Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

The AT72EDII is out!

  • Please log in to reply
480 replies to this topic

#51 Astronomics

Astronomics

    Vendor: Astronomics

  • *****
  • Administrators
  • Posts: 6,627
  • Joined: 07 Jun 2004
  • Loc: Right Here

Posted 11 June 2017 - 01:55 PM

 

 

 

 

 

It weighs 4.65 pounds with the dovetail and rings. We will not have an 80mm doublet. I can't justify the 8mm difference in the line and prefer the jump to a triplet. We have tried same sizes in different optical configurations in the past and it would lock customers up to the point of not purchasing anything.

In that case, any plans for a doublet somewhere between the 80 and 115 mm triplets?

 

   Stuart

 

Not at the moment.  We have another project we are getting final quotes on at the moment.  I have a TMB designed 107mm FPL-53 doublet we had looked at, but the odd glass size was causing an issue getting blanks which made the price very high.

 

TMB 92SS? bounce.gif

 

 

Shawn

 

Sort of.  Roger Ceragioli went over the original TMB92 lens design and optimized it using glass that wasn't available 10 years ago.  Roger's optical knowledge is truly legendary, so I can't wait to see the optic if we can get it done.  We can't call it a TMB as it is a collaborative effort.  IF, big if, cost can be held in check we would call it an AT92.

 

 

Wow an AT92... just saying if you do come out with one I will be ordering.  I absolutely love my AT115.

 

cheers

 

k

 

It will be a much different animal than the EDT series.  We are looking at FPL53 or FCD100 center element with a lanthanum rear element, f/5.5 like the original, 90mm tube like the light version, 2.5" focuser, .96 strehl or better, 1/6th wave or better.  It will be the same great performer the TMB92 is, just packaged a little differently.


  • zjc26138, sparrowhawk, Tyson M and 1 other like this

#52 Jon Isaacs

Jon Isaacs

    ISS

  • *****
  • Posts: 84,139
  • Joined: 16 Jun 2004
  • Loc: San Diego and Boulevard, CA

Posted 11 June 2017 - 02:06 PM

Unfortunately, if you want to use heavy 2" eyepieces with this scope, you either deal with an imbalanced OTA when pointing toward zenith or you deal with awkwardly positioned focuser knobs.  Neither option is ideal.

 

 

One of the advantages of sidesaddle mounting the AT-72ED on the 3047 head is that one can easily add a touch of friction if necessary to balance those heavy 2 inch eyepieces. 

 

To eliminate focuser clearance issues, I swapped the fine focus over to the left side. 

 

Jon



#53 erinsastroimages

erinsastroimages

    Explorer 1

  • *****
  • Posts: 71
  • Joined: 25 May 2012

Posted 11 June 2017 - 02:38 PM

Count me in for the AT92 too! :-)


  • Augustus likes this

#54 dagadget

dagadget

    Viking 1

  • *****
  • Posts: 891
  • Joined: 16 Jun 2016
  • Loc: Avon Park, Florida

Posted 11 June 2017 - 03:29 PM

Count me in for the AT92 too! :-)

If it performs like the TMB 92 but the packaging is different or Better you will sell a lot of them I would also be interested and I would be giving my 114 Celestron reflector and the GT mount it is on away very quickly.....


  • Augustus likes this

#55 gwlee

gwlee

    Surveyor 1

  • *****
  • Posts: 1,880
  • Joined: 06 Sep 2015
  • Loc: 38N 120W

Posted 11 June 2017 - 06:43 PM

One problem that I see for both the old and new versions of the AT72ED - and similar scopes as well - is the tendency for the OTA to be imbalanced when observing with heavier 2" diagonals and 2" eyepieces.  

 

To compensate for the heavier back-end when using a heavy 2" eyepiece and diagonal, either the OTA needs to be shifted forward on the mount or a weight needs to be added toward onto the front-end of the OTA.  I don't want to install a counterweight onto the OTA of this telescope.

 

To shift the OTA forward, the dovetail needs to be extended farther back.  Installing a longer dovetail on the new version of the AT72ED - or piggybacking a longer one onto the smaller dovetail of the old version - does not help unless that longer dovetail extends much farther back.  Extending it forward will not help.

 

However, if you extend the dovetail back far enough to compensate for the imbalance caused by a heavy eyepiece, the dovetail has a good chance of hitting the focuser knobs.  You can avoid this by positioning the dovetail directly below the telescope and keeping the focuser knobs horizontal, on the left and right sides of the OTA.  But then, if you want to keep the focuser knobs horizontal, you have to attach the telescope on top of the mount, as on a photo tripod head.  Positioned directly on top of a mount makes the OTA subject to being off balance and falling back when the OTA is pointed toward zenith.  Not too good.

 

On the other hand, if you attach the OTA to the side of the head - as in the Dwarfstar, Microstar and M2 heads - then you need to position the focuser knobs vertically in order to avoid the long back-extended dovetail.  But in that case, the finder base will be in an awkward position.  So in order to place the finder base in a non-awkward position, you end up positioning the focuser knobs diagonally, which is an awkward position for the focuser knobs.

 

Unfortunately, if you want to use heavy 2" eyepieces with this scope, you either deal with an imbalanced OTA when pointing toward zenith or you deal with awkwardly positioned focuser knobs.  Neither option is ideal.

 

That is, unless possibly you place the AT72ED on a mount which is so much heavier and beefier than what I've been using, that it overwhelms the inherent tendency to imbalance.  But IMO putting a little scope on a big mount obviates the grab-n-go advantage of the little scope.

 

Or you can just mount the scope on top of a decent photo-tripod style head - like my 501HDV - and clamp it down real hard when pointing toward zenith.  IMO, not a good solution.  Been there, done that, don't want to go back.

 

Mike

I know the AT72ED doesn't balace using the stock mounting foot when it's equiped with a 1.25 diagonal and EP. A standard vixen-style bar attached to the foot and extending rearward allows it to balance with the focus knobs vertical or horizontal. Don't use 2" EPs with this scope, so don't know if there's a way to balance it. I orient the knobs vertically sometimes and haven't noticed and problems besides looking odd. I could post a photo if anyone is interested. 

 

Looks to me like the stock AT72ED2 should balance setup for 1.25" accessories, but Michael is the only person who could really know at this time. 

 

If 2" accessories won't balance, it could be a show stopper for people want to use them. 


Edited by gwlee, 11 June 2017 - 07:11 PM.


#56 sparrowhawk

sparrowhawk

    Ranger 4

  • *****
  • Posts: 382
  • Joined: 02 Sep 2007
  • Loc: Minnesota / United Arab Emirates

Posted 11 June 2017 - 07:43 PM

 

 

 

 

 

 

It weighs 4.65 pounds with the dovetail and rings. We will not have an 80mm doublet. I can't justify the 8mm difference in the line and prefer the jump to a triplet. We have tried same sizes in different optical configurations in the past and it would lock customers up to the point of not purchasing anything.

In that case, any plans for a doublet somewhere between the 80 and 115 mm triplets?

 

   Stuart

 

Not at the moment.  We have another project we are getting final quotes on at the moment.  I have a TMB designed 107mm FPL-53 doublet we had looked at, but the odd glass size was causing an issue getting blanks which made the price very high.

 

TMB 92SS? bounce.gif

 

 

Shawn

 

Sort of.  Roger Ceragioli went over the original TMB92 lens design and optimized it using glass that wasn't available 10 years ago.  Roger's optical knowledge is truly legendary, so I can't wait to see the optic if we can get it done.  We can't call it a TMB as it is a collaborative effort.  IF, big if, cost can be held in check we would call it an AT92.

 

 

Wow an AT92... just saying if you do come out with one I will be ordering.  I absolutely love my AT115.

 

cheers

 

k

 

It will be a much different animal than the EDT series.  We are looking at FPL53 or FCD100 center element with a lanthanum rear element, f/5.5 like the original, 90mm tube like the light version, 2.5" focuser, .96 strehl or better, 1/6th wave or better.  It will be the same great performer the TMB92 is, just packaged a little differently.

 

Are you considering having a removable section like the TMB92 to accommodate binoviewers?

 

 

Shawn



#57 Astronomics

Astronomics

    Vendor: Astronomics

  • *****
  • Administrators
  • Posts: 6,627
  • Joined: 07 Jun 2004
  • Loc: Right Here

Posted 11 June 2017 - 07:58 PM

Are you considering having a removable section like the TMB92 to accommodate binoviewers?

 

 

 

 

Shawn

 

Not sure yet.  I would say probably no.  I don't like the idea of unthreading a tube section.


  • Sarkikos likes this

#58 Sarkikos

Sarkikos

    ISS

  • *****
  • Posts: 31,220
  • Joined: 18 Dec 2007
  • Loc: Per sylvam ad astra

Posted 12 June 2017 - 06:00 AM

 

Unfortunately, if you want to use heavy 2" eyepieces with this scope, you either deal with an imbalanced OTA when pointing toward zenith or you deal with awkwardly positioned focuser knobs.  Neither option is ideal.

 

 

One of the advantages of sidesaddle mounting the AT-72ED on the 3047 head is that one can easily add a touch of friction if necessary to balance those heavy 2 inch eyepieces. 

 

To eliminate focuser clearance issues, I swapped the fine focus over to the left side. 

 

Jon

 

My Microstar is a sidesaddle head.  It has detention knobs for altitude and azimuth.  But IMO clamping down to compensate for imbalance is a partial fail.  Ideally the OTA should be balanced well enough front to rear so that it will not move when the altitude detention knob is relaxed.  "Balancing" by clamping down on a knob is not balancing.

 

IIRC, a longer dovetail, even when piggybacked on the short attached dovetail, will not clear either side of the focuser.  In any case, I prefer to have the fine focus on the right side because I am right handed.

 

Mike


Edited by Sarkikos, 12 June 2017 - 06:05 AM.


#59 Sarkikos

Sarkikos

    ISS

  • *****
  • Posts: 31,220
  • Joined: 18 Dec 2007
  • Loc: Per sylvam ad astra

Posted 12 June 2017 - 06:16 AM

I know the AT72ED doesn't balace using the stock mounting foot when it's equiped with a 1.25 diagonal and EP. A standard vixen-style bar attached to the foot and extending rearward allows it to balance with the focus knobs vertical or horizontal. Don't use 2" EPs with this scope, so don't know if there's a way to balance it. I orient the knobs vertically sometimes and haven't noticed and problems besides looking odd. I could post a photo if anyone is interested. 

Looks to me like the stock AT72ED2 should balance setup for 1.25" accessories, but Michael is the only person who could really know at this time. 

 

If 2" accessories won't balance, it could be a show stopper for people want to use them. 

Heavy 2" accessories will balance as long as you install a long enough dovetail and have it extended backwards, not forward.  Having the dovetail pointed toward the front of the scope doesn't do any good.  

 

But as I said, a backward facing dovetail long enough to compensate for a heavy 2" eyepiece will probably interfere with the focuser knobs.  The solutions to that problem are to attach the scope on top of the mount (causing imbalance when pointing toward zenith), or if the scope is attached side-saddle, to position the focuser knobs vertically.  But positioning the focuser knobs vertically when the scope is mounted side-saddle can put the finder base in an awkward position.

 

IIRC, I have not had balancing problems with 1.25" diagonals and eyepieces.

 

Mike


Edited by Sarkikos, 12 June 2017 - 06:23 AM.


#60 gwlee

gwlee

    Surveyor 1

  • *****
  • Posts: 1,880
  • Joined: 06 Sep 2015
  • Loc: 38N 120W

Posted 12 June 2017 - 11:02 AM

 

I know the AT72ED doesn't balace using the stock mounting foot when it's equiped with a 1.25 diagonal and EP. A standard vixen-style bar attached to the foot and extending rearward allows it to balance with the focus knobs vertical or horizontal. Don't use 2" EPs with this scope, so don't know if there's a way to balance it. I orient the knobs vertically sometimes and haven't noticed and problems besides looking odd. I could post a photo if anyone is interested. 

Looks to me like the stock AT72ED2 should balance setup for 1.25" accessories, but Michael is the only person who could really know at this time. 

 

If 2" accessories won't balance, it could be a show stopper for people want to use them. 

 

But as I said, a backward facing dovetail long enough to compensate for a heavy 2" eyepiece will probably interfere with the focuser knobs. 

 

 

Mike

 

 

I am confused. Are you speculating (see above) that 2" accessories will interfere with the focuser knobs of the AT72ED, or do you know this from experience using 2" accessories?

 

I think anyone buying a scope with a 2" focuser expects it to balance with both 1.25" and 2.0" accessories in the normal orientation and without modifications when mounted on an alt/az mount. If it doesn't, the manufacturer or importer should disclose this shortcoming and be prepared for some returns. 

 

The AT72ED definitely does not balance with 1.25" accessories without installing an accessory rail, which is a PITA. After installing the rail and perfectly balancing the scope, i found that the rail does not interfere with the focuser in either the horizontal or vertical orientation. I am right handed and prefer the horizontal orientation, but found the focuser and multi retical finder were usable in both orientations. I have not used the AT72ED with 2.0" accessories, so defer to those with experience. 

 

As far as I know Michael is the only one with any ED2 experience, so I am hoping he will let us know what to expect with this product. 

 

The photos show both orientations with 1.25" accessories. Dew shield extended, dew cap removed, focused at infinity, perfectly balanced, zero tension on the altitude axis. The mount is a UA DwarfStar. 

 

BTW, I haven't tried it, but the scope might balance with 1.25" accessories by simply reversing the stock mounting foot. Has anyone tried this simple fix?

Attached Thumbnails

  • IMG_0486.JPG
  • IMG_0487.JPG

Edited by gwlee, 12 June 2017 - 12:49 PM.


#61 Sarkikos

Sarkikos

    ISS

  • *****
  • Posts: 31,220
  • Joined: 18 Dec 2007
  • Loc: Per sylvam ad astra

Posted 12 June 2017 - 01:20 PM

 

But as I said, a backward facing dovetail long enough to compensate for a heavy 2" eyepiece will probably interfere with the focuser knobs. 

 

Mike

 

I am confused. Are you speculating (see above) that 2" accessories will interfere with the focuser knobs of the AT72ED, or do you know this from experience using 2" accessories?

 

Read the next paragraph in my post:

The solutions to that problem are to attach the scope on top of the mount (causing imbalance when pointing toward zenith), or if the scope is attached side-saddle, to position the focuser knobs vertically.  But positioning the focuser knobs vertically when the scope is mounted side-saddle can put the finder base in an awkward position.

I am not speculating.  I am speaking from my experience using 2" eyepieces with the AT72ED.  Of course, I don't have experience with the AT72ED II, but I don't expect it to be any different in this regard.  

 

I'm not talking about 2" accessories interfering with the focuser knobs, but the longer backward-extended dovetail (necessary to balance 2" accessories) interfering with the focuser knobs.

 

Keep in mind that whether or not a longer dovetail interferes with the focuser knobs depends on how long the dovetail is, and how far back it is extended.  You really need a longer dovetail extended well back to balance heavy 2" eyepieces and diagonals.

 

I was assuming that the dovetail would be positioned at the side of the OTA, not underneath it.  When the dovetail is at the side, it can be attached to a side-mounting head like the Dwarfstar, Microstar, M2, etc.  But when a long back-extended dovetail is at the side of the AT72ED OTA, it will interfere with the focusing knobs, unless the knobs are shifted toward a vertical position by rotating the focuser.  

 

Mounting a telescope by a dovetail below the OTA is more suitable for terrestrial use.  This is because in such a setup the OTA will tend to fall down and back when the OTA is pointed toward zenith.   I know this for a fact because I've mounted different small telescopes and binoculars on my 501HDV head, which has the saddle on top, not at the side.   Unless the instrument is very light and well balanced front and back, it will start to tip down and backwards when pointed up.  Of course, you can stop the backward movement by clamping down hard, but that is not the best solution.  It is better to mount instruments meant for astronomy on a side-mounting head.

 

So I think any time you use heavy 2" eyepieces with a small, short refractor like the AT72ED - or the AT72ED II - there is going to be a compromise among convenience, ergonomics and balance.  A long dovetail extended backwards on a side-saddle mount can get in the way but it does let you reach true balance.

 

IME & IMO, forced, hard clamping of the altitude detention knob is a worse compromise.  I think forced clamping and a top-mounted scope is probably the worst option.

 

Mike


Edited by Sarkikos, 12 June 2017 - 02:03 PM.


#62 gwlee

gwlee

    Surveyor 1

  • *****
  • Posts: 1,880
  • Joined: 06 Sep 2015
  • Loc: 38N 120W

Posted 12 June 2017 - 02:53 PM

 

 

But as I said, a backward facing dovetail long enough to compensate for a heavy 2" eyepiece will probably interfere with the focuser knobs. 

 

Mike

 

I am confused. Are you speculating (see above) that 2" accessories will interfere with the focuser knobs of the AT72ED, or do you know this from experience using 2" accessories?

 

Read the next paragraph in my post:

The solutions to that problem are to attach the scope on top of the mount (causing imbalance when pointing toward zenith), or if the scope is attached side-saddle, to position the focuser knobs vertically.  But positioning the focuser knobs vertically when the scope is mounted side-saddle can put the finder base in an awkward position.

I am not speculating.  I am speaking from my experience using 2" eyepieces with the AT72ED.  Of course, I don't have experience with the AT72ED II, but I don't expect it to be any different in this regard.  

 

I'm not talking about 2" accessories interfering with the focuser knobs, but the longer backward-extended dovetail (necessary to balance 2" accessories) interfering with the focuser knobs.

 

Keep in mind that whether or not a longer dovetail interferes with the focuser knobs depends on how long the dovetail is, and how far back it is extended.  You really need a longer dovetail extended well back to balance heavy 2" eyepieces and diagonals.

 

I was assuming that the dovetail would be positioned at the side of the OTA, not underneath it.  When the dovetail is at the side, it can be attached to a side-mounting head like the Dwarfstar, Microstar, M2, etc.  But when a long back-extended dovetail is at the side of the AT72ED OTA, it will interfere with the focusing knobs, unless the knobs are shifted toward a vertical position by rotating the focuser.  

 

Mounting a telescope by a dovetail below the OTA is more suitable for terrestrial use.  This is because in such a setup the OTA will tend to fall down and back when the OTA is pointed toward zenith.   I know this for a fact because I've mounted different small telescopes and binoculars on my 501HDV head, which has the saddle on top, not at the side.   Unless the instrument is very light and well balanced front and back, it will start to tip down and backwards when pointed up.  Of course, you can stop the backward movement by clamping down hard, but that is not the best solution.  It is better to mount instruments meant for astronomy on a side-mounting head.

 

So I think any time you use heavy 2" eyepieces with a small, short refractor like the AT72ED - or the AT72ED II - there is going to be a compromise among convenience, ergonomics and balance.  A long dovetail extended backwards on a side-saddle mount can get in the way but it does let you reach true balance.

 

IME & IMO, forced, hard clamping of the altitude detention knob is a worse compromise.  I think forced clamping and a top-mounted scope is probably the worst option.

 

Mike

 

I understand that you are saying it's the additional rail extending to the rear that interferes with the focuser when the scope is balanced with 2" accessories. Can you post a photos of your AT72ED with 2.0" accessories, so we can see the severity of the problem your are describing? 

 

I would expect the ED2 to behave somewhat differently because it uses rings and a rail instead of the mounting foot used on the ED. It also uses a different focuser, and might not have the weight of the camera angle adjuster. We'll have to wait for Michael to come along to find out whether the ED2 works (balances) natively with both 1.25 and 2.0 accessories. 

 

I agree it's a challenge for anyone to design a short focal length refractor that includes all these features and might be used for astrophotography as well as visually. I have noticed that the 76mm TAK comes in two versions, one for 1.25" accessories and another for 2" accessories, and both are longer focal length than the AT72ED, which might make it easier to achieve balance. If I could be sure the Tak doesn't have other unknown problems, I might just buy it and be done with it. 


Edited by gwlee, 12 June 2017 - 02:56 PM.


#63 Astronomics

Astronomics

    Vendor: Astronomics

  • *****
  • Administrators
  • Posts: 6,627
  • Joined: 07 Jun 2004
  • Loc: Right Here

Posted 12 June 2017 - 03:40 PM

 

Do you know who you talked too?  The e-mail that went out gave a date of 3-4 months.  I can only assume the person here thought it was the current 72.  We don't expect the scopes until October.

 

 

Also, what is the diameter of the ED2 dew shield? Is it same diameter as the ED? I ask because i want to order a solar filter now for the eclipse in August. 

 

Thanks

 

gary

 

It is 88mm.



#64 gwlee

gwlee

    Surveyor 1

  • *****
  • Posts: 1,880
  • Joined: 06 Sep 2015
  • Loc: 38N 120W

Posted 12 June 2017 - 04:37 PM

 

 

Do you know who you talked too?  The e-mail that went out gave a date of 3-4 months.  I can only assume the person here thought it was the current 72.  We don't expect the scopes until October.

 

 

Also, what is the diameter of the ED2 dew shield? Is it same diameter as the ED? I ask because i want to order a solar filter now for the eclipse in August. 

 

Thanks

 

gary

 

It is 88mm.

 

Michael,

 

Are you sure? 88mm doesn't sound plausible for the OD of the ED72ED2 dew shield. 

 

That's about a quarter inch smaller than the AT72ED dew shield. Are both dew shields the same size are different sizes?

 

Thanks

 

Gary



#65 Astronomics

Astronomics

    Vendor: Astronomics

  • *****
  • Administrators
  • Posts: 6,627
  • Joined: 07 Jun 2004
  • Loc: Right Here

Posted 12 June 2017 - 04:42 PM

 

 

 

Do you know who you talked too?  The e-mail that went out gave a date of 3-4 months.  I can only assume the person here thought it was the current 72.  We don't expect the scopes until October.

 

 

Also, what is the diameter of the ED2 dew shield? Is it same diameter as the ED? I ask because i want to order a solar filter now for the eclipse in August. 

 

Thanks

 

gary

 

It is 88mm.

 

Michael,

 

Are you sure? 88mm doesn't sound plausible for the OD of the ED72ED2 dew shield. 

 

That's about a quarter inch smaller than the AT72ED dew shield. Are both dew shields the same size are different sizes?

 

Thanks

 

Gary

 

Just measured it twice with two micrometers.  The new ED72 comes from different manufacturer, so some differences will pop up.



#66 gwlee

gwlee

    Surveyor 1

  • *****
  • Posts: 1,880
  • Joined: 06 Sep 2015
  • Loc: 38N 120W

Posted 12 June 2017 - 05:08 PM

 

 

 

 

Do you know who you talked too?  The e-mail that went out gave a date of 3-4 months.  I can only assume the person here thought it was the current 72.  We don't expect the scopes until October.

 

 

Also, what is the diameter of the ED2 dew shield? Is it same diameter as the ED? I ask because i want to order a solar filter now for the eclipse in August. 

 

Thanks

 

gary

 

It is 88mm.

 

Michael,

 

Are you sure? 88mm doesn't sound plausible for the OD of the ED72ED2 dew shield. 

 

That's about a quarter inch smaller than the AT72ED dew shield. Are both dew shields the same size are different sizes?

 

Thanks

 

Gary

 

Just measured it twice with two micrometers.  The new ED72 comes from different manufacturer, so some differences will pop up.

 

OK Michael, thanks for double checking. I asked because the AT72ED measures 95-96mm at the OD of the dew shield. 

 

 If the clear diameter of AT72ED2  objective lens is 72mm, and the OD of the dew shield is 88mm, that leaves a budget of 16mm for the lens cell walls, main tube walls, and dew shield walls. Much tighter budget than the AT72ED, but possible. 

 

Unfortunately, I won't be able to order a solar filter for my AT72ED and expect to work on the AT72ED2,  but that's what i needed to know. Thanks again.



#67 Simon Alderman

Simon Alderman

    Vostok 1

  • *****
  • topic starter
  • Posts: 119
  • Joined: 22 Aug 2012

Posted 12 June 2017 - 07:59 PM

Michael,

Any idea of a ballpark timeframe for the "AT92"?


  • erinsastroimages likes this

#68 Jon Isaacs

Jon Isaacs

    ISS

  • *****
  • Posts: 84,139
  • Joined: 16 Jun 2004
  • Loc: San Diego and Boulevard, CA

Posted 12 June 2017 - 08:03 PM

I understand that you are saying it's the additional rail extending to the rear that interferes with the focuser when the scope is balanced with 2" accessories. Can you post a photos of your AT72ED with 2.0" accessories, so we can see the severity of the problem your are describing?

 

 

This might be filed under, "Why Jon uses the Bogen 3040 with his AT-72ED.  Note that the fine focuser is on the left, the added offset/clearance between the focuser knob and the mount.  The reason I have the AT-72ED is that it provides wider fields than anything I have but to provide those wide fields, 2 inch eyepieces are required.

 

Jon

Attached Thumbnails

  • AT-72ED Sidesaddle .jpg


#69 Astronomics

Astronomics

    Vendor: Astronomics

  • *****
  • Administrators
  • Posts: 6,627
  • Joined: 07 Jun 2004
  • Loc: Right Here

Posted 12 June 2017 - 08:07 PM

Michael,

Any idea of a ballpark timeframe for the "AT92"?

Late this year at best.  We have a long way to go on it.  I think it will probably be early 2018, if everything works out.


  • Phil Cowell, Simon Alderman and dagadget like this

#70 Simon Alderman

Simon Alderman

    Vostok 1

  • *****
  • topic starter
  • Posts: 119
  • Joined: 22 Aug 2012

Posted 12 June 2017 - 08:20 PM

Sounds very good! Another highly enticing scope to look forward to...


  • Astronomics likes this

#71 Sarkikos

Sarkikos

    ISS

  • *****
  • Posts: 31,220
  • Joined: 18 Dec 2007
  • Loc: Per sylvam ad astra

Posted 13 June 2017 - 07:36 AM

I understand that you are saying it's the additional rail extending to the rear that interferes with the focuser when the scope is balanced with 2" accessories. Can you post a photos of your AT72ED with 2.0" accessories, so we can see the severity of the problem your are describing? 

 

I would expect the ED2 to behave somewhat differently because it uses rings and a rail instead of the mounting foot used on the ED. It also uses a different focuser, and might not have the weight of the camera angle adjuster. We'll have to wait for Michael to come along to find out whether the ED2 works (balances) natively with both 1.25 and 2.0 accessories. 

 

I agree it's a challenge for anyone to design a short focal length refractor that includes all these features and might be used for astrophotography as well as visually. I have noticed that the 76mm TAK comes in two versions, one for 1.25" accessories and another for 2" accessories, and both are longer focal length than the AT72ED, which might make it easier to achieve balance. If I could be sure the Tak doesn't have other unknown problems, I might just buy it and be done with it. 

 

If I have time I will post a photo.  But if you really do understand what I'm saying, why do you need a photo?  Apparently,  you only need a photo because you don't believe what I'm saying.  grin.gif

 

Believe it - or not, as you wish.  In any case, if you install a dovetail that is long enough and extended backwards enough to allow the AT72ED to be completely balanced when using a heavy 2" eyepiece and 2" diagonal, the dovetail will strike one of the focuser knobs, unless you move them out of the way.  I guarantee it.

 

The AT72ED has a rotatable focuser.  The AT72ED II has rings that can be rotated.  In both cases you can set up the telescope so that the focuser knobs are out of the way of a long, backward-extended dovetail.  However, if you mount the AT72ED on a side-saddle mount - which you should do if you want to use the telescope for astronomy - you must set the focuser knobs vertically in order to prevent their striking a long, backward-extended dovetail.  

 

I bet the AT72ED II will have the same balancing/focuser-knob problem when using heavy 2" eyepieces.  My ST80 with 2" Crayford focuser has the same problem.  I don't see how you can avoid the problem with a small, short refractor.  Well, you can either use the scope on a top-mounted head and clamp down hard when pointing toward zenith, or use the scope on a side-saddle mount and get used to observing with the focuser knobs set vertically.  But IMO & IME neither of these solutions are ideal.  They are compromises.

 

Or you can attach a counterweight toward the front of the OTA to compensate for the added weight of the heavy 2" eyepiece at the rear.  I actually did this when I upgraded the focuser on my ST80 to a 2" Crayford and started using it with a heavy 2" eyepiece and 2" diagonal.  I bolted a small weight to the front end of the dovetail.   The telescope balanced, but at the cost of extra weight for the setup.  

 

Mike


Edited by Sarkikos, 13 June 2017 - 08:08 AM.


#72 Sarkikos

Sarkikos

    ISS

  • *****
  • Posts: 31,220
  • Joined: 18 Dec 2007
  • Loc: Per sylvam ad astra

Posted 13 June 2017 - 07:46 AM

 

BTW, I haven't tried it, but the scope might balance with 1.25" accessories by simply reversing the stock mounting foot. Has anyone tried this simple fix?

 

If you reverse the stock mounting foot, it will get in the way of the focuser knobs when you rotate the focuser.

 

Mike



#73 Sarkikos

Sarkikos

    ISS

  • *****
  • Posts: 31,220
  • Joined: 18 Dec 2007
  • Loc: Per sylvam ad astra

Posted 13 June 2017 - 07:55 AM

 

I understand that you are saying it's the additional rail extending to the rear that interferes with the focuser when the scope is balanced with 2" accessories. Can you post a photos of your AT72ED with 2.0" accessories, so we can see the severity of the problem your are describing?

 

 

This might be filed under, "Why Jon uses the Bogen 3040 with his AT-72ED.  Note that the fine focuser is on the left, the added offset/clearance between the focuser knob and the mount.  The reason I have the AT-72ED is that it provides wider fields than anything I have but to provide those wide fields, 2 inch eyepieces are required.

 

Jon

 

But ... will the telescope remain in place without your clamping down hard on the altitude detention knob?  Or will the OTA fall down at the rear when not clamped down?  If it falls down, then the telescope is not balanced.  That is my point.   

 

By the way, when my AT72ED is attached to the Microstar head and Vanguard Auctus tripod, the focuser knob does not hit against any part of the mount or tripod.  That was never a problem for me.  I don't feel the need to disassemble the focuser and switch around the placement of the fine focus knob.  Besides, I like to keep that fine focus on the right, since I'm right handed.

 

The problem is having to use a long, extended-backwards dovetail to balance the scope, and the fact that the dovetail can hit the focuser knobs. This can occur with either knob, not just the side with fine focus.  

 

When using a heavy 2" eyepiece, if you don't have the OTA set forward sufficiently on the mount, it is not really balanced.  To have the OTA set forward sufficiently, you need a longer dovetail extended backward.  Clamping down on the altitude knob is not equivalent to balancing the scope.

 

Mike


Edited by Sarkikos, 13 June 2017 - 11:32 AM.


#74 gwlee

gwlee

    Surveyor 1

  • *****
  • Posts: 1,880
  • Joined: 06 Sep 2015
  • Loc: 38N 120W

Posted 13 June 2017 - 09:47 AM

 

I understand that you are saying it's the additional rail extending to the rear that interferes with the focuser when the scope is balanced with 2" accessories. Can you post a photos of your AT72ED with 2.0" accessories, so we can see the severity of the problem your are describing? 

 

I would expect the ED2 to behave somewhat differently because it uses rings and a rail instead of the mounting foot used on the ED. It also uses a different focuser, and might not have the weight of the camera angle adjuster. We'll have to wait for Michael to come along to find out whether the ED2 works (balances) natively with both 1.25 and 2.0 accessories. 

 

I agree it's a challenge for anyone to design a short focal length refractor that includes all these features and might be used for astrophotography as well as visually. I have noticed that the 76mm TAK comes in two versions, one for 1.25" accessories and another for 2" accessories, and both are longer focal length than the AT72ED, which might make it easier to achieve balance. If I could be sure the Tak doesn't have other unknown problems, I might just buy it and be done with it. 

 

If I have time I will post a photo.  But if you really do understand what I'm saying, why do you need a photo?  Apparently,  you only need a photo because you don't believe what I'm saying.  grin.gif

 

Believe it - or not, as you wish.  In any case, if you install a dovetail that is long enough and extended backwards enough to allow the AT72ED to be completely balanced when using a heavy 2" eyepiece and 2" diagonal, the dovetail will strike one of the focuser knobs, unless you move them out of the way.  I guarantee it.

 

The AT72ED has a rotatable focuser.  The AT72ED II has rings that can be rotated.  In both cases you can set up the telescope so that the focuser knobs are out of the way of a long, backward-extended dovetail.  However, if you mount the AT72ED on a side-saddle mount - which you should do if you want to use the telescope for astronomy - you must set the focuser knobs vertically in order to prevent their striking a long, backward-extended dovetail.  

 

I bet the AT72ED II will have the same balancing/focuser-knob problem when using heavy 2" eyepieces.  My ST80 with 2" Crayford focuser has the same problem.  I don't see how you can avoid the problem with a small, short refractor.  Well, you can either use the scope on a top-mounted head and clamp down hard when pointing toward zenith, or use the scope on a side-saddle mount and get used to observing with the focuser knobs set vertically.  But IMO & IME neither of these solutions are ideal.  They are compromises.

 

Or you can attach a counterweight toward the front of the OTA to compensate for the added weight of the heavy 2" eyepiece at the rear.  I actually did this when I upgraded the focuser on my ST80 to a 2" Crayford and started using it with a heavy 2" eyepiece and 2" diagonal.  I bolted a small weight to the front end of the dovetail.   The telescope balanced, but at the cost of extra weight for the setup.  

 

Mike

 

I believe you, but i would like too see the severity of the problem, and I don't have any 2" accessories to use to duplicate  it. There are other people reading this thread who might be having difficulty following our discussion, so I posted my photos, so they could see what i was describing. 

 

I agree it's possible the AT72EDII mounting modifications do not fix all the mounting problems we've encountered with the ED because it's such a challenging problem with a short OTA, but we'll have to wait and see. If they are not fully corrected, i might reconsider my decision to purchase the ED2 though. 

 

I agree that rotating the focuser to the vertical position or adding weights to the front of the OTA are inelegant work arounds. For some, it will be a show stopper. Others won't care or will consider it a worthwhile tradeoff for such a compact OTA.

 

I tried Jon's fix when I first got the AT72ED, putting it side sadle on a Bogen 3047 photo tripod head. It works, but falls into the inelegant bin IMO. Fine for static terrestrial targets, just OK for low power astro use (Jon's principal use), and close to unusable for tracking at high power without lots of practice, and i hope i never get that much practice. 


  • Sarkikos likes this

#75 glend

glend

    Surveyor 1

  • *****
  • Posts: 1,919
  • Joined: 04 Feb 2014

Posted 13 June 2017 - 10:28 AM

It would make a nice guidescope.




CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics