4mm or 6mm eyepiece???

[KC Stargazer]

Hi,

I am about to buy a new eyepiece for my 150p and would like to know your thoughts? I have a mid to wide angle set (10mm 12mm 25mm and a nice barlow) at the moment and really want to boost the image size a bit. Am I being to greedy by wanting a 4mm? I don't have a big budget and this will probably be my last item I treat myself to for a while so I want to get it right.

Can anyone recommend a make of eyepiece that is mid ranged price and they are happy with.

Any help/advice would be great thanks.

Kirk.

[Bart]

Hi Kirk,

I also have a 150mm. 4mm is getting near to the edge of what provides good views in that aperature and focal length. I dont have one because my chosen ranges dont have a 4mm but have a look for Vixen NPLs, they get good reviews and good value at £30ish. They are not wide angle, that would be something you yourself need to decide.

Bart

[paul schofield]

Hi Kirk personally I think you would get more use from a 6mm. Or you could Barlow the 10mm or 12mm giving you 5mm and 6mm respectively. Personally I think 4mm would be pushing magnification to its limit. Good luck with your choice.

[Qualia]

I have found that for planetary observing my sweet spot of magnification is anything between 140x to 200x. For that reason, I have a 7mm, 6mm & 5mm. Nevertheless, I tend to use the 140x a lot more, than, say, the 166x or the 200x.

I think the 150P has a focal length of 750mm, right? So, just to throw a wobbly into the choice mix, maybe a 5mm will be your best shot?

[Naemeth]

The 6mm will probably get more use, but the 4mm will give you more satisfying when you can use it. I'm sure you'll be happy with whatever you choose .

[KC Stargazer]

Thanks guys,

I think i'll go for the 6mm and look at getting a 5mm sometime else.

Much appreciated!

[Ad Astra]

For what it's worth, I find that the more extreme the magnification the eyepiece has, the more finicky it is regarding good seeing and dark skies. Simply put, the high magnification lens will push your scope to the limit and your view will be more strongly affected by seeing (turbulence in the air), and light pollution.

To put it another way, the 4mm generates 50% more magnification than the 6mm (250x vs 167x on a 1000 mm scope). A 2mm change in EP focal length doesn't sound like much, but it is really a tremendous difference in magnification!

Field of view is likewise decreased by the same ratio. So tracking and centering your object in a 4mm is significantly more difficult than with a 6mm. Again, you are asking your mount to perform with 50% more tracking accuracy, just as you are asking your optical system to deliver 50% more magnification.

End result - you will get lots more observing time out of the 6mm, I think. Especially if you live in an area where light pollution and seeing are not often optimum.

Dan