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Why is Orion the only dob with a handle under the front opening?

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#26 Joe1950

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Posted 01 December 2019 - 11:10 PM

Yea, seriously!  On a cool night look at a bright star with some power and defocus it to about half the field. Then put your hand on the metal tube or in front of the scope and you’ll see the waves of heat rippling across the image.


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#27 wrvond

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Posted 01 December 2019 - 11:10 PM

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#28 Joe1950

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Posted 01 December 2019 - 11:14 PM

What?  There’s no question about it. I’ve seen it hundreds of times myself. The cooler it is, the more pronounced the effect.

 

And, if Mr Isaacs posts something, I always read it and I always learn something. He is one of the most knowledgeable and experienced people on this site!


Edited by Joe1950, 01 December 2019 - 11:25 PM.

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#29 Jon Isaacs

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Posted 02 December 2019 - 02:24 AM

Hmmmm... seriously?

 

Seriously.  As Joe says, try it. Defocus a star and then put your hand on the tube for a few seconds, not necessarily on the end, and look at the image.  If you really want to see a show, put your hand in the light path or just below the light path. 

 

It does require a fully cooled scope and decent seeing.  Just defocusing the image and looking at the stability of the disk is a good way to evaluate the thermal acclimation of the scope as well as the seeing.  

 

Jon


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#30 stargazer193857

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Posted 02 December 2019 - 03:23 AM

Seriously. As Joe says, try it. Defocus a star and then put your hand on the tube for a few seconds, not necessarily on the end, and look at the image. If you really want to see a show, put your hand in the light path or just below the light path.

It does require a fully cooled scope and decent seeing. Just defocusing the image and looking at the stability of the disk is a good way to evaluate the thermal acclimation of the scope as well as the seeing.

Jon


How do you tell acclimation from seeing?

#31 Miranda2525

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Posted 02 December 2019 - 04:16 AM

Skywatcher, zhummel, explorescientific all don't put handles under the ends of their dobsonians. Why?

https://www.cloudyni...24454-dob-knob/

That is what I'm talking about. The poster says other companies used it, but I've only ever seen it on Orion scopes.

How long have those been around? Also called navigation knobs, for slewing the scope.

Most companies will not make a small handle like the one in your link to save money.

 

Grabbing the end of the tube will induce heat plumes into the light path. Also, a dew shield should be on the end of the tube anyways, which negates grabbing the end, unless you live in a really dry area and you don't need a dew shield, or you may use a dew shield to stop stray light from reaching the EP.

I made my own handle. I drilled a couple of holes and added a brass slewing handle. Very easy to do. The handle is needed as I cannot grab the edge of the front of the tube because I have a dew shield on my telescope, plus I don't want heat plumes in the light path.


Edited by Miranda2525, 02 December 2019 - 04:23 AM.

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#32 Miranda2525

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Posted 02 December 2019 - 04:18 AM

Seriously.  As Joe says, try it. Defocus a star and then put your hand on the tube for a few seconds, not necessarily on the end, and look at the image.  If you really want to see a show, put your hand in the light path or just below the light path. 

 

It does require a fully cooled scope and decent seeing.  Just defocusing the image and looking at the stability of the disk is a good way to evaluate the thermal acclimation of the scope as well as the seeing.  

 

Jon

Oh yea, you sure can see it. I have tried that before.


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#33 Darren Drake

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Posted 02 December 2019 - 07:42 AM

This is all absolutely correct just as you dont want a person standing under the optical path especially in winter...


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#34 outofsight

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Posted 02 December 2019 - 05:02 PM

My 10" SkyWatcher has two knobs on it, my 12" Orion only has one knob. Thanks a lot for bringing this up, I was never concerned about this before, now I have to throw the Orion away.


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#35 Joe1950

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Posted 02 December 2019 - 05:09 PM

I'll be out by the curb!  grin.gif 


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#36 lphilpot

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Posted 02 December 2019 - 05:10 PM

This is all absolutely correct just as you dont want a person standing under the optical path especially in winter...

Defocus a star and hold your hand in the optical path... Pretty obvious!  :)


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#37 nirvanix

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Posted 02 December 2019 - 05:27 PM

I learned to love the knob because I was getting too much Cheetos dust on the primary. grin.gif

 

Seriously, I added my own plastic $1.50 knob from HD and find it so much better for slewing. Gives a feeling of precision, and if your ota is balanced nicely on the mount it's even better.



#38 SteveG

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Posted 02 December 2019 - 07:23 PM

Lot's of options here. I buy from these guys all the time:

 

https://www.jwwinco....and-knobs/knobs


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#39 rowdy388

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Posted 02 December 2019 - 09:16 PM

I installed navigation knobs on my solid tube, metal OTA  dobs and enjoy using them. 

I didn't feel the need to put one on my truss dob with its wooden ring at the top of the

secondary cage.


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#40 25585

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Posted 03 December 2019 - 05:06 AM

Depending on the curvature of an OTA, a suction knob or handle might work. 


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#41 wrvond

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Posted 03 December 2019 - 08:02 AM

OK, I'm convinced. wink.gif

 

solved.jpg


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#42 25585

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Posted 03 December 2019 - 11:39 AM

Nob-ody does it better..


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#43 clearwaterdave

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Posted 03 December 2019 - 05:51 PM

I like my joystick better than the nob.,I can control my scope with my hands in my lap rather than held up in the air.,Much more comfy for me.,

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#44 Astrojedi

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Posted 03 December 2019 - 07:59 PM

Skywatcher, zhummel, explorescientific all don't put handles under the ends of their dobsonians. Why?

https://www.cloudyni...24454-dob-knob/

That is what I'm talking about. The poster says other companies used it, but I've only ever seen it on Orion scopes.

How long have those been around? Also called navigation knobs, for slewing the scope.

I have one on my Sky-Watcher 10" F4.7 solid tube dob. Quite handy for swinging the OTA around.


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#45 peleuba

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Posted Yesterday, 04:41 PM

Skywatcher, zhummel, explorescientific all don't put handles under the ends of their dobsonians. Why?

 

I don't know, but I thought it was a fantastic idea so copied it for myself on my StarMaster 11.

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#46 Asbytec

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Posted Yesterday, 11:43 PM

How do you tell acclimation from seeing?


Defocus inward on a bright enough star to see the secondary shadow clearly. If you see slow moving waves or lines and spikes along with slowly evolving dark areas (avail light is constant), then you are seeing effects of acclimation. It's like seeing caustic lines on the bottom of a pool on a sunny day. The star will exhibit some spikes in focus, too.

To best see atmospheric affects, focus outward (almost as if focusing on the atmosphere above) and look for faster moving sheets of air blowing over the defocused image. Or look at the limb of the moon or a planet. It will exhibit a rapid waviness of the image. In focus, stars are more messy.

Basically, acclimation is slow moving affects in a defocused star image, and atmospheric seeing tends to be faster moving affects.
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#47 stargazer193857

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Posted Today, 10:18 AM

Defocus inward on a bright enough star to see the secondary shadow clearly. If you see slow moving waves or lines and spikes along with slowly evolving dark areas (avail light is constant), then you are seeing effects of acclimation. It's like seeing caustic lines on the bottom of a pool on a sunny day. The star will exhibit some spikes in focus, too.

To best see atmospheric affects, focus outward (almost as if focusing on the atmosphere above) and look for faster moving sheets of air blowing over the defocused image. Or look at the limb of the moon or a planet. It will exhibit a rapid waviness of the image. In focus, stars are more messy.

Basically, acclimation is slow moving affects in a defocused star image, and atmospheric seeing tends to be faster moving affects.


Interesting. Can anyone else comment on slow vs fast and in vs out?


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