Explore Scientifics 12" dob

[earth titan]

Tom, what is the diametre of the truss poles? I want to source some foam tubing that has a minimal overall diametre and will be a nice tight fit.

Russell

I'll measure them later. I just picked standard 15mm pipe lagging TBH.

[swamp thing]

Tom, what is the diametre of the truss poles? I want to source some foam tubing that has a minimal overall diametre and will be a nice tight fit. Russell

Why not use some heat shrink rubber Russ. That's what I used on my 20" Dob. It gives a nice warm grippy feel in winter and adds little to the diameter. It's also harder wearing than pipe lagging. It obviously is a super tight fit

Just a suggestion

[russ.will]

Now, the idea of heat shrink did cross my mind, as I saw that whilst Googling suppliers of foam tubing, so it's nice to hear from someone who has done that already. I could even get it in ES yellow.....

Russell

[BinocularSky]

Now, the idea of heat shrink did cross my mind,... I could even get it in ES yellow.....

Extending that idea: use it to colour-code ťhe poles. Hmmm....

On the batphone, so expect weird autocorrect

[emadmoussa]

Erm.. heat shrink, that's a good idea indeed.

Speaking of colour coding, does that mean you can't use the poles interchangeably?

[estwing]

Don't see the point you've either got the shroud on or if it's cold you've got gloves on

[emadmoussa]

Don't see the point you've either got the shroud on or if it's cold you've got gloves on

Speaking of which, what type of fabric do you use for you nice shroud?

[BinocularSky]

Tom,
 I've just noticed a 12" lightbridge shroud going for £11 on Astroboot. I don't know if it would fit, but might be worth investigating.

I'll measure them later.

On the 16" , they are 25mm diameter.

Speaking of colour coding, does that mean you can't use the poles interchangeably?

The point is that you can use the poles interchangeably, but they are bound to be slightly different so (theoretically anyway) if you always put the same poles in the same place, collimation (essential every time you assemble it) may be easier.

[emadmoussa]

Tom,

 I've just noticed a 12" lightbridge shroud going for £11 on Astroboot. I don't know if it would fit, but might be worth investigating.

On the 16" , they are 25mm diameter.

The point is that you can use the poles interchangeably, but they are bound to be slightly different so (theoretically anyway) if you always put the same poles in the same place, collimation (essential every time you assemble it) may be easier.

Makes sense I guess..

[swamp thing]

Don't see the point you've either got the shroud on or if it's cold you've got gloves on

It's not a necessity true but there are some reasons I fitted them.

1) light scatter. Anything shiny near the optical,path isn't clever.

2) Warmth to the touch. I don't wear gloves when setting up I don't like that lack of feel they give. The rubber also provides a grippy surface. Wet ally is slippery.

3) keeps ya hands clean. Ally soon gets a coat of black filth on it. This prevents that getting on your hands.

This last point can be ignored if you keep cleaning your scope instead (get a life )

[BinocularSky]

It's not a necessity true but there are some reasons I fitted them.

1) light scatter. Anything shiny near the optical,path isn't clever.

2) Warmth to the touch. I don't wear gloves when setting up I don't like that lack of feel they give. The rubber also provides a grippy surface. Wet ally is slippery.

3) keeps ya hands clean. Ally soon gets a coat of black filth on it. This prevents that getting on your hands.

4) If (as I do) you wear fingerless gloves unless it's really cold, the "warmer to the touch" (actually, reduced thermal conductivity) is still an advantage.

5) The paint flakes off the ES tubes. Uncovered, it will eventually find its way onto the optics.

[estwing]

I can see your point about light scatter Steve ,I may just tape the inside of the poles

[russ.will]

I've just had first light with mine.

Secondary collimation is certainly different.... How the heck do you measure where the central axis is with no central bolt holding the secondary?

Russell

[John]

I'll be very interested to hear what you think of it's performance Russell. I've been fishing around on the Cloudynights forum for feedback but no one there seems to have one.

Mars is looking good tonight from here (despite the Moon) so that would be a nice test object if it's clear for you too

[BinocularSky]

I've just had first light with mine.

Secondary collimation is certainly different.... How the heck do you measure where the central axis is with no central bolt holding the secondary?

Not really relevant: the central bolt is usually on the physical, not optical, central axis.  I assume the secondary in the 12" is offset like it is in the 16", so you really need to be collimating on the optical axis, or you will get astigmatism.

[russ.will]

Yes, but I assumed the central bolt was on the optical axis, as it was offset relative to the mirror on all the previous Newts I've owned. How do you find it on this one?

Sent from my Nexus 5 using Tapatalk

[BinocularSky]

Not sure exactly what you're trying to do, but:

* Your offset should be 3.75mm (minor axis / (4* focal ratio) = 75mm  / (4*5) = 3.75mm)

* The optical centre of the secondary is 5.3mm from the physical centre ( sqrt (2*(3.75^2) ) ) (if you want to mark it)

* Assuming your offset is correctly set (mine is) the secondary should appear circular through a peep-tube and the reflection of the primary should be central in it.

HTH

[Moonshane]

in other words, just collimate as normal with a cheshire?

[BinocularSky]

in other words, just collimate as normal with a cheshire?

That's what I did.

[russ.will]

Okay, that's what I did in a quick and perfunctory fashion last night. It just crossed my mind that the lack adjustment up and down the optical axis might make things different somehow.

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[earth titan]

Okay, that's what I did in a quick and perfunctory fashion last night. It just crossed my mind that the lack adjustment up and down the optical axis might make things different somehow.

Sent from my Nexus 5 using Tapatalk

I pondered on the lack of up and down adjustment the other day. When I looked through it with a collimation cap though, it looked about right so I left it.

I always find a Cheshire impossible to use in the dark so generally rely on a laser. I think once the secondary is set, it is unlikely to be too far out when reassembled - even on a truss dob.

[Moonshane]

the first adjustment (position re the focuser) will be fine but you may need to tweak the tilt every now and again depending on construction. the primary will always need it (probably). I use my dim torch on the 45 degree face when using a cheshire at night but just find a way that works and then get on with it

[estwing]

I've not touched my secondary yet

[swamp thing]

I've not touched my secondary yet

Have you actually done anything collimation wise Cal?

[BinocularSky]

Okay, that's what I did in a quick and perfunctory fashion last night. It just crossed my mind that the lack adjustment up and down the optical axis might make things different somehow.

If it's too far out, you will probably notice some astigmatism.

I always find a Cheshire impossible to use in the dark

I try to set up in twilight, then it's not a problem; otherwise I do the same as Moonshane (dim torch). (Never got on with laser collimators.)