Fast scope/coma correction/normal eyepieces??

[Paul73]

Hi Folks

I’ve decided that 50° eyepieces are just too claustrophobic (TV Plossls).

My bank manager is certain that a box full of 100° exotica is out as well.

My 16” likes wide wide eyepieces but at f4, only the best will do.....

Then I remembered that lurking somewhere, I have an old Parracor. So my question is this; will the Parracor clean things up enough for me to use middle of the road eyepieces like the ES 82° range? The only eyepiece range that I have been entirely happy with uncorrected is the TV Delos range (not tried the Delites).

So, before I start looking for a Lunt 20mm 100° and used Delos, Ithought that I would ask your opinions.

Paul

[Ruud]

A coma correcting eyepiece would introduce a kind of "anti-coma" to correct for the coma produced by the objective. This makes coma correcting eyepieces  unusable  on coma free  telescopes. So there are no coma correcting eyepieces on the market.

Coma is a property of the objective, not of the eyepiece. Eyepieces are almost always  coma free. A good eyepiece shows the focal plane of the objective faithfully, including the coma that is there.

Separate coma correctors exist  for Newtonians. You adjust them  per eyepiece. I'm not sure why but I think this is needed because eyepieces usually aren't parfocal and the distances between the field stop of the eyepiece and the corrector matters. It must be something like this. 

---

Fast telescopes: I have an f/5 which is fast enough to see the difference between for instance a Hyperion (not so good) and a Morpheus or Delos (both very good). Some designs just don't work very well on fast telescopes and produces unsharp off axis views. The same eyepieces may work very well on slow telescopes.

 

[Peter Drew]

I use a Parracor on a 20" F3.5 Newtonian, it seems to suit all the eyepiece types I have tried.  

[Paul73]

I guess that I’ll just suck it and see! 

The ES 82 performed well at f4.7 (my 10”). With the Barlowing of the Parracor(x1.25), my f4 should act like an f4.6??

Paul

[Louis D]

1 hour ago, Paul73 said:

I guess that I’ll just suck it and see! 

The ES 82 performed well at f4.7 (my 10”). With the Barlowing of the Parracor(x1.25), my f4 should act like an f4.6??

Paul

Your math is correct, but your text isn't.  It's 1.15x.  Perhaps a typo?

Is it the original Paracorr?  Does it have the tunable top?  2" or 1.25" version?  The new Paracorr II is supposed to offer better correction for scopes faster than f/4.

You'll be surprised how much better the view is with the coma corrector than without in wide field eyepieces.  It also helps flatten the field.

[Paul73]

Yes. Typo. x1.15.

It is the turntable top, but sadly not the one with the extra baring. I believe that the eye wateringly £££ mkII was engineered to cope with the new breed of 100° Eyepieces.

The Parracor definitely helps. The question is more around would a Parracored 24mm ES82° beat a non-corrected 100°, say, the Lunt/APM 20mm?

24 82° / 1.15=21mm x76.5 fov 1.1°

             vs

20mm x 80 fov 1.25°

So similar mags and fov, but which will give the clearer view?

Paul

[Louis D]

1 hour ago, Paul73 said:

I believe that the eye wateringly £££ mkII was engineered to cope with the new breed of 100° Eyepieces.

It was primarily engineered to cope with the new breed of sub-f4 Dobs.  It is designed to work down to f/3.  It also corrects the field better than the original Paracorr for f/4+ scopes, so there is some truth that 100°+ eyepieces will look better with the new Paracorr-2 than with the original.

My money would be on the 82° with CC over the non-CC 100°.  My 17mm ES-92 look pretty bad without CC at f/6 and perfect with CC.  I'll agree that my 10mm Delos looks about the same with and without CC, but that's probably mostly because of the strong Smyth lens it contains extending the f-ratio and the non-agressive 72 degree field.  At 20mm and 24mm, that barlowing effect is much weaker.  That, and coma grows stronger the farther away from on-axis you go at any power.  Thus, the non-CC 100° will be at an increased disadvantage over the CC'ed 82°.

[Paul73]

I guess that is why we don’t see 20+ mm Delos. But, not pushing a design too far is something of a TV strong point.

As it happens, a nice ES 24mm 82° arrived today. I’ll test drive and report back.

Paul

[John]

8 minutes ago, Paul73 said:

I guess that is why we don’t see 20+ mm Delos. But, not pushing a design too far is something of a TV strong point.

As it happens, a nice ES 24mm 82° arrived today. I’ll test drive and report back.

Paul

There is a 25mm 100 in the 2 inch format and a 30mm 100 in 3 inch. Both by Explore Scientific. Tele Vue decided not to push the Ethos further than 21mm though.

 

[Paul73]

Interesting about the Parracor 2 being developed as a response to the proliferation of sub f4 scopes. I thought that the driver was the fact that there isn’t enough Intravel in the Mk1 for the 17 and 21mm Ethos (think that this is true for the Nagler 31mm too). The Delos range are only 1.25” so a cunning adaptator is used to get that intravel.

Probably a combination of faster scopes and the intravel issue.

Paul

[Paul73]

4 minutes ago, John said:

There is a 25mm 100 in the 2 inch format and a 30mm 100 in 3 inch. Both by Explore Scientific. Tele Vue decided not to push the Ethos further than 21mm though.

 

Yes. They don’t get wonderful reviews, but you’ve got to give the guys at ES points for trying. ?.

[John]

12 minutes ago, Paul73 said:

Yes. They don’t get wonderful reviews, but you’ve got to give the guys at ES points for trying. ?.

Well its good to see them trying some original designs rather than plagiarising others work

 

[Paul73]

Bl£&@y Clouds!!!!

It is nice to feel the weight of a proper eyepiece again! 

[Paz]

I use a paracorr 2 with a f4.6 Newtonian and Nagler and Delos eyepieces. I keep it in for all targets. The coma correction is great for clusters etc and the flat field benefits are good for things like lunar. I also use its Barlow effect to collimate laser Barlow style. Here's an old action shot...

[Paul73]

I’m delighted to report that £150 second hand ES82° 24mm and Parracor mk1 (turntable top) in an f4 scope is outstanding. Cleans things up a treat! I’ve seen sharper stars in fracs but the air was very moist with the Devil’s Orb glinting off every droplet. It will be interesting to see how it the combination performs in the dark and in drier air.

I would rate the view as better than the ES100° 20mm uncorrected or corrected (using the same Parracor and scope). Possibly a more modern corrector with enough intravel might beat it. I haven’t used an E21 in this scope but the older Parracor does rob you of a bit of the wow factor. If money allowed it would be SIPS / Parracor 2 and Ethos. However, for most of us, cash is in limited supply; so an old Parracor teamed with mid tier 82° eyepieces such as the ES range seems like a winner!

I’ll try a few more from this range and report back.

Paul

[Paul73]

Incoming!

Thanks to James and mystery guy on eBay; the ES 82° 18,11 & 8.8mm’s all winging their way towards me as I type. Can’t believe my luck. I decide to go the ES82 route yesterday and three pop up used. The chancellor isn’t going to be happy (but I will be)! ???

Paul

[Paul73]

The gang’s all here! I really shouldn’t be this happy about some glass.

 

[John]

Three Ar's and an N2 - oh no, they don't match !!!!!

Only joking  what they are purged with makes no difference whatsoever of course

Hope they do a great job for you

[Paul73]

Yes. They seem to have jumped back & forth between Nitrogen and Argon. I guess that I’ll just have to live with the fundamental mismatch!

[estwing]

Nice glass Paul...