Posts Made By: Ed Moran

I picked up my new 12.5" PDHQ Saturday She's a biggun', but very pretty. It's a split tube and that seems to work very well. It comes apart and goes back together easily and holds collimation pretty well after doing so. Just a tweak or two of the primary adjuster screws was all that was necessary.

All of my eyepieces (31mm T5 through 7mm T6) reach focus except my 12mm T4. That one requires about an inch more outward focuser travel (back focus?) than is available. The 31mm focuses the farthest inward, about an inch from all the way racked in. I could move the mirror to try to make both ends meet (so to speak) but I'd have to position it within a tolerance of plus or minus .10" to get both to work. Maybe a 11mm T6 instead of the 12mm T4?

One funny thing though...late in the session I noticed a bit of astigmatism. It wasn't evident early on when I was collimating and star testing, but showed up a couple of hours later. I don't think it's my eyes, the direction of the astigmatic artifacts stayed in the same position no matter where I rotated my head (or the eyepiece).

The primary mirror seems to be mounted in a stress-free manner (sitting on 3 pads of silicone RTV) but the secondary mirror has an overly generous amount of foam behind it. It seems to be exerting a noticeable amount of pressure, perhaps more than is necessary to hold it in place securely. I lightened the load a bit and will observe again tomorrow night to see if that helps. I've attached a pic of the dark blue beastie for your viewing pleasure...

I added a brace to the front section of my 12.5" PDHQ rocker box to reduce flexure. The increased stiffness is noticeable but there's still room for improvement...

Here's my second Moon pic ever, from 5-15-05.

12.5" Discovery PDHQ
Nagler 17mm T4
Canon G3, 1/125th sec @f/3 (I think!)

It is the best of 86 pics taken that night! A lot of blurry, under and over exposed shots with one really good one.

Last Saturday on Mt. Pinos. I've replaced the JMI focuser with a Moonlite CR1 and added a stiffener panel to the rocker box. It got down into the mid-high 30's but as you can see I'm well insulated

All I needed was my Santa hat to complete the outfit...

Hi,

I have a Konus 80mm f/5 short tube refractor I received in trade and am looking for some eyepiece advice. I will be using my 7 & 9mm T6's, along with my 12mm T4 with it but all my long focal length eyepieces are currently 2" types so I'm thinking an Ultima/Ultrascopic/Parks GS in the 25-35mm range might be a good choice.

Or, just to be extreme, does anyone know of a 2" focuser that fits this scope? Would my 22mm T4 & 31mm T5 work or would there be edge problems or vignetting?

Thanks!

Ed

P.S. I should note that I am currently recovering from a severe cold or flu so the question about the 2" focuser may be the result of a high fever....

Ok, sanity seems to have prevailed (partially). I'm going for a 24mm Pan with a decent mirror diagonal for my 80mm f/5 shorty. I used the scope last Saturday night on Mt. Pinos with a cheapo 20mm 70 degree afov eyepiece and a 45 degree erect image diagonal and was pleased with the result. I've placed an ad in the Eyepieces section looking to trade my 17mm T4 for a 24 Pan with a mirror diagonal if anyone is interested:

http://www.astromart.com/classifieds/details.asp?classified_id=363536

Thanks,

Ed

After a friend helped me check the collimation of my scope using a 2" INFINITY autocollimator last weekend (thanks, Floyd!)I decided to buy one for myself, along with a BLACKCAT cheshire. These tools will come with instructions so this post may be moot at that point, but I would like to know if I understand the process correctly from reading various posts Jim Fly's and Vic Menard's websites.

Forgive me for rehashing some of the obvious here (steps 1 & 2 come to mind...)but I want to understand.


1. Locate the secondary mirror using a sight tube. The secondary should be centered under the focuser and rotated so as to appear to be a circle, concentric with the focuser tube.

2. Next, the tilt of the secondary is adjusted so that the reflection of the primary mirror is centered within the secondary mirror. Step one may need to be revisited after this adjustment and step two checked again after that. Repeat as required...

3. Aim the secondary at the center spot of the primary using a crosshair sighttube or laser. Revisit steps 1 and 2 and adjust if necessary, verify step 3, repeat as required...

4. Using the BLACKCAT cheshire, adjust the primary mirror tilt as required to center the newly installed triangular center spot within the image of the reflective ring of the cheshire.

5. Now comes the autocollimator? If my previous adjustments have been successful I will see up to 4 reflections (1 primary, 3 ghosts?) in the autocollimator and these need to be "stacked" through small adjustments to the secondary and/or primary mirrors? How do I tell which mirror needs tweaking?

Or are these questions answered in the instructions and I'm wasting valuable bandwidth?

Thanks,

Ed

Mars was a pleasant surprise last night. At only 30 degrees above the horizon it showed great detail at first glance, with the small South Polar Cap and Sinus Sabaeus and Sinus Meridiani standing out from the rest of the planet. As Mars continued to rise the seeing decayed somewhat (or my eyes got tired) but there were still a few moments of sharp seeing to be enjoyed.

The best views were had at 228x with a medium orange filter. The attached image is from Mars Previewer II, CM 355 deg, South at top. Other than the white areas it is representative of the detail observed during the moments of best seeing.

Thanks,

Ed

12.5" PDHQ Newtonian
7mm eyepiece

I got a 4.5" diameter 27 cfm pc cooling fan and a 14" pressboard disk(lined with cork on one side, from Home Depot, garden dept.) for my 12.5" PDHQ. By good fortune, the disk is a friction fit in the end of the OTA. If vibration is a problem, I have a 10" disk that I'll mount with rubber bands to isolate the fan vibes...

Ed

I want to get a bit more power out of my 12.5" f/5 dobbie

My shortest f/l eyepiece is a 7mm T6 which, when used with my soon-to-be-ordered Paracorr, will deliver about 260x. I'm thinking about a 6mm Radian (about 304x w/Paracorr) and/or a 5mm T6 (365x w/Paracorr). Or maybe a Pentax 5mm XW?

With my hand-driven dobbie I'm partial to wide field ep's so that limits my choices a bit and with the extra glass of the Paracorr I want to avoid barlows...

TIA for your input

Ed