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Explore Scientific 16" dob

BinocularSky

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AlexB67

AlexB67

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In my case, I exclusively observe from my back garden...so perhaps if I end up taking the plunge it'll be permanently assembled and probably living in a booth shed since the base is not that wide.

Do you think going as far as 16 inch would be really worth it from urban gardens and the gain you get for home sessions, a lot of which would be of the grab and go type with our glorious weather and all that.  I wonder how often you'd use it versus a 10 - 12 inch in the long run at home.

Not that I ever looked through one mind you, and not saying dark skies are exclusive to just bigger scopes, that said the 16 inch are really DSO hunters aren't they ?, No doubt you'd get some gain from aperture at home, but wondered whether it would be worth it if it is not going to be taken anywhere and is for home use only.    Personally spending that money  and if it was for home I'd like to see the differences in views with skies similar to where you are, before plunging in to be convinced that the tradeoffs are worth it as an often used scope, unless you really have some half decent skies at home. 

No doubt at a dark site it will be a killer scope if you can take it somewhere, that where I see its niche :smiley: , not a gab and go, but a transport and go, and go daaaark  :grin:  

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emadmoussa

emadmoussa

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I understand your reasoning, but given my circumstances and the type of skies I have, I see it as a sound investment. It'll be ideal if I can go to a dark sky location, but first: my skies are decent enough (with 12" I can make out the arms of M51 for instance - ) and second: I don't drive. And for my environmental convictions having a car is not an easy decision to make. Of course unless the new street lights screw it up completely for me..but I pretty much doubt it.

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AlexB67

AlexB67

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Good luck with the house mate.  You can see the arms, such luxury, that sounds like quite good skies, no chance of that from my backyard with the 10 inch, the only arms I ever see are my own when putting in the eyepiece from my backyard.  :grin:

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emadmoussa

emadmoussa

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Good luck with the house mate.  You can see the arms, such luxury, that sounds like quite good skies, no chance of that from my backyard with the 10 inch, the only arms I ever see are my own when putting in the eyepiece from my backyard.  :grin:

 I couldn't see the arms with the 10" ( I think), but I could make them out in the 12"...so 14" or 16" Dob will do it better :)

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BinocularSky

BinocularSky

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Do you think going as far as 16 inch would be really worth it from urban gardens

I do. Aperture is a good remedy for light pollution (which is how we once split Albireo in broad daylight - with the 28" at the RGO). [emoji1]

On the batphone, so expect weird autocorrect

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knobby

knobby

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This is one thing I didn't appreciate with Newtonians...spikes on bright planets especially Jupiter. But hey...they make star look beautiful!

stop it down with a hole in a cap in between the spider arms...
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John

John

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Not quite: they just smear them across the entire image.

On the batphone, so expect weird autocorrect

Mine seem pretty effective - I don't notice any "smearing", just the lack of diffraction spikes and very nice resolution :smiley:

Edit: anyway, this is going off topic, sorry.

Nice scope Steve and I look forward to reading your reports on how it performs  :smiley:

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russ.will

russ.will

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I used an aperture mask on my old SW 12" dob and it was an experiment well worth doing. I effectively ended up with a 4" F15 Newt with zero CA. The moon was breathtaking and the planets weren't to shabby either!

If the ES webshop ever starts working, I'll build another for the 12" dob I'm trying to order....

Russell

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BinocularSky

BinocularSky

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Mine seem pretty effective - I don't notice any "smearing", just the lack of diffraction spikes and very nice resolution :smiley:

At the risk of doing a "Custer":

* Diffraction is an edge effect: whilst it is true that you don't notice diffraction spikes with curved vanes, it is there all the same; it is just omnidirectional (perpendicular to each point on the vanes). All else being equal, curved vanes will be longer than straight ones, so will have more diffraction. It affects contrast.

* Resolution is dependent on aperture, not diffraction.

* Ultimately, it's a matter of preference - not a case of one being "right" and the other "wrong". :laugh:

Edit: anyway, this is going off topic, sorry.

Nice scope Steve and I look forward to reading your reports on how it performs  :smiley:

Indeed & thanks... :laugh:

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emadmoussa

emadmoussa

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Curved secondary supports eliminate them altogether. 

Yep, seen some of these. However, they're not commercially very available, are they? Anyhoo, Jupiter aside I love the spiky stars...isn't it the point of ''twinkle twinkle little star"?! :) Out of curiosity, how do they curved secondary show stars?

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Mike73

Mike73

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I recently asked OOUK why they didnt supply their scopes with curved spider vanes anymore, they said that although it does stop diffraction spikes it can show a faint halo in images. Worth considering if you have CCD's for eyes. :)

I only notice diffraction spikes on the brightest of stars and I agree with Emad, they are actually quite nice. I dont notice them on Jupiter at all because I'm too busy looking at the planets surface and not its surrounding area.

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John

John

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.... Out of curiosity, how do they curved secondary show stars?

As condensed points of light. It splits Sirius and one or two sub arc-second doubles. 

I wish I'd not mentioned them now though, bit of a diversion. Sorry  :embarrassed:

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Ptarmigan

Ptarmigan

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All else being equal, curved vanes will be longer than straight ones, so will have more diffraction.

That is interesting thanks,

I had followed, over the years, the debate about straight vanes concentrating the diffraction effects into 'thin' well defined areas removed out of some other parts of the image - cf. curved spreading these effects diffusely over the whole image.

I had not thought, till now, about your length point ! Interesting !

So, now I am thinking [all else maybe not being equal ! ]  there is the possibility that just two or three curved vanes will be mechanically adequate to support the secondary instead of four in the classical form ?

then which is the shorter ?

It's late, I need another drink ;)

tomorrow is another day  :)

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BinocularSky

BinocularSky

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So, now I am thinking [all else maybe not being equal ! ]  there is the possibility that just two or three curved vanes will be mechanically adequate to support the secondary instead of four in the classical form ?

then which is the shorter ?

As it's OT, continuing this thread-drift topic at http://stargazerslounge.com/topic/213403-curved-v-straight-secondary-support/#entry2285203

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Scosmico

Scosmico

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Hi Steve,

Did you figure out how the altitude bearings fit into the rocker box?

OK, tutorial given, time for some more detail:

Enter one packing box. (The set-square on top of it has a hypotenuse of 24cm):

attachicon.gif20140402_140931.jpg

The box is actually a double box, inside which are the trusses, the collimating rod, and m ore boxes:

attachicon.gif20140402_141032.jpg

attachicon.gif20140402_141204.jpg

 The mirror box has a massive lump of packing foam that holds it the mirror in place and also has recesses for other bits and pieces:

attachicon.gif20140402_141542.jpg (Top is the left of this image.)

attachicon.gif20140402_141555.jpg

The underside of the rocker box. The ground board is the triangle. The silver-coloured stuff is a sort of textured aluminium. There is the same on the altitude bearings:

attachicon.gif20140402_142112.jpg

I wouldn't like to put this together in the dark. I found ti very awkward to attach the truss poles and there is significant danger of cross-threading the M5 securing bolts. M6 would have been better. The eyepiece is the ideal height for my eye. Someone asked: I'm 5' 10" (ish) More importantly, my eye is about 1.65m above ground level when I am wearing normal shoes.

attachicon.gif20140402_150409.jpg

Haven't yet figured out how the altitude bearings are meant to fit into the rocker box (anybody?). However, it's going to be easier to pack/transport than my 300P was.

attachicon.gif20140402_175838.jpg

(In addition to giving a sense of scale, the book is meant to be ironic :laugh: )

The secondary assembly  is going to need a cover, and I'm going to have to make a bag for the truss rods, and a shroud. The finder, as Tom noted in the other thread, is a horrid little thing. Telrad will be an early upgrade, & possibly a proper finder as well.

Not sure about the eyepiece location; I may have to remount the truss fittings on the secondary cage 45* from where they are now (but a lot of people do like the eyepiece on the RHS, so I'll try it. Has the advantage that you can't breathe on the eyepiece when using the finder with the right eye (which I do).

The altitude bearings are sufficiently stiff so as not to slip when the focuser is empty and also when it has a coma corrector and a 2" eyepiece in it. It seems smooth, but I'll need to try it under the stars (typically, it is now overcast and rain is predicted) The azimuth bearing is too stiff. I'm going to need to fix it, either with a lazy susan or with some Ebony Star.

I think this is a very adaptable bit of kit. Unless the optics are rubbish (Tassilo specified a Strehl of 0.8 minimum), I think I'm going to like this. A lot.

Happy to answer questions, but I doubt there'll be much more of substance to say until I've actually tried it under a decent sky.

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