Jump to content


Photo

Upgrading a diagonal on a "MAK-CASS" (??)

  • Please log in to reply
22 replies to this topic

#1 Grandpa Jim

Grandpa Jim

    old fogey

  • *****
  • Posts: 411
  • Joined: 04 Aug 2012
  • Loc: GREAT AMERICAN DESERT

Posted 03 January 2013 - 12:38 AM

I found a good deal on one of these used as an "OTA", and I want to upgrade the diagonal (possibly 2 inch??)
First, I'm wondering if there are any drawbacks to going 2", and second & MOST important.......I'm at a loss as far as what adapter(s) I need to accomplish this??

THIS IS THE SCOPE: http://www.telescope...tarMax-127mm...

THIS IS THE DIAGONAL I HAD CONSIDERED: http://agenaastro.co...ar-mirror-di...

Do I need anything additional, or...........does anyone have a better suggestion?? (I had considered "Baader Click-Lock", but that got too expensive too fast).

Thanks for any help.........this is my first telescope of this type, trying to set it up right from the start and avoid costly mistakes.

#2 Tom and Beth

Tom and Beth

    Soyuz

  • -----
  • Posts: 3714
  • Joined: 08 Jan 2007
  • Loc: Tucson, AZ

Posted 03 January 2013 - 04:28 AM

Does the scope have SCT type connecter on the back you can attach that diagonal to, and more importantly, is the opening in the back of the scope large enough to warrant a 2 inch diagonal. I suspect the answer to the second question is "NO"

I realize 2 inch EPs are nice, heck I have several for my scopes, but if the light bundle goes through a 25MM hole...you'll never get the benefit of the bigger EP.

Hopefully someone will chime in with the dimension....

#3 Eddgie

Eddgie

    Voyager 1

  • *****
  • Posts: 12975
  • Joined: 01 Feb 2006

Posted 03 January 2013 - 07:08 AM

I agree with Tom and Beth, or Tom, or Beth.. LOL.

The very small port on the rear of these scopes makes the use of a 2" diagonal rather problematic. If you use eyepieces with much wider field stops you can see vignetting.

Also, depending on the scope, the aperture might be reduced slightly.

And finallly, it raises the magnification for that focal lenght eyepices. In SCTs and MCTs with moving mirrors, when you add back focus, you increase the focal lenght, and this increas is not linear. In other words, adding 50mm of back focus can cause your focal lenght to increase by 150mm, so your power is higher and your true field is narrower than you would think.

These scopes were designed for optimal use with 1.25" eyepeices, but don't let that stop you from using a 2" diagonal if you want to, but don't expect to get a super-wide field of view. You can go up a little in 2" focal lenght eyepcies, but the field vignettes after you get to only a little wider than you can get with a 1.25" eyepiece.

#4 Grandpa Jim

Grandpa Jim

    old fogey

  • *****
  • Posts: 411
  • Joined: 04 Aug 2012
  • Loc: GREAT AMERICAN DESERT

Posted 03 January 2013 - 11:06 AM

OK..........I can see some of the issues with a 2 inch diagonal now (I thought there might be some).
Any suggestions beyond that?............

#5 Grandpa Jim

Grandpa Jim

    old fogey

  • *****
  • Posts: 411
  • Joined: 04 Aug 2012
  • Loc: GREAT AMERICAN DESERT

Posted 03 January 2013 - 12:12 PM

Does the scope have SCT type connecter on the back you can attach that diagonal to, and more importantly, is the opening in the back of the scope large enough to warrant a 2 inch diagonal. I suspect the answer to the second question is "NO"


Is "this" the connector you meant?? http://www.telescope...productId=52067
If so, why do they make it sound as if a 2" is almost recommended?? -- Not doubting your word, just trying to learn something here. :)

#6 johnnyha

johnnyha

    Fly Me to the Moon

  • *****
  • Posts: 6500
  • Joined: 12 Nov 2006
  • Loc: Sherman Oaks, CA

Posted 03 January 2013 - 02:14 PM

There is simply no reason to try using 2" eyepieces with this scope, I would use it at 1.25" as designed to avoid multiple issues.


#7 Grandpa Jim

Grandpa Jim

    old fogey

  • *****
  • Posts: 411
  • Joined: 04 Aug 2012
  • Loc: GREAT AMERICAN DESERT

Posted 03 January 2013 - 02:17 PM

There is simply no reason to try using 2" eyepieces with this scope, I would use it at 1.25" as designed to avoid multiple issues.


I have listened to advice, and agree about the 2" diagonal....what I would like advice on though is a GREAT 1.25 inch diagonal to upgrade to, so that I get the most from the scope.

#8 johnnyha

johnnyha

    Fly Me to the Moon

  • *****
  • Posts: 6500
  • Joined: 12 Nov 2006
  • Loc: Sherman Oaks, CA

Posted 03 January 2013 - 02:23 PM

Astro Tech makes an excellent 1.25" dielectric diagonal, especially for the price. They appear to be out of stock at Astronomics but they do have the quartz version in stock for just $10 more at $79.

#9 Grandpa Jim

Grandpa Jim

    old fogey

  • *****
  • Posts: 411
  • Joined: 04 Aug 2012
  • Loc: GREAT AMERICAN DESERT

Posted 03 January 2013 - 03:18 PM

There we go!...........Thanks!
Any other "tune up" suggestions??

#10 Tom and Beth

Tom and Beth

    Soyuz

  • -----
  • Posts: 3714
  • Joined: 08 Jan 2007
  • Loc: Tucson, AZ

Posted 03 January 2013 - 10:43 PM

Does the scope have SCT type connecter on the back you can attach that diagonal to, and more importantly, is the opening in the back of the scope large enough to warrant a 2 inch diagonal. I suspect the answer to the second question is "NO"


Is "this" the connector you meant?? http://www.telescope...productId=52067
If so, why do they make it sound as if a 2" is almost recommended?? -- Not doubting your word, just trying to learn something here. :)


Yes it is. I would SUSPECT one reason they would make a 2 incher sound like the best thing since sliced bread would be more dinero in THEIR pocket, but I'm a sceptic :smirk:

At the same time, there are so many accessories with SCT type threads, from camera adapters to better 1.25 inch diagonals..I'd get this ring if I was buying this scope.
A rather lose analagy is that the SCT thread is "standard".

#11 Grandpa Jim

Grandpa Jim

    old fogey

  • *****
  • Posts: 411
  • Joined: 04 Aug 2012
  • Loc: GREAT AMERICAN DESERT

Posted 04 January 2013 - 12:54 AM

[quote name="Tom and Beth"]Is "this" the connector you meant?? http://www.telescope...productId=52067
If so, why do they make it sound as if a 2" is almost recommended?? -- Not doubting your word, just trying to learn something here. :) [/quote]

Yes it is. I would SUSPECT one reason they would make a 2 incher sound like the best thing since sliced bread would be more dinero in THEIR pocket, but I'm a sceptic :smirk:

At the same time, there are so many accessories with SCT type threads, from camera adapters to better 1.25 inch diagonals..I'd get this ring if I was buying this scope.
A rather lose analagy is that the SCT thread is "standard". [/quote]

Is there a 1.25 inch diagonal that you would recommend that fits this adapter??

#12 Gary Riley

Gary Riley

    Mariner 2

  • -----
  • Posts: 297
  • Joined: 01 Dec 2011
  • Loc: White Bluff, TN

Posted 04 January 2013 - 02:02 AM

Stick with 1.25 inch diagonal. The Orion 1.25 dielectric diagonal is a pretty good diagonal. You also might consider using a 9x50 RACI finder scope and also mount a Telrad as well to aid in pointing and locating your targets. And you will want a decent dew shield for it as well.

Gary

#13 hottr6

hottr6

    Vanguard

  • *****
  • Posts: 2442
  • Joined: 28 Jun 2009
  • Loc: 7,500', Magdalena Mtns, NM

Posted 04 January 2013 - 08:30 AM

And you will want a decent dew shield for it as well.

Given that the OP lives in the desert, this may be unnecessary. Buying accessories for a 'scope should be based on need, not because it sounds like a good idea.

Having said that, IMHO, the absolutely most important reason for a 2" VB on a MCT is the ability to use a decent focuser and avoid mirror shift that accompanies the stock focuser. Some folk have used the 1.25" helical Borg focuser, but consensus appears that SCT Crayford focusers may be the best bet. The long f/l of MCTs does not mandate a two-speed focuser, so pennies can be saved and reliability gained by looking for a single-speed. Alas, SCT Crayfords only come in 2" sizes.
Posted Image
Crayfords are pretty "long", and will change the focal length of the 'scope, so it is pretty important to look for a SCT focuser that is "low profile". I have found the SCT focusers from Crawmach and JMI are shorter than the focusers from Asia. There may be others.

All this "stuff" adds weight. Make sure your mount is up to the task.

#14 Eddgie

Eddgie

    Voyager 1

  • *****
  • Posts: 12975
  • Joined: 01 Feb 2006

Posted 04 January 2013 - 12:59 PM

I would actually recommend the Baader T2 Prism Prism diagonal.

This is a very high quality diagonal that offers several advantages.

First, it has a very short light path, keep ing the focal lenght of your scope as short as possible and Alpine Astro might even have an adapter that allows it to be connected direclty to the scope, though the easiest thing to do would be to just use the 1.25" nose in your current visual back.

Second, it has a built in micro-focuser making fine focusing easier to achieve. Alternatly, you can add the Twistlock eyepeice holder so there are no more retention screws to deal with.

Third, if has numerous connection capbilities because of the modular design,

And last, if you ever decide to go to a Maxbright binoviewer or Televue binoviewer, the can connect directly to the top of the diagonal, giving you the widest possible field.

These are excellent diagonals. Anyone wanting a strong, high quality 1.25" diagonal should consider the added benefits. It is strong because it was designed to take the load of a binoviewer with heavy Hyperion eyepieces.

If you haven't made your decision yet, you should consider the Maxbright standard prism (not the Baader Ziess. It costs almost twice as much and I don't see how it could be meaningfully better).

Second set of pictures down on this page, picture on the right...

#15 Scott Beith

Scott Beith

    SRF

  • *****
  • Administrators
  • Posts: 44514
  • Joined: 26 Nov 2003
  • Loc: Frederick, MD

Posted 04 January 2013 - 01:07 PM

The first upgrade for my Orion Starmax 127 I used to own was a Stellarvue 1 1/4" enhanced diagonal. Any of the current dielectrics by AstroTech, Stellarvue, etc... will serve you well.

#16 Grandpa Jim

Grandpa Jim

    old fogey

  • *****
  • Posts: 411
  • Joined: 04 Aug 2012
  • Loc: GREAT AMERICAN DESERT

Posted 04 January 2013 - 02:11 PM

I would actually recommend the Baader T2 Prism Prism diagonal.

This is a very high quality diagonal that offers several advantages.

First, it has a very short light path, keep ing the focal lenght of your scope as short as possible and Alpine Astro might even have an adapter that allows it to be connected direclty to the scope, though the easiest thing to do would be to just use the 1.25" nose in your current visual back.

Second, it has a built in micro-focuser making fine focusing easier to achieve. Alternatly, you can add the Twistlock eyepeice holder so there are no more retention screws to deal with.

Third, if has numerous connection capbilities because of the modular design,

And last, if you ever decide to go to a Maxbright binoviewer or Televue binoviewer, the can connect directly to the top of the diagonal, giving you the widest possible field.

These are excellent diagonals. Anyone wanting a strong, high quality 1.25" diagonal should consider the added benefits. It is strong because it was designed to take the load of a binoviewer with heavy Hyperion eyepieces.

If you haven't made your decision yet, you should consider the Maxbright standard prism (not the Baader Ziess. It costs almost twice as much and I don't see how it could be meaningfully better).

Second set of pictures down on this page, picture on the right...


That IS my first choice, but it's definitely "budget dependent" :)

#17 Gary Riley

Gary Riley

    Mariner 2

  • -----
  • Posts: 297
  • Joined: 01 Dec 2011
  • Loc: White Bluff, TN

Posted 04 January 2013 - 04:10 PM

The dew shield would also help to cut down on any stray light that would try to enter the front of the scope as well.

#18 Tom and Beth

Tom and Beth

    Soyuz

  • -----
  • Posts: 3714
  • Joined: 08 Jan 2007
  • Loc: Tucson, AZ

Posted 04 January 2013 - 04:24 PM

[quote name="Grandpa Jim"][quote]Is "this" the connector you meant?? http://www.telescope...productId=52067
If so, why do they make it sound as if a 2" is almost recommended?? -- Not doubting your word, just trying to learn something here. :) [/quote]

Yes it is. I would SUSPECT one reason they would make a 2 incher sound like the best thing since sliced bread would be more dinero in THEIR pocket, but I'm a sceptic :smirk:

At the same time, there are so many accessories with SCT type threads, from camera adapters to better 1.25 inch diagonals..I'd get this ring if I was buying this scope.
A rather lose analagy is that the SCT thread is "standard". [/quote]

Is there a 1.25 inch diagonal that you would recommend that fits this adapter?? [/quote]

I use the diagonal that came with my C-8, but just about any 1.25 inch diagonal would work. Oh, BTW, the C-8 uses a SCT to 1.25 inch adapter, EDIT: I see there's a few suggestions for some really good diagonals above. Save your pennies and pic them up as funds allow

IIRC this scope you're looking at also comes with a diagonal that slips into a 1/25 inch adapter of some sort. There's no reason not to use that diagonal.

FWIW. like any hobby there's a bit of snake oil to avoid. Try your new scope with what it comes with, maybe pick up some good 1.25 inch EPs here and there. But USE whatever you have. It's darn easy to get wrapped up in the goodies and miss the absolute beauty of the sky. For on axis views, it's REALLY hard to beat a TV Plossl, or a simple Abbe Ortho. Maybe some day move up to 1.25 inch TV Naglers, like the 13MM Type 6.

#19 Starman1

Starman1

    Vendor (EyepiecesEtc.com)

  • *****
  • Vendors
  • Posts: 23167
  • Joined: 23 Jun 2003
  • Loc: Los Angeles

Posted 04 January 2013 - 10:44 PM

I've owned one of these scopes for years:
1) Upgrade to a dielectirc 1.25" diagonal for brightness and longevity.
2) Shorten the visual back on the scope. It has threads on the end that are unnecessary and lengthen the effective focal length and reduce the field of view unnecessarily. I simply machined off the threads, taking about a centimeter off the visual back. It had no impact on diagonal attachment and it slightly widened the true field of view in a "maximum" field eyepiece
[examples: 40mm Plossl, 32mm Plossl, 24mm wide field eyepieces, 35mm Ultrascopic/Eudiascopic/etc.
3) maximum field of view with shortened visual back is:
25/1500*57.3 = 0.955 degrees. Toleration for a little vignetting stretches this to just over a degree with the above eyepieces.
4) Do not add a rear-mounted focuser. It is unnecessary because there is little image shift in this scope and because it lengthens the focal length of the scope.
5) You can improve the focuser a bit. Make sure the rubber cap on the focuser screw does not touch the back of the scope. I trimmed mine and it seemed to remove 50% of the effort to turn the focuser knob. Run the focuser from one end to the other several times (it's a LOT of turns!) and this will definitely smooth out the movement.
6) You can make the focuser knob a two speed by adding this to the focus knob. If they don't have one that fits, you can easily make your own out of styrofoam or rubber.

Enjoy the scope. If you got one anywhere near the optical quality of mine, you'll never get rid of it.

P.S. a S&T test of this scope indicates the clear aperture is really more like 121mm, not 127. It turns out the rays from the edge of the corrector miss the primary mirror entirely. That makes the scope as it comes 1540/121 or f/12.7

#20 Grandpa Jim

Grandpa Jim

    old fogey

  • *****
  • Posts: 411
  • Joined: 04 Aug 2012
  • Loc: GREAT AMERICAN DESERT

Posted 05 January 2013 - 06:20 PM

Thanks Don!!.........GREAT tips! :) Jim Jeffries

#21 astro_baby

astro_baby

    Viking 1

  • -----
  • Posts: 998
  • Joined: 17 Jun 2008
  • Loc: United Kingdom

Posted 06 January 2013 - 02:04 PM

Actually there was a long thread on this in the Maks section. Adding an external focuser shouldnt affect this scope as its effective aperture is only 117mm anyway, at least that was the consensus in the Mak forum.

i have the 180 version and adding an external Crayford. Akes no difference to the aperture as the true aperture of the s ope is only about 170mm anyway and adding the external focuser and using a 2" diagonal doesnt truncate the light path in any way, though it does increase the focal ratio by a bit.

If you search using my name as a poster in the Maks forum you should find the thread. i dont post much in that forum so it should t be hard to find as a thread.

This issues was much discussed in there and may be food for thought.

#22 astro_baby

astro_baby

    Viking 1

  • -----
  • Posts: 998
  • Joined: 17 Jun 2008
  • Loc: United Kingdom

Posted 06 January 2013 - 02:08 PM

Ps I added the external focuser because good as the focuser is on these s opes it does still introduce mirror shift and I found at high mags, heck everything is at high mags in this scope, the mirror shift was driving me nuts. I seemed to spend all night either twiddiling the focuser or bumping the mount to recentre the target.

The advice I got was so long as the EPs field lens was smaller than the exitort on the scope there shouldnt be much in the way of problems. Its kind of aademic to me because ai mostly use Orthos in the Mak.

#23 astro_baby

astro_baby

    Viking 1

  • -----
  • Posts: 998
  • Joined: 17 Jun 2008
  • Loc: United Kingdom

Posted 06 January 2013 - 03:30 PM

PPS heres the thread I mentioned, i couldnt give a link earlief

http://www.cloudynig...5093831/page...






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics