GTX 110 Voyager visual question


weems@...
 

Reading the description for the Voyager on the web site it says "the polychromatic spot radius stays well below the Airy disc limit for all visual wavelengths and over a field of almost 1 degree...without adding any extra optics (field flatteners) to the optical train." Since there are various eyepieces that will yield an exit pupil of less than 5mm but give a field of 3 to 4 degrees for this design, what will be the effect outside of the central 1 degree? Will there be coma, and/or color, or something else? I couldn't derive it from reading the technical design materials. 

There are some objects that span more than a degree, such as M45, or where it can be a goal to see multiple in a view (e.g., M81, M82, NGC3077). So, for that or wide field sweeping, would the TBD field flattener be needed?

Chip


Jeff B
 

IMO it will be a fantastic low power, wide FOV scope.  At those large exit pupils the aberrations in your eye (s) will dominate.  At those low powers, any color aberrations you see will be due to, again, your eye and the eyepiece.  Eyepiece off axis astigmatism will dominate at the edge.  There may be some field curvature visible, but, again, again, the power is low and will most likely be ignored.

I'm visual only and will sign up when AP cuts loose with the lottery announcement.

Jeff 

On Sun, Sep 18, 2022 at 10:13 PM <weems@...> wrote:
Reading the description for the Voyager on the web site it says "the polychromatic spot radius stays well below the Airy disc limit for all visual wavelengths and over a field of almost 1 degree...without adding any extra optics (field flatteners) to the optical train." Since there are various eyepieces that will yield an exit pupil of less than 5mm but give a field of 3 to 4 degrees for this design, what will be the effect outside of the central 1 degree? Will there be coma, and/or color, or something else? I couldn't derive it from reading the technical design materials. 

There are some objects that span more than a degree, such as M45, or where it can be a goal to see multiple in a view (e.g., M81, M82, NGC3077). So, for that or wide field sweeping, would the TBD field flattener be needed?

Chip


Roland Christen
 

The lens is coma-free, so there won't be coma at the edges of a 3-4 degree field. All lenses have field curvature, which means that the outer part of the image focuses slightly shorter than the middle. For imaging we would add a field flattener lens to bring the outer part of the image to a perfect focus. In the past, for visual we always relied on the eye not being able to resolve the Airy Disc of a star at low powers and generally most eyepieces at that time had some field curvature and astigmatism issues of their own. With most eyepieces you won't see these defects unless you have very sharp eyes. For instance, I have a 35 Panoptic that has a 40mm field stop that shows a 3.5 degree field. The power is so low (19X) that it won't resolve a star's Airy Disc or the inherent field curvature of the lens. For me it shows a nice sharp image.

However, now we have much wider eyepieces of 100 degrees and they produce high enough power so that small discrepancies of the Airy Disc (or star points if you will) may show up for people with sharp eyes. So, the only way to get really sharp stars at the edges of a 4 degree field would be to add a simple field flattener in front of the eyepiece. I'm working on that, a design that threads into the front of the Maxbright diagonal.In fact, there may already be something like this available from another manufacturer.

Roland


-----Original Message-----
From: weems@...
To: main@ap-ug.groups.io
Sent: Sun, Sep 18, 2022 9:13 pm
Subject: [ap-ug] GTX 110 Voyager visual question

Reading the description for the Voyager on the web site it says "the polychromatic spot radius stays well below the Airy disc limit for all visual wavelengths and over a field of almost 1 degree...without adding any extra optics (field flatteners) to the optical train." Since there are various eyepieces that will yield an exit pupil of less than 5mm but give a field of 3 to 4 degrees for this design, what will be the effect outside of the central 1 degree? Will there be coma, and/or color, or something else? I couldn't derive it from reading the technical design materials. 

There are some objects that span more than a degree, such as M45, or where it can be a goal to see multiple in a view (e.g., M81, M82, NGC3077). So, for that or wide field sweeping, would the TBD field flattener be needed?

Chip


weems@...
 

Thanks for the explanation. I suspected it might be something like that. Cataract surgery improved the sharpness of my eyes, and also the light transmission and color. But that still doesn't help increase my pupil diameter, so I have to use a wide field, higher power eyepiece to get the exit pupil into my range. It's good to know that an appropriate flattener is in the works. This will be an amazingly versatile scope. 

Chip


Roland Christen
 

I have the scope outside right now. With a 4.8mm Nagler 90 degree eyepiece I can just resolve the Airy Disc at 138x and the stars stay sharp to the edge of the field. I also have a 13mm 100 degree Ethos which provides 66x and the stars are just pinpoints until you get to the very edge. I can't even see the whole field in one get-go, have to physically move my eye around to see every part of the field. My 35mm Panoptic gives me 18.9x and the stars are again just pinpricks and totally unresolvable. With that eyepiece my eyes show some astigmatism because the exit pupil is almost 6mm. I can't really tell if they are out of focus because my eyes are not good enough at 6mm opening.

Rolando

-----Original Message-----
From: weems@...
To: main@ap-ug.groups.io
Sent: Mon, Sep 19, 2022 8:15 pm
Subject: Re: [ap-ug] GTX 110 Voyager visual question

Thanks for the explanation. I suspected it might be something like that. Cataract surgery improved the sharpness of my eyes, and also the light transmission and color. But that still doesn't help increase my pupil diameter, so I have to use a wide field, higher power eyepiece to get the exit pupil into my range. It's good to know that an appropriate flattener is in the works. This will be an amazingly versatile scope. 

Chip


weems@...
 

I was thinking of something like a 20mm ES 100, or 21mm Ethos that gives about a 3 degree field and 33X, with a 3.5mm pupil. The 35mm Panoptic would probably exceed my pupil opening, given my bright surroundings, although a 27mm would be another way to get close to 3 degrees and still have just a 4.5mm pupil. A 31mm Nagler would also get close to 4 degrees with an exit pupil of just over 5mm. 

The other interesting thing is that pushing towards the 100X per inch limit, which this will likely support, is going to need a 3X barlow, even with something as short as a 5mm. A short eyepiece with nice eye relief, like a 3mm Delite, will just barely start to scratch the potential at 51X per inch. Doubling that may be too much, and doubling a 4mm will only get to 76X per inch. 

It's rather boggling to wrap one's mind around the idea of a single scope that will support that broad a range of uses.

Chip 


 

Any size telescope set up at 100X per inch shows a dimished object in brightness (and not addressing the seeing conditions either), especially this 110 mm scope.  I suppose 100X per inch is only useful for double star observing, and brighter stars.


weems@...
 

Besides double stars, I’ve also pushed my Pentax 85 to 330x on Venus given excellent seeing. But I haven’t taken my 6” f9 NASA glass triplet beyond about 75x per inch. Seeing here rarely allows more than around 450x. 

Chip