To find a ideal low powered EP for Orion 127

simei-sky · Post by **simei-sky** » Thu Feb 01, 2007 7:56 pm

Hi guys any advice if I am looking for a low powered EP for my Orion, MCT 127, f/12.1, focal lenght=1540mm?

Currently, I have a 32mm plossl with a mag of 48X and TFOV=1.08deg.

I am hoping to get a EP to achieve:
1) below mag 50x
2) TFOV about 1.4-1.9 deg ???
3) $ of course (still don't know what is consider a good price)
4) And not have vignetting effect??( is it blur vision at the outer core?)

Don't know if the above is a "tall order" to achieve :? :? . Strangely I was keeping tab of a current tread titled "All about SCT". In that tread, it seems that a 1.9 deg TFOV is achievable. in a 5" SCT, which is quite close to Orion's specification(but the focal length differ, SCT focal length is shorter).

I 've also read in another article that the guy used a 24mm panoptic with his orion 127 to achieve 1.4 TFOV at a mag of 64x! 8-) 8-)

Because my scope has a long FL, it has constrain my low powered viewing on DSO . According to the specification, the limitation of the field view is 1 deg, is that correct and how to calculate?

After reading the "All about SCT" tread, it seems that there is a grey area where this additional field of view is subjected to some form of distortion and may varies from different equipment used.....Yes, I have also come to know that most of the DSO are under 1 degree view.

So, if my intention is to get a low powered EP, why not try to achieve a wider TFOV too (others have already achieved 1.4 to 1.9 deg!!)

So which EP or EPs best match my hope? ...well other then the 24mm Panoptic...

Post by **weixing** » Thu Feb 01, 2007 8:09 pm

Hi,
Hmm... I think you can give it a try. You can get all the necessary adapters from scopestuff:
http://www.scopestuff.com/ss_smsa.htm

As a F12.1 scope, you don't need those very expensive eyepiece to perform well... that an advantage of using slow scope. Anyway, I got a GSO 2" 42mm 65degree AFOV eyepiece which I can loan it to you to try out (provided that it not sold yet) after you got all your adapters.

Have a nice day.

jiahao1986 · Post by **jiahao1986** » Thu Feb 01, 2007 9:21 pm

I think if you use Panoptic 24mm Ep, you should get the same true FOV as a 32mm Plossl as they have the same field stop - 27mm.

simei-sky · Post by **simei-sky** » Thu Feb 01, 2007 10:38 pm

Weixing:
Thanks for the offer on your GSO 2"... I may not want to expend my collcetion with 2" stuff. I am looking for alternative to the 24mm Panoptic ep(Those expensive ep).

Jiahao:
Can you tell me how to calculate the 32mm ep has a field stop =27mm?
Getting more interested in this.....

Post by **weixing** » Thu Feb 01, 2007 10:54 pm

Hi,

Thanks for the offer on your GSO 2"... I may not want to expend my collcetion with 2" stuff.

Then you may want to try using a Focal Reducer or you won't be able to get more than 1 degree true field of view by using only 1.25" eyepiece.

I am looking for alternative to the 24mm Panoptic ep(Those expensive ep).

How about Pentax XW eyepieces, Meade Super/Ultra Wide, Vixen LVW, Celestron Ultima/Axiom LX??

Can you tell me how to calculate the 32mm ep has a field stop =27mm?

The field stop is measured or given by manufacturer, not calculated. Most manufacturer don't give the field stop size, but TeleVue ( http://www.televue.com/engine/page.asp?ID=144 ) and Pentax ( http://www.pentaximaging.com/products/s ... eyepieces/ ) do. You can check on their website.

jiahao1986 · Post by **jiahao1986** » Thu Feb 01, 2007 11:28 pm

simei-sky wrote: Jiahao:
Can you tell me how to calculate the 32mm ep has a field stop =27mm?
Getting more interested in this.....

Because the most field stop a 1.25" can have is 27mm, and the design of a 32mm Plossl eyepiece is supposed to provide the most field stop, so as the Panoptics 24mm. If you want the most true FOV with 1.25" eyepieces, your choices are 32mm Plossl(or 40mm Plossl, but the 40mm design only has a aFOV of 40 degrees), TeleVue 24mm Panoptics and Orion 35mm Ultrascopic. These eyepieces can give you similar true FOV of around 1 degree...

Canopus Lim · Post by **Canopus Lim** » Fri Feb 02, 2007 10:42 am

If you want the largest possible without changing to 2 inch eyepieces (needing adapter, 2 inch diagonal), the way to go is to buy a focal reducer. I am selling my focal reducer which will reduce the focal length of the scope to 0.63x of its original focal length. Then you can use your 32mm eyepiece and achieve about 1.6 degree true field. However, I think you need an adapter to mount SCT focal reducer to your scope. So, probably there is no way to increase the true field without getting a focal reducer+adapter or 2inch eyepieces+2inch diagonal+adapter. The focal reducer path would be cheaper alternative though.

simei-sky · Post by **simei-sky** » Fri Feb 02, 2007 1:38 pm

Goodness gracious me. Looks like there are a few options here to try out... Thanks man. will toy around with my existing 32 ep and maybe try the formula to determine the TFOV: TFOV=transit time(sec) / 240 sec....practical session

Post by **acc** » Fri Feb 02, 2007 1:43 pm

IMO getting 2" eps would be a better idea than buying another piece of glass in the form of a focal reducer. Eps you can always keep for your next scope

cheers
cc

ariefm71 · Post by **ariefm71** » Fri Feb 02, 2007 6:41 pm

The MCT127 can only take 1.25" i believe.

How to calculate TRUE field of view: http://www.singastro.org/viewtopic.php?t=1651