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Fitting an ST80 to an SW150P (Guide Scope)


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Hi,

As in the photo, I have a SW150P and I am trying to attach an ST80 as a guide scope.

post-27902-0-45591900-1421065896_thumb.j

My understanding is that I need to connect the ST80 to a dovetail and then the dovetail onto the top of the 150p? 

If that's the case In the box of my 150p I found a dovetail that looks identical to the one already on it (See photo). Do they come with 2?

So, can I use this dovetail to connect the ST80 to the 150p?

Hope this makes sense,

Thanks
 

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Yes. But, you will notice that the 2 centre holes in the dovetail are rather too close together. Either redrill the dovetail to match the spacing of the ST80 shoe, or if the 2 brass outer sockets on the ST80 shoe match the dovetail center holes then bolt shoe to the dovetail and use the shoe outer holes to attach the tube rings, and bolt this on top of the 150.

Aligning the 2 scopes is another issue all together.:( because the ST80 rings do not have adjuster screws.

PS, you don't have enough bolts in the picture to complete the job.

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Pretty much as per RichM63s answer. Just get another 1/4" stud / bolt to attach the second dovetail to the top of the 150P rings. You do need to put the bolts into the 150P rings from the inside and then into the second dovetail. No need to buy guidescope rings - they introduce flexure and you do not need to align the two scopes. They will be aiming close enough to each other. I have done the same as you are planning and I have never had a problem finding a  guide star.

Ian

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Wow, this is a hobby that won't let up on the spending. Them Guidescope rings aren't cheap!

Unfortunately (as you said RichM63) the shoe holes don't line up with the pre-drilled holes in the dovetail as they are two close together. 

The pre-drilled holes are threaded anyway and will not accept the bolts. They accept that screw that sits atop the rings. Is it for a camera?

So It looks like I need to drill two holes into the dovetail to match the spacing on the shoe. Is this recommend or does it sound silly for a beginner to try!?
Obviously these new holes will not be threaded so I guess I need to get some normal bots and nuts to fit the new holes too?

So the scopes do not have to be aligned? 
Would you only align them if you want the ST80 as a finder too, or is it preferable for astrophotography to have them aligned? 

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You may in fact not need to get any guidescope rings. Just bolt the standard ST80 rings to the 150 tube rings using the spare dovetail and two M6 countersunk photo screws (and M6 nuts to match). Ive noticed in you photo you only have one - you need two otherwise you stand a chance of denting the 150 if using normal M6 bolts.

Ive noticed that even if guidescope and imaging OTA arent pointing at the same spot(ish) the guiding is unaffected. As long as its pointing in roughly the same patch of sky, you will be ok.

Give it a go before splashing out on guidescope rings.

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Picture of mine on a SW 200P here: - http://stargazerslounge.com/gallery/image/25675-st80-mounted-as-a-finderscope-on-my-sw-200p-the-st80-is-fitted-with-an-ae-125-diagonal-bresser-32mm-plossl-eyepice-works-very-well-as-a-finder/

And here : - http://stargazerslounge.com/gallery/image/25676-st80-mounted-as-a-finderscope-on-my-sw-200p-pictured-from-the-front/

Sorry the pictures aren't brilliant, it started to rain just as rolled the obsy roof back to take the photo's.

I only had to buy some aluminium channel & a short 1/4" whitworth bolt (std tripod mount size) to mount it. 

Bolt purchased here: - http://www.ebay.co.uk/itm/Bolt-Hex-Head-Set-Screw-1-4-UNC-x-1-2-Black-BSW-Packs-1-to-20-/261562234040?pt=UK_DIY_Material_Nails_Fixing_MJ&var=&hash=item3ce652f4b8

Accurate alignment is not needed as both the ST 80 & the 200P have lower power eyepieces in to find objects.  I aligned them near enough using a neighbours chimney.

Bresser 32mm Plossl & Astro Engineering 1.25" diagonal on the ST 80 & Nirvana 28mm on the SW 200P.  I found Comet Lovejoy easily with this combination.

I didn't use the ST 80's spreader bar, I used the bolts from it to bolt the ST80 mounting rings to the channel.  Rear channel mount to the 200P is a 1/4 whitworth bolt & I used the plastic nut on the front channel mount.  (The one near to the ST80 focuser on your picture).

T0ny wrote above: -

"Unfortunately the photo screw is a different thread size to the bolts that came with the ST80 rings.
The ST80 ring bolts only seem to fit the rings and nothing else :("

The bolts on the ST 80 rings to the spreader bar are metric thread, they look the same size but the thread pitch is different, that's why I had to buy a 1/4 whitworth bolt to fix the channel to the rear SW 200P mounting ring.

Well worth the effort & much better than a standard finderscope.

Cheers,

Fondofchips.

Edited by fondofchips
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Picture of mine on a SW 200P here: - http://stargazerslounge.com/gallery/image/25675-st80-mounted-as-a-finderscope-on-my-sw-200p-the-st80-is-fitted-with-an-ae-125-diagonal-bresser-32mm-plossl-eyepice-works-very-well-as-a-finder/

And here : - http://stargazerslounge.com/gallery/image/25676-st80-mounted-as-a-finderscope-on-my-sw-200p-pictured-from-the-front/

Sorry the pictures aren't brilliant, it started to rain just as rolled the obsy roof back to take the photo's.

I only had to buy some aluminium channel & a short 1/4" whitworth bolt (std tripod mount size) to mount it. 

Bolt purchased here: - http://www.ebay.co.uk/itm/Bolt-Hex-Head-Set-Screw-1-4-UNC-x-1-2-Black-BSW-Packs-1-to-20-/261562234040?pt=UK_DIY_Material_Nails_Fixing_MJ&var=&hash=item3ce652f4b8

Accurate alignment is not needed as both the ST 80 & the 200P have lower power eyepieces in to find objects.  I aligned them near enough using a neighbours chimney.

Bresser 32mm Plossl & Astro Engineering 1.25" diagonal on the ST 80 & Nirvana 28mm on the SW 200P.  I found Comet Lovejoy easily with this combination.

I didn't use the ST 80's spreader bar, I used the bolts from it to bolt the ST80 mounting rings to the channel.  Rear channel mount to the 200P is a 1/4 whitworth bolt & I used the plastic nut on the front channel mount.  (The one near to the ST80 focuser on your picture).

T0ny wrote above: -

"Unfortunately the photo screw is a different thread size to the bolts that came with the ST80 rings.

The ST80 ring bolts only seem to fit the rings and nothing else :("

The bolts on the ST 80 rings to the spreader bar are metric thread, they look the same size but the thread pitch is different, that's why I had to buy a 1/4 whitworth bolt to fix the channel to the rear SW 200P mounting ring.

Well worth the effort & much better than a standard finderscope.

Cheers,

Fondofchips.

Wow,that's an impressive looking set-up.

I was mentally prepared to find Astrophotography a steep learning curve, but not at the building the scope bit!

So hopefully I can get some 1/4" whitworth bolts (B&Q???) to fix the dovetail to my 150p and then drill two holes to get the ST80 Rings bolted onto the dovetail?

Does this sound right?

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Cheers Mr Chips, I couldn't find a picture of mine on the 200P and the ST80 is currently doing daytime duty as a mounted photography lens for the 700D.

t0ny the Aluminium used in the dovetail is pretty soft. If you drill slightly smaller than 1/4 and then use a hard steel bolt you will be able to cut a thread into your new holes (screw in a little, screw out a little until you get all the way through) and then use your correct bolts to bolt it all together. The advantage of cutting the thread is that you are not relying on a simple sandwich dovetail conection.

Mark your hole positions accurately and punch them with a nail if you dont have a proper punch, before drilling to prevent slip.

It's a very easy job, batt drill will be OK, maybe using the kitchen table was not my best idea. ;)

The 'building scope bit' is the easy part, sorting out the right 'rain go away dance' takes practice. LOL

Edited by RichM63
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If you are stuck or don't fancy drilling and tapping it yourself just mark it where you want the threaded holes (stick masking tape on then draw on the masking tape) and post it to me.

I can drill and tap 1/4 whitworth holes easily and I have a box of suitable length 1/4 whitworth stainless steel bolts.

No charge just cover the return postage. I can turn it round in 24 hours.

PM me for my address if you want me to do it for you.

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If you are stuck or don't fancy drilling and tapping it yourself just mark it where you want the threaded holes (stick masking tape on then draw on the masking tape) and post it to me.

I can drill and tap 1/4 whitworth holes easily and I have a box of suitable length 1/4 whitworth stainless steel bolts.

No charge just cover the return postage. I can turn it round in 24 hours.

PM me for my address if you want me to do it for you.

Thanks Skipper Billy,

I got some bits earlier to have a go, but in the highly likely event of failure that would be great!

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T0ny wrote: -

"So hopefully I can get some 1/4" whitworth bolts (B&Q???) to fix the dovetail to my 150p and then drill two holes to get the ST80 Rings bolted onto the dovetail?"

You will have to buy the whitworth bolts from Ebay as they are not very common now, for some reason the standard tripod mount is still whitworth 1/4" thread, you may need a longer bolt than I used depending on the thickness of the support bar you use for the ST80. 

Cheers,

Fondofchips.

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T0ny wrote: -

"So hopefully I can get some 1/4" whitworth bolts (B&Q???) to fix the dovetail to my 150p and then drill two holes to get the ST80 Rings bolted onto the dovetail?"

You will have to buy the whitworth bolts from Ebay as they are not very common now, for some reason the standard tripod mount is still whitworth 1/4" thread, you may need a longer bolt than I used depending on the thickness of the support bar you use for the ST80. 

Cheers,

Fondofchips.

Argh, you are right.

Do these look correct?

http://www.ebay.co.uk/itm/4x-1-4-BSW-x1-Whitworth-Stainless-Hex-Bolts-Nuts-Washer-VINTAGE-CAMERA-TRIPOD-/261329018300?pt=UK_Photography_VintagePhotography_VintagePhotoAccessories&hash=item3cd86c5dbc

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Yes they are the correct ones, try & order the correct length and you will not have to cut them down to size.

Cheers,

Fondofchips.

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Yes they are the correct ones, try & order the correct length and you will not have to cut them down to size.

Cheers,

Fondofchips.

Yep, I risked it already for the money. 1" Long.

So that gets my Dovetail onto the 150p.

Now I need to get the ST80 onto the dovetail which looks like the drilling part. The ST80 bolts are not the 1/4" whitworth bolts the 150p uses.

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Destroyed a 5.5 drill bit and had to get a new one, but finally (I'm sure you've all been on the edge of your seats) I managed to attach the ST80 to the Dovetail.

post-27902-0-67230300-1421252525_thumb.j

As recommended I cut a thread in the holes so everything is nice and snug, which I believe is how you describe such a fitting. 

Now I'm just waiting on the 1/4" whitworth bolts that should have arrived today, but didn't. Then I can rush outside and test this guiding stuff out against a cloud! So many to choose from right now.

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