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Several of my friends have commented at different times that at a similar magnification an eyepiece and barlow combo will show some Planetary's central stars much more clearly than an eyepiece by itself. I've seen this myself too a couple of years back, switching back and forth enough to say it was not atmospheric.

What makes this apparently work, does the barlow, by making an effectively longer FL system, reduce coma and therefore produce tighter star images, or what? Have others seen this?

Steven

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Barlows have little if any effect on coma. They do help reduce the off-axis astigmatism which some eyepieces generate when used in the steep light cones of short f/ratio instruments, but otherwise, they don't do anything for coma. On-axis, I have never really noticed much of a difference between Barlowed and unBarlowed systems as far as central stars are concerned, but I generally work at f/10, so the light cones are pretty shallow to begin with. Clear skies to you.

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David W. Knisely
Hyde Memorial Observatory
http://www.hydeobservatory.info

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Thanks Dave. Two seasoned observers independantly commented this and I saw for myself with one of their scopes that it was an obvious difference in seeing the central star, the second commented over the phone just the other day so I figured I'd ask around here and see what others may have noticed.

If one has an eyepiece to reach a certain magnification I would guess they may not be likely to use a barlow, if they have one at all. I don't have one as it does not work with a Paracorr.

Anybody have any ideas on how an improvement in seeing a central star of a Planetary Neb when using a barlow/eyepiece over an eyepiece alone, given the same or similar magnification? I don't know what optics were used since they were not mine, but surely both these guys don't have the same eyepieces or same type of barlow.

Any input is appreciated....
Steven

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Well, there might be something going on with the coatings, as they tend to be more efficient when light is coming in more towards normal incidence. There also might be some light scatter issues, but other than this, I don't quite know what would cause such a difference. I will have to check on this in a couple of weeks at NSP and try some different setups to see when this kind of behavior happens. That might give some idea of what is really going on. Clear skies to you.

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David W. Knisely
Hyde Memorial Observatory
http://www.hydeobservatory.info

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If one has an eyepiece to reach a certain magnification I would guess they may not be likely to use a barlow, if they have one at all. I don't have one as it does not work with a Paracorr.

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Steven:

I'm not sure why you say barlows won't work with a Paracorr adapter? I don't think there are any issues with combining them. I tend to use them separately because putting the two together represents a significant perpendicular stack. Adding a 2-inch Nagler on the end of that combo represents a serious collimation issue, IMHO. That's really the only reason I won't do it, honestly. I have combined them a few times just out of curiousity, and they seem to work fine together. Tele Vue even recommends a certain connection order. I don't recall if the Powermate/barlow is supposed to be inserted into the Paracorr or if it is the other way around. But the fact that Tele Vue even provides a recommended configuration suggests that they work together.

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Fiske Miles
Nikon 8x42 LX / 12x50 SE Binos
Mini Borg 60ED, TV-101, AT80Ach, XT-8, C11/CI-700, 22-Inch Dob
Way too many Nagler eyepieces
http://www.fiskemiles.blogspot.com/
www.fiskemiles.com

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So was this only on the tough to show central stars, or just any old central star in general?
Bill

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Let us know Bill....

I only use Televue Naglers (plus the 35 Pan)ep's, but both guys that commented on this apparent improvement use other designs which I have no first-hand knowledge of their performance, besides that one evening. Since Dave K. shot down the only suggestion so far for this effect being real, that the barlow has no effect on coma when it alters the light cone to a longer FL, then this effect might not be real. No other objects were viewed with ep/barlow that night that guy showed me the cs to conclude that the improvement was poor optics related v. optics manipulation related.

(Also, one should try hard not to point out flaws in another man’s optics if one wants to continue looking into said man’s optics…. (Well, there was that one time…, but that was someone putting a brand new 40mm, 1.25” barrel, 50 degree avof eyepiece in my scope when I was expecting an 80 degree afov. My friends still bring up the comments I made because the ep owner was right behind me when I looked for the first time not knowing it was really his ep. ))

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Mr. Wizard
Elements in Harmony I, an 8"f6 German Equatorial - Stellafane Winner,
II a 20"f4.2 Newt-Dob - Astrofest Winner,
III a 6"f3.5 Finder/Newt-Dob, and
IV a 36"f4.5 Newt-Dob - "If it's up there, it's in here."
www.DarkSkyObserving.com

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The one my buddy saw, and I happen to be there and see using his scope and eyepieces/barlow, was NGC 6543, the Cat's Eye. As for the other buddy who made a similar comment just last week, I'm unsure what object he viewed.

I saw what he said to be happening, but I don't know what optics these guys were using and quite possible they could have been using a poor high power ep and a good low power ep/good barlow, idk.

There might not be anything real happening here, but since two people found it to apparently improve the cs viewing (although possibly not real) I thought I'd toss it out there for people to comment. I don't have a barlow to investigate for myself if eyepiece quality is the root cause, or what else might be happening.

It may have just been an overall improvement in viewing but was attributed to cs's because that was the object viewed at the time it was noticed, I'll ask what high power ep's these guys use.

Steven

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Good, that object's central star gives me a "constant" to use in some tests (and will be well-placed for NSP). I did observe NGC 6543 a couple of nights ago in my NexStar 9.25, and the central star was visible pretty much all the time, although at certain magnifications, there were "sweet spots" where it seemed to stand out somewhat more. It appears fairly well at low to moderate power due to a brightening of a tiny inner shell right around the star that seems to help it a bit. At high power, it tends to come and go with the seeing, so even slight seeing changes might lead one to see an apparent change in visibility that was not actually due to some optical combination's effect. Of course, I use *really* high power on NGC 6543 (typically from 480x to as high as 744x), as that really brings out the inner arc-like detail in the main bright shell. Clear skies to you.

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David W. Knisely
Hyde Memorial Observatory
http://www.hydeobservatory.info

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At high power, it tends to come and go with the seeing, so even slight seeing changes might lead one to see an apparent change in visibility that was not actually due to some optical combination's effect.

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