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Eyepiece/ Barlow for AR-80 640mm acro.


Adam J
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Rightly or wrongly just picked up a AR-80 640mm F8 acro up for my 5 year old to take a look at the moon with. Not letting him hang off the end of my Esprit. 

Going to throw it onto my AZGTI and hope for the best with the packaged tripod. 

Recommended max mag, eyepiece and Barlow please. Have a 12mm polssl and it comes with a 28mm that looks questionable. Was thinking a SV bony 2x Barlow with the 12mm on the moon? That pushing it too far?

 

https://www.bresser.de/en/Astronomy/Telescopes/BRESSER-NANO-AR-80-640-AZ-Telescope.html

Hopefully a nice match to the AZ GTI. 

Adam

 

 

 

Edited by Adam J
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1 hour ago, Louis D said:

At least eye floaters shouldn't be an issue for a 5 year old at high powers and small exit pupils like it can be for us gray hairs.

Yes unlikely to have any of those at his age, I believe it works out about 0.8mm pupil. 

Just trying to decide on the best 2x Barlow. Possibly looking at a used celestron Omni X2. 

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I went back and forth between this and a Mak, but at least this can be wide enough for some clusters like M45 etc. The Mak was moon and planets only at its focal length. 

Edited by Adam J
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That's Mak (as in Maksutov, the Russian designer or it).  I thought of the Apple product at first for Mac.  My next thought was, why the choice between a computer and a telescope for a 5 year old? :icon_scratch: Then I got it by your second sentence.  I'm a bit slow.

As far as Barlows, I'm a sucker for 1990s Japanese made Barlows only available used, so I can't really make any modern, off-the-shelf recommendations for them.

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1 hour ago, Louis D said:

That's Mak (as in Maksutov, the Russian designer or it).  I thought of the Apple product at first for Mac.  My next thought was, why the choice between a computer and a telescope for a 5 year old? :icon_scratch: Then I got it by your second sentence.  I'm a bit slow.

As far as Barlows, I'm a sucker for 1990s Japanese made Barlows only available used, so I can't really make any modern, off-the-shelf recommendations for them.

Just autocorrect on the phone.

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On 16/09/2022 at 08:46, Stu said:

I think the x106 with 12mm and x2 Barlow would be fine. Higher may well be possible but much less useable, particularly for a 5 year old. He should be pretty impressed hopefully 👍

Quick question. As I can only afford a cheap 2x Barlow £30 and a cheap 12mm eyepiece £25, looking at the one I have it's not even coated. Would I be better off just paying more for a 5/6mm mid range eyepiece 62 degree and forgetting the Barlow? Or is the acro lens going to be the limiting factor in either case. 

Adam 

Edited by Adam J
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33 minutes ago, Adam J said:

Quick question. As I can only afford a cheap 2x Barlow £30 and a cheap 12mm eyepiece £25, looking at the one I have it's not even coated. Would I be better off just paying more for a 5/6mm mid range eyepiece 62 degree and forgetting the Barlow? Or is the acro lens going to be the limiting factor in either case. 

Adam 

I think you would be much better off with one decent eyepiece, poor quality barlows can trash the image completely.

FLO has the BSTs at £49. Treble is they are only available in 5mm and 8mm, x128 and x80. I suspect you should just go for the 5mm but best to get input from actual owners as to whether the scope will cope with that power.

https://www.firstlightoptics.com/bst-starguider-eyepieces.html

I think @Mark at Beaufort has or had one of these so may be able to comment.

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39 minutes ago, Adam J said:

Quick question. As I can only afford a cheap 2x Barlow £30 and a cheap 12mm eyepiece £25, looking at the one I have it's not even coated. Would I be better off just paying more for a 5/6mm mid range eyepiece 62 degree and forgetting the Barlow? Or is the acro lens going to be the limiting factor in either case. 

Adam 

I probably would not push such scope past x100-120.

Quick calculation of CA index gives 2.53, so that is quite colorful. More magnification - more CA will be an issue, so it's best to keep it up to about x120.

In all likelihood with 80mm aperture and with young eyes, those sort of magnifications will be just right.

How about this eyepiece:

https://www.svbony.com/sv135-1-25inch-zoom-eyepiece-/

I've read good things about it - and it should cover wide range of magnifications

 

 

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On 16/09/2022 at 13:51, JeremyS said:

I’ll get my mac🧥 …..

 

Reminds me of the old joke:

A ship went down in the north sea in the night and the people on board got off in their night clothes only.

When picked up by a rescue vessel, one of the crew went down to the lifeboat to help people up the rope ladder.

One sweet young thing in her nightie was shivering, so the crewman hollered up to the deck, "Is there a MacIntosh up there to help keep this young lady warm?"

And a voice from the deck boomed back, "No, but there's a MacDonald here who's willing to try!"

Edited by Don Pensack
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14 minutes ago, vlaiv said:

I probably would not push such scope past x100-120.

Quick calculation of CA index gives 2.53, so that is quite colorful. More magnification - more CA will be an issue, so it's best to keep it up to about x120.

In all likelihood with 80mm aperture and with young eyes, those sort of magnifications will be just right.

How about this eyepiece:

https://www.svbony.com/sv135-1-25inch-zoom-eyepiece-/

I've read good things about it - and it should cover wide range of magnifications

 

 

Yeah am good with 100x and can ignore some purple. Just trying to get the best out of around 60-70 pounds in terms of eyepiece or Barlow and eyepiece combinations. I think that a wider apparent feild would be nice as it would show the whole moon at 100x.

Edited by Adam J
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4 minutes ago, Adam J said:

Yeah am good with 100x and can ignore some purple. Just trying to get the best out of around 60-70 pounds in terms of eyepiece or Barlow and eyepiece combinations. I think that a wider apparent feild would be nice as it would shot the whole moon at 100x.

That will work if you get well corrected eyepiece. Not much use of large FOV on lunar if outer 10% is soft and blurry.

Quick calc for that sort of thing goes:

you need 6.4mm or lower FL eyepiece to get x100 or higher.

you also need at least 60 degrees (or higher) to fit whole lunar disk in FOV as moon is half a degree so at x100 it will be 50 degrees. You want at least few degrees on each side for nice framing.

Eyepieces of those specs won't be cheap though.

5mm Starguider will fall short on showing full lunar disk as it gives x128 magnification - which makes moon 64 degrees and EP can only render 60 degrees.

Affordable "wider" lines are these:

https://www.firstlightoptics.com/skywatcher-eyepieces/skywatcher-uwa-planetary-eyepieces.html

https://www.firstlightoptics.com/bst-starguider-eyepieces.html

https://www.firstlightoptics.com/stellalyra-eyepieces/stellalyra-6mm-125-ler-eyepiece.html

I just checked all combinations - and none gives that whole lunar disk with a bit room to spare (in cheap category).
Closest feel to this gives 7mm SkyWatcher planetary (58 degrees AFOV):

image.png.20689e533f13c88d1caf718cb30e6b4c.png

But that is only x91 magnification

 

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2 minutes ago, vlaiv said:

That will work if you get well corrected eyepiece. Not much use of large FOV on lunar if outer 10% is soft and blurry.

Quick calc for that sort of thing goes:

you need 6.4mm or lower FL eyepiece to get x100 or higher.

you also need at least 60 degrees (or higher) to fit whole lunar disk in FOV as moon is half a degree so at x100 it will be 50 degrees. You want at least few degrees on each side for nice framing.

Eyepieces of those specs won't be cheap though.

5mm Starguider will fall short on showing full lunar disk as it gives x128 magnification - which makes moon 64 degrees and EP can only render 60 degrees.

Affordable "wider" lines are these:

https://www.firstlightoptics.com/skywatcher-eyepieces/skywatcher-uwa-planetary-eyepieces.html

https://www.firstlightoptics.com/bst-starguider-eyepieces.html

https://www.firstlightoptics.com/stellalyra-eyepieces/stellalyra-6mm-125-ler-eyepiece.html

I just checked all combinations - and none gives that whole lunar disk with a bit room to spare (in cheap category).
Closest feel to this gives 7mm SkyWatcher planetary (58 degrees AFOV):

image.png.20689e533f13c88d1caf718cb30e6b4c.png

But that is only x91 magnification

 

Was hoping for a ES 62degree 5.5mm used. Might put up a wanted advert. 

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5 minutes ago, vlaiv said:

That will work if you get well corrected eyepiece. Not much use of large FOV on lunar if outer 10% is soft and blurry.

Quick calc for that sort of thing goes:

you need 6.4mm or lower FL eyepiece to get x100 or higher.

you also need at least 60 degrees (or higher) to fit whole lunar disk in FOV as moon is half a degree so at x100 it will be 50 degrees. You want at least few degrees on each side for nice framing.

Eyepieces of those specs won't be cheap though.

5mm Starguider will fall short on showing full lunar disk as it gives x128 magnification - which makes moon 64 degrees and EP can only render 60 degrees.

Affordable "wider" lines are these:

https://www.firstlightoptics.com/skywatcher-eyepieces/skywatcher-uwa-planetary-eyepieces.html

https://www.firstlightoptics.com/bst-starguider-eyepieces.html

https://www.firstlightoptics.com/stellalyra-eyepieces/stellalyra-6mm-125-ler-eyepiece.html

I just checked all combinations - and none gives that whole lunar disk with a bit room to spare (in cheap category).
Closest feel to this gives 7mm SkyWatcher planetary (58 degrees AFOV):

image.png.20689e533f13c88d1caf718cb30e6b4c.png

But that is only x91 magnification

 

Also people on Amazon seem happy with these, but not sure the opinion of people on Amazon counts for much. 

https://www.amazon.co.uk/Svbony-Eyepiece-Telescope-Degree-Accessories/dp/B07B8KJ9KT/ref=mp_s_a_1_3?crid=3RM0VJCUXVHG1&keywords=6mm+eyepiece&qid=1663450023&sprefix=6mm+eyepeice%2Caps%2C75&sr=8-3

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18 minutes ago, Adam J said:

Was hoping for a ES 62degree 5.5mm used. Might put up a wanted advert. 

I've got that eyepiece, and it is excellent eyepiece, but I don't think it will provide that feel that you are looking for:

image.png.4473e2a552225a40871f49f4c4d86022.png

It is really tight fit. Most of the time - FOV is not quite as big as stated by manufacturers, so you will probably struggle to fit whole moon in FOV.

Otherwise, if you accept that it's not going to give you whole disk at high mag - then yes, that is excellent choice - very sharp eyepiece and easy on the eye.

19 minutes ago, Adam J said:

These are known as gold line or red line eyepieces (Orion expanse clones), not good in fast scopes.

Some people say they are good in slower scopes F/8 and above (9mm being the best reportedly), while other don't recommend them.

There has been some reports of kidney beaning/blackouts with these.

 

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The 6mm and 9mm Red/Gold line Expanse clones are supposed to be pretty decent in faster scopes thanks to the integrated Smyth/Barlow lens slowing down the light cone.  However, they are poorly matched to the upper positive section leading to strong SAEP (kidney-beaning).

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13 hours ago, Stu said:

 

I think @Mark at Beaufort has or had one of these so may be able to comment.

I have a SvBony 90mm 5.5 Acho which I rate very well. I usually use a SvBony 7-21 zoom which works very well. To be honest I have never used my Televue Ethos 6mm EP  on this set up and my 3-6mm Nagler zoom has been used but it's been a long time ago and I cannot remember how it performed.

So for the money the SvBony frac and the EP are great value and I would recommend them for anybody never mind a 5 year old although I appreciate the owner has bought the scope. If I was thinking of changing the EP I would consider a zoom to Adam J.

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