SpaceWalk 2" EP

weehan · Post by **weehan** » Mon Feb 19, 2007 9:19 pm

Hi everyone,

I'm looking for a 2" "spacewalk" EP...Currently using a 8" f/6 Dob with a 30mm Celestron Ultima being the widest EP. I took the setup out and was disappointed that the Pelaides (1 deg wide) was not visible in the entire frame.

Thus Im looking at one EP that can accomodate say the Double Cluster, Pelaides entirely with some space to drift before I need to centre the subject again. Image quality is quite high a priority (coming from a photography background, I am quite strict about it) and it will be used more for urban observing. Budget may be around 500 (stretchable).

Was looking at the 35mm/41mm Panoptic and the TMB 40mm Paragon.

Cheers

WeeHan

weehan · Post by **weehan** » Mon Feb 19, 2007 9:34 pm

I should apologize as I should have posted in the Beginner's Forum.

Mods: Im ok with this thread being moved as I truly am a greenhorn.

ariefm71 · Post by **ariefm71** » Mon Feb 19, 2007 11:30 pm

The 30mm Ultima should give you slightly more than 1 degree to barely frame the entire pleiades. I agree that upgrading to 40mm TMB Paragon is probably the best option (the 35/41mm Pan I think is a bit outside your budget). Want to check out that EP myself.

Arief

Post by **acc** » Tue Feb 20, 2007 12:15 am

Hi Weehan
No problem posting in this forum.

Anyway, I can loan you my 35mm Pan for a week or two to try. And if you really like it, I can consider selling it to you. But this will be your first step down the slippery slope you know...

cheers
cc

weehan · Post by **weehan** » Tue Feb 20, 2007 9:44 pm

Thanks alot Arief and Chee Chien for the kind advice. I have been reading up and I am baffled as to why there are shorter FL Eps with 82 deg views while the longer FLs are about 65-68 deg. Is there any reason why they do not have 82 deg, long FL Eps?

CheeChien, I have PMed you.

Cheers

WeeHan

weehan · Post by **weehan** » Tue Feb 20, 2007 9:47 pm

Apologies here but may I ask what will the Panoptics or Pentaxes give me over the TMB Paragon? The latter is currently on backorder and I dun see much about it other on CN.

Cheers

WeeHan

Post by **acc** » Tue Feb 20, 2007 10:52 pm

The few reviews of the TMB Paragon have been very positive, and if I recall correctly, the 40mm Paragon outperformed the Panoptic. So it seems like an ep with very good potential. So dun rush into buying any just yet. You can try out my 35mm pan first, just for fun.

Post by **acc** » Tue Feb 20, 2007 10:57 pm

weehan wrote:Thanks alot Arief and Chee Chien for the kind advice. I have been reading up and I am baffled as to why there are shorter FL Eps with 82 deg views while the longer FLs are about 65-68 deg. Is there any reason why they do not have 82 deg, long FL Eps?

CheeChien, I have PMed you.

Cheers

WeeHan

I do not know the exact physics behind it but briefly, at longer FLs, the light cone in the eyepiece is so fat that a 2" barrel/focuser cannot accomodate a 82 deg FOV. Maybe the optical experts can chime in

Canopus Lim · Post by **Canopus Lim** » Wed Feb 21, 2007 9:19 am

"I have been reading up and I am baffled as to why there are shorter FL Eps with 82 deg views while the longer FLs are about 65-68 deg. Is there any reason why they do not have 82 deg, long FL Eps? "

There is the Nagler 31mm T5 which is a Long focal length 82 degree EP but has about the same true field as a Panoptic 35mm eyepiece which has 68 degree AFOV. It could be a design issue as the size may be too heavy..especially the 31mm Nagler is already so huge, and making a 35mm Nagler would mean being heavier. Also there is the cost issue etc..

The widest field (as in true field..the angular area you see of the sky) eyepieces you can get is the Pentax 40XW, Paragon 40mm, Panoptic 41mm and UO MK70 40mm. It is the largest because the field stop (which can be the lens or pupil inside the eyepiece which limits the true field) of the 2inch eyepieces is the largest with these eyepieces.

What I feel the most advantageous of wide field eyepieces 70 degree or 80 degree AFOV eyepieces is that they allow you to frame the DSO etc at a higher magnification (for the same true field) which means more detail, better contrast than another eyepiece (example Plossl/ ortho). For example, for X true field, a Ymm ortho (40 degree AFOV) is needed to achieve this true field. However, you can achieve the same X true field with a 82 degree eyepiece at Y/2mm focal length, meaning at double the magnification which will give darker background (looks more contrasty) and more details as fainter stars, galaxies etc are more easily seen at higher magnification.

Also, the larger apparent field of view eyepieces are more immersive because of the larger 'field stop' seen when you look through them.

As what Chee Chien said.. it is a slippery slope!

weehan · Post by **weehan** » Wed Feb 21, 2007 10:22 am

Thanks alot Chee Chien and YangBeng for your explanation and advice!

I may go for the Paragon and Arief, I can pass it to you for testing and comparison!

Yang Beng, you brought me to the start of the slope the night you sold me your scope...

Cheers

WeeHan