Posts Made By: Ed Blankenship

Roman,

Looks like good progress to me !!! Can you show a photo of the back of the scope with your plate ?

If you want to check collimation using your "stand", you should consider using Polaris as a target Star. Assuming you are in the northern hemisphere, Polaris moves very little in the night sky because it is near the North Celestial Pole (NCP) and is very convenient as a star for checking your collimation with a mount that does not track.

Ed (aka eblanken)

Hi Roman,

Thanks for posting the photo of the back with the plate installed. Interesting to read about how you acquired the Questar and what you have done to it so far.

Oh and by the way, welcome to Astromart. You may or may not get much response here, but I can help you so far as what is in your immediate future.

Getting a diagonal is a next logical step and you have already got one "on-the-way" so that is good. There are ways to check for gross-mis-alignment that are pretty easy. Then there is a much more precise alignment that will be more challenging.

As you can imagine, the entire optical path must be aligned for optimal performance. However, for your purposes, checking for gross-mis-alignment is your next task after you figure out how to "position" the diagonal and the eyepiece in the "best" positions in that optical path. Good external focusers are available to supplement the internal  MIRROR Moving Mechanism (which has it's limitations), but that's where you are starting. 

Do you have any eyepieces at all ? If no, then getting even a cheap one would be a step in the right direction. So far you have seemed to be somewhat cost concious, which is understandable. Perhaps I can help you buy or borrow an eyepiece or two or three ?

Oops, gotta check on something here at work.

Later,

Ed (aka eblanken)

Hi Roman,

Sorry to be absent: Worked 12 hours each day in the last three. Some parts of my job allow time for AstroMart, some parts not.

So your Mak (Maksutov) is a Cassegrain often referred to as a MCT. I have 8 inch Schmidt Cassegrains (SCTs for short) and (smaller) MCTs as well. It is standard to have a single speed focuser. I have upgraded the focus knob/mechanism on my each of my three SCTs to a Feathertouch(R) branded dual speed focuser which has both a course and a fine focus (with a gear ratios of 10:1 or 11:1, I just can't remember). Others put an external focuser on the back of their MCT or SCT especially if their SCT has what is called "focus shift" or "Mirror flop" limiting their ability to do a proper fine collimation. Your Questar is probably better quality and precision that many of the SCTs out there so may be just fine with only a single speed focus knob, but may also suffer from some lesser level of this "Mirror Flop" as well. I don't know. Some prefer using an external focuser, especially for imaging to avoid the problem. They only use the internal focus knob for "course" focus like you infered. The problem you have is to be able to locate an eyepiece or diagonal/eyepiece precisely enough onto the back of your Questar. That will take some clever engineering on your part.

One thing you should know is that as you move the focus knob which moves the primary mirror, you change the spacing between the primary mirror and the secondary mirror, which changes the focal ratio, so stating the ratio to 4 significant figures (f/13.48) is a bit of being over-precise. I'd round that to f/13.5 and know that as you run the focus knob from one extreme to the other you are going to change the value slightly. Some others know how much, I just round. Your value of 2400mm will also change by a related amount as well, but don't get hung up on that.

Whatever you do to try and locate the diagonal/eyepiece or camera needs to have adjustments for up/down, left/right and tilt but also needs to have provisions to lock those down after you find the precise location after you find it.

Ed (aka eblanken)

Hello Paul Brunning and welcome !

This site (AstroMart) is known worldwide for the Classifieds, but has fallen into less than it was in the past for Forums.

You might have better response from the "Cloudy Nights" website forums. Just Google it.

Ed (aka eblanken) on both sites.

Originally Posted by Barry Young

Hey:

First post on Astromart.

We are moving to our new to us retirement home in SE Missouri. This place has awesome seeing. The nearest town is 23 miles away with a population below 300. The nearest neighbor is more than half a mile away. I mean it is in the middle of nowhere just left of in back of beyond. The expectation is to have the most wonderful clear skies ever experienced. 

The intention is to try to do world class amateur astrophotography on a retirement budget.  We will build an observatory with a concrete pier. We have a complete machine shop that is moving with us. Not sure whether to purchase or build a GEM. If anyone has scratch-built a heavy mount We would love to hear from them. Why do people build steel piers when steel embedded in concrete is more rigid?

For an OTA, we are thinking a C14, or something along those lines. Need advice on that. We loved our Meade ETX90, but that is the largest telescope we have owned or used. We see lots of advice about jumping up in small increments. But that would not satisfy our desire to do astrophotography of planets and deep sky objects. We can only afford to do this once rather than trading up over and over. Perhaps a refractor would be better? There is an older gray colored C14 OTA only for sale from a friend at $2K. We would like to help our friend, but do not want to buy the wrong telescope. We get one chance only and need your help. 

Thank you

Barry

Hello Barry and welcome to AstroMart !!!

Much of what Greg says makes sense to me. It is a HUGE step from an ETX-90 Mak to a C-14 SCT. I have read and re-read you post several times. I understand the situation about helping your friend and obtaining the gray C-14 at the very favorable price of $2k, (which assumes the optics are great).

I have a friend who has a C-14 that has been "upgraded' from the Celestron fork mount to a much sturdier Mathis 500 fork mount. He's even considering a mount upgrade beyond that 500 lb (edit-make that 120 lb) payload rating. He is considering the upgrade because his mount is old and needs a modernization of motor controls. Modern mounts have computer controls that make GOTO happen "seamlessly" in the background. The C-14 also needs a DOME or a Roll-off-Roof enclosure to protect it from the weather in SE Missouri. What are your plans for housing the mount that would "properly" carry a C-14 ?

Respectfully,

Ed Blankenship (aka eblanken in both places: AstroMart and Cloudy Nights)

Hi again Barry,

I was impressed with your experience base. You have worked on some "cool stuff" which I can relate to (40+ years in high tec & BS Physics). I am employed as a Radio Interference Expert (IEEE EMC member with 12 published papers).

It sounds like common sense and "stepping back to see the bigger picture" has prevailed. I am a strictly visual observer that travels 100 miles to dark skies. I do some observing from my backyard, but the "sky glow" from nearby Portland Oregon washes out many objects, so I don't have any permanent setup at my house.

I wish you all-the-best in your relocation. I find that between AstroMart (for buying and selling) and Cloudy Nights (for the better forum paticipation these days) I can stay up-to-date with happenings in the astronomy hobby community. I also mentioned my friend who has two domes and much bigger scopes than my 8 inch SCTs and 6 inch refractors.

Very Best Regards,

Edward A. "Ed" (aka eblanken) Blankenship

Barry,

If the fork on a wedge is aligned with the North Celestial Pole (NCP) then you are fine with a fork on a wedge instead of a GEM. The problem with a fork NOT on a wedge, is field rotation. Think of the constellation Orion: When it rises, it is on its side, When it is high in the Southern sky it is upright, When it sets in the West it is on the other side. Fork on a wedge keeps the OTA oriented correctly like a GEM, Fork NOT on a wedge does not keep field rotated correctly.

One issue is that the fork needs to be stiff enough to keep from flexing from the load held "at arms length", so the forks are rated for a lower payload than a GEM which has the OTA closer to the axis.

Ed (aka eblanken)

Hi Robert and Rod,

Good review !!!

I am quoting Robert's summary: "In summary, the Mewlon 210 is a fine telescope, but does not have the dramatic clarity of the AP130 with which I have it paired nor of the TEC 180 which it replaced. It’s a fussier scope, being more sensitive to altitude and skies than the apos.  The 1.25 inch EPs are easier to observe with than are the 2 inch EPs.  Prolonged observation is more comfortable for me with this scope, so I will likely be spending more time in my sadly-neglected observatory than I have this year.  While this is a good thing, I was sorry not to experience a first night of dramatic, breath-taking views with the scope."

I have to agree with Rod about the seeing being more of a problem for the larger aperture. No surprise.

Ergonomics = +1, Refractor-like contrast = -0.5.

I, like Rod, am similarly confused: Did you buy from Herb in WA or from TX ?

Ed (aka eblanken)

Hello Herb York,

I am sorry for your loss. I will pray for you and your family that are left behind. Please message me or email me if there is anything that I might be able to do for you beyond my prayers. Thank you for your many years of service to our community here on AstroMart. I believe in Jesus and Heaven. Some day (perhaps soon) my Mom will join yours.

Ed (aka eblanken) Blankenship

P.S. I am interested in your posted photo. When you get time, perhaps you and I could discuss it. No hurry.

I concur with Greg:

This should work with the 20mm extension. Or there might be enough focuser travel to not need that extension.

It might possibly vignette a little (Is that the word Greg ?), but that would be minor.

Ed (aka eblanken) Blankenship