What size eyepiece for my 100mm achro

[RobertI]

I was recently viewing Jupiter using my Tal100RS, but unfortunately I have a limited range of eyepieces so I was either viewing with the 5mm BST Starguider (giving 200x with exit pupil of 0.5mm) or the 10mm Hyperion (giving 100x and exit pupil of 1mm). At 200x I felt that there was plenty of detail to see, but a combination of dimness of the disc and floaters in my eye was making the detail hard to spot. At 100x the image was brighter and floaters less of a problem, but the disc was too small to see the level of detail which I felt was achievable for the good seeing conditions. So my question is what size eyepiece would be a good middle ground? I was thinking possibly 7mm giving 140x and 0.7mm exit pupil (there seem to be a limited range of 7mm eps available). Would this be a good enough improvement? Would I get a brighter image using better/different eyepieces, meaning that 6mm might be achieveable? As far as budget goes, I guess I don't want to soend too much on an eyepiece for this scope, so premium eyepieces are not really an option.

Any thoughts on best sizes and types/makes to get me better views of Jupiter with the Tal 100RS would be appreciated. 

 

[nightfisher]

If you can find a used one the Antares 7mm HD ortho would be very good, also FLO are doing a promotion on the Vixen SLV range so worth a look, they have the 6mm but i think you are looking at 7mm ortho to hit the sweet spot

[Davesellars]

I always think that Jupiter looks good at around 150x. Perhaps see if you can find a second hand ES82 6.7mm?

[Ricochet]

In terms of brightness a 7mm is the right call, having twice the brightness of the 5mm and half the brightness of the 10mm. However, you may still see floaters with the small exit pupil. I guess the only way for you to find out is to try it. 

[Charic]

A 10mm perfectly matches the focal ratio giving 100x and 1mm exit.
A  5mm you have, my next EP would be twice the focal ratio so a 20mm, hitting the sweet spot, based on using the scopes focal ratio, thats how I would choose my first three EP's, Im sure refractors work on the same principle. After the first three, anything in-between is a bonus.

However, for an immediate solution either/or both the 8 or 12mm  Starguider (  the 12mm can be Barlowed for a 6mm ) would be  a good choice. 

[AndyH]

6 or 7mm would get my vote for the two big gas giants on a Tal 100rs. At least that were my experiences when i had a 100rs.

 

Andy

[Louis D]

Look into get an entry level binoviewer, a pair of 12mm to 25mm plossls and a 2x nosepiece from a barlow to overcome your floaters problem.

[RobertI]

Thanks for all the replies, very helpful, sounds like a 7mm should do the trick, I've just remembered i have fine tuning rings for the 10mm Hyperion which will take it down to around 8mm I think, so although not a solution, it may help to confirm I am moving in the right direction with floaters/brightness. The Vixen SPL's look good on sale, but even at that price they are almost as much as I paid for the scope! What are the Skywatcher Planetary UWA like? Bit more in the range I was looking at.  @Louis Dif floaters continue ti bug me then I may look t the bino route, I have aways fancied some and never realised the anti-floater properties. Thank you 

[RobertI]

Just an addendum to this thread, I have realised that my two Baader fine tuning rings coupled to my Hyperion 10mm will give me three possible focal lengths of 6mm, 7mm and 8.5mm so I can experiment to my heart's content to find the optimum planetary mag for the Tal100RS under good seeing conditions. I shall report back on my findings, if I ever get a clear night.

[Moonshane]

The cheapest and often most speedy resolutions often come from rethinking what you already have.

[wookie1965]

I have the same Scope I have all the BST'S I have found the 5mm no good at all the 25mm is brilliant. I have found a 20mm plossl which I'm going to try and I'm bidding on a meade 4000 12.5mm if I get that I will look for a 6/7mm that will do for me. I do have a BST ED zoom which I have not tried yet that is a 7 to 21mm so I will have good selection. 

[MattJenko]

FLO sale on Vixen SLVs right now. Just saying  

[Louis D]

On 4/22/2017 at 16:35, wookie1965 said:

I have the same Scope I have all the BST'S I have found the 5mm no good at all

One of the few negative reports on these.  Can you elaborate a bit on what you found to be lacking in the 5mm BST?

[wookie1965]

5 minutes ago, Louis D said:

One of the few negative reports on these.  Can you elaborate a bit on what you found to be lacking in the 5mm BST?

Everytime I have used it can never get my eye in right position seems like I`m searching around seeing eyelashes, half the FOV all the other`s are brilliant even the 25mm which was supposed be runt of the litter I find it great for searching the sky.

[Louis D]

2 minutes ago, wookie1965 said:

Everytime I have used it can never get my eye in right position seems like I`m searching around seeing eyelashes, half the FOV all the other`s are brilliant even the 25mm which was supposed be runt of the litter I find it great for searching the sky.

Sounds like SAEP, spherical aberration of the exit pupil.  I ran into similar problems with the TV Radian line during daytime usage.  It usually crops up with negative/positive designs when the negative smyth group doesn't interface particularly well with the positive group.  Since Paul Dellechiaie took over design at TV, none of their new eyepiece offerings have SAEP.

[wookie1965]

Just now, Louis D said:

Sounds like SAEP, spherical aberration of the exit pupil.  I ran into similar problems with the TV Radian line during daytime usage.  It usually crops up with negative/positive designs when the negative smyth group doesn't interface particularly well with the positive group.  Since Paul Dellechiaie took over design at TV, none of their new eyepiece offerings have SAEP.

It could be just a bad one I don`t know have to compare it with someone else`s saying that a friend who is a lot more competent than me sold his 5mm as well as he did not get on with it. 

[MattJenko]

A 5mm EP in a 200p is about x240, so not an EP that will work on every occasion, although that translates into mushy views, not the symptoms you describe.

[Moonshane]

Sounds like small exit pupil syndrome to me

[RobertI]

10 hours ago, MattJenko said:

FLO sale on Vixen SLVs right now. Just saying  

Troublemaker.  They do look really nice though, I don't have enough Japanese kit in my arsenal.

 

 

[Moonshane]

You're safe then as they are Chinese

[RobertI]

Had chance to test the 6mm and 7mm configurations of the Hyperion on Sunday under similar conditions to my original session. I found floaters were still a problem at 6mm but at 7mm I could 'tune them out' sufficiently for them to not to interfere. At 140x the detail was very good indeed with orange GRS easily visible, numerous belts visible and two prominent dark festoons in the North Equatorial Belt. For £100 this scope this is producing remarkable views!

Unfortunately I need the 10mm back for the C8 so the next question is which 7mm eyepiece? Sadly many eyepiece ranges seem to miss the 7mm size, including the Vixen SLVs which are on offer (blast) and the more budget BST Starguiders.  The Skywatcher UWA planetary eyepieces seem good value at £42 - anyone tried them?

Rob

[wookie1965]

1 hour ago, MattJenko said:

A 5mm EP in a 200p is about x240, so not an EP that will work on every occasion, although that translates into mushy views, not the symptoms you describe.

My 200p is F5 so the 5mm will give me a magnification of 200X still on the edge for skies in Britain. 

[ronin]

Different planet but the best I have observed Saturn at was through a Tal 100RS and an 8mm eyepiece - no idea which make it was. Although still relatively small the detail was very sharp.

Think that the problem is that an 8mm may work, so might a 7mm and so might a 6mm and on a good night and the right eyepiece so might a 5mm. For planets I have a 3.2mm (more to complete the BST set), 5mm, 6mm, 8mm, 9mm, 10mm, 11mm, 12mm and the usualy assortment of longer ones. Looks like I need a 7mm.

The 6mm is an Altair Lightwavre (think WO SPL clone), 9mm is an Antares Ortho, 11mm TV plossl, not sure what the 10mm is. The rest are BST's.

At a guess you will find you need a 6mm, 7mm, 8mm for the different times and conditions.