How far can you push a Skywatcher 130?

[CumbrianGadgey]

It's okay, i'm calming down...I am...really I am...any minute now, I'll be so settled that i will almost be able to sit down.

Ahhh! that's better. You see, the thing is, I got a new scope and was happy with it but thought it could do better. Armed with the kind and enthusiastic advice from SGL and Alan at Skies_unlimited, I settled on BST starguiders. My kit is now:

Skywatcher Explorer 130 newtonian, F7, 900mm

Mount: Skywatcher EQ-2

Eyepieces: BST Starguider 5mm; 8mm; 15mm; 25mm.

So what's the problem? Well, the problem turns out to be that the BST starguiders were just too good! Let me explain. I looked at Jupiter and it was so much clearer and brighter. The bands were much better defined, using the 5mm EP where I had used the standard 10mm and 2x Barlow before.

This is where it gets interesting.

Ridiculously, I wondered about trying the original x2 Barlow (the 'least best' of the original kit, I think) with my new BST 5mm.

The result? Well, 2x magnification, obviously, but Jupiter was blurry, as it had been using the original EPs and Barlow. It was much brighter than I recall, when using the original kit at half the magnification. Also, I had no problem viewing it through the starguider, despite an exit pupil of 0.37mm (am I right here? (5mm/2)/F7=0.37).

After all this, I am asking myself, can my scope take more useful magnification with decent eyepieces?

Can I push a Skywatcher Explorer 130 to an EP lower than 5mm f/l for viewing planets and if so, how far? From what I've seen, I'm tempted to go for 3.2mm TMB Planetary 2. This gives about x280 and an exit pupil just under 0.5.

Worth a risk? Don't tell me that to see Jove better I need a 200 aperture. If you do, please send donations to the following address......

Am I daft?

[ronin]

If you have the eyepieces and the barlow then stick them in and see what the result is.

It's not going to cost anything other then a bit of time and at least you will know the situation.

A lot comes down to what you find acceptable, and that is different for everyone.

[cantab]

The general rule of thumb is maximum useful magnification is 2x per mm / 50x per inch aperture. So 260x for your scope. But bear in mind that in Britain days when the seeing permits more than 200x aren't common. A 4 or 3.5 mm EP thus might be a thought, just don't be surprised if you end up rarely using it.

[YKSE]

Agree with Ronin, try to barlow your 8mm to see.

I'd expect 5mm BST is already at limit for you F7 scope at good seeings for Jupiter, 8mm without barlow should work better than 5mm most of time.

[rory]

As above really , you might get a 4 mm that gives over x200 , but you'll probably find although the image is slightly larger , the sharpness will simply diminish and you'll get few chances to use it with any conviction.

I hardly even used my 5mm with a 8" dob , I found the 6mm and 7 mm offered better views 99% of the time.

Maybe look out for a second hand 4mm tmb planetary to test . These are reasonably cheap and if you find your not getting any joy from it you can get most if not all your money back upon a resale. That's what I'd do .

[Mark in Macc]

Glad you like the BST Explorers. It's nice to hear that people's advice is sound. You might end up with either aperture or focal length fever at this rate as well

[Naemeth]

I've done 325x on my 130P (equivalent to a 0.4mm exit pupil) on the Moon and 260x (0.5mm exit pupil) on Jupiter before. While it's great to use that much magnification just for fun, all it does is make the image bigger, and often you lose detail unless the seeing is exceptional. So while you can use higher power, that doesn't mean you should .

For the most detail to be seen in planetary observing under our atmosphere we should use the minimum magnification we can to see what we are trying to, using magnification to make the detail large enough to be seen, but not so much the atmosphere makes the image blurry.

If we were on Hubble, push the magnification as much as the Dawes limit allows .

[NGC 1502]

As above really , you might get a 4 mm that gives over x200 , but you'll probably find although the image is slightly larger , the sharpness will simply diminish and you'll get few chances to use it with any conviction.

I hardly even used my 5mm with a 8" dob , I found the 6mm and 7 mm offered better views 99% of the time.

Maybe look out for a second hand 4mm tmb planetary to test . These are reasonably cheap and if you find your not getting any joy from it you can get most if not all your money back upon a resale. That's what I'd do .

Good advice.  A smaller and sharper view easily trumps larger and fuzzier any day ( I mean night  )

Regards, Ed.

[John]

Blasting up the power to get a larger image seems a great idea. In reality though dropping back a bit usually gives crisper and more contrasty views, especially of Jupiter and those are the ones that actually show the details on the planet more clearly. Your scope will be showing as much detail as it can a much lower magnifications than the theoretical max - blowing things up further is like magnifying a newspaper photo - yes it's bigger but it's also less distinct. At least with Jupiter that is.

[Alien 13]

Is there a real limit to magnification i noticed in the sky at night mag review on the WO ZS71 that they pushed it to x232 which is way beyond the rule of thumb figures?

[CumbrianGadgey]

I reckon it depends where you are and what the viewing conditions are.

In Cumbria, when we get a clear night it's darned black. Maybe I can get better out of my scope than you could in the south where light pollution becomes a problem. I'll try it. All that can happen is that I'm disappointed with the result. Since jupiter was so clear and bright with the 5mm Satarguider and bright enough but more blurred with the cheap and chearful x2 Barlow plus 5mm starguider, I can push it further. Let's face it that would be x360 with a combination that reduced light and definition quite severely.  Theoretically my maximum useful magnification is around x260. I'll experiment around the 230 to 350 mark and see what happens. For a proper scientific experiment, you have to push the limits. Even if it means I can only use this sort of magnification on a few days in the year, what a few days they'll be!

After all, there are few advantages to living here...maybe dark skies are one of them.

Cheers.

I'm going to try. I'll let you know the result.

Cheers!

[Reeny]

I have a 280x eyepiece combination which has never worked for me yet.

160x is always sharp.

210x is good for 50% of the time (weather dependant).

230x is variable - with views coming and going as conditions change.

280x is never any good (yet)

I have a lot more confidence in the 210x than the 230x combination.

But it is nice to know that you have max'd out and had the best, sharpest views available.

I suggest that 230x will be a good set-up to match your 5mm at 180x.

If you can do it without a Barlow - even better (for less glass between you and the target)

Revelation do a 52degree Plossl in 4mm for £22 (plus £3 delivery).

I use a Barlowed 12mm Revelation Plossl at 210x and it is very good on the brighter objects like the Moon and Jupiter.

I am not sure how the smaller lensed 4mm will perform.

They aren't going to be as comfortable for eye relief as the BST's.

But for £25 delivered, it might be worth a punt to find out.

[Naemeth]

Reeny, I wouldn't advise a 4mm plossl. The eye relief will be about 2.4-2.8mm, pretty uncomfortable, the 5mm is be a safer and more comfortable bet .

[Reeny]

Maybe a different make of 4mm eyepiece then.

Gadgey already has the 5mm BST starguider.

I know that our 3" scope doesn't like Barlows.

So a straight 4mm should give a better view than a 2x 8mm.

This is where a try before you buy option is useful.

[John]

A reasonably priced and comfortable eyepiece for high power observing is the TS Planetary HR. In the shorter focal lengths the range includes 5mm, 4mm, 3.2mm and even a 2.5mm. They give 60 degree fields of view and a comfortable 16mm of eye relief. Modern Astronomy sell them at £49 each which is around the same as the BST explorer and the optical quality is comparable I believe.

[bingevader]

I reckon it depends where you are and what the viewing conditions are.

In Cumbria, when we get a clear night it's darned black. Maybe I can get better out of my scope than you could in the south where light pollution becomes a problem. I'll try it. All that can happen is that I'm disappointed with the result. Since jupiter was so clear and bright with the 5mm Satarguider and bright enough but more blurred with the cheap and chearful x2 Barlow plus 5mm starguider, I can push it further. Let's face it that would be x360 with a combination that reduced light and definition quite severely.  Theoretically my maximum useful magnification is around x260. I'll experiment around the 230 to 350 mark and see what happens. For a proper scientific experiment, you have to push the limits. Even if it means I can only use this sort of magnification on a few days in the year, what a few days they'll be!

After all, there are few advantages to living here...maybe dark skies are one of them.

Cheers.

I'm going to try. I'll let you know the result.

Cheers!

It's great to come to SGL for a little reassurance, but I think you've answered your own question! 

Only you can determine the maximum useful magnification at your site with your kit.

Best we can do is give general ball park figures.

Personally, I know it can change quite dramatically from one observing session to another, so it's handy to gradually (or not, if you have the cash, but I'd take the time to find out myself) build up a range of EPs to cover the eventualities.

Have fun experimenting!

Cheers

[Reeny]

.............................I'm tempted to go for 3.2mm TMB Planetary 2. This gives about x280 and an exit pupil just under 0.5.......................

If you decide to go for the 4mm TMB Planetary II at 225x, let us know how it performs.

I am after a decent 6mm eyepiece, and those TMB's are only £40 at Skys the limit.

http://stores.ebay.co.uk/Skys-the-Limit-Astro-and-Optical/TMB-Planetary-II-/_i.html?_fsub=2568751014&_sid=53377064&_trksid=p4634.c0.m322

[NickK]

There's a big big difference between eyepieces that are available separately.

Although I've not tried TMBs, the difference between WO, Baader and Televue for instance is very marked when looking through the pentax - WO I found soft, Baader is my normal EP and gives decent views and the TV gave almost 3D views.. but the cost difference - I could buy more imaging kit (or a dob!).

[Reeny]

I may hang on and go for the 6mm Delos then.

The £40 would be better spent towards offsetting the cost of the TeleVue.

It may take a year or two to save up.

[esxste]

Thanks for a great read, I've recently got my hands on the same scope and after getting used to limits of the supplied EP's I'm starting to look at purchasing another EP or two. Your experiences with your BST starguider EP's have certainly added to my consideration.

Sadly I don't think that down here I'll be able to get quite the same results from very high magnification, but I am keen to push the limits.

Sent from my iPad using Tapatalk

[rwilkey]

An exit pupil of less than 0.5mm is not at all practical to use.  Why go for more magnification when the BST 5mm gives good views of Jupiter already?  Jupiter does not respond to massive magnification in my opinion.  However, Saturn does respond to good magnification.

[swamp thing]

In Cumbria, when we get a clear night it's darned black. Maybe I can get better out of my scope than you could in the south where light pollution becomes a problem.!

I think your confusing light pollution and seeing conditions here. LP has no effect on seeing conditions and how much power you can use.

One can be in town with steady seeing and be able to use way more power than someone else observing from a dark sky site with poor seeing.

I never alter my magnification because of LP only seeing effects this.

[ollypenrice]

Magnification is not the be all and end all of seeing detail. The trick is patience, waiting for the good moments of stable seeing. I have excellent skies but I rarely bother going over 200x in scopes for which 300 plus is theoretically possible. As Nameeth says, it becomes a curiousity. I once (only once) had a stable image of the moon at 500x. Yes it was stable and quite entertaining, but if I'm honest there was no new information in this view over a less magnified one. The errors were growing as fast as the details.

Back off, relax, enjoy.

Olly

[CumbrianGadgey]

Thanks for all the comments.

One thing I can't stress enough is how much of an improvement the BST starguiders give. I went back to looking at the moon tonight, thinking only that it would be clearer and sharper than the original skywatcher EPs. Oh, it was that alright, it also darned nearly blinded me! I now know what my moon filter is for. The original gear must have been cutting out an awful lot of light. I had a bright after-image burnt onto my retina for several minutes.

With the filter in place the level of detail visible was hugely better than the original EPs showed. I stuck on the 5mm and just wandered around the moon for a while.

I think I'll give a shorter focal length a try and I will report back as requested, when I have the results.

P.S. I finally got to see all the Gallilean satellites of Jupiter last night and tonight, too. Up until now, Europa has been very shy whenever I've had a clear sky and always been in hiding. My daughter got to see them all as well, so she's happy. Result!

[Reeny]

A quick update from last night using the 200p dob.

I have had good views using the 280x combination (9mm Plossl, Barlowed down to around 4mm-ish)

It has taken 3-months, and needed the moon to be high in the sky nearer to the Zenith, but it worked.

It was good for a quick look at the moon.

Jupiter, Bodes Nebula, and double stars needed lesser magnification for a clear view.

So I won't be spending big bucks on a 4.5mm TV or 4.7mm ES just yet.

200x seems to be the maximum for best viewing at my location.

Then I have the 230x and 280x option for dark skies, or once a month moments.