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Equipment Discussions >> Eyepieces

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Keith
sage
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Reged: 05/14/05

Loc: Costa Mesa, CA USA
Re: A 30mm 100 degree 3 inch barrel in the works! new [Re: SeattleScott]
      #5508056 - 11/07/12 08:58 AM

Quote:

The problem with a 3" eyepiece is then you need a bigger secondary, which means lower contrast and light transmission. Maybe for a large aperture scope it would be ok, but there is going to be that compromise. I believe the CO on an 11" SCT is almost 4" already. Do you really want to make it 5" to get a wider field of view? Maybe on an F5 18" dob it would work well. But then you have to balance what looks like a 5-lb eyepiece!

I don't know, I do not see a lot of interest in this outside of observatories that use larger than 2" eyepieces for their huge telescopes. But it is fun to think about!




I missed this one earlier. The bigger secondary applies to newtonians, not SCTs, the narrower light cone of the SCT could possibly allow this to work well, especially on 14". Since the 1.5(or 1.75 I forget) inch rear opening on an 8" SCT works well with full field 2" eyepieces, I am sure this sucker will work fine on an 11" with its nearly 3" rear baffle. It might require a low profile thread on diagonal vs one sliding into a visual back as I mentioned earlier, but I am not sure to what degree that would be necessary, if at all.

But "redesigning" the optics of a cassegrain for this eyepiece would not be necessary. What Jon was referring to were newtonians, which are typically optimized for the most acceptable illumination at the edge of a 2" field, typically 70% or better for visual, and 100% or more in an astrograph. A visually optimized newtonian would likely show darker edges with this, and that is where a larger secondary would be needed. On an SCT the secondary is no where near the point of focus, on a newt it is much closer and is an important factor in the design.


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Sarkikos
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Reged: 12/18/07

Loc: Suburban Maryland, USA
Re: A 30mm 100 degree 3 inch barrel in the works! new [Re: Keith]
      #5508069 - 11/07/12 09:13 AM

Keith,

Quote:

wondering what you mean by big scts that are not yet available. Were you just referring to the diagonals not being available? IIRC ES might have been planning a 3"barrel refractor type diagonal (which makes sense since Scott was ref their APO). Even if that is the only diagonal they offer, and they do not offer 3" visual backs for SCTs, OPTEC already does for their 314 and 316 3" .75 reducers, for folks who want the benefit of those reducers (imaging) without having to shell out the big bucks for the TCFS-3 focuser. 3" slide in optics are already on the market in the imaging scene, so getting a visual back for the SCT is not a problem, should ES intend their diagonal only for refractors.




SCT's are the only major type of scope that I've never owned, and I don't really plan on owning one ... well, maybe a nice C6 for grab-n-go. And I'm not into AP at all, so I've not really kept up with what is available in both those areas. But just reading this thread I got the impression that 3"-EP-ready SCTs are not out there now. I suppose that was a false impression?

Quote:

Either way that EP looks to be 10lbs easily, It is one thing to have to slide a CW to rebalance for a 31 nagler, but this would require adding another weight for sure in some cases.




Yes, the weight could be a deal breaker for many observers. I had a hard enough time balancing my scopes for my 2 lb ES 82 30mm, much less some 10 lb monster.

Overall, I don't see 3" eyepieces having a big market among consumers of astro gear. Barely a notch in a niche.

Mike


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Keith
sage
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Reged: 05/14/05

Loc: Costa Mesa, CA USA
Re: A 30mm 100 degree 3 inch barrel in the works! new [Re: Sarkikos]
      #5508144 - 11/07/12 10:18 AM

C11/14 and Meades 10/12/14 all have a 3" thread on the rear cell. Hence the peterson eye opener option. On a standard LX200 with microfocuser, there is a step down ring to standard 2" threads that has about 1.5" clear aperture, so widefield 2" eps get light loss at the edges. Taking off that step down ring, and attaching a visual back or focuser directly to the 3" rear cel, opens the aperture to the full 2" and then some. So all it takes is a 3" visual back and diagonal (not common) and theoretically this could work. Since the 11" and the 14" celestron both use the same thread, it is already possible to add a 3" JMI or optec focuser to the scope, so all that would be needed was the diagonal. I would be interested to see a field lens pic of that monster 30, to see how much of the 3" field it is using. Since the light cone is a narrow f10, I have a feeling this could work well on even a c11.

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Darren Drake
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Reged: 10/09/02

Loc: Chicagoland
Re: A 30mm 100 degree 3 inch barrel in the works! new [Re: Keith]
      #5508162 - 11/07/12 10:39 AM

Keith
I would estimate based on the 31 nagler being what it is that the field lens is about 2.4 inches across but that's just an educated guess. I'm pretty sure its not the full 3 inches.


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Keith
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Reged: 05/14/05

Loc: Costa Mesa, CA USA
Re: A 30mm 100 degree 3 inch barrel in the works! new [Re: Darren Drake]
      #5508191 - 11/07/12 11:03 AM

a full 3" in 82deg or 68deg would be pretty sweet though, or even 42mm82 and 55mm68, even if they are not full 3" (I think the pentax 60mm XL was 65deg at full 3" thread on)

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Darren Drake
Carpal Tunnel
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Reged: 10/09/02

Loc: Chicagoland
Re: A 30mm 100 degree 3 inch barrel in the works! new [Re: Keith]
      #5508200 - 11/07/12 11:14 AM

Yes and if I'm not mistaken that Pentax goes for over $3000.

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Keith
sage
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Reged: 05/14/05

Loc: Costa Mesa, CA USA
Re: A 30mm 100 degree 3 inch barrel in the works! new [Re: Darren Drake]
      #5508211 - 11/07/12 11:27 AM

so the ES is quite a bargain!

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Sarkikos
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Reged: 12/18/07

Loc: Suburban Maryland, USA
Re: A 30mm 100 degree 3 inch barrel in the works! new [Re: Keith]
      #5508219 - 11/07/12 11:30 AM

Always! ... except for that ES 82 14mm. Too much FC for my eyes at any price.


Mike


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Junn Chavez
super member


Reged: 02/24/09

Re: A 30mm 100 degree 3 inch barrel in the works! new [Re: Darren Drake]
      #5508489 - 11/07/12 02:53 PM

I guess I have to start saving money to purchase two for binoviewing

Clear skies.


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pbsastro
professor emeritus
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Reged: 03/21/07

Re: A 30mm 100 degree 3 inch barrel in the works! new [Re: Sarkikos]
      #5508504 - 11/07/12 03:02 PM

One is already sold! It will be perfect in my 175/1400 APM-LZOS with FT35 fcouser. Small apos with FL below 1000mm may have FC issues, although that is dependent on the individual eye capability to adjust. From 1000mm and longer FL will be OK I think. So the TEC140 will be the starting apo for this eyepiece. A TV 102 with 2.4" focuser may work as well for many people.

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Starman1
Vendor (EyepiecesEtc.com)
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Reged: 06/24/03

Loc: Los Angeles
Re: A 30mm 100 degree 3 inch barrel in the works! new [Re: Shneor]
      #5508529 - 11/07/12 03:19 PM

Quote:

Quote:

Quote:

Scott Roberts is reporting on FB that he will soon be field testing one of these. There is a pic and it is enormous. Wow now SI or someone is gonna have to start making more 3 inch focusers for dobs....




Won't be of much use in a fast Dob until someone makes a 3 inch Coma Corrector... The modern F/3 Dobs are using the 21mm Ethos as the widefield because the 31mm Nagler results in an oversized exit pupil...

Jon



Not necessarily true. The 9mm ES120° shows pinpoint stars from center to edge in my f/4 without any correction needed. It apparently has a quite different design. Unfortunately, as far as I know, only three CN members have one of these, but several observers have viewed through mine. All were amazed by the sharpness across the entire field.

Clears,
Shneor



A little reality, here:
At f/4, your coma free field is only 1.4mm wide. The field stop of the 9mm 100 degree ES is over 14mm. This eyepiece produces significant visibility of coma at the edge of the field of view in my f/5 dob. At f/4, comatic star images would be significantly larger than the 3' resolution of the eye less than half way to the edge.
The 9mm 120 degree is wider still.
Only in a coma-corrected field could you have no coma at the edge of the field.
So what you suggest is not physically possible.

It is, however, psycho-physiologically possible to not be aware of coma, and while I won't go into the multiple reasons why that is, the noticeability of coma varies significantly from person to person. I see coma in 82 degree eyepieces at f/6, and the math says I'm only seeing what's really there. It's not too bad, so I could live with it. By f/5, I can't live with it and need to correct it. By f/4, I must have coma correction to even make the scope usable.
Others blissfully use f/4-f/4.5 scopes without any coma correction at all and are not bothered by it.

So, perhaps a better way to state your case would be to say that YOU don't notice any coma at the edge in that eyepiece.

The only alternative, and I have not heard this to be the case, is that the 120 degree eyepiece has built-in coma correction like the old Praetoria eyepieces did.


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GeneT
Ely Kid
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Reged: 11/07/08

Loc: South Texas
Re: A 30mm 100 degree 3 inch barrel in the works! new [Re: Darren Drake]
      #5508580 - 11/07/12 03:43 PM

For me, probably not a buy.

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star drop
Snowed In
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Reged: 02/02/08

Loc: Snow Plop, WNY
Re: A 30mm 100 degree 3 inch barrel in the works! new [Re: Jon Isaacs]
      #5508604 - 11/07/12 03:53 PM

Quote:

Quote:

Scott Roberts is reporting on FB that he will soon be field testing one of these. There is a pic and it is enormous. Wow now SI or someone is gonna have to start making more 3 inch focusers for dobs....




Won't be of much use in a fast Dob until someone makes a 3 inch Coma Corrector... The modern F/3 Dobs are using the 21mm Ethos as the widefield because the 31mm Nagler results in an oversized exit pupil...

Jon



Where is Ron Popeil and his 3" pocket coma corrector when you need him?


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GlennLeDrew
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Reged: 06/18/08

Loc: Ottawa, Ontario, Canada
Re: A 30mm 100 degree 3 inch barrel in the works! new [Re: star drop]
      #5508639 - 11/07/12 04:11 PM

I find the concept of this eyepiece intriguing. Being one who uses the outer field to illuminate my poor-in-resolution outer retina, additional aberration out there is not so objectionable. I don't tend to gaze at or near the field edge, instead striving to place the bits of interest closer to the field center. With this tactic, I enjoy the benefits of the uber fields without becoming hung up on off-axis unsharpness. My own (and your) eye's off axis performance is in some ways already horrid, and so big field eyepieces should be utilized in the way that mates them best to the eye; using the extra field to more fully fill the more sensitive outer retina.

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maroubra_boy
professor emeritus


Reged: 09/08/09

Loc: Sydney, Australia
Re: A 30mm 100 degree 3 inch barrel in the works! new [Re: GlennLeDrew]
      #5508808 - 11/07/12 06:15 PM

If TV started to make a 3" eyepiece, there would be an almighty rush on. No question about it. Just hint at it an these forums will be abuzz.

Explore Scientific, Sieberts, these aint TV.

So, Al, when's it due?

Very interesting reading. Will be needing to redesign the entire structure and bearings of existing dobs to accomodate a 3" focuser, not just a CW. A 10lb EP, and a focuser not less than 3, maybe even 6 or 7. That's a lot of dead weight that's leavering off the secondary cage.

Edited by maroubra_boy (11/07/12 06:16 PM)


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pbsastro
professor emeritus
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Reged: 03/21/07

Re: A 30mm 100 degree 3 inch barrel in the works! new [Re: maroubra_boy]
      #5508823 - 11/07/12 06:28 PM

Quote:

If TV started to make a 3" eyepiece, there would be an almighty rush on. No question about it. Just hint at it an these forums will be abuzz.



Agree completely.

Quote:

Will be needing to redesign the entire structure and bearings of existing dobs to accomodate a 3" focuser, not just a CW. A 10lb EP, and a focuser not less than 3, maybe even 6 or 7. That's a lot of dead weight that's leavering off the secondary cage.




I don't think this eyepiece is for dobs. For small dobs (usually slow) it is too expensive. For large dobs (usually fast) 30mm is too much focal length.

This eyepiece is ideal for refractors from 1000mm FL up and for flat field (Edge HD) SCTs 10" up.
The eyepiece virtual field stop should be about 52mm, which is exactly the clear aperture of my Meade 12" SCT baffle tube. Issue here is it is not flat field. So as soon as get this eyepiece I will be swapping my 12" SCT for a 11" or 14" Edge HD.

Edit: Oh, it will be perfect also for flat field small refractors, like Televue NPs with 2.4" focuser, the irony...

Edited by pbsastro (11/07/12 06:45 PM)


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johnnyha
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Reged: 11/12/06

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Re: A 30mm 100 degree 3 inch barrel in the works! new [Re: Mark9473]
      #5508841 - 11/07/12 06:44 PM

Quote:

Siebert has been offering large format eyepieces and diagonals for years. I wonder why ES think they will be more successful with it.



Better web page?


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Keith
sage
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Reged: 05/14/05

Loc: Costa Mesa, CA USA
Re: A 30mm 100 degree 3 inch barrel in the works! new [Re: maroubra_boy]
      #5508957 - 11/07/12 08:03 PM

Quote:

If TV started to make a 3" eyepiece, there would be an almighty rush on. No question about it. Just hint at it an these forums will be abuzz.

Explore Scientific, Sieberts, these aint TV.

So, Al, when's it due?

Very interesting reading. Will be needing to redesign the entire structure and bearings of existing dobs to accomodate a 3" focuser, not just a CW. A 10lb EP, and a focuser not less than 3, maybe even 6 or 7. That's a lot of dead weight that's leavering off the secondary cage.




Siebert and ES not in the same catergory. ES is literally taking the televue inspired designs and using a state of the art factory in china, to replicate near TV quality at lower prices. Siebert is not making eyepieces that are literally nagler , panoptic and ethos clones. So before comparing ES to TV, it helps to look through both, not counting the 14mm 82 which didn't quite live up to its japanese series 4000 UWA predecessor. Meade was the first to copy TV with good results in the early 90s, and then in the early 00's the 5000 series came out from china, and that is the embryo which ES matured from. Quite different from Siebert's boutiqe machine shop style (and Siebert has not come out with any exotic widefields with edge correction coming close to televue, where most ES perform 90% as good as the televue, especially in the 100's)


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aa5te
Genial Procrastinator
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Reged: 08/30/08

Loc: Clinton, TN
Re: A 30mm 100 degree 3 inch barrel in the works! new [Re: johnnyha]
      #5509047 - 11/07/12 09:10 PM

Quote:


Better web page?



I LOL'd and received funny looks. Sorry, carry on.


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gezak22
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Reged: 08/15/04

Loc: On far side of moon. Send help...
Re: A 30mm 100 degree 3 inch barrel in the works! new [Re: Keith]
      #5509310 - 11/08/12 01:46 AM

The real question here is how are we going to use these in bino mode?

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