# Thread: 42mm Orion lanthanum EP use?

1. ## 42mm Orion lanthanum EP use?

Club has a 42mm Orion 2" Lanthanum EP for sale for \$40. Seems like a good deal. Scope is 1200mm though so that would only get me 28x.....smallest I have now is 25mm. Question is....Is there a use at 28x and what might those be?? Mostly hunt DSO but never know might venture out.

3. ## Re: 42mm Orion lanthanum EP use?

I think you might want to calculate the exit pupil on that one, Doug. Too big an exit pupil is gonna let the secondary mirror shadow show up as a dark splotch on brighter stuff and otherwise offer a little light loss.

Exit pupil is aperture (in mm) divided by your magnification.

If that eyepiece gets you above 6mm exit pupil, might want to take a pass on it.

A good calculator is here: N.A.A. Telescope Math Calculator

5. ## Re: 42mm Orion lanthanum EP use?

Originally Posted by BrokeStarGazer
Good article here, buddy: A Pupil Primer - Sky & Telescope

6. ## Re: 42mm Orion lanthanum EP use?

A good eyepiece for a longer focal length refractor or SCT/ Mak, not so good for most reflectors though.

7. ## Re: 42mm Orion lanthanum EP use?

I think you might want to calculate the exit pupil on that one, Doug. Too big an exit pupil is gonna let the secondary mirror shadow show up as a dark splotch on brighter stuff and otherwise offer a little light loss.

Exit pupil is aperture (in mm) divided by your magnification.

If that eyepiece gets you above 6mm exit pupil, might want to take a pass on it.

A good calculator is here: N.A.A. Telescope Math Calculator
Well just when you think you kinda know something about telescopes this comes out of left field and makes you realize you know nothing.

According to the calculator
Optimum mag 63x - 133x
19mm - 9mm EP's
Min mag 37x which is a 32mm EP.

Some good info to know

Thanks

8. ## Re: 42mm Orion lanthanum EP use?

This is a very good quality EP, and price is a steal. If you ever consider getting a good refractor you should grab it. I would

Not very useful for your DOBs as Gabby and Bryan indicated, since the exit pupil will be over 7mm.

9. ## Re: 42mm Orion lanthanum EP use?

I had this same EP in the Vixen version, the 42mm Vixen LVW. It is a sleeper EP that has very good performance even in fast F5 optics. In a shoot out I did using a 25" Obsession F5 classic the Vixen beat out a Meade 40mm Series 4000 SWA and a custom made Seibert optics 38mm 2" Obsevatory EP. I owned all 3 and only one was going to be the keeper. The vixen was the clear winner with the Seibert coming in a very close second. The Meade Series 4000 SWA was in no way a "slouch" of an EP and in it's time held high regard. I sold the Meade and donated the Seibert to a local college. The Vixen was my wide field sweeper EP used for low power viewing. From dark sites the so called secondary shadow was not noticeable in my F5 equipment. Even with the large exit pupil when using F5 equipment contrast was very good. Well corrected to the field edge which is the field stop or actually the 2" barrel of this EP.
For the price you cannot go wrong. I sold mine to fund astrophotography ventures and wish I hadn't. Get it and try it..if you don't like it PM me I'll take it.
JJ

10. ## The Following User Says Thank You to Johnny J. For This Useful Post:

j.gardavsky (03-08-2017)

11. Just a reminder - although the form factor of the Vixen LVWs, Baader Hyperions, and some of the Orion eyepieces (stratus? - not sure) are very similar, the optics are DIFFERENT - this isn't a case where the same eyepieces are sold under different brands.

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