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Captured by
Lawrence Parchman

Sculptor Galaxy (NGC 253)

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Posts Made By: Doug Scobel

September 10, 2003 08:45 PM Forum: Solar System Observing

Colour in Mars?

Posted By Doug Scobel
Darren,

Mars is so big and bright these days, I would think that it is entirely possible. I generally see the darker markings as a bluish-greenish gray, but I'm using a bigger scope (8").

One thing to look out for is atmospheric dispersion. I'm at 42 degrees north, so Mars barely makes it up to 30 degrees altitude these days. I always notice a slight red coloration around the southern limb, and a slight blue coloration around the northern limb. But since you said that SM was just "appearing 'round the preceding limb", that would put it nearly half way between N and S, so that's probably not what you saw.

Regards,
Doug

September 10, 2003 09:00 PM Forum: Equipment Talk

Best improvements in performance

Posted By Doug Scobel
The most cost effective thing I did was to add a tube extension to the end of my 13" f/4.5 (Sonotube, homemade) dob. It dramatically improved sky darkness/contrast, by reducing the amount of stray light in the eyepiece end of the tube. It cost next to nothing.

Next is refiguring the nearly one wave (!) Coulter primary to around 1/4 wave. If you count not only the cost of recoating but also my time, then it was definitely not a cheap fix.

But the biggest improvement regardless of cost came from upgrading my eyepieces, but you can't call that a "big bang for the buck". I have more $$$ tied up in eyepieces than I do in the scope!

Regards,
Doug

September 10, 2003 09:17 PM Forum: Equipment Talk

Best improvements in performance

Posted By Doug Scobel
OOh, how could I forget. Lumicon OIII filter. Just looking at the Veil Nebula was worth the price. Much cheaper than most all "premium" eyepieces.

Doug

September 15, 2003 07:48 PM Forum: Solar System Observing

Mars 9/12/03 22:00 EDT

Posted By Doug Scobel
Hey, Mark, really, really nice drawing! Welcome to the forum!

Doug

September 15, 2003 09:28 PM Forum: Equipment Talk

Parabolic mirror coatings

Posted By Doug Scobel
I just had a 8 inch mirror done by Spectrum (standard Al + quartz) and they did an excellent job.

I would avoid Clausing.

I also had a 13" mirror done by Precision Applied Products more than ten years ago, enhanced Aluminum, and it looks as good today as it did then. Remarks re: surface roughness of enhanced coatings notwithstanding, I use it for deep sky, and get many compliments regarding the high contrast images it produces.

Decisions, decisions...

Clear skies and smooth coatings -
Doug

September 18, 2003 07:19 PM Forum: Equipment Talk

Best Coatings In the West?

Posted By Doug Scobel
Tom,

More than ten years ago I had my refigured 13.1 inch mirror recoated (enhanced aluminum) by Precision Applied Products, and in my opinion they did a fantastic job on it. The coating looks as good today as it did then. And I found no problems with the figure being upset afterwards.

At that time PAP catered more to the amateur astronomy community than they do now, e.g., they advertised in S&T. But if it's the same folks running the place now then I can recommend them. I'm not a professional optician, just an amateur who's made a few mirrors, so take my comments for what they're worth.

Doug Scobel

September 19, 2003 01:22 PM Forum: Solar System Observing

Blue Color on Mars Northern Limb

Posted By Doug Scobel
Indeed I often see a bluish haze on the northern limb, but still I suspect that what I'm really seeing is artificial. My reasons for thinking so is because when it is most noticeable, I also see a reddish tinge along the southern limb. It also gets more and less noticeable when I move Mars around in the field of view. And, I remember it being quite symmetrical. This suggests to me that it's either a small amount of chromatic aberration in the eyepiece, or maybe some atmospheric dispersion (Mars barely gets up to 30 degrees altitude from my location), or maybe some of both. If it were really a Martian feature, then I would simply see the bluish fringe without the red. Plus, its very narrow, not 1/7 of the Martian disk as Sol mentioned.

I have #25 red, #58 green, and #80A (light) blue filters, but not a #38 (dark) blue. Next time I'm observing I'll give it a closer look.

Thanks,
Doug Scobel

September 25, 2003 02:18 PM Forum: Telescope Making

Pinched mirror

Posted By Doug Scobel
Floyd, what do star images look like out of focus? Start with a brightish star in focus, then slowly defocus. If the star image expands into a circular or nearly circular disk, then the primary is probably not pinched. If it is pinched, then the out of focus star image will have some kind of peculiar outline, like triangular (in a cell with three too-tight clips like you described), or some other irregular outline.

Doug Scobel

September 30, 2003 05:09 AM Forum: Solar System Observing

Mars Sketch 9.29.03

Posted By Doug Scobel
Hey, Sol, nice to see more of your usual excellent work. I just finished an observation myself, and now that you mention it, the contrast in the eyepiece did seem to be a little low. I wonder if it's a side effect of the disk getting smaller and details getting a little harder to see. Maybe we're just spoiled from when it was 25 arc seconds across? Still looked great, though!

Best regards,
Doug Scobel


October 1, 2003 01:45 PM Forum: Equipment Talk

Good focuser for a dob?

Posted By Doug Scobel
Tom,

I recently added a Moonlite dual rate to my 13" dob and I highly recommend it. The fine focus side is very precise and very smooth. The eyepiece set screw is nylon so it will never mar the eyepiece barrel. It weighs in at 15.8 oz. Moonlite's single rate is lighter yet.

Best regards,
Doug Scobel

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