Eyepieces and 4" Fracs

[cyborg421]

Hi All,

A quick question, are there any size of eyepieces that are not suitable to use wth a 4" refractor. Currently my eyepieces range from 6mm Delos to 31mm T5.

Thanks

Simon

[foundaplanet]

Yes, the ones you have listed are terrible in them, you would be better off swapping with me for my old set of .965 orthos from the late seventies. I don't mind paying postage from my end.

[cyborg421]

Wow! .965 Orthos, my dream eyepieces.

It was a serious question though, any reason apart from balancing that here would be any issues?

Sion

[Mr Spock]

What kind of 4"? You'll need a decent apo to make best of those eyepieces. Maybe the question should be the other way round?

[cyborg421]

APM 100/800 or APM 115/805

Simon

[rwilkey]

Your eyepieces should work well in the APM. Clear skies!

[RikM]

You just have to take into account the focal lengths of your scope and eyepieces to make sure your exit pupils and range of magnification will be in a sensible range, and that the focuser will accommodate the EP barrel sizes.

[Qualia]

I sometimes worry about heavier eyepieces slipping in the diagonal when pointing the frac up towards the zenith and if paranoia overtakes me, I'll just swop over to something lighter. Apart from that, it's just as Rik suggests, a sensible range of field-of-view, magnification and exit pupil is good to work out so you have a coherent run of eyepieces. I also find a run of high mag eyepieces are very useful for planertary, lunar and double star work and a 50x eyepiece for general white light solar viewing.

[damnut]

As with rikm above, you have not mentioned the fl of the scope so with that lovely 31mm you may be below the useful minimum mag for your scope.

Enjoy.

[cyborg421]

The focal length of my scopes could be 800mm f8 or 805mm, f7.

Does that help answer my original question?

I am not good with calculating exit pupils.

Simon

[John]

I have eyepieces ranging from 3mm (Radian) to 31mm (Nagler) and all of them are very useful with my 4" F/6.5 and 4.7" F/7.5 ED refractors. The 31mm Nagler coupled with the 4" F/6.5 gives a 3.9 degree true field and, when used with an O-III filter, which show the whole of the Veil nebula in the field of view. One of my favorite views in this hobby

The 31mm Nagler has an exit pupil of 4.76mm with the F/6.5 refractor which is very usable. It's going to be perfectly alright with even the fastest of the options you are considering.

[damnut]

Links for you to play with - does all the calculations for you, just plug in the values..

http://www.stargazing.net/naa/scopemath.htm

http://www.12dstring.me.uk/fov.htm (remember to switch to visual view!)

[cyborg421]

Excellent.

Thanks for all your help.

Simon

[alan potts]

I have the same scope as you mention, 115mm and I have from 3mm to 41mm, all work well. I would not go to 2.5mm myself but I am sure on some targets it would work. I have not had a problem with eye-floaters myself but some do at the lower focal lengths.

Alan