Aspheric eyepiece

[sandycorgi44]

Ive seen something on Ebay called a new  4mm/10mm/23mm Aspheric eyepiece.    It says its one eyepiece so Im confused by how this is ?  Manufacturer is SVBONY.   The telescope I have is 150 x 75, so can anyone explain if this would be a good buy or not ?  

Thanks in advance for any guidance .....Never heard of these before.   

[alanjgreen]

Hi,

As your scope is f5 (750/150) then it is unlikely that these will be very good. Expect the outer 25% of the view to not be sharp

At f5 you should be looking at something like the BST starguider 

https://www.firstlightoptics.com/bst-starguider-eyepieces/bst-starguider-60-25mm-ed-eyepiece.html

(sandycorgi has the bresser table top reflector 150 aperture, 750 focallength fyi)

https://www.telescopehouse.com/bresser-messier-6-dobsonian-telescope.html?gclid=Cj0KCQiAieTUBRCaARIsAHeLDCTwJvYEqPzdDdb7BkM42aaRdFZWZyj_3xb4FNk67UxEK6CT78EPrtwaAl8cEALw_wcB

You will need to spend more on eyepieces as your scope is a fast scope.

Do you wear glasses?

[sandycorgi44]

Hi 

I wear glasses for reading but not for distance ( just had cataracts on both my eyes removed ), so no need for glasses except for reading for first time in 38 years .

I have Plossl's at the moment for eyepieces 25, 12.5 and 6.    Also have a Barlow X 2 

 

[sandycorgi44]

Missed out a lens there.....a K 9mm

[alanjgreen]

Ok, if you don't wear glasses for observing then you need eyepieces with min 10mm of  "eye relief"  (distance from top lens glass to eyeball), if you were a glasses wearer then min 15mm eye relief would be needed.

These eBay eyepieces you found don't even state what the eye relief is on them. 

I recommend you purchase from a good astro shop where you can get the full spec and determine if the eyepiece fits your needs.

if you read the bst descriptions then it states specifically that they work down to f5 so they will work with your scope.

so, check the descriptions to make sure f5 scopes are supported and check eye relief is at least 10mm.

FLO do deals on bst if you buy multiples and they come up on astrobuysell if you don't mind second hand (I think second hand is fine by the way)

[Ricochet]

I presume there is some way to choose the focal length that you want. I picked up a pair of 23mm eyepieces to try in my binoviewer. They are surprisingly good, especially considering the price. The 10mm is also supposed to be good but the 4mm has been reported to be of lesser quality. 

[alanjgreen]

1 minute ago, Ricochet said:

I presume there is some way to choose the focal length that you want. I picked up a pair of 23mm eyepieces to try in my binoviewer. They are surprisingly good, especially considering the price. The 10mm is also supposed to be good but the 4mm has been reported to be of lesser quality. 

Is your scope f5?

[Ricochet]

39 minutes ago, alanjgreen said:

Is your scope f5?

No, f6. 

From what I remember the edges aren't great at f6, similar to the edges on a standard plossl, but better than the 25mm starguider. (The 25mm starguider lacks a smyth lens group to slow the light cone and so isn't as good at low focal ratios as the rest of the line.) Eye relief seems quite long, but that may be due to the almost existent eye cup. Glasses wearers would have no problem but for people who observe without glasses it might be too long (is is for me). 

[Louis D]

I have a pair of the 23mm I use for binoviewing.  They are quite light at 1.5 ounces each.  They are quite good over the inner 50 to 55 degrees.  With the rubber eye cups removed, there's plenty of eye relief for eyeglass wearers like me.  I prefer them to my 26mm plossls because the eye relief is too tight with the eye lens being so far recessed.

Here's an older CN thread about the 23mm with a Bill Paolini quick review.

I don't have the 10mm, but folks on CN repeatedly praise it as well.

Here's the most recent CN thread on them.  CrazyPanda is adamant the 10mm isn't as sharp as the 10mm Delos.  Given that the Delos is also about 40 times more expensive than the aspheric, that's not surprising.

The 4mm tends to be the dog of the line with reports of chromatic aberration due to a poor design with a built in barlow on the 10mm.