faackanders2
Pooh-Bah
Reged: 03/28/11
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Re: Explore Scientific 3" 30mm Prototype
[Re: faackanders2]
#5573062 - 12/15/12 07:38 PM
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Make the widest TFOV 3" eyepiece possible for 100 AFOV and 82 AFOV and 70 AFOV, to take full advantage of 3". I don't feel I would ever be able to afford a 120 AFOV max TFOV.
P.S. These may be the eyepieces people will build telescope around (3" refractors, 3" reflectors, and 3" SCTs).
Anybody know what would be the theoretical widest TFOV eyepiece focal length for a 3" diameter 70 AFOV, 82 AFOV, 100 AFOV, and 120 AFOV eyepiece? Also what would be their exit pupils?
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Starman1
Vendor (EyepiecesEtc.com)
Reged: 06/24/03
Loc: Los Angeles
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Re: Explore Scientific 3" 30mm Prototype
[Re: faackanders2]
#5573139 - 12/15/12 08:20 PM
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OK, 3" is 76.2mm.
It's likely an eyepiece barrel for that large and heavy an eyepiece will be 2mm thick, maybe 2.5mm thick counting threads.
That means the maximum field stop would be 71.2mm.
With a negative/positive design, that might result in vignetting, so I'll go with a more conservative maximum of 70mm.
With NO distortion (of course unlikely), that would mean
an apparent field of:
99 degrees in 30mm
90 degrees in 35mm
82 degrees in 40mm
75 degrees in 45mm
70 degrees in 50mm
With a little distortion at the edge, the apparent fields could be slightly larger than that in each focal length. For example, the 24mm 1.25" widefield eyepieces would have a field of 59 degrees instead of 68 were it not for some distortion.
Which means 100 degrees for the 30mm 3" is entirely plausible, even if the effective field stop is less than 70mm.
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edwincjones
Close Enough
Reged: 04/10/04
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Re: Explore Scientific 3" 30mm Prototype
[Re: Starman1]
#5573707 - 12/16/12 07:58 AM
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oh no
I went from 1.25" to 2",
back to 1.25" for binoviewers
now I have to go to 3"
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Thomas Karpf
Pooh-Bah
Reged: 02/09/09
Loc: Newington, CT
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Re: Explore Scientific 3" 30mm Prototype
[Re: edwincjones]
#5582309 - 12/21/12 11:26 AM
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Should we expect that Explore Scientific will soon be selling refractors with 3" focusers (and 2" inserts and 1.25" inserts)?
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faackanders2
Pooh-Bah
Reged: 03/28/11
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Re: Explore Scientific 3" 30mm Prototype
[Re: Starman1]
#5584975 - 12/23/12 12:56 AM
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OK, 3" is 76.2mm.
It's likely an eyepiece barrel for that large and heavy an eyepiece will be 2mm thick, maybe 2.5mm thick counting threads.
That means the maximum field stop would be 71.2mm.
With a negative/positive design, that might result in vignetting, so I'll go with a more conservative maximum of 70mm.
With NO distortion (of course unlikely), that would mean
an apparent field of:
99 degrees in 30mm
90 degrees in 35mm
82 degrees in 40mm
75 degrees in 45mm
70 degrees in 50mm
With a little distortion at the edge, the apparent fields could be slightly larger than that in each focal length. For example, the 24mm 1.25" widefield eyepieces would have a field of 59 degrees instead of 68 were it not for some distortion.
Which means 100 degrees for the 30mm 3" is entirely plausible, even if the effective field stop is less than 70mm.
If I got a 3" focuser, I would probably be most interested in a 50mm 70 AFOV for widest TFOV, folo  wed by either 40mm 82 AFOV or 30mm 100 AFOV.
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faackanders2
Pooh-Bah
Reged: 03/28/11
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Re: Explore Scientific 3" 30mm Prototype
[Re: Thomas Karpf]
#5584976 - 12/23/12 12:58 AM
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Should we expect that Explore Scientific will soon be selling refractors with 3" focusers (and 2" inserts and 1.25" inserts)?
If you build it, they will come.
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faackanders2
Pooh-Bah
Reged: 03/28/11
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Re: Explore Scientific 3" 30mm Prototype
[Re: faackanders2]
#5584980 - 12/23/12 01:00 AM
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What is the AFOV of this ES 3" 30mm prototype?
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Astrojensen
Post Laureate
Reged: 10/05/08
Loc: Bornholm, Denmark
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Re: Explore Scientific 3" 30mm Prototype
[Re: faackanders2]
#5585070 - 12/23/12 03:49 AM
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100°
Clear skies!
Thomas, Denmark
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Cyclop_si
professor emeritus
Reged: 03/13/08
Loc: Slovenia
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Re: Explore Scientific 3" 30mm Prototype
[Re: frebie]
#5588196 - 12/25/12 08:32 AM
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.... The 30mm will be the first in a series of 4 or 5 3" 100 degree eyepieces. ES is contemplating a 40mm as the next in the series and would like CN feedback on what other focal lengths might be desirable...
I agree that it would be smart move for ES to offer 35-40mm 100° eyepiece next, since I think this would maximize 100° potential in 3" format. Also, I think many APO and SCT users would prefer this focal length over 30mm, since difference between existing 30-31 mm 82° and new 3" 30mm 100° eyepiece might not be beneficial enough for potential customers to mess with bulk and weight of new system. Contrary, 35-40mm 100° eyepiece would give them significantly increased TFOV to deal with related cost, bulk and weight. This eyepiece would give reasonably small exit pupil for most APOs (f/7 and slower) and SCT users of course.
For large SCT users, I think 3" eyepiece with 45-50mm 82° and also 55-60mm 70° would be interested as well.
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faackanders2
Pooh-Bah
Reged: 03/28/11
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Re: Explore Scientific 3" 30mm Prototype
[Re: Cyclop_si]
#5590544 - 12/26/12 11:47 PM
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.... The 30mm will be the first in a series of 4 or 5 3" 100 degree eyepieces. ES is contemplating a 40mm as the next in the series and would like CN feedback on what other focal lengths might be desirable...
I agree that it would be smart move for ES to offer 35-40mm 100° eyepiece next, since I think this would maximize 100° potential in 3" format. Also, I think many APO and SCT users would prefer this focal length over 30mm, since difference between existing 30-31 mm 82° and new 3" 30mm 100° eyepiece might not be beneficial enough for potential customers to mess with bulk and weight of new system. Contrary, 35-40mm 100° eyepiece would give them significantly increased TFOV to deal with related cost, bulk and weight. This eyepiece would give reasonably small exit pupil for most APOs (f/7 and slower) and SCT users of course.
For large SCT users, I think 3" eyepiece with 45-50mm 82° and also 55-60mm 70° would be interested as well.
30mm 120 AFOV, 40mm 100AFOV, 50mm 82AFOV, 60mm 70AFOV really would be pushing the limit of maximum TFOV for given power. They probably would all require a paracorr coma correcttor.
But hopefully they would allow 2" filters to be screwed in the eye side of the eyepiece also; till we have enough 3" eyepieces to upgrade filters also.
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gatorengineer
Carpal Tunnel
Reged: 02/28/05
Loc: Hellertown, PA
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Re: Explore Scientific 3" 30mm Prototype
[Re: faackanders2]
#5591037 - 12/27/12 11:36 AM
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Well, I just pre-ordered mine. With the reason being, is that with the 25 F5, I will now have 105x at 1 degree with a 6mm exit pupil.
A E21 in a 25 F3.3 gets you .86 with a 5.5mm exit pupil, an E21 in an F3.7 gets you .77, at a 5mm exit both requiring paracorrs
So now I can get wider field of view then the fast scopes, still have the ladder, but am about 15k less invested....
Next step will be the 3" feathertouch.
In this regard, as there is not a standard for 3" eyepices, would it be possible for Astronomics (who I ordered through), to ask what the exact interpretation of 3" is and what the taper is... Thanks.
BTW I dont expec the eyepiece until 14, but hey its on order....
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Starman1
Vendor (EyepiecesEtc.com)
Reged: 06/24/03
Loc: Los Angeles
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Re: Explore Scientific 3" 30mm Prototype
[Re: gatorengineer]
#5591267 - 12/27/12 02:18 PM
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Well, I just pre-ordered mine. With the reason being, is that with the 25 F5, I will now have 105x at 1 degree with a 6mm exit pupil.
A E21 in a 25 F3.3 gets you .86 with a 5.5mm exit pupil, an E21 in an F3.7 gets you .77, at a 5mm exit both requiring paracorrs
So now I can get wider field of view then the fast scopes, still have the ladder, but am about 15k less invested....
Next step will be the 3" feathertouch.
In this regard, as there is not a standard for 3" eyepices, would it be possible for Astronomics (who I ordered through), to ask what the exact interpretation of 3" is and what the taper is... Thanks.
BTW I dont expec the eyepiece until 14, but hey its on order....
Just a note about Coma and Paracorr:
It is not the exit pupil or true field that determines whether coma is visible in a field of view, it is the apparent field of the eyepiece.
I'll explain.
Take two eyepieces of 25mm--one of 50 degree field and 1 of 100 degree field. Since the field of the 100 degree eyepiece is twice as wide, coma at the edge (a linear feature) is twice as wide a star image in the 100 degree field as it is in the 50 degree field.
Now, use a 12.5mm 100 degree eyepiece. The field is 1/2 as wide, so the comatic star image at the edge is 1/2 as wide--the same width as the comatic star at the edge of the 50 degree field in the 25mm eyepiece.
BUT, the magnification is now twice as great. That increase in magnification makes the apparent size of the comatic star image at the edge exactly the same as it appeared in the 25mm 100 degree eyepiece.
And so it is with all magnifications--the apparent size of the comatic star image will be the same at all magnifications in 100 degree eyepieces.
So what eyepiece seems to present a comatic star image at the edge of the field is determined by the apparent field. Don't like coma? Stick to scopes longer than f/5 or apparent field eyepieces of 50 degrees or less.
Or, use a scope not known to have visible coma: refractor, Maksutov, etc. The SCT does have coma unless it is corrected (such as the Meade ACF or the Celestron Edge, both of which are corrected to eliminate coma). The standard f/6.3 reducer does a pretty good job of that in a standard SCT (it is a reducer/corrector).
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faackanders2
Pooh-Bah
Reged: 03/28/11
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Re: Explore Scientific 3" 30mm Prototype
[Re: gatorengineer]
#5591555 - 12/27/12 06:05 PM
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Well, I just pre-ordered mine. With the reason being, is that with the 25 F5, I will now have 105x at 1 degree with a 6mm exit pupil.
A E21 in a 25 F3.3 gets you .86 with a 5.5mm exit pupil, an E21 in an F3.7 gets you .77, at a 5mm exit both requiring paracorrs
So now I can get wider field of view then the fast scopes, still have the ladder, but am about 15k less invested....
Next step will be the 3" feathertouch.
In this regard, as there is not a standard for 3" eyepices, would it be possible for Astronomics (who I ordered through), to ask what the exact interpretation of 3" is and what the taper is... Thanks.
BTW I dont expec the eyepiece until 14, but hey its on order....
I can just see it now; 3" focuser soon to become the new standard for large dobsonians. Many may feel it is time to upgrade their scope or buy a new one.
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Astrojensen
Post Laureate
Reged: 10/05/08
Loc: Bornholm, Denmark
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Re: Explore Scientific 3" 30mm Prototype
[Re: faackanders2]
#5591569 - 12/27/12 06:15 PM
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And why not? Rafael Benner has a 4" focuser on his 30". It has 5" of travel, allowing to change from a single eyepiece to a binoviewer without fumbling with extension tubes or use barlows. On a 30" this is of course similar to a 2" with 2.5" travel on a 15"... Nothing ordinary. A 4" focuser doesn't look all that big on a 30". In Rafael's case, there's no need to worry about balance issues, when using a 30mm/100° eyepiece. It takes some real muscle power to track that huge dob.
Clear skies!
Thomas, Denmark
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gatorengineer
Carpal Tunnel
Reged: 02/28/05
Loc: Hellertown, PA
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Re: Explore Scientific 3" 30mm Prototype
[Re: Astrojensen]
#5591657 - 12/27/12 07:24 PM
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Well long focus big dobs are a dying breed, Until they come up with a Paracorr X in 3", I dont expect to see many of these in todays generation F5 big dob..... For me its a worthwhile investment. I love my 9 120.... The next problem is the near $700 focuser from feathertouch. The other thing not to be discounted for me, is going from this thing to a small Nagler will be a heck of a balance change.... But fun...
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Astrojensen
Post Laureate
Reged: 10/05/08
Loc: Bornholm, Denmark
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Re: Explore Scientific 3" 30mm Prototype
[Re: gatorengineer]
#5592148 - 12/28/12 04:51 AM
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Until they come up with a Paracorr X in 3",
But these already exist! Well, sort of...:
http://www.astrooptik.com/sonstiges/Newton4Inch/NewtWynne.htm
Not really plug 'n play, but it exists!
Clear skies!
Thomas, Denmark
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faackanders2
Pooh-Bah
Reged: 03/28/11
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Re: Explore Scientific 3" 30mm Prototype
[Re: Astrojensen]
#5593415 - 12/28/12 09:52 PM
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Until they come up with a Paracorr X in 3",
But these already exist! Well, sort of...:
http://www.astrooptik.com/sonstiges/Newton4Inch/NewtWynne.htm
Not really plug 'n play, but it exists!
Clear skies!
Thomas, Denmark
This is for a 4" coma corrector. It would be even a bigger leap from 2" to 4", but the cost would likely be out of reach for many; so 3" (or 2") may be the limit for most.
P.S. Moderator, Could this be moved to the eyepiece forum so it is easier to find?
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Astrojensen
Post Laureate
Reged: 10/05/08
Loc: Bornholm, Denmark
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Re: Explore Scientific 3" 30mm Prototype
[Re: faackanders2]
#5593750 - 12/29/12 02:52 AM
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This is for a 4" coma corrector.
Oops!  Well, it will fully illuminate a 3" eyepiece, that's for sure.
Let's try again:
http://www.astrosysteme.at/images/Corr_3Zoll_Wynne.pdf
Clear skies!
Thomas, Denmark
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gatorengineer
Carpal Tunnel
Reged: 02/28/05
Loc: Hellertown, PA
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Re: Explore Scientific 3" 30mm Prototype
[Re: Astrojensen]
#5596607 - 12/30/12 05:30 PM
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Well the issue with the Wynn is that it may not work visually. I dont know that it will or wont, but I was interested in buying one a few years back before the Paracorr 2 for an F3.5 scope. I called the US distributor and frankly he laughed at me on the phone.... Needless to say this vendor will never get a dime from me, it would be interesting to know if the wynns work visually. There are a bunch of F3ish dobs out there that arent fully illuminated with a 2" P2....
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Astrojensen
Post Laureate
Reged: 10/05/08
Loc: Bornholm, Denmark
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Re: Explore Scientific 3" 30mm Prototype
[Re: gatorengineer]
#5596702 - 12/30/12 06:39 PM
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Why shouldn't it work visually??? The 3" Wynne corrector from Philipp Keller has ~55mm working distance and the 4" around 60mm. I would email Keller directly and ask. I am pretty sure he could also design something with greater working distance, if the edge correction tolerances are relaxed a bit, as would be perfectly possible in visual observing.
Clear skies!
Thomas, Denmark
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