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Messages - rennlispuring

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Beginners Forum / Re: Can't see North American Nebula
« on: January 20, 2018, 01:56:40 PM »
I find many of the responses to the OP's question interesting and at the same time disturbing. They are a clear indication of just how poor today's skies are for the great majority of amateur astronomers.

Just as Nicknacknock did indicate, the NAN is a naked eye object without using any filters at all if your skies are truly dark. When reasonably high in the sky I always saw it as a faint, yet distinct, triangular mass in the milky way not far removed from Deneb...right from my backyard which is only 75 miles removed from Manhattan! That was back in the 1970's and such skies (Bortle class 0-1 & NELM 7.5) were still all very wide spread anywhere outside cities back then. It was a time when fully a third of the Messier objects could be spotted without any optical aid and even very modest binoculars showed them all quite easily.

So, the simple answer to the question of the NAN's visibility is nothing more than just needing honestly good skies...and good skies really don't begin unless your NELM is 6.5 or better.


Reflectors Telescopes Forum / Re: Aluminizing a 20" f/5 Galaxy...
« on: January 18, 2018, 01:58:19 AM »
For SoCal, try:

I would favor the first and last because of experience and quality.

Mounts Questions & Expirience / Re: Pointing off?
« on: January 18, 2018, 01:36:15 AM »

I'd kill for 10" pointing accuracy.

Good thought, but my mount is blind. I'm a visual observer, no camera.[/quote]
Poor thing. Did it come with a white cane with a red tip?[/quote]
Nope, since I only let it out of the house in the dark, I didn't get the white cane option. I just lead it around carefully by the counter weight shaft. Besides, a bright white cane would ruin my night vision.


I've got a 38mm Q70 eyepiece that I want to use on a 10" reflector f/4.7.

I'm aware that this is going to give an exit pupil wider than what my eye is capable of.

1) How do I determine my maximum eye pupil width?
2) Will the longer eyepieces provide its corresponding low magnifications even if some light is not reaching my eye? I want something wide to help me find objects easier.
3) How do I calculate the maximum FOV a telescope can provide?
4) Is there some benefit to having a larger light cone than my pupil? Perhaps I can be less strict about where I position my eye and still catch all the light?

I have the Agena Astro SWA 38 mm 2"/70 degree. Basically the same eyepiece with a different label.

I use it in an Orion XT8i.  I have no focus problems.  however I do have a Explore Scientific that won't come to focus unless I pull it out of the focuser about 1/4 to 3/8" of an inch. I lock it in place and it works fine. Try that.

I would not worry about maximum Pupil size.  That 38 mm gives me a 6.4 mm pupil and there is no way my eye is open that much with all the ground light pollution I have. But it doesn't matter. I just move my head/eye around a little, like I am looking out a window, and I get great views.

FOV is based on the eyepiece and the focal length of the scope. 

FL scope / FL eyepiece = magnification

AFOV of eyepiece / mag of eyepiece = FOV, or close enough for practical purposes. I think there is a more complex approach but this works.

Where a reflector will reach a limit will be that if you get the mag too low you start to see the secondary mirror and the spider.  I don't know what that would be for your scope but to get the maximum FOV you get the longest eyepiece with the widest AFOV, but they are pricy.

Orion uses a 7 mm exit pupil to state the lowest practical mag for their scopes. you can go lower if you can find the right eyepiece to make it worth it.

That 38 mm Q70 is a very cost effective low power wide field eyepiece. An Orion XT10 is an F 4.7 /1200 mm FL so you will get 31.5 X and about 2.2 degree FOV, same I as get in my Orion XT8i F5.9.If you want to go wider than that you could get a Tele Vue Panoptic 41 mm/68 degree.  29.2X and 2.3 degrees.  That costs about $500.
Or you can get an ES 40 mm 68 degree for about $300, but you won't gain much FOV over the Q70 38 mm.If you want to go wider than that you need a scope with a shorter FL.  I have a 3" refractor with a 400 mm FL. With a 32 mm Plossl I have 12.5X and over 4 degrees FOV.
You said no focus problems? Did you have coma? With wide eyepieces, I think coma would be visible along the edges.

Beginners Forum / Re: telescope information for beginners
« on: January 17, 2018, 01:28:48 AM »
The Z10 weighs 18 lbs. more overall than the XT8+. The suggestion of the Z10 might have been a bit hasty, and due to the fact that the Z8 won't be back in stock until after the first of the year... http://www.telescope...ector-telescope

The Zhumells are preferred over the Orions for the former's superior altitude-bearing, if not that of the azimuth in addition. If you can't wait on the Z8, then go ahead with the XT8+. It's a fine kit. There's not enough of an improvement going from an 8" to a 10" to disregard the considerable advantages of an 8".

A 10" Newtonian, on a Dobson-mount or other, occupies a "twilight zone" of sorts among the larger Newtonians. An 8" f/6 is better balanced between observing within the solar system and beyond into deep space for globular clusters, nebulae and brighter galaxies; all-purpose, in other words. Quite a few move on to a 10", but only after having owned a 6" or 8" for awhile...

...and only because the size and scope of this "galaxy killer" is an armful and a back-breaker that fewer choose instead...


A 12" will begin to show considerable structure within the brighter galaxies. The intensity of colour within nebulae also becomes increasingly appar...

I better stop while I'm ahead, lest I get aperture fever myself.

A comparison of an 8", 10" and 12"... Telescopes.JPG

It is noticeable -- I have compared 130mm scopes with spiders like that to others with narrow spiders and you _can_ see the difference in intensity very close to the source.

On these 114mm scopes you have other worries, though: typically the obstruction of the focuser tube intruding in the light bundle is colossal and dwarfs contributions of the spider.

Reflectors Telescopes Forum / Re: Dobson 10" for planets/moon ?
« on: January 16, 2018, 11:39:50 PM »
I find that 300x is about the upper limit for manual tracking my dob, before it gets to be more trouble than it's worth.

I have an old Orion 7 to 21mm zoom (made in Japan) that came with a scope I purchased. For some stupid reason, I've always been a bit reluctant to sell it because it does provide high quality images for planetary viewing. Beyond that, these cheap zooms are pretty worthless, especially since they're almost all come from lower quality Chinese manufacturers these days.

At 21mm (low power), where you want a wide field of view, the zoom's apparent field of view is only 30 degrees (so narrow that it's about like looking down a drain pipe) and at 7mm (high power) where you kind of expect a narrower field of view, it's at it's widest of 43 degrees (still looking down a drain pipe!). Yes, the field of view from 7mm to 21mm is just the opposite of what you'd expect and want in an eyepiece.

Bottom line, I'd avoid cheap zooms like the plague if you want to enjoy what you're looking at. There are many quality used eyepieces available at low cost that are much, much better than what probably came with your telescope. Almost anything with a 65 to 82 degree field-of-view will make your viewing practically like looking through a porthole into space!

I actually use the default 25mm that came with my 6SE and the eyepieces that came with the Celestron Eyepiece Case that I bought. I wouldn't say they are terrible but the FOV on the high power is pretty small on them. I hear people say that eyepiece quality is the difference between a just clear image and a crystal clear image, how true is this btw?

Beginners Forum / Re: Five Planet Alert
« on: January 16, 2018, 03:10:46 AM »
Thunderstorm here.

General Astronomy & Observing / Re: Skeeter control...
« on: January 15, 2018, 04:01:51 PM »
If you want to avoid sprays and chemicals here's the deal. Get a "bug jacket". jacket&psc=1

Cut small slits for your eyes so you can see through the EP, or sew clear pieces of plastic into it. For your hands get a box of nitrile/latex gloves. The kind they use at your doctor. The little buggers CAN"T bite through them, and they're very dexterous for handling small items. gloves

Oils and sprays will destroy the gloves so you have to choose one or the other.

I have that very bug jacket, and on one night where I used it above a t-shirt, I got 11 bites on my upper half--5 on the arms and 6 on my back, which required biting through the jacket and t-shirt. From that point on, I only used it on top of a long-sleeved shirt *and* a fall jacket, and didn't get bitten after that. Oh, and with gloves, of course. At that point, it was only really protecting my head and neck, since the fall jacket was probably a good enough barrier for my trunk.

I never tried cutting out slits or sewing plastic, however; I just started noting the temperature and progressively stopped going out until I reached a temperature where I could wear winter clothing (as I was already doing beneath the jacket) without the jacket and not get bitten. Right now that seems to be at 57F, which is a temperature we don't see here much in the summer. Oh well. We're in August and it's going to get cooler....

ATM, Optics and DIY Forum / Re: Building a 4" F15 Dall-Kirkham Cassegrain
« on: January 14, 2018, 06:57:01 AM »
The way to have a hybrid for this scope it to have a place on the tube to "drop" in a diagonal (on a support) that just sits barely in front of the convex secondary that stays put at all times.

No way! If that was really the way to do it, Takahashi and Parks would have both done it that way. There are some weird things about the geometry of my Parks and I wonder if they would have been "corrected" if they'd used starcanoe's idea.

Beginners Forum / Re: Which scopes to complement each other?
« on: January 14, 2018, 04:56:07 AM »
Yes, you are wrong. There is nothing magical about the design of a Mak-Cas that makes it perform well under city skies. Insofar as light pollution handicaps a Dob, it will also handicap a Mak.

The only advantage of the Mak is that it would be easier to place on a motor-driven mount, which is indeed a benefit for viewing the Moon and planets at high magnifications. On the other hand, Maks take much longer to cool down than Dobs, which is a serious liability. And they cost much, much more than equivalent Newtonian reflectors.
My 4" Mak is definitely my favorite city scope, because it is extremely portable and easy to use. When I'm observing in the city, I need to go to a park. It's way too bright around my apartment building. Compared to a 4" refractor:
Takes up much less space in a bag, leaving room for accessories. My 4" f/6.5 refractor barely fits, and it's really short for a 4" refractor.
Balances better on a mount. a 4" apo would weigh a lot more than a 4" Mak, increasing mounting requirements and decreasing portability.
Optically, a Mak with a 30% CO performs like a 4" f/10 achromat, while being 1/4 the length.
The eyepiece doesn't move around nearly as much, greatly facilitating viewing at zenith (helpful under light pollution). More comfortable to use in general.
Unfortunately, the optics of most mass-produced MCT models are pretty mediocre. But in reality, I usually don't push either of my small scopes to their limits. If I really want high detail, that's a job for the 8" SCT. The Mak wins out on sheer practicality the rest of the time.

Light Pollution Topics / Re: Full moon LP at dark site
« on: January 14, 2018, 02:05:32 AM »
I am new to this topic. Can you explain SQM and how it is measured?

 This should do it.

I'll just throw in my opinion on EPs Allen. A lot depends on the scope, in particular the F/ratio. I can see differences in eyepieces using my 6" f/6. Not huge, but some differences.

With my C-5, they all work well, at f/10. I can't tell the difference except for the FOV and eye relief. I have a few XCel-LX EPs and a few less expensive BST models. At F/10 they all perform very well.

Even the TeleVue Plossls I have that are somewhat sharper than others at faster F ratios, equal out as the slower ones.

So, if you are going to use them at a slow ratio, f/8, f/10 and above, I would choose one type that is most comfortable in terms of field of view and eye relief.

Of course, you do want an eyepiece that is free of high scatter, and the ones mentioned are.

Just my conceded opinion, and everyone is entitled to my opinion.

General Astronomy & Observing / Re: Name for new telescope? (vote)
« on: January 13, 2018, 09:16:48 PM »
Thanks to everyone for their votes! I will tally them up after I purchase the scope tomorrow. Then I will take a piece of advice and use the scope before naming it. Most likely I'll go with the most votes considering I'm very easily amused and probably won't have one thing that stands out above the others.

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