Jump to content


Photo

Meade's MA Eyepieces and Apparent Field of View


  • Please log in to reply
8 replies to this topic

#1 jiangshi

jiangshi

    Member

  • Members
  • PipPip
  • 13 posts
  • LocationArizona

Posted 11 September 2015 - 12:34 AM

Just recently, I purchased a Meade Polaris 130 telescope, and I am delighted with it, especially considering the price. My question is: What is the apparent field of view (AFOV) for the MA eyepieces that are included with the scope? The AFOV is very important for calculations pertaining to measurements, and I am a bit surprised that this spec is not readily available from Meade.

 

Thank you!



#2 Keith

Keith

    Newbie

  • Members
  • Pip
  • 7 posts
  • LocationAlabama

Posted 11 September 2015 - 02:25 AM

From the information that I've found so far online the MAs typically have a 40° FoV.

 

I have the 12mm Illuminated Reticle EP, and the specs for it show 40°, and I found the same FoV on the 25mm MA.



#3 jiangshi

jiangshi

    Member

  • Members
  • PipPip
  • 13 posts
  • LocationArizona

Posted 11 September 2015 - 06:12 AM

From the information that I've found so far online the MAs typically have a 40° FoV.

 

I have the 12mm Illuminated Reticle EP, and the specs for it show 40°, and I found the same FoV on the 25mm MA.

 

So far, the general information I am finding agrees with yours. Typical values are around 40 degrees. I have been hoping to find more of an exact value for the lenses that came with my scope, as they might be different from 40. I know how to calculate the AFOV by doing a drift test that finds the actual FOV and then working the formula for actual FOV backwards to find the AFOV, if I could ever get a clear night. I bought my telescope 4 weeks ago and have had 1 and a half clear nights to use it. BTW, I just received my MA 12mm illuminated reticle astrometric ep. The reticle has 4 scales, but I can find no AFOV spec for it. You will have to post back and say what you think of the ep. Thanks for your reply!



#4 MistrBadgr

MistrBadgr

    Advanced Member

  • Administrators
  • 2800 posts
  • LocationBroken Arrow, Oklahoma

Posted 11 September 2015 - 09:37 AM

Todd,

You made me curious. I have been thinking the MA eyepieces were around 45 degrees, which is what I told you in our correspondence. Just now, I pulled out a high end 25 mm orthoscopic I have and the 26 MA that came with either the Polaris 130 or Infinity 102 that I have. The field in the MA is smaller than in the orthoscopic enough to notice with the direct comparison. The ortho should be 45 degrees, so I am thinking the MA is probably around 40. If you need an exact number for what you are wanting to do, I think doing a timing test using a star very near zero declination, like you referred to, is the thing to do.

I hope you have a lot of fun with your Polaris 130. I certainly have with mine. It is now my travel buddy when I go by car on a monthly, one week long circuit as part of my regular job.

Best Regards,

Bill Steen
Bill Steen, Sky Hunters' Haven Observatory, Broken Arrow, Oklahoma

#5 jiangshi

jiangshi

    Member

  • Members
  • PipPip
  • 13 posts
  • LocationArizona

Posted 11 September 2015 - 01:03 PM

Todd,

You made me curious. I have been thinking the MA eyepieces were around 45 degrees, which is what I told you in our correspondence. Just now, I pulled out a high end 25 mm orthoscopic I have and the 26 MA that came with either the Polaris 130 or Infinity 102 that I have. The field in the MA is smaller than in the orthoscopic enough to notice with the direct comparison. The ortho should be 45 degrees, so I am thinking the MA is probably around 40. If you need an exact number for what you are wanting to do, I think doing a timing test using a star very near zero declination, like you referred to, is the thing to do.

I hope you have a lot of fun with your Polaris 130. I certainly have with mine. It is now my travel buddy when I go by car on a monthly, one week long circuit as part of my regular job.

Best Regards,

Bill Steen

Hi Bill, I was just now poking around on the Tele Vue site, and I found an equation that relates the field stop of the eyepiece, which they define as the metal ring inside the barrel, and the focal length of the telescope to the TFOV. So I got out my MA 9mm, unscrewed the metal part of the barrel, and measured the field stop at 7mm. The formula is TFOV = (field stop diameter / telescope focal length) * 57.3. So plugging in my numbers, I get a TFOV of 0.617 degrees. Then using that value, I plug it into the formula for calculating TFOV based on AFOV/mag, and solve it for AFOV. I get 44.56 degrees for AFOV.  Next, I do the same calculations for the MA 6.3 and get 45.49 degrees for AFOV. Then I did the calculations for the MA 26mm and got about 50 degrees for the AFOV. So that one does not seem to fit. However, the field ring is about 24mm, so it stands to reason that the AFOV will be wider. So I'm thinking that your recollection of 45 degrees is pretty much right on. Anyway, as  you said, doing the drift test is the way to do the test. All I need now is a clear sky.

 

As an aside, I have been looking at Meade's HD 60 5000 series eyepieces. They seem to rate well with their higher end counter parts. Do you have any experience with the 5000 series?

 

Todd



#6 MistrBadgr

MistrBadgr

    Advanced Member

  • Administrators
  • 2800 posts
  • LocationBroken Arrow, Oklahoma

Posted 11 September 2015 - 02:00 PM

Todd,

Yes, I have a set of the HD 60 eyepieces and two sets of the 5000 series 5 and 6 element Plossles that the HD 60 eyepieces replaced.

For most things, the HD 60 eyepieces are what I am using with the LX 70 8 inch reflector I recently purchased.

The 5 and 6 element Plossles are good for longer f-ratio scopes. I use either those or my 4000 series Plossles on my long refractors. My 60mm by 700 mm focal length refractor really needs the 4000 series Plossles for weight reasons, even though I have used 5000 Plossles with it. The 5000 series Plossles have a 60 degree apparent field of view, like the HD 60 eyepieces, but have a little more trouble around the outside edges of the field. I have used and enjoyed them with my Polaris 130 f/5 scope, but I normally use them with a 90mm f/11 and a 100 mm f/8 refractors.

The advantage of the HD 60 eyepieces shows up with shorter focal ratio scopes, like your Polaris 130. With the four element Plossles, the cut off the edge of the field where it starts to get too weird. As the number of elements in the eyepieces increase, along with using different types of glass, they are able to control things on the edge better. The HD 60 eyepieces are a good example of that.

You will also notice as you go wider and wider with the view, and have a good image at whatever edge limit the eyepiece has, the price goes up. Light transmission is another factor as well as light scatter. Exactly what eyepiece type is best depends on a lot of factors, including the type and nature of the telescope, the type of objects to be observed, the light conditions, how much money someone can or is willing to spend, ....and on and on.

I still believe that a good set of four element Plossles is about as good as anyone really needs, but some of the others are nice.

There are some specialty eyepieces that can beat the HD 60 series for the particular type of viewing they have been designed for, but for one good set of general purpose viewing for most scopes, the HD 60 eyepieces are a good way to go....if you are in a position to spend the extra money for them.

They are too heavy for my small scopes, but for larger ones, starting with something like the Polaris 130, or Infinity 102, they work very well. They are all the same weight, so people using a Dobsonian telescope do not have to worry about a changing weight balance as one changes focal length.

Hope this helps,

Bill
Bill Steen, Sky Hunters' Haven Observatory, Broken Arrow, Oklahoma

#7 jiangshi

jiangshi

    Member

  • Members
  • PipPip
  • 13 posts
  • LocationArizona

Posted 13 September 2015 - 08:45 AM

I still believe that a good set of four element Plossles is about as good as anyone really needs, but some of the others are nice.

 

Hi Bill,

 

I have been thinking about what you are saying about four element Plossles. I was out the night before last, and looking at the Great Orion Nebula. I swapped my MA 26mm for the MA 9mm, and as expected, the image was significantly dimmed. With a 130mm mirror, I need all the light I can get! I am thinking that a set of the 4000 series is the best bet for increasing eyepiece performance.

 

I also decided that the red-dot finder scope is not going to work except maybe for the Moon, Jupiter, and Saturn. Does Meade sell finder scopes separately, and will any of them fit the Polaris 130?

 

~todd



#8 MistrBadgr

MistrBadgr

    Advanced Member

  • Administrators
  • 2800 posts
  • LocationBroken Arrow, Oklahoma

Posted 13 September 2015 - 06:43 PM

They do not have any listed, but I called them to find out if I could get a second one like my Lightbridge has to put on my LX 70 8 inch reflector. They did.

The issue with the red dot finder on the Polaris 130 is the kind of base it has on it. It has one where you simply drop the finder over two bolts, and then tighten down two thumb nuts. The other ones that I think are available have a base that the bottom part of the finder slides into and you just tighten up a thumb screw on the base piece. You can mount a base on your optical tube by locating a spot where you thing you want it, then hold the base to that spot and mark where the holes are with a felt tipped marker. Tilt the scope at a downward angle with the spot you want to drill holes rotated to the upward position on the tube. Put a piece of paper inside the scope to catch any metal pieces, then drill the holes. The base pieces that I have bought normally come with two nuts and bolts. I am not sure about the ones Meade sells, so I would ask. Call customer support with their 1-800 number or email them at the new email address and ask to see what they have available.

I think they have base pieces for sale and you could buy one of those to fit a different kind of finder. Even though I have not put one on my Polaris 130, I personally like to have both types. What I currently have on my LX 70 is a right angle, correct image 6X30mm finder on one side of the focuser. I look at a lot of things directly overhead or nearly so. Having a right angle finder helps me from bending over at exactly one spot to look into the eyepiece of a straight finder. I then put a red dot finder on the other side of the focuser.

What I like to do is look the area over where the object I want to see is located with a pair of binoculars (if needed), then go to the red dot finder and put the dot on the spot where I think the object is. The next step is to go to the correct image finder (has the same image perspective as binoculars and red dot finder) to zero in better, then on to the main scope. This works out very well if I am trying to hunt down dimmer double stars.

There are times, however, that I have been able to put the red dot on an object that I could see with my eyes and then look straight into the scope with a shorter focal length eyepiece and see the object in the field.

Don't sell your red dot finder too short, they can work out well with practice. My biggest beef with them is that I have a habit of forgetting to turn them off and end up running down the batteries.

Bill
Bill Steen, Sky Hunters' Haven Observatory, Broken Arrow, Oklahoma

#9 jiangshi

jiangshi

    Member

  • Members
  • PipPip
  • 13 posts
  • LocationArizona

Posted 15 September 2015 - 10:46 PM

Hi Bill, you make a good point about the red dot finder, and I am going to keep practicing with it, and make sure I have an extra battery or two. Actually, I've been thinking about how I usually find objects in the first place, and that is to do a decent polar alignment and then get the scope pointed in the general area and hunt around on low power. I generally find what I am looking for.

 

I very much appreciate your comments and suggestions!!

 

~todd






0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users