Moving away from stock eyepieces for an 8 inch dobsonian

[jetstream]

6 hours ago, John said:

- Baader Classic Orthos in the 6mm, 10mm or 18mm focal lengths (around £50 each)

I like these, espc the 10mm.

[Charic]

...which makes that set in the classifieds good value for someone!

 

[John]

1 hour ago, Charic said:

...which makes that set in the classifieds good value for someone!

 

Ha, ha !

Are you related to this chap by any chance Charic ?

 

[Charic]

........fork handles, or four candles ? lol. great sketch from the two ronnies!

 

[Rick_It]

I also have a 8" dobsonian. I believe you can do with three eps; in order of importance:

1) A low power wide field eyepiece to find objects and to view large DSOs. I bought a 28mm/68° Maxvision (still on sale on display item - bresser.de). Do not go cheap here (Erfle) or the view will be horrible

2) A medium power general purpose eps. You should come close to 100x mag and close to but above 2mm exit pupil. So a 12mm-14mm eyepiece with at least 60°. However I'm seriously considering a zoom instead of a fixed focal lenght eyepiece. Perhaps I will buy a spotting scope and I will use its zoom on my dobson.

3) An high power eyepiece for hi-res. I have a 7mm orthoscopic, to be used also with a barlow.

[Charic]

I agree but using the focal ratio as my guide allows me to match the numbers particular to the scope.
f/6 suggests a 6mm 12mm and one for the wide angle,  I have 32mm?

On the 8" 200P Skyliner a 6mm provides 1mm exit pupil at 200x power, no issue there.
12mm provides 2mm exit pupil and 100x, very comfortable on the Skyliner, the sweet spot!
My 32mm is random to some degree? I could have gone for a 24mm if I kept doubling, but there are limits to the lowest useable eyepiece  one can use on a Newtonian before the secondary interferes with the image?  The 32mm in my case is just the actual size of the Sky-Watcher Panaview that was recommended,  and back then, my understanding and knowledge was a little less, though improving all the time!
The method I advise now is to find the entry pupil size for my dominant eye and multiply that by the focal ratio. This method provides an eyepiece whereby the exit pupil should be no wider than the entry pupil of the eye ( wasted light - aperture reduction ). My eye  dilation is 4.9mm according to the latest laser scan? so an eyepiece somewhere around 29mm would suffice, but as you can see, I have exceeded the rule of thumb that I have adopted, but then nothing is set in stone as to what's right, correct or best for every user. In your case Rick_It they suit you give or take a mm or two! Going any higher in the power stakes, I would half the ratio to give me 3mm eyepiece, but we know thats asking for a lot under UK skies, but its doable, even Barlowed looking at the Moon provides some detail.

Whatever methods we choose in our decisions over eyepieces, we can't change the laws of physics, you/we get what we get, if it works, fine, if not, why not, rectify and move on. Its the reason there's a good supply of second hand decent EP's on the market. Some folk have already been there, wanting, craving, expecting, from a certain type of eyepiece or brand only to find........"is that it!". We know whats right when its right, and when its right, its good, when conditions allow.

[alex1978]

20 hours ago, John said:

I'm giving a short talk to my astro society this evening on this very topic

The above are ones which, to me, give the best performance boost over the stock eyepieces per £ spent during the years that I've been testing eyepieces. There are many other options out there of course but I've personally tried the ones that I've listed so can vouch for those.

Hi John, many thanks for the list - wish I could have been at the talk, couldn't be more apt! The BST's really are sounding like winners. On my list to now try! 

19 hours ago, Charic said:

There is one fact that's true, John would not know how good/bad these eyepieces were/are without trying himself,  the same for you and I, and although John is fortunate enough to have a pile of EP's to be testing for the rest of his Years, we will never know until your hands on, and looking through!

I think the way to go is buy and try - FLO have told me they'll let me do that which is amazing. So will get a few and pick the fave! 

1 hour ago, Rick_It said:

3) An high power eyepiece for hi-res. I have a 7mm orthoscopic, to be used also with a barlow.

Thanks Rick_It - a good guide and one I'll be working towards. It seems to be the case on the very high powered ep's that the exit pupil will be less than desirable, but I guess that is the price I might pay with the 8 inch dob?

[Charic]

18 minutes ago, alex1978 said:

I think the way to go is buy and try - FLO have told me they'll let me do that which is amazing. So will get a few and pick the fave! 

That's good news!
I have no allegiance to either vendor, I don't profit from referrals, and I have the full set now, but in business, there's still competition and always will be?

[ronin]

First is really how much per eyepiece? Once that is decided you have likely reduced the options by a large degree. In simple terms you have:
£0 -£50:: GSO Plossl's, Vixen NPL Plossl, BST Starguiders.

£50-£100:: X Cel-LX (are more but I cannot think of them???), (got some) TV Plossl's, Altair Lightwave's

£100-£150:: ES 68's and 82's. Baader Hyperons(<< may just fall into the £50-£100)

£150+:: TV Delites, Delos, etc, Pentax.

Meade 5000 series are said to be good, check as there may be 2 Meade 5000 series of eyepieces running around, think they fall into the £50-£100 bunch.

That is about it for the commonly mentioned ones, Alan at Skies the Limit has other BST's and if I recall 365Astro sell others (Lacatera ?) but not sure of the brand and specification. Basically it is no use myself suggesting ES 82's if the idea is to spend no more the £50 an eyepiece. Equally if you intend to buy up at the £150 region once and once only then picking up the BST's is again irrelevant. £300 will get a Delos or the set of BST's.

Interesting that you had the Orion at 3.7mm, I nearly bought a couple of those some years ago but didn't, came out under another name or brand also (Widescreen sold them) but they never caught on.

Have left Ortho's out as they are a bit specialist and I assume that if you wantr one then there ia a specific reason for it.

 

[alex1978]

1 hour ago, ronin said:

Interesting that you had the Orion at 3.7mm, I nearly bought a couple of those some years ago but didn't, came out under another name or brand also (Widescreen sold them) but they never caught on.

 

Thanks for the ideas ronin - yes, the 3.7mm was a bit of a mistake for me. I think it was a question of wrong eyepiece for my scope. I haven't even looked into orthos! Might leave that for another day to keep more confusion at bay!