5mm EP on a 6" F10 SCT

[steve_bham]

Would a 5mm EP be too much magnification on a 6" F10 scope 1500/5mm = 300x.

Or would it be ok for those rare time when see is very good?

[GazOC]

Its would be handy to have for the moon and double stars but the nights would be VERY few and far between where it would give useful magnification on anything else.

[steve_bham]

Hi Gaz,

Thanks for that, was going to use it just for moon etc. whats the highest mag ep that would be useful?

[Merlin66]

On my SCT's around 220 or so is pretty high enough magnification

A 6.5 or a 7mm plossl or ortho would do the job.

[steve_bham]

Thanks merlin, might try a plossl as am very happy with the 32mm one i have.

[Capricorn]

Would have said a 5mm on a 150mm f10 was too much.

If the image is poor I fail to see why it is worth while looking at the moon? Surely you still want a good image even if the moon?

Think that there has been a marketing plot hatched where someone claimed Magnification = 2xDia in mm. So others jumped on the same advertising.

You can put a 5mm in the eyepiece aperture and "get" 300 but the detail will be blurred and unusable. Would have said the maximum you would get is with an 8 or possibly 7 mm, but conditions would have to be good even then.

[GazOC]

TBH I've found on good nights I can push smaller scopes like 5" refractors up to x300 on the Moon without the image being poor, of course planets are a different matter.

[brianb]

I can't imagine ever using a 5mm EP on a f/10 scope except for collimating using an artificial star, or a natural star in exceptionally steady seeing. 50x per inch is just TOO MUCH for ANY target even if the optics and the seeing conditions are perfect.

[steve_bham]

So would the 7mm of the below be the max "useable"

Skywatcher - Skywatcher Nirvana UWA 82-degree FOV

[Mark at Beaufort]

Steve

Hope you are keeping well. I had a Celestron 6" SCT and if I was buying a new EP I think the 7mm Nirvana would give you good mag and a useful FOV. 214x would be good on the Moon and the planets. Useful with double stars as well. 23' arc minutes is very good for high mag EP. If you go much higher (eg 5mm) the number of times you would use it would be limited. If you going for a new EP I would opt for the Nirvana.

Hope we meet at the next star party.

Regards

Mark

[steve_bham]

Hi Mark,

Cheers for that. Glad its payday next friday

[steve_bham]

A bit off topic, but what are the benefits of Ortho EP? do they give sharper images. I know they have smaller eye relief.

[arad85]

They are a simple eyepiece so have less glass in the way. This leads to more contrast. Downsides are narrow FoV (40 degrees I think) and, as you pointed out, little eye relief.

[steve_bham]

Not got my head round the FOV bit yet, if they have 40 FOV would that show you all of jupiter or saturn?

[arad85]

Will show you all of the planets (they are supposed to be very good planetary eyepieces), but may not show you all the moons, depending on their phase.

[brianb]

if they have 40 FOV would that show you all of jupiter or saturn?

Oh yeah, the 25 degrees of a monocentric will do that even in a huge scope.

Jupiter is less than one minute of arc across, so is the long axis of Saturn's rings. At say x300 one minute of arc in the sky is 300 minutes or 5 degrees in the eyepiece. So Jupiter will fit more than 8 times across the field of a 40 degree EP ...

Unless you need to wear glasses for astigmatism, orthos have plenty of eye relief in sizes down to about 8 or 9mm which is about as short as you need on an f/10 scope. The Baader Genuine Orthos are excellent planetary EPs irrespective of price, at their upper budget price level they're a steal.