Best way to achieve 250x with 120mm f8.3 refractor??

[MartinB]

Wurzil, a decent barlow will serve you well. For planetary and lunar viewing you are sending the light through a bit more glass but I doubt very much that you will notice the difference between a 4mm plossel and a barlowed 8mm. I think your plan of addin an 8mm to your 10mm and getting a barlow is a good one. Given that your barlow can be used with all your EPs it's worth investing a bit of money in a something decent though.

[russ]

The main thing to remember from all this is that the sums are only a rough guide to what you can expect. Astronomy is science, and any science is all about experimentation. That's what makes it fun. There's no hard and fast rules that you must adhere too. You do what ever you want to do. Take the FR x 0.85 as a guideline to what should work and then play around and see what actually works best for you.

Not all scopes are the same, some will perform at their best beyond what that equation recommends (even if NASA say so). One example of the top of my head:

William Optics SD66 Apo. Has a focal ratio of f5.9, which means the recommended high power eyepiece is 5mm. This will only give 78x, yet the two SD's i've owned both achieved 105-120x. That was their sweet spot for a sharp and detailed view. Anything after more than that, regardless of seeing, was not as sharp. That fits in nicely with the recommendation of 50x per inch. But i've seen others post that their SD's were achieving 200X.

Another example is the Synta ED80. All mine (i have owned 5 of them) have achieved 180-200x on nights of good seeing and give or take, matched the view through a Skymax 127. With a FR of 7.5, the highest power eyepiece should be 6.4mm. But mine were working at their best with a TMB 3mm giving 200x or 66.7x per inch.

They are only very rough guidelines to give a rough idea of what should be possible. Martin's recommendation of a barlow is a good one. I bought a secondhand GSO 2x, it only cost £9 delivered and yet performs close to the Tal 2x i bought to replace it.

[great_bear]

-----------------------------

Celestron OMNI XLT 120

soft contact lenses

Do you take out your contact lenses when observing?

Whilst I miss the naked-eye views, I find the light-scatter on bright stars and planets is dramatically reduced when I remove my contact lenses.

[great_bear]

Whichever option you go with, I recommend dealing second-hand.

Eyepieces hold their second-hand value, so you can buy and sell in order to swap around and see what you like the most, and the only money you lose is the postage costs of sending an eyepiece onwards to its next owner.

It's a good way of "trying out" eyepieces you can't really afford to keep

- and "trying out" is important; Shane highlights the fact that there are more features than just optics to consider when it comes to eyepieces. Viewing comfort is extremely important. Also, whilst sufficient eye-relief is important (very few people get on with a 4mm Plossl or Ortho), it's equally possible to find an eyepiece unusable due to too much eye-relief (which leads to uneven illumination and kidney-beaning).

Then there's personal preference to contend with. For example, at around £170, the William Optics 16mm UWAN is considered a top-class performer, and is loved by many.

I've got one. But guess what? - I don't like it!

I think I just don't "get" the whole "superwide revolution". I find such wide views distracting and annoying. Give me a £30 32mm Revelation Plossl anyday! I just prefer the viewing circle to neatly frame whatever it is I'm trying to look at - instead of having the entire view bleed into my peripheral vision. One of the things I the most about (for example) Baader Genuine Orthos, is their precisely-defined 40° field-of-view.

But that's just me. My wife likes the UWAN, so I'm keeping it.

[Mark at Beaufort]

Warren the first thing I was state is that your scope, for the money, is one of the best buys available. I think it had a very high rating with one of the astro mags. The points made by Shane are very sensible and as you gain experience your judgement on different astro gear will improve.

With my 4" APO there has been nights of exceptional clarity that I have been able to use mags of 220x and the image of Jupiter remained very stable but these nights are rare.

Great Bear has also made some interesting and reasonable points about EPs which again shows that they are very much a personal point of view. I have two Ethos lenses 13mm and 8mm which I think are brilliant but others are no so keen. If you talk to Steve at FLO I am sure he prefers EPs with a 68 degree FOV. So horses for courses.

Certainly some of the higher power EPs have a narrow FOV and eye review and it feels you are looking down a straw when viewing objects. It is for this reason many visual astronomers buy a quality barlow lens so that they can use a medium power eyepiece to gain the extra magnification.

If you can wait you can always visit Astrofest in London which is next February and you will see virtually ever make of eyepiece available.

Finally if I was buying an EP for viewing the planets/moon and wanted a mag of around 150/160x with had good eye relief, colour correction and an ok FOV and not spend a fortune I would look seriously at the TMB planetary EPs. An example is here http://www.astronomica.co.uk/components/com_virtuemart/shop_image/product/TMB_6mm_Planetar_49d0ce3c085c8.jpg

Best of luck whatever you decide.

Mark

[russ]

I'll give another huge thumbs up to the TMB Planetaries. Owned the 2.5, 3.2, 5, 7 and 9mm. Just love them to bits for the money. I sold them and now have Antares and Baader Orthos. Can't deny they are good but i miss the 60deg field and 16mm ER from the TMB. The Ortho is not ideal for my dob.

[Mark at Beaufort]

Just in case anyone wants further information on the Planetary EPs here is a link which gives details.

Telescope-Service Eyepieces and Barlow Lenses

Mark

[Wurzil]

hi Wurzil

Thankfully I have ordered an 8mm Paradigm so this should work ok on the planets and maybe I will also occasionally use the 5.2 on planets when seeing allows.

Shane

whereabouts you ordering these from shane - i cant find them anywhere except from the manufacturers website.

also nice to hear from someone in the same boat as me - your experience with the omni pretty much matches mine. The 25mm that came with it is actually OK isnt it

Ive had some good views of jupiter with the 10mm plossl ive got as as well.

w

[Wurzil]

I cant possibly reply to everyone who posted on here - who would have thought that one little question could spawn so much useful info!!

So thanks to everyone who has replied - I have read all of what you have said and have digested it....so my wish list now looks like:

A quality 2xbarlow (second hand-if i can find a good one)

& A good quality 7 or 8mm EP (as my scopes max before losing detail is 7mm-and higher mag than that will only be good for splitting double stars and making things big but fuzzy in the EP)

Ill have a look at the TMB EPs, thanks guys.

Again the quantity and quality of the replies on this forum amazes me:hello2: Amateur astonomers must be the most friendly and informative bunch of people ever.

PS - great bear - my contact lenses are always in when I use the scope - theyre monthly sleep-in ones so i wouldnt normally take them out and put them back in again.

w

[great_bear]

A quality 2xbarlow (second hand-if i can find a good one)

A recommendation: The Celestron Ultima (also known as the Orion Shorty Plus) is a very good Barlow - a best-seller in fact - which you should be able to find second-hand for about £50. Of course, you can get other types second-hand - or even new - for less, but the Ultima / Shorty-Plus is an excellent Barlow which you would probably never feel the need to replace (make sure it's the Shorty-Plus not the basic Shorty)

my contact lenses are always in when I use the scope - theyre monthly sleep-in ones

Oh - I never got on with those. Good though they were, I just felt naughty going to bed without taking them out - like going to bed without brushing your teeth

[russ]

Ill have a look at the TMB EPs, thanks guys.

You can source the TMB's (TS HR Planetary) from Bern at Modern Astronomy. His price is very good, competitive with TS in Germany.

http://www.modernastronomy.com/eyepieces.html

Or the new Series II Burgess TMB 6mm from SCS Astro:

http://www.scsastro.co.uk/it080002.htm

I'll give another thumbs up to the Orion Shorty Plus/Celestron Ultima 2x barlow. It's a step up from the Tal 2x. But does cost twice as much.

Russ

[Moonshane]

whereabouts you ordering these from shane - i cant find them anywhere except from the manufacturers website.

also nice to hear from someone in the same boat as me - your experience with the omni pretty much matches mine. The 25mm that came with it is actually OK isnt it

Ive had some good views of jupiter with the 10mm plossl ive got as as well.

w

hi there

I'll send a PM on this as I don't wish to advertise - I understand that they may possibly be confirmed as available later this week.

[great_bear]

Russ,

What's the difference between the TS HR Planetary and the new Series II Burgess TMB?

[EDIT] Later: Scratch that Russ! I see the information is in the review at the bottom of the SCS Astro Page.

[Moonshane]

Russ,

What's the difference between the TS HR Planetary and the new Series II Burgess TMB?

[EDIT] Later: Scratch that Russ! I see the information is in the review at the bottom of the SCS Astro Page.

this is slightly off this thread but related to the review that great bear pointed us to above. I have read several times about flocking the inside of a newtonian OTA but this article refers to flocking the inside of the eyepiece barrels to improve contrast. can anyone please confirm what sort of material is used for this and unless this is readily available where I might get some?

cheers

Shane

[John]

this is slightly off this thread but related to the review that great bear pointed us to above. I have read several times about flocking the inside of a newtonian OTA but this article refers to flocking the inside of the eyepiece barrels to improve contrast. can anyone please confirm what sort of material is used for this and unless this is readily available where I might get some?

cheers

Shane

Here is a contact for flocking paper:

Telescope Parts UK

Be aware that flocking an eyepiece is a rather delicate operation and will almost certainly invalidate any warranty. If you dismantle an eyepiece do note which order the spacers and lenses go back in - I've noticed a few posts on forums where this precaution has been overlooked !.

[Moonshane]

cheers for that John

I will probably have a go at this. I was only thinking of a series 500 40mm plossl which is great apart from the distracting reflections off the barrel. this can be screwed off without affecting the lenses and I reckon flocked it would be much better. it only cost £25 so no great loss either way I suppose.