Possible Future Newt

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Kawx4d
Post subject: Possible Future Newt
Posted: Thu Aug 16, 2012 8:54 am
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This thread was inspired by Erik mentioning a planetary Newt up against an APO in another thread.

A new large(ish) Newt has been occupying my thoughts for quite some time. What is happening is a raging internal debate about the replacement scope for the 14.5 Starmaster I sold 4 years ago. (Has it really been that long :?: :?: ) Let this be a lesson boys and girls.........Never sell one scope FIRST, in order to fund another you want to buy. That decision was FUBAR in a big way. My overwhelming desire for a 20" clouded my judgement, so I sold the 14.5 with every intention of calling Rick and ordering that 20. Obviously, that never happened. In my defense, at the time I was traveling to dark sites all the time (40-60 nights per year - every weekend when the moon was gone, and some extended trips to southern AZ) and really was moving into a phase of my observing where a 20" would have been a very desirable size. My unforeseen and abrupt halt to dark skies pretty much screwed me, and it turns out I probably sold off what was a fairly ideal scope for me.

Obviously that 20" is no longer a practical choice for me because I just don't see this degree of astronomy travel ever happening in my future. Some trips, certainly, but nothing like it once was. 20" is also not a good choice for backyard use with no observatory, and I have no way of just leaving it assembled for "roll out". I am considering another truss from Rick, Teeter, or Star Structure. As we all know, I'm not a fan of the hyper-fast dobs, so anything I get will have a Zambuto mirror - either f/4.3 from Starmaster, f/4.5 from Star Structure, or whatever I want if I have Teeter build one - 16" f/4.5, 14.5" f/5, 12.5" f/6 - something like that. Size would probably cap at 16" if I go the truss route.

However, I'm giving serious thought to having Joe at Parallax build me a highly customized solid-tubed Newt, probably a 12.5" f/5.5 - f/6. (However I may do a 10" f/7) The mirror will be Zambuto, and I'd get a Destiny curved 3-vane spider, and probably a 1/20 wave Antares secondary. Either a FT focuser, or a really nice 2" Helical ( I do like helical for fine focus). It would have some type of open-cell design, with fans, & a rotating tube. It's going to be all about achieving excellent contrast through the entire system and good thermal management to minimize boundary layer and tube current effects. By natural extension, if I do all of this to make an excellent L/P scope, it should automatically be a killer deep-sky instrument as well, for those times when I can get to dark skies.

I welcome any thoughts on these choices above so feel free to add, subtract, or dissect!! :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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Erik
Post subject: Re: Possible Future Newt
Posted: Thu Aug 16, 2012 11:38 am
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Obviously, I'm a bit biased towards the 16" f/4.5. I've found that its the best balance for me as far as aperture and portability (if a 16" scope can be considered "portable"!). The focal length still allows over a full degree TFOV which makes finding objects easy. And it seems much less sensitive to seeing conditions compared to a 20". Whenever I visit my friend down the street who has a 24", I realize how easy my scope is to use and point. The 24" is great but it takes several minutes to find and point the scope to objects. The 16" takes a coule of seconds.

The paracorr works great at f/4.5 making it an effective f/ratio of 5.1. Though I have well corrected eyepieces, I didn't when I first built the scope and I found this much, much more forgiving than the 10" SN f/4 I used to own.

Really, anything with great optics between 8" and 16" will be great on planets. You may get a more asthetically pleasing view with planets on certain nights if you keep it around 12". But it's hard to beat aperture on deep sky.

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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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Kawx4d
Post subject: Re: Possible Future Newt
Posted: Thu Aug 16, 2012 12:14 pm
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Thanks Erik. It is tough to beat aperture on deep sky, which has been the most difficult part of this - capping at 12.5, even though I do find 12.5 an ideal size for most situations. Although I'm not one of these guys that subscribes to the "aperture rules in all cases", there is a noticeable difference to me between 12.5 and 16. Not like 12.5 to 20, but definitely a nice step up IMHO. Theoretically of course aperture does rule, which is why professional observatories house larger and larger scopes. But when we amateurs don't have a climate controlled observatory to keep the equipment at ambient, with adaptive optics, sitting on top of a mountain at an elevation of 3,000m - 5,000m with perfect laminar airflow, we have to consider other things besides aperture. Your comparison between your 16 and the 24 down the street is perfect. The 16 is extremely tempting for me for a couple reasons. It's still easily manageable, will certainly cool faster than a 20, yet won't take that much longer than a 12.5, and it's still a bit larger than what I had before and will give me that extra punch when I do get to dark skies. In other words, I'll be glad I have the 16 when I'm out there, yet it's still workable for my main home use.

But whereas dark skies used to be 98% of my observing, right now it's 0%, and at most would probably be somewhere between 10% and 20% for quite a stretch into the future. So, for a killer planetary scope for home use, and observing some of the brighter DSOs, a solid-tube in my white-zone light-polluted environment, with neighbor's glaring security lights, the street lights, and school football field lights, is going to be much better than a truss for controlling glare and stray light. Not to mention it should be better at deflecting swirling air currents in my yard and helping deflect body heat, etc for planetary observing. My prior 10" solid-tube was much better at this than the 14.5 when I used it at home. I'm not saying it's impossible to do with a truss, but it is much easier to achieve with a solid tube. So if I do decide on the solid tube, the 12.5 is really the largest size I would want for that. Any bigger and it's just too much bulk to move around, and it won't travel well when the time comes.

Tough choice to make.

_________________

Kerry

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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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Chopin
Post subject: Re: Possible Future Newt
Posted: Thu Aug 16, 2012 6:59 pm
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Well, the easy answer is to refer you to my own (perpetually ongoing and slow as sloth) project. I've settled in on building the best 10" solid tube that I can because it is the best balance of all aspects for me. The f4.5 design of my scope will mean more time spent collimating, but save me on a butt load of size and weight for mounting considerations. Btw, typing these posts from a phone sucks, because I really want to get into a lengthy discussion, but tonight at work I'm feeling lazy as f_ck.

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Erik
Post subject: Re: Possible Future Newt
Posted: Thu Aug 16, 2012 11:52 pm
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A solid tube definitely has advantages as far as keeping stray light out. But it has disadvantages as far as cooldown times. When my 16" was a solid tube in a former life, it took forever to cool down- the warm air in the tube is difficult to completely get rid of, and that's before the mirror has a chance to begin cooling down.

But as far as stray light, I'm always reminded of a specific time I met up with a CN regular (Craig C) at Henry Coe State Park. He had his 18" and I had my 16". We were looking at M51 from this relatively dark spot and were surprised that the view was noticeably better and less washed out through my 16". We finally realized that it was because he didn't have the shroud on his truss dob and I did. As soon as we put the shroud on his scope, suddenly it was his scope that had a slightly brighter view. Since then, I always use the shroud. I imagine the effect would be even more prevelant with a solid tube scope under a poor sky.

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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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Kawx4d
Post subject: Re: Possible Future Newt
Posted: Fri Aug 17, 2012 7:21 am
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Jason, a 10" f/4.5 will be nice, and I really don't think you will find it any harder to collimate than an f/5 or f/6. I'm not sure what method you use, but I use the old standard Cheshire and auto-collimator. One of these days I might break down and get one of Howie's barlowed TuBLUGs, but I've found the old tried & true tools to be just fine for me. The only difference I found was at the end with the auto-collimator, in that with a faster scope I took maybe an extra minute to make damn sure the light path was closed down, and get those doughnuts stacked as tightly as possible. Honestly, that was me being anal about it. The actual process is no more difficult for f/3 than it is for f/9. I think the issue lies with the mechanics of the mirror cell being able to hold those tighter tolerances without pinching the optics. BTW, how are you planning to mount the 10"? Dob or EQ with rotating rings?

Erik, nice story about the shroud. So at that time your 16 was still a solid tube? I had different experiences with my shroud so I rarely used it at our dark sites because they were usually dark enough not to cause problems of that nature. I would use it if there was a night where the Zodiacal Light was too bright, or if an imager was nearby with a computer, but I also found that the shroud acted like a tube and *caused* currents. Not sure if it was harnessing body heat, or what, but often I had more issues with the shroud, but then again the Star Master did not have a fan either. Something none of us could ever get Rick to put on his scopes. I never found a good solution for it until after I had decided to *upgrade*, so never implemented it.

So at a minimum, if I go solid-tube, I'll have an open cell with a rear-mounted fan pulling air down through the tube, over the mirror, and out the back. I'd have to talk to Joe about a boundary layer fan and whether or not it will introduce more problems than it would solve. I think with air movement down through the tube and over the mirror, the rear fan might naturally break up any boundary layer because the air would already be flowing over and around the mirror. Not to mention the rear-mounted fan is creating a steady laminar flow rather than stirring up air like a side-mounted fan would do. Venting on the opposite side would probably be key with a separate boundary-layer fan on the side of the OTA. I'm thinking I'd prefer to stick with one good isolated fan on the rear cell and just put down a heavy carpet or blanket to isolate the scope from the ground heat. Of course set up early enough as well.

I had also given some thought to having it built in a tube one size bigger to allow for a larger *dead-zone* for both excellent air movement around the primary, and added space to reduce any tube current effects in the optical path. However here, I'm then facing the problem of having the bulk of a larger scope. I've read there are advantages to doing it this way, but is the increase in performance enough to justify the added weight and tube diameter? I suppose that would be a very subjective aspect and would differ from person to person.

Lots to think about! Truss or tube.....tube or truss! :lol: Once I figure out this part, the size will be easy to pick.

_________________

Kerry

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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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Erik
Post subject: Re: Possible Future Newt
Posted: Fri Aug 17, 2012 10:24 am
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Definitely a lot to consider- a truss is just so much easier in that size range. Aside from the weight for transport, a truss is usually smoother to slew around the sky. But then, a solid tube may vibrate less in breezy conditions or when focusing etc. There are many trade offs each way, unfortunately.

Sorry, Kerry- I should have been more specific. My scope was already a truss at the time we noticed the stray light issue at Henry Coe State Park. But my scope had the shroud- in fact, at the time I believe I was using a very thick shroud designed for the 16" Meade truss dob (which I had the company modify for me). I now simply use a stretchy spandex like material that I got from the fabric store several years ago. It's not as thick but seems to do the job. And my skies are very dark with no nearby light sources so it seems to work fine. It would be interesting to compare it with a 16" solid tube side by side and see if there was any difference.

_________________

-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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Kawx4d
Post subject: Re: Possible Future Newt
Posted: Fri Aug 17, 2012 12:29 pm
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OK, so truss with shroud was best even under darker skies. I don't know what the deal was with my shroud. I used it regularly, for probably half the time I had the scope, and I think I discovered the tube current effect quite by accident on night when it must have been particularly bad. In the end I'd rather find a way to deal with the currents (through fans and such) than risk stray light. What's really strange is that in my 10" f/5.6 solid-tube, I only had one night in the 5 years I owned it where tube currents manifested in the star test. It was never an issue in that scope, and it didn't have a fan either. But I would think they might be harder to control as the mirror-mass gets larger. I can't imagine a 16" solid-tube!!

BTW I agree - trusses are easier to slew. Usually much better motions in both axes.

If I didn't already have the Mewlon, this would be a no-brainer..........10" f/6 solid-tube as the work-horse, and a 16" f/4.5 truss for the great nights and the dark site trips! I just can't bring myself to part with the Mewlon because it's optically & mechanically excellent, and quite literally the simplest scope to move around. Pick it up by the extremely solid, permanently fixed finder bracket and use it as a handle to carry it. Seated observing, very rare collimation needed, and much quicker cool down than a Piece of Schmidt or Mak of the same size due to the open tube in front - no corrector.

Hmmm........I wonder if SWMBO would give me grief for having FOUR scopes instead of three :?: :?: :?:

Might experience this if I ask............

:adminvsmodvsuser:

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Kerry

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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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Chopin
Post subject: Re: Possible Future Newt
Posted: Tue Aug 28, 2012 1:18 pm
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Have you asked for a 4th scope yet?

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Chopin
Post subject: Re: Possible Future Newt
Posted: Tue Aug 28, 2012 1:46 pm
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Kawx4d wrote:
Jason, a 10" f/4.5 will be nice, and I really don't think you will find it any harder to collimate than an f/5 or f/6. I'm not sure what method you use, but I use the old standard Cheshire and auto-collimator. One of these days I might break down and get one of Howie's barlowed TuBLUGs, but I've found the old tried & true tools to be just fine for me. The only difference I found was at the end with the auto-collimator, in that with a faster scope I took maybe an extra minute to make damn sure the light path was closed down, and get those doughnuts stacked as tightly as possible. Honestly, that was me being anal about it. The actual process is no more difficult for f/3 than it is for f/9. I think the issue lies with the mechanics of the mirror cell being able to hold those tighter tolerances without pinching the optics. BTW, how are you planning to mount the 10"? Dob or EQ with rotating rings?
EQ, but no rotating rings. Weight is the most important factor in my project. I'll be using the old Meade Starfinder GEM which came with straps to hold down the tube. The straps are some sort of resin, and damn light. Other weight saving considerations are the focuser, and fan plate at the rear. I currently own a Moonlight CR2, which is one of the lightest of the premium 2" focusers. I have been pondering the purchase of a Kineoptics HC2 helical. The impractical tradeoff of going that route for weight savings is the twisting effort when switching between non-parfocal EPs. Given my frugal side I'll likely stick with the CR2, especially since it will be a moot point once the 26T5 is sitting up there. :lol: As for the fan plate, a 10" mirror doesn't require loads of airflow to remain stable. I'll pickup a dinky 15-20 cfm fan and mount it on nearly weightless foam board, then isolate the rounded plate with rubber bands. Ultimately, I regard weight to be as important as the quality of the optics, especially if it's GEM mounted. Vibrations suck, and I loathe them. The sturdier the tube is, the happier I'll be. I'm taking the KISS approach with the whole project:

1) Shortest/lightest tube I can get away with - flocked
2) Light weight/premium focuser
3) Reverse mounted fan at back
4) Curved vane spider

Quote:
So at a minimum, if I go solid-tube, I'll have an open cell with a rear-mounted fan pulling air down through the tube, over the mirror, and out the back. I'd have to talk to Joe about a boundary layer fan and whether or not it will introduce more problems than it would solve. I think with air movement down through the tube and over the mirror, the rear fan might naturally break up any boundary layer because the air would already be flowing over and around the mirror. Not to mention the rear-mounted fan is creating a steady laminar flow rather than stirring up air like a side-mounted fan would do. Venting on the opposite side would probably be key with a separate boundary-layer fan on the side of the OTA. I'm thinking I'd prefer to stick with one good isolated fan on the rear cell and just put down a heavy carpet or blanket to isolate the scope from the ground heat. Of course set up early enough as well.
A single fan is all you need. I have this setup on my 4" newt, and the difference is night and day in the "cool" autumn and spring months, when evening temperature fluctuations are enough to be noticeable even for a small mirror. If you go with a really big mirror (20"+) then a second smaller fan right above the center of the mirror blowing directly downward is better than side fans, IME.

Quote:
I had also given some thought to having it built in a tube one size bigger to allow for a larger *dead-zone* for both excellent air movement around the primary, and added space to reduce any tube current effects in the optical path. However here, I'm then facing the problem of having the bulk of a larger scope. I've read there are advantages to doing it this way, but is the increase in performance enough to justify the added weight and tube diameter? I suppose that would be a very subjective aspect and would differ from person to person.
Having a single fan makes more difference than all other design considerations for airflow, IMO. Keep it simple and it should work splendidly.

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Jason® (Admin...and spoke-folk)
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Kawx4d
Post subject: Re: Possible Future Newt
Posted: Tue Aug 28, 2012 5:50 pm
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Chopin wrote:
Have you asked for a 4th scope yet?
No I have not. Not a good time to broach the subject given her job is literally keeping her up at night because of the stress. The project she's on right now is the worst kind of nightmare, so I won't be adding to it.

Thanks for the tips on the other aspects. I was not all that serious about increasing the tube diameter; that is to say not all that excited about it. While it may be a great feature for a permanently mounted Newt, I can't see it being practical for a scope that needs to be moved and setup for each use. Good to hear the single fan should work best as well. I don't want any vibrations, and more fans give rise for the opportunity.

Sounds like you will have a nice light-weight scope when all is said and done. The only reason I mentioned the rotating rings is because of the awkward positions in which a GEM can place a Newt's focuser. Personally I'd have to have the rotating tube, but of you can live without it, that's awesome. It will save a lot of weight and expense. BTW, I had a Moonlite CR2 on my 10" Spooner, and it was a very nice focuser, which will handle the 26N with no trouble! :lol:

_________________

Kerry

[ img ]


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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