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What eyepieces to use with fast APO?

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#1 Eric H

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Posted 10 November 2019 - 06:53 PM

Are there any specific designs that work best for fast refractor with lots of field curvature? Want to try out something for wide field and possibly medium.

 

Frac is 152 F6 triplet.

 

Also, let me add, don't really want anything much more than 82 degrees.


Edited by Eric H, 10 November 2019 - 06:55 PM.

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#2 junomike

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Posted 10 November 2019 - 07:01 PM

I find the 31T5 best but I'm not over sustainable to FC.

What is this 6" F6 Apo you speak of?


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#3 Eric H

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Posted 10 November 2019 - 07:03 PM

I find the 31T5 best but I'm not over sustainable to FC.

What is this 6" F6 Apo you speak of?

An old APM LZOS fluorite triplet, Pre TMB.


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#4 Tyson M

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Posted 10 November 2019 - 07:04 PM

 

What is this 6" F6 Apo you speak of?

 

 

 

 

Frac is 152 F6 triplet.

 

 

Did you snag that fluorite Lzos triplet off AM recently?  That was a unicorn if I ever saw one.


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#5 Eric H

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Posted 10 November 2019 - 07:07 PM

Did you snag that fluorite Lzos triplet off AM recently?  That was a unicorn if I ever saw one.

I did.


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#6 Tyson M

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Posted 10 November 2019 - 07:09 PM

bow.gif  I thought about listing my perfect 8" mak cass to buy that rare scope, but decided against it as I am still putting it through the paces and havent given it a fair shot yet under the stars.

 

Congrats!


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#7 Eric H

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Posted 10 November 2019 - 07:11 PM

bow.gif  I thought about listing my perfect 8" mak cass to buy that rare scope, but decided against it as I am still putting it through the paces and havent given it a fair shot yet under the stars.

 

Congrats!

I'd be really hard pressed to sell an 8" Mak cass!



#8 Eddgie

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Posted 10 November 2019 - 07:14 PM

With a field curvature for a 900mm focal length refractor, 31mm Nagler will be quite good.  If you struggle you might see that the edge of field is a tiny tiny tiny bit out of focus, but it is at the point where you have to really be looking for it.

 

20mm T5 Nagler will be excellent.  I think that the 22mm T4 is not as tight at the outside, but I have not used it in this particular scope, but in scopes with about the same amount of field curvature, I thought the 20mm T5 was better than the 22mm T4. 

 

Shorter than this, and nothing to worry about.  Almost all decent eyepieces will not show enough defocus to see.


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#9 Tyson M

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Posted 10 November 2019 - 07:17 PM

I'd be really hard pressed to sell an 8" Mak cass!

Yea tell me about it- I'd never see it again. It is a specialist tool though for sure with 4000mm focal length! 

 

I have had poor seeing lately, super amounts of dew, and more particularly mount alignment issues (user error) which have put a damper on my viewing sessions with it.

 

I solved the dew issue with the reflectix wrap, and think I got the mount issues under control now.

 

It has show me my best ever view of the Ring nebula to date though :)

 

I like rare scopes.  But yea I digress- yours should be a rare beauty as well.  Never seen one before.

 

You will have to give us some observing session breakdowns with your new frac.


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#10 junomike

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Posted 10 November 2019 - 07:30 PM

I did.

I recall seeing that beast (40lbs).  Wow, looks nice, congrats.


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#11 Tyson M

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Posted 10 November 2019 - 08:02 PM

Back to the eyepieces, fast scopes need good correction.  The 22N is an amazing eyepiece but does suffer a bit of FC in faster scopes.  I thought the 20 T5 was the most uncomfortable eyepiece I have ever looked through, but if you can handle the ER then it is likely better corrected.

 

I think maybe you should look at the 31N, or alternatively the APM 30UFF, Pentax 30XW. 

Possibly medium, depends on what magnification range you consider medium. The 12.5 Docter might fit the bill here. Or the 17 delos if you want something in the 17-22mm range. 22LVW maybe if you can find one preowned.  The 17Nagler T4 might a better choice than the 22nagler with respects to field curvature, and would be the perfect pairing with the 31Nagler in a fast scope.



#12 russell23

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Posted 10 November 2019 - 08:21 PM

Eyepieces I thought performed really well in a 61mm f/5.9 APO were the 18.2mm DeLite, 5mm DeLite,  Nikon NAV SW,  Pentax XW, and 9mm and 6.5mm Morpheus.


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#13 213Cobra

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Posted 10 November 2019 - 08:51 PM

My fastest scope is f/3.3 but it's a reflector. Of my refractors, the fast ones are f/4.9, f/5, f/5.3 and f/6. First, if you get a fast scope that is not a flat field quad, I suggest adding a flattener to a fast triplet for visual. Your eyepieces are not going to correct scope FC, unless by happenstance your eyepiece has some intrinsic FC that happens to cancel scope FC. You can't readily know that from specifications. There are other issues wrt the fast light cone and for that, TeleVue Delites, Naglers, Panoptics, Ethos do well. I assume Delos are equally effective in fast scopes; I've just never looked through one. But since TeleVue scopes are fairly fast, it's natural their eyepieces perform in them. Takahashi UW are outstanding. Baader and Leica zooms cope with fast scopes when they have the focal range for those eyepieces to reach focus. The Pentax XW range are more than competent. At short FLs, the Takahashi TOE are exemplary. But the best thing you can do is start by using a visual flattener to make it easier on the eyepiece, if you haven't chosen a fast, flat-field quad. On my f/6 & f/7.5  LOMO triplets, I use a TSFlat2.

 

Phil


Edited by 213Cobra, 10 November 2019 - 08:51 PM.

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#14 havasman

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Posted 11 November 2019 - 01:37 AM

31T5, 13T6, 5T6 maybe 3.5T6 too

 

I'm sold on all of those in all my scopes. They're just really good every time I use them. They should match up with that beauty you picked up too. Nice scope.


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#15 25585

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Posted 11 November 2019 - 09:56 AM

With my F5 TV Genesis, the 35 Panoptic is good.


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#16 noisejammer

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Posted 11 November 2019 - 01:42 PM

I was sorely tempted by that scope too - enjoy it!

 

If it turns out that the field curvature is a problem, I'd echo giving a try to a field flattener. TS is offering the 3" model that was originally matched to the WO FLT series (respectively 770 & 925 mm focal lengths.) The back focus (116mm) is enough to install a 2" diagonal at the optimal location if you remove its nose and make a custom adapter to suit the M80x1(m) thread.

 

On eyepieces - I recognise your desire for 82o or less so my go-to set would be the Naglers, Delos or XW. I can't speak to APM, Baader or ES equivalents. Although they are off your list, you might consider the ES 12/92o or 17/92o eyepieces - these really changed my ho-hum opinion of ultra-wides. Their exit pupils would be 2 & 2.8 mm respectively. I routinely use them on a flat-field scope between f/3.3 and f/10.


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