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Report: the f/6.3 reducer dispute--as a tool for visual wide field with >30mm oculars

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#26 Sarkikos

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Posted 22 June 2022 - 07:35 AM

I don't know of any 1X SCT flatteners designed and marketed for the purpose. However, there is a famous thread somewhere where somebody tested a bunch of different flatteners with an SCT with surprising results. At least one or two produced excellent results. Maybe somebody can dig up a link.

They were experimenting with FF's intended for refractors, but using them in SCT's?

 

Mike



#27 Sarkikos

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Posted 22 June 2022 - 07:39 AM

Have to quibble with this. The standard SCT f/6.3 reducer/corrector is incapable of flattening the field. It's a corrector, as in a coma corrector, not a flattener. It doesn't matter what brand, Celestron, Meade, Antares; they are all the same basic design. A standard (i.e. not EdgeHD) SCT with a standard f/6.3 R/C is akin to a Meade ACF scope. It has zero improvement in field curvature, but the coma correction is essentially perfect. When people think they are seeing a "flatter field", what they are actually seeing is a coma free field.

Yes, this is one of the criticisms of the ACF.  It is corrected for coma, but not FC.  AFAIK, the EdgeHD is corrected for coma and FC.  I am "sensitive to FC."  In other words, my eyes no longer accommodate for focus.  I need the optical system to do it for me.  If there is FC in the system, I will see it.  If the system has been corrected for FC - like an EdgeHD - I will notice that the field is flat.  To my eyes, my 8" EdgeHD has a flat field, even with 100 or 110 degree AFOV eyepieces.  By the way, I don't see coma in the 8" EdgeHD either.

 

Mike


Edited by Sarkikos, 22 June 2022 - 07:41 AM.

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#28 Borodog

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Posted 22 June 2022 - 07:41 AM

They were experimenting with FF's intended for refractors, but using them in SCT's?

 

Mike

Yes. Found the link. Starts off with reducer/flatteners but moves on to pure flatteners. The results are surprising.

 

https://stargazerslo...corrector-test/


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#29 Borodog

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Posted 22 June 2022 - 07:43 AM

Yes, this is one of the criticisms of the ACF.  It is corrected for coma, but not FC.  AFAIK, the EdgeHD is corrected for coma and FC.  I am "sensitive to FC."  In other words, my eyes no longer accommodate for focus.  I need the optical system to do it for me.  If there is FC in the system, I will see it.  If the system has been corrected for FC - like an EdgeHD - I will notice that the field is flat.  To my eyes, my 8" EdgeHD has a flat field, even with 100 or 110 degree AFOV eyepieces.  By the way, I don't see coma in the 8" EdgeHD either.

 

Mike

Yes; the trade-off in the EdgeHD scope is that field curvature is traded for astigmatism at the edge of the field. But the spot size is so small that you don't really notice it.


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#30 Sarkikos

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Posted 22 June 2022 - 07:45 AM

Yes. Found the link. Starts off with reducer/flatteners but moves on to pure flatteners. The results are surprising.

 

https://stargazerslo...corrector-test/

Maybe I should try my TSFLAT2 in my standard SCTs?  grin.gif

 

By the way, often I don't notice as much difference between photos as imagers seem to be able to do.  But with my eye looking at the sky through an optical system at night, I do not have a problem seeing aberrations or the absence of aberrations.  I need to have my eye at the eyepiece and my hand on the focuser.  Often photos don't mean much to me.  So, unless the differences in photos are very obvious, my reaction to photos is typically: shrug.gif

 

For the series of photos in the link to mean much to me, the poster should have commented on the results of each one.  I'm not an imager.  I really don't like it when they throw out some pics with little if any comment.

 

Mike


Edited by Sarkikos, 22 June 2022 - 07:54 AM.

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#31 Borodog

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Posted 22 June 2022 - 07:58 AM

Maybe I should try my TSFLAT2 in my standard SCTs?  grin.gif

 

By the way, often I don't notice as much difference between photos as imagers seem to be able to do.  But with my eye looking at the sky through an optical system at night, I do not have a problem seeing aberrations or the absence of aberrations.  I need to have my eye at the eyepiece and my hand on the focuser.  Often photos don't mean much to me.  So, unless the differences in photos are very obvious, my reaction to photos is typically: shrug.gif

 

For the series of photos in the link to mean much to me, the poster should have commented on the results of each one.  I'm not an imager.  I really don't like it when they throw out some pics without little if any comment.

 

Mike

It took me a while to get over pixel peeping my DSO images. I am trying to be less picky about star shapes.


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#32 Borodog

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Posted 22 June 2022 - 07:59 AM

As for trying the TSFLAT2, I say go for it. You will have to experiment with the back focus.


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#33 Sarkikos

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Posted 22 June 2022 - 07:59 AM

Yes; the trade-off in the EdgeHD scope is that field curvature is traded for astigmatism at the edge of the field. But the spot size is so small that you don't really notice it.

This seems to be the typical result when FC is corrected, even in refractors.  My AT60ED is pushing the envelope for field flattening with the TSFLAT2.  The field is flattened, but apparently at the price of some induced astigmatism.  The good news, though - at least for me! - is that I only really notice the astigmatism in a defocused image, not at focus. 

 

It's also typical to see SA in a defocused image through even a high-end APO.   So ...?  lol.gif


Edited by Sarkikos, 22 June 2022 - 08:02 AM.

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#34 Echolight

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Posted 22 June 2022 - 08:20 AM

In my C5 (which recently I've been using the most,... thanks to the 100*F weather) with RC and a 20mm Hyperwide (~35mm field stop), I start seeing evidence of a not so flat field about 50-60% out. And coma right at the field stop.

I suppose that if I was using something with a narrower AFOV but similar field stop (30 UFF?) or slightly smaller field stop (ES68 28?) , the field curvature might not be noticeable until farther out in the field.

 

I'll have to set up the deuced and reduced C8 this weekend to investigate the field curvature with the 28 PWA, which provides the widest field without noticeable to me vignetting.


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#35 MrJones

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Posted 22 June 2022 - 08:41 AM

An obvious problem with this discussion is no actual measurement of FOVs. Such as:

 

https://www.cloudyni...ct-maximum-fov/

 

And an issue with AP flatteners and reducers for visual is the spacings needed will not usually accommodate a diagonal. There's probably some that would work but I've never read or heard of anyone trying for optimal visual results.



#36 Sarkikos

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Posted 22 June 2022 - 03:03 PM

Are these f/6.3 reducer/correctors or f/6.3 reducer/field flatteners?  Do they correct for coma or do they flatten the field?

 

I have heard posters on CN say both these things.  Right now there are discussions in other threads on CN in which these f/6.3 gizmos are said to definitely flatten the field, not correct for coma.

 

For instance:  https://www.cloudyni...rvature-issues/

 

So, which is it?

 

Look at these two accessories.  Are they the same thing under different brandings?  Or does one "correct" while the other "flattens?"  Or do they both actually correct for coma, and any field flattening is incidental?  What is going on here?

 

Celestron f/6.3 Reducer/Corrector

https://www.bhphotov...1f8ce51b26ea50f

 

 

ASTRO-TECH SCHMIDT-CASSEGRAIN F/6.3 FOCAL REDUCER FIELD FLATTENER

https://www.astronom...-flattener.html

 

A field flattener flattens the field.  A coma corrector corrects for coma.  "Corrector" by itself is ambiguous at best.  What does the "Corrector" correct?  Words should be used consistently and unambiguously. 

 

The basic question to ask is:  Will a Reducer/Corrector (Reducer/Field Flattener) make a standard SCT more like a Meade ACF (correct for coma) or more like a Celestron EdgeHD (flatten the field)? 

 

Of course, though, the EdgeHD is corrected for coma and has a flattened field.  So to get the effect of an EdgeHD, you apparently need to buy an EdgeHD!  grin.gif  

 

Or can you get a separate field flattener for an ACF?  thinking1.gif

 

Mike


Edited by Sarkikos, 22 June 2022 - 03:12 PM.


#37 Borodog

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Posted 22 June 2022 - 05:36 PM

People are confused by the bad marketing copy of companies like Celestron, which themselves refer to the f/6.3 "flattening the field." But they are wrong. If you look at the ray tracing of the design and the resulting spot diagrams, it is absolutely clear that they are coma correctors and not flatteners.

 

https://www.telescop...ptics.htm#units

 

"Next, an illustration of performance level of the common f/6.3 SCT focal reducer/corrector. It is similar with both, Meade and Celestron, consisting of two cemented doublets. The configuration can entirely correct for coma, but lenses add some astigmatism of the same sign as the mirror Petzval curvature, thus the field cannot be flattened. Still, mainly due to the correction of coma, flat field performance is significantly improved, and visual field is free of visible aberrations."

 

https://s3.amazonaws...paper_final.pdf

 

 

Attached Thumbnails

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  • corrected_sct.jpg

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#38 Sarkikos

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Posted 22 June 2022 - 07:24 PM

The spot diagrams certainly look like it is coma that is being corrected.  I notice that when the name of the product is "reducer/corrector," exactly what aberration is being corrected tends not to be mentioned in the product description.  When the product is called a "reducer/field flattener," then the product description will probably say that it does flatten the field.  I mean, the horse is out of the barn at that point.  What else can they do?  grin.gif

 

I wish I had a dollar for every time an expert on CN - and other platforms - said that an f/6.3 R/C was a reducer and field flattener.  Coma correction is virtually never mentioned.

 

In the field, the visual test for FC is to see if star images are sharp at center of field while fuzzy at edge of field, and vice versa, and that stars at center of field or edge of field can be focused sharply separately but not simultaneously.  The visual test that proves FC has been corrected is to be able to focus stars sharply at center of field and edge of field simultaneously.  Of course, if the observer's eye can accommodate for the difference in focus between center of field and edge of field, the observer is not a good candidate to test the optical system for the presence of FC.  grin.gif

 

Coma, if present to a degree that can be detected by the observer, cannot be focused into a sharp star image at edge of field.  The wider the AFOV, the more obvious coma will be at edge of field.  (Magnification does not have an effect on appearance of coma, except to widen the diffraction limited area at center of field as magnification is increased, and to decrease obviousness of coma at low magnifications.  AFOV is the important factor overall.)   If coma is corrected, and FC and astigmatism are not present, then chances are good that stars will be sharp simultaneously from center to edge of field. 

 

The next time I take out my C5 or C6, I should experiment with and without the f/6.3 Celestron R/C and pay close attention to the aberrations I see or don't see.

 

Mike


Edited by Sarkikos, 22 June 2022 - 07:32 PM.


#39 GGK

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Posted 22 June 2022 - 07:50 PM

Clips from the Celestron instructions which can be read here: 

https://celestron-si...es/94175 IM.pdf

 

"In addition to reducing the focal length and f/ratio the

Celestron Reducer/Corrector Lens also reduces field
curvature significantly so you get a flatter, well
corrected field."

 

and 

 

"Although the Reducer/Corrector Lens diminishes the
small amount of field curvature common to all
Schmidt Cassegrain telescopes, it does not completely
eliminate it."

 

and 

 

"Because the field of view is very close to flat, you can

leave the Reducer/Corrector Lens in place at all times.
High power views will provide flatter fields all the
way to the edge, both visually and photographically."

 

Gary


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#40 Sarkikos

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Posted 22 June 2022 - 07:52 PM

I think it's entirely possible that instructions from a manufacturer for the consumer can have incorrect information about their own product.  And that persons who are otherwise experienced and knowledgeable can read that information and become misinformed.

 

And so the controversy continues.

 

Mike


Edited by Sarkikos, 22 June 2022 - 07:55 PM.


#41 Borodog

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Posted 22 June 2022 - 09:39 PM

Clips from the Celestron instructions which can be read here: 

https://celestron-si...es/94175 IM.pdf

 

"In addition to reducing the focal length and f/ratio the

Celestron Reducer/Corrector Lens also reduces field
curvature significantly so you get a flatter, well
corrected field."

 

and 

 

"Although the Reducer/Corrector Lens diminishes the
small amount of field curvature common to all
Schmidt Cassegrain telescopes, it does not completely
eliminate it."

 

and 

 

"Because the field of view is very close to flat, you can

leave the Reducer/Corrector Lens in place at all times.
High power views will provide flatter fields all the
way to the edge, both visually and photographically."

 

Gary

Yep. That is the bad marketing copy in question. It's wrong.



#42 gnowellsct

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Posted 23 June 2022 - 02:01 PM

I wasn't aware of a new reducer aside from the one designated for Edge scopes. The one I am using is an old used one that I got with a box full of goodies.

 

[...]

 

But EdZ goes on to say that he wouldn't hesitate to use the 2 inch diagonal in combination with a reducer.

Now who am I to side with Greg? EdZ or yourself?

 

And if not $7000, how much are these 92mm apos, that you mention so frequently as a part of your SCT setups (and a reason not to use 2 inch eyepieces in conjunction with a reducer), ... how much are these going for these days? Wasn't one of those a Stowaway?

 

Also, from my experience using the 1.8 degree field of view, for not just finding but also viewing, if there are stars that are dimmed at the edge, they are generally not bright stars. As the brighter stars, and even semi-bright stars, do not show noticeable dimming to my eye.

The top tier triplet 92mm apos (which as far as I know can't even be bought new at this point) were running, before COVID, at $3.5k and change depending on accessories.

I have seen the AT92 triplet in action, it is owned by a friend.  It is also quite popular here on CN and costs considerably less than the "bespoke" brands:  

https://www.astronom...ctor-ota.html  

 

So that's half the price.  

 

There are 80mm scopes of good optical quality that go for less than $1k.  I used an 80mm for a while.

 

I'm not sure I would recommend top-mounting a refractor for you.  You mentioned you were using bungee cords instead of a counterweight system.  There would be the refractor scope, some kind of dovetail to go on the c8, some kind of ring or other attachment system for the dovetail to the refractor.  When I first ventured in this direction, it posed a lot of challenges that were expensive to resolve.  For the C14 I had to upgrade from the G11 to another mount.  The G11 got demoted from C14 duty to carrying refractors and the c8 (together or singly).

 

In other words if you put a ten to fifteen pound load on top of your c8/mount your current mounting system could become unworkable.  That's basically what happened to me.  I added a four inch refractor to a C14 and it was getting bouncy in a way that I didn't like.   If someone had a super polaris and was using a c8 (I used a c8 that way) and wanted to put a three inch refractor on it, that wouldn't work.  (You could use the 3 inch refractor by itself to good effect)

 

When I recommend two-scope viewing I usually attempt to recommend a refractor sized to the rig.  In some cases that is 70 or 80mm.  I lack the coordination and risk inclination to mount a 5" or larger refractor on or on a dual saddle mount with an SCT.  Better people than me have pulled it off.

 

As for the budget the user base of the forums is all over the map.  I spend about $2k a year on astro gear, or at least I used to.  I can't think of anything else to buy that I'm interested in.  And on top of it the kid's in college and it's a $$$ black hole.

 

But the discrepancies in budgets are part of the life of the forums.  You see refractor threads for $3k and even $30k options and you see refractor threads for $300 options including mounts.

 

If I see someone using a CPC 8" though I infer they are not in the hobby on a rock bottom budget basis and might be willing to explore a two scope set-up.  People who are really budget constrained typically are using 8" solid tube Dobs.

 

Back in the day when I was using a Super Polaris + c8 (Celestron sold them that way) I didn't have a refractor.  I did have an f/6.3 reducer corrector which I got the same way you did: in a bunch of stuff in a box and a "hmmm what's this."  (I sold that reducer corrector but it is the way of the world, another box of stuff showed up and there was another f/6.3 reducer corrector.  For all I know it was the same one I sold!)  I pretty quickly concluded it wasn't for me and that the c8 is not really a wide field scope.  A couple years later I had a second mount and set up a refractor next to the SCT.  This was a lot of fun but it was also a lot of work.    I had to find every object twice.  And I had two set ups and two break downs and two power supplies and everything else.  It was then that the light bulb went off and I began to look hard at how people were putting refractors on SCTs.

 

It wasn't a new practice.  You can see pictures of refractors mounted on top of Newtonians in a 1965 Optical Craftsman catalog.  When I was a kid I never understood why one would do that.  As an adult I still don't understand why they did that.  I guess for guiding.  In the age of the Kellner it's not as if they were getting huge wide fields off their f/12 to f/15 refractors.  

 

Some our eminent authorities in this forum recommended the f/6.3 reducer in general use as field flattener and as a way to economize on eyepieces (the Barlow lets 15 to 30mm eyepieces pretend to be 7 to 15mm eyepieces, the RC lets 15 to 30mm eyepieces pretend to be upper 20mm and 30-40 mm eyepieces).   I did use it for a while on that premise.  But I thought the views were better in dedicated eyepieces and moved in that direction.  (using Russell and Rini wide fields, in the beginning)  So yes: Using the r/c with a two inch diagonal.  I have a twofold dislike of the system.  1.  It does not really give a wide field view with the 30 to 40mm wide fields.  Not a good (unvignetted one) anyhow.  2.  I just don't like it generally.   You have to screw it on.  If you're looking at a planet and you want more magnification you have to "overcome" the negative effect of the RC by using shorter fl eyepieces or barlows.  It makes no sense to me to barlow a scope with an RC to take a gander at Mars, for example.  I also don't particularly like the visual effect and reduced sky contrast of the lower power views that come out of the RC.  

 

In this matter I have disagreed with virtually everyone (and there are quite a few) who like to say that (when the topic comes up in a refractor forum etc) that an SCT can give a wide field as a visual scope.  The SCT really doesn't compete there.   I push hard on the matter because I think it's an error and gives people the wrong idea of the product.  

 

Given some of the points you have made about your rig (very light weight mount) and use habits (apparently in the back yard, which I can't do) I wouldn't recommend the kind of rig I use or an up-top refractor.*  I drive 30 miles to a remote site.  It's an expedition.  We leave early so we can stop for tuna sandwich from the convenience store, and as the sun sets I do the rituals of setting up.  I enjoy the gear and working with it. 

 

It's also the case that a person should really only pursue a top mounted refractor if the skies are dark enough to let the open clusters pop.  Absent that, the game is not worth the candle.

 

Greg N  

 

*you might get good use out of a stellarvue 50mm 9x50 which can take regular 1.25" eyepieces.  The weight penalty would not be huge.  I saw NGC 5053 (9th mag glob) in this scope!  


Edited by gnowellsct, 23 June 2022 - 02:20 PM.

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#43 Echolight

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Posted 23 June 2022 - 02:39 PM

The top tier triplet 92mm apos (which as far as I know can't even be bought new at this point) were running, before COVID, at $3.5k and change depending on accessories.

I have seen the AT92 triplet in action, it is owned by a friend.  It is also quite popular here on CN and costs considerably less than the "bespoke" brands:  

https://www.astronom...ctor-ota.html  

 

So that's half the price.  

 

There are 80mm scopes of good optical quality that go for less than $1k.  I used an 80mm for a while.

 

I'm not sure I would recommend top-mounting a refractor for you.  You mentioned you were using bungee cords instead of a counterweight system.  There would be the refractor scope, some kind of dovetail to go on the c8, some kind of ring or other attachment system for the dovetail to the refractor.  When I first ventured in this direction, it posed a lot of challenges that were expensive to resolve.  For the C14 I had to upgrade from the G11 to another mount.  The G11 got demoted from C14 duty to carrying refractors and the c8 (together or singly).

 

In other words if you put a ten to fifteen pound load on top of your c8/mount your current mounting system could become unworkable.  That's basically what happened to me.  I added a four inch refractor to a C14 and it was getting bouncy in a way that I didn't like.   If someone had a super polaris and was using a c8 (I used a c8 that way) and wanted to put a three inch refractor on it, that wouldn't work.  (You could use the 3 inch refractor by itself to good effect)

 

When I recommend two-scope viewing I usually attempt to recommend a refractor sized to the rig.  In some cases that is 70 or 80mm.  I lack the coordination and risk inclination to mount a 5" or larger refractor on or on a dual saddle mount with an SCT.  Better people than me have pulled it off.

 

As for the budget the user base of the forums is all over the map.  I spend about $2k a year on astro gear, or at least I used to.  I can't think of anything else to buy that I'm interested in.  And on top of it the kid's in college and it's a $$$ black hole.

 

But the discrepancies in budgets are part of the life of the forums.  You see refractor threads for $3k and even $30k options and you see refractor threads for $300 options including mounts.

 

If I see someone using a CPC 8" though I infer they are not in the hobby on a rock bottom budget basis and might be willing to explore a two scope set-up.  People who are really budget constrained typically are using 8" solid tube Dobs.

 

Back in the day when I was using a Super Polaris + c8 (Celestron sold them that way) I didn't have a refractor.  I did have an f/6.3 reducer corrector which I got the same way you did: in a bunch of stuff in a box and a "hmmm what's this."  (I sold that reducer corrector but it is the way of the world, another box of stuff showed up and there was another f/6.3 reducer corrector.  For all I know it was the same one I sold!)  I pretty quickly concluded it wasn't for me and that the c8 is not really a wide field scope.  A couple years later I had a second mount and set up a refractor next to the SCT.  This was a lot of fun but it was also a lot of work.    I had to find every object twice.  And I had two set ups and two break downs and two power supplies and everything else.  It was then that the light bulb went off and I began to look hard at how people were putting refractors on SCTs.

 

It wasn't a new practice.  You can see pictures of refractors mounted on top of Newtonians in a 1965 Optical Craftsman catalog.  When I was a kid I never understood why one would do that.  As an adult I still don't understand why they did that.  I guess for guiding.  In the age of the Kellner it's not as if they were getting huge wide fields off their f/12 to f/15 refractors.  

 

Some our eminent authorities in this forum recommended the f/6.3 reducer in general use as field flattener and as a way to economize on eyepieces (the Barlow lets 15 to 30mm eyepieces pretend to be 7 to 15mm eyepieces, the RC lets 15 to 30mm eyepieces pretend to be upper 20mm and 30-40 mm eyepieces).   I did use it for a while on that premise.  But I thought the views were better in dedicated eyepieces and moved in that direction.  (using Russell and Rini wide fields, in the beginning)  So yes: Using the r/c with a two inch diagonal.  I have a twofold dislike of the system.  1.  It does not really give a wide field view with the 30 to 40mm wide fields.  Not a good (unvignetted one) anyhow.  2.  I just don't like it generally.   You have to screw it on.  If you're looking at a planet and you want more magnification you have to "overcome" the negative effect of the RC by using shorter fl eyepieces or barlows.  It makes no sense to me to barlow a scope with an RC to take a gander at Mars, for example.  I also don't particularly like the visual effect and reduced sky contrast of the lower power views that come out of the RC.  

 

In this matter I have disagreed with virtually everyone (and there are quite a few) who like to say that (when the topic comes up in a refractor forum etc) that an SCT can give a wide field as a visual scope.  The SCT really doesn't compete there.   I push hard on the matter because I think it's an error and gives people the wrong idea of the product.  

 

Given some of the points you have made about your rig (very light weight mount) and use habits (apparently in the back yard, which I can't do) I wouldn't recommend the kind of rig I use or an up-top refractor.*  I drive 30 miles to a remote site.  It's an expedition.  We leave early so we can stop for tuna sandwich from the convenience store, and as the sun sets I do the rituals of setting up.  I enjoy the gear and working with it. 

 

It's also the case that a person should really only pursue a top mounted refractor if the skies are dark enough to let the open clusters pop.  Absent that, the game is not worth the candle.

 

Greg N  

 

*you might get good use out of a stellarvue 50mm 9x50 which can take regular 1.25" eyepieces.  The weight penalty would not be huge.  I saw NGC 5053 (9th mag glob) in this scope!  

Yeah, bungee-balanced.lol.gif

C2CD82E7-39C9-4563-B266-D752C0F4A5E2.jpeg

 

I never think of 1.8 degrees as "wide field". So I agree it is not a wide field scope. 
 

Sometimes I set my wide field scope (up to 5 degrees) next to the C8 though. When I get it to a dark site I'll start calling the ST102 a "richfield scope".

D193B43B-5AE1-40A4-BBF0-0C90F8CD561D.jpeg



#44 Rick-T137

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Posted 23 June 2022 - 03:24 PM

When I recommend two-scope viewing I usually attempt to recommend a refractor sized to the rig.  In some cases that is 70 or 80mm.  I lack the coordination and risk inclination to mount a 5" or larger refractor on or on a dual saddle mount with an SCT.  Better people than me have pulled it off.

 

As for the budget the user base of the forums is all over the map.  I spend about $2k a year on astro gear, or at least I used to.  I can't think of anything else to buy that I'm interested in.  And on top of it the kid's in college and it's a $$$ black hole.

 

But the discrepancies in budgets are part of the life of the forums.  You see refractor threads for $3k and even $30k options and you see refractor threads for $300 options including mounts. 

I'm more at the budget end of the spectrum. I have too many hobbies (guitars, computers, cycling, cars) that compete with astronomy and it forces me to be miserly in all endeavours.

 

To that end, I have an relatively old and inexpensive Meade 2080 SCT (8") and on top of it I have a Sky-Watcher 70mm f/7.1 achromat. I think I paid $300 for the SCT, and $50 for the refractor. Oh! And another $30 for the Antares bracket that lets me mount one to the other.

 

The 70mm is simply meant to be used as a finder scope, and for wide angle, low power views (max 3.2° with my PL32) and the SCT takes care of the rest. This combo has been working tremendously for me and I really find it difficult to justify buying an APO to put on top of my rig since the 70mm is essentially doing what it's supposed to do... perfectly!

 

Clear skies!

 

Rick



#45 Sarkikos

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Posted 23 June 2022 - 03:33 PM

I have seen the AT92 triplet in action, it is owned by a friend.  It is also quite popular here on CN and costs considerably less than the "bespoke" brands:  

https://www.astronom...ctor-ota.html  

I have one and would recommend it.  Plenty good enough for visual, which is all I do or will ever do.  As I said, when I bought mine a couple years ago, it was $300 less than it is now.

 

"Bespoke."  I don't think I had ever heard that word before I started reading posting here on CN.  Like "whilst," it's from the other side of the Pond.  grin.gif

 

Mike


Edited by Sarkikos, 23 June 2022 - 03:35 PM.


#46 gnowellsct

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Posted 23 June 2022 - 03:54 PM

I have one and would recommend it.  Plenty good enough for visual, which is all I do or will ever do.  As I said, when I bought mine a couple years ago, it was $300 less than it is now.

 

"Bespoke."  I don't think I had ever heard that word before I started reading posting here on CN.  Like "whilst," it's from the other side of the Pond.  grin.gif

 

Mike

It's new, like using "litigate" to mean "argue."  In my vocabulary litigating requires a lawyer.  These days politicians "litigate" a highway bill and all they do is argue about it.

 

Bespoke has been propagating as a synonym for crafted or customized products.  I've even seen (in WSJ) "bespoke" securities for select clients.

 

Greg N


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#47 gnowellsct

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Posted 23 June 2022 - 03:58 PM

Yeah, bungee-balanced.lol.gif

 

I never think of 1.8 degrees as "wide field". So I agree it is not a wide field scope. 
 

Sometimes I set my wide field scope (up to 5 degrees) next to the C8 though. When I get it to a dark site I'll start calling the ST102 a "richfield scope".

 

Two easy set up alt-az mounts and an ST102.   You will have the inconvenience of finding every object twice but it seems to work out for you.  With the refractor right there I'd ditch the f/6.3 rc but it seems to make you happy.

 

GN



#48 Sarkikos

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Posted 23 June 2022 - 04:05 PM

It's new, like using "litigate" to mean "argue."  In my vocabulary litigating requires a lawyer.  These days politicians "litigate" a highway bill and all they do is argue about it.

 

Bespoke has been propagating as a synonym for crafted or customized products.  I've even seen (in WSJ) "bespoke" securities for select clients.

 

Greg N

Yes.  Similar to "artisanal."  Watch Portlandia for examples.  

 

And I hear everyone down to the fish mongers and chimney sweeps say "whilst" in England.  In America, I doubt even Supreme Court Justices use the word.  grin.gif

 

Mike


Edited by Sarkikos, 23 June 2022 - 04:08 PM.


#49 Sarkikos

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Posted 23 June 2022 - 04:11 PM

Two easy set up alt-az mounts and an ST102.   You will have the inconvenience of finding every object twice but it seems to work out for you.  With the refractor right there I'd ditch the f/6.3 rc but it seems to make you happy.

 

GN

Try the ST120 f/5.  It's a RRFT (Really Rich Field Telescope).

 

Mike



#50 David Knisely

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Posted 23 June 2022 - 06:14 PM

When I bought my old NexStar 9.25GPS XLT, I also got a Celestron 0.63 focal reducer/corrector from a friend here on CN.  I tried it visually for a while before I got a 2" visual back and star diagonal, but visually, it didn't give me more true field than my longer focal length 2" eyepieces did.  It also induced a little mild chromatic aberration at very high powers.  After that, I put it back in its box for a number of years until I started doing a little imaging, where it has been somewhat useful in getting the image scale down a bit.  Still, with its placement and 40mm clear aperture, it does induce a little vignetting, so as far as getting significantly wider fields, it has not been very effective.  If I want wide fields, I will use my 100mm f/6 refractor.  Clear skies to you.


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