be spot on otherwise but you have a poor quality eyepiece which lets you down on the best night for ages as you want to see the moon/Jupiter at high power.

your optics need to be collimated (as in the case of some scopes including yours), cooled (or warmed) to the same temperature as outside, free of dew and shielded from light.

the answer to your question really is everything. it's amazing we get any sort of views really but consider the following:

1) improve the things you can affect - collimation, cooling and optical quality. give yourself time to collimate and put your scope out for about 5 minutes per inch of aperture for high power. I tend to start observing straight away at low power and work my way up as the scope cools. buy the best optics you can afford. to me, eyepiece quality makes up at least 50% of the quality of the view.

2) adapt to the things you cannot change - seeing, transparency, local light pollution. if the seeing is poor, choose targets which require lower powers (open clusters, galaxies, nebulae). if the transparency is poor, choose bright objects which need higher powers (planets, moon, double stars). thankfully when seeing is poor, the transparency is often good and vice versa. try to observe from a place where there is no light pollution (a darker site) or in a spot in your garden where lights are less of a problem.

ultimately you need to just do your best and as with most things in life, it's all about compromise. e.g. you can get the quality of a 100 degree field eyepiece costing £300+ second hand but with a 50 degree field for about £50 second hand. quality does not need to cost the Earth.

[Moonshane]

sorry I realised I had not mentioned about 'how' to observe at high magnifications. even when seeing is good, optics are good and the observer is fresh and experienced, the image of say Jupiter at 200x is not 'solid' and stable all the time. you are looking through atmospheric soup and the effects are increasingly worse the lower in the sky the object is. you will find that the image wavers in and out of sharpness as though someone is flexing it in and out of focus. this is normal and to be expected. what you need to do is find the best focus point and then leave it alone.

then watch as the image comes in and out and 'soak up' the detail. eventually with more experience you'll register the detail more and build up a bank of images in your head resulting in you eventually seeing the image as a whole but in your mind. sketching is a good way to concentrate on one or two features and get the best from them but takes practice.

[ronin]

At this time the main limiting factor will be the barlow and eyepieces, they just are not that good.

Seeing conditions come in the form of turbulance and transparency. Transparency is fairly obvious - high cloud and mist, most probably that the main stars get through but not the fainter ones. Turbulance easy way to look for is "Are the stars twinkling?" if they are then the atmosphere is somewhat turbulant. They will however always twinkle to some extent.

Focuser should not be a problem if it is on straight/flat.

Skill, like everyone you learn useful bits.

Eyeballs, probably a more common problem then many admit, usually associated with assorted bits failing and getting old.

Do not go expecting the many large magnifications mentioned. All the mirrors and lenses in our instruments are not ideal, so what comes out is not ideal. Being a small diameter fast mirror your's will have a fair curvature to it, which is difficult to make.

For a "high" magnification eyepiece look to getting a 5mm for 130x. You will need a reasonable 5mm and most 5mm plossl will very likely not be good enough. That leaves ones like Celestron X-Cel's, WO SPL's, BST Starguider, TMB's (not 100% convincesd of the TMB against the previous 2). BST's have a wide angle eyepiece that is available at 5mm (I think) just no idea of how good.

A 5mm as one of the above should be fine.

If more then that you are looking at 4mm and 3.5mm, I would not suggest thinking of lower then 3.5mm. Minor hiccup is not many 4mm eyepieces, and personally I would have doubts of a 3.5mm in the scope. The alternative is a good eyepiece and a good barlow, means buying 2 bits. An 8mm and 2x barlow would give 4mm. Catch is if 4mm doesn't do it, then a 5mm mightl, so you could want a 5mm as well and welcome to the world of collecting eyepieces :grin: . The change between 5mm and 4mm sounds insignificant but it is really a 20% change.

[chiefgibbon]

Hello,

good choice, the telrad or rigel will make things much easier.

:-)

The 10" Sumerian weighs 9, 9.5kg (depending on the configuration), takes 10-15 minutes to assemble depending on my clumsiness... ;-) But amazing and fair priced... And really my only option if I travel by bike or foot.

Or, for me, for packing into a small space in the car for camping trips with the kids!

Looks like one of those rare objects you'd be proud to own.

[chiefgibbon]

sorry I realised I had not mentioned about 'how' to observe at high magnifications. even when seeing is good, optics are good and the observer is fresh and experienced, the image of say Jupiter at 200x is not 'solid' and stable all the time. you are looking through atmospheric soup and the effects are increasingly worse the lower in the sky the object is. you will find that the image wavers in and out of sharpness as though someone is flexing it in and out of focus. this is normal and to be expected. what you need to do is find the best focus point and then leave it alone.

then watch as the image comes in and out and 'soak up' the detail. eventually with more experience you'll register the detail more and build up a bank of images in your head resulting in you eventually seeing the image as a whole but in your mind. sketching is a good way to concentrate on one or two features and get the best from them but takes practice.

Thanks Moonshane and for your previous post, I hadn't really got this idea before!  Great description!

[chiefgibbon]

Hi ChiefGibbon

I would say the red dot finder is quite adequate on the Heritage and easy to use, that coupled with a 25mm is enough to locate things with some practice, I find personally anyway. It may be worthwhile just practicing with it some more before changing it, how to look through it correctly and avoid parallex, but after a while you get the knack.

The telrad I would warn in advance,...

Hi AlexB67,

OK maybe I need to practice more!  I have found it difficult to find objects that I can't see with the naked eye, for example the other night I was trying to find M13 (which I _really_ want to see well and haven't yet) - found it OK with the binocs but had real trouble getting the scope on it (and didn't manage before it clouded up).  I figured the circles on the rigel would help! (I'd gathered the telrad would be too big / heavy).

Anyway yes please I'd appreciate your thoughts as to whether it would go OK on the little scope!

[chiefgibbon]

OK so to summarise:

My scope is easily good enough for 130x, provided it's fairly well collimated (I think it is).

Light pollution is an issue for me for sure, I have one horrible, horrible street light blaring into my back garden.  A shroud is on my todo list    I will also look into a dew shield.  And a catapult. (No not really officer.)

But it seems like the concencus is that seeing and EPs + barlow are the main factors.  I'm still not going EP shopping yet!  But when I do a nice 5mm will be first on my list.  I'd rather spend a bigger amount on something I can keep and use for a long time with future scopes, so he ones you mention Ronin sound fine.  The Baader Hyperion's seem very well regarded but cost quite a bit more; how much to spend will be something I'll have to give some more thought later.

I would just also like to say what a brilliant forum this is, quite possibly the most helpful bunch of folks I've ever encountered on the interweb!

[stevend]

But when I do a nice 5mm will be first on my list.  I'd rather spend a bigger amount on something I can keep and use for a long time with future scopes, so he ones you mention Ronin sound fine. 

I would consider a BST 15mm, it is a nice EP. That would give you an EP to supplement your current ones and assess how well it works with your barlow, then maybe get the BST 12mm (to barlow to 6mm).

[umadog]

I don't want to derail the thread, but watch out for the Hyperions: they only work well in slow scopes. On faster scopes they're dreadful and very astigmatic in at least the outer third of the field. There are few compelling reasons to buy one, given that there are cheaper eyepieces that perform better. I don't know how the prices break down in the UK, but in the US the Explore Scientific 82 degree eyepieces are substantially cheaper and beat the Hyperions in every way but eye relief (which I think is about 5 mm longer for the Hyperion). The 68 degree ES eyepieces have longer eye relief than that 82. I don't know if the ES are available (relatively) cheaply in the UK, but there will be equivalent designs that are.

[chiefgibbon]

I would consider a BST 15mm, it is a nice EP. That would give you an EP to supplement your current ones and assess how well it works with your barlow, then maybe get the BST 12mm (to barlow to 6mm).

So many things to buy, so little cash!

Slotting in an EP in that range does make some sense actually, I hadn't considered that; an alternative approach to consider.  Thanks!

One of the reasons I've decided not to buy anything for a while is that both the  there are so many ways to approach

[chiefgibbon]

Hmmm I don't seem to be able to edit the escaped half complete sentence off my last post... please ignore!

[Schorhr]

Hello chiefgibbon,

M13 and other smaller DSO can be tricky, but be patient and make sure you take som sort of map or note to find an object along. This can be "turn left at orion" or printed free maps.

M13 can be a bit of a disappointment... While it's probably one of the famous "beginner objects", it's really not all that great in low magnifications especially under light poluted skies. You may note that it is just a smudge then, but with averted vision, all of the sudden the little cloud's outer region does resolve into hundred stars.

hχ is awesome to view, especially with kids.

Consider a 30mm el-cheapo-Plössl (Orbinar, 13gbp or so) with self-build eye-cup, or 32mm Plössl (TS for example) - It will make searching easier as it will show the maximum field of view on the 1.25" focuser and is cheaper then a 24mm wide angle eyepiece.

Of course practice does play a role. I was pretty frustrated finding the ring nebula the first time with the red dot finder, especially as the light pollution didn't even show the whole lyra constellation here.

But boy, was it an amazing view once I found it.

Ever since it's so easy to find, as I now know exactly where it is, and what to expect seeing in the eyepiece at lower magnification.

The Freeware Stellarium's eyepiece/telescope simulation helps a lot to practice searching and teaches one what to expect with a certain eyepiece's field of view.

I allways take my Binoculars with me, as it can help to locate an object and navigate up or sideways until I have a bright star in the view, so I can just trace the route with the heritage then.

Especially useful if I didn't bother taking my maps along...

I have not tried to fit my telrad on the heritage yet due to lazyness (it's on my other scope) and the red dot finder is not bad - for most objects, but sometimes it can be tiresome.

Do the light-shroud mod (just cardboard that slides into the tube for transport), and you will be amazed what difference a darker location will make.

M51 for example looks fascinating from a dark place, while from my balcony it's hard to find at all...

And even bright objects such as the open cluster M44 looks so much more impressive when it's dark...

But still, the heritage is great to just drag outside infront of the house, or on the balcony. I don't want to miss it's portability. The best DOWNGRADE I ever made. It is true, the telescope that's used the most is the best telescope!

:-)

Regarding eyepieces (again), no rush, and consider different options. None of the entry level eyepieces will work great if you ever upgrade to a even faster telescope (f/4.7 for example), but even the 27gbp 66degree eyepieces (just saw them for 19gbp at aliexpress, and that's below most EU countries duty/tax-free-limits...)

The 6mm is a nice eyepiece, the 8mm HR Planetary a bit better, but it's amazing to view the moon at 108x COMPLETELY in the view with the 6mm.

Plus if you like tinkering, both the TMB and 66deg can be extended to increase magnification. Either with the commercial Astrozoom adapter or simply a tube from the hardware store.

As the lower focal length eyepieces mentioned have a barlow element their performance is not too bad at f/5, though if you can and want to spend as much as your telescope costs for a single eyepiece, something like the ES are awesome for the price I take it.

Though even with the 25 and 10mm from the Heritage amazing things are possible.

Patience, a dark location and interest will show much more then the best eyepiece in the wrong hands :-)

Often, buying more equipment is what happens when the weather is bad long enough or if we are looking for an excuse for not going out more frequently It's not like there is not enough to see out there...

[AlexB67]

So many things to buy, so little cash!

Slotting in an EP in that range does make some sense actually, I hadn't considered that; an alternative approach to consider.  Thanks!

One of the reasons I've decided not to buy anything for a while is that both the  there are so many ways to approach

One thing SGL is very good at is spending your cash  in no time at all . 

Coming back to finding things in the sky with the RDF, Yes the rings will help, that being said with the Heritage the technique I use for finding the easier targets I'll describe. None of the harder easier targets like most of the Messiers I have ever held a chart in my hand outside. Some will say this is a necessity and you will not find anything without it,  For more difficult targets it is handy for sure but I would not agree with that it is needed a lot of the time once you develop a feel for the sky.  One you visited some targets more often you'll remember it anyway.

I often have quite bad light pollution, sometimes better than others  and I need to make do with the brighter reference stars that can be some distance from the actual target and no finder scope, just the RDF.  For example M31, I use a few brighter reference stars with respect to Pegasus and cassiopiea, Mirach and one brighter one above I can usually see, with practice in Stellarium I have a good look at the geometry and develop a feel for the spacing. When I am actually out under the sky I have  no chart or stellarium,  for most targets I prepare this way inside beforehand, make a mental note of what the sky looks like or even a scribble on a piece of paper with some stars for newer trickier targets and bits of sky I do not know well for the newer targets ( Of course for difficult advanced stuff this will be next to impossible without a chart).

Outside I take a step back from the scope. I  look up and imagine where M31 would be, it helps if you can see it naked eye but if not imagine it there, I then look through the RDF and sweep to that point, use peripheral vision around the red dot to see the other reference stars around it to nail the location where I think it is.  With a 25mm you have about 2 degrees of FOV so usually I find I am very near if not straight away, if not, within a short space of time I find it very quickly by searching around that spot for a little bit with a lowest power eyepiece, in my case that is a 25mm that offers  2.3 degrees, but the stock eyepiece offers 2 degrees, so not vastly different.

I got the rigel delivered today and where the RDF is located I don't think it will just fit out of the box, at least the mounting bracket would not work that is shipped, that is not to say it cannot be done, but obviously on the Heritage there is very limited space where the RDF is to tape it on there.  I'll have a more careful look for you later and let you know, this was just a very quick look at the rigel when it came in the post today,  and a quick walk over to the Heritage to see.

[chiefgibbon]

Hi AlexB67,

Your technique is similar to how I try to find things but I guess more practiced .  I find Stellarium good for virtually looking around and getting a feel for where things are (and also Mobile Observatory on Android, which I play with during quiet moments out and about); although I do like paper charts, I do a fairly technical job during the day and I like my spare time to be quite analog!  I have Nightwatch which I really like, plus the S&T pocket atlas which is probably a bit advanced for me just now.

So I'll go practice then!  (If ever the rain stops).

It certainly doesn't help having a street light in view from my garden because it stops my eyes from adjusting properly so I can only dimly make out the fainter stars, I'm thinking about some screens to block the light.  So for example in finding M31 I can usually see Mirach, but usually only just make out mu or nu when looking with both eyes; then these fainter stars kind of dissappear from view when I look through the RDF even though I do keep both eyes open.

I know what you mean though, and I can find some targets quickly and reliably (like M31, the Double Cluster, and a couple of beautiful doubles in Lyra and Draco).  I know the list will grow with time.