High mag lens?

[cyroflame]

Hello again guys! does any one know what lens i would need to reach my max 260x mag for a SW explorer 130p? so ar i got 180x, but says it can go to 260x where abouts could i find this lens capable of such things? i assume i need like a 3 or 4 mm lens?

[Chris H]

For x260 you would need a 2.5mm ep, divide the focul length of the telescope by the focul length of the eyepiece 650 / 2.5 = 260 magnification. Or focul length / magnification 650 / 260 = 2.5mm eyepiece. But that is a very high magnification to use, it will be a rare night when you could use a that in a 5 inch reflector. Also a 2.5 mm eyepiece will have very tight eye relief.

For the 130p scope I would take x200 to be a max and probably even then stick to a max power of x150 more often than not.

[John]

I agree entirely with what Chris says here - you will only be able to use 260x with a 130mm scope very rarely. 180x is a much more realistic max magnfication on most nights. This is due as much to the limitations of the average seeing conditions in the UK as much as any limitations with the scope. My 10" newtonian has a theoretical limit of 500x but the most I've ever used is 340x and I don't expect to exceed that.

[Andrew*]

I agree with what's been said.

What eyepiece are you using to get 180x in the 130P? If its focal length is 650mm, this would need a 3.61mm eyepiece. Are you sure you're not getting confused with teh 130, which has a f/l of 900, so the 10mm and supplied 2x barlow would give 180x? If you are using the 10mm and 2x barlow in the 130P, you are not getting 180x but only (650/10, x2) 130x magnification.

130x is a useful magnification for a few small DSOs, but I would recommend getting a 3mm or 3.5mm (186x-217x) as well for planets.

Andrew

[cyroflame]

Hi all thanks for the great comments as always, and yes i did get it wrong, with the 130p my highest mag is 130, so would like to get a lens piece that will give me 200x mag. I have a 2xbarlow so i assume i only need a lens piece that gives me 100x

so if my focul length is 650mm would this calc be correct

650/100=6.5mm eyepiece needed? then get 200 from barlow?

so would this eyepiece be adequate?

Skywatcher - Skywatcher SP Plossl eyepieces

[Andrew*]

It won't perform particularly well in your scope, but maybe a little better than the supplied 10mm or 25mm eyepieces. I think you will soon find the limitations of the eyepieces and need to upgrade. If you can put a little more money into it, or if you are willing to purchase second hand, I think you will be satisfied for longer.

I'm not really clued up on the better makes of plossl, but you should be able to get an excellent 6 or 7mm plossl or orthoscopic for under £30

HTH

Andrew

[Chris H]

I have a Skywatcher Heritage 130p and have found that barlowing eyepieces does not work very well at higher powers. Adding the barlow lens adds another layer of glass for the light to have to pass through and with the scope being a 5" its light grab is not partucularly large, adding the barlow simply made the images dim. For my 5" refelector the highest power eyepiece I have used was a 5mm (x130). IMHO If you want to go higher go for a 4mm (x162) but not any higher it would be a waste of money.

[Andrew*]

Good call re: the barlow. The supplied one seems to be a very variable product. If you have a bad one, replace it as soon as possible. A Tal 2x barlow would make a good, but reasonably priced upgrade.

Andrew

[Pete Presland]

i think the 5-7mm ortho is a great idea for high power planetary work.they are fery well recommended on here and turn up regulary,or maybe a televue plossl the change hands for £40-50