Posts Made By: Mike Hosea

Greg Nowell said:
So now I pay attention because maybe someone out there is "seeing" something I'm going to be "seeing" pretty soon too.

Yes, this is very common, but as the years have passed it happens to me less and less. There's also a big difference between being happy with your equipment because you don't know "how the other half lives" and being happy with your equipment because in fact you do.
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Mike

Floyd Blue said:
I did not disassemble these, but someone that did stated that edges of the lenses were not all blackened and had rough edges. I cannot confirm this however and did not see this with a loop when I inspected them.

The edges are blackened, although as with most eyepieces, this can be improved upon. The eye lens is a singlet, however, and its lens edges are not blackened. This is true of most eyepieces which have singlet eye lenses, including, for example, most Abbe orthos (or all of them that I have disassembled, which includes the UO classics), and the 5mm Tak LE for example. There is nothing particularly "rough" about the edges of these lenses on any that I have seen, but generally (not specifically with BO/TMBs), one may see what appears like rough edges at edges of the cemented interface of a doublet, particularly if there is a deep "indentation" on the side at the interface which is not well blackened. Also, if a retaining ring or flange isn't wide enough, one can sometimes see coatings taper off around the edges of a lens.

Interesting that you like the Pentax XLs so much. I certainly enjoyed mine. I even went through Pentax XL-only phase for awhile, but it fell apart because of the field curvature in the 14mm and 21mm and just eroded from there. I sometimes wish I hadn't let go of my 5.2mm Pentax XL, but I wasn't quite as convinced of the superior contrast as you. Note that I don't have anything faster than f/5, however, and I'm not surprised that the B/TMB's weren't as nice compared to Radians at f/4.3. I find the edge of field correction in the B/TMBs a little lacking at f/5. Thanks for the observations.
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Mike

Floyd,

I don't read everything, so I miss a lot of "concern" like this. I think there are some requirements, like stating the equipment used and conditions. This puts everything in context, and you did that. It's not about absolute truth, its about "seeing". If you think you see something, it doesn't matter if we have it all figured out. The POINT is that I might think I see the same thing under those conditions with that equipment as well. We should all understand that "transporting" findings to different f-ratios and telescope designs is a tricky thing. People shouldn't get uptight about it. I can tell you about (the relative lack of) lateral color and field curvature of my B/TMBs in my 7" f/6.7 and 10" f/5. When somebody asks about using an f/4-ish Newt, we can cite your results. It will help. Please keep it up.
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Mike

I'm not familiar with the design, but I'm not sure that it's a problem. It's common to leave the lower quarter of an inch of threads unblackened for easy use of filters. Maybe you could post a photo?

If there are no optics in the barrel, I would turn the eyepiece upside down (just to be on the safe side) and remove the barrel, tape the outside, apply a flat black spray paint (blackboard paint looks pretty good and is harder, although a bit more gray than ultra flat black) from both ends, bake it dry, and return the barrel to the eyepiece after it cooled.

On the other hand, if there are optics in the barrel, it won't help to remove it, and you can't use spray paint (or at least I wouldn't).
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Mike

Mark Webb said:
Are they really high quality Japanese optics? Or, are they cheap Taiwanese just equal to other lower-priced budget moderate performance eps.

I asked the country-of-origin question on these in another forum not long ago. The answer was that they are not made in Japan as I had hoped, but I can't remember if they were made in Taiwan or mainland China. To me it didn't matter. My suspicion was that these were Vixen-branded, not Vixen-made.

This is one of those times when I think it is necessary to start with a simplified answer. I'm going to emphasize just two concepts.

The first thing to consider is the Apparent Field of View (AFoV). The bigger the AFoV the more using it is like looking with the naked eye, the smaller the AFoV, the more it will be like looking through a narrow tube. I'm not talking about magnification here, or how much of the real sky you can see, just how the image comes across to the mind, how it feels to look.

The second thing to consider is how sharp the design is wherever you look in the field of view. Most eyepieces are about as sharp as possible in the center of the view, i.e. stars are pinpoint in the center, but stars near the edge are smeared.

So, some eyepieces have wider AFoVs than others, and some maintain sharpness better than others as you look farther from the center of the field. Not surprisingly, these two things tend to be connected in the sense that if the sharpness at the edge is good, the designer may increase the AFoV until it starts to deterioriate.

In terms of sharpness as you look away from the center, in increasing (improving) order we would have Kellners, then Plossls, then Naglers. The ranking happens to be the same for AFoV because the designers increased the AFoV to take advantage of the sharpness that their designs could provide farther away from the center of the field.

More advanced considerations would be to sort out the particular classification of unsharpness (aberration) at the edge of the field and issues like contrast. Generally speaking, eyepieces with more glass elements tend to achieve better sharpness at a given distance away from the center of the field, but it is thought that more air-to-glass interfaces scatter more light, which reduces contrast. It's a tradeoff, but I don't want to get into "contrast" because it's one of those things that we tend to treat very subjectively, and people will debate ad infinitum which of two eyepieces has greater contrast. Point is that there is a reason why we don't just pile a lot of glass into every eyepieces. Also, more glass elements tends to be more expensive.

A faster f-ratio in the telescope will reduce sharpness in a given eyepiece at the edge of field when compared to using the same eyepiece in a slower f-ratio. So, we tend to recommend more complex eyepieces for faster telescopes because they tend to have sharper edge performance. Simpler eyepiece designs (fewer elements), often perform poorly at fast f-ratios, such as your f/5 telescope. Many amateurs have observed that what might have been their favorite wide-angle DSO eyepiece in an f/10 telescope just isn't acceptable at f/5. However, because planetary observation normally requires only a very narrow AFoV with the planet in the center, people often choose simpler designs for that specific purpose even in faster scopes (because the edge of field sharpness is not important).

Like I said in the beginning, this is simplified, but understanding the AFoV and away-from-center (off-axis) sharpness issues is key. I debated whether to add eye relief to make it 3 things, but like magnification, it's a concept that people tend to grasp immediately when confronted with any pair of eyepieces with dramatically different eye relief. You don't seem to have any short eye relief in your collection, but when you get a chance, just look through a 12mm Plossl or a shorter focal length.
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Mike

Just checked. In practical terms I would call my 7mm and 9mm parfocal. The 5mm required just a touch of out-focus from these other two, less than 1/8 of a turn of my Kineoptics HC-1 focuser.
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Mike

Richard Anderson said:

I know the new one is less than half the price of the Super Monos, is that the reason for issuing a second kind?

Here's what TMB wrote about that very subject:

http://www.burgessoptical.com/EPs/Planetary-TMB.html

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Mike

Bennett Burbank said:

I put them all back together just as they were

I understand that you think this to be true, but the ring of light suggests otherwise. Do you have the diagram? Maybe somebody can post it.
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Mike

No free lunch. Easiest to describe by example. Suppose that an eyepiece with a 50 degree apparent field of view when used in your telescope produces a 1 degree true field of view. When you use a 2x Barlow the apparent field of view will (hopefully) still be 50 degrees, but the true field of view drops to 0.5 degrees.

I said "hopefully" because some eyepieces cannot handle what the Barlow does at the edge of field and then the apparent field of view goes down a little bit also. People call this "vignetting", but that's a detail that only affects some eyepieces, i.e. one 25mm 50 degree eyepiece may vignette with a given 2x Barlow while another 25mm 50 degree eyepiece may not. The general principle, however, is if the magnification goes up by 2, the true field goes down by a factor of 1/2.