Ben the Ignorant

24 minutes ago, VisualBod said:

 I'm curently thinking that 253 might be a good test of a small refractor's performance.

It's always interesting to search for a scope's limit but first, you can't judge it on one target, and second, that would be more a test of air dryness and blackness than a test of the scope itself. Performance varies wildy with conditions: just remember that the naked eye can see up to 7th mag in great air, or no better than 4th in so-so atmosphere.

31 minutes ago, VisualBod said:

Any thoughts as to whether a 100mm will buy me much in the way of light-gathering capacity, in real life terms, over an 80mm refractor? I found one site that suggests the gain might be just 0.1 magnitudes

A 100mm objective has 125% the diameter of an 80mm one, thus it takes in 1.25 x 1.25 = 1.56 as much light. That is a 0.5 magnitude gain, coupled with the lenses' natural strong contrast compared to mirrors, the 100mm would clearly sharpen and brighten the views.

I don't have a spotting scope but I've considered them a few times because of the weatherproofing and shockproofing. They have very short dewshields but it's easy to make a longer one. The only real problem is how to attach a finder, but since it does not have to be a permanent mod screwed to the body, that shouldn't be too difficult, either.

Finally, don't limit yourself to the Messier list. Messier never scanned the sky to find all the faint fuzzies and clusters, he just stumbled upon a few while following comets. The Herschel list, on the other hand, is the result of a true systematic scan, and has four times as many possible targets. That's why good pocket star atlases are never limited to the Messier iist.

Orion makes push-to scopes, they are the Intelliscope line if I remember well.

1 hour ago, Nova2000 said:

Idont have any problem to use a manual or automatic (goto) both are fun their own ways. 

A middle ground exists between the go-to scope and the fully manual scope: the push-to. It has no motors, so no heavy batteries and machinery, its only electronics are sensors and a palm computer that tell it where it's pointed. You move it with your hands like a bare dob, but it has thousands of targets in its memory so you don't need an atlas and a flashlight.

47 minutes ago, Nova2000 said:

Hi. 

My current setup is 6''newtonian on a eq3,mount. My scope is becoming old and the mount is getting rusty. I now want to upgrade it. Can youll recommend me a new scope? Anything works, dobsonian, refractor, reflector and Schmidt cassigrane. 

Thankyou 

The largest dob you can manage.

Briefly put: Explore 24/68.

...is neat but can take some improvements. Here's how:

Safety first! So, to prevent breakage I limit the bottom knob's range, or someone unaware of its lacking design can tighten it too hard, and break the plastic clamp. Nearly happened when a friend turned that knob real hard, thinking he was making the mount more stable for photo, but the clamp couldn't split thanks to the washers that stop the knob before it causes damage. An undersize O-ring keeps the washers in place in case you remove the knob, they won't get lost.

Next fault in design, there's a 2mm gap on each side of the spreaders. I fill it with washers and/or O-rings. Two washers are tricky to insert, better superglue them together to form a single thick one.

Next large play and ungainly fit: the central aluminum stud plays between the others:

Filing the plastic inserts to bring the outside tubes close to the central one:

And the result:

The three tubes now clamp together over their whole length, better stability, better looks, and improved feel. These tripods are too lightweight even for my 80mm achro; to make the complete scope assembly heavier with a lower center of mass, filling the tubes with aquarium (clean) gravel is an easy and invisible solution:

Some fill it with cement, which is even heavier because it leaves no empty space between the stones but I prefer reversible mods.

Inside the clamp there is a rib that's supposed to guide or support the central tube but it doesn't even touch it, so I remove it with a file (masking tape protects the aluminum):

Instead ot the useless rib I stick two felt pads that press hard against the tube, making its motion silent and way more controlled. Since it is now much heavier, sliding free and bumping against the clamp would cause noise and maybe damage.

Note the piece of sponge that clogs the bottom of the hollow tube. Not indispensible with large gravel but it's needed when I use smaller grain sand.

The steel ashtray has dangerous corners that a lens could hit, so I take segments of a junk guitar cable (degrades the tone), and pile them up between clamps so the top one is at at a convenient height and easy to split open:

Like so, then I remove the cable's core:

The ashtray itself is like a gong (steel is quite resonant), putting accessories on it always makes a nasty clunky sound that irritates me, and would annoy neighbors if the scope was in a backyard. So I put felt pads at the underside, around the screw holes, plus a large neoprene cushion in the middle. Besides making the thing look like a cool famous UFO, this dampens the noise that made me cringe every time.

Finally, I slide the split guitar cable over the ashtray's edges, and add a sheet of the white material architects use to build models. I often moved my scopes around with accessories rolling aroung in the ashtray, simply because I forgot they were there for they are black on black. This happened even in the daytime during solar watching. However black on white is noticed even with the corner of the eye, no risk of that absent-mindedness again. The foamy white sheet holds thanks to a little strip of double-side tape, and helps dampen those irritating clunker noises in the still of the night. The difference in visual contrast is obvious, but even more so at night.

I'll replace the foam with tougher vinyl when I come across a leftover piece, in the meantime it does a good enough job. There you have it, several mods even an astro gearhead might not notice, except the white ashtray, but they do give a better feel, a better look, and even a better sound to the setup. The joints between cable rubber are just acceptable, I'll rectify them later, but what matters now is a danger of scratching lenses is done away with.

Hope you'll pick up a few ideas that can be useful to you.

1 hour ago, Alan White said:

I like the 50 degree viewm mainly because I started with Kelners many years ago and the narrower FOV is 'normal' in my mind.

The "normal" field of view is the one you have with both naked eyes, and it's about 180°. Better use as much of it as possible when you're at the eyepiece.

2 minutes ago, Star Struck said:

I am sure somebody will correct me, but a 24mm 68 degree eyepiece shows the same amount of sky as a 32mm 50 degree eyepiece

but with different magnifications. I have owned both the eyepieces mentioned, but I only kept the televue 

32mm plossl. It is excellent across all of my scopes.

 

No one will correct you, you're right. As I said above, the Explore has a wider apparent field, but the same true field.

14 minutes ago, Alan White said:

 I have a 750mm FL f5 Newtonian, which shows up EP performance good or bad.

My friend runs a Hyperion and that's a nice EP, is the ES 24mm really better?  Having not looked through one I do not know.

I have a 300 f/5 dob, and I dobsonized a 150 f/5 newtonian tube for my brother (that's why he got the eyepiece). I tried the Explore on both, coma and other edge distortions were negligible.

Yes, the Explore is really better, at first sight. More definition across the whole field and less curvature (very little focus change from center to edge). Stars remain tight and round at the edge, whereas they become little seagulls in the Hyperion. The latter keeps lines straighter, which makes it good as a terrestrial eyepiece, and the Explore has the needed pincushion effect to keep stars tight. Unless you want your astro eyepiece to double duty as terrestrial, go for the Explore.

1 hour ago, Alan White said:

Is the 32mm Telvue Plossl as good as they say?

Why do you want to limit yourself to a 50° eyepiece when you could have an Explore 24mm/68° with splendid sharpness and more apparent field (same true field) for a little less money? My 24mm/68° Explore has so much more clarity and edge sharpness compared my Hyperion 24mm/68°, I gave the Hyperion to my brother who is only a casual observer.