Troubleshooting My ST80

[Dave In Vermont]

So I finally finished outfitting my Skywatcher-branded ST80 - an achromatic 80mm objective with a focal-distance of 400mm, yielding F/5. My modifications being a GSO visual-back with 10:1 Crayford focuser, an older (metal-body) William Optics 2" Dielectric Diagonal - brand new and was living in one of my cases, a decent GSO 8 X 50mm RACI finder-scope, and a Helio-Pod solar-finder (these things are great).

I'd cleaned all the optics. Mounted it on a discontinued Orion USA G4 Alt/Az mount that was sold for $60 as they were bad. Rated to hold 10 pounds, less than 2 pounds caused the clutch in the mount to slip and drop it's payload - the telescope. I took it apart and installed a strip of 8-grit sandpaper around the smooth steel-drum. Twisting the brass-bolt inwards was supposed to hold the payload (!), and it, of course, couldn't do so. Smooth, steel-sphere being gripped by a brass-bolt? Get a grip! So now it had coarse sandpaper to grab. Easily holding the original 10 pounds. If / when this wears out, I'll take a file to the drum and have at - permanently.

So it was finally all set for some nice & easy tours of the star-fields. Starting at Albireo, I began to cruise Cygnus and points south. Many nice clusters and the several NGC-objects to meditate on. When I noticed a smudge at 8:00 in my view. It had a distinct sideways 'V' shape. So I changed EP's. Nope - the 'V' was still there. So back inside I went - with the WO diagonal.

Checking its' essentially new mirror, I could see nothing to account for 'V.' Some dust I brushed off. And just to be sure, I swapped to another WO 2" dielectric. Went out and: 'V' was still in the house. Now I was getting quite concerned. Back to troubleshooting. So I rotated the OTA. There was 'V' moving positions. So I went in and took apart the lens-assembly. Nothing was showing. I gently hit it with some 91% iso-propyl alcohol, followed by distilled water. Let it dry and examined it. It was spotless. Re-assembled the scope.

And 'V' was very much in attendance. Occam's Razor met Murphy's Law. There was only one possibility left, and the one I was most dismayed by: A defect in the lens/glass itself..

So I looked about the web. Orion USA had the ST80 available. On sale at $109 (£70) + shipping. They are identical to the old Skywatcher I'd bought in 2003. If I can, I'll put the new achromat in the blue-tube Skywatcher, and set-up the other - with lens' defect & all - as a terrestrial & astro scope. And give it to a kid - keep Junior from wandering the streets. At least I'll get rid of some of my extra astro-goodies.

Never a dull moment,

Dave

[Stu_2011]

Hi

Did you take apart the objective lens? I think the inside lens looks symmetrical buts it's not, if it's the wrong way round the convex surface of the inside lens can just about touch the concave surface of the outer lens and this can produce funny effects. Just a thought.

My ST80 is a bit like yours with an upgraded GSO Crayford. I have a flip mirror as well.

Thanks

Sent from my iPad using Tapatalk

[Dave In Vermont]

Thank you for the input. But I had everything in the correct order. And the inner lens in this is more flat on the back-side. Standard achromat set-up. And I always mark the lens of refractors once I have them out of the OTA. So no go on that. I wish it were! No point in trying to return it - it's from 2003. So I'm stuck, so some young person will get it once I'm finished swapping lenses. I'm just surprised I hadn't noticed this before, as I hadn't, up until the other night, used it for astro purposes.

These are very nice little scopes - minus any defects in manufacture. Well worthy of upgrading. I don't even see any CA worth mentioning.

Thanks again,

Dave

[ringz]

Have you tightened the objective too much when you refitted it.

Martyn.

[John]

Uneven lens spacer thickness can cause such issues. I've been playing around with spacers in an old TAL 100 refractor that I've got and they only need to be a tiny bit uneven for optical issues to be noticeable. Touching lens elements can also result with similarly unwelcome effects.

[Dave In Vermont]

Uneven lens spacer thickness can cause such issues. I've been playing around with spacers in an old TAL 100 refractor that I've got and they only need to be a tiny bit uneven for optical issues to be noticeable. Touching lens elements can also result with similarly unwelcome effects.

I ran this through my mill, too. The lenses were put back as was and spaced with their own spacers. And not too tight - you want them together, but able to expand / contract with variations of temperature, etc. But thanks for the possibilities. I'm an old hand with refractors - they're what I started with many Moons ago.

So a new one should be pulling up tomorrow. Then I'll see to any swapping I need do. Then I'll have an extra that works, and I figure a kid won't notice the imperfection until he/she's old enough to buy themselves a new scope. If they catch the astronomy-bug - which is my evil plan.....

Misery loves company!

Dave

[Dave Lloyd]

Nice sentiments mate, hope the "new" one is all you expect.

[happy-kat]

What's the new one like?

I think it has arrived now.

[Dave In Vermont]

Well, since you asked, it did indeed arrive. And it was optically flawless. I decided to keep the new OTA and swap all my upgrades onto it. Man - those stock focusers are the worst! You need to be Arnold Schwarzenegger to rack it in & out. Anywho, it had it's first-light on Vega after I checked the collimation, which was fine out-of-the-box, and no 'V' in sight . So all is well. Been checking some filters with it's fast F/5 optics on the dimunitive 80mm. Anyone play with an Astronomik CLS-filter? It puts too much blue-green out in my opinion.And I really appreciate the orange-yellow Sun my Thousand Oaks solar-filter gives me. Much more pleasing to my eye over the Baader. Of course this goes to heck-on-a-sled once i pop in the Baader Solar-Continuum filter, which looks like a Martian-invasion: Everything is green. But granulation is easy to spot.

The former scope is rebuilt - flaw & all - and stands ready to give to a worthy cause when I meet one. I'll throw in a Meade 1.25" diagonal and a new Meade Super-Plossl 26mm EP. Keep the little monsters off the streets at night.

Cheers, all!

Dave

[happy-kat]

Great :-)

The r&P is adjustable doesn't need to be tight I don't think. Deon has a guide on YouTube on fettling it if it needs it.

[Dave In Vermont]

Right you are. However my fix is easier still: Remove it and replace with a GSO Crayford with a 10:1 option. Thus -

This little Dicken's is lots of fun!

Dave

[andrew63]

That's a a good looking job Dave.  Now it's all been optimised, what sort of magnification will the optics take before the image breaks down ?

andrew

[Dave In Vermont]

The 'seeing' has been off lately. Unusually high temperatures for this time of year with resulting haze, and toss in a layer of high wood-smoke from the massive forest-fires out west = 80 to 100X is as far as I go. I used a Baader Hyperion 5mm @80X on Venus the other morning, fitted with a Baader Semi-APO Filter and a variable polarizing two-cell filter. Still had some quivering present from the upper atmosphere. But Venus was at it's brightest at -4.55 and revealed itself as a beautiful cresent.

The weather is starting to push south out of Canada now, with cooler temperatures, and this should allow me to see how far up it will allow. Any CA present is not a problem to me. And Mars is beginning to ascend - so I have a plan.

These are fun little scopes. A far cry from the far larger members of the tribe.

Enjoy -

Dave

[Stu_2011]

The 'seeing' has been off lately. Unusually high temperatures for this time of year with resulting haze, and toss in a layer of high wood-smoke from the massive forest-fires out west = 80 to 100X is as far as I go. I used a Baader Hyperion 5mm @80X on Venus the other morning, fitted with a Baader Semi-APO Filter and a variable polarizing two-cell filter. Still had some quivering present from the upper atmosphere. But Venus was at it's brightest at -4.55 and revealed itself as a beautiful cresent.

The weather is starting to push south out of Canada now, with cooler temperatures, and this should allow me to see how far up it will allow. Any CA present is not a problem to me. And Mars is beginning to ascend - so I have a plan.

These are fun little scopes. A far cry from the far larger members of the tribe.

Enjoy -

Dave

Looks really good. ST80s are great.

Just out of interest how do you find the 2 cell variable polarisers at high mag? I have the Celestron ones and they produce horrible astigmatism at high magnification.

I assume that the single axis polarisers are based on some form of aligned polymers chains and this produces the astigmatism??

Thanks

Sent from my iPad using Tapatalk

[Dave In Vermont]

Geesh. I don't think I've ever had occasion to use that at high-mag on the Moon. I only use it when the Moon is full, or near to it. At that diameter of, or near, totality I would'nt be looking to eke out detail from the lunar-features. More likely I'd be just using them as a dimmer-switch while trying to get a look at something quite near the searchlight-of-a-Moon. For details on the surface, I'd be waiting for a good view along the terminator somewhere. And then I'd be more inclined to play with a Baader Fringe-Killer. Or something similar. Maybe experimentally stacked with something else from my filter-trove.

Mine is from Orion USA. Possibly from the same manufacturerer as yours? Who knows. I just hope Edwin Land didn't glean any money from my purchase. I'm not about to forgive him for all the help he knowingly gave the government of South Africa to enforce it's apartheid-policy at the time. I'd say it's causing astigmatism rings of poetic-justice..... You don't want to know.

Forecast for clear-skies on the 27th here,

Dave