Widest View EP - Nexstar 6SE

[JGM1971]

I'm looking to add to my EP range and boost the FOV when looking a Clusters or Faint fuzzies. Ive spotted several comments, some conflicting, that due to the 1.25" internal baffle (?) on the 6SE, I'll be wasting my money on a 32mm or 40mm EP, as the FOV can't be increased much more than the standard 25mm Plossl that came with scope.

Can anyone confirm if this is indeed the case?

If not, any recommendations for a good 32 EP. Budget is only about £70. (was going to go with Celestron Omni 32mm)

I've got a 25, 15 and a 6mm already, just need one more to cover all the bases.

[fredster]

A friend has the C6SGT and it is fully capable of using any 1.25" eyepiece available. His personal favourite being the 24mm Panoptic. But he has previously used it with a Televue 32mm Plossl....absolutely no problems, as there shouldn't be with a 28mm rear opening. You will get a benefit from using a 32mm Plossl.

25mm Plossl + C6 = 0.86deg true field

32mm Plossl + C6 = 1.11deg true field

29% increase.

[fredster]

There is another way to approach it if you are looking for the max field possible. And that's to use a Celestron or Meade F6.3 reducer. Will bring the focal length down to 945mm and the true field of view with your 25mm eyepiece will go from 0.86deg too 1.37deg. That's a big jump and a nice size fov. You could increase it further with a 32mm Plossl, with the reducer that would give 1.76deg, double what you currently get.

[JGM1971]

Thanks Fredster.

A lot to consider. The Focal Reducer route is one i'm considering, as it will also assist my basic astrophotography skills. Having an AltAz, I'm a long way off taking any WOW shots yet, but f10 is just too slow.

[fredster]

The Celestron reducer works well and is highly recommended. Not cheap though.

[E621Keith]

I think you have the field stop restriction and eyepiece focal length confused.

The C6 1.25" baffle restricted the FOV to 1.25" eyepieces. There are nothing to gain by using 2". The 32mm plossl is a 1.25" eyepiece and it works fine on a C6. You will reach the field stop limit with a 25mm 70deg AFOV widefield eyepiece, but not a with 25mm 55 deg AFOV plossl. The 1.25" field stop limited is reached by a 32mm plossl.

A C6 with reducer would not help, because the 1.25" baffle limits the field to 1.1 deg. Using a reducer will cause vignetting with a 32mm plossl.

[JGM1971]

Thanks Keith. As a novice with limited funds, I'd hate to buy something then discover it wasn't of use. Just got to find a 25mm 70 AFOV EP now.

[alan potts]

There is another way to approach it if you are looking for the max field possible. And that's to use a Celestron or Meade F6.3 reducer. Will bring the focal length down to 945mm and the true field of view with your 25mm eyepiece will go from 0.86deg too 1.37deg. That's a big jump and a nice size fov. You could increase it further with a 32mm Plossl, with the reducer that would give 1.76deg, double what you currently get.

Fred,

32mm will work in 11/4 eyepieces with a reducer but will vignet badly if you go to 2 inch eyepieces. With the larger ones you can get away with 28mm, well a least I do with my LX 200.

Alan.

[John]

Antares used to have a 1.25" 25mm 70 degree AFoV eyepiece as part of the W70 series. I would not recommend them in scopes faster than around F/7 but it would work OK in your F/10 SCT. A "wanted" advert on the UK Astro Buy & Sell website might turn one up and they don't cost much - £30 I'd guess for a used one.

Here is a review of the range so you know what you are looking out for:

http://www.cloudynights.com/documents/w70.pdf

They are by no means any competition for the Panoptic 24mm or similar but do show the largest physical field of view that is possible in the 1.25" format.

[E621Keith]

Thanks Keith. As a novice with limited funds, I'd hate to buy something then discover it wasn't of use. Just got to find a 25mm 70 AFOV EP now.

A used 24mm Baader Hyperion cost around £70. They turn up on ABS and fleabay all the time.

[fredster]

I think you have the field stop restriction and eyepiece focal length confused.

The C6 1.25" baffle restricted the FOV to 1.25" eyepieces. There are nothing to gain by using 2". The 32mm plossl is a 1.25" eyepiece and it works fine on a C6. You will reach the field stop limit with a 25mm 70deg AFOV widefield eyepiece, but not a with 25mm 55 deg AFOV plossl. The 1.25" field stop limited is reached by a 32mm plossl.

A C6 with reducer would not help, because the 1.25" baffle limits the field to 1.1 deg. Using a reducer will cause vignetting with a 32mm plossl.

Really sorry but that doesn't sound right at all. The reducer is changing the focal length of the telescope to 945mm and allowing the 32mm Plossl to reach the 1.11deg limit of the C6. The 32mm Plossl and reducer will work 100% perfectly and without vignetting.

[fredster]

Just back up what i said this is a bit of blurb from Celestron:

"A Celestron focal reducer/corrector increases the versatility of any f/10 or f/11 SCT, from the C5 to the C14." To achieve a wider field of view from our" f/10 SCT's, Celestron offers an f/6.3 focal reducer/corrector (#94175) for a 2010 MSRP of $144.95 ($129 from OPT). This four-element, multi-coated optic screws directly to the rear cell of the telescope and, in the case of the C6, creates an effective focal length of 945mm.

[E621Keith]

The true field of view is related to the eyepiece field stop. A 24mm 70deg hyperion will show the same amount of sky as a 32mm plossl.

Every scope has a image circle which it can fully illuminate and this is related to the baffle diameter. A C6 with its 1.25" baffle can only provide full illumination to a limited image circle. A focal reducer reduces effective focal length by shrinking this image circle to a smaller diameter, thereby concentrating the light into a smaller area and reduces magnification, thus reducing effective focal length. You will see the same amount of sky with a 20mm plossl + 0.63 reducer as a 32mm plossl without, hence the wider FOV. The reducer is also most useful for imaging because the imaging chip has a fixed area.

A 32mm plossl will accept the whole 1.25" image circle coming out of the C6. If you installed a focal reducer, you will see the reduced and concentrated image circle surrounded by an area that is not fully illuminated.