Posts Made By: Bill Meyers

Inge Skauvik said:

Easily transportable Dobsonians are very attractive scopes for persons living in areas with light pollution and unstable weather conditions. With my increasing interest for astro tourism, I'm even interested in something that can be transported as checked luggage with the airlines. Presently I'm using a 12.5-inch Portaball which I have brought with me to the Canary Islands on two occasions. In these cases I have brought along the mirror in its cell as hand luggage. The trips has given me many great views, but I have to admit that even the Portaball is a bit large and heavy as air luggage.
In Europe it is possible to get Dobsonians with larger aperture (up to 16") which are considerably lighter than the Portaball and can be collapsed to much smaller volumes for transportation. The trade-off is (probably) less stability and (definitely) a higher price. Optically they are said to be very good even though the thickness of the mirrors are much smaller than the old standard.
My question is: Is ther anything similar presently available on the American market? Is there anyone willing to take the challenge of constructing an ultralight scope in the 15 - 18-inch range? I have seen photos of the new 18-inch Obsession. Definitely a step in the right direction, but still too heavy for me.

Inge S

Mark Aguirre said:

The newbie here again. I have found the andromeda galaxy through my 8" dob. Unreal. Can anybody suggest something else 'awesome' that I might be able to find? Like another galaxy or . . . .??

Mark Aguirre said:

The newbie here again. I have found the andromeda galaxy through my 8" dob. Unreal. Can anybody suggest something else 'awesome' that I might be able to find? Like another galaxy or . . . .??

Angel Gomez said:

Who said folks in Alaska are the only ones getting their very own ICBM interceptors?

With the help of my daughters we decided to assemble our very own missile defense. I'm happy to report South Florida is much safer now. The ladder in the back leads to the super secret command post made to look like a tree house / tiki hut.

The axil of evil will never know what hit them!

Enrique Barrio said:

What is it about the design and execution of newts that makes them so sensitive to collimation. I understand that all telescopes require proper alignment; but, once that is achieved why isn't the mounting system designed to hold the correct collimation indefinitely? Is there a need for the variable mirror cell, or can the mirror simply be mounted in a more riggid and durable cell and tube assembly?

Michael Garretson said:

I have an 8" Celestron Star Hopper that I've been happy with for over 10 years. It's the second generation "white rocker box" type that I believe were made for Celestron by Discovery.

While I've enjoyed the scope, I have a nagging suspicion that I have never been able to accurately achieve proper collimation.

Some background:

The secondary is held in place by a single post. This post is in turn mounted to the inside of the OTA and held in place by one of the screws that are used to mount the focuser.

Looking down the focus tube without an eyepiece, I can swear that it appears that the secondary looks like it's mounted too far "down" the OTA, and should be moved "up" closer to the "front" of the OTA.

I say this because it "looks" like the secondary isn't centered under the focus tube. I can clearly see the leading edge of the secondary as well as it's "back".

When I try to collimate the scope I go through the following process:

I marked the center of the primary years ago.

I use the Celestron supplied Collimation Tool that came with scope for the initial "rough" collimation.

This is followed up by a "fine" collimation using an Orion Laser Mate Deluxe.

Everything appears to go smoothly up to this point, but when I go out and do a star test, the shadow of the secondary and post is always off center, and the location of this off centered shadow is consistently in the same location, no matter how many times I repeat the process.

The diffraction rings are concentric and consistent – both in and out of focus – around this off center shadow, and the images from the scope are on par with that found on my other scopes.

If I move the primary to try and center the shadow when performing a star test, the resulting images are no better - or in fact may be a hair worse.

While I'm basically happy with the scope, I always have this nagging feeling that if I moved the secondary to a more "centered" position underneath the focus tube I could improve the situation.

Since I'm afraid to start "hacking away" at the scope, I wonder if anyone else has had the same issue, and what did they do about it?

Any help would be appreciated.

Thanks.

Mike Garretson

Theodore Goodman said:

Hi - I am new to this forums and need some assistance.
I just had my scope (Orion 8" Newtonian) collimated by a "professional". When I brought it home, I sky tested it on a normal dry evening. The results were good using a 20mm eyepiece, but not good when using a 12.5mm eyepiece. I wrote back to the professional and the response was that the result of using a 20mm meant that the scope was collimated, but the night was not a good night for viewing with the 12.5mm.

I leave in the NY Long Island area.

The scope now does not work well with the 20mm on one of the best nights of viewing.
Here are my questions.
1. How can I collimate this scope so I do not have to bring it a professional?
2. If the primary mirror does not have a center spot or line, is there a way to collimate?
3. I purchased a Orion LaserMate Collimator, but I am not really sure how to use it. Can any one assist?

Thanks in advance.

Linton Rohr said:

Okay...I'm cheating...it's not my scope...it's my architects.
He just recently took it out to test the tracking.
I was pretty impressed...
I hope our house turns out that nice!
Linton

Linton Rohr said:

Okay...I'm cheating...it's not my scope...it's my architects.
He just recently took it out to test the tracking.
I was pretty impressed...
I hope our house turns out that nice!
Linton