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Equipment Discussions >> Eyepieces

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faackanders2
Carpal Tunnel


Reged: 03/28/11

Re: A 30mm 100 degree 3 inch barrel in the works! new [Re: panhard]
      #5531110 - 11/20/12 09:43 PM

Would it be possible to make a 40+mm 100 degree 3inch eyepiece for even wider TFOV? What would be the upper limit where TFOV is maxed out with a 3" barrell?

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rmollise
Postmaster
*****

Reged: 07/06/07

Re: A 30mm 100 degree 3 inch barrel in the works! new [Re: panhard]
      #5531774 - 11/21/12 09:29 AM

Who you callin' "boy"? That baby was Fat MAN.

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Shneor
scholastic sledgehammer
*****

Reged: 03/01/05

Loc: Northern California
Re: A 30mm 100 degree 3 inch barrel in the works! [Re: faackanders2]
      #5532407 - 11/21/12 02:40 PM

Quote:

Would it be possible to make a 40+mm 100 degree 3inch eyepiece for even wider TFOV? What would be the upper limit where TFOV is maxed out with a 3" barrell?



The field lens on the 3" did not look as though it left much room for an even wider field lens.

Clears,


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Keith
sage
*****

Reged: 05/14/05

Loc: Costa Mesa, CA USA
Re: A 30mm 100 degree 3 inch barrel in the works! new [Re: Shneor]
      #5536951 - 11/24/12 10:05 AM

field lens size is not always an indicator in that type of eyepiece, but holding it up to the light and looking at the size of the field from the bottom, is a good indicator of how much room is left, since the field stop is inside the eyepiece, and is usually smaller than the field lens.

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faackanders2
Carpal Tunnel


Reged: 03/28/11

Re: A 30mm 100 degree 3 inch barrel in the works! new [Re: faackanders2]
      #5537621 - 11/24/12 06:11 PM

Quote:

Would it be possible to make a 40+mm 100 degree 3inch eyepiece for even wider TFOV? What would be the upper limit where TFOV is maxed out with a 3" barrell?




Or 50mm 82 AFOV, or 60mm 68-70 AFOV. What would be the theroretical wideest TFOV configuration with a 3" barrel?


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Starman1
Vendor (EyepiecesEtc.com)
*****

Reged: 06/24/03

Loc: Los Angeles
Re: A 30mm 100 degree 3 inch barrel in the works! new [Re: faackanders2]
      #5537804 - 11/24/12 08:30 PM

It would depend on how much vignetting to put up with.
You would think a field stop of 72mm would be possible, but what if that meant the lenses in the upper body had to be 150mm in diameter?
I'm not saying they would, but at some point focuser technology would have to keep up with the weight of eyepiece and correctors used, and if the load exceed ten pounds? Then, a rethinking of the design of the 3" to 2" reducer to adequately hold that 3 lb 2" eyepiece.
I think it can be done, but lets assume a 4000mm focal length 16" SCT for starters. A 72mm field stop yields a field of a little over 1 degree.
But if you did it just for the FOV, a 16" f/4.5 dob could do the same thing with a 21 Ethos and a Paracorr and provide an even bigger field with a 31 Nagler.
And the mount for the 16" SCT would have to be redesigned to handle the extra weight and clearance needed.
It could be done, but would the manufacturers want to do all the necessary re-engineering to accommodate a visual observer?
I'm dubious.


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faackanders2
Carpal Tunnel


Reged: 03/28/11

Re: A 30mm 100 degree 3 inch barrel in the works! new [Re: Starman1]
      #5537856 - 11/24/12 09:13 PM

Just a visual observer who loves looking at Multiple objects. Currently have a 17.5" f4.1 Dob; but if I got a larger one I think I would like a 3" eyepiece to provide wider TFOVs (as an option to the great higher powered views).

I think of it as the fifference from goning from 0.995 to 1.25" or 1.25" to 2".

Now many will say just get a smaller scope for wide views (and I do have many binos up to 25x100), but I would only want to take one scope out and use it to the max full range limits.


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Starman1
Vendor (EyepiecesEtc.com)
*****

Reged: 06/24/03

Loc: Los Angeles
Re: A 30mm 100 degree 3 inch barrel in the works! new [Re: faackanders2]
      #5537970 - 11/24/12 10:33 PM

Do you need 3", though?
Let's say you have a 28", f/3.6 (it's a size I've looked through).
A 21 Ethos yields a true field of 42' That's not overly large, but there are entire nights I don't use a larger field than that on my 12.5", interestingly, at the same magnification.
Would I get a 28" scope to try to see a true field of 1.5 degrees?
No, why bother? The objects you'd look at don't require 28" of aperture to view them.
Out of the more than 11,000 objects in my log, only 79 of them are larger than that 42' field. Admittedly, it's fun to see groups of objects in one field, like M65/66/N3628 or M81/82 or N6939/6946, etc. But I recognize that this is not what you get a truly large scope to do. You get it to see things you cannot see in smaller scopes, and to see deeper into the universe--to see all the Abell planetaries or the Shakbazian galaxies.
And you don't need a 3" eyepiece to do that.


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faackanders2
Carpal Tunnel


Reged: 03/28/11

Re: A 30mm 100 degree 3 inch barrel in the works! new [Re: Starman1]
      #5538781 - 11/25/12 02:02 PM

Quote:

Do you need 3", though?
Let's say you have a 28", f/3.6 (it's a size I've looked through).
A 21 Ethos yields a true field of 42' That's not overly large, but there are entire nights I don't use a larger field than that on my 12.5", interestingly, at the same magnification.
Would I get a 28" scope to try to see a true field of 1.5 degrees?
No, why bother? The objects you'd look at don't require 28" of aperture to view them.
Out of the more than 11,000 objects in my log, only 79 of them are larger than that 42' field. Admittedly, it's fun to see groups of objects in one field, like M65/66/N3628 or M81/82 or N6939/6946, etc. But I recognize that this is not what you get a truly large scope to do. You get it to see things you cannot see in smaller scopes, and to see deeper into the universe--to see all the Abell planetaries or the Shakbazian galaxies.
And you don't need a 3" eyepiece to do that.




But supposed you would like to do both with the same scope?
I already have 40mm 70 AFOV, 30mm 82 AFOV, 20mm 100 AFOV 2" eyepieces; and although I can see M31/M32/M110 in the same FOV; I still cant see all of M44 nor M45, viel nor North American, nor more of Marakains chain, etc. The wider the FOV the more multiple objects you can see.

The larger scope would be to see dimmer objects, but I probably would still like to see the wider/multiple objects also without having to carry a second scope (although I would likely be willing to also bring my 25x100 and smaller binos since these don't take as much room nor weight of another Dob.


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Starman1
Vendor (EyepiecesEtc.com)
*****

Reged: 06/24/03

Loc: Los Angeles
Re: A 30mm 100 degree 3 inch barrel in the works! new [Re: faackanders2]
      #5538873 - 11/25/12 02:46 PM

You just gave the best reason for having 2 scopes.

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Shneor
scholastic sledgehammer
*****

Reged: 03/01/05

Loc: Northern California
Re: A 30mm 100 degree 3 inch barrel in the works! new [Re: Keith]
      #5539242 - 11/25/12 06:49 PM

Quote:

field lens size is not always an indicator in that type of eyepiece, but holding it up to the light and looking at the size of the field from the bottom, is a good indicator of how much room is left, since the field stop is inside the eyepiece, and is usually smaller than the field lens.




Assuming the same proportionality is required between the field lens and the field stop, the field lens is the limiting factor in this case.

Clears,
Shneor


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faackanders2
Carpal Tunnel


Reged: 03/28/11

Re: A 30mm 100 degree 3 inch barrel in the works! new [Re: Starman1]
      #5539641 - 11/25/12 11:42 PM

Quote:

You just gave the best reason for having 2 scopes.




Perhaps if I had an observatory, and didn't need to transport scopes to a dark site.


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watcher
Carpal Tunnel
*****

Reged: 11/21/07

Loc: St. Louis, MO
Re: A 30mm 100 degree 3 inch barrel in the works! new [Re: Starman1]
      #5539759 - 11/26/12 02:35 AM

Sounds like a great eyepiece for something like this.

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