Image of the day

Captured by
Herb Bubert

Crescent Nebula

My Account

New to Astromart?

Register an account...

Need Help?

Posts Made By: Ed Zarenski

November 22, 2002 04:16 PM Forum: TeleVue

TeleVue Plossl's

Posted By Ed Zarenski

TV8 thru TV20 range between 65$ to $75. Other larger sizes can cost a bit more. Certainly age and condition have a lot to do with it. I picked up 8, 11, 15, 20, 26, 40. The 40 cost the most but still under $100. The 26 cost the least but its the oldest. In my opinion its a gem. Every one I bought I'm pleased with.

edz

November 24, 2002 12:29 PM Forum: Equipment Talk

Best shorty Barlow

Posted By Ed Zarenski

I think it's the Celestrom Ultima shorty at about $80.

December 4, 2002 11:22 AM Forum: Equipment Talk

Strange looking Telescope balance...image.

Posted By Ed Zarenski

That doesn't look to far off from mine. The tube is way front heavy. Mitch is right, doesn't matter what it looks like if it balances. This tube is notorious for placing the eyepiece way down low.

Do this. With everything mounted secure, turn RA axis so counterweight shaft is parallel to floor. Then adjust Dec axis so tube is parallel to floor. CAREFULLY, keep moving tube and/or rings until tube balances. Do this with all your normal accessories inserted in the eyepiece end and with finder in place.

One way to help occasionally is when you are at a real dark site with no lights, you can take the heavy metal shade off the front end. Let's you move everything forward an inch or two.

edz

December 8, 2002 06:38 AM Forum: Equipment Talk

13.8 & 18mm Meade SWA's???

Posted By Ed Zarenski

I've been using an 18 SWA for a few years. It's great in my f10 5" SCT, although I have a 17mm plossl that has far better edge sharpness and therefore provides nearly as much sharp field of view as the 18. The 18SWA edge sharpness deteriorates rapidly in my f5.6 ST90 to the point it is not a good choice for that scope. Likewise it doesn't do very well at the edges in my f5 6" newt, but it is giving a 1.5° fov at 42x. Several times I was ready to sell the 18, but I keep it because it is a very easy eyepiece to look through. Comfortable eye relief, instant image and a nice clear contrasty view.

edz

December 13, 2002 09:57 AM Forum: Equipment Talk

Field Stop... what is it?

Posted By Ed Zarenski

Not only does the field stop ring inside the eyepiece barrel give a clear clean edge around the field of view, which makes the view to the eyee more pleasing, but also it is the determining factor in how much a True field of view you get. It eliminates the need to rely on the stated Apparent fov rating of the eyepiece which may or may not be accurate.

The correct formula is 57.3(1 radian)/(scope F/ep field stop)= Tfov in degrees. Multiply by 60 to get Tfov in minutes.

example: for scope with F = 1200

I have two meade 9.7 eyepieces one is stamped SERIES 4000 SP, the other one is stamped SUPER PLOSSL. The series 4000 has a field stop of 7.5mm while the super plossl has a field stop that measures 8.2mm.

S4000 fs=7.5 57.3/(1200/7.5)*60 = Tfov = 21.5 arcmin.

SP fs= 8.2 57.3/(1200/8.2)*60 = Tfov = 23.5 arcmin.

They are both the same power but the SP has a wider field of view. The simpler Tfov calc based on mag would give the same result for both, 49/(1200/9.7)*60 = 23.8

Only about 8 out of 45 eyepieces that I have recorded data for have a field stop that produces the same field of view as that calculated by the simpler formula which is Afov published/mag. More than 30 of the eyepieces have a field stop that is smaller and results in a True fov slightly to substantially smaller than you would get based on the Afov/mag calculation.

I have verified more than of dozen of these by drift times to get the true field of view. All the drift times agree within 1% of the field stop calc. The field stop formula almost always produces a more accurate indication of what will be the True field of view than the Afov/mag formula.

edz

December 16, 2002 09:39 AM Forum: Deep Sky Observing

Top 5 objects to observe right now?

Posted By Ed Zarenski

You've got to take a look at M37 Auriga. You can find it with binoculars but you need high power on this to bring up the faint stars that cannot be seen with low to moderate power. Try 125x to 150x.

M35 Gemini at a lower power maybe 50x to try and spot 2158 very nearby to the south west. M35 is bright and easy, 2158 is small, faint and difficult. 2158 is more difficult at higher powers.

Late night or early morning M46 in Puppis. Close by is M47, a group of bright scattered stars. but M46 is kind of like M37, very densely populated with very many faint stars. And M46 also has an embedded planetary nebula. You find it with low powers maybe 30x or 40x, but then you need high powers to bring out the very faint stars.

The galxay pair M81/M82 in Ursa Major. You need maybe a 45' fov to see both at once, but higher power brings out more detail in each one seperately. You can easily bump up the power and turn back and forth between the two because they are lined up nearly N-S. There are two other faint galxies and a few very faint close double stars just off the southern edge of this pair. You need to look closely to see the doubles.

The double cluster 869-884 in Perseus will blow you away. Low power will show both together. You need 1.25 to 1.5 degree to surround the two clusters. Even binoculars are a good view, but powers of 60x to 100x will show so many more faint stars in each of the clusters it's amazing. You can count up to 150 stars in one to 200 stars in the other.

December 31, 2002 03:40 AM Forum: Equipment Talk

Good book on Star Testing your Scope

Posted By Ed Zarenski

The two hole mask is not used for collimation. It is used for focusing. When you have a camera attached to the back end of your scope its very difficult to see best focus thru the camera viewfinder. Put the mask over the objective, focus the two wholes until they appear as one, take the mask off and you are ready to go.

Suiter's book ia not easy to find. You can try the "available used" option on Amazon. That's how I got mine. It's brand new.

edz

January 6, 2003 06:57 PM Forum: Deep Sky Observing

Re: Oops

Posted By Ed Zarenski

Just a few week back I put my Meade 8.8mm Ultrawide into my 2" focuser and it looked like the whole sky clouded up. I couldn't figure it out, checked to see if the objective fogged up, but everything looked good. Of course, in the 2" focuser, the eyepiece fits very nicely while it still has it's 1 1/4 lens cap on.

edz

January 7, 2003 08:07 AM Forum: Deep Sky Observing

Belt of Orion

Posted By Ed Zarenski

Gamma Cas to Eta Cas = 3.1° (25mm in SkyAtlas 2000.0)
My 20x80 Oberwerks are slightly wider than this (3.2°)26mm.

74 Tau to 63 Tau = 2.7° (22mm in SkyAtlas 2000.0)
had a pair of 25x70s recently, this was a little larger than the fov

the triangular head of Serpens Caput = 3.3°
d1d2 (11,12) Lyra to e1e2 4,5) Lyra = 3.3° exact
These views were recorded with Orion giant 16x80s (3.3°)27mm

Orions belt stars = this fits easily in the 16x80s
just checked this, they are much less than 3.3°

Was out last night(Tues) and checked out the belt stars again. These just fit across the fov of my Oberwerk 20x80s with little room to spare. The 20x80 have a 3.15° fov. Belt takes up about 90% of the fov.

The Kids (7, 10, 8 Aur) in one view = 2.75°

Castor to star just north of Pollux (75Gem) 3.5° exact

the body 12-9-11-10-6-4 of Delphinus = 3.1° exact
this view was recorded with Oberwerk 20x80s

add 3 Del ( from 12 to 3) to the above = 36mm = 4.4°
this view was recorded with 15x70 Oberwerks

edz

January 7, 2003 09:29 AM Forum: Equipment Talk

Widest True Field?

Posted By Ed Zarenski

For a distributor of UO eyepieces try
http://www.helix-mfg.com/eyepieces.htm

or go to UO
http://www.universityoptics.com/uoep.htm#.

The maximum field of view in any 1 1/4" eyepiece is limited by the field stop. The outside diameter of the 1 1/4" sleeve is 31.75mm. The largest the field stop can be is limited by the thickness of the sleeve wall, a few mm. The widest field stop I've ever measured is 27.4mm, for a Celestron 40mm plossl. My TV 40mm plossl measures 27.3mm. The Celestron Ultima 30mm is 26.1mm. The difference between these is 66arcmin for the Ultima versus 69arcmin for the 40s in my scope, less than 5%. The big difference is that the 30mm, with only a 5% smaller fov provides 35% higher magnification and makes things much easier to see.

The Meade 24mm SWA is advertised as 68° afov. In my scope that would produce a 72 arcmin True fov. In order for that to really happen the field stop in the 24SWA would need to be 28.5mm. I don't own one, but I'll go out on a limb and say, I't ain't so. (Anybody want to turn their 24SWA upside down and measure the field stop. Got calipers? I bet it's no more than 27.5mm). I do own the 18mm SWA. The Tfov that it really produces indicates that it is not 68° afov but is really only 63° afov. I suspect the 24mmSWA is similar, maybe up to 65° afov. The point is, the 24SWA can only equal the Tfov of the largest possible field stop, not exceed it. The benefit would be that it does it at a much higher magnification.

If I were you I'd be more concerned with picking an eyepiece that doesn't have a tendency to kidney bean, or black out on me as I moved my eye around. From what I've read, both the 35mm Ultima and the 32mm Konig might fall into that category. I'd want to pick an eyepiece that is easy to hold the view and doesn't have eye relief so far back that I can't find the right place to keep my eyes.

Clear aperture is the diameter of the eye lens, nice, but no benefit to field of view. The 30mm ultima has a 30mm clear aperture. The 40mm TV plossl has a 26mm clear aperture.

edz