7mm 2" ep for f5 frac

[nightfisher]

Having nearly sold my 6" f5 frac and then changed my mind

i would like to get an ep around 7mm 2" fit, as i have a 15mm wide angle moonfish clone and a 32mm, and these two ep`s wont give me a lot much magnification, the budget would be no more than £70, prefer a lot less, any suggestions

[Stephen]

Can you even get 2" EPs that small?

[4lefts]

even the 8mm ethos is still a 1.25" ep right? though it has a 2" adapter?

[John]

even the 8mm ethos is still a 1.25" ep right? though it has a 2" adapter?

Yes thats right. The 13mm Ethos is the same. They are pretty bulky eyepieces though and need the support that the 2" fitting gives.

On nightfishers question, I wonder how the 15mm Ultrawide would perform with a 2x 2" ED barlow lens ?

[4lefts]

or, i know it's not 2 inch, but maybe you could find a 7mm nirvana? they seem to get good reviews and you find them on abs for about that money sometimes.

btw, what do you mount the st150 on?

[nightfisher]

John that might be an idea, get a x2 barlow, would an achromat barlow be worth trying?

4lefts, i mount it on my EQ5 and it works very well, but i have upgraded my tripod to the 2" CG5 tripod, so even more stable now

[A McEwan]

The Revelation ED 2x 2" Barlow at £37 from TH is a steal and performs excellently.

[John]

John that might be an idea, get a x2 barlow, would an achromat barlow be worth trying?....

I just think it might be worth a try Jules. The 2" 2x ED barlows are not too pricey and can be re-sold quite easily if they don't work out. The investment is quite low too - this one is just £37:

Revelation ED 2x Barlow 2"

The risks would be i) too much astigmatism and ii) not being able to bring the EP to focus with the barlow.

Anyway, it might be worth considering.

Edit: Ant beat me to it !

[nightfisher]

Yes thats right. The 13mm Ethos is the same. They are pretty bulky eyepieces though and need the support that the 2" fitting gives.

On nightfishers question, I wonder how the 15mm Ultrawide would perform with a 2x 2" ED barlow lens ?

or, i know it's not 2 inch, but maybe you could find a 7mm nirvana? they seem to get good reviews and you find them on abs for about that money sometimes.

btw, what do you mount the st150 on?

I just think it might be worth a try Jules. The 2" 2x ED barlows are not too pricey and can be re-sold quite easily if they don't work out. The investment is quite low too - this one is just £37:

Revelation ED 2x Barlow 2"

The risks would be i) too much astigmatism and ii) not being able to bring the EP to focus with the barlow.

Anyway, it might be worth considering.

Edit: Ant beat me to it !

Thanks for the heads up link, im very tempted, but im concerned about focus travel, also am i right in thinking by using a x2 barlow im turning the f5 into an f10, still might be worth a punt and if it dont work the imagers will buy it, and cheaper than a new ep

[A McEwan]

No, using a Barlow doesn't affect the focal ratio of the scope. It will still be f5. It does affect the focal length of the eyepiece though (or that is the effect anyway) so you get twiuce the mag, half the true field, and generally keep the same eye relief.

Ant

[nightfisher]

Gonna keep this idea in mind, but still think the barlow will prevent inward focus, also the st150 was bought for its wide field views, seems a shame to halve them, will 15mm be enough for galaxy hunting?

[A McEwan]

I'm sure I've read that a 2mm exit pupil is the best for study of deep sky objects. This would mean in your 150mm frac an eyepice of 10mm focal length or so. I would think that 75x and a nice large unobstructed objective would be pretty good for finding a host of galaxies. Once found, you may then want to increase magnification - which might take you to your proposed 7mm eyepiece (107x and 1.4mm exit pupil).

Ultimately, can you arrange to try some other observers eyeieces and see which focal lengths give he best DSO performance in your scope?

Ant

[damnut]

Hi Jules,

I have a 15mm 2" that I use on my ST120, I can barlow that to 7.5mm very satisfactorily.

Link below for you to play with regarding exit pupil , saw your 'pimped' scope for sale too!!.

Cheers

N.A.A. Telescope Math Calculator

[nightfisher]

Hi Jules,

I have a 15mm 2" that I use on my ST120, I can barlow that to 7.5mm very satisfactorily.

Link below for you to play with regarding exit pupil , saw your 'pimped' scope for sale too!!.

Cheers

N.A.A. Telescope Math Calculator

Thanks Damian, very tempted to give it a go, think i will.

Yes i decided to put the 150 up for sale, due to not using it very much, but its unique and i put it together for a reason, galaxies!

decided to keep it as its a good un

[RME1]

Hi Nightfisher

I live in the Hudderfield area and have a revelation 2" 2x ED barlow you can try out with your scope. I did find that I had to use it without the diagonal for my 2" E/P. If you are still interested give me a PM.

Richard.

[Gina]

N.A.A. Telescope Math Calculator

Thanks for that link - very useful