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Do your eyepieces still work fine behind a 0.63 FR on your Schmidt-Cassegrain ?

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#1 AOHANA

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Posted 08 April 2021 - 12:34 AM

Hi everyone,

 

I would like to hear about your visual experiences using eyepieces (mainly 1.25" i guess) behind a 0.63 focal reducer paired with your SCT.

All brands are welcome (particular interests in 82es14/6.7, 68es24, XW7/10/14, XF, Morpheus 6.5/14/17.5, Delos, Delite, SSW, NLV, LVW)

 

Thanks you all bow.gif


Edited by AOHANA, 08 April 2021 - 12:38 AM.


#2 PJBilotta

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Posted 08 April 2021 - 02:03 AM

I have encountered no issues with any of my eyepieces - Televue Pans and ES 68's, many different 82s, Pentax XLs and XWs, Morpheuses, and many others. Many perform a tad bit better due to the correction and field flattening the focal reducer provides. These days, I generally observe with an R/C almost all the time, and encounter zero issues with any 1.25" eyepiece.

Simple fact is that pretty much every good-quality 1.25" EP will play well with an R/C, as long as you remember that you are making your SCT a faster f/6.3 scope. Going from f/10 to f/6.3 will mean that edges will not be as sharp in less well-corrected eyepieces as in a more forgiving, slower f/10 system. This is why less expensive wide fields - Superviews, Hyperions, Luminoses, etc. - tend to soften at the edges in scopes that are faster than f/7.

That is - BIG IF HERE - you use the reducer with the recommended 1.25" diagonal and eyepieces for which it was designed.

Introduce a 2" diagonal and 2" eyepieces into the equation, and all bets are off. The added focal length of most 2" diagonals combined with an f/6.3 R/C makes it dicey. Most 2" diagonals (not all) are too long and exceed the proper corrector-to-eyepiece distance. This makes it impossible to bring some EPs to focus, and also effectively stops down the aperture of your scope. Essentially, by adding the 2" diagonal behind your R/C, you are moving your EP so far back that you run out of in-travel on your focuser to bring it to proper focus. You also cut off the edges of the light cone coming into your EP, effectively turning your 8" SCT into a 7" scope.

I (and many others) do successfully use 2" accessories with an R/C, but you need a diagonal with the shortest possible light path to reliably do so - often a 2" prism (expensive), an SCT nose piece that threads directly onto the R/C, or one with a shorter EP holder. I actually use negative profile 2" to 1.25" adapters that drop the EP farther down into my 2" diagonal to shorten the focal length even further.

There's a reason there are many threads here advising using either 2" alone, or 1.25" with an R/C, but not both to max out the field on your SCT.

Edited by PJBilotta, 08 April 2021 - 02:42 AM.

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#3 AOHANA

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Posted 08 April 2021 - 03:42 AM

I have encountered no issues with any of my eyepieces - Televue Pans and ES 68's, many different 82s, Pentax XLs and XWs, Morpheuses, and many others. Many perform a tad bit better due to the correction and field flattening the focal reducer provides. These days, I generally observe with an R/C almost all the time, and encounter zero issues with any 1.25" eyepiece.

Great news, i am gad to hear it.

 

Simple fact is that pretty much every good-quality 1.25" EP will play well with an R/C, as long as you remember that you are making your SCT a faster f/6.3 scope. Going from f/10 to f/6.3 will mean that edges will not be as sharp in less well-corrected eyepieces as in a more forgiving, slower f/10 system. This is why less expensive wide fields - Superviews, Hyperions, Luminoses, etc. - tend to soften at the edges in scopes that are faster than f/7.

Do you also consider 1.25" 82ES EPs as less expensive wide fields too ? I'd be glad that they could work flawlessly on a R/C SCT system

 

That is - BIG IF HERE - you use the reducer with the recommended 1.25" diagonal and eyepieces for which it was designed.

My SCT has a 2"clicklock EPs clamp, a T2 maxbright diagonal (with t2 2"nosepiece and 1.25 eyepiece clamp). It is a few mms more than the stock diagonal/visualback...

Don't plan to go 2" EPs, that is why i would like to be sure that the 1.25 eyepieces work nicely with the reducer


Edited by AOHANA, 08 April 2021 - 06:36 AM.


#4 Virtus

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Posted 08 April 2021 - 06:42 AM

Sorry to go off topic but I'm curious if a binoviewer (without OCA) can still come into focus with a reducer? 



#5 AOHANA

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Posted 08 April 2021 - 07:02 AM

Sorry to go off topic

Don't be;)
 


Edited by AOHANA, 08 April 2021 - 07:09 AM.

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#6 SeattleScott

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Posted 08 April 2021 - 08:53 AM

Sorry to go off topic but I'm curious if a binoviewer (without OCA) can still come into focus with a reducer?

Realize you are asking for serious vignetting. Most binoviewer have limited clear aperture. For example there is a reason the WO ones come with a pair of 20mm SWA eyepieces. Because if you go any wider, they will vignette. Now it should be fine for a 5mm eyepiece, but why would you bother messing with a reducer to get a wider view with a 5mm? You could just change eyepieces to a lower power pair. The reason for a reducer would be wider view at lowest power, which is almost certain to vignette with a reducer.

Scott

#7 AOHANA

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Posted 08 April 2021 - 10:04 AM

Now it should be fine for a 5mm eyepiece, but why would you bother messing with a reducer to get a wider view with a 5mm? You could just change eyepieces to a lower power pair. The reason for a reducer would be wider view at lowest power, which is almost certain to vignette with a reducer.

Scott

Hi Scott,

I guess the answer concerning a 5mm is adressed to me. The binoviewer one isn't.

For DSO, using a reducer with 6,7mm to 24mm 1.25" eyepieces let the scope magnify from x60 et x230 without unscrewing the FR

For planetary observing (or moon), let's unscrew the FR to go 6.7mm


Edited by AOHANA, 08 April 2021 - 10:51 AM.


#8 PJBilotta

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Posted 08 April 2021 - 01:54 PM

Great news, i am gad to hear it.

 

Do you also consider 1.25" 82ES EPs as less expensive wide fields too ? I'd be glad that they could work flawlessly on a R/C SCT system

 

My SCT has a 2"clicklock EPs clamp, a T2 maxbright diagonal (with t2 2"nosepiece and 1.25 eyepiece clamp). It is a few mms more than the stock diagonal/visualback...

Don't plan to go 2" EPs, that is why i would like to be sure that the 1.25 eyepieces work nicely with the reducer

I'd consider the ES 82's to be higher-quality ones with good edge correction, and they work very well with an R/C, as do Stellarvues, Meades, and many other mid-to-higher priced 82s. The wide angles that don't do as well at f/6.3 are the 5-element modified Erfle designs like the GSO Superviews, Agena SWAs, Williams Optics Swans, and budget 82s like the Luminos. Hyperions are on the border line, as they generally do better at f/7 and above. Keep in mind that these will do better than in your average f/6 scope because the Reducer/Corrector also corrects and flattens the SCT's field, giving you a little cleaner edge correction than from a straight f/6 scope without a corrector.

 

I also use a 2" click lock on my corrector, and a T2 prism with a 2" nose and 2" EP holder w/1.25" adapter to shorten the light path enough to use a couple of 2" EPs. Works fine for me with no visible vignetting with my ES 28/68. Your light path for the Maxbright mirror will be a little longer, yielding a slightly greater reduction and requiring a bit more in-focus.

 

I have actually made this work very successfully with a basic 2" diagonal as well: a 2" GSO-made Highpoint (several other brands too) dielectric diagonal. This specific GSO model is the one with the "notched" 2" EP holder where the 2-1.25 adapter set screw slots into the notch on the 2" holder, making it shorter than most comparable 2-inchers. The adapter also has a recess on the top that drops the EP about 7-8mm further into the diagonal (a negative profile adapter), shortening the focal length a bit further. The net result is a 2" diagonal that is 10-15mm shorter than most, and can still be used successfully with a click-lock and R/C without focus issues.


Edited by PJBilotta, 08 April 2021 - 01:57 PM.

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#9 noisejammer

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Posted 09 April 2021 - 05:51 AM

About 20 years back, I tried my Meade 32 SWA (Series 4000) with the f/6.3 reducer. I estimate the optical path was about right so the ~38mm entrance pupil was reduced to ~24mm at the focal plane.

 

The field stop of the eyepiece is around 41 mm and the eyepiece was strongly vignetted. Nevertheless, it gave me a 5mm exit pupil, an unvignetted field of ~40 moa and the only rose-coloured image of M42 that I've experienced. I did try with the 14 mm UWA and a couple of others - it didn't really make much sense.

 

Here's the important thing - large aperture eyepieces will be vignetted when using a f/6.3 reducer but you can sometimes benefit from a large exit pupil even if it is vignetted. I use this trick with my refractors - I have modified things so that I can achieve focus at ~f/5. Add a 31T5 and you can have a wonderful instrument for really dark skies. (Of course,the images are not vignetted when I use a large aperture reducer.)


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#10 SeattleScott

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Posted 09 April 2021 - 08:26 AM

Rose colored M42? That’s a new one. We’re you using a filter?

#11 noisejammer

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Posted 09 April 2021 - 10:35 AM

Rose colored M42? That’s a new one. We’re you using a filter?

Nope - I had my LX200/12 - 6.3 reducer - horrible Meade 2" diagonal and the 32 mm eyepiece.

 

It was 2002.12.03 and perhaps an hour after sunset. The sky had not completely darkened and there was some ambient light (from knee height path lighting covered in brown paper bags) which may have extended my scotopic vision a bit.
 



#12 SeattleScott

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Posted 09 April 2021 - 12:28 PM

Nope - I had my LX200/12 - 6.3 reducer - horrible Meade 2" diagonal and the 32 mm eyepiece.

It was 2002.12.03 and perhaps an hour after sunset. The sky had not completely darkened and there was some ambient light (from knee height path lighting covered in brown paper bags) which may have extended my scotopic vision a bit.

Gotcha, maybe a little reflection of the sunset or something. If anything M42 should have a greenish cast. Although I have seen purple tones when doing EAA on it with a fast achro... I kind of thought the purple was pretty, even if it wasn’t real.

Scott

#13 noisejammer

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Posted 09 April 2021 - 01:19 PM

Gotcha, maybe a little reflection of the sunset or something. If anything M42 should have a greenish cast. Although I have seen purple tones when doing EAA on it with a fast achro... I kind of thought the purple was pretty, even if it wasn’t real.

Scott

Not a chance - M42 emits predominantly hydrogen-alpha (656.3 nm) which is deep red. The green-blue colour comes from hydrogen-beta (468 nm) and OIII (496/501 nm.) Only one h-beta photon is emitted for every three h-alpha's.

 

The reason many people report M42 as green-blue is that human scotopic vision is insensitive to just about anything else. The same can be said for cameras - most have very low sensitivity to the deep red.

 

In my case, I think my vision was still partly photopic which means the sensitivity to deep red had not been completely lost - I think because of the ambient light.

 

Anyhooo - this is way off topic. Let's return to the thread. If you're still interested, you can start a separate thread (probably here) and we can take it further.


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#14 muller

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Posted 13 April 2021 - 06:01 AM

I have tried to put an Ethos 13 behind the 0.63xFR on my C11, and I have to say that I was quite happily surprised by the result.

Gone the awful vignetting occurring with some other narrower eyepieces.

Got dark sky background and good contrast views.




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