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Jarrod
Pooh-Bah

Reged: 01/20/13

Loc: SE USA
Inexpensive 1.25" maximum TFOV EPs
#5775127 - 04/03/13 10:07 AM

I want to get an inexpensive 1.25" EP that maxes out the TFOV that can be offered by a 1.25" barrel.

Currently I'm looking at these two GSO Super Plossls at Agena, which Agena rates thusly:
32mm -> 52* AFOV
40mm -> 45* AFOV

Now, if I plug these into the TFOV = AFOV/Mag equation for my scope (1200mm f/5.9), I get:
32mm -> 1.39*
40mm -> 1.50*

However, I've read here that the 32mm and 40mm 1.25" Plossls do not offer a different TFOV, but rather you just get a smaller image in the 40mm EP. So that would argue to go for the 32mm EP. But the results from my equation say to get the 40mm EP. Can someone explain the discrepancy to me?

I've asked a similar question on the forum before, inside my other EP threads, but nobody ever answered. Basically, what is the physical limitation of TFOV as a function of barrel diameter and how do you *really* calculate it? The TFOV equation above has no terms that relate to the diameter of the EP barrel.

Many thanks!

Edited by Jarrod (04/03/13 10:09 AM)

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dan_h
Carpal Tunnel

Reged: 12/10/07

Re: Inexpensive 1.25" maximum TFOV EPs [Re: Jarrod]
#5775334 - 04/03/13 11:28 AM

Given that the barrel restricts the absolute maximum field, you can compare the actual FOV as the ratio of the focal lengths.

32/40=0.8, 52 degrees X 0.8 = 41.6 degrees for the 40mm eyepiece, not 45 degrees. That is one source of error and 41 degrees is probably closer to reality.

If you calculate the size of field for a 40mm FL and a 41 degree view, it comes to approximately 29.9mm, or just about equal the inside diameter of the eyepiece barrel.

Hope this helps,

dan

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Thomas Karpf
Carpal Tunnel

Reged: 02/09/09

Loc: Newington, CT
Re: Inexpensive 1.25" maximum TFOV EPs [Re: Jarrod]
#5775345 - 04/03/13 11:32 AM

http://www.televue.com/engine/TV3b_page.asp?id=79

It's based on the maximum field stop of the eyepiece.

For a 1.25" eyepiece, the maximum field stop is about 27mm. For a 2" eyepiece, the maximum field stop is about 46mm.

Simple trigonometry will give you the maximum field of view of a scope. It's based on a long, skinny triangle with long sides = the focal length of the scope and the short side = the field stop of the focuser.

maximum field of view with a 1.25" focuser is about 1.29 degrees (27mm / 1200mm * 180 / pi), and
maximum field of view with a 2" focuser is about 2.19 degrees (46mm / 1200mm * 180 / pi).

Frankly, I'd expect that the AFOV of the 40mm is probably more like 40* rather than 43*.

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MingoT
member

Reged: 09/12/10

Loc: Zaragoza, Spain
Re: Inexpensive 1.25" maximum TFOV EPs [Re: Jarrod]
#5775352 - 04/03/13 11:34 AM

Hi,

The True Field of View is:
TFOV = 57.3 * Eyepiece_Field_Stop / Telescope_Focal_Length

The maximum Field Stop for a 1.25" eyepiece is 27mm, for a 1200mm telescope, this gives TFOV = 1.29 degrees. A given eyepiece could offer a little more TFOV than that, at the cost of some vignetting (darkening in the outer part of the image), how noticeable it is, depends on your sensitivity.

Unless you have very dark skies, you are quite young, and you want to maximize exit pupil, I would recommend the 32mm. It will show the same portion of the sky with more magnification and darker background.

Best,
Mingo

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BDS316
Carpal Tunnel

Reged: 09/16/09

Loc: Sol 3
Re: Inexpensive 1.25" maximum TFOV EPs [Re: MingoT]
#5775414 - 04/03/13 12:04 PM

Quote:

I would recommend the 32mm. It will show the same portion of the sky with more magnification and darker background.

Agree. I can't think of a single situation in which it would be better to use a 40mm Plossl over a 32mm Plossl.

Unless it's the 40mm Sterling Plossl, but that's a 2 inch eyepiece, of course

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Mark9473
Postmaster

Reged: 07/21/05

Loc: 51°N 4°E
Re: Inexpensive 1.25" maximum TFOV EPs [Re: Jarrod]
#5775561 - 04/03/13 01:23 PM

Quote:

Basically, what is the physical limitation of TFOV as a function of barrel diameter and how do you *really* calculate it? The TFOV equation above has no terms that relate to the diameter of the EP barrel.

Jarrod, the best calculation goes as follows:
FOV = ATAN (eyepiece field stop diameter / scope focal length).

You can get actual field stop sizes from Don's spreadsheet (or ask the supplier). Some of the widest:
Orion Sirius Plossl 40mm : 28.6 mm
Orion Sirius Plossl 32mm : 28.5 mm
TV Plossl 40mm : 27.3 mm
Baader Hyperion 24mm : 28.5 mm
TV Panoptic 24mm : 27.0 mm

The only way to go wider than that in a 1.25" barrel, that I know of, is by using a Baader Hyperion Aspheric eyepiece (31 or 36 mm) with the supplied 1.25" nosepiece. Field stop diameter is then 30 mm.

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Jarrod
Pooh-Bah

Reged: 01/20/13

Loc: SE USA
Re: Inexpensive 1.25" maximum TFOV EPs [Re: Mark9473]
#5775680 - 04/03/13 02:09 PM

Thanks all, that is very helpful.

Mark, I spent some time with the atan() function earlier trying to find the correct triangle. I was using the FL of the EP divided by the field stop diameter thinking I might get the AFOV but that doesn't appear to work. Thanks a lot for giving me the triangle that gives you the TFOV from the field stop diameter - that will come in handy!

Edit: I guess Tom gave the triangle too, but it didn't sink in because I didn't recognize the rad -> deg conversion

Edited by Jarrod (04/03/13 02:33 PM)

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Thomas Karpf
Carpal Tunnel

Reged: 02/09/09

Loc: Newington, CT
Re: Inexpensive 1.25" maximum TFOV EPs [Re: Jarrod]
#5775729 - 04/03/13 02:42 PM

Quote:

Edit: I guess Tom gave the triangle too, but it didn't sink in because I didn't recognize the rad -> deg conversion

Chuckle... Yeah, my formula included the 180/pi instead of 57.3, but half the time when I see an equation here that includes 57.3, somebody will ask 'what is 57.3'?

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Mark9473
Postmaster

Reged: 07/21/05

Loc: 51°N 4°E
Re: Inexpensive 1.25" maximum TFOV EPs [Re: Jarrod]
#5775822 - 04/03/13 03:34 PM

Quote:

I spent some time with the atan() function earlier trying to find the correct triangle. I was using the FL of the EP divided by the field stop diameter thinking I might get the AFOV but that doesn't appear to work.

Two problems that I see is that (1) the eyepiece FL may be off a bit (few % not uncommon), and (2) for a given FL and TFOV, the actual AFOV will depend on the geometric distortions in the eyepiece, so any AFOV calculation will be only an approximation.

That said, the formula that I would use for this approximation is:
AFOV = field stop size x 57.3 / EP focal length

 Post Extras:
David Knisely
Postmaster

Reged: 04/19/04

Re: Inexpensive 1.25" maximum TFOV EPs [Re: Mark9473]
#5776004 - 04/03/13 05:12 PM

Quote:

Quote:

Basically, what is the physical limitation of TFOV as a function of barrel diameter and how do you *really* calculate it? The TFOV equation above has no terms that relate to the diameter of the EP barrel.

Jarrod, the best calculation goes as follows:
FOV = ATAN (eyepiece field stop diameter / scope focal length).

You can get actual field stop sizes from Don's spreadsheet (or ask the supplier). Some of the widest:
Orion Sirius Plossl 40mm : 28.6 mm
Orion Sirius Plossl 32mm : 28.5 mm
TV Plossl 40mm : 27.3 mm
Baader Hyperion 24mm : 28.5 mm
TV Panoptic 24mm : 27.0 mm

The only way to go wider than that in a 1.25" barrel, that I know of, is by using a Baader Hyperion Aspheric eyepiece (31 or 36 mm) with the supplied 1.25" nosepiece. Field stop diameter is then 30 mm.

Going much wider than around 28mm field stop with an 1.25" barrel eyepiece will result in some vignetting at the field edges. Indeed, I have tried the 36mm Hyperion Aspheric with its silly 1.25" adapter, and the vignetting in the outer field is horrid (31.5mm field stop with that adapter in-place). It was far better to just go with the eyepiece in its "native" 2" mode. Clear skies to you.

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Jarrod
Pooh-Bah

Reged: 01/20/13

Loc: SE USA
Re: Inexpensive 1.25" maximum TFOV EPs [Re: David Knisely]
#5776022 - 04/03/13 05:25 PM

I want this EP for one thing: initially locating alignment stars so I can center them up and swap in my 12mm illuminated reticle EP. It won't see much if any use beyond that. I'm looking for "cheap and easy" just like, ummm, fast food? I'll stop there

Edited by Jarrod (04/03/13 05:28 PM)

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BDS316
Carpal Tunnel

Reged: 09/16/09

Loc: Sol 3
Re: Inexpensive 1.25" maximum TFOV EPs [Re: Jarrod]
#5776033 - 04/03/13 05:37 PM

Quote:

I want this EP for one thing: initially locating alignment stars so I can center them up and swap in my 12mm illuminated reticle EP. It won't see much if any use beyond that. I'm looking for "cheap and easy" just like, ummm, fast food? I'll stop there

You want an Asian 32mm Plossl, either Orion Sirius or GSO, whichever is less costly considering shipping

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Starman1
Vendor (EyepiecesEtc.com)

Reged: 06/24/03

Loc: Los Angeles
Re: Inexpensive 1.25" maximum TFOV EPs [Re: Jarrod]
#5776084 - 04/03/13 05:59 PM

Quote:

I want to get an inexpensive 1.25" EP that maxes out the TFOV that can be offered by a 1.25" barrel.

Currently I'm looking at these two GSO Super Plossls at Agena, which Agena rates thusly:
32mm -> 52* AFOV
40mm -> 45* AFOV

Now, if I plug these into the TFOV = AFOV/Mag equation for my scope (1200mm f/5.9), I get:
32mm -> 1.39*
40mm -> 1.50*

However, I've read here that the 32mm and 40mm 1.25" Plossls do not offer a different TFOV, but rather you just get a smaller image in the 40mm EP. So that would argue to go for the 32mm EP. But the results from my equation say to get the 40mm EP. Can someone explain the discrepancy to me?

I've asked a similar question on the forum before, inside my other EP threads, but nobody ever answered. Basically, what is the physical limitation of TFOV as a function of barrel diameter and how do you *really* calculate it? The TFOV equation above has no terms that relate to the diameter of the EP barrel.

Many thanks!

First, without severe angular magnification distortion, a 32mm 1.25" eyepiece maxes out at 50 degrees and a 40mm maxes out at 43 degrees. However, that is if the field stop is held to 27-27.4mm.
If the field stop is slightly larger, then the field stop must be positioned above the 1.25" barrel. Though uncommon, this has been done in the 35mm Parks Gold Series, the 24mm Konig, and a few others through the years. Because of the high position of the field stop, these eyepieces require a lot more inward focuser travel than others. Plus, the edge of the field of view is vignetted, though not terribly so. The field stop of the Parks, for example, is 29mm.

If you are figuring out the field of view, it's reasonable to presume the field stop maxes out at 27.0-27.4mm in a 1.25" eyepiece.
Using the formula:
TF=(EPFS/TFL) * 57.3
where TF = true field, EPFS = eyepiece fieldstop, and TFL is telescope focal length.
Since your telescope has a 1200mm focal length, the largest possible true field in 1.25" is (27.4/1200) * 57.3 = 1.31 degrees.
The TeleVue 40mm Plossl has a 27.3mm field stop (1.30 degrees) and the 32mm Plossl has a 26.9mm field stop (1.28 degrees).
If you just figure than any 1.25" Plossl will deliver a max of 1.3 degrees with 32-40mm, you'll be very close. Note that many 24mm Widefields will also yield the same field size (24mm ES 68 degree, Baader Hyperion 24, TeleVue Panoptic 24, etc.)

My Eyepiece Buyer's Guide spreadsheet calculates field stops for eyepieces where the MFR doesn't give data, but the presumption is 4% distortion at the edge of the field. With more distortion, the true field can be squeezed into a smaller width, so distrust any figures you see above 27.4mm.

The 40mm focal length is primarily for users of long focal ratio telescopes in order to get a decently large exit pupil. At almost f/6, your scope gives a nice big exit pupil with a 32mm, so no reason to restrict the apparent field and go to a 40mm. Frankly a 24mm Widefield, with the same field size and a magnification of 50X might be an eyepiece you use for observing rather than just finding.

Edited by Starman1 (04/03/13 06:02 PM)

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Jarrod
Pooh-Bah

Reged: 01/20/13

Loc: SE USA
Re: Inexpensive 1.25" maximum TFOV EPs [Re: Starman1]
#5776652 - 04/03/13 10:26 PM

Quote:

a 24mm Widefield, with the same field size and a magnification of 50X might be an eyepiece you use for observing rather than just finding.

I have the ES68 24mm on backorder but ended up with the Meade 5000 24mm/82*. I should cancel the 24mm/68* since it probably will not get used much now and I feel would be overkill as a locator EP. Thanks for the help.

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buddyjesus
Carpal Tunnel

Reged: 07/07/10

Loc: Davison, Michigan
Re: Inexpensive 1.25" maximum TFOV EPs [Re: Jarrod]
#5776673 - 04/03/13 10:39 PM

good eyepiece from what I gather. gl with it.

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Jon Isaacs
Postmaster

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Inexpensive 1.25" maximum TFOV EPs [Re: Mark9473]
#5776839 - 04/04/13 12:10 AM

Quote:

Orion Sirius Plossl 40mm : 28.6 mm
Orion Sirius Plossl 32mm : 28.5 mm
TV Plossl 40mm : 27.3 mm
Baader Hyperion 24mm : 28.5 mm
TV Panoptic 24mm : 27.0 mm

Are these all measured values? Given that OD of a 28mm filter thread measures about 28.2mm, this implies that a filter would not fit the barrel of the 24mm Hyperion and the Sirius Plossls.

Jon

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Starman1
Vendor (EyepiecesEtc.com)

Reged: 06/24/03

Loc: Los Angeles
Re: Inexpensive 1.25" maximum TFOV EPs [Re: Jon Isaacs]
#5776951 - 04/04/13 02:15 AM

Quote:

Quote:

Orion Sirius Plossl 40mm : 28.6 mm
Orion Sirius Plossl 32mm : 28.5 mm
TV Plossl 40mm : 27.3 mm
Baader Hyperion 24mm : 28.5 mm
TV Panoptic 24mm : 27.0 mm

Are these all measured values? Given that OD of a 28mm filter thread measures about 28.2mm, this implies that a filter would not fit the barrel of the 24mm Hyperion and the Sirius Plossls.

Jon

Mfr's claims, not test results.
I just measured a 24 Baader Hyperion and got 27.0mm, so I don't know where that larger figure came from.
And I recall the 32mm Sirius Plossl had an iris in the barrel, so the field stop of that one is definitely less than 28mm, though I have no way to measure one now.
As I mentioned before, if the manufacturer or a calculator claims a 1.25" eyepiece is over 27mm of field stop, distrust it until you measure it. The Parks Gold Series 35 was 29mm, but then its field stop was above the 1.25" barrel, so was vignetted somewhat by the barrel itself.

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Jon Isaacs
Postmaster

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Inexpensive 1.25" maximum TFOV EPs [Re: Starman1]
#5777132 - 04/04/13 07:45 AM

Quote:

Mfr's claims, not test results.
I just measured a 24 Baader Hyperion and got 27.0mm, so I don't know where that larger figure came from.
And I recall the 32mm Sirius Plossl had an iris in the barrel, so the field stop of that one is definitely less than 28mm, though I have no way to measure one now.
As I mentioned before, if the manufacturer or a calculator claims a 1.25" eyepiece is over 27mm of field stop, distrust it until you measure it. The Parks Gold Series 35 was 29mm, but then its field stop was above the 1.25" barrel, so was vignetted somewhat by the barrel itself.

Don:

Thanks for the clarification. I know that the 30mm and 35mm Ultima/Parks Gold/Antares Elite/Orion Orthoscopic eyepieces used that set back design with the larger field stop, I have never looked through one... one expect significant vignetting???

Otherwise, it would seem anything over about 27mm is suspect and anything over 28mm is definitely so. I have the 32mm and 40mm Celestron orange and black Taiwanese Plossls from the mid 90's, both have 27.5 mm field stops as measured with a caliper.

In Jarrod's scope with the 1200mm focal length, both would provide a TFoV of 1.31 degrees. With a 2 inch eyepieces with the maximum 46 mm field stop, a 2.2 degree TFoV is possible. One 2 inch eyepiece can make a great finder/widefield eyepiece, great ones will break the bank but reasonable ones, both performance wise and cost wise, are available.

Jon

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Jarrod
Pooh-Bah

Reged: 01/20/13

Loc: SE USA
Re: Inexpensive 1.25" maximum TFOV EPs [Re: Jon Isaacs]
#5777149 - 04/04/13 08:10 AM

Quote:

With a 2 inch eyepieces with the maximum 46 mm field stop, a 2.2 degree TFoV is possible. One 2 inch eyepiece can make a great finder/widefield eyepiece, great ones will break the bank but reasonable ones, both performance wise and cost wise, are available.

The scope came with a 2" 28mm 56* EP that gives a 1.3* TFOV in my scope, and it does do the job. This might sound silly to some, but the issue I have is that during alignment, I hate fumbling around with the 2"-1.25" adapter when swapping (frequently) between the 2" finder EP and the 1.25" illuminated reticle EP. And I certainly wouldn't enjoy swapping my HUGE Meade UWA EPs in and out while aligning. It should be much more convenient to just swap between two 1.25" EPs and leave the adapter in place. It's a small thing, but it hopefully should make for less hassle and get me observing sooner.

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Jon Isaacs
Postmaster

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Inexpensive 1.25" maximum TFOV EPs [Re: Mark9473]
#5777156 - 04/04/13 08:23 AM

Quote:

FOV = ATAN (eyepiece field stop diameter / scope focal length).

A few thoughts:

If one uses the arc-tangent, I believe the formulation is something like:

TFoV = 2 x Atan (field stop/(2 x focal length scope))

To use the ATan, a right triangle is necessary, that is where the 2 comes from... divide the Isosceles triangle down the middle to make a right triangle, use the Atan and then double the angle.

But for any possible field stop and focal length of the telescope, the angles are so small that there is no practical difference between the arctangent and the angle itself. With the widest field combination I have, a 42mm field stop in a 400mm focal length telescope, the difference between using the TFoV = 2 x Atan(FS/2xFL) and TFoV = FS/FL radians is less than a tenth of a percent. With the combinations being discussed here, the difference is less than 0.005%.

As far as the source of the 57.3.. I always write the equation:

TFoV = 57.3 degrees/radian x (FSeyepiece/FLscope) or

TFoV = 57.3 deg/rad x FS/FLscope

The difference between using 57.3 degrees/radian and 180/pi is 0.0074%... One cannot determine the focal length of the scope or the field stop accurately enough to make this tiny difference matter.

Jon

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bdcmd
sage

Reged: 03/14/08

Loc: Glen Rose, Texas
Re: Inexpensive 1.25" maximum TFOV EPs [Re: Jarrod]
#5777197 - 04/04/13 09:07 AM

Quote:

The scope came with a 2" 28mm 56* EP that gives a 1.3* TFOV in my scope, and it does do the job. This might sound silly to some, but the issue I have is that during alignment, I hate fumbling around with the 2"-1.25" adapter when swapping (frequently) between the 2" finder EP and the 1.25" illuminated reticle EP. . . . It should be much more convenient to just swap between two 1.25" EPs and leave the adapter in place. It's a small thing, but it hopefully should make for less hassle and get me observing sooner.

Maybe you should try a 2" illuminated reticle eyepiece to use as a finder AND alignment eyepiece. Stellarvue has their E7032R or E7026R, both about \$150, so a little pricey, but very convenient. University Optics has their 32mm 2" illuminated reticle eyepiece also, seems much like the SV version, but only \$130, and it looks like it comes with the illuminator, as well. Just a thought, if you are looking for the true minimum hassle way to go.

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Jarrod
Pooh-Bah

Reged: 01/20/13

Loc: SE USA
Re: Inexpensive 1.25" maximum TFOV EPs [Re: bdcmd]
#5777220 - 04/04/13 09:30 AM

Quote:

Maybe you should try a 2" illuminated reticle eyepiece to use as a finder AND alignment eyepiece.

Hmmm, those are interesting. My only concern would be the accuracy. At 1/3rd the magnification of my 12mm reticle, I think I might not be able to get the stars perfectly centered? I don't know. But it is a good idea...

Edited by Jarrod (04/04/13 09:31 AM)

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Starman1
Vendor (EyepiecesEtc.com)

Reged: 06/24/03

Loc: Los Angeles
Re: Inexpensive 1.25" maximum TFOV EPs [Re: Jon Isaacs]
#5777303 - 04/04/13 10:21 AM

Quote:

Quote:

Mfr's claims, not test results.
I just measured a 24 Baader Hyperion and got 27.0mm, so I don't know where that larger figure came from.
And I recall the 32mm Sirius Plossl had an iris in the barrel, so the field stop of that one is definitely less than 28mm, though I have no way to measure one now.
As I mentioned before, if the manufacturer or a calculator claims a 1.25" eyepiece is over 27mm of field stop, distrust it until you measure it. The Parks Gold Series 35 was 29mm, but then its field stop was above the 1.25" barrel, so was vignetted somewhat by the barrel itself.

Don:

Thanks for the clarification. I know that the 30mm and 35mm Ultima/Parks Gold/Antares Elite/Orion Orthoscopic eyepieces used that set back design with the larger field stop, I have never looked through one... one expect significant vignetting???

Jon

No, it was a reasonable compromise. I never noticed significant vignetting in the eyepiece, though calculations did show a fair amount of light loss at the field edge, because the scopes I was using the eyepiece in could easily illuminate the 29mm field.
In a scope where vignetting from the secondary mirror would result in more light loss at the edge of a 29mm field from the scope itself, then the natural vignetting in the eyepiece might be more noticeable.
But probably not in any scope designed to take 2" eyepieces. A 29mm field stop wouldn't be considered large for a 2" eyepiece.

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Tamiji Homma
Post Laureate

Reged: 02/24/07

Loc: California, USA
Re: Inexpensive 1.25" maximum TFOV EPs [Re: Starman1]
#5777336 - 04/04/13 10:41 AM

Hi Don,

Quote:

I just measured a 24 Baader Hyperion and got 27.0mm, so I don't know where that larger figure came from.

What do you get field stop for Panoptic 24?

I measured:

26.9mm Televue Plossl 32
27mm Panoptic 24
28.5mm Hyperion 24
29mm Ultrascopic 35
31mm Hyperion 31 with 1.25" nosepiece
35mm Hyperion 31 2" mode with Baader Prism Star diagonal (clear aperture supposed to be 34mm)
37.8mm Hyperion 31 2" mode with 2" mirror diagonal

Hyperion 24 is definitely wider than Panoptic 24, no significant vignetting.
Ultrascopic 35 vignetting is acceptable level, not bother me.
Hyperion 31 with 1.25" nosepiece has noticeable vignetting but OK.

Tammy

 Post Extras:
Starman1
Vendor (EyepiecesEtc.com)

Reged: 06/24/03

Loc: Los Angeles
Re: Inexpensive 1.25" maximum TFOV EPs [Re: Tamiji Homma]
#5777417 - 04/04/13 11:07 AM

Quote:

Hi Don,

Quote:

I just measured a 24 Baader Hyperion and got 27.0mm, so I don't know where that larger figure came from.

What do you get field stop for Panoptic 24?

I measured:

26.9mm Televue Plossl 32
27mm Panoptic 24
28.5mm Hyperion 24
29mm Ultrascopic 35
31mm Hyperion 31 with 1.25" nosepiece
35mm Hyperion 31 2" mode with Baader Prism Star diagonal (clear aperture supposed to be 34mm)
37.8mm Hyperion 31 2" mode with 2" mirror diagonal

Hyperion 24 is definitely wider than Panoptic 24, no significant vignetting.
Ultrascopic 35 vignetting is acceptable level, not bother me.
Hyperion 31 with 1.25" nosepiece has noticeable vignetting but OK.

Tammy

Tammy,
I think you meant Baader 24. The Panoptic figure came from TeleVue, and I trust it.
I took a 24 Hyperion out of the box, unscrewed the 1.25" bottom and calipered the opening in the bottom ring. It was 27mm. I didn't see a field stop in the 1.25" barrel, but this eyepiece requires a lot of in-travel, so I think the field stop may be the bottom lens retaining ring. It's possible that the field stop is lower than that, and in the barrel, and if so is larger than the opening in the lens retaining ring, but it would also mean there is no field stop per se in the eyepiece.

EDIT: I just compared the 24 Baader Hyperion and 24mm Panoptic in a TeleVue NP101 on land targets several miles away. The Baader DOES have a slightly wider field of view, but the edge of the field is a little unsharp and a little dimmer. This DOES imply the field stop for the Baader IS the inside diameter of the 1.25" barrel, and so is larger than the opening in the lens retaining ring. Interesting. It also explains why people who have used this eyepiece as a 2" eyepiece without the bottom barrel have commented about the "vague" edge of the field and serious vignetting. From what I see, the eyepiece, if used as a 2" eyepiece, should have the 1.25" bottom barrel left attached.

Edited by Starman1 (04/04/13 11:22 AM)

 Post Extras:
jrbarnett
Eyepiece Hooligan

Reged: 02/28/06

Loc: Petaluma, CA
Re: Inexpensive 1.25" maximum TFOV EPs [Re: Jarrod]
#5777494 - 04/04/13 11:46 AM

As a general rule of thumb, in 1.25" format, the largest TFOV eyepieces will be: 32mm to 35mm at ~50-deg AFOV; 24mm to 25mm at ~68-deg AFOV and 16mm to 18mm at ~82-deg AFOV. Each of these will produce fairly similar TFOVs. The wider AFOV designs will just do so at a higher magnification, larger image scale and smaller exit pupil (darker background, better control of any astigmatism in your eye).

It's not exact, but it does provide a practically useful equivalency model.

Regards,

Jim

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Tamiji Homma
Post Laureate

Reged: 02/24/07

Loc: California, USA
Re: Inexpensive 1.25" maximum TFOV EPs [Re: Starman1]
#5777504 - 04/04/13 11:52 AM

Quote:

I think you meant Baader 24. The Panoptic figure came from TeleVue, and I trust it.

Hi Don,

I meant Panoptic 24.

I noticed that there is some discrepancy in Televue eyepiece field stop number.

For example,

27.4 mm Nagler 20T5
27mm Panoptic 24
27mm Plossl 32

If you measure TFOV, Panoptic 24 gives the widest among 3 eyepieces.
The Nagler 20T5 gives the narrowest TFOV among them.

Nagler 20T5 field stop is more like 26.6mm instead of 27.4mm.

That's why I asked what you get for Panoptic 24 if you found Baader Hyperion 24 field stop was 27mm. Because I see wider TFOV with Baader Hyperion 24 than Panoptic 24.

Tammy

 Post Extras:
Starman1
Vendor (EyepiecesEtc.com)

Reged: 06/24/03

Loc: Los Angeles
Re: Inexpensive 1.25" maximum TFOV EPs [Re: Tamiji Homma]
#5777734 - 04/04/13 01:26 PM

Thanks for making me take a look at the 24 Hyperion.
TeleVue says:
32 Plossl--27.0 field stop
24 Panoptic--27.0 field stop
20 Nagler T5--27.4 field stop.

But remember, the field stop size is only part of the equation for determining true field.

For example, hypothesize an eyepiece with severe angular magnification distortion, in which the magnification at the edge was 50% as great as in the center.
Timing the passage of a star, you would get a large true field. Yet, the apparent field and field stop would both be smaller than the figures you would derive from the true field size.

Hypothesize an eyepiece in which the edge of the field had twice the magnification of the center. A timing of the passage of a star would yield a smaller true field than that derived from the apparent field or the field stop.

And remember than RD and AMD both distort the edge of the field.

So if the true fields differ for the 3 eyepieces, and the Nagler is not larger than the others in terms of true field, the difference is due to differences in distortion at the edges of the field. The Nagler may have a different amount of distortion than the others.

A ZERO distortion eyepiece (impossible in eyepieces this wide) of 20mm and 27.4mm field stop would have a 68.8 degree field. And a 24mm eyepiece with a 27.0mm field stop would have a 56.9 degree field. And a 32mm with a 27.0mm field stop would have an apparent field of 45.7 degrees. The differences are due to distortion.

The differences in apparent field are:
82deg.20mm--16.1%
68deg.24mm--16.3%
50deg.32mm--8.6%
And all 3 have pincushion distortion.

Since distortion at field edge grows along with apparent field, I see some vindication for the comments from some here on CN that the 24 Panoptic has more rectilinear distortion than it should have to correct angular magnification distortion.

Judging from the figures, I would guess the 24 Panoptic to have the largest true field of the 3, but not because of its field stop size.

In order to be able to pre-calculate the true field seen by an eyepiece, you would have to know the amount of distortion at the edge of the field.
You could derive an "effective" field stop size for the eyepiece based on that, but it might not be the same as the actual field stop size.
When you use true field to derive a field stop size, you too are deriving an "effective field stop" size. In my experience, those derived field stop figures make figuring out the true field in a second instrument more accurate than measuring the actual field stop in the eyepiece.

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David Knisely
Postmaster

Reged: 04/19/04

Re: Inexpensive 1.25" maximum TFOV EPs [Re: Starman1]
#5777819 - 04/04/13 02:04 PM

My 24mm Panoptic has a measured field stop of 27.00mm +/- .02mm (the accuracy of the caliper). In my 10 inch telescope with its measured focal length of 1410mm +/- 0.5mm, it yields a true field of view of 1.113 degrees via multiple timings using the star-drift method. The field stop equation yields a value of 1.097 degrees which is only 1.4% off the actual value. I also measured the eyepiece's apparent field at 68.0 degrees as well, so at least for this eyepiece, Tele Vue's values here jive with actual physical measurement. Clear skies to you.

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bdcmd
sage

Reged: 03/14/08

Loc: Glen Rose, Texas
Re: Inexpensive 1.25" maximum TFOV EPs [Re: Jarrod]
#5777918 - 04/04/13 03:10 PM

Quote:

Quote:

Maybe you should try a 2" illuminated reticle eyepiece to use as a finder AND alignment eyepiece.

Hmmm, those are interesting. My only concern would be the accuracy. At 1/3rd the magnification of my 12mm reticle, I think I might not be able to get the stars perfectly centered? I don't know. But it is a good idea...

Stick a 2" 2x barlow on it if you need more magnification. Agena or Astro-Tech both have suitable inexpensive barlows.

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dyslexic nam
Carpal Tunnel

Reged: 01/28/08

1.25" maximum TFOV EPs - lightweight option? [Re: bdcmd]
#6493962 - 04/28/14 01:57 PM

I am looking for a fairly light weight 1.25" ep that approaches max TFOV. I will be using it in an Astroscan (in conjunction w/ a 1.25” Paracorr) and an 80mm Antares finder. Both would potentially have/introduce balance issues – the Astroscan due to its mounting mechanism, and the Antares because it is adding weight at the end of my dob – so the lighter the ep, the better.

It looks like there are a few clusters of ep’s that approach max TFOV using similar focal length ranges and similar AFOVs. As Jim noted above, the general groupings are:
32mm to 35mm = 50 deg AFOV
24mm to 25mm = 68 deg AFOV
16mm to 18mm = 82 deg AFOV

What I am wondering is if there are relatively lightweight options in the wider categories? I know a 32mm plossl is feasible in terms of scope balance, but I would prefer a wider view if possible. Plus, the fast focal ratios (Antares finder is f4.4, Astroscan is f4 – though slower with Paracorr if balance isn’t too bad) suggest the need for a shorter fl ep to avoid exit pupil issues. Anything above around 24mm would waste light, and ideally it would be in the 19-20mm range. Unfortunately (and unsurprisingly), the general trend seems to be more weight as the focal length decreases and AFOV increases. I know much of this weight is driven simply by the physics of providing the wide view, but I am hoping that someone has found some workarounds.

If anyone knows of a wide, lightweight option in 1.25” (ideally between 18mm and 24mm), suggestions would be appreciated.

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Shneor
scholastic sledgehammer

Reged: 03/01/05

Loc: Northern California
Re: 1.25" maximum TFOV EPs - lightweight option? [Re: dyslexic nam]
#6494032 - 04/28/14 02:46 PM

The widest field 1.25" eyepiece I have ever owned was a 30mm Rini, with a field stop measured at 29mm. The claim was a 60° AFOV. It was a pretty nice eyepiece for having single-coated lenses. I used a pair in a binoviewer for awhile.

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JustaBoy
Post Laureate

Reged: 06/19/12

Re: 1.25" maximum TFOV EPs - lightweight option? [Re: Shneor]
#6494061 - 04/28/14 02:58 PM

The Very Best answer for those requirements (over-looking the weight) is the Vixen 22mm LVW - Bar None!

That is all that I will say about this, as repeating it is even beginning to tire me.

I'm very sorry, but it's the Only Answer that I have...

:-)

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dyslexic nam
Carpal Tunnel

Reged: 01/28/08

Re: 1.25" maximum TFOV EPs - lightweight option? [Re: JustaBoy]
#6494065 - 04/28/14 03:00 PM

Quote:

The Very Best answer for those requirements (over-looking the weight) is the Vixen 22mm LVW - Bar None!

That is all that I will say about this, as repeating it is even beginning to tire me.

I'm very sorry, but it's the Only Answer that I have...

:-)

Unfortunately, a 22 LVW is too heavy to meet my needs (you may be able to overlook it as a consideration, but I can't under the circumstances).

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JustaBoy
Post Laureate

Reged: 06/19/12

Re: 1.25" maximum TFOV EPs - lightweight option? [Re: dyslexic nam]
#6494078 - 04/28/14 03:08 PM

You could perhaps "get by" with a 19mm Pan, but it would be No Where Near as Good. - Might try a 20mm or 21mm TV Plossl.

If I were in this same boat I would lie awake at night, thinking about how to modify these scopes to where the balance would no longer be an issue.

Anyway - I said that I wasn't going to say anything more and I did - Sorry.

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dyslexic nam
Carpal Tunnel

Reged: 01/28/08

Re: 1.25" maximum TFOV EPs - lightweight option? [Re: JustaBoy]
#6494089 - 04/28/14 03:13 PM

Interestingly, a 19mm Pan or 20mm ES68 were a couple I was thinking of. Around 1/2 pound, 5mm(ish) exit pupil, and still a good sized TFOV. If the Meade 18mm UWA wasn't so heavy, it would be a frontrunner as well.

As for addressing the balance issues, I could do it with counterweights for the Antares Finder, but the Astroscan would be more challenging, and it is the main reason I am thinking of this.

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John Huntley
scholastic sledgehammer

Reged: 07/16/06

Loc: South West England
Re: 1.25" maximum TFOV EPs - lightweight option? [Re: dyslexic nam]
#6494102 - 04/28/14 03:17 PM

The out of production Kokusai Kohki Widescan III 20mm claimed 84 degrees AFoV. It's reasonably light too - about 185 grams I think. Trouble is that the edge correction starts to crumble at around F/8.

I think the challenge is that to do wide field tricks with the light cone of a fast scope without messing the outer half of the field of view up takes skillful design, quality build and a fair amount of carefully ground and polished glass. These factors add up to both cost and weight not to mention bulk in some cases.

Edited by John Huntley (04/28/14 03:17 PM)

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dyslexic nam
Carpal Tunnel

Reged: 01/28/08

Re: 1.25" maximum TFOV EPs - lightweight option? [Re: John Huntley]
#6494111 - 04/28/14 03:21 PM

That sounds interesting, but if it gets sketchy at f8, I can only think what it would look like at f4-4.4. I wonder how much the Paracorr would clean things up?

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penguinx64
Pooh-Bah

Reged: 11/12/13

Loc: Holland
Re: 1.25" maximum TFOV EPs - lightweight option? [Re: dyslexic nam]
#6494456 - 04/28/14 06:28 PM

I think a Ganymede 26mm Erfle is a good low power wide angle eyepiece with a 56 degree AFOV. I picked up one of these on the Cloudy Nights Classifeds for \$13. Can't beat it at that price. Not too heavy if you decide to barlow it.

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EuropaWill
sage

Reged: 02/12/09

Re: Inexpensive 1.25" maximum TFOV EPs [Re: Jarrod]
#6494715 - 04/28/14 08:56 PM

In the spirit of your original question: Inexpensive and largest TFOV in 1.25"... That would be the GSO 32mm and 40mm Plossls.

Since there is a plethora of theory being presented in this thread, i'll take a different route and let you know that I own both GSO's. Neither is barrel limited so they have an installed field stop. I have not measured it. Despite the manufacturer's claims the GSO 32mm is probably at around 50 degrees AFOV while the GSO 40mm is at around 43 degrees AFOV.

For the record: The 40mm has in fact a slightly larger TFOV than the 32mm and I have confirmed this on multiple occassions including just a few minutes ago during an indoor test. Although the 40mm's ~43 degree AFOV seems much smaller on paper, due to the longer eye relief it feels larger at around 44-45 degrees. Not a big "seat of the pants" difference, but perceived nonetheless and worth mentioning.

The 40mm is brighter than the 32 due to the larger exit pupil. The 40mm is easier to use with glasses and doesn't require you get up and personal with the eyecup to see the entire FOV like the 32mm does. The 32mm is more immersive feeling due to the larger AFOV.

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John Huntley
scholastic sledgehammer

Reged: 07/16/06

Loc: South West England
Re: Inexpensive 1.25" maximum TFOV EPs [Re: EuropaWill]
#6494763 - 04/28/14 09:32 PM

With the Astroscan at F/4 a 32mm eyepiece will deliver an 8mm exit pupil and a 40mm an exit pupil of 10mm. Both far too large to be anything like effective unless your eye dilates far more than the average.

I'd stick with the idea of finding a reasonably corrected, reasonably lightweight eyepiece around 24mm in focal length.

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russell23
Post Laureate

Reged: 05/31/09

Loc: Upstate NY
Re: 1.25" maximum TFOV EPs - lightweight option? [Re: dyslexic nam]
#6494806 - 04/28/14 09:55 PM

Quote:

Interestingly, a 19mm Pan or 20mm ES68 were a couple I was thinking of. Around 1/2 pound, 5mm(ish) exit pupil, and still a good sized TFOV.

I would lean toward the 20mm ES68 in this comparison. I have both of these eyepieces and like them both. There is something very engaging about the presentation of the 19mm Pan, but I think the 20mm ES68 goes slightly deeper in resolving faintest stars.

Dave

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Scanning4Comets
Markus

Reged: 12/26/04

Re: Inexpensive 1.25" maximum TFOV EPs [Re: EuropaWill]
#6494984 - 04/28/14 11:27 PM

Best inexpensive low power EP I have used in my scope is a 25mm X-Cel LX.

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dyslexic nam
Carpal Tunnel

Reged: 01/28/08

Re: Inexpensive 1.25" maximum TFOV EPs [Re: Scanning4Comets]
#6495275 - 04/29/14 07:43 AM

Quote:

Best inexpensive low power EP I have used in my scope is a 25mm X-Cel LX.

Interesting. That's not one I had been thinking of, to be honest.

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Starman1
Vendor (EyepiecesEtc.com)

Reged: 06/24/03

Loc: Los Angeles
Re: Inexpensive 1.25" maximum TFOV EPs [Re: dyslexic nam]
#6495994 - 04/29/14 02:29 PM

Widest possible true field: 35mm Parks Gold or Orion Ultrascopic. A hard 29mm field stop. Requires about 3/8" additional in-focus.
Widest possible true field with 24mm? TeleVue Panoptic (small and light), 24mm Explore Scientific 68 degree (a fairly small eyepiece), 24mm Konig (used, complete with seagulls at the edge of the field at f/4), 24mm Baader Hyperion (28.5mm field stop, but too heavy AND so-so at f/4).
Hint: find a used 24mm Panoptic. Maximum field AND large exit pupil and good correction.

 Post Extras:
EuropaWill
sage

Reged: 02/12/09

Re: Inexpensive 1.25" maximum TFOV EPs [Re: John Huntley]
#6496060 - 04/29/14 03:11 PM

Quote:

With the Astroscan at F/4 a 32mm eyepiece will deliver an 8mm exit pupil and a 40mm an exit pupil of 10mm. Both far too large to be anything like effective unless your eye dilates far more than the average.

I'd stick with the idea of finding a reasonably corrected, reasonably lightweight eyepiece around 24mm in focal length.

What f4 Astroscan? The OP wrote of his intended scope "...my scope (1200mm f/5.9)..."

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dyslexic nam
Carpal Tunnel

Reged: 01/28/08

Re: Inexpensive 1.25" maximum TFOV EPs [Re: EuropaWill]
#6496158 - 04/29/14 04:03 PM

My fault. I resurrected the thread to avoid duplication, but I introduced a new scope (Astroscan) - and thus new considerations.

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CollinofAlabama
Carpal Tunnel

Reged: 11/24/03

Loc: Lubbock, Texas, USA
Re: Inexpensive 1.25" maximum TFOV EPs [Re: Scanning4Comets]
#6497058 - 04/29/14 10:44 PM

I concur with Markus. The Celestron X-Cel 25mm 60* ep has the same TFOV as a 32mm Plossl of 47* AFOV, so probably a bit more than a BCO 32mm ocular. It's not too heavy, and takes care of the widest field 1.25" ep to all but the most fanatical. And it can be had brand new for \$60 shipped, and handles an F/4.7 light cone very well at the edge. Folks, happy days are here again.

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dyslexic nam
Carpal Tunnel

Reged: 01/28/08

Re: Inexpensive 1.25" maximum TFOV EPs [Re: CollinofAlabama]
#6497153 - 04/29/14 11:41 PM

So I have to add another to the running list for consideration. So far, I am thinking of:

Pan 24mm (8.2 oz)
Pan 19mm (6.6 oz)
Meade SWA 24mm (slimmed down weight?)
Meade SWA 20mm (slimmed down weight?)
ES68 24mm. (329grams, 11.6 oz)
ES68 20mm (247grams, 8.7oz)
LVW 22mm (355-420 grams)
Celestron x-cel lx 25mm (207 grams, 7.3 oz)

I'm basically thinking of them in terms of (reported) weight and ability to handle fast optics.

 Post Extras:
Lew Zealand
Pooh-Bah

Reged: 06/28/04

Re: Inexpensive 1.25" maximum TFOV EPs [Re: dyslexic nam]
#6499456 - 05/01/14 01:12 AM

FYI, I just weighed my Meade 5000s (w/o caps) and their un-slimmed down weights are:

18mm UWA - 14oz
24mm SWA - 13oz
20mm SWA - 9oz

There looks to be quite a bit of weight that could be saved in the slim down on each. Probably down to 11oz on the 18, 10oz on the 24 and 7oz on the 20. Maybe these are competitive for you and maybe not.

 Post Extras:
Eddgie
Postmaster

Reged: 02/01/06

Re: Inexpensive 1.25" maximum TFOV EPs [Re: Lew Zealand]
#6499861 - 05/01/14 09:31 AM

The widest field in a 1.25" eyepeice that I personally know of is with a Baader 31mm Aspehric. Field stop is almost 29 millimeters.

I can confirm that the 35mm Ultima and 24mm Hyprions both have wider true fields than the 24mm ES or Televue.

The difference is not large.. Maybe 2%.

But bigger is bigger, and I read all the time that you can't get a bigger field than 27mm fields top, but this is clearly not accurate, and I think stems from the myth that the 24mm Panoptic has the widest true field of any 1.25" eyepiece.

That is likely a very dated message and should be removed from the Televue site.

Not saying that the Teleuve is not a great eyepeices, only that bigger is bigger, and there are several eyepecies out there that give a bigger true field.

The 31mm Hyperion in 1.25" mode is the biggest though. Baader lists it at 32mm, though I don't know how that is possible.

Edited by Eddgie (05/01/14 10:25 PM)

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dyslexic nam
Carpal Tunnel

Reged: 01/28/08

Re: Inexpensive 1.25" maximum TFOV EPs [Re: Lew Zealand]
#6499879 - 05/01/14 09:38 AM

Quote:

FYI, I just weighed my Meade 5000s (w/o caps) and their un-slimmed down weights are:

18mm UWA - 14oz
24mm SWA - 13oz
20mm SWA - 9oz

There looks to be quite a bit of weight that could be saved in the slim down on each. Probably down to 11oz on the 18, 10oz on the 24 and 7oz on the 20. Maybe these are competitive for you and maybe not.

I almost pulled the trigger on a Meade 20mm SWA with the intention of slimming it down, but I walked into a local pawn shop yesterday and found a Leica Galen III microscope for what I think it a great price. Demonstrating my trademark lack of willpower and good judgement when it comes to deals on quality optics, I immediately paid full sticker price (?).

The bottom line is that any discretionary funds are now spent, at least until I sell some surplus astro gear. Another 'bits and bobs' classified ad will likely be coming soon to a theatre near you.

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russell23
Post Laureate

Reged: 05/31/09

Loc: Upstate NY
Re: Inexpensive 1.25" maximum TFOV EPs [Re: dyslexic nam]
#6499885 - 05/01/14 09:41 AM

Quote:

So I have to add another to the running list for consideration. So far, I am thinking of:

Pan 24mm (8.2 oz)
Pan 19mm (6.6 oz)
Meade SWA 24mm (slimmed down weight?)
Meade SWA 20mm (slimmed down weight?)
ES68 24mm. (329grams, 11.6 oz)
ES68 20mm (247grams, 8.7oz)
LVW 22mm (355-420 grams)
Celestron x-cel lx 25mm (207 grams, 7.3 oz)

I'm basically thinking of them in terms of (reported) weight and ability to handle fast optics.

All of those are excellent in their own ways. It really comes down to which one gives you the presentation/aesthetics that you find most pleasing. You will probably only know that by trying them out. If you don't need to wear glasses the 20mm ES68 is really a great option. If the 25mm X-cel is in consideration then you might also consider the 25mm HD-60 and the 25mm Paradigm.

Dave

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Starman1
Vendor (EyepiecesEtc.com)

Reged: 06/24/03

Loc: Los Angeles
Re: Inexpensive 1.25" maximum TFOV EPs [Re: Eddgie]
#6500002 - 05/01/14 10:44 AM

Quote:

The widest field in a 1.25" eyepeice that I personally know of is with a Baader 31mm Aspehric. Field stop is almost 29 degrees.

I can confirm that the 35mm Ultima and 24mm Hyprions both have wider true fields than the 24mm ES or Televue.

The difference is not large.. Maybe 2%.

But bigger is bigger, and I read all the time that you can't get a bigger field than 27mm fields top, but this is clearly not accurate, and I think stems from the myth that the 24mm Panoptic has the widest true field of any 1.25" eyepiece.

That is likely a very dated message and should be removed from the Televue site.

Not saying that the Teleuve is not a great eyepeices, only that bigger is bigger, and there are several eyepecies out there that give a bigger true field.

The 31mm Hyperion in 1.25" mode is the biggest though. Baader lists it at 32mm, though I don't know how that is possible.

By allowing a reduction in edge-of-field illumination.
The 35mm Ultima/Gold Series/Ultrascopic has a field stop that is larger than the inside diameter of the 1.25" barrel. So it's placed slightly above the barrel (which is why the eyepiece requires so much in-travel to focus) and the edge of the field is vignetted by the barrel.
Ditto on the 24mm Hyperion.

We, as humans, are fairly tolerant of vignetting at the edge (our own vision is a good example). Ironically, even some eyepieces with field stops smaller than the I.D. of the barrel have edge of field vignetting.
The 2" diameter 31mm Hyperion Aspheric, with the 1.25" adapter, is a good example of a large amount of vignetting that is (somewhat) tolerable. I used to use a 22mm Nagler (31.1mm field stop) with an f/6.3 reducer in an 8" SCT (50% illumination at the edge of a 24mm field) yet the vignetting wasn't severe to my eye. In contrast, the 31 Hyperion is only vignetting the 32mm field down to 28.5mm, not as severe at all (though the field stop is no longer sharp).

We can tolerate a bit of vignetting easily, and so some eyepieces can have a fair amount (the 35 Ultima, the 24 Hyperion) and we don't even notice it unless we set up a test to specifically look for it.

Since the I.D. of a typical 1.25" barrel is around 28.5mm, why a 27mm field stop in the first place? It's to put a knife-edge at the field stop, and that's a tough iris to make: 28.5mm O.D./27.0mm I.D.
Putting the field stop above the barrel is a brilliant move, I think. Unless you need to make the eyepiece parfocal with other 1.25" eyepieces.

 Post Extras:
Scott Beith
SRF

Reged: 11/26/03

Loc: Frederick, MD
Re: Inexpensive 1.25" maximum TFOV EPs [Re: Starman1]
#6501317 - 05/01/14 09:54 PM

In a 1 1/4" barrel - the 35mm Ultrascopic gets my vote.

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JustaBoy
Post Laureate

Reged: 06/19/12

Re: Inexpensive 1.25" maximum TFOV EPs [Re: Scott Beith]
#6501352 - 05/01/14 10:05 PM

With the 35mm it seems to be either Love it or Hate it, so try one first if you can...

I LOVE IT!

:-)

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Scanning4Comets
Markus

Reged: 12/26/04

Re: Inexpensive 1.25" maximum TFOV EPs [Re: JustaBoy]
#6501787 - 05/02/14 07:24 AM

Quote:

So I have to add another to the running list for consideration. So far, I am thinking of:

Pan 24mm (8.2 oz)
Pan 19mm (6.6 oz)
Meade SWA 24mm (slimmed down weight?)
Meade SWA 20mm (slimmed down weight?)
ES68 24mm. (329grams, 11.6 oz)
ES68 20mm (247grams, 8.7oz)
LVW 22mm (355-420 grams)
Celestron x-cel lx 25mm (207 grams, 7.3 oz)

I'm basically thinking of them in terms of (reported) weight and ability to handle fast optics.

Best in fast optics below are:

Pan 24mm (8.2 oz) <----EXCELLENT
Pan 19mm (6.6 oz) <----NOT
Meade SWA 24mm (slimmed down weight?) <----OK
Meade SWA 20mm (slimmed down weight?) <----OK
ES68 24mm. (329grams, 11.6 oz) <----OK
ES68 20mm (247grams, 8.7oz) <----OK
LVW 22mm (355-420 grams) <----EXCELLENT
Celestron x-cel lx 25mm (207 grams, 7.3 oz) <----EXCELLENT

I've tried them all in my fast telescope.

 Post Extras:
dyslexic nam
Carpal Tunnel

Reged: 01/28/08

Re: Inexpensive 1.25" maximum TFOV EPs [Re: Scanning4Comets]
#6501836 - 05/02/14 08:13 AM

Thanks Mark. Nice to know you have tried all of them. That is definitely good information. The x-cel may be the right solution, even if the resulting exit pupil (6mm-ish) is a bit large for me. Then again, the Astroscan is actually owned by my kids, and I am envious of their luxuriously big pupils (its like looking at a couple of black pie plates), so it would be a good accessory for them.

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