sw200 poor tolerances on ep holder

[triton1]

Just wondering if anyone else has noticed the bad tolerances on the skywatcher reflectors.I finally bought a laser collimator and noticed when nipping up the locking screw in the sw ep holder how much the laser moved.What chance have i got to get it perfectly collimated!

I decided to measure the 1/4 to 2 inch ep holder with a vernier and was mortified.The outside diameter was as low as 0.08mm compared to that of the focuser lock.It even had a reverse taper of that amount over 12mm.I,m an engineer and if i turned work out like that I would have been sacked.

However,proceeded to check the holder that came with the collimator(a cheap one).It was only 0.02mm wow and turned perfectly straight.Thats saying somthing.So I checked the collimators fit into its holder,slight play so carefully wrapped masking tape around it and its a perfectly snug fit.At least i'm within 0.02mm.Will check with barlow method to confirm but at least collimation was a doddle.

I,m seriously considering drilling and tapping another hole in the cheaper collimators adaptor and use that as my ep holder.How can skywatcher get away with this?

Anyway thanks everyone for letting me vent my spleen

Jonn

[John]

Have you checked the laser collimators collimation John ? - that might give you a shock too !

The laser inside the collimator is often not aligned with the central axis of the collimator body rendering them rather inaccurate.

Fortunately the optics in these mass produced scopes are pretty good. All the mechanics that surrounds them can be tweaked and / or upgraded if you require more precision.

If they were built to really precise tolerances I fear they would much, much more expensive and out of the reach of many.

As you say, the barlowed method of laser collimation is more accurate despite some focuser "slop" and even uncollimated laser collimators !

[Tinker1947]

It quiet likely why there's a good market for upgraded Focuser's , like Baader, Moonlite, Feathertouch but at a cost that really shouldn't be required if the supplied item were made better....

[triton1]

Yes I did check collimators collimation(mouthful)with a v-block in vice.Over 10ft no movement.The supplier did say he checks every one he sells.

[John]

Yes I did check collimators collimation(mouthful)with a v-block in vice.Over 10ft no movement.The supplier did say he checks every one he sells.

Thats good - it must be time consuming for the seller.

What Skywatcher scope do you have by the way ?

Having owned some scopes that were manufactured to quite high mechanical standards (Japanese Vixens and Russian Intes) I agree that the Skywatcher and Meade scopes are not of the same standard. The Vixen and Intes scopes do cost a lot more though. I guess you get what you pay for.

[Amra]

Oh yes, the slop in the focuser annoys me greatly. Even though I have a perfectly collimated laser collimator I can't get it to fit snugly without wobbling around, I tried using a single layer of thin tape, but that made it far too tight! So I've tried to do the best I can visually instead.

[triton1]

I have a skywatcher 200 reflector on a cg5 mount.

regards Jonn

[triton1]

Oh yes, the slop in the focuser annoys me greatly. Even though I have a perfectly collimated laser collimator I can't get it to fit snugly without wobbling around, I tried using a single layer of thin tape, but that made it far too tight! So I've tried to do the best I can visually instead.

I managed to carefully wrap masking tape around it.I Also have put some around the 2-1 1/4 sw holder.Now fits tight in focuser

Jonn

[tich]

If you have a 2" adapter then I use one of these & find it holds the eyepieces & collimators much more snuggly. I'm sure they can be found a bit cheaper if you shop around.

[triton1]

If you have a 2" adapter then I use one of these & find it holds the eyepieces & collimators much more snuggly. I'm sure they can be found a bit cheaper if you shop around.

You Know what That will probably do the job

many thx Jonn

[Amra]

Bought one of those, might save me a lot of frustration. Thanks Tich!

[Galilean]

All the mechanics that surrounds them can be tweaked and / or upgraded if you require more precision.

A pity that the buyer should have to upgrade the fittings to get an acceptable scope. One of the reasons I bought a GSO 8" - good quality dual speed focuser and a solid steel tube - not floppy aluminium. Cost a little more, but we all know you get what..................

[cotterless45]

You can check your collimation by using a Barlowed laser. This works accurately especially at night and in dependant of focuser slop.You'll find the stock primary springs will make and hold collimation easier if replaced with Bob's Knobs,

Nick.

[scuffer]

A pity that the buyer should have to upgrade the fittings to get an acceptable scope. One of the reasons I bought a GSO 8" - good quality dual speed focuser and a solid steel tube - not floppy aluminium. Cost a little more, but we all know you get what..................

This is a bit harsh , the sw 200p is a very adequate scope .

[Carbon Brush]

The Skywatcher 'entry' scopes are very competitively priced. Something has to give way to sell at this price. Fortunately, on those I have used, the installed optics have been good. At various times I have modified or adjusted mechanical bits, dimmed an RDF, etc. The end result has been a scope well worth the money spent. The 'out of the box' performance has always been good enough for the ££ spent. It is only when comparing with more expensive scopes that the weaknesses have showed.

A quality eyepiece, or focusser can cost the same as an SW200 dob complete kit.

[ronin]

It is called Mass Production, building to a budget and maximising profit.

The OTA costs about £250, factor in retailers profit, shipping, manufacturers profit, government taxes, that doesn't leave a lot of money that is actually used to make the scope. So the bits are fairly budget, that means non-precision.

Orion Optics are reputed to produce better precision scopes, their 8" OTA is £530. Can we assume that a bit more precision costs double the amount ?

Concerning the focuser they have to be bigger then an eyepiece, they also have to be bigger then the tolerance for the max diameter of eyepieces, does 1.25" include the chrome that is plated on?. Otherwise some eyepieces would fit and others would not, so the holder will be somewhat wider then 1.25+ whatever tolerance is applied to the eyepiece diameter. So they are in general going to be loose, even very loose. Look at it like this, you can get the eyepiece in, if you could not get the eyepiece in the focuser you would scream a lot more.

There are often posts saying how inexpensive the scopes are now compared to 20 years ago, for lower costs something has to suffer and we want things as cheap as possible. Skywatcher are budget scopes.

[Bizibilder]

Ronin is quite right - virtually all our equipment is finished with some sort of surface coating, either plating or paint - making the machined finished dimension more or less irrelevant. Additionally all the kit from different manufacturers has to be interchangeable - and without any agreed international standards (in the engineering sense that is). Thus we have "big" holes and small "shafts" to fit into them! There is also the problem of temperature - our kit is used around the world in all temperatures from well below freezing to high summer at the equator, probably a range of getting on for 80°C or similar. That can make quite a difference to the expansion and contraction of some of the materials that are used in scopes and accessories. You really would not want your (perfectly fitting) eyepiece to become "locked" in the focusser as the scope was outside cooling down!

All this adds up to a situation where engineering fits and tolerencies are really only academic. The only way you will get round this is with carefully designed and manufactured components, to a set of non-existant standards, that will ultimately mean prices that noone can afford. There are some fittings made with a split collet type "grip" operated by a screwed ring - a quick rummage around the adapters section of any suppliers website shows these to be at least twice the cost of the "standard" item.

[E621Keith]

You need to take into account there are no agreed international standard for astronomical eyepiece, just 1.25" barrel and 2" barrel. There is no mention of min diameter for the holder or max diameter of the eyepiece barrel, let alone tolerance. If you have very tight tolerance you may find yourself in a situations where some eyepiece are too wide to fit.

My Vixen eyepiece turret is an example of the disadvantage of tight tolerance, some of my eyepiece have trouble fitting into the barrel.

[kirkster501]

I think the Skywatcher reflectors give you a good general scope - score 70%. To get that score up to 95% and above you need to make a few after market additions and alterations.

Focuser - generally rubbish.

Screws that hold the thing together - rubbish (they rust)

Not flocked

Mirror not blackened on side and back

Ditto Secondary

Back of scope not covered to prevent stray light.

Mirror centre spot not 100% accurate

Collimation screws on secondary rubbish. Goodness sake how much would three knurled bolts cost?

Springs on mirror rubbish.

Other than the focuser, these things would hardly cost anything to put right. Goodness knows why they don't take heed of us. Putting these things right turns a SW Tube into a thing of beauty!

Just my two penneth....

[Tinker1947]

My 250PDS has a Moonlite Cr2, and i use a Baader MkIII laser,,,,the Baader goes in the Moonlight 2" adapter, its a nice snug fit,,,but at a price....

[John]

I think the Skywatcher reflectors give you a good general scope - score 70%. To get that score up to 95% and above you need to make a few after market additions and alterations.

Focuser - generally rubbish.

Screws that hold the thing together - rubbish (they rust)

Not flocked

Mirror not blackened on side and back

Ditto Secondary

Back of scope not covered to prevent stray light.

Mirror centre spot not 100% accurate

Collimation screws on secondary rubbish. Goodness sake how much would three knurled bolts cost?

Springs on mirror rubbish.

Other than the focuser, these things would hardly cost anything to put right. Goodness knows why they don't take heed of us. Putting these things right turns a SW Tube into a thing of beauty!

Just my two penneth....

Meade, Celestron, Revelation and other mass produced scopes suffer from a similar list of issues (some the same, some different) so it's not really fair to single out the Skywatcher brand.

FWIW the standard ranges of Orion Optics scopes suffer from such mechanical issues too, despite their higher price. Their optics are the reason that they are worth owning, not necessarily the mechanicals.

You could expand this list to include why refractor dew shields are mostly too short ?, why SCT's and Mak's aren't supplied with dew shields as standard ?, why straight through finders on scopes which would benefit much more from RACI ones ?, why low quality standard eyepieces ?, why cheap metal for dovetails and tube rings ?. Etc, etc, etc.

I guess if we stopped buying these products they might make some improvements in the above areas, eventually.

[bingevader]

I can remember bringing this issue up a while back, no one seemed interested then!

I noticed the same when collimating.

If I tightened the focuser screws on to the collimator in a different order it would make a surprising difference to the collimation!

Cheers

[twotter]

Other than the focuser, these things would hardly cost anything to put right. Goodness knows why they don't take heed of us. Putting these things right turns a SW Tube into a thing of beauty!

At the risk of being controversial I don't want the telescope companies to do this. The increased price would mean I almost certainly would have been unable to afford to buy a telescope in the first place and I would not have taken up this fascinating hobby.

[tich]

At the risk of being controversial I don't want the telescope companies to do this. The increased price would mean I almost certainly would have been unable to afford to buy a telescope in the first place and I would not have taken up this fascinating hobby.

Agreed I've had an interest in this hobby for many years but was unable to afford a scope, ok I've had some issues but I've always managed to get by & lets face it there is a lot worse out there.

[kirkster501]

...... so it's not really fair to single out the Skywatcher brand.

I'm not. I am delighted with both my SW scopes and my mount. How they do it for the money how do not know. What I am suggesting is that other than the focuser it would cost peanuts - pence literally - to turn a good scope into a fabulous one.