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Posts Made By: David Jackson

April 10, 2005 12:57 PM Forum: Equipment Talk

Mirror issues with Discovery 15" PDHQ -Help!

Posted By David Jackson

I have a 15"pdhq with possible mirror issues. My issues are soft images and dim dso’s the planets lack detail and look like I'm
viewing through a yellow haze as there is a glow around them anything over 200x is mostly unusable. I assumed that it was my secondary not property aligned. I purchased a Glatter holographic collimator and centered the secondary and then used a cheshire to final collimate,
and also upgraded to Pentax eyepieces. This did not help much. I've
now re-aligned the secondary many times and I'm sure that its tweaked
as best as can be done and still not much improvement.
Now the point where I need help. As I'm sure that the secondary is
aligned I have now started checking the primary, It’s not perfectly
centered in the tube but its close. I also noted that my mirror holder
has 3 legs all equally spaced so that the holder could be rotated and
the tube/bolt holes would still match. There are 3 corresponding bolt
holes in the tube, one on the opposite side of the focuser, one that
would be on top of the tube when it’s tilted level and the 3rd on the
bottom. The hole on top is marked with a green stick-on as is one of
the legs of the mirror holder, I assume that this is an alignment mark
and installed the mirror green to green. No matter where I've aligned
the secondary, in order to collimate, I've always had to tighten the
collimation wing nut fully on the leg with the green mark while he
wing nut on the leg opposite the focuser was always fully loosened.
This did not seem correct but it was the only way to
collimate it, I just assumed that this was just a correction of improper bolt holes or mirror set and that
the mirror was not really tilted, well I measured and the mirror is
tilted about 1/4" between the 2 legs. This shows that the mirror
is tilted towards the focuser, can this be correct? Is it suppose to
be tilted?
I then loosened all of the wing nuts so as to level the mirror and
looked through the focuser w/o an eyepiece and it can be seen that the
mirror tilts away from the focuser enough to show a cresent of the
top of the tube reflected in the mirror. This accounts for having to re-tilt the mirror when
collimating. Now the tricky part where I become totally lost. I
rotated the mirror with the leg with the green dot counter clockwise
so that the green dot leg is now matched with the bolt hole opposite
the foucser. I again looked through the focuser and now the mirror
looks level, no longer tilted. Why? I then collimated and noted that the collimating wing nuts are much closer to being the same only about 1 turn difference
and the viewing looks to be better but I’m not sure how much as it was
poor seeing last night.
I tried a star test and inside focus did show center obstacle
(centered) and rings, poor seeing so not clear. But outside focus
could not see center obstacle, looked like rings just got smaller and
smaller. What to do now? I'm thinking I should send the mirror out for
testing. Any suggestions, recommended mirror testers?
Thanks for the help, I'm really frustrated.

August 5, 2005 12:01 PM Forum: Equipment Talk

Pinholes in Coatings?

Posted By David Jackson

I have read that all coatings have pinholes. Is this about normal?
20x view of my 3.1" Discovery secondary. The area shown is about the center, the pinholes get worse towards the outer edges. This secondary has enhanced coatings and was purchased new in Oct 2004. As I have nothing to compare with I don't know it this is average for enhanced coatings. The pinholes can not bee seen without magnification. I'm having it recoated with standard coatings as I'm also having my primary refigured and recoated.

September 18, 2005 07:41 PM Forum: Equipment Talk

Secondary mirror comparsions?

Posted By David Jackson

I'm looking at recoating my 3.1" secodary mirror or possibly upgrading to an Antares or Protostar and I'm confused as to how to compare these 3 mirrors,

Discovery $175.00 "EVERY diagonal mirror is tested in our own Fizuea interferometer...We guarantee 1/8 wave or better" About $60.00 to recoat.

Antares $175.00 "Each piece is tested before and after the coating process" 1/14 wave PV

Protostar $175.00 "Each new batch is randomly sampled with a Zygo interferometer" 0.080 typ 0.110min FLATNESS,
(fraction of wavelength).

Discovery 1/8 wave, PV?,RMS?,Surface?

Protostar .080 typ, .110 min? How does this compare to wave PV?

Antares 1/14 wave PV, now I think I understand this and I like that they test each mirror.
Would the Antares or Protostar be much of an upgrade to a Discovery 1/8 wave? Should I see a difference if I upgrade?

November 8, 2005 06:27 PM Forum: Binoviewers

Williams Optics Binoviewer

Posted By David Jackson

I just received my WO binoviewer and it will not come to focus with the included OCS, it will when the OCS is used in combo with a 1.8x Televue barlow and it will when used with a short 2x barlow with or w/o the OCS. It will not focus with the 1.8x alone. This is with a Discovery 15" sonotube dob. Bino's arrived well packaged and look well made,image of the moon is good, even when looking at it through clouds. No problem merging. I think they are worth the money.
Extra grease from somewhere as I now have sticky fingers.

December 7, 2005 11:32 AM Forum: Eyepieces

Siebert coma corrector

Posted By David Jackson

I just ordered the new coma corrector from Siebert Optics. I'm going to give it a try with my 24mm Meade UWA 5000. The Meade shows coma at about 50% in my 15" f5 dob. I'll report the results here.

February 22, 2006 04:21 PM Forum: Reflectors

Collimation question

Posted By David Jackson

Secondary issues. Why is it that when I raise the secondary away from the primary and collimate, it requires that I tilt the secondary away the focuser so that it looks more offset than when I lower it. When I lower the secondary I have to tilt it towards the focuser to collimate. This then look less offset. It will appear collimated at either setting with both a laser and cheshire showing the same collimation. The only difference I can see is when I look through the empty focuser and can see the reflected primary and secondary, it looks to be slightly off center on the secondary, lower on the secondary when the secondary is lowered and more centered when the secondary is raised. Should the reflected primary be slightly off center or centered?
Dave Jackson

June 4, 2006 10:20 AM Forum: CCD Imaging and Processing/Deep Sky

Super Sensitive Image Sensor

Posted By David Jackson

I don't know anything about astrophotography and as my scope is a non tracking dob, I haven't given much thought to it. However, I saw the article in PC Mag. and was wondering if this new sensor would make astrophotography w/o tracking possible?

From PC Mag.
"Planet82 is demonstrating its new Single Carrier Modulation Photo Detector (SMPD) for the first time in the U.S. The company says the sensor is 1000 times more sensitive to light than traditional photo sensors—it can take picture in near total darkness. Planet82 says the sensor can capture images when light level is less than 1 lux (or up to 0.1 lux). One lux is the same brightness from one candle one meter away in a dark room. Human eyes can barely distinguish images at less than 1 lux.

Planet 82's Single Carrier Modulation Photo Detector
The sensor Planet82 uses what the company calls "principles of quantum mechanics to produce thousands of electrons out of one photon." The company also minimized the aperture ratio and increases the number of pixels per unit density on the chip. The sensor is manufactured using a CMOS process and is half the size of current CCD sensors.

Planet82 expects the SMPD image sensor to be available in CCTVs, digital cameras, video cameras, camera phones and vehicle parking sensors beginning in the first quarter of 2006."

April 15, 2009 10:54 AM Forum: Equipment Talk

Shipping scratches on primary is recoating necessa

Posted By David Jackson

I shipped my mirror off to be fit into a custom made truss system and it came back with light scratches around the outer edge. It looks like the mirror shifted and rubbed against the tissue paper cover. I can only see the scratches when the light is at an angle. The mirror coating is about 4 yrs old. I have tried it a few times and I do see some softness but that is not unusual for Western Washington this time of year. Are these scratches bad enough to require a recoating? I don't want to wait for good weather to confirm that I have to send it out for recoating, I also don't want to spend the money if recoating is not necessary. I don't have a lot of experience with this so, I am asking for opinions.

August 15, 2005 01:08 PM Forum: Telescope Making

Looking for air filter ideas

Posted By David Jackson

Hi Doug,
I don't know if these will fit or how well it will work but not expensive to try at $3.49. 80mm filter for computer fans at CompGeeks.