Planetary Eyepiece for ED80

[Dave-Ryan]

I have a Skywatcher Equinox 80 APO and am thinking of buying a high power planetary eyepiece.

My question is would the TMB 3.2mm or 4mm be my better option?

[Capricorn]

I assume that it is the Equinox 80 Pro ?

Says;

Highest Practical Powre (Potential): x240

Objective Lens Diameter: 80mm

Telescope Focal Length: 500mm (f/6.25)

240x on a 500mm is close to a 2mm eyepiece equilant.

A 4mm would give 125x, the 3.2 would give ~155x

Would expect the scope to be good and handle 155x.

The point is that you are taking an eyepiece and adding it to a scope, they may have been produced/designed such that they simply do not operate together very well. Whoever diesigned the EP will not have done so specifically for the scope you have.

The safest would be the 4mm, less magnification, if you have a good barlow then you have to option to try for the quoted max but doubtful if it is of any use. However the 3.2 would give what I suspect you would like.

If you get the 4mm you will wonder about the 3.2mm, damn it 3.2 then.

Umm both?

That's what I did.:evil6: Bought a 4.3 and a 4.9 as I could chosse between a couple.

[SiriusB]

Hi Dave,

I have the plain vanilla skywatcher 80ed f7.5, i find a 5mm (120x) ep to be the best for planetary, i've pushed it to 200x plus on rare steady nights, but i don't think there's much if anything to be gained above 120x ish- the exit pupil gets so tiny for starters!

I use vanilla Orthoscopics for the planets- can't comment on the tmb's, but at least consider Ortho's.

& FLO sell Baader orthos i believe, which enjoy an excellent reputation.

[perrin6]

240 X for an 80mm refractor ? That's about 80X per inch and .33mm exit pupil - a very dim image. 50-60X per inch is usually considered the absolute upper limit and that's only for v. bright objects such as the moon and v. close double stars in v.good seeing conditions.

[russ]

I had both the 3.2mm and 4mm TMB's with my ED80. Used the 4mm more than the 3.2mm. So would play it safe with the 4mm for starters. Although my ED80 f7.5 was very happy at 150x on brighter objects.

Ortho's are great but they are an 'acquired taste'. I like them most of the time but there are lots that just don't get on with the pin hole view of sky and tight eye relief. I cannot get on with 3-4mm Ortho's. Things are silly tight at that focal length. I would recommend trying a secondhand Ortho first before shelling out a heap on the Baader. The secondhand University Optics and Antares HD Orthos are almost a match for the Baader anyway. And can be picked up for silly money.

[Moonshane]

If you can possibly stretch to a total spend of £200, then my recommendation would be a used 4-2 or a 6-3mm Televe Nagler zoom. Personally, I'd get the former if I were you with the scope you mention but if you are ever likely to buy a slower scope or one with a lot more focal length then I'd get the latter.

This will cover the whole range of high magnification, they have decent field of 50 degrees and good eye relief of 10mm. They are expensive but you get a whole lot of superb quality eyepieces rolled into one. BUT there's an argument that you could also get 5 TMBs for the same money so you pay your money and take your choice!

[A McEwan]

FWIW I regularly used 170-odd x on my ED80 when I had it, and could go higher sometimes too. I strongly believe that the "50x per inch" rule should now be discarded - optics have moved on so much.

[PeterM]

I use a 6mm TMB clone (one of the TS ones) and it works well some of the time with a x2 barlow lens but it is really pushing at the upper limit of what you might regularly expect to be able to use in the UK. If you want something shorter than 6mm a 4mm would probably be a safer bet.

[dmahon]

I've got the same scope and ordered just the other day a Nagler 3-6mm zoom.

Don't count on one coming up in the second hand market - I've been waiting for one for the last 2 months.

[Moonshane]

they do come up every now and again for about £200 but you have to be quick.

Telescope House have the 6-3 on offer at 9% off (£268) currently.

TeleVue Ethos & Zoom

I'll never sell mine it is truly superb on the moon in my scopes.

I have managed 500x on some occasions but usually it's best between 250-350x.

[Dave-Ryan]

I do have a longer focal length scope (10" LX200) but never really try anything under a 12mm eyepiece with that.

I think its looking like the 4mm.

Thanks for all your advice.

[Kef9]

I strongly believe that the "50x per inch" rule should now be discarded - optics have moved on so much.

I agree 100% with this!

I would also like to add that the nagler zooms are great eyepieces! Regarding your options stated, either would be good as I've heard people saying that the TMB's are great performers. I personally would go with the 3.2.

[Dave-Ryan]

Maybe I should just get both and have done with it.

I was just concerned that the 3.2mm might be pushing it a bit and not get used.

[Kef9]

155x is nothing. I push my C100ED to 450x some nights depending on how bright the target is. I suspect that if you got both you would not regret it. They are exceptional value for money and you can see how it goes. If you did then want to sell you could recoup most of your money here.

[Kef9]

Have a read of this.

http://www.cloudynights.com/documents/Burgesstmb.pdf

[Monty86]

I'll add another vote for the 3-6mm Nagler Zoom. I recently got one for my 6" f/5 Newtonian and I'm glad I did - it cost as much as the OTA but is well worth it. I generally use it at 6mm (125x) but when the conditions are right I can crank it up to 3mm (250x). Decent eye relief too and none of that kidney beaning that can come with wide FOV naglers.

[SiriusB]

Dave, i think your original enquiry was about a high power planetary eyepiece for your 80ed

FWIW I regularly used 170-odd x on my ED80 when I had it, and could go higher sometimes too. I strongly believe that the "50x per inch" rule should now be discarded - optics have moved on so much.

I agree optics have moved on, unfortunately physical laws stubbornly refuse to budge. An 80mm lens still has a resolving power of 1.45 arc sec, While i agree the optics will "take" >50x per inch, not sure such high mag will show any more planetary detail with an 80ed? Feel free to contradict guys, i won't be offended, & may indeed learn something!

If you can possibly stretch to a total spend of £200, then my recommendation would be a used 4-2 or a 6-3mm Televe Nagler zoom...

Sounds like a great idea, you could then play endlessly with the mag to see what works best for you.

155x is nothing. I push my C100ED to 450x some nights depending on how bright the target is. I suspect that if you got both you would not regret it.

Again, i agree the optics are probably up to it,-i've had 300x on the 80ed, but for planetary views?- can you really see anything more than at around 200x kef? & i also suspect if you get both you won't regret it- the 3.2mm would be good for globulars for example.

Just a little maths for you Dave, hopefully without confusing you.

Resolving power of telescope =116/d where d=aperture in mm.

=116/80= 1.45 arc sec.

A typical, & not overly optimistic resolving power of the eye is 4 arc mins- some people can do a lot better.

4 arc mins= 240 arc sec.

so the magnification required for us to resolve to the telescopes limit

is given by:

Mag= 240/1.45= 165x, as i said i consider this a little conservative,as many do better at the eyepiece than they manage with the naked eye(i certainly do)- you could try seeing what the closest naked eye double you can resolve is & substitute it in the equation?

Something else to consider is that planetary detail is generally lowish contrast so tends, IMO to wash out at a lower magnification than say lunar, or stars.

Just my 2pence worth, hope it helps.

[Andrew*]

I had the 600mm f/l version of the ED80 and a perfect planetary eyepiece for it was the 3-6mm Nagler zoom as it offered 100-200x. The scope was very happy with this magnification range, as was I!

Regarding the choice between the 4mm and 3.2mm, I think the 3.2 would be better. I think the 4mm wouldn't get a lot of use....

Andrew

[Kef9]

can you really see anything more than at around 200x kef?

Nope I can't see more but I just like a nice big planet in my scope! .....and its good for splitting doubles too.

It just increases the wow factor and your not really loosing much brightness either I find. For something like Jupiter though the 8mm TV plossl gives me the most superb sharpest view.

Next time im out im going to powermate the nagler zoom to get a 1mm eyepiece and see what the views are for a laugh. It will probably be terrible!