Posts Made By: Roland Christen

Your images are getting better all the time. One thing, though: I always feel that I have to back off 5 ft from my monitor in order to appreciate your images because they just seem way too big for my eyes. I have taken the liberty to reduce your image to 1/2 size, and you can see that there is no loss of detail. In fact, the contrast goes up somewhat, and now you can see some detail that was not so evident before (upper left white oval - you can see what looks like swirling motion below it and to the left).

Keep up the good work,

Rolando

FPL53 is the most advanced ED glass with the highest V number, which allows a lens of fastest focal ratio to be made. It is the most expensive of the lot. FPL52 is an intermediate ED glass and FPL51 is a first generation ED glass, which is least expensive. OK4 is the Russian equivalent to FPL52.

The overall color correction is dependent on the mating element, and all of these glasses can be made into lenses with any kind of color correction from poor to essentially perfect. The only difference would be that the glasses with the highest V number would have the lowest sphero-chromatism for any given design and F-ratio. Therefore, for equal performance, the ED with the lower V number would need to have a longer focal ratio for equal performance.

Roland Christen

This is the major highway which encircles the southern part of the island. The picture shows a typical Molokai "Traffic Jam".

Whenever it rains, there are numerous places where the water races across the road and drivers are warned not to drive through. One has to make sure that there are enough food for a couple of days in case the rain persists, because you can get stranded on the east part of the island with no grocery store available.
Rolando

They are not here yet. They are a new product which is being made for me as we speak. Delivery is slated some time later in July. When we get them in, I will post info on this group, the AP Yahoo group and our web site.

Please don't call or e-mail the office on this since no sales info has been written up for our staff yet. There will be NO list for this product either.

Rolando

Closeup of the galaxy

Rolando

When I first started in this hobby, I had an eyepiece which came from an old Bausch & Lomb microscope. It was a 10x Widefield eyepiece (25mm FL). I thought that this was the most perfect eyepiece in existence, and never saw any aberrations in it. The images were crisp, clear and contrasty in all the scopes that I had at the time (a 3"F15 refractor and 8" SCT).

Now that I have been in the astronomy business for more than 30 years and seen and tested numerous eyepieces, I have a better understanding of what constitutes a good eyepiece. The old B&L Widefield is quite poor indeed. It is a simple Kellner design, and I don't know what made me think it was so great back then. It has ghosting, severe aberrations toward the edge, chromatic aberration, astigmatism, lateral color etc., and at 45 degree apparent field, it is not exactly wide field.

When you first start out in this hobby, everything is great. The longer you are at it, the crappier things become. That is the curse of this hobby (besides the weather).

Rolando

>>I bought Rutten and van Venrooji's book, Telescope Optics. What grabbed my attention was a chart on page 219 and another on page 221 that shows that contrast is higher in obstructed scopes vs. refractors at the highest magnifications possible with diffraction limited optics.>>

That comparison chart is actually wrong. In this chart, both curves are normalized at the low end (i.e. they start out at the same level). The real comparison chart for the obstructed scope would actually start at a lower level depending on the amount of obstruction. For instance, a 33% obstruction would put the obstructed curve at 80% of the unobstructed scope. This 20% reduction is carried all the way to the end point. If you place the curves this way, then the higher contrast of the obstructed scope at the highest magnification disappears, and the two actually become more equal.

What really happens is that the resolution increases a small amount for normally obstructed optics at a lower level of contrast. However, that small gain can quickly evaporate if any atmospheric induced aberration is present. The extra energy in the diffraction rings begins to degrade the resolution quite rapidly.

Some studies were done recently in optics that have extreme obstructions, 99% or greater. These obstructions result in resolutions far exceeding Dawe's limit, but of course with contrast and light grasp approaching zero. The idea then was to figure a way to filter or supress the light from the diffraction rings, leaving only the faint ultra-tiny central Airy disc. With such unorthodox methods, the researchers were able to sparate two point sources that were 10 to 20 times closer than a normal aperture would be able to separate. Essentially creating a 200" out of a 10" aperture.

Roland Christen

>>I can machine a new cell to a tolerance of +/-.0001" if I have to. So my question to you is this: What are some of the "points" to remember in fabricating a cell for a APO doublet?>>

The main problem is that metal has a much larger expansion co-efficient that glass. So, if you make a cell to fit the glass as close as .0001", it will seize up as soon as the temperature drops 2 degrees F.

In order for an aluminum cell to always clear the glass down to -20 degrees F, the initial clearance at room temperature must be .001" per inch of aperture. Therefore, for a 7" glass, the clearance must be .007". If you just want to go from room temperature to freezing, you can cut this in half, but you must allow for it. If you don't have enough clearance, the glass will seize up and eventually spring or bust in half.

The clearance of the glass to the cell is not really your problem with this doublet. When you have the lens aimed even slightly off the zenith, both elements will naturally slide towards the lowest part of the cell, and they will line themselves up properly, even if the clearance were 1". What is really the problem is the spacer thickness. This will vary ever so slightly, and will throw the collimation off 10 to 100 times faster than any edge misalignment.

Of course, any slight spacer shifting can be compensated to most extent by shifting one of the elements laterally. That is why their advanced cell has the "collimation screws", which are not really for collimating, rather they are for compensating for spacer thickness variation and shifting.

Even if you managed to make a very tight fitting cell, you will still have the exact same problem. It will not go away.

Roland Christen

The image is severely clipped at the low end of the histogram.

Rolando

The 10.5x70 and 15x70 binoculars are now available from AP, if y'all are still interested.

Rolando