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 Post subject: Shhhh....don't tell
PostPosted: Sat Jan 11, 2014 4:25 am 
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Velocepedist
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I know I'll get the "Why do you need another telescope" comment from the CFO. But I'm seriously entertaining the construction of another Newtonian reflector. So here goes my reasoning (not like anyone here needs it, but anyway)...

My first project was a rebuild of a Bushnell (same as every other) 4½" ƒ8. Redid the primary with Carry at OWL, new smaller secondary, flocked and cooled. Really just a supercharging.

The second project was a complete ground up job using an "available-to-me" 10" ƒ4.5 mirror. All parts were new aftermarket pieces, of custom construction, so it was a true "scope build" project is every sense. However, I was attempting to do it on a budget, so I kept the mirror as is and just recoated it. Some of you may recall that I convinced myself that it would be fine. And frankly it was. The scope performs beautifully. But despite my best efforts to reduce the OTA weight compared to the OTA that the primary was shucked from, it's still a beast on my Starfinder GEM.

So I have two excellent Newts, but neither is the design I would have chosen had I started from scratch. By that I mean starting with a primary mirror design of my own choosing. Despite this, I've learned a ton from both projects.

The 4½" is a bit small for my liking with regards to light gathering, and the 10" is definitely larger than I prefer regarding size and weight. Funny, the 10" was just acceptable...before I got the binoviewer. But I'm not making the same mistake twice. I sold my Denk because it caused too much cantilever vibration on my scopes, and getting rid of the BV was the easiest solution. Unfortunately I have missed the "two-eye" experience ever since. So the Maxbrights are here to stay. I could just get a bigger mount...but that's probably not going to happen. The Starfinder is not small as it is, and my expectation for vibration "free" mounting is probably unreasonable to expect from anything less than $1500-2000 with a 30-ish pound 10" OTA (with accessories attached) to make me truly happy. BTW, Kerry, I was looking seriously at those Optic-craft mounts, and I very much appreciate the link. The vintage appearance appeals to me more than something new and their prices are certainly very good for the strength. But adding a drive nearly doubles the price. Just too rich for my blood right now.

That puts me in the 6" or 8" range for a scope that appeals to my observing tendencies, which is mostly L&P (and solar wl) with wide field DSO observing as a requirement for good dark summer nights, and April (Virgo, of course). I've recently modified my 4½" with a 2" focuser, and it's amazing to use my 40mm SWA 5000 in that scope which gives me 3º of TFOV and stars that are razor sharp to the edge! So I think I want to stay below 1000mm of fl for sake of low power observing, and together with a smaller mirror I'm hoping it will keep the vibrations on the mount that I already own to visually acceptable levels.

Honestly I think I'm leaning toward the 6". I could really keep the weight and length down from my 10", nearly double the light gathering of my 4½ ", and have a collimation friendly focal ratio. On that note, I could use my 40mm SWA more often again. The exit pupil is just a wastefully ginormous 9mm (!!!!) in my 10" ƒ4.5, but I have to say that I really love that piece, possibly as much or more than my 26T5.

Blah, blah, blibby, blah, blah.

Okay, now that I've wasted the time of anyone who actually read this...

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 Post subject: Re: Shhhh....don't tell
PostPosted: Sat Jan 11, 2014 9:18 am 
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Jason, are you going to keep the 10'? I think you may miss the aperture for the deep-sky observations. If you keep it great, but if you are thinking of parting with it, you may want to hold onto it for a while until the other scope is finished, and make sure you are good with the situation. I learned the hard way to never sell a scope first in order to fund another one.

For L/P work I agree with the 6" ~f/6.5 (1000mm f/l). I'd rather have the f/6.5 myself, but I'd also rather have at least 7" for L/P work. I find 6" a bit small for L/P. Too bad you can't do a 7" f/5.6. That would be a nice little scope, still above f/5 but a little extra punch for the fine L/P detail. I used a 7" f/6 Mak-Newt and it was a fantastic scope. More detail than in a 6, but easier to handle than an 8". Great deep-sky wide-field views, but easy spiral arm detail in M51, and some fantastic views of Jupiter. 7" is a good compromise size if you can get someone to do the mirror.

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Oh, yeah. The Stifmeister's coming back to Grand Harbor. Deck the halls. Bye-bye, Great Falls. Wipe my a$$ and lick my ba!!s It's Stifler time, baby. Whoo-hoo-hoo. Whoo-hoo-hoo. ~Steve Stifler-American Pie 2 :lol: :lol: :lol:


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 Post subject: Re: Shhhh....don't tell
PostPosted: Sat Jan 11, 2014 11:49 am 
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I would go with an 8". I know the weight is a bit more than the 6" but there's a pretty large difference in light gathering power. I think an 8" Newtonian f/5-f/6 is a perfect balance of weight, light gathering ability, and planetary performance. I've owned a couple of 6" scopes and I ended up getting rid of them (well, the 6" Meade SN was a complete piece of Schmidt but that's another story). Just not enough light gathering for deep sky and resolution on planets to be satisfying. YRMV.

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 Post subject: Re: Shhhh....don't tell
PostPosted: Sat Jan 11, 2014 12:47 pm 
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All good recommendations, guys. Thanks! :smile:

Well, I've been thinking all morning about this.

First off, no I'm absolutely not parting with the 10". So much went into that project that it's kind of like a child now. :lol: The aperture, combined with 96% coatings, makes for a superb DSO scope. I've already seen some of the best views of galaxies with that mirror and I don't intend to give it up. Mono viewing with Naglers from 40-130x is the bees knees. Planetary performance is also very good. But again, at those magnifications the vibration is just more than I like. Call it a specialty scope that comes out when Jupiter, Saturn and Mars are out of season.

I'm also not parting with the 4½" scope. The quality of the mirrors (1/10 primary, 1/23 secondary) makes it perform like a 90mm apo, or better. I've had that scope up to 300x with no notable breakdown of image on good nights. Yes it is dim, which is why I am not content just using this one for L&P. Less for the aperture itself, but more because of the magnitude loss with BV attached. Call it another one of my babies.

This is where the 6-8" scope comes in. Much of this project comes down to the fact that I love building scopes, and I'm just looking for an excuse to do so. :grin:

So, Kerry, your recommendation for a 7" is actually quite funny because I've done a little research today and discovered that plate glass blanks aren't all that hard to come by. And they are available in odd sizes, like 7", 9" and 11". That discovery spawned some additional research, because I was a tad resistant to the idea of plate glass as opposed to Pyrex. It seems there is a 20% improvement in thermal equilibrium of Pyrex over plate. Turns out that the only logistical benefit to Pyrex in smaller sizes is during the manufacturing process. It allows less time between each grinding step and the measurement of the progress, since grinding friction will inevitably cause some expansion, and thus warping. Cooling down the mirror before an observation is of less consequence for me, since I always keep my scope of use in the garage on the mount (less time to equalize). I also use active cooling. Add to that that mirrors below 8", and thinner than an inch will cool quickly anyway.

So I'm thinking A) 7" ƒ6. Yes it puts me just above 1000mm, but the ƒ ratio threshold is more important to me than nitpicking the fl. Call it close enough for government work. And B) possibly (oh you guys are going to have to hold me to this) grinding the mirror myself. :shock:


To be continued...

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 Post subject: Re: Shhhh....don't tell
PostPosted: Sat Jan 11, 2014 7:05 pm 
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Correction: make that a 300% time improvement in thermal equilibrium using Pyrex instead of plate. That might be a consideration having never ground a mirror before. I am reading that if you can compensate for the thermal sluggishness, it is easier to achieve a smooth finish with plate. More to think about.

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 Post subject: Re: Shhhh....don't tell
PostPosted: Sun Jan 12, 2014 10:06 am 
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Jason, interesting info on the plate vs Pyrex.

I'm very glad to hear you are keeping the 10". OK, so the truth comes out - you really want to build something!!!! :grin: I completely understand that!

Glad you fessed-up because in all honesty if it were me with your scopes (and building didn't matter) I'd find a mount to better handle the 10" and be done. That 10" with no vibrations on a proper mount that will be left setup in the garage, ready for roll-out & practically already cooled.......why would you want anything smaller between it and your 4.5? Because you want to build!!! :mrgreen:

Alright, so with that said if you really want to build, I'm with Erik - forget the 6". I suggested the 7" because it's a nice compromise size that will show more than a 6" but remain a bit more manageable with a slower f/ratio than an 8" of the same ratio. I also feel 7" is a minimum to truly start doing some serious work for L/P. If you can't make a 7" work because of the odd-ball size, then do like Erik said and go with the 8", even if you have to shorten it down to f/5.5 or f/5 to make the weight & moment-arm work for you. F/5 might be a tougher go however if you decide to grind the mirror yourself. I would think f/5 would be a quite a challenge for the first mirror.

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Oh, yeah. The Stifmeister's coming back to Grand Harbor. Deck the halls. Bye-bye, Great Falls. Wipe my a$$ and lick my ba!!s It's Stifler time, baby. Whoo-hoo-hoo. Whoo-hoo-hoo. ~Steve Stifler-American Pie 2 :lol: :lol: :lol:


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 Post subject: Re: Shhhh....don't tell
PostPosted: Sun Jan 12, 2014 6:50 pm 
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Ha ha ha ha. Kerry you busted me. Now, after a day of thinking, and researching, I'm actually leaning toward the mount. I must be painful to deal with. :lol:

I kept thinking about it and realized that I already have an amazing scope with that 10", and I believe I even admitted that in my second post. So why on earth am I going to build another scope?!? Yes it would be fun. But it's just not pragmatic. The problem is, as I sit and ponder this new scope, I have come to realize that I want top notch everything...otherwise why bother?!? That will obviously increase the price of the project and at that point I could have just saved up for the heavier mount.

Hmmm. If you guys are lucky my prefrontal carnival will be back in town tomorrow with a whole new idea. :lol:

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 Post subject: Re: Shhhh....don't tell
PostPosted: Sun Jan 12, 2014 8:40 pm 
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:lol:

Well, whatever you decide- at least you're not resting on your laurels. :grin:

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Homebuilt 16" Truss Dob
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SV 80mm ED Nighthawk NG on M1 ALT/AZ
Nikon Prostaff 65mm spotter on Trekpod
Konusvue 20x80 binos/Peterson PipeMount


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 Post subject: Re: Shhhh....don't tell
PostPosted: Mon Jan 13, 2014 7:18 am 
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Ah hell Jason, you know how many times I change my mind on scopes & mounts and how long it takes me to make a darn decision about them. Making business decisions is MUCH easier! :lol:

Always my problem with astro-equipment, and I'm not sure why. I guess I went for the good stuff early on and got spoiled after having the opportunity to make lots of comparisons. Optically and mechanically I have a hard time settling. Mirrors must be Zambuto or Royce, structures must be mechanically sound and just get out of the way, which means Starmaster, Star Structure, JP Astrocraft or Teeter for trusses; Parallax for tubes. If I choose a refractor it will be TEC or Tak, or a used AP. If cash were a non-issue the scope decisions would be simple! But my cash flow isn't infinite and I don't like constantly buying and selling so it takes forever to make sure I get the right piece of equipment.

It drives me nuts because I can compromise on almost everything else I buy. I usually buy at least good quality, but it doesn't have to be top of the line to satisfy my needs and give me years of good service. Change to astronomy equipment & I'm screwed.

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Oh, yeah. The Stifmeister's coming back to Grand Harbor. Deck the halls. Bye-bye, Great Falls. Wipe my a$$ and lick my ba!!s It's Stifler time, baby. Whoo-hoo-hoo. Whoo-hoo-hoo. ~Steve Stifler-American Pie 2 :lol: :lol: :lol:


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 Post subject: Re: Shhhh....don't tell
PostPosted: Tue Jan 14, 2014 5:13 am 
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Erik wrote:
:lol:

Well, whatever you decide- at least you're not resting on your laurels. :grin:



Like this guy...?

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 Post subject: Re: Shhhh....don't tell
PostPosted: Tue Jan 14, 2014 5:17 am 
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Kerry, you said it. Although I have admittedly made decisions of compromise in the past because of my impatience. I now realize that a year or two of hemming and hawing beats having to buy/sell/trade to fix my irrational mistakes.

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 Post subject: Re: Shhhh....don't tell
PostPosted: Tue Jan 14, 2014 5:50 pm 
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Chopin wrote:
Erik wrote:
:lol:

Well, whatever you decide- at least you're not resting on your laurels. :grin:



Like this guy...?

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That's hilarious! Kind of like the fat fifty year old guys that talk about how many touchdowns they scored on their high school football team. :lol:

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-Erik Wilcox
Homebuilt 16" Truss Dob
8" Antares f/5 Newt
SV 80mm ED Nighthawk NG on M1 ALT/AZ
Nikon Prostaff 65mm spotter on Trekpod
Konusvue 20x80 binos/Peterson PipeMount


"Newt Gingrich is what stupid people think smart people sound like."
-The Great Paul Krugman

Evolution is both fact and theory. Creationism is neither. -Anonymous


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 Post subject: Re: Shhhh....don't tell
PostPosted: Wed Jan 15, 2014 6:24 am 
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:lol:

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Oh, yeah. The Stifmeister's coming back to Grand Harbor. Deck the halls. Bye-bye, Great Falls. Wipe my a$$ and lick my ba!!s It's Stifler time, baby. Whoo-hoo-hoo. Whoo-hoo-hoo. ~Steve Stifler-American Pie 2 :lol: :lol: :lol:


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