Return to the Cloudy Nights Telescope Reviews home pageAstronomics discounts for Cloudy Nights members
· Get a Cloudy Nights T-Shirt · Submit a Review / Article

Click here if you are having trouble logging into the forums

Privacy Policy | Please read our Terms of Service | Signup and Troubleshooting FAQ | Problems? PM a Red or a Green Gu… uh, User

Equipment Discussions >> Eyepieces

Pages: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | (show all)
george tatsis
professor emeritus
*****

Reged: 11/20/08

Loc: Flushing, NY - Europe
Re: Eyepiece Performance using a Prism Diagonal new [Re: Hesiod]
      #6226840 - 12/01/13 11:42 AM

Quote:

I have the Baader-Zeiss 1.25" and I feel that it is better than any other prism I have ever tried, but the "standard" Baader prism follows him quite closely.
Anyway I have not ever tried the Takahashi (which at 90€ could be a real bargain) and I use the prism mainly behind my 8" SCT which somebody could judge a rather junkish telescope compared to a TSA.




Where did you find the Tak for 90 Euros?

George


Post Extras: Print Post   Remind Me!   Notify Moderator  
Sarkikos
Postmaster
*****

Reged: 12/18/07

Loc: Scotophobe Maryland, USA
Re: Eyepiece Performance using a Prism Diagonal new [Re: Sarkikos]
      #6226843 - 12/01/13 11:43 AM

Hesiod,

You anticipated and answered my question.

Mike


Post Extras: Print Post   Remind Me!   Notify Moderator  
Sarkikos
Postmaster
*****

Reged: 12/18/07

Loc: Scotophobe Maryland, USA
Re: Eyepiece Performance using a Prism Diagonal new [Re: Sarkikos]
      #6226852 - 12/01/13 11:46 AM

Also, check this out:

Improving Refractor Performance with a Prism Diagonal

Mike


Post Extras: Print Post   Remind Me!   Notify Moderator  
Hesiod
sage


Reged: 01/13/13

Re: Eyepiece Performance using a Prism Diagonal new [Re: Sarkikos]
      #6226857 - 12/01/13 11:49 AM

I do not know if it is the same BillP is speaking of, but the EU official importer optique unterlinden has a 1.25" prism at 89€ (and a mirror at 400€...), sub voce "Renvois coudés"

Post Extras: Print Post   Remind Me!   Notify Moderator  
Sarkikos
Postmaster
*****

Reged: 12/18/07

Loc: Scotophobe Maryland, USA
Re: Eyepiece Performance using a Prism Diagonal new [Re: Sarkikos]
      #6226858 - 12/01/13 11:49 AM

What is this? It doesn't say it has a Zeiss prism, but ...?

Baader T-2 90° Prism Star Diagonal Body # T2-01C 2456005

Mike


Post Extras: Print Post   Remind Me!   Notify Moderator  
george tatsis
professor emeritus
*****

Reged: 11/20/08

Loc: Flushing, NY - Europe
Re: Eyepiece Performance using a Prism Diagonal new [Re: Sarkikos]
      #6226870 - 12/01/13 11:56 AM

Quote:

What is this? It doesn't say it has a Zeiss prism, but ...?

Baader T-2 90° Prism Star Diagonal Body # T2-01C 2456005

Mike




Neither the nosepiece, nor the eyepiece holder is included!!!

Take a look at the TS option I previously mentioned. It covers both!

George

Edited by george tatsis (12/01/13 11:59 AM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
Eddgie
Postmaster
*****

Reged: 02/01/06

Re: Eyepiece Performance using a Prism Diagonal new [Re: george tatsis]
      #6226879 - 12/01/13 12:01 PM

This version comes with 1.25" nose and micro-focusing eyepiece holder for $159.

Baader 1.25" diagonal with nose and eyepecie holder


Post Extras: Print Post   Remind Me!   Notify Moderator  
Hesiod
sage


Reged: 01/13/13

Re: Eyepiece Performance using a Prism Diagonal new [Re: Sarkikos]
      #6226889 - 12/01/13 12:05 PM

Quote:

Hesiod,

You anticipated and answered my question.

Mike


You are too fast, or I am too slow

Post Extras: Print Post   Remind Me!   Notify Moderator  
Eddgie
Postmaster
*****

Reged: 02/01/06

Re: Eyepiece Performance using a Prism Diagonal new [Re: Sarkikos]
      #6226908 - 12/01/13 12:13 PM

From the review you posted...

Quote:

Owners of refractors by Astro-Physics, Takahashi, TeleVue, TMB and other very premium makes likely won't see significant performance benefits from using a prism.




I have a SV110ED and a 6" f/8 refractor.

I have the Baader Prism (non Zeiss) and the Maxbright Mirror Dielectric.

I have also owned the Tak several years ago and did A/B with the AP with both the Tak and a Televue Dielectric.

Sady, my result was not the same as the OPS.

In the 110ED, I actually felt that the Maxbright Mirror gave a tiny difference in performance, but it was not in any way meanigful, but I like the longer light path of the mirror, so I continue to use it.

In the 6" APO though, nada. Both the Tak prism and the Baader (non-zeiss) gave as best as I could determine, identical views. I could see absolutly no difference in detail between the two units.

Now a change that did matter was going to a GPC in the 110ED with binoviewers for solar white light, and going from a glass filter to a Baader Film filter.

In these cases, the differecne in performance was quite noticable.

But the difference between the prism and the mirror, at least at f/8 and an Astro-Physics APO was to small a difference for me to see.

So to me, this report from the OP is clearly in the "Your mileage may vary" catagory.

This comes around from time to time, and people will say that the prism made a big difference, and others will say that it did not.

Like so many dialogs on CN, there are arguments on both sides of any proclamation (this is better than that).



Most of the times I have tired the "Miracle Cure", I have been disappointed.


The GPC in the binoviewer and the Baader Film filters were two excepetions.

The "dielectric diagonal" mania was a huge disappointment. The dielectric performed no better than the Televue Enhanced Aluminum.

The XLT coatings was another, with initial hysteria reports of big performacne increases, when it is a struggle to see the difference between XLT and Starbright visually.

So, not saying that people should not try a Prism. The Baader standard is a great prism to be sure. I own 2 and use them with my binoviewer (for the short light path).

But for uses where I don't need a short light path, tried the prisms, went back to the mirror. Not that it was better optically, but it is a heck of a lot easier to clean than a Prism.

Edited by Eddgie (12/01/13 12:17 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
Hesiod
sage


Reged: 01/13/13

Re: Eyepiece Performance using a Prism Diagonal new [Re: Hesiod]
      #6226915 - 12/01/13 12:16 PM

The Baader prism are a sort of "LEGO", you may choose the nose (even a 2" if you will) and the eyepiece holder, either from Baader or from any other (the prisms are T2
threaded, male on the EP side and female on the scope side).
I do not recommend the non Click-Lock holder because it
is a real hassle change eyepiece, to the point that often I use instead a 3cm extension tube whit a brass compressing ring


Post Extras: Print Post   Remind Me!   Notify Moderator  
Sarkikos
Postmaster
*****

Reged: 12/18/07

Loc: Scotophobe Maryland, USA
Re: Eyepiece Performance using a Prism Diagonal new [Re: Eddgie]
      #6226976 - 12/01/13 12:41 PM

Quote:

This comes around from time to time, and people will say that the prism made a big difference, and others will say that it did not.

Like so many dialogs on CN, there are arguments on both sides of any proclamation (this is better than that).




Yes, I've read many of these threads. Much heat, little light. Well, not really so much heat ... but really little light, that I could see. Basically it distills to: "Choose your experts and purchase accordingly."

But once again I think I'll pass on an upgrade. A high-end prism diagonal is still on my list, but not my short list. We'll see...

Mike


Post Extras: Print Post   Remind Me!   Notify Moderator  
jrbarnett
Eyepiece Hooligan
*****

Reged: 02/28/06

Loc: Petaluma, CA
Re: Eyepiece Performance using a Prism Diagonal new [Re: Eddgie]
      #6227126 - 12/01/13 01:49 PM

However, there is no question that prism diagonals introduce slight overcorrection and mirror diagonals do not, so assuming a refractor is not under-corrected, a prism introduces spherical aberration whereas a mirror does not. You can also see from many, many reports on astroforen.de that introduction of a prism diagonal in many different refractor systems alters color correction; generally to the better. See Rohr's description of "RC Index" and note how that metric alters when a "glasweg" (prism diagonal) is introduced. For example:

http://www.astro-foren.de/showthread.php?10380-Zeiss-APQ-100-640-Glasweg

So if your scope was perfectly corrected for spherical, the prism should have produced a worse quality image to some degree. Note, though, that the color shift properties of the prism are not limited to under-corrected scopes. That APQ tested in the link was pretty well figured prior to introduction of the prism.

I think rational diagonal choice requires that the user know something about both the effects of a prism on the system and the state of correction of his refractor. Otherwise it's all pretty much seat of the pants guesswork.

Regards,

Jim


Post Extras: Print Post   Remind Me!   Notify Moderator  
Roy McCoy
Pooh-Bah
*****

Reged: 10/13/05

Loc: Glendale, AZ
Re: Eyepiece Performance using a Prism Diagonal new [Re: jrbarnett]
      #6227235 - 12/01/13 02:32 PM

Quote:

So if your scope was perfectly corrected for spherical, the prism should have produced a worse quality image to some degree.




My AT106 f6.5 did get worse with the prism.



Quote:

I think rational diagonal choice requires that the user know something about both the effects of a prism on the system and the state of correction of his refractor.




I agree.


Post Extras: Print Post   Remind Me!   Notify Moderator  
BillP
Postmaster
*****

Reged: 11/26/06

Loc: Vienna, VA
UPDATE: Prism Diagonal new [Re: urassner]
      #6227348 - 12/01/13 03:39 PM

Guys,

Have an update. A fellow CNer on PM asked me to check the collimation of the 2 prism diagonals. I did not do this prior to the 1st light as just assumed the Tak would be ok.

To do the test I took my 80mm APO and removed the objective so I would have a mounted platform to take the diagonals. I then projected the laser dot on a wall about 20 feet away with no diagonal in the focuser. I then marked the spot as the reference spot. I also rotated and reinserted the laser several times to ensure a consistent location. It was. I then put the AstroTech Dialectric in the scope housing and reshot the laser. It landed on the same spot so this diagonal was fully square with the focuser. When I put the Tak Prism in the scope housing and attached the laser and tightened the Tak's collar on the laser, the spot painted the wall about 2" low!! What a surprise...it was off and not square yet it still gave a better view. I also noted that if the eyepiece is not tightened in the Tak Prism then it is way further off than the 2". So fully tightening the Tak collar is important. The conventional compression ring of the AT Dialectric was not as sensitive when the ocular was not tightened in it.

I have added a few layers of painters tape to the Tak Prism's housing so when it sits in the focuser it now paints the laser dot accurately. Will redo the experiment later this week when things clear up. So...should I expect it to perform even better now? I mean it beat the Dialectric uncollimated...can't wait to see what occurs now.

PS - I will also conduct tests with a short f/6 refractor as well to see how they compare with shorter focal ratio...and will try some low & high magnification bright star observing to see if that teases out any color.


Post Extras: Print Post   Remind Me!   Notify Moderator  
junomike
Carpal Tunnel
*****

Reged: 09/07/09

Loc: Ontario
Re: Eyepiece Performance using a Prism Diagonal new [Re: Roy McCoy]
      #6227475 - 12/01/13 04:50 PM

Quote:

My AT106 f6.5 did get worse with the prism.




Same thing for me with my AT111EDT....Twice!
The first Tak 1.25" Prism induced CA that was not otherwise seen. It was soon sold. Then due to these type of threads I figured It might have been a dud. A second one was purchased. Result..........same! The Tak Prism induced CA on a friends Meade 102ED as well.

Hey Jim, give It a go with you AT111EDT and see what result you get!.

Mike


Post Extras: Print Post   Remind Me!   Notify Moderator  
BillP
Postmaster
*****

Reged: 11/26/06

Loc: Vienna, VA
Re: Eyepiece Performance using a Prism Diagonal new [Re: junomike]
      #6227564 - 12/01/13 05:39 PM

Mike,

What was the magnification and targets where the CA showed up in your testing? Want to see if I can replicate or come close to same conditions.


Post Extras: Print Post   Remind Me!   Notify Moderator  
skullpin
sage
*****

Reged: 03/13/09

Loc: Edmonton, Alberta, Canada
Re: Eyepiece Performance using a Prism Diagonal new [Re: BillP]
      #6227692 - 12/01/13 06:35 PM

I used an AP MaxBright, a Tak 1.25 prism, and the Zeiss 2" prism with my f/6 Borg 125SD scope, my findings on Jupiter last winter at 200-250X:

AP MaxBright: At optimum focus, color fringing appeared well stamped out to my eye. Greenish on one side of focus, purple on the other, fairly easy to achieve optimum focus with no fringing visible.

Tak prism: Fringing was a little more finicky, though it was possible to achieve an optimum focus with no color fringing. I was convinced that this prism gave a more detailed view than the dielectric mirror.

Zeiss 2" prism: Fringing was quite finicky, and it was almost impossible to achieve an optimum color free focus. The detail visible was no different than the dielectric mirror.

I sold the Zeiss prism, and, regrettably, the Tak prism too. I am tempted to find another Tak or perhaps the Baader T2 Zeiss prism.

Keith


Post Extras: Print Post   Remind Me!   Notify Moderator  
Sarkikos
Postmaster
*****

Reged: 12/18/07

Loc: Scotophobe Maryland, USA
Re: Eyepiece Performance using a Prism Diagonal new [Re: skullpin]
      #6227821 - 12/01/13 07:52 PM

OK, I hear a lot of talk about 'fractors. I mostly use them for finders on my other scopes. Just sayin'.

Now how will a good prism diagonal perform vs a mirror diagonal in an SCT or Mak? I supposed that will depend on whether the Cat is undercorrected or overcorrected or has a good figure?

Mike


Post Extras: Print Post   Remind Me!   Notify Moderator  
fjs
Pooh-Bah
*****

Reged: 03/25/13

Loc: Olympic Peninsula, USA
Re: UPDATE: Prism Diagonal new [Re: BillP]
      #6227826 - 12/01/13 07:53 PM

Quote:

Guys,

Have an update. A fellow CNer on PM asked me to check the collimation of the 2 prism diagonals. I did not do this prior to the 1st light as just assumed the Tak would be ok.

To do the test I took my 80mm APO and removed the objective so I would have a mounted platform to take the diagonals. I then projected the laser dot on a wall about 20 feet away with no diagonal in the focuser. I then marked the spot as the reference spot. I also rotated and reinserted the laser several times to ensure a consistent location. It was. I then put the AstroTech Dialectric in the scope housing and reshot the laser. It landed on the same spot so this diagonal was fully square with the focuser. When I put the Tak Prism in the scope housing and attached the laser and tightened the Tak's collar on the laser, the spot painted the wall about 2" low!! What a surprise...it was off and not square yet it still gave a better view. I also noted that if the eyepiece is not tightened in the Tak Prism then it is way further off than the 2". So fully tightening the Tak collar is important. The conventional compression ring of the AT Dialectric was not as sensitive when the ocular was not tightened in it.

I have added a few layers of painters tape to the Tak Prism's housing so when it sits in the focuser it now paints the laser dot accurately. Will redo the experiment later this week when things clear up. So...should I expect it to perform even better now? I mean it beat the Dialectric uncollimated...can't wait to see what occurs now.

PS - I will also conduct tests with a short f/6 refractor as well to see how they compare with shorter focal ratio...and will try some low & high magnification bright star observing to see if that teases out any color.




Thanks Bill!


Post Extras: Print Post   Remind Me!   Notify Moderator  
junomike
Carpal Tunnel
*****

Reged: 09/07/09

Loc: Ontario
Re: Eyepiece Performance using a Prism Diagonal new [Re: BillP]
      #6227959 - 12/01/13 09:04 PM

Bill, The scope was the AT111EDT (FPL-51 F7 Triplet) and the target was the edge a 3/4 Full Moon.
I don't recall exactly, but I believe I was using a 5mm XO yielding 155X.

I didn't even get around to comparing other characteristics (scatter. etc) as the induced CA was something I couldn't get past.

Interesting though that Roy seen a worse Image as well with his AT106 although his is a little faster but uses FPL-53.

Mike


Post Extras: Print Post   Remind Me!   Notify Moderator  
Pages: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | (show all)


Extra information
15 registered and 29 anonymous users are browsing this forum.

Moderator:  ausastronomer, droid, Scott in NC 

Print Thread

Forum Permissions
      You cannot start new topics
      You cannot reply to topics
      HTML is disabled
      UBBCode is enabled


Thread views: 5785

Jump to

CN Forums Home


Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics