Posts Made By: William Paolini

You've got a great lens...designed, my the accounts of many, a legend. Why not build a very special OTA for it. I have recently visited some of the old Alvan Clark refractors and love the look of the tube -- wide in the middle and tapered at each end, classic white, bolts all around it (you could put faux bolts). Would be really impressive seeing your lens mounted in something looking like this...would be a big draw IMO.

Michael,

Another interesting experiment to do with masks, is to mask the instrument down to other commonly available telescope sizes, like 114mm, 102mm, 90mm, then look at a variety of objects you normally observe on a routine evening to see if you still enjoy observing with that reduction in aperture (relative to light gathering loss and resolution loss). This would then tell you what is the minimum aperture APO you could really live with happily if you ever decide to spend all that cash on an refractor.

In my case, I have a 10" Dob which most of my observing is done in. However I have a 152mm Achro also and I did the downsize test for myself and determined for me, being used to a 10", that I could live with as little as 102mm but only for planets/lunar/doubles. If I was going to also use the scope for any DSO, nebula, clusters, Globs, then 127mm would be my minimum if I wanted to be marginally happy observing them with a refractor. So was an intersting experiment to ferret out exactly how I would feel using differing apertures as a general purpose observing instrument.

I've found it works best on DSO, actually really well in my 6" refractor. Tried it on Luna and Mars and didn't see noteworthy difference.

Pentax 30XW

http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Board/Eyepieces/Number/1374848/page/2/view/collapsed/sb/7/o/o/fpart/all

Paragon 30mm (if as good as the 40)

I had a 1.25" Paracorr at one time...not a Starblast though. I can tell you it is a very long tube that you insert. Don't recall if it ever entered the light path of my 10" Dob though. I did notice with it a very obvious loss of transmission though. Enough so that I eventually sold it since dim stars I could see without it on-axis were not visible with it.

Brian,

The inability to focus close as you get old, does not change the optical precision of your eye. i.e., if you have 20/20 vision, then when you can't focus close you still have 20/20 vision. The inability to focus close with age is due to the "drying out" of the lens and it then becomes less pliable so your eye muscles can no longer bend it enough for close focus.

In any event, as long as you don't also have astigmatism and such, this should have no impact at the eyepiece. It has zero impact for me...all it means is I always have a pair of the cheapie dollar store +1.75 diopter reading glasses in my pocket for when I need to read a chart or such.

Jim,

Indeed Tom was and is a legend, if not the best, and in many other ways also, including as a uniquely special kind and compassionate presence in this industry.

While many of his wonderful designs will continue to be marketed I'm sure, I would wager we will see many more fruits of his labor in the comming years. He was quite prolific from what I understand there are a multitude of innovative designs that if we are all lucky we will see in the coming years as his family settles the estate and continues the legendary legacy of this man.

A great loss for sure.

-Bill

I think you need to be willing to accept not feeling bad if you have an accident and don't mind the loss. If you are, then fine to try.

The most complex design I have taken fully apart is a Hyperion (8 elements). To start the process, the special tool to take the retaining rings off will make things easier and less prone to accidents. Otherwise a small sheet of metal that can span the ring to fit in the 2 notches or a fine screwdriver can work if you are extremely careful -- you accept the risk of not using proper tool.

Good to have soft cotton gloves as you will need to use your fingers on the glass many times. Just saves on re-cleaning time with fluids.

Very important to have a large work surface and a padded area to place all the components. Also good to lay them out in sequence so you know how to put them back in in proper orientation and sequence. Also good to note in writing or drawings if it is complicated where each component was in the housing.

One of the most error prone things I have found is not knowing what is going to happen as you take it apart and not knowing what is in there. These unknowns lead to most accidents. For instance, you never know if a retaining ring is holding a lense in place or maybe the EP housing itself when you unscrew it apart. So sometimes the 1.25" barrel is actually serving a dual purpose and acting as a retaing ring also, so if pointed down, then all the elements fall to the floor. So you must always be thinking about gravity impacts when you take something apart.

Also...even though same line, they may be retained in whole different ways. For example, the Hyperions do unscrew (after you break the glue bond) in the middle of their housings just below the rubber grip. For the 5mm Hyperion there is a seperate retaining ring which holds the upper elements in place. For the 17mm Hyperion there is no retaining ring so the lower body housing serves this dual purpose and all will cascade out if not careful once you unscrew.

Finally, after you get apart and clean and blow out dust and put together, you often dotice a missed dust partical and you need to take it all apart again :-0 This I find quite common. So expect multiple attemtps unless you have a clean room and clean tools.

But is certainly is possible even for complex eyepieces. The risk comes from one not being trained in this so skills are just rusty (it's not rocket science), using makeshift tools, and finally not knowing what is in there in the 1st place so the unexpected is always present.

It's fun though, once you get used to it...and rewarding I find as you can start improving some EPs and making them better gems by improving baffling, better blackening lens edges and housings, even experimenting with switching lenses and such. I've had some good surprises by playing with the elements. Case in point is the 5mm Hyperion...if you open it up, remove the lower 4 elements (so the 2 in the 1.25" barrel and the two large ones just above it) you end up with a 68 deg afov EP that is approx 28mm Focal Length, and is actually edge corrected better than the 24mm Hyperion! Down side is that the focal plane is deep inside and above where it stops on the focuser so when you put it on a 2x barlow, the housing of the EP bascially acts as en extension tube increasing the barlow's magnification significantly -- in effect it becomes a low mag wide field and a high power planetary when barlowed -- fun.

Good luck...but accept the risk, expect the unexpected, and also reap the rewards when all goes well.

-Bill

btw - I forgot to mention, am using this for lunar/planetary observing.

Alan,

There is an easy way to determine if the afov's are same or different. It won't tell you by how much, but at least you will know there is a difference.

During the day, together hold each eyepiece up to your eyes (like binoculars) so the field stop is seeable thru each eye. The image of course will just be white fovs. Your brain will see both images overlapping. It's just a simple matter then to tilt the eyepieces slightly towards each other so the FOV images overlap and then it's easy to "see" if one circle is larger or smaller than the other.

Tom T from over at CN told me about this trick, which he learned from TV folk. Very intuitive method and much more effective than trying to A-B two eyepieces thru the scope to tell if there is an afov difference.

-Bill