SW 130PDS queries

[Tommohawk]

Hi all.

Following on from my fruitless search for an off the shelf F4 130mm newt, I'm still considering (obsessed with) the idea of modifying a stock SW 130PDS.

So, could some kind 130PDS owner check a couple of details for me please.

1. The OTA diameter. It's quoted as 160mm on the TS website, but need to check.

2. The minimum focuser height ie from the tube to the top of the black 54mm to 2" adaptor. Hope that makes sense. TS website says 90mm but my 200P is only 75mm.

3. Has anyone succesfully fitted a low profile focuser, and if so which one?

Really gratefull for any input.

PS where's all the clear sky gone??

[beamer3.6m]

I appreciate it is not F4 bit does the coma corrector not alter the fl of the 130pds to 4.7 anyway.

Is that not close enough?

[Tommohawk]

I appreciate it is not F4 bit does the coma corrector not alter the fl of the 130pds to 4.7 anyway.

Is that not close enough?

Hi and thanks for that. The problem is that the stock 130PDS is too long for budget airline hand baggage. I'm thinking of doing a hatchet job on one, if I can source an F4 mirror for a sensible price. But to get good sensor illumination without a big increase in secondary size requires as low profile a focuser as possible, and the design is somewhat dependent on tube diameter - hence the queries. 

[Tommohawk]

Sorry for the bump - anyone have any details please for 130PDS tube diameter, focuser height, and low profile focuser possibilities?

[Skyline]

Maybe contact Ron at Moonlite about making a focuser plate for your 130PDS.

Al.

[Tommohawk]

Maybe contact Ron at Moonlite about making a focuser plate for your 130PDS.

Al.

Thanks and useful to know that someone might be able to do a custom job. TBH I'm trying to keep the costs sensible, and custom parts may push the cost beyond whats reasonalbe, but good to have the options.

Not much feedback regarding the stock 130 PDS focuser height or tube diameter - can anyone help please?? (see#1)

[beamer3.6m]

I cannot measure mine with any real accuracy.

Why not email FLO - I'm sure they could supply the necessary no probs.

[Uranium235]

Im not sure whether its worth upgrading the focuser becuase it will cost at least twice as much as the OTA itself. The stock one should be fine, unless your planning to hang an anvil off it!

It might be worth following the above advice and use the SW coma corrector, which brings the FR down to roughly f4.4 - which is close enough to f4 (a difference of 0.4 isnt worth arguing about). Remember, the faster you go - the more difficult it becomes. But if I recall correctly, the internal diameter of the OTA is ~150mm.

If you really want f4, its probably easier to get a 5" f4 mirror ground and shorten the tube. But then you would probably need a larger secondary to handle the bigger light cone (which would cause a larger central obstruction)... all swings and roundabouts im afraid!

[beamer3.6m]

I think the reality is that you will spend more on this mod than you gain.

I know you want an F4 scope but have you thought about an alternative design - MAK for example to keep the scope short.

F/L will be far longer but not sure what your planning on imaging etc.

[Lonestar70]

Im not sure whether its worth upgrading the focuser becuase it will cost at least twice as much as the OTA itself. The stock one should be fine, unless your planning to hang an anvil off it!

It might be worth following the above advice and use the SW coma corrector, which brings the FR down to roughly f4.4 - which is close enough to f4 (a difference of 0.4 isnt worth arguing about). Remember, the faster you go - the more difficult it becomes. But if I recall correctly, the internal diameter of the OTA is ~150mm.

If you really want f4, its probably easier to get a 5" f4 mirror ground and shorten the tube. But then you would probably need a larger secondary to handle the bigger light cone (which would cause a larger central obstruction)... all swings and roundabouts im afraid!

Hi Tom,

The 130PDS uses the same 2 speed focuser as the 150PDS and the height dimension you enquired about is 70mm on my 150PDS.

I must agree with Uranium 235 as regards the proposed modification since even after obtaining an F4 mirror you would need to take approx 125-130mm off of the tube length... this would most definitely require a somewhat larger secondary mirror than the existing one, which is already a bit larger than the standard 130p scope... thus enlarging the centre obstruction even further.

I can't verify the 130PDS tube dia, however, the 150PDS is 170mm inside dia. which would equate to the value of 150mm given for the 130PDS above by Uranium 235 (Mirror Dia + 20mm).

Good luck and clear skies.

Sandy.

[Tommohawk]

I cannot measure mine with any real accuracy.

Why not email FLO - I'm sure they could supply the necessary no probs.

Thanks - I did call FLO but they dont have one in stock to measure.

Im not sure whether its worth upgrading the focuser becuase it will cost at least twice as much as the OTA itself. The stock one should be fine, unless your planning to hang an anvil off it!

It might be worth following the above advice and use the SW coma corrector, which brings the FR down to roughly f4.4 - which is close enough to f4 (a difference of 0.4 isnt worth arguing about). Remember, the faster you go - the more difficult it becomes. But if I recall correctly, the internal diameter of the OTA is ~150mm.

If you really want f4, its probably easier to get a 5" f4 mirror ground and shorten the tube. But then you would probably need a larger secondary to handle the bigger light cone (which would cause a larger central obstruction)... all swings and roundabouts im afraid!

YEs, thanks for that. I'm sure the stock focuser is up to the job, but the object is to fit an F4 mirror to make it shorter for travel puposes. The CC makes it faster, but not shorter. Once its shortened though the focuser height needs to be minimal to avoid oversizing the secondary. 

I think the reality is that you will spend more on this mod than you gain.

I know you want an F4 scope but have you thought about an alternative design - MAK for example to keep the scope short.

F/L will be far longer but not sure what your planning on imaging etc.

As you say, Mak more compact but much slower. The idea is to get as fast as I can for imaging when on holiday. I dont especially need widefield, but I do need fast.

Hi Tom,

The 130PDS uses the same 2 speed focuser as the 150PDS and the height dimension you enquired about is 70mm on my 150PDS.

I must agree with Uranium 235 as regards the proposed modification since even after obtaining an F4 mirror you would need to take approx 125-130mm off of the tube length... this would most definitely require a somewhat larger secondary mirror than the existing one, which is already a bit larger than the standard 130p scope... thus enlarging the centre obstruction even further.

I can't verify the 130PDS tube dia, however, the 150PDS is 170mm inside dia. which would equate to the value of 150mm given for the 130PDS above by Uranium 235 (Mirror Dia + 20mm).

Good luck and clear skies.

Sandy.

Right that really useful - the focuser on the 130 looks the same as the 150 or 200, but I wasnt sure. And my 200P has the single speed with x2 conversion, so I couldnt use that to compare.

Shortening the tube is fine, thats the object of the exercise. My original sums showed that if fitted with a CCD with only minimal length, the stock 47mm would work OK - but I didnt allow for the backfocus of the coma corrector, and the thickness of the Filterwheel. Unfortunately this does require an increase in the secondary size. If this goes too big as you say the obstruction would be excessive. 

So I'm doing some final sums/ray trace to see how it looks. But it may well be that the cost of a custom F4 + new focuser + secondary + hassle would be too much in which case its plan B, an APO frac.... or plan C a fast Canon lens.

Thanks for alll the input.

[Thalestris24]

Hi Tom

The external tube diameter of my 130pds is approx. 160mm. It isn't exactly the same as the 150pds focuser since the tube curvature is different.

Um, I suspect if you try and modify a 130pds to f4 you'll be into a world of pain! The only off the shelf f4 newt I know of is the SW Quattro which has a 205mm mirror and fl=800mm. I understand it can be difficult to collimate... Wouldn't it be easier to just get a short tube frac?? Or maybe the cheap and cheerful Skyhawk 1145p which is f4.5 though don't know what it might be like to image with...

Louise

[beamer3.6m]

What about the 130p which collapses.

[Tommohawk]

Hi Tom

The external tube diameter of my 130pds is approx. 160mm. It isn't exactly the same as the 150pds focuser since the tube curvature is different.

Um, I suspect if you try and modify a 130pds to f4 you'll be into a world of pain! The only off the shelf f4 newt I know of is the SW Quattro which has a 205mm mirror and fl=800mm. I understand it can be difficult to collimate... Wouldn't it be easier to just get a short tube frac?? Or maybe the cheap and cheerful Skyhawk 1145p which is f4.5 though don't know what it might be like to image with...

Louise

Hi Louise and thanks for that - your measurement of 160mm accords with TS specs, although varous figures seem to be quoted. 160mm seems large for a 130 mirror but I think its to avoid vignetting at the front of the tube. One hears a lot about problems collimating F4s, but I handle a modicum of pain to get a good result.. maybe not a world of pain though!

I looked at the SkyHawk and optically its not a bad compromise - but the focuser isnt great and only 1.25" so not great for imaging + no coma corrector option. 

Its a bargain though for an F4.4 scope at £119 including EQ1and fits the bill for portability. Maybe I should look at putting a 2" focuser on it? I'll do some sums....

.... Right, done the sums and it doesnt work for imaging, Basically, and not surpisingly I suppose, the problems are much as for the 130 but even greater. 

What about the 130p which collapses.

I looked at the flextube, and the focuser supposrt id very flimsy looking - great for travel + visual, but I dont think so good for imaging.

[Thalestris24]

Hi Louise and thanks for that - your measurement of 160mm accords with TS specs, although varous figures seem to be quoted. 160mm seems large for a 130 mirror but I think its to avoid vignetting at the front of the tube. One hears a lot about problems collimating F4s, but I handle a modicum of pain to get a good result.. maybe not a world of pain though!

I looked at the SkyHawk and optically its not a bad compromise - but the focuser isnt great and only 1.25" so not great for imaging + no coma corrector option. 

Its a bargain though for an F4.4 scope at £119 including EQ1and fits the bill for portability. Maybe I should look at putting a 2" focuser on it? I'll do some sums.

I looked at the flextube, and the focuser supposrt id very flimsy looking - great for travel + visual, but I dont think so good for imaging.

Yeah, a 114mm tube will obviously have it's limitations! So unlikely to be able to change the focuser. I don't know what sort of coma it has either oor even whether it can be used at prime focus. The eq1 will be pretty useless and naturally the mount you use will be important for imaging. The scope might be portable but the mount - not so much! You haven't really explained your plans?

Louise

[Tommohawk]

Yeah, a 114mm tube will obviously have it's limitations! So unlikely to be able to change the focuser. I don't know what sort of coma it has either oor even whether it can be used at prime focus. The eq1 will be pretty useless and naturally the mount you use will be important for imaging. The scope might be portable but the mount - not so much! You haven't really explained your plans?

Louise

Yes I posted the masterplan on another thread, and started this afresh just to try and get the 130PDS specs without muddling the issue.

So - I'm trying to get a superfast widefield set up partly for home use but mostly to allow portability in an airline cabin bag. DSLR at the mo, but swapping to CCD. Options are a sawn-off newt, APO frac, or Canon lens. Something which fits with my existing 200PDS would be best. (Eg ability to share coma corrector)

Newt looks like too much grief, though possible in theory. About £750 with custom F4 + lo-pro focuser. Lot of money, but faster than an APO. Plus lots potential grief.

APO about same as above including flattener/reducer. Easy, but not superfast.

Canon 70-200 or 300mm about £500 but cant use filterwheel even with CCD. Also needs spooky fine focuser attachment.

The 130PDS has an inexplicable lure, the APO is the sensible/mainstream option, but the Canon lens is also attractive for being very versatile.

So thats where I'm at!

[Thalestris24]

Yes I posted the masterplan on another thread, and started this afresh just to try and get the 130PDS specs without muddling the issue.

So - I'm trying to get a superfast widefield set up partly for home use but mostly to allow portability in an airline cabin bag. DSLR at the mo, but swapping to CCD. Options are a sawn-off newt, APO frac, or Canon lens. Something which fits with my existing 200PDS would be best. (Eg ability to share coma corrector)

Newt looks like too much grief, though possible in theory. About £750 with custom F4 + lo-pro focuser. Lot of money, but faster than an APO. Plus lots potential grief.

APO about same as above including flattener/reducer. Easy, but not superfast.

Canon 70-200 or 300mm about £500 but cant use filterwheel even with CCD. Also needs spooky fine focuser attachment.

The 130PDS has an inexplicable lure, the APO is the sensible/mainstream option, but the Canon lens is also attractive for being very versatile.

So thats where I'm at!

Mount? That's the most important thing! Portable mounts are tricky. Of course, a short  focal length always makes life easier!

[Tommohawk]

Mount? That's the most important thing! Portable mounts are tricky. Of course, a short  focal length always makes life easier!

Yes mount is an issue as you say. Looking at Astrotrac or SW adventurer, payload being an issue of course. Or maybe a small driven conventional EQ. The 130PDS is 4kg + 1-2kg for extras say puts it on the limit for adventurer. Has to be said that the mount issue does point to the lighter weight of a camera lens.

BTW I only mentioned the EQ1 mount above because it added to the bargain value of that package - but not much use for me agreed.

So ... I  was leaning back toward the idea of a camera lens, and then the phone rang this morning and I've got a really good quote for a custom F4 mirror, so now I'm leaning back to the 130PDS conversion!

[Thalestris24]

Yes mount is an issue as you say. Looking at Astrotrac or SW adventurer, payload being an issue of course. Or maybe a small driven conventional EQ. The 130PDS is 4kg + 1-2kg for extras say puts it on the limit for adventurer. Has to be said that the mount issue does point to the lighter weight of a camera lens.

BTW I only mentioned the EQ1 mount above because it added to the bargain value of that package - but not much use for me agreed.

So ... I  was leaning back toward the idea of a camera lens, and then the phone rang this morning and I've got a really good quote for a custom F4 mirror, so now I'm leaning back to the 130PDS conversion!

The Star Adventurer is quite good but really only with a camera and shorrtish lens. I couldn't get mine to run reliably with an ST80 and guide scope - everything quickly becomes too heavy. You can forget trying a 130pds on it! The Astrotrac may be a bit better with a small frac but the whole package is expensive.

Good luck with the custom mirror.

Louise

[Peter Drew]

Referring back to #3, does the telescope really have to go in the hand luggage?. I have often taken them, including a C8, in the hold luggage without any issues.  

[Tommohawk]

The Star Adventurer is quite good but really only with a camera and shorrtish lens. I couldn't get mine to run reliably with an ST80 and guide scope - everything quickly becomes too heavy. You can forget trying a 130pds on it! The Astrotrac may be a bit better with a small frac but the whole package is expensive.

Good luck with the custom mirror.

Louise

OK thats useful to know re the capacity of the SW mount. 

Referring back to #3, does the telescope really have to go in the hand luggage?. I have often taken them, including a C8, in the hold luggage without any issues.  

Wow thats brave! Have you ever seen baggage handlers at work??

Seriously though I guess its a good point. Aside from anything else, if a stock 130PDS only costs £159 its not like risking my life savings (....£169)  And I guess it would be possible to remove the primary and carry as hand baggage.

OK, so thats plan D then.

[Robp]

Not sure what your budget is, but what about something like the WO Star 71?

http://www.firstlightoptics.com/william-optics/william-optics-star-71-f49-5-element-refractor.html

[Tommohawk]

Not sure what your budget is, but what about something like the WO Star 71?

http://www.firstlightoptics.com/william-optics/william-optics-star-71-f49-5-element-refractor.html

Thanks for the suggestion. I'd already considered the idea of a frac and the WO is well regarded as you say. But I'm after something superfast and the WO71 is only F4.9.

That said I have given up the 130PDS conversion project for now, and have just bought a 300mm F2.8 Tamron 360B which seems to get good reviews, even though its some years old. I've checked it out and it seem to OK for terrestrial stuff, so just gotta wait for some clear sky and see what happens!

I'll post some more details when i have a moment re the technical problems with the F4 130 Newt.

[Thalestris24]

Thanks for the suggestion. I'd already considered the idea of a frac and the WO is well regarded as you say. But I'm after something superfast and the WO71 is only F4.9.

That said I have given up the 130PDS conversion project for now, and have just bought a 300mm F2.8 Tamron 360B which seems to get good reviews, even though its some years old. I've checked it out and it seem to OK for terrestrial stuff, so just gotta wait for some clear sky and see what happens!

I'll post some more details when i have a moment re the technical problems with the F4 130 Newt.

Hi Tom

There are some images here taken with the Tamron 300mm. However, there's obviously a big difference in fov between 300mm and 650mm... (or even a theoretical f4/520mm)

Louise

[Tommohawk]

Hi Tom

There are some images here taken with the Tamron 300mm. However, there's obviously a big difference in fov between 300mm and 650mm... (or even a theoretical f4/520mm)

Louise

Hi Louise and thanks for the link. Actually I had found that during my earlier research, but thanks for picking up on it.

Agreed this is a bit different to the original proposal for FOV/FL but in truth I think it's probably a better fit with my existing 1000mm scope.