Posts Made By: Stephen Bolser

I am looking to spend $300 - $350 on a quality starter set of eyepieces for an 8"f6 dob. After a little research I put together two options.

1) Celstron Ultima 30mm, 18mm, 12.5mm, 2x barlow. This would give me focal lengths of 30, 18, 15, 12.5, 9, & 6.25.

2) Televue 25mm Plossl, 15mm Plossl, 2.5x Powermate. This would give me focal lengths of 25, 15, 10, & 6.


Any thoughts or other suggestions?

Just a visitor from the astronomy groups popping in to ask:

What type of bird is this?
My wife snapped this shot at a Wendy's drive through in Ft. Worth Texas.

Thanks,

Steve

While reading thru posts on Pentax eyepieces I found the following link posted by Mike Hosea.

http://www.pentax.co.jp/japan/tech/xo-xw/gif/p6-syusa.gif

Mike, I was wondering if you could explain these plots, I couldn't seem to figure out what properties of the eyepieces are shown. What is is X-axis, Y-axis? What do the solid and dashed lines represent?

I stumbled on a pictoral summary of the lense arrangements of the XW line.
I find it interesting that each eyepiece does not appear to be just a scaled version of the others.

http://www.pentax.co.jp/japan/tech/xo-xw/61.html

Thanks for the help,
Steve Bolser

Back in my college days I owned and enjoyed a set of Celestron Ultimas (30mm, 18mm, 12.5mm, & 2x barlow) From reading this forum, I found out that these are no longer being manufactured.

When recently re-entering the hobby I went the TV plossl route (25mm, 15mm, 11mm, & 2x barlow). I've had a love-hate relationship with these eyepieces...sharp optics to be sure, but not as comfortable to use as I remember the Ultimas being. Also, the field of view is restricted when barlowed...vignetting Mike Hosea called it.

I recently noticed that the Takahashi LE eyepieces come in similar focal lengths with similar field of view in a 5 element design like the Ultimas. Is this just coincedence? or is the family resemblence more than skin deep. The prices are twice what I remember the Ultimas being which makes me think no. But A-mart may help me out here. =)

Does anybody know?

Thanks,

Steve

After viewing explicitly with a 6” f8 scope for 2 years, I recently acquired an Orion XT10. As I have found out, careful collimation is much more important at f4.7 than at f8.0. The scope came with a Lasermate which helped in aiming the secondary, but was frustratingly “twitchy” when trying to adjust the primary. A bit of web surfing turned up the barlow-laser technique which works quite well, other than the need to run back and forth between the adjustment screws and viewing the target screen.
But, I recently noticed that the “donut” is also visible in the viewing window of the lasermate. It is enlarged, due to the barlow I assume. In fact, by chance, it neatly fills the 2nd of 3 rings in the viewing window(see attached image). Sure makes final tweaking a snap, and it doesn’t seem to be bothered by the less than snug fit of the lasermate.

OK, finally my question (hehe)

Is there anything technically wrong with this approach? A bit of web surfing did not turn up anybody else using this approach.

Thanks in advance for your comments.

Steve
Fort Worth, TX

The recommended Paracorr setting of 5(minimum height of tuneable top) is for when you use the Ethos in 1 1/4" mode. For 2" mode the Paracorr setting of 1(maximum height) is recommended.

Note that you should not need to refocus hardly at all when switching between a nagler and the ethos in 2" mode in the paracorr. Lets say you have a nagler 26mm T5. With paracorr set to 3, and focuser adjusted for nice pinpoint stars, remove the 26T5, adjust the paracor setting to 1(max height) and insert the ethos in 2" mode. There should be very little readjustment of the focuser neccessary.

The reason for this is that the whole purpose of the paracorr tuneable top is to account for the different positions of the eyepiece focus planes and move them to the optimal 54mm above the paracorr lense. So, once you know the correct paracor setting for one eyepiece and have the focus adjust for it, you can lock the focuser in place and stick in any other eyepiece and "focus" by moving the tuneable top and you will arrive at the correct paracorr setting for that eyepiece.

In effect the tunable top makes all your non-parafocal eyepieced parafocal to the paracorr once the tunable top is adjusted correctly for each eyepiece.


OK. getting back to your question of a parafocalizing ring...
You didn't mention which nagler you were trying to get parafocal with, but as an example to make the ethos parafocal with say the 17T4 and 26T5 you would need to add a 1/4" thick ring. Then the paracorr setting would be 3, same as for the 17T4 and 26T5 naglers. Whatever nagler you make the ethos parafocal with, you can use the known paracorr setting for that nagler.

Hope this makes sense.

Tim,

For me the 26mmT5 is probably the most comfortable Nagler I have used. Blackouts are a complete non-issue, unlike the 17mmT4 which I also could not live with. If you have used any of the Vixen LVWs, it has a very similar feel as far as eyeplacement...super easy and comfortable but with a much wider AFOV.

The only potential negatives to the 26T5 are:
1) Most eyeglass wearers will not be able to see the full 82deg AFOV. In fact I have to flip down the rubber eyecup to take in the full field without glasses.
2) There is quite a bit of pincushion distortion that takes some getting used to when panning around. I was really turned off by it when I first got the eyepiece. But after a few viewing sessions my eyes/brain got accustomed to it. Others have explained that this type of distortion was purposefully allowed in the design by Televue to achieve pinpoint stars to the edge of the field.
3) To get the sharp edge of field in a reflector faster than f/5 you will need to plunk down the $$$ for a paracorr.


Steve