2in vs 1.25in EP's

[TycMozo]

I know there is a lot of chat and advise about recommended EP's so i don't want to ask questions that have already been answered but there are a couple of points i'm unsure about.

I managed to get about 10 mins of clear sky last night and although i don't think the seeing was very good, i was shocked at the poor clarity of my 10mm EP. With the 25mm everything looked crystal clear but with 750mm f/l viewing was no better than with the naked eye (x30 mag). Swapping to the 10mm i assumed i'd get x75 but the image was almost 'smokey' like looking through a foggy day, and with the x2 Barlow it was very poor. I tried to view what i'm sure (Stellarium) was Mars but it was barely distinguishable as an orange coloured disk.

I have read others reports that to see any kind of detail i need at least x250 magnification and the only way to do that is with a 3mm EP (or would a 6mm and a x2 Barlow achieve this ?).

Now obviously i need a new EP, i have a Crayford focuser which is both 2" and 1.25" so my questions are:

a) Is a 5mm 2" Ep equivelent to a 3mm 1.25" - in other words are there any advantages to buying a 2" eyepiece (larger aperture ?) over a 1.25" one.

Should i buy a 3mm or a 6mm and a decend Barlow x2 or x3 perhaps.

I should add that the 25mm, 10mm & x2 Barlow that i have are the 'Super' type that i believe come with the Skywatcher Explorer 150p.

Thanks in advance.

[Moonshane]

a couple of points in answer to yours:

Mars is always (usually) challenging in all scopes and is currently moving away from us, therefore really small even for Mars (and increasingly so as days go by). The detail only emerges after prolonged viewing. I agree that 200x+ is required to get a decent level of detail but the polar caps are visible at much lower magnifications.

The 10mm eyepiece is generally seen as poor but should give a relatively crisp view on its own. if held up to a light (the eyepiece) does it appear clear?

2" and 1.25" refers to the (usually shiny silver) nosepiece size of the eyepieces - i.e. the bit you insert in the focuser. the magnifications are the same with a 20mm 2" and a 20mm 1.25" eyepiece but the view can be wider, depending upon the design. to get a good quality 2" eyepiece can be expensive but you don't really need them unless you crave wide views.

hope this helps a bit.

[Capricorn]

To get 250x means 3mm eyepiece, that also means the eyepiece has to be good, and that in turn usually means expensive. And after all that there is still no guarantee that the eyepiece and scope will actually work well together.

I have read of Mars coming round into view twice since I joined SGL and each time there are more wails of dispair then whoops of pleasure. About a 3:1 ratio.

If you give up on 250x and stick to 150x then the BST explorer comes to mind. Someone asked about the Lacerta eyepieces from 365 Astronomy, they are described as planetary and are £47 a piece. If you were willing to chance it they do a 4mm and a 3.2mm, so 187x and 234x. Just short focal length eyepieces are best considered a bit of a gamble. They do 5, 6, 7, 8 and 9mm also.

[Moonshane]

ps. Saturn will be much more rewarding

[knobby]

ps. Saturn will be much more rewarding

Absolutely

[Frank the Troll]

You dont say what scope or lens you are using, so quite hard to answer, you just say the standard lens, so I assume you mean the one shipped with a skywatcher, these are fairly basic

Are you using 2" or 1.5"

A 2" is always going to be better than the standard 1.5" ones, also you should try to avoid using a barlow if you can, the less glass the better, I'm not going to tell you what lenses to buy, its a learning curve, but watch for the letters ED

Check my sig for lense ranges

[Jiggy 67]

Don't expect too much of Mars, at its best its very difficult to see any detail, also don't forget X250 mag is getting towards the highest mag you can use in the UK, you need really good seeing for that, but can be rewarding on a good night, you might want to lower your expectations a bit and Iwouldn't bother with 2inch, not much difference other than the price!!

[Frank the Troll]

Iwouldn't bother with 2inch, not much difference other than the price!!

Sorry, there's a big difference, its called FOV

[ollypenrice]

We saw nothing much on Mars last night with a 20 inch Newtonian. It can be like that.

It isn't true that you need at least 250x. It's nice if you can get it but a lot less, 180 to 200x, can be very rewarding on planets if the seeing is stable and the sky is clear.

The point about 2 inch EPs, as stated above, is that they give a wider field for extended objects, notably at low power. So a 2 inch low power EP has huge advantages over a 1.25 if you want to see wide in a large scope. For looking at planets on a high power a simpler EP with fewer elements is likely to be better - and cheaper.

Olly

[Jiggy 67]

Sorry, there's a big difference, its called FOV

Yeh I realise that, but there is a trade off and when the OP is talking about planetry magnification, FOV doesn't compensate for the difference in price and isn't as relevent, I would invest in a good barlow that would be good across a bigger range of ep's

[TycMozo]

Thanks all once again for the answers.

The 10mm does 'look' clear best as i can tell, i have treated it to a cotton bud and a bit of 'huff' as i'm guessing it was probably not getting much use from it's previous owner.

Hoping i can try again tonight and maybe *fingers crossed* get more than a ten minute window in the clouds.

[RikM]

With a 150P I find that about 150x magnification (5mm EP or 10mm + 2x barlow) are about the highest that I use other than in exceptional circumstances.