6mm or 5mm eyepiece?

[bendiddley]

Hi all. Can anyone help me with this? I want to get a high power eyepiece that sits at the maximum magnification for my telescope. I have a Skywatcher skyliner 200p dob (1200fl) which if the calculation (objective = max magnification) is right then my max mag is 200x. So to get 200x I need a 6mm eyepiece. I'm very interested in the BST/explorer eyepieces which have 5mm as the closest to this, but my question is, is this extra 1mm (which equates to an extra 40x taking it to 240x) going to be too much for the telescope and yield lower quality results or is there not much in it, so won't make much difference? Any thoughts?

[Stargazer33]

Hi bendiddley!

The theoretical maximum magnification for your scope is 2x the objective, or in your case 400x. However any mag over 240x isn't going to work that well in our climate and at our altitude - too much air and therefore water between the scope and the edge of our atmosphere.

You work out your magnification by dividing your focal length by your eyepiece size therefore a 6mm eyepiece in your scope would be 1200/6 = 200x. Going to the 5mm eyepiece would be 1200/5 = 240x.

Your scope could theoretically cope with this magnification. It would be about the maximum that you would want to push your mag for the UK unless you had a really, really clear night!

HTH

Bryan

[spaceboy]

^{Always handy to have an eyepiece giving you x200 for those nights when seeing and transparency is good. With your scope this would be the 6mm and I'd recommend something like an ortho unless you wear glasses that is and in this case maybe a radian. If this is the case you will have to look out on the S/H market as I think they stopped doing the 6mm Radian when the Delos came out.}

[Naemeth]

Remember that these limits are to a certain extent object limited. For example, the Moon takes magnification much better than Saturn (and practically everything else), Double Stars take high magnification well too. I've tried 325x on the Moon (Barlowing my 4mm for me) and it worked and produced quite a pleasing image, but no more detail was revealed than at 162.5x, it was really just bigger, image quality about the same.

[TheThing]

The 5mm BST is a very good EP and will give you a great image.

Back when I was starting out, everyone used to say don't go over 300x but now it seemed to be 200x. Being an awkward so and so, I regularly try to see the maximum I can get away with and have been know to view the moon at daft mags like 450x. Sometimes it works, often it's a train wreck!

I think you'd probably be ok at 240x in your set up.

TheThing

[John]

Ideally you would want both in your eyepiece set plus a 7mm. The seeing conditions govern what gives the best views at a given time and it's great to be able to step up, or down, the power to find that "golden spot" on that occasion. As has been mentioned, some objects respond to high magnifications better than others. Jupiter does less well than Saturn in this respect. Mars seems to need as much as the conditions will stand.

If you need to go for just one at the moment then I'd pick the 6mm as it's going to get a little more use than a 5mm I feel.

[Moonshane]

I'm with Hugh. I often use 'impossible' magnifications on the moon and doubles. with my 6" f11 I have used 533x on the moon and regularly use 400x on doubles with good success. the issue you may have is tracking manually at such mags. that said, if your bearings are smooth and you are seated there's no reason you cannot do so successfully.

that said many objects as stated above, need lower mags to either get them in the field or to provide anything like sharp detail more often than not. if on a limited budget (aren't we all?) then a barlow really would be a good move.

[TheThing]

533x?!? I bow to your craziness!

TheThing

[umadog]

As stated above, the highest useful power you can achieve on a given night depends on the object. So there isn't one single maximum number. 200x to 300x represents a reasonable range for observing Jupiter and Saturn. You want to tile that range in 2 or 3 steps. There will be nights when 240x is too much but 200x is just right. If you only have the 240x then you may be missing out on some views. There's no need to get them all at once, though. If you find a good 5mm now then go for it. Just keep in mind that there'll be a use for a 6mm and even a 4mm.

[moriniboy]

If you can afford them then get both.

IMO the 6mm will probably be used more due to the variable seeing conditions in the UK.

However I regularly use 5mm and below for viewing the moon, it depends on what you want to look at.

[Capricorn]

You really need several at the low focal lengths.

Sometimes a 5mm will be fine, sometimes a 6mm will be better, occasionally you will pop a 4mm in and see things pretty good.

The BST's are only in 5mm and then 8mm.

I would say that the 5mm will be OK as long as you realise that sometimes it will not be as good as you might like.

Possibly consider the TMB planetary's as they come in a greater range of options at the smaller focal lengths.

[bendiddley]

You really need several at the low focal lengths.

Sometimes a 5mm will be fine, sometimes a 6mm will be better, occasionally you will pop a 4mm in and see things pretty good.

The BST's are only in 5mm and then 8mm.

I would say that the 5mm will be OK as long as you realise that sometimes it will not be as good as you might like.

Possibly consider the TMB planetary's as they come in a greater range of options at the smaller focal lengths.

hi capricorn. do you know where you can get the tmb's from? i've seen skies the limit do them but have been unsure as to whether they are copies or not, which has put me off.

[John]

hi capricorn. do you know where you can get the tmb's from? i've seen skies the limit do them but have been unsure as to whether they are copies or not, which has put me off.

The HR Planetary eyepieces from Telescope Services in Germany are the closest I've tried to the original Burgess / TMB Planetaries that Thomas Back of TMB (now sadly passed away) designed:

http://www.teleskop-...Weitwinkel.html

The originals are no longer sold new as far as I know.

[Kef9]

I would go with the 6mm to start. Then if you feel you want more mag you can then make an informed desicion to go either to 5 or 4mm.

[bendiddley]

Thanks all for your comments. I didn't realise that there was so much potential for a range of high power eyepieces, actually helps me to stop worrying about which is 'the one', because they all have their purposes. ain't a cheap hobbey is it!

[ChrisThePuma]

I use the BST 5mm on my 150PL which has the same focal length - and i am very happy with the results.

[John]

...... ain't a cheap hobbey is it!

Try and avoid the lure of Pentax and Tele Vue eyepieces - they will really make dents in your wallet !

[bendiddley]

Try and avoid the lure of Pentax and Tele Vue eyepieces - they will really make dents in your wallet !

lol! my wallet is already dented from buying the scope and bits to get me started. but don't worry those EP's aren't even on my radar. hoping christmas and birthdays are going to help me build my supply of eyepieces.