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Alan White

Explore Scientific HR Coma Corrector or Paracorr Mk1 ?

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If your funds do not stretch to a new TV Paracorr, which would you buy,
ES HR Coma Corrector or a used TV Paracorr Mk1 later types??

If you answer please say why.¬†ūüĎć

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I don't feel the need for a coma corrector but I have read that the ES one requires 38mm of inwards focuser travel which has caused issues for some users.

 

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3 hours ago, John said:

I don't feel the need for a coma corrector but I have read that the ES one requires 38mm of inwards focuser travel which has caused issues for some users.

 

I think its actually about 35 mm outward travel with a digital SLR (I must check with mine), were you meaning with an eyepiece.

John 

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44 minutes ago, johnturley said:

I think its actually about 35 mm outward travel with a digital SLR (I must check with mine), were you meaning with an eyepiece.

John 

Yes, with an eyepiece. I've not actually used one though but I've read about the need for quite a lot of inwards focuser travel with this coma corrector frequently.

 

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If funds are an issue, I'd do what I did and get the GSO/Revelation CC with a 25mm spacer tube.  It has a 65mm to 85mm separation distance where correction is quite good, so there isn't much need to find tune the separation visually.  I'd say for most eyepieces that focus within 5mm of the shoulder, I get about 95% or more reduction in coma, which is plenty good for visual usage for me.  I need somewhere between 10mm and 15mm of inward travel, so not bad at all there.

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12 hours ago, Louis D said:

If funds are an issue, I'd do what I did and get the GSO/Revelation CC with a 25mm spacer tube.  It has a 65mm to 85mm separation distance where correction is quite good, so there isn't much need to find tune the separation visually.  I'd say for most eyepieces that focus within 5mm of the shoulder, I get about 95% or more reduction in coma, which is plenty good for visual usage for me.  I need somewhere between 10mm and 15mm of inward travel, so not bad at all there.

Thanks Louis, that is something I had dismissed from my thoughts, but perhaps I shouldn't dismiss it at all.
Do you have an image of the GSO with the spacer fitted at all?

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On 11/10/2019 at 00:47, Louis D said:

If funds are an issue, I'd do what I did and get the GSO/Revelation CC with a 25mm spacer tube.  It has a 65mm to 85mm separation distance where correction is quite good, so there isn't much need to find tune the separation visually.  I'd say for most eyepieces that focus within 5mm of the shoulder, I get about 95% or more reduction in coma, which is plenty good for visual usage for me.  I need somewhere between 10mm and 15mm of inward travel, so not bad at all there.

So a question to add please @Louis D, do you still use the GSO unit or has it been replaced with something more exotic?

Edited by Alan White
typos of course

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4 hours ago, Alan White said:

So a question to add please @Louis D, do you still use the GSO unit or has it been replaced with something more exotic?

Still using it.  The only quibble I have with it is that one of the thumbscrews stripped in the eyepiece holder because they're made of pot metal instead of brass or steel.  Luckily, there's a second one.  Don't over tighten the screws.

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To answer the OPs exact question...I've owned both the Paracorr MK1 and the ES HR coma correctors..at the same time.

Mainly using a CT8 f/4.5 scope, sometimes a 12" f/4,  I always felt the Paracorr had the edge over the ES for visual use...the image was a little cooler and more transparent (the ES added a very faint sepia tint). The ES slightly but noticeably degraded the image on-axis at very high magnifications using a 4.7mm Ethos eyepiece, but to be fair you don't actually need the correction at this magnification and are better off without either. But it can be nice just to keep it in the focuser to maintain balance or avoid faffing around swapping with extension tubes. 

Both are very well made.

Both give good correction with a 21 Ethos at f/4.5 and f/4. 

If you buy the ES secondhand make sure it has both the camera adapters. ES don't sell them as spares...I found out the hard way. 

The adjustment thread on the ES is very fine in comparison to the twist-and-lock on the paracorr, making it a bit of a pain to make large adjustments for perfection with different eyepieces, but to be fair the correction is good enough over a wide range of adjustment so as to just leave it set for your favourite low-power eyepiece. 

For photography I preferred the ES; the fine adjustment with an accurate scale then becomes a benefit. And the field is certainly very, very flat. It's as good as the Skywatcher aplanatic in this regard. 

In the end I sold the Paracorr simply because it raised more money and there was little point in keeping both. . 

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6 hours ago, rl said:

but to be fair the correction is good enough over a wide range of adjustment so as to just leave it set for your favourite low-power eyepiece. 

Sounds similar to the GSO/Revelation CC in this regard.  Only my 12mm NT4 shows coma because it focuses about 19mm from the shoulder which is well beyond the 10mm on either side of the best correction zone which I've centered on shoulder focusing eyepieces.  The rest of my well corrected eyepieces focus within that 20mm band of best correction.

6 hours ago, rl said:

I always felt the Paracorr had the edge over the ES for visual use...the image was a little cooler and more transparent (the ES added a very faint sepia tint).

I've noticed a color tint when swapping the GSO/Revelation CC in and out of the focuser.

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3 hours ago, Alan White said:

@Louis D, do you think the Baader 28mm spacer would be ok.
FInding a 25mm in the UK is being a pain or costs a great deal more.

https://www.firstlightoptics.com/baader-planetarium/BhyperionTuningRing-2.html

The Coma Corrector from GSO branded Revelation Astro is on offer in the Uk at present, so very tempting.

Yes, the 28mm would probably be close enough for starters.  It's only a 3mm difference, and would only affect eyepieces focusing significantly above their shoulder.  There was an interesting thread on the GSO CC on CN recently and how screwing the optical nosepiece onto the bottom of the Baader 2" ClickLock with 2" CL Extension 47mm gives exactly the desired separation and you have a much nicer eyepiece holder to boot.

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@Louis D thank you for that link, made me smile as I had thought of exactly that mixture for my 10" Dob as well.
I prefer the price of the GSO (et al) CC to the Paracorr, but concerned I am wasting money trying.
I do like TV kit, just don't like paying the price required for that fine kit.

 

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29 minutes ago, Alan White said:

@Louis D thank you for that link, made me smile as I had thought of exactly that mixture for my 10" Dob as well.
I prefer the price of the GSO (et al) CC to the Paracorr, but concerned I am wasting money trying.
I do like TV kit, just don't like paying the price required for that fine kit.

 

I haven't tried a Paracorr in my Dobs, but I notice right away when I forget to put the GSO CC in the focuser and start observing.  My first thought is, why are my premium eyepieces showing so much aberration at the edges?  Then a moment later I realize I had forgotten the CC.  I slip it in, and all is right with the world again.  It does so well, I never feel the need to upgrade it.  Just remember to remove it for high power viewing (below about 1mm exit pupil).  I find the views sharper without it, but YMMV.

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