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Mead 16" Starfinder

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#1 Brett Carlson

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Posted 09 December 2012 - 10:03 PM

Hello all,

I'm new to CN and am fairly new to astronomy picking back up on my childhood interest many years later.

1 picked up a 16" Starfinder this summer for what I think is a steal at $180.00. It certainly needed work and I have completed many modifications. I've Strengthened the base, added three fans for cooling the mirror, added a 2" dual speed focuser (which caused the scope to be rebalanced).

I shipped the mirror off for recoating and it was tested to a PV wave of 1/1.7 and a Streyl ratio of .327. Is this typical of a commercial mirror such as this?

I'm having the mirror re-figured by OWL labs. They promised a PV of at least 1/8 and a Streyl ratio of .950 minimum....more that likely even better than that. Then a 96% reflective coating applied. I can't wait to see the difference. Is it the difference going to be that noticeable? Judging by the numbers it certainly should but I'm a bit of a rookie when it comes to these things.

Any suggestions on reasonably priced eyepieces to take advantage of the newly clear views? What max and min eyepiece sizes would you use? Currently I have a 32mm Meade 2 inch, a 18mm Meade HD-60 and a Celestron X-cel 12mm & 7mm. Should I go lower than 7mm? I was thinking about getting a 38mm Orion Q70 and a 2" in the 20 range...any suggestions?

Thanks in advance for your advice!

Brett

#2 herrointment

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Posted 09 December 2012 - 11:33 PM

You seem to have matters well in hand and your EP choices will work just fine.

Welcome to CN. Any other 16's for 180.00 you could direct me to?

Have fun with that new monster of a telescope......

#3 CosmoSat

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Posted 10 December 2012 - 09:26 AM

A barlow lens is a good accessory to hve in your inventory...for high power planetary viewing I would suggest the GSO 1.25" 2X barlow lens which u can also use with the 6" u hve.

Clear Skies!

#4 KerryR

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Posted 10 December 2012 - 10:12 AM

That's a heck of a deal, even including the cost of re-figuring!

I bought my Starfinder 16" new, so I paid a bit more... I'm content with the images provided by my mirror. It's under-corrected, 1/4 wave or so, MAYBE slightly better. Eventually, I'll get it re-figured, probably when it's time for a re-coat anyway.

You might consider getting the secondary tested as well. It's been said that the large flats made by Meade for these scopes often had edge issues. If yours does, you won't get everything out of your 'new' mirror....

Let us know what you think of the images when you get your mirror back!

#5 aatt

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Posted 10 December 2012 - 10:35 AM

Congrats on that deal-I missed one this summer that was selling for $20-that's right $20. It was gone an hour after posting...

#6 Bill Kocken

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Posted 10 December 2012 - 12:09 PM

I had my 16" Meade refigured last year by OWL. He told me the mirror was about like yours. It came back at 1/12 wave and Strehl of .979. I'm not sure if I believe eith the initial figures or the final ones, but my mirror is noticeably better.
As for eyepieces, I wouldn't go to a 38mm eyepiece. The exit pupil on your 32mm is already 7mm. with a 38 it would be over 8mm. As people say, you're wasting light because your eyes cannot take in that big of beam of light.
My observing is done with a 27mm Panoptic, a 15mm Explore Scientific 82 degree and a 9mm Nagler. When I want more power I can use my barlow in the 15 or the 9.

#7 Mike B

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Posted 10 December 2012 - 12:53 PM

Welcome to CN, Brett- glad you found us! :grin:

Congrats on snagging such a big scope for such a modest price- the glass/pyrex/whatever in the mirror is prob'ly worth quite a bit more than what you paid? :bow: If the mirror's current Strehl values are anywhere near accurate (and they're believable), you should see a marked improvement in the views! :D

Currently I have a 32mm Meade 2 inch, a 18mm Meade HD-60 and a Celestron X-cel 12mm & 7mm. Should I go lower than 7mm? I was thinking about getting a 38mm Orion Q70 and a 2" in the 20 range...any suggestions?


Well, to start with, i'd say go slowly here... the tendency is to go a li'l nuts, and it's likely quite unnecessary. :lol: What type of 32mm EP is the Meade?

Chances are the 32mm will be as long of a FL as you'll ever want- the sky will appear pretty bright thru it. Thye mirror's coma (naturally occuring ;)) will also be fairly pronounced. The newer 68* EPs from Meade, Celestron, & ExploreSci in the ~28mm flavor may be more pleasing, visually, than the 32mm? But i don't think i'd start there.

My personal hunch is that a decent "ultrawide" (ie. 82* field) i the 8-12mm range would get a real workout in such a scope! That'd be 150x to 230x, with a good amount of field to take in. The ExploreSci 8.8mm & 11mm UWA's might fit the bill nicely... and since you've already shown yourself to be a savy "used-market" buyer, they ought to be attainable in the $100 range.

Then i'd pick up a good Barlow- either a 1-1/4" 2x model (as was suggested), or else a 2" 1.6x unit, like this one. It'll take both 1-1/4" and 2" EPs, so will work mightily to expand the range of your current glass.

That ~$200 wisely invested should keep you stoked at the focuser for a lonnng time!... unless you give into the dark side :evillaugh:... as tends to happen if you hang around the EP forum too much. :grin:

Keep us posted on how the "new" mirror turns out!

#8 Brett Carlson

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Posted 10 December 2012 - 01:51 PM

Thanks for all the great responses.

Here is a link that will show what my Meade 32mm eyepiece is:

http://www.optcorp.c...t.aspx?pid=4267

I do already have a meade 1.25 barlow but I haven't utilized it much....I might get more use out it if I get a 2" model like Mike B suggested.

Can't wait to get it back. Glad to hear that your mirror came back so nice Bill...I hope mine does as well. I did get a few responses from friends that they thought the mirror didn't look at bad as the numbers say but they did say that it's not all that surprising with a stock Meade mirror.

Thanks again for the responces....next step is to make her more portable but that is for another thread!

#9 Brett Carlson

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Posted 10 December 2012 - 01:54 PM

You might consider getting the secondary tested as well. It's been said that the large flats made by Meade for these scopes often had edge issues. If yours does, you won't get everything out of your 'new' mirror....

Let us know what you think of the images when you get your mirror back!


I'm still waiting on the test results for the secondary but he did say the edges looked fine.

#10 Brett Carlson

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Posted 10 December 2012 - 01:57 PM

As for eyepieces, I wouldn't go to a 38mm eyepiece. The exit pupil on your 32mm is already 7mm. with a 38 it would be over 8mm. As people say, you're wasting light because your eyes cannot take in that big of beam of light.
My observing is done with a 27mm Panoptic, a 15mm Explore Scientific 82 degree and a 9mm Nagler. When I want more power I can use my barlow in the 15 or the 9.


I guess I don't understand the exit pupil side of things....I'll have to do research on this! Lots to learn in this hobby but I love it! :grin:

#11 Mike B

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Posted 10 December 2012 - 05:57 PM

Exit pupils are fairly easy. You get to their value a couple of ways:
1) take the scope's overall aperture (400mm for that scope?) & divide that by the magnification of the EP used... so 400/57 (for the 32mm) = 7.00mm---> that's the diameter of the light's beam exiting the EP & entering your eye. A human eye fully dilated is probably 6-8mm in dia, so this EP maxes out how wide of an exit-pupil (ExP) most folks can take in. If the ExP gets too large, it means your eye is only seeing (& enjoying benefit of) part of the mirror... plus the secondary mirror will loom in the center of what you're seein', and at some point will show up as a darkening of the field's center. A very annoying effect. :vomit:

2) the other way to get there is to divide the EP's FL by the scope's F-ratio... so a 32mm EP / F4.5 = 7.1mm ExP.

And you prob'ly already knew that an EP's magnification is the scope's FL divided by the EP's FL... so 1829mm scope / 32mm EP = 57.2x

Most viewing is done typically between 5mm on the wide side, and 1-2mm on the small side. At 1mm ExP your Meade scope is cranking at ~400x... quite a bit of horsepower!

Additionally, it is commonly reported by many that there exists a kind of "sweet zone" at around 2mm ExP, so ~200x in that scope. That's where the image brightness & the human cornea kinda hit an optimum. Figuring backwards, that's 1829mm / 200x = ~9mm EP FL.

Hope that makes some sense?
:grin: mike b

#12 Achernar

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Posted 10 December 2012 - 08:47 PM

No, that is not typical of mass produced mirrors, the specs are those of a mirror that's grossly defective. You will see an enormous difference, stars during steady seeing will be sharp points of light, planetary details will be clearly visible and the contrast will be greatly improved too. Star tests will show clear diffraction patterns that will at least look for the most part identical on both sides of focus. When stars snap into focus, that means the optics are good, correctly collimated and properly mounted. You will find the money spent reworking the mirror very worthwhile.

Taras

#13 KerryR

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Posted 11 December 2012 - 10:42 AM

No, that is not typical of mass produced mirrors...


It shouldn't be, that's for sure, but it seems it was fairly common with these Meade Starfinder 16's. Many were decent enough (like mine), but many were pretty poor. Even at full pop like I paid, it was still a very affordable way to get big aperture, even including the cost for re-figuring.

#14 Brett Carlson

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Posted 11 December 2012 - 06:10 PM

thanks for the explanation of the exit pupil....makes total sense now. The main reason that I was going to the 38mm was to have an eyepiece that could see all of the double cluster in a view. It's a real hit at the public star parties that the club I'm in holds during when weather permits.

Should I then look for an eyepiece with a wider field of view?

#15 Brett Carlson

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Posted 12 January 2013 - 09:53 PM

Well...the newly re-figured mirror is back and looking beautiful! Specs ended up with a 1/9.5 and a streyl ratio of .968. I was able to get a glimpse of Jupiter before the clouds rolled in. It looked a good as it could for the conditions.

Can't wait for a nice clear night!

#16 acochran

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Posted 14 January 2013 - 08:29 PM

I saw the double open cluster in Perseus last Saturday night in my Meade Lightbridge 16" F4.5. Both clusters showed up in the field of my ES 20mm 100 degree eyepiece (about 92 power), which shows 1.09 degrees of the sky. Also in one field of view was M81-82, and 2 galaxies in the bottom of Leo. This eyepiece is too small for M31. I wish I had a lower power, like a 59 power 31mm with 82 degree field of view which would show me about 1.3 degrees of sky, and an exit pupil of 6.9, probably too much for my 59 year old eyes, but what the heck...

#17 ccaissie

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Posted 18 January 2013 - 10:54 AM

Our club received a 16 Starfinder, and we mounted it in our observatory on a big GEM. It performed badly and star testing it gave me the impression it was about a full wave overcorrected.

When we had it recoated back in 2005, I put it on the stand, and it tested like yours, bad. I took a soft sub lap and got it to about 1/5 wave, and we lived with it like that until recently.

The improvement was very noticeable from 1 wave to 1/5th.

Now it's ready to go out to OWL after I spent some time, smoothing and correcting it. I expect it's up in the mid nines Strehl, and sure it's going to be a nice scope.

We also have a second 16 Starfinder as a Dob, that has a noticeably better mirror than the first one, probably 1/5th wave undercorrected with some definite zones showing in the star test.

In my experience, you are going to NOT BELIEVE the views in the refigured mirror. You are in for a major head change.

Congrats on the luck in finding the scope, the decision to refigure it, and to make some other enhancements.

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#18 Brett Carlson

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Posted 19 January 2013 - 09:48 PM

I had about a hour of relatively clear skies so I wheeled "Tubby" out into my suburban driveway. Jupiter again looked awesome. I was also able to get M42 and the double cluster before clouds rolled in. I'm blown away by the clarity of the newly re-figured mirror.

Before....when I used more and more magnification the views got fuzzy...dim. Now using my 5mm Celestron X-cel X (263x) it looks perfectly clear! It makes me want to get a 5mm or a 3.5mm and see how that looks! Any suggestions?

I was able to get the double cluster in a single view in my 32mm Meade Series 5000 2" eyepiece! Beautiful sight! Not sure if it was just me but I saw colors of stars in the clusters that I never noticed before.

#19 Glen A W

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Posted 22 January 2013 - 02:38 PM

I use that same 32mm Meade in my 10" f/5 and it is really very good. You would have to spend a lot more to beat it - it's easily superior to the low-cost Chinese eyepieces from the various sellers. I can just see that view of the double cluster in my mind. My 10" is not as big as yours but the colors in these objects always jump out at me. The red stars in particular are so apparent once you get more than 8". GW

#20 Brett Carlson

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Posted 23 January 2013 - 08:44 PM

I'm happy with that eye piece...I'd like to try one of the 82* wide field eyepieces. Maybe an explore scientific

#21 Jim T

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Posted 27 January 2013 - 09:12 PM

Brett

The eyepieces that I use most with my 16" SF dob include a cheap 2" BW Optik 30mm (80*). It is my 'finder' eyepiece at 61x. The edges may not be so good with an f/4.5, but the eyepiece is much smaller and lighter than the better corrected ones. Easier to get it in and out when switching eyepieces than the full-sized grenades are. My ES 30mm 82* seriously gets much less use! I hope that'll change with a better focuser later on (thumbscrews are buried under the "mushroom").

I also love to use my 9mm ES 100* eyepiece with this scope. After that there's a big dip in usage, with my 14 mm ES 82", then my 7mm 82* UWAN. I have occasionally used a 2x barlow with a 14mm and a 9mm eyepiece, but rarely is the seeing good enough here for that, nor is the object in the FOV long enough to appreciate the view.

My 2 cents.

Jim

#22 Brett Carlson

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Posted 28 January 2013 - 10:01 AM

I've been using my 32mm Meade for my finder eyepiece. I'd love to get one of the 82* or 100* eyepieces in the 7 to 14 range....sometime soon.

Do you use a Paracor with your Starfinder?

#23 Jim T

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Posted 28 January 2013 - 07:43 PM

A Paracor is on my wish list. I was really never bothered too much by the coma, until I worked the A.L.'s double star list last year. You don't get bothered by it too much with the faint nebulae and galaxies, especially at low power.

#24 Project Galileo

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Posted 28 January 2013 - 09:23 PM

Congratulations on your new to you telescope and welcome.

#25 Brett Carlson

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Posted 29 January 2013 - 02:00 PM

Now I'm just waiting for a clear night or two! They come few and far between in NY in Winter!






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