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Equipment Discussions >> Reflectors

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Aperturefever
super member


Reged: 12/12/10

Loc: Lake Macquarie, Australia
Webster F3 24"
      #5849205 - 05/09/13 02:17 AM

Ok. Here's my aperture fever cure. Webster have recently completed this F3 24". It has a Kennedy mirror and a zenith eyepiece height of 67".
That's the good news ... the bad news I wasn't the customer! Time to start saving.
But seriously - I think I have found my dream scope. I've been pondering a really short 24" for a while now. This is exactly what I pictured. What an awesome bit of gear.

http://webstertelescopes.com/forum/viewtopic.php?f=8&t=634

Edited by okieav8r (05/12/13 11:20 AM)


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Pinbout
Postmaster
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Reged: 02/22/10

Loc: nj
Re: Webster F3 24" new [Re: Aperturefever]
      #5849382 - 05/09/13 07:47 AM

nice picture, thanks for the tease, it's not yours!



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tigerroach
Pooh-Bah


Reged: 08/13/08

Loc: Houston, TX USA
Re: Webster F3 24" new [Re: Pinbout]
      #5849481 - 05/09/13 08:49 AM

Coolness!

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mak17
scholastic sledgehammer
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Reged: 02/08/11

Loc: Central Florida
Re: Webster F3 24" new [Re: tigerroach]
      #5849651 - 05/09/13 09:46 AM

Lovely indeed. I've looked thru a 28 f3 Webster. Views were amazing.

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Danagoo
member


Reged: 04/16/13

Loc: Stafford, VA
Re: Webster F3 24" new [Re: Aperturefever]
      #5849738 - 05/09/13 10:42 AM

That scope gets a Tim "the Tool-man" Taylor: "Rrrr, Rrrr, Rrrr"

Neat looking cart mount too.


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JMW
Pooh-Bah


Reged: 02/11/07

Loc: Nevada
Re: Webster F3 24" new [Re: Danagoo]
      #5850521 - 05/09/13 05:36 PM

It's the perfect BIG mirror with feet on the ground dob. I personally am saving up for the 18 f/4. I want a scope I can grow old with. I would have to have a personal assistant to help me with the weight of a scope this big when I got older 70+.

An f/3 (f/3.5 with Paracorr) scope would force me to totally rethink my eyepieces. My Ethos 21mm would would have an exit pupil of 5.99. I would be limited to Ethos 17mm for matching my pupil dilation and typically limited to 7mm or longer do to typical seeing.


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UmaDog
Carpal Tunnel
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Reged: 09/15/10

Loc: Basel, Switzerland
Re: Webster F3 24" new [Re: JMW]
      #5851273 - 05/10/13 02:02 AM

Quote:


An f/3 (f/3.5 with Paracorr) scope would force me to totally rethink my eyepieces. My Ethos 21mm would would have an exit pupil of 5.99. I would be limited to Ethos 17mm for matching my pupil dilation and typically limited to 7mm or longer do to typical seeing.




If the exit pupil is a little larger than your own pupil it really is no big deal at all. No reason that I can see to avoid using the 21 mm Ethos on such a scope.


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gatorengineer
Carpal Tunnel
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Reged: 02/28/05

Loc: Hellertown, PA
Re: Webster F3 24" new [Re: UmaDog]
      #5852698 - 05/10/13 08:34 PM

Quote:

Quote:


An f/3 (f/3.5 with Paracorr) scope would force me to totally rethink my eyepieces. My Ethos 21mm would would have an exit pupil of 5.99. I would be limited to Ethos 17mm for matching my pupil dilation and typically limited to 7mm or longer do to typical seeing.




If the exit pupil is a little larger than your own pupil it really is no big deal at all. No reason that I can see to avoid using the 21 mm Ethos on such a scope.





It will perform just like a 16 F4.5 with a 31 Nagler in it... Way too much wasted light.... as you say with a smaller EP, you wont waste, light on the exit pupil, but it will vignette badly... your looking at least a 6" secondary not to vignette terribly, and now you are back to 25 percent CO. Compared to 14% in my 25 F5 so contrast should suffer over a traditional dob.

Shipping it with a 2" focuser shows they don't understand light cones.....

Put a Wynn 3" corrector in a 3" focuser, and a 17 E in it an it would make some sense...

Other than that its a scope for someone with lots of money that doesn't understand optics, Exit Pupil, and vignetting. That wants big and cool, but not necessarily better. I have never read about a shoot out of superfast versus F4.5ish of comparable quality optics.......


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Wozzel
super member
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Reged: 12/01/10

Re: Webster F3 24" new [Re: gatorengineer]
      #5853170 - 05/11/13 02:02 AM

Quote:



Put a Wynn 3" corrector in a 3" focuser, and a 17 E in it an it would make some sense...






Make none sense how?

Wynn 3" make only photography. No insert eyepiece ever still.

Paracor#2 good use to still f/2.2 make nice, make for eyepiece use.


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Wozzel
super member
*****

Reged: 12/01/10

Re: Webster F3 24" new [Re: Wozzel]
      #5853172 - 05/11/13 02:06 AM

Make small for woman is nice, yes.

They make detail about:

http://webstertelescopes.com/forum/viewtopic.php?f=8&t=634

Edited by okieav8r (05/12/13 11:22 AM)


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UmaDog
Carpal Tunnel
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Reged: 09/15/10

Loc: Basel, Switzerland
Re: Webster F3 24" new [Re: gatorengineer]
      #5853256 - 05/11/13 05:00 AM

Quote:


It will perform just like a 16 F4.5 with a 31 Nagler in it... Way too much wasted light.... as you say with a smaller EP, you wont waste, light on the exit pupil,




All depends how you look at it: with the lower power you get a wider field of view. So that's a gain. The image won't be any dimmer when the exit pupil is over-sized, it will just cease to get brighter. Is that so bad? What's the alternative? To also set up a 16" and put the 31 Nagler in it so as not to waste light? Might as well just bung the 31 in the larger scope and forget about it, no?

As you say, you could go for a large secondary and a 3" focuser. But then you're looking at some pricey gear. Also, I know Webster don't like overly large secondaries. To use a 3" focuser I imagine you'd also need a pretty large secondary and that's something they want to avoid. TBH, at these large apertures I don't think the small secondary obsession makes that much sense.


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dscarpa
Post Laureate
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Reged: 03/15/08

Loc: San Diego Ca.
Re: Webster F3 24" new [Re: Aperturefever]
      #5853668 - 05/11/13 12:04 PM

Quite a scope! I would want to get good on collimation with my some day 11" F/5 before taking that on. David

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careysub
Carpal Tunnel
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Reged: 02/18/11

Loc: Rancho Cucamonga, CA
Re: Webster F3 24" new [Re: gatorengineer]
      #5854497 - 05/11/13 10:27 PM

Quote:

... your looking at least a 6" secondary not to vignette terribly, and now you are back to 25 percent CO. Compared to 14% in my 25 F5 so contrast should suffer over a traditional dob.




Hmm.. plugging the specs into Mel Bartel's calculator, and assuming a 15" intercept distance, it looks like a 5" diagonal gives very good field illumination for the widest EP this scope can profitably use (the 21" Ethos with the essential Paracorr). This is only 21% CO, usually thought to be a very good ratio.

(I have no idea what size they are actually using.)

The case for significant visible improvement much below 21% seems in doubt (only small MTF curve improvements occur).

If a low-rider (tilted secondary-focuser axis) design were used you could get bragging rights of 26" or so at the same ZEPH.


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mark cowan
Vendor (Veritas Optics)
*****

Reged: 06/03/05

Loc: salem, OR
Re: Webster F3 24" new [Re: careysub]
      #5854587 - 05/11/13 11:19 PM

Yes, the geometry works out very well re. CO, so long as the secondary is sized correctly.

Best,
Mark


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turtle86
Pooh-Bah Everywhere Else
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Reged: 10/09/06

Re: Webster F3 24" new [Re: UmaDog]
      #5854649 - 05/11/13 11:57 PM

Quote:

Quote:


An f/3 (f/3.5 with Paracorr) scope would force me to totally rethink my eyepieces. My Ethos 21mm would would have an exit pupil of 5.99. I would be limited to Ethos 17mm for matching my pupil dilation and typically limited to 7mm or longer do to typical seeing.




If the exit pupil is a little larger than your own pupil it really is no big deal at all. No reason that I can see to avoid using the 21 mm Ethos on such a scope.




Totally agree. Sometimes it's worth wasting a few photons to get a larger TFOV...


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gatorengineer
Carpal Tunnel
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Reged: 02/28/05

Loc: Hellertown, PA
Re: Webster F3 24" new [Re: turtle86]
      #5855449 - 05/12/13 12:57 PM

The New Explore 30 100 gives me a little more field (and better correction) in my 25F5, and leaves me with roughly $20,000 in the bank....

Lets look at illumination for a second... the 21 Ethos has a 36mm field stop. Your well illuminated is roughly 0.25" or about 6mm, or you could say at the EP, where you are desing to have a wide field of view, less than 5% of the field is fully illuminated. At F3, I would guess your edges are at best 60% illuminated.... the drop off at F3 is tough.

The scope has its niche, its feet on the ground, no falling off a ladder, weighs a boat load less than my 25 F5 (probably 100 lbs or more). and a reasonable van could carry it assembled. Yes there are pluss certainly, its a beaut, its bleeding edge of the technology... But with that type of stuff there are buts....

By the way, I havent even checked Newt to see if the upper cage vignettes at that fast (it might have to be bigger to take the incomming light cone).... this would ripple through secondary sizing etc...


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FastMike
sage


Reged: 09/22/10

Loc: Florida 27° 15' N
Re: Webster F3 24" new [Re: gatorengineer]
      #5855573 - 05/12/13 02:06 PM

Quote:

Shipping it with a 2" focuser shows they don't understand light cones.....




Using a Paracorr 2 there is no need for a focuser larger than 2". The lens on the Paracorr will be approximately flush with the inside of the UTA. A larger focuser will accomplish nothing, which is why they ship with a 2" focuser.

Quote:

Put a Wynn 3" corrector in a 3" focuser, and a 17 E in it an it would make some sense...




That makes no sense, a 2" focuser and a Paracorr 2 is all that's needed.

Quote:

Other than that its a scope for someone with lots of money that doesn't understand optics, Exit Pupil, and vignetting.




You're sure about that?

- Using a 21E my 28" f/2.75 (with Paracorr 2) has a 6.6mm exit pupil 94% edge illumination and .92 degree TFOV.
- Using a 31N your 25" f/5 (without a Paracorr) has a 6.2mm exit pupil ~80% edge illumination and .76 degree TFOV.

Quote:

Lets look at illumination for a second... the 21 Ethos has a 36mm field stop. At F3, I would guess your edges are at best 60% illuminated.... the drop off at F3 is tough.




My 28" f/2.75 has the following illumination:
0.00 in 100.0%
0.10 in 100.0%
0.20 in 100.0%
0.30 in 99.59%
0.40 in 98.51%
0.50 in 97.23%
0.60 in 95.88%
0.70 in 94.49% <-- 21 Ethos (your guess was wrong)
0.80 in 93.07%
0.90 in 91.63%
1.00 in 90.18%

Quote:

I havent even checked Newt to see if the upper cage vignettes at that fast




It doesn't. The internal baffling of the eyepieces is the limiting factor in off axis illumination.


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gatorengineer
Carpal Tunnel
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Reged: 02/28/05

Loc: Hellertown, PA
Re: Webster F3 24" new [Re: FastMike]
      #5856192 - 05/12/13 07:42 PM

Look at Mike Lockwoods, own website, for secondary illuminations. Your figures unless you have around a 7+" secondary are not possible. 7" Secondary is 25% CO....

If you are getting 0.4" at the SIPS, what happens in the distance between the SIPS field lens and the Eyepiece field lens? Answer The light cone drops as a function of distance between is what happens. If you have 1.5" or so between the SIPS exit lens and the field lens of the 21E you actually have well, 0 fully illuminated. Hence the need for the Wynn and a 3 inch focuser, and an even Bigger Secondary. There is at least one person who uses it visually and that I believe was posted here a while ago.

Also check out this post

http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/4360360/page...

It shows in the Ethos family the range of focal locations is -9 +19.5MM or 28.5MM, So you are almost to 0 fully illuminated IF there were NO distance betwen the SIPs exit and the field lens of the 21 E. Lastly this also doesnt account for the SIPS' other shortcomming which is that it can be optimized for the distance from the EP to focuser, like a normal Paracorr 2 (over that range the SIPS effectiveness would vary significantly)

If you let me know your secondary size, cage ID, I would be interested in running the numbers.

Also my analogy is for the yet to be delivered 30 Explore which will give me a degree. Granted your 21E does give you a 0.1 degree more than my 25 with the 100E, and yes its quite an improvement over the 31 Nagler I currently use. And Yes I am concerned about Illumination at F5 with a 3.5" secondary

I take it you also havent read the recent post on Paracorr 2 performance at F2.8 in Mikes group? check it out makes for a good read.....

Lastly Think through what you are saying? Why do they make 3 and 4 inch focusers and Wynn correctors? To illuminate a full frame 35 Millimeter chip without clipping in the focuser.... How big is a 35MM chip compared to a 21 E Field lens?

You have a great cutting edge scope. But I stand by what it says cutting edge has limits, and Kudos to you for pushing the hobby.

Edited by gatorengineer (05/12/13 07:42 PM)


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gatorengineer
Carpal Tunnel
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Reged: 02/28/05

Loc: Hellertown, PA
Re: Webster F3 24" new [Re: gatorengineer]
      #5856215 - 05/12/13 07:52 PM

oh, and here is another reference that contradicts Seroniks work on secondary sizes.

http://www.brayebrookobservatory.org/BrayObsWebSite/HOMEPAGE/gleanings/diagon...

Go to the 3rd set of computations and if you look at the F4 calculation......


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Mike Lockwood
Vendor, Lockwood Custom Optics
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Reged: 10/01/07

Loc: Usually in my optical shop
Re: Webster F3 24" new [Re: gatorengineer]
      #5856348 - 05/12/13 09:09 PM

Quote:

Look at Mike Lockwoods, own website, for secondary illuminations. Your figures unless you have around a 7+" secondary are not possible. 7" Secondary is 25% CO....

If you are getting 0.4" at the SIPS, what happens in the distance between the SIPS field lens and the Eyepiece field lens? Answer The light cone drops as a function of distance between is what happens. If you have 1.5" or so between the SIPS exit lens and the field lens of the 21E you actually have well, 0 fully illuminated. Hence the need for the Wynn and a 3 inch focuser, and an even Bigger Secondary. There is at least one person who uses it visually and that I believe was posted here a while ago.



I don't follow your reasoning. By my calculations, assuming no internal vignetting, at F/3 the SIPS has about a 13mm diameter fully illuminated spot.

Here's the dimensioned diagram that I made up to show the relevant SIPS dimensions:


First, note the focus position without the SIPS - 88mm from the bottom. Next, note that the focus position with the SIPS, when set properly, is 47mm higher.

Therefore, the light is not a simple converging cone as it passes through the lenses in the Paracorr lenses - it follows a more complex path that we can't know.

So, we calculate illumination based on the focal plane location without the SIPS. I measured my Paracorr 2 lens (can't get to my SIPS right now) opening at 42mm. At f/3, a 29mm diameter light cone will focus 88mm from the bottom of the SIPS. This is obviously smaller than the 42mm lens, so the central spot is easily fully illuminated at f/3.

Additionally, there is a 6.5mm margin around the edge of the lens, so we can estimate about a 13 mm-diameter fully illuminated field at f/3 with the SIPS.

Using these assumptions, we can also calculate the fastest f/# that will have a fully illuminated central spot with the SIPS: 88/42 = f/2.09

Quote:

I take it you also havent read the recent post on Paracorr 2 performance at F2.8 in Mikes group? check it out makes for a good read.....



Not sure what you're referring to... I said it worked fine, but I didn't recommend going faster. F/3 works great.

As for a 6" secondary, it sounds about right to me.


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FastMike
sage


Reged: 09/22/10

Loc: Florida 27° 15' N
Re: Webster F3 24" new [Re: gatorengineer]
      #5856351 - 05/12/13 09:11 PM

Quote:

If you are getting 0.4" at the SIPS, what happens in the distance between the SIPS field lens and the Eyepiece field lens? Answer The light cone drops as a function of distance between is what happens. If you have 1.5" or so between the SIPS exit lens and the field lens of the 21E you actually have well, 0 fully illuminated.





I believe this is where your calculations went wrong. You don't add the distance between the Paracorr lens and the eyepiece lens when figuring illumination. I don't know how it's calculated maybe someone else knows (TV rep?). The Paracorr *moves* the focal plane. So all you need to do is illuminate the telescope focal plane without a Paracorr to get a fully illuminated eyepiece with a Paracorr.

Quote:

Lastly this also doesnt account for the SIPS' other shortcomming which is that it can be optimized for the distance from the EP to focuser, like a normal Paracorr 2 (over that range the SIPS effectiveness would vary significantly)




I don't understand what you are trying to say? Think of it this way: The SIPS is a Paracorr 2 with a tunable top, it's just the tunable top on the SIPS is a Feather Touch focuser rather than the twist top like a regular Paracorr 2. Other than that there is no difference between the SIPS and the regular Paracorr 2.

Quote:

If you let me know your secondary size, cage ID, I would be interested in running the numbers.




29" inside diameter of the UTA
28" primary
7" secondary
Secondary to focal plane 18.25"
Focal length 77.1" f/2.75

Quote:

I take it you also havent read the recent post on Paracorr 2 performance at F2.8 in Mikes group? check it out makes for a good read.....




Link or quote? I have not seen it.

Quote:

Why do they make 3 and 4 inch focusers and Wynn correctors? To illuminate a full frame 35 Millimeter chip without clipping in the focuser.... How big is a 35MM chip compared to a 21 E Field lens?




The eye does not work like a camera. You can't just take what is used for photography and apply it for visual.

I have tested my scope to see what was vignetting the edge of field by placing post-it-notes on various components. What I found was the internal baffles of the eyepieces are the limiting factor. So you might calculate the UTA is too small or the Paracorr field lens is too small but neither of those matter because the internal baffles of the eyepiece clip the light cone first before anything else does.

Some other food for thought. My f/2.75 is better corrected than your f/5 everywhere except possibly in the center few millimeters of the focal plane. I have used f/5 telescopes without a Paracorr and they had far too much coma for me. I didn't like the view. I would use a Paracorr in your f/5 scope if it was mine. The edge of my f/2.75 has so little coma you have to look hard to see it. Your f/5 is loaded with coma (relatively speaking compared to mine). Plus your scope has a narrower field of view, less edge of field illumination, not to mention the ladder.


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Aperturefever
super member


Reged: 12/12/10

Loc: Lake Macquarie, Australia
Re: Webster F3 24" new [Re: FastMike]
      #5856901 - 05/13/13 07:16 AM

Thanks to the two Mikes for your education on this cutting-edge design. Given I see this seriously as a very usable big-aperture dobsonian your hands-on experience and comments are invaluable. I guess there is always something to learn when others are at the forefront of this pursuit. To me this looks to be such a useable telescope, and light years away from the solid-tube Meade DS-16 I used to wrestle onto an equatorial mount in the late 1980s!

Edited by Aperturefever (05/13/13 07:21 AM)


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maire
member


Reged: 09/23/11

Loc: France
Re: Webster F3 24" new [Re: Pinbout]
      #5856930 - 05/13/13 07:58 AM

My aperture fever is just closed... because of my new homemade scope:

http://www.astrosurf.com/voute/T600/secLum/T600sec.jpg

Edited by maire (05/13/13 07:59 AM)


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gatorengineer
Carpal Tunnel
*****

Reged: 02/28/05

Loc: Hellertown, PA
Re: Webster F3 24" new [Re: Mike Lockwood]
      #5857157 - 05/13/13 10:29 AM

Mike at F3 you say the sips has a fully illuminated spot of 13 MM at the focal plane (which is what i think you are saying), I agree with you IF the field lens of the SIPS is fully 100% illuminated. This would require a MONSTER Secondary to accomplish.

In The adjustable 20-40MM distance the light cone is still doing its thing (e.g. coning, so 13MM would like correspond to the 20MM side of the adjustment, less so at the 40mm side), What I am trying to get at is that the focal distance of various ethos eyepieces require over a 1" movement of the eyepiece relative to the focal plane, the light cone is again their coning.....

all of this put together is at F3, I do not beleive an Ethos 8 would have any areas 100% illuminated, even with a fully illuminated SIPS....


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Mike Lockwood
Vendor, Lockwood Custom Optics
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Reged: 10/01/07

Loc: Usually in my optical shop
Re: Webster F3 24" new [Re: gatorengineer]
      #5857314 - 05/13/13 11:57 AM

Quote:

Mike at F3 you say the sips has a fully illuminated spot of 13 MM at the focal plane (which is what i think you are saying), I agree with you IF the field lens of the SIPS is fully 100% illuminated. This would require a MONSTER Secondary to accomplish.



Let's assume 16" from the secondary to the focal plane. 16"/3 = 5.33" means that a 5.33" secondary is required to fully illuminate the center spot. So, add 13mm which is just over 1/2", that's 5.83", and a 6" secondary comfortably covers it. At 25% obstruction, that's not a monster by my definition.

Quote:

In The adjustable 20-40MM distance the light cone is still doing its thing (e.g. coning, so 13MM would like correspond to the 20MM side of the adjustment, less so at the 40mm side), What I am trying to get at is that the focal distance of various ethos eyepieces require over a 1" movement of the eyepiece relative to the focal plane, the light cone is again their coning.....



No. The adjustability that I indicate is that the entire SIPS unit moves up and down, with a range of 20mm of movement, within the mounting plate, and the locking ring screws down against the plate. This is how the focal plane is positioned properly using the spacer that is included.

Think about it like a helical focuser - the entire unit screws in and out of the plate to properly position it. Then the locking ring simply holds it in place.

One set, the primary to SIPS lens and SIPS lens to focal plane distances do not change (unless the primary is moved significantly closer or farther from the SIPS by using the collimation adjustments). The focuser merely positions the eyepiece with respect to the stationary focal plane.


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mark cowan
Vendor (Veritas Optics)
*****

Reged: 06/03/05

Loc: salem, OR
Re: Webster F3 24" new [Re: Mike Lockwood]
      #5857799 - 05/13/13 03:42 PM

Quote:

So, we calculate illumination based on the focal plane location without the SIPS. I measured my Paracorr 2 lens (can't get to my SIPS right now) opening at 42mm. At f/3, a 29mm diameter light cone will focus 88mm from the bottom of the SIPS. This is obviously smaller than the 42mm lens, so the central spot is easily fully illuminated at f/3.




Mike, thanks for fully illuminating this thread.

Best,
Mark


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Eric Webster
Vendor (Webster Telescopes)


Reged: 10/04/06

Loc: Detroit Michigan
Re: Webster F3 24" new [Re: mark cowan]
      #5858392 - 05/13/13 07:13 PM

This picture was deleted earlier in the thread:

Edited by okieav8r (05/13/13 11:30 PM)


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Eric Webster
Vendor (Webster Telescopes)


Reged: 10/04/06

Loc: Detroit Michigan
Re: Webster F3 24" new [Re: Eric Webster]
      #5858396 - 05/13/13 07:14 PM

As was this one:

Edited by okieav8r (05/13/13 11:30 PM)


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Eric Webster
Vendor (Webster Telescopes)


Reged: 10/04/06

Loc: Detroit Michigan
Re: Webster F3 24" new [Re: Eric Webster]
      #5858403 - 05/13/13 07:18 PM

Sorry about the delay for you guys who emailed us about the pictures being deleted by the CN Moderators.

I could not remember what email address or password we used for these forums, as we have not posted here in many years.

Hopefully everything is now straightened out as far as using pictures from our site/forums.

Keep up the lively discussions!


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Project Galileo
scholastic sledgehammer
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Reged: 11/14/07

Loc: Jefferson County, Colorado
Re: Webster F3 24" new [Re: Eric Webster]
      #5858416 - 05/13/13 07:29 PM

Every time my wife walks by my computer monitor and these pictures are on it she laughs at me and says, "are you looking at telescope porn again?"

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okieav8rAdministrator
I'd rather be flying!
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Reged: 03/01/09

Loc: Oklahoma!
Re: Webster F3 24" new [Re: Project Galileo]
      #5858974 - 05/13/13 11:57 PM

There have been some issues in this thread over the last few days with regard to the posting of photographs on Cloudy Nights forums from other websites. Please note that with regard to the Cloudy Nights TOS, a blanket permission statement on another website allowing the use of photos does not meet CN's requirement for the posting of photos on these forums. The Cloudy Nights TOS prefers that users instead post a link to the website where the photograph resides. If a photo is posted by a member who does not own the photgraph, a permission statement that specifically states that permission is granted to post the photo on the CN website must also be posted with the photo. Please refer to the Cloudy Nights TOS, or feel free to contact an administrator (red user) for further clarification.

The thread is now reinstated.


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gatorengineer
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Re: Webster F3 24" new [Re: okieav8r]
      #5859238 - 05/14/13 07:20 AM Attachment (16 downloads)

Here is running the dimensions that Mike provided in Web Newt.

Edited by gatorengineer (05/14/13 07:24 AM)


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gatorengineer
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Re: Webster F3 24" new [Re: gatorengineer]
      #5859248 - 05/14/13 07:25 AM Attachment (12 downloads)

Here are the results, perhaps I got a parameter wrong but he scope vignettes at the secondary cage. The focuser to front of tube distance is also likely short.

Edited by gatorengineer (05/14/13 07:26 AM)


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gatorengineer
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Re: Webster F3 24" new [Re: gatorengineer]
      #5859263 - 05/14/13 07:38 AM Attachment (10 downloads)

Heres how I might play with it..... Extend the cage forward a bit, and give a little more backfocus. As it sits I am going to get alot of light from above the cage on the field lens of the Eyepiece.... and If I put a flockboard up the scope will again vignette. so backing out the focal plane with a 3" focuser and a paracorr 2 is imho a better solution....

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gatorengineer
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Re: Webster F3 24" new [Re: gatorengineer]
      #5859265 - 05/14/13 07:39 AM Attachment (12 downloads)

the corresponding ray trace.....

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FastMike
sage


Reged: 09/22/10

Loc: Florida 27° 15' N
Re: Webster F3 24" new [Re: gatorengineer]
      #5859569 - 05/14/13 10:47 AM Attachment (9 downloads)

Quote:

Heres how I might play with it..... Extend the cage forward a bit, and give a little more backfocus. As it sits I am going to get alot of light from above the cage on the field lens of the Eyepiece.... and If I put a flockboard up the scope will again vignette. so backing out the focal plane with a 3" focuser and a paracorr 2 is imho a better solution....




What your calculations didn't to take into account is the use of a Paracorr. The Paracorr (SIPS) is at a fixed distance with respect to the primary mirror.

The Paracorr will be at a fixed point in space regardless of how large the UTA is. So as you make the UTA larger the Paracorr will just protrude further and further inside the UTA (see picture).

The UTA could be lowered on the truss poles to place the Paracorr farther outside the UTA. But then a larger secondary mirror would be needed to fully illuminate the focal plane. I think this is what you were trying to accomplish with a 31.5" UTA?


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FastMike
sage


Reged: 09/22/10

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Re: Webster F3 24" new [Re: gatorengineer]
      #5859595 - 05/14/13 10:58 AM Attachment (11 downloads)

Quote:

Here are the results, perhaps I got a parameter wrong but he scope vignettes at the secondary cage. The focuser to front of tube distance is also likely short.




Here is a picture of the Paracorr 2 (SIPS) from inside the UTA. As you can see the lens is flush with the inside of the UTA. Having a 3" focuser will accomplish nothing.

It's very possible the UTA is vignetting the light cone.

Answer this -> what good is having a larger UTA if the Paracorr 2 vignetts the light cone *more* than the UTA? Having a larger UTA will accomplish nothing if the Paracorr 2 vignetts more than the UTA does.


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FastMike
sage


Reged: 09/22/10

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Re: Webster F3 24" new [Re: gatorengineer]
      #5859616 - 05/14/13 11:09 AM

Quote:

all of this put together is at F3, I do not beleive an Ethos 8 would have any areas 100% illuminated, even with a fully illuminated SIPS....




Sorry, but I trust Televue more than you to design optics.

Televue states the Paracorr 2 is designed to work with f/3.0 telescopes. I take them at their word. I trust they would properly design the Paracorr 2 so it would provide 100% illumination with their own Ethos eyepieces.

Plus I can tell you this from experience. The 8mm Ethos is 100% illuminated in the center with a f/2.75 telescope.


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gatorengineer
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Re: Webster F3 24" new [Re: FastMike]
      #5859627 - 05/14/13 11:12 AM

Mike,

You and Mike L have an entirely different explanation of the functioning of the sips device. I have a paracorr 2, not a SIPS, so I do not know. Mike L says the SIPS field lens Moves... if I read your post correctly, you say it is fixed relative to the primary?

You need roughly 30MM of focus travel so if the field lens of the SIPS is fixed, then you are right, 3" does nothing. If it goes "up the focuser" like a Paracorr 2 would, then 3" definitely gets you something...

If it is fixed, its a completly different optical formula than a paracorr 2..... and a 3" focuser would get you nothing....

Edited by gatorengineer (05/14/13 11:19 AM)


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gatorengineer
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Re: Webster F3 24" new [Re: gatorengineer]
      #5859636 - 05/14/13 11:18 AM

Mike,

Televue designs the Paracorr, and has a done a great job of it no doubt.... Mike L does an outstanding job of figuring the optics..... These two items get integrated by the scope manufacturer.... You have a correctly sized secondary, some fast scopes (at least early ones), didnt have correctly sized secondaries....... Secondary cage size, is a mix of a bunch of factors, its a compromise ( diameter, weight secondary size, and the need to baffle above the cage to keep stray light off of the field, are just a few of the factors)


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FastMike
sage


Reged: 09/22/10

Loc: Florida 27° 15' N
Re: Webster F3 24" new [Re: gatorengineer]
      #5859675 - 05/14/13 11:39 AM Attachment (16 downloads)

Quote:

You and Mike L have an entirely different explanation of the functioning of the sips device.




I know it's confusing if you never used a SIPS before. Maybe Mike L can explain it better.

When using a SIPS the Paracorr lens never moves once it's installed. So what you seen in the picture below is where the Paracorr lens is always located. Which is why I keep saying a larger 3" focuser is not needed.

The SIPS lens can be moved when first installing the SIPS. This is done to set the lens at the proper distance from the primary. Once the distance is set the lens is locked down and never moves again.

Here is a link to installing the SIPS from Mike L.

http://www.loptics.com/documents/SIPS.pdf

Try this the next time you use the Paracorr 2. Adjust it to the proper setting for an eyepiece (A-B-C etc) and focus the scope. Next look into the UTA and note where the Paracorr 2 field lens is located. The lens on your Paracorr 2 will be at the exact same location as a SIPS lens would be. Now put in a different eyepiece and use the tunable top to focus (don't use the focuser). Note the position of the tunable top (A-B-C etc). If you did it right the tunable top will be in the correct position (A-B-C etc) for the new eyepiece you are now using. Now you can now go the rest of the night without ever using the focuser again, just use the tunable top to focus.


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gatorengineer
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Reged: 02/28/05

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Re: Webster F3 24" new [Re: FastMike]
      #5859835 - 05/14/13 12:40 PM

Mike,

I appreciate the tip, but the Optimal locations for the different eyepieces a 17E, is different than the 3.7sx on the paracorr 2, necessitate the focuser... If I werent waiting on the 30mm 100 degree explore, I might go to a SIPS, but I need a 3" focuser for that beast, along with about 30 lbs more of tail weight....


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Jarad
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Reged: 04/28/03

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Re: Webster F3 24" new [Re: gatorengineer]
      #5859861 - 05/14/13 12:53 PM

Quote:

I appreciate the tip, but the Optimal locations for the different eyepieces a 17E, is different than the 3.7sx on the paracorr 2, necessitate the focuser...




Yes, that is the whole point of the SIPS - the focuser does not move the paracorr lens, it moves the eyepiece relative to it. As someone else pointed out a few posts back, the SIPS basically replaces the tunable top of the paracorr with a Feathertouch focuser. You adjust the paracorr to the proper position once, then the focuser adjusts the eyepiece relative to the fixed paracorr.

Ideally, you should be doing the same thing with the Paracorr II. Focus one eyepiece with the tunable top set properly for it, lock your focuser, then when you switch eyepieces you don't move the focuser, you just change the tunable top setting.

Jarad


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gatorengineer
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Re: Webster F3 24" new [Re: Jarad]
      #5859895 - 05/14/13 01:13 PM

That would work if Ethos Eyepieces were parafocal, or had the same Paracorr setting. They dont....

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Mike Lockwood
Vendor, Lockwood Custom Optics
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Reged: 10/01/07

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Re: Webster F3 24" new [Re: gatorengineer]
      #5860066 - 05/14/13 02:26 PM

Quote:

That would work if Ethos Eyepieces were parafocal, or had the same Paracorr setting. They dont....




Tuning the Paracorr IS parafocalizing to put the focal plane in the right spot: The tunable top positions the eyepiece so that when focused, the focal plane is always 135mm above the bottom of the lens group.

That is all the Paracorr "setting" does - the lens group is unaffected.

The tunable top simply makes up for the physical differences in how the eyepieces are constructed. With the SIPS, the focuser does it.

For the Paracorr 2 (either SIPS or tunable top), the focal plane must be 135mm from the bottom of the lens group for optimal performance.


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Jarad
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Re: Webster F3 24" new [Re: gatorengineer]
      #5860081 - 05/14/13 02:32 PM

They don't need to be parfocal or use the same setting - that is the point of the focuser or tunable top. The paracorr lens stays still, the eyepiece moves.

In the picture of the SIPS that Mike L posted above, the focal plane is at the line just above the "47mm" at top right. The lens at the bottom does not move relative to the focal plane or relative to the mirror. You put the eyepiece in the focuser, and the focuser moves the eyepiece only up or down to place the eyepiece's focal plane at the telescope focal plane.

The tunable top does the same thing, only without as fine a motion (so most people adjust it to the closest setting, then use the focuser, which does move the paracorr lens slightly away from where it should ideally be).

Once again, the paracorr lens stays still, the eyepiece moves. If you change eyepieces and they are parfocal, the eyepiece won't need to move either. If they are not parfocal, the focuser will move the eyepiece only, not the paracorr lens.

Jarad

Edited by Jarad (05/14/13 02:34 PM)


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Pinbout
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Re: Webster F3 24" new [Re: Jarad]
      #5860981 - 05/14/13 09:21 PM

I never used either so here's my question, I find myself adjusting focus cause of seeing conditions... a lot, so would I keep my hand on the tunable top or the focuser for those nights when seeing is not so good a lot.

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Jarad
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Re: Webster F3 24" new [Re: Pinbout]
      #5861559 - 05/15/13 07:13 AM

Assuming you have the tunable top set correctly, you make adjustments with the focuser.

Jarad


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mark cowan
Vendor (Veritas Optics)
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Reged: 06/03/05

Loc: salem, OR
Re: Webster F3 24" new [Re: Jarad]
      #5868090 - 05/17/13 08:30 PM

Hi y'all,

I chatted with Wayne at Starlight Instruments about the SIPS, this thread and the confusion factors, ended up just revising a couple of paragraphs in the installation instructions to clarify what seemed to be unclear to me. They took that and used it, but I'm not trying to take away from Mike L's time and effort in preparing the instructions and enabling the product development in any way.

Here's where it all is: http://starlightinstruments.com/store/index.php?route=product/product&pro...

Anybody who'd like to review the documentation there and provide feedback to Starlight, I'm sure they'd appreciate it. This is the information that people get when they're trying to figure out how to use it. One point that I'm not yet sure is clear there is what Mike addressed early on, the relative position of the PII corrector, the original FP, and the new FP with the PII installed. This seems to be the heart of the matter regarding confusion about field illumination, but it also needs to be taken into account while laying out the OTA.

Best,
Mark


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Mike Lockwood
Vendor, Lockwood Custom Optics
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Reged: 10/01/07

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Re: Webster F3 24" new [Re: mark cowan]
      #5868359 - 05/17/13 10:49 PM

Quote:

One point that I'm not yet sure is clear there is what Mike addressed early on, the relative position of the PII corrector, the original FP, and the new FP with the PII installed.



I think the diagram is quite clear. This diagram was developed based on conversations that I had with Al Nagler.

Quote:

They took that and used it, but I'm not trying to take away from Mike L's time and effort in preparing the instructions and enabling the product development in any way.
Here's where it all is:



Well, since your name is now literally in the .pdf file name, one of your companies is mentioned right by it on their site, and I am merely a footnote in the instructions, someone in fact did take away from the many hours of effort that I put into that manual and all of the photos that go with it.

Wayne should have contacted me, the author, to help clarify and update those paragraphs if that was desired. You don't make minor changes in a written work and then put someone else's name on it.


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a__l
professor emeritus


Reged: 11/24/07

Re: Webster F3 24" new [Re: Mike Lockwood]
      #5868374 - 05/17/13 10:57 PM

There is another flaw in the instructions to the SIPS (in the early instruction at least). Not focus the image with the E-17, 21 and N-31 (at a certain myopia).
Or with myopia needs another choice FP during the initial installation? How?

Edited by a__l (05/17/13 11:19 PM)


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Mike Lockwood
Vendor, Lockwood Custom Optics
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Reged: 10/01/07

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Re: Webster F3 24" new [Re: a__l]
      #5868430 - 05/17/13 11:23 PM

Quote:

There is another flaw in the instructions to the SIPS (in the early instruction at least). Not focus the image with the E-17, 21 and N-31 (at a certain myopia).



No, that's not a flaw in the instructions, that's a design issue that you should bring up with the manufacturers.

Changing the instructions will not change it.


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a__l
professor emeritus


Reged: 11/24/07

Re: Webster F3 24" new [Re: Mike Lockwood]
      #5868446 - 05/17/13 11:30 PM

SIPS this is fully complete device, including design.

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eastwd
member


Reged: 08/21/11

Loc: Nashville
Re: Webster F3 24" new [Re: FastMike]
      #5868494 - 05/17/13 11:56 PM

FastMike and Mike Lockwood, I want to thank you guys for your contributions to this thread. I've been fascinated by the 28" Webster/Lockwood f/2.75 since I first read about it. I've read and re-read every post and article I could find on it. Please keep posting. And Mike L., please keep making those big, fast mirrors.

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FastMike
sage


Reged: 09/22/10

Loc: Florida 27° 15' N
Re: Webster F3 24" new [Re: eastwd]
      #5868544 - 05/18/13 12:24 AM

Quote:

FastMike and Mike Lockwood, I want to thank you guys for your contributions to this thread. I've been fascinated by the 28" Webster/Lockwood f/2.75 since I first read about it. I've read and re-read every post and article I could find on it. Please keep posting. And Mike L., please keep making those big, fast mirrors.




I posted more information recently on Mike Lockwoods yahoo group including 10 links to CN on past discussions as well as an eyepiece review using my f/2.75 scope.

Here is the link. You should check it out if you haven't seen it already.


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mark cowan
Vendor (Veritas Optics)
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Reged: 06/03/05

Loc: salem, OR
Re: Webster F3 24" new [Re: Mike Lockwood]
      #5870509 - 05/18/13 11:38 PM

Quote:

Quote:

One point that I'm not yet sure is clear there is what Mike addressed early on, the relative position of the PII corrector, the original FP, and the new FP with the PII installed.



I think the diagram is quite clear. This diagram was developed based on conversations that I had with Al Nagler.




They didn't have the illustration you posted earlier in this thread on their product page for some reason, and I asked them to fix that specifically. I agree it made it clear, but if it couldn't be seen it wouldn't make it clear.

Quote:

Quote:

They took that and used it, but I'm not trying to take away from Mike L's time and effort in preparing the instructions and enabling the product development in any way.
Here's where it all is:



Well, since your name is now literally in the .pdf file name, one of your companies is mentioned right by it on their site, and I am merely a footnote in the instructions, someone in fact did take away from the many hours of effort that I put into that manual and all of the photos that go with it.
Wayne should have contacted me, the author, to help clarify and update those paragraphs if that was desired. You don't make minor changes in a written work and then put someone else's name on it.




I've forwarded these complaints to Wayne and asked them to remove any credit to myself (which I never asked for). Credit belongs where credit is due, but in the end it's up to them how they handle their product documentation.

Best,
Mark


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