4mm blur

Hi Folks,

This is definitely a nooby question I have a 4mm eyepiece which just presents a blur. Originally I thought it was just that I was hoping for too much from the small scope (etx70)it came with. But last night I used it with the 10" I saw this blur. It presents itself as if the image is alway out of focus. I was looking at Jupiter and the 25mm and 12mm gave lovely crystal clear images, I saw the two equatorial bands clearly with the 12mm.

With the 4mm I can move it through the focus point, but at it's best the image is still out of focus. When viewing the moon with it I can see detail but it is very dull.

What are the likely problems with this eyepiece? Am I the problem - expecting too much :whistle:

John

Hi John,

that 4mm eyepiece (or just about any 4mm eyepiece) is just a paperweight. 4mm is an unreasonable magnification to have, especially with a small telescope (small as in anything below 10" or 12" reflector, nevermind the ETX-70!). What you're seeing is probably a combination of either poor colimation, extreme magnification, bad optics or a small telescope.

I wouldn't worry about it and I also wouldn't bother with it!


Seanie.

*Moved to the Observing Equipment forum*

Hi Seanie,
This is great - I've learned something new already .
What would you recommend to be the largest mag (smallest FL eyepiece) to use with the 10" reflector.
I thought the collimation was ok - I'll get that checked in case.
John

Hi John,

Collimation is a problem at higher magnifications, so if your test appears to be 'spot on' (pardon the pun!) with your eye then you're ok as seen with a 32mm, 25mm or 12mm (whichever of these came with the scope as standard). With the 10" reflector I think the usual 12mm that would come with it (if it did) is fine. You could also go to 9mm. I have 12mm, 9mm and 6mm eyepieces that I have used with a 12" Dob and found that the 6mm is pushing the limits of decent magnified visibility. Even at that, the eye is not going to pick up the kind of detail you're hoping for anyway. Maybe an astrophoto would benefit from such magnification, but not by much in my opinion.

Sometimes, less is more! (less magnification offers a greater visual experience at the eyepiece)

Seanie.

Hi Seanie,
I haven't actually checked the collimation on this reflector since it arrived last May. I've only just finished the mount! It was in its box up to last week!
Although to the eye, viewing through a hole in a old film canister, it looked to be ok, I should really test it with a proper collimator.
It came with a 28mm 2" eyepiece, the others I have are 25mm,12mm,4mm (1.25")that came with the Meade.

I must try out a few different sizes at our (CAC) next meet and get a feel for what is reasonable.

Thanks for your advice - it is all very helpful.

John