Spectacles and 100deg eyepiece off axis CA problem?

[E621Keith]

I just had my first session (white light solar) with my Borg 77ED and 12.5 HW this afternoon and noticed some horrendous lateral chromatic aberration (blue-yellow) when the sun is placed near the field stop. When I removed my spectacles and tried again the CA completely disappeared. It was clear the CA came from my glasses rather than the eyepiece. I'm aware of the off axis CA in my glasses in normal use, but it never affected observation because my previous widest spectacle compatible eyepiece were 65deg LVWs which were sufficiently 'on-axis' that CA from spectacles were negligible.

It seems like despite the HW having spectacles compatible eye relief, my spectacles simply can't cope with the 100deg AFOV. I don't know whether the problem is caused by the ultra thin aspheric lens in my spectacles or whether it's a problem with glasses in general. I will try to dig out my old pair of glasses with basic normal thickness lens and try again, but it's looks like a TV dioptrx is now on my shopping list.

Has anyone else noticed this problem with their 100deg eyepieces?

[alan potts]

Keith,

Is it not possible to observe without your glasses. That is a great deal of money for the eyepiece that I think you got in Japan, you must be very upset, I know I would be.

alan.

[Capricorn]

Cannot comment as I do not have a 100 deg anything.

Reason is that over the last few years I have read of many problems. not overly major, when you get above the 68-70 degree mark.

Generally it seems that above that the field of view is simply so wide that the observer cannot make full use of the field of view.

Most common remark is that to see the edges the observer has to move their head round to see everything.

To me that seems a bit pointless.

So I have never bothered.

The wider the field then the more difficult it is to produce an acceptable eyepiece also.

How many times is it said that the central 60% is nice and sharp, the edges being "soft", really means the eyepiece has a narrower usable field then is cliamed.

Cannot see the insertion of your glasses causing a great problem, they tend to be pretty thin so CA shouldn't be great. Also CA need distance to become pronounced, the seperation from specticle lens to eye/retina is small.

Can you view without the glasses ?

[mytola]

I've found similar problems when trying to use glasses with my 14mm ES 100deg. Solution for me is one-time use contact lenses for astigmatism.

[E621Keith]

Keith,

Is it not possible to observe without your glasses. That is a great deal of money for the eyepiece that I think you got in Japan, you must be very upset, I know I would be.

alan.

I wear my glasses to correct for my astigmatism. While it's possible to observe without my glasses, my astigmatism will blur the image a little bit. Luckily as it turns out, the lateral CA was not a big issue for night time DSO observing.

As it turns out, the lateral CA was not a serious problem when observing DSO at night.

Cannot comment as I do not have a 100 deg anything.

Reason is that over the last few years I have read of many problems. not overly major, when you get above the 68-70 degree mark.

Generally it seems that above that the field of view is simply so wide that the observer cannot make full use of the field of view.

Most common remark is that to see the edges the observer has to move their head round to see everything.

To me that seems a bit pointless.

So I have never bothered.

The wider the field then the more difficult it is to produce an acceptable eyepiece also.

How many times is it said that the central 60% is nice and sharp, the edges being "soft", really means the eyepiece has a narrower usable field then is cliamed.

Cannot see the insertion of your glasses causing a great problem, they tend to be pretty thin so CA shouldn't be great. Also CA need distance to become pronounced, the seperation from specticle lens to eye/retina is small.

Can you view without the glasses ?

The central 95% of the HW was sharp. At least as sharp as the LVW13 on axis. The lateral CA was a problem with my glasses rather than the eyepiece, as those CA were absent after I removed my spectacles. My specs have off axis CA issue outside of the central 40deg, it becomes a objectionable around 40 deg off axis. When I look at white street lights at night, I can see the street light split into a blue image follow by a white image and then a yellow orange image near the edges of my specs (around 50deg off axis). It's annoying but I've learned to live with this and I usually rotate my head to face the object when it's that far off axis.

This was not a serious problem before as none of my previous eyepiece allowed me to see more than 35 deg off axis. My 82deg S5K UWA didn't have enough eye relief for spectacles, so this problem never surfaced. This only became a problem now when I can see 40-50deg off axis with the HW.

I can see the whole 100deg field by moving my eyes only and doesn't need to move my head. The larger field also made focusing a lot easier, because I have a better chance of getting a brighter star in the FOV compared to the 65deg. I can view with out my glasses when but my astigmatism will affect image quality. It's not a problem in my F10 SCT as the exit pupil was only 1.3mm, but my eye's astigmatism may become a problem in my f6 refractors.