Posts Made By: John Holt

"I was thinking about the edmonds but there may be an issue with a fast scope."

Hi,
If you are refering to the Edmunds RKE 2.5x barlow, then there is no issue with fast scopes. It has been sold for years by them as their barlow for their f/4 Astroscans.

Optically it is a good barlow. However, it is not a Powermate. It is just an old style two element, loooong body barlow: 7"long! And rather heavy as a result. Perhaps because of it's configuration, it does not seem to add much eye relief to an ep. But to be honest, you have to feel strongly about using one, to be using one, because I have not found it to be any better than other good quality barlows.

John

Respectfully, I don't think any Kellners or RKE's will be any kind of a cost effective upgrade over the ep/barlow combination you have.

Regarding eyeglasses: I have found an adjustable strap on my glasses to be of enormous benefit at the scope. Adjusted so the glasses stay up on my head, or forehead (depending on hat) when at the ep. I can then pull the glasses down in a wink to use the finder or charts. This works much, much better than glasses dangling around my neck, or worst yet, set aside somewhere on a table or in a pocket.

Regarding older ep designs, due to your long focal ratios, most of the simple and affordable wide field designs will work well. This has been my experience. My 2 cents is to not duplicate any ep focal length combo's you already have. At least not right away!

John

Sir,
That is a great looking scope. It was interesting to read your design goals, and see your solutions. Very neat scope!

john

"The collimation is impossible with the current configuration. A thick single metal bar is all that holds the mirror. No adjustments can be made to the secondary mirror."
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Hello,
This is adjustable. By loosening the mounting bolts that hold the bar to the tube. This allows for changing the angle of the secondary, as well as some small movement toward/away from the focuser, and up/down the tube. If this is not enough, then the mounting holes can be enlarged, or the secondary bar reshaped. My old Coulter manual suggested reshaping the bar as needed. I loosened the bars' mounting bolts first, prior to removing it for this. A little of both gave enough movement for the adjustment required.

While it is not the the acme of collimational perfection, these old Coulters have oversized secondaries by todays standards anyway, so perfect millimetric centering of the secondary is not going to really cost anything in illumination. The primary is aligned with the focuser.

Regarding minor defraction/contrast loss issues due to this(and then there is secondary offset -vs- non offset) it pales by comparison to the thermal issues that occur with a scope of this size. That will have a far larger effect on the image.

john

A Klee 2.8x combined with a lower power ep you may already own? These are light weight, and optically good.

Large and heavy is a real deterent and requires countermeassures. If you consider placing the scope outside in your yard, then perhaps a storage shed would work. They are pretty darn affordable. It can be dedicated to _just_ your scope/astro gear and nothing else. Or your scope and whatever else you want, obviously. It can be used for that whatever else at any time in the future too. The shed can be a win, win solution if the garage is really not an option.

Due to the urban forest, I do not do much observing from my yard anymore. I choose rural sky, with some horizon and darkness. Therefore my heavy newt has spent the last five or so years in the back of my pick-up truck. That's not a recommendation. It was just the countermeasure I choose due to the size and weight of the scope being a deterent to using it. It also gives me instant mobility for rural sky. If I lived in rural sky, I would definately store the scope outside in a garage or shed.

I have seen it in a 13" without filters.
The sky needs to be dark. If the atmospherics are allowing good structural detail in the nearby Flame Nebula, then it is a good night to try for the Horse Head. Detailed charts of it's field help greatly.

Pass on the UO cell.
There is a reason that these cost so much less than other aluminum cells. Yes, they are open, light weight, and collimate quickly. The catch is mirror support, or rather lack of.

Their 12.5" cell that I had was a only 3 point. Their 13" is a nine point, but it's three groups of three in radial lines like spokes. This poor support yields astigmatism. Your images will certainly suffer, in my experience. Any additional adaption to the cell in the way of mounting bolts, stiffer springs etc, will nibble away at the cost savings.

Their cells are in fact very robust. And affordable. They are a good cell for smaller mirrors. But, they are poorly designed for a scope this size, IME.

If it is in it's original configuration, then it will be pretty heavy for a ten inch dob. Very stable, but heavy. Plate glass mirror in a closed cell. So it can take a while to cool to ambient temp. Original equipment Coulter's are functional, but by today's standards they are very much a project scope: lots of improvements possible/desirable.
However, if the scope already has upgrades (often in bearing surfaces, active cooling, focuser etc) then it will perform on par with any 10" f/4.5 newt.

"I know that I should spend money on EPs but please...."

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No you shouldn't.
You are going in the right direction now: aperture and focal length, on the mount of your choice.

Chicago is cold in the winter. If you want to view in this weather, then also consider scopes that will reach thermal equilibrium in a reasonable amount of time.