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Reducer/Corrector for Field Flattening & Coma Correction?

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#1 Sarkikos

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Posted 23 June 2022 - 07:50 PM

Is an R/C (R/FF) worthwhile in a standard SCT for the field flattening and coma correction, regardless of the reduction in f number and potentially wider TFOV?  If you are going to use Ethos or Ethos-SX or other 100 degree+ AFOV eyepieces in the SCT, won't the flatter field and coma correction be worth stacking the R/C into the system?

 

You don't even need to bump up against any potential vignetting problem due to the faster f number and the baffle-tube bottleneck.  Just shift the focal lengths of the set of eyepieces you use to avoid vignetting.  Is the R/C worthwhile for the flatter field and coma correction?

 

Actually, this is why I like my 8" EdgeHD with or without the 0.7x reducer.  I enjoy the flat field and sharp image.  My eyes no longer accommodate for focus.  I appreciate any optics which deliver a flat field without my eyes having to do the work - because my eyes can no longer do the work!  That's also why I like flat field eyepieces, flat field binoculars, and field flatteners in fast refractors. 

 

To my eyes, the image in my 8" EdgeHD is very similar to the flat fields I enjoy in my Canon 10x42 IS and my NP101is.  Yes, it's that good.

 

Mike


Edited by Sarkikos, 23 June 2022 - 08:16 PM.

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#2 Sarkikos

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Posted 23 June 2022 - 07:55 PM

In fact, I'd like the option of a 1x field flattener / coma corrector for standard SCTs.  I don't necessarily want a reduction in the f number, because of the potential for vignetting.  But I do like a flat field and coma correction!

 

AFAIK, there are no 1x FF/CC's for SCTs.  Does anyone know of any?  Or are most observers fixated on reducing the f number?

 

Mike


Edited by Sarkikos, 23 June 2022 - 08:22 PM.


#3 Sarkikos

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Posted 23 June 2022 - 08:01 PM

Ideally, to have a flat field and coma correction, you should start with an EdgeHD, rather than attach an R/C to a Classic SCT.  Also, a Meade ACF - "Coma Free" SCT - does not include field flattening.

 

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

 

https://www.cloudyni...ars/?p=11971668

 

But then, there isn't a 5" or 6" EdgeHD.  For those apertures, you can put on the R/C.

 

Mike

Attached Thumbnails

  • SCT vs EdgeHD.jpg
  • SCT vs SCT+RC.jpg

Edited by Sarkikos, 23 June 2022 - 08:13 PM.


#4 Sarkikos

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Posted 24 June 2022 - 10:32 AM

So, no one is interested in a gizmo that flattens the field and corrects coma in a standard SCT?  All observers care about is getting a larger TFOV?  Get a Dob!  :lol:

 

Mike



#5 Echolight

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Posted 24 June 2022 - 10:37 AM

So, no one is interested in a gizmo that flattens the field and corrects coma in a standard SCT?  All observers care about is getting a larger TFOV?  Get a Dob!  lol.gif

 

Mike

I tried a dob on for size. But it didn't fit right.


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#6 Sarkikos

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Posted 24 June 2022 - 11:34 AM

Advantages of a Dob - besides the much wider TFOV - are that a Dob with a Paracorr is corrected for coma and has a comparatively flat field, unlike a standard SCT.  Wider TFOV, flat field, corrected for coma.  Sounds pretty good to me.

 

But I can easily see the difference in my 8" EdgeHD vs my standard SCTs.  The EdgeHD has a flat field and tighter star images.  The 0.63x R/C in a standard SCT apparently flattens the field and corrects for coma, but not to the level of an EdgeHD.  And you also have the 0.63x reduction in the f number, whether you want it or not. 

 

I would like to see the option for a 1x field flattener/coma corrector for SCTs.  An extra bonus would be to then add a reducer if you want it, maybe a selection of reducers with different reduction factors.  More options, please.

 

Mike


Edited by Sarkikos, 24 June 2022 - 11:39 AM.


#7 Hesiod

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Posted 24 June 2022 - 11:44 AM

For AP cutting the focal ratio used to be the deal.

Now, with the growth of digital sensors' performances and of "EAA" it may be that such a tool will start to show, but probably first large-sensor cameras will have to become cheaper.

I think I have seen a 1x field flattener designed to work with RCs and FF sensors, but guess that's all.



#8 Sarkikos

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Posted 24 June 2022 - 12:24 PM

For AP cutting the focal ratio used to be the deal.

Now, with the growth of digital sensors' performances and of "EAA" it may be that such a tool will start to show, but probably first large-sensor cameras will have to become cheaper.

I think I have seen a 1x field flattener designed to work with RCs and FF sensors, but guess that's all.

Thanks for the info on the 1x FF.  But I have absolutely zero interest in AP, except maybe to see pics others have taken.  I'm visual only.  I might go into NVD at some point in the future - I've been saying that for about ten years now!  lol.gif - but don't want to do EAA.  

 

Hyper-wide AFOV eyepieces like Ethos and Ethos-SX are reason enough to want a flat, well-corrected field for visual in all the telescopes I use, as far as that's possible.

 

Mike


Edited by Sarkikos, 24 June 2022 - 12:28 PM.


#9 Clouzot

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Posted 24 June 2022 - 01:59 PM

So, no one is interested in a gizmo that flattens the field and corrects coma in a standard SCT?  All observers care about is getting a larger TFOV?

I would be interested in such a x1 FF for the very same reasons as you (my eyes don't get younger as time passes) but for any imaging venture (be it EAA or serious AP) I don't really see the point. SCTs already have pretty long focal lengths and optimal sampling already mandates the use of quite large pixels (around 9um at f/10 in typical seeing conditions). Yet, the industry trend is to pack more pixels into a sensor, not less, with new offerings from ZWO having pixels as small as 2um.


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#10 Sarkikos

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Posted 24 June 2022 - 02:53 PM

So I guess in the meantime we have to make do with the 0.63x R/C for field flattening and coma correction for our standard SCTs.  For SCTs 8" and larger, you have a nice selection of EdgeHD's which are well-corrected for FC and coma at f/10.  But for less than 8", you have to put on the 0.63x R/C.

 

Mike



#11 gnowellsct

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Posted 24 June 2022 - 03:05 PM

So I guess in the meantime we have to make do with the 0.63x R/C for field flattening and coma correction for our standard SCTs.  For SCTs 8" and larger, you have a nice selection of EdgeHD's which are well-corrected for FC and coma at f/10.  But for less than 8", you have to put on the 0.63x R/C.

 

Mike

Back in the day, before he graduated to $100k rigs in Namibia, Wolfgang Promper did work like this with an f/6.3 and a c8.  And even bigger panoramas by making mosaics.

 

So nearly as I have seen he went further than anyone I know in using the simple c8 to achieve magnificent deep sky results.  He became a maestro of the c8 and once he had mastered technique moved on to some real serious kit.  His c8 work is still up, you have to scroll all the way down to get to it.

 

which is a good thing, because the humble origins are a lesson for the rest of us.  

 

Greg N


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#12 Lumix.guy

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Posted 29 June 2022 - 04:30 PM

I also would like a 1X corrector for my carbon fiber C11 tube.  In the mean time, I'm experimenting using an AT2FF field flattener with it at f/10.  I believe it does provide some improvement in star images at the edge of the field.  It's probably doing nothing for coma, but it should be helping flatten the field.  YMMV.

 

John


Edited by Lumix.guy, 29 June 2022 - 04:30 PM.

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