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Posts Made By: Mark Peterman

August 3, 2005 02:16 PM Forum: Equipment Talk

Fast Scope - Bad Scope?

Posted By Mark Peterman

Just looking for a little nudging in the right direction on a scope purchase.

I have previously owned and used 2 dobs and a SCT being 8" f/6, 10" f/6, and 10" f/10 but now considering a 10" f/4.5 dob with a Discovery mirror.

Is the fast f/4.5 going to be dissapointing after using only f/6 and f/10 scopes in the past? Obviously I'm worried about coma and how much of the field will be crisp and "usable", especially on open clusters.

My viewing runs the full spectrum of planets, open and globular clusters, galaxies, and nebula.

My eyepieces will eventually be Naglers, Panoptics, and Radians.

Should I take the plunge or look for a slower scope?

Thanks,

Mark


August 4, 2005 08:47 PM Forum: Eyepieces

EP Recommendation for Fast Scope

Posted By Mark Peterman

I'm looking for eyepiece recommendations for a 10" f/4.5 dob.

Being a fast scope, for the best views, it sounds like I need to stick with the Tele Vue Panoptics and Naglers. ??? Does one work better with an f/4.5 than the other?

I would like to have around 50x, 100x, and 200x on the magnifications. I'm worried about going any lower because
I figure coma will rear its ugly head big-time.

I would like to keep eye relief above 12mm on all eyepieces.

My focuser will accomodate both 1.25" and 2" eyepieces.

I am not planning on using a Paracorr.

I've tentatively picked:

22mm Nagler (52x)
12mm Nagler (95x)
6mm Radian (190x)

Suggestions? Changes? Comments?

Thanks,

Mark

August 12, 2005 01:51 PM Forum: Eyepieces

Got a 10" f/4.5? What's your favorite EP's?

Posted By Mark Peterman

I have a Discovery PDHQ 10" f/4.5 enroute and am trying to make a final call on my first three eyepieces for it.

I'm into DSO's as much as I am the planets. I do not plan on purchasing a Paracorr anytime soon.

If you have experience with a 10" f/4.5, what have been the best EP's you've used with it?

Thanks,

Mark

September 2, 2005 01:51 PM Forum: Equipment Talk

Help with Sticktation

Posted By Mark Peterman

I have a dob that has a slight problem with "sticktation" in the altitude axis.

Once moving, the feel and motion is smooth. The problem is that the initial force required is more than what is needed to move/track so when looking through the eyepiece, you launch past your target.

This is a Discovery PDHQ dob, so it has large altitude bearings with Ebony-Star on Teflon.

I have read suggestions from car wax and armoral on the Ebony-Star to sanding the Teflon.

I don't care for the car wax/armoral idea so I was going to start with sanding the Teflon but what grit do I use? 80 grit for a rough finish or something finer like 200?

Are there other ways besides the two mentioned above for getting rid of the sticktation?

Any help is appreciated.

Thanks,

Mark

September 11, 2005 06:40 PM Forum: Equipment Talk

Barlow Question

Posted By Mark Peterman

Trying to decide between two Tele Vue Barlow's - the standard 1.25" inch 2x barlow and the 1.25" 2.5x Powermate barlow.

Besides the obvious magnification difference and the price difference would there be a visual quality difference when used with a 10" f/4.5 scope and the following EPs:

24mm Panoptic
13mm Nagler T6
9mm Nagler T6
6mm Radian

Thanks,

Mark

September 26, 2005 06:38 PM Forum: Equipment Talk

Polarizing or Neutral Density Filter?

Posted By Mark Peterman

I would like to turn down the brightness on Mars. wink

Which of these filters would work best for this purpose?

Would you forego both and get a particular color filter?

Thanks,

Mark

September 27, 2005 01:41 PM Forum: Eyepieces

What's causing my spike?

Posted By Mark Peterman

I will try to explain this the best that I can. I am interested in learning what is happening here.

Note: In case it is a factor, I have some astigmatism that is being corrected in my lenses.

The other night while viewing with my glasses, I noticed that when looking at a fairly bright and focused star, if I moved my head a little, a single spike would appear coming off the star.

Wondering if this was me or the eyepiece/scope, I turned my head 90 degrees and looked again. The spike appeared again, this time in the new direction that I had turned my head, so it was following the same orientation as my eye.

What do you think is causing this?

I haven't noticed this when wearing my contacts while viewing.

Thanks,

Mark

October 27, 2005 04:00 PM Forum: Telescope Making

To change secondary size or not???

Posted By Mark Peterman

I have a 10" f/4.5 dob that currently has a 2.6" secondary mirror. I am contemplating changing to a 2.1" secondary. The attached photo shows the current (top) performance and dimensions with the 2.6" secondary, and the performance and dimensions if I were to change only the secondary (bottom). The reduction in the obstruction (from 26% to 21%) is a plus (more contrast) but I'm not sure what to expect visually by the angular field of view of the 75% and 100% illuminated area. They are significantly smaller in size with the 2.1".

While not dedicated to planetary viewing, I enjoy the planets and spend time on them when they are in good position but I spend most of my time on DSO's. If it makes a difference, the scope has a 2" focuser but all my eyepieces are of the 1.25" format. (24mm Pan, 13 and 9 Nagler, 5mm TAK)

Would changing from a 2.6" to 2.1" secondary on this scope be of benefit or should I leave it as is?

Thanks,

Mark

November 7, 2005 04:59 PM Forum: Telescope Making

3-Point Cell vs 9-Point Flotation

Posted By Mark Peterman

In my never ending desire to "tweak" I am now looking at a mirror cell for my 10", f/4.48, 1.875" thick, Pyrex mirror.

Using the calculator found here:

http://www.digilife.be/club/johan.vanbeselaere/atm/optics/mirrorcell/Mirrorcell.htm

I get the following:


supported by 3 points on the edge = lambda/12
supported by 3 points on 70% of the radius = lambda/35
supported by 9 points flotation system = lambda/299
supported by 18 points flotation system = lambda/451

If we tolerate 1/4 of the Rayleigh tolerance (lambda/32 surface peak-to-valley), which seems reasonable, allowing room for other defects such as figure errors in both mirrors, bad seeing, etc., than this mirror should be supported by 3 points on 70% of the radius!


Is the difference in the 3-point lambda/35 and the 9-point flotation lambda/299 going to be something noticable at the eyepiece?

Thanks,

Mark

November 18, 2005 04:40 PM Forum: Equipment Talk

DSC Cable Question

Posted By Mark Peterman

Will the Sky Commander cables (Part # CAB-EN-0608) work with a NGC-Max computer?

Thanks,

Mark