12 replies to this topic

[gitane71]

Hi,

  I eventually intend to make an 8" f/10 achromat. 

I will not have money to coat the lenses.  I don't want noticeable coma.  So, I intend to make R2=R3 and use oil between the crown and flint and make it no faster than f/10.  I'm not so much worried about chromatic aberration as I am about light transmission and pinpoint star images.  

  There are a lot of new (to me anyway) and costly eyepieces.  I think of a 32mm or 50mm plossl as reasonable eyepieces for low power viewing.  I will not be spending $500 for an eyepiece.   What am I 'missing'?  What would be a good low power eyepiece for such a scope?  

  Thanks,

  Drew

[The Ardent]

The 32 ploss will work fine.

A nice 2” is the Pentax 40mm XL. It’s very lightweight and has good qualities, and will give you the maximum FOV possible (or close to it) And it’s a bargain on the used market.

[fishhuntmike]

I use a 35 panoptic, 31 nagler, and 20 ethos in my 8" f5.9

All perform well with pinpoint stars out to the edge or very close. All should work great at f10. The 35 is comfortable with glasses and easy for anyone to look thru with pin **** stars in my scope.

[fishhuntmike]

Congratulations on your project! I wish you great success! Im hoping to build a home around my 228mm f7.7 in the next few months (wood ota).

[Arthur NY]

I don't own one, but I'd look into the Explore Scientific 82° 30mm. I have the 24mm in that series and it's quite nice.

[bridgman]

I have an inexpensive Antares 40mm Erfle which has become one of my favorite eyepieces. It has a 65 degree FOV and IIRC the Erfle design should work well with your f/10 scope.

 

With a 2000mm focal length you're going to want long FL and/or wide AFOV eyepieces to get any kind of wide field view. A 32mm Plossl will give you 0.8 degree FOV while a 55mm Plossl or 40mm Erfle will give you 1.3 to 1.375 degrees FOV.

[dan_h]

I have a 6.5" f10 achromat that is my most used scope. I have not had issues with any eyepieces I have tried with this scope. 

 

For low power I have a 35mm Pan that causes some balance difficulties but give wonderful views. When I don't want to deal with the balance troubles I use a 32mm Antares Erfle, a 30mm Superview, a 56mm Meade Plossl, a 24mm Pan. and occasionally a 28mm RKE.  The eyepieces I use often depends on what other scope I may have out at the same time.  

 

At f10, most any eyepiece will work well and astigmatism and/or lateral color at the edges really isn't a problem.  

 

dan

[daquad]

If yo want to save money, try the Agena 38 mm 2" Super wide at $95.  Should be pretty good at f/10.

 

https://agenaastro.c...a-eyepiece.html

 

Dom Q.

[SeattleScott]

A 42lvw can be had for under $300 if you want a really nice eyepiece but don’t want to pay for a 41 Panoptic or 40XW. Not particularly heavy either. A noticeable albeit slight improvement over the 38 SWA in slow scopes.

Scott

[gitane71]

Thanks a lot everyone.  I really appreciate you help and information.  

I'll be referring to this a lot, trying to figure things out.  

 

ya, daquad, I will be  looking to save money.

Not familiar with the 40XL, but in just starting to learn about it, it sounds great, but ?

I assume they are now hard to find?  What do they go for, used?

 

And, a quick search, I didn't find the Antares 40mm erfle.  are they still made?

 

38mm Agena SWA......looks very interesting !  and thanks for the link daquad !!  

 

Thanks a Lot everyone !  

[gitane71]

any opinions on the 38mm erfle sold by Surplus shed?

[bridgman]

And, a quick search, I didn't find the Antares 40mm erfle.  are they still made?

Looks like they don't make it any more, unfortunately. It was a 6 element EP while most Erfles are 5 element, although there is still debate about whether it was better or worse than other Erfle EP's.

 

The closest thing these days seems to be something like the GSO Superview EP's, eg:

 

https://agenaastro.c...w-eyepiece.html

 

There is also a 55mm Superview which according to the numbers should give you an even wider field of view, but I'm having a bit of trouble with the numbers (they suggest a bigger field stop than I think can be fitted into a 2" barrel).

 

any opinions on the 38mm erfle sold by Surplus shed?

No experience with it but looks good at first glance. Only consideration is that it seems to have a fixed eyecup which lowers eye relief down to 16mm. The thing is that for a lot of people too much eye relief gives them problems finding the right eye position to avoid blackouts, while for other people (like me) the much larger eye relief of other eyepieces in the same range is more of an "ahh, finally" thing.
 

[gitane71]

Thanks, John !

That 42  Superview looks great and I Like the price !!   

That may be it !!