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Questions Mak Cass diagonals

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#26 graffias79

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Posted 13 January 2018 - 05:03 PM

https://www.widescre...ter-2-diagonals

 

 

the other side of the Carbon Fibre diagonal has a temperature thermometer

I was looking at this on Agena's website.  There is no mention of the thermometer.  What is the purpose of knowing the temperature inside the diagonal?



#27 SeattleScott

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Posted 14 January 2018 - 09:18 AM

Maybe knowing when the diagonal has reached equilibrium? It can take 30 minutes on cold nights. My 4" refractor cools faster than the diagonal so knowing when the diagonal is cooled would let me know when I can start high power observation. The Mak will take longer to cool though.

 

Scott



#28 graffias79

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Posted 14 January 2018 - 10:20 AM

Oh wow. I'd probably also need one measuring the temperature of the primary mirror, one for the meniscus, and one for the ambient air inside the tube. That kind of obsession would seriously kill the fun of observing for me!

Also I wonder why no mention of it is made in the description or any of the many reviews.

#29 luxo II

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Posted 18 January 2018 - 01:23 AM

Oh and don’t forget you’ll need a cooling fan for the diagonal and a dew heater for when it’s really cold and foggy ;)

Edited by luxo II, 18 January 2018 - 01:24 AM.


#30 dotnet

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Posted 18 January 2018 - 08:25 AM

So... my suggestion to you is to get a Baader T-2 90° Prism Star Diagonal Body with Carl Zeiss Spec Prism and BBHS Coating. You can get a number of different adapters to configure that diagonal to work with your Mak or with refractors, or with bino-viewers. (Agena Astro has the diagonal and adapters and will be able to help in the selection of what is needed.)

This. I got my Intes MK-67 in 1999 and it took me 15 years of money-wasting meandering to arrive at that conclusion. Get the Baader T2 Zeiss prism with 2" nose (or SCT adapter, as required) and 1.25" Click-Lock clamp, and be happy.



#31 dotnet

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Posted 18 January 2018 - 08:34 AM

I doubt you can use a 55mm plossl to good effect in a 6" MCT f12. Going to have significant light drop off and vignetting. So the effective fov will be much smaller than 1.2 degrees. I cant use one in my 8", the widest fov I get is with a 31mm Nagler which has a 42mm field stop and has a slight light drop off at the edge of the fov. The 55 has a 46mm field stop.

I tried the 55mm TV Plössl in my MK-67. It didn't work well. I didn't mind the restricted (as opposed to theoretical) TFOV. The biggest issue was the vignetting "from within" grin.gif

 

The illuminated field was clipped so much that the central obstruction became a dominating feature. There was a very noticeable central shadow, which made me sell the eyepiece after just one night.



#32 bcm00re

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Posted 28 November 2018 - 07:42 PM

BTW, one does not have to spend $275 for the Baader T2 prism. Baader makes a T2 mirror diagonal that is a lot less $$ than the prism version. And there are 1.25” prism diagonals that perform quite nicely and cost less than $100.

So what brands/models are good diagonals? I am a newbie so I don't have enough experience to know. We do have an ES 127mm Mak, and I just ordered a Baader 8-24mm zoom eyepiece for it. My stock diagonal is cheap plastic one with mirror. I am considering getting a prism. I notice some are fully "corrected" and some only fix the up/down but not the left/right.

#33 luxo II

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Posted 28 November 2018 - 08:05 PM

OP I used a standard 2” dielectric diagonal on the back of my SW180mm mak and now my MK91 - no issues.

An alternative I found quite nice was a TEC turret, holds 5 x 1.25” eyepieces though if you have a zoom you won’t need this.

I also have a diagonal with a ClickLock on the back - however this does not suit some eyepieces with undercuts - it can’t grip them securely unless each and every one has the undercut filled with tape. This is particularly tricky for the ones that have tapered undercuts where too much tape and it will jam in place.

For this reason I’m back to an ordinary diagonal with compression ring.

Edited by luxo II, 28 November 2018 - 08:10 PM.


#34 dscarpa

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Posted 28 November 2018 - 08:09 PM

 I use a a 2" Meade dielectric refactor diagonal in my IM715D which has a GSO Crayford  which is helpful because the focuser is on the stiff side. It looks like my scopes gone from F15 to F16. With my 31 Hyperion Aspheric I can frame close to 3/4 of the Double Cluster with only a bit of brightness drop off at the edge. I recently got a 30 ES 82  but haven't used it in the mak yet.  I  think mak is as good for DSOs as lunar-planetary and doubles. I've never tried in prism diagonal in it . David


Edited by dscarpa, 28 November 2018 - 08:11 PM.


#35 graffias79

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Posted 29 November 2018 - 11:13 AM

I've been using the 1.25" Celestron 94115-A prism star diagonal since I got the Mak last February and it's been fine for me.  I haven't wanted to experiment with 2" eyepieces (mainly because I only have one).



#36 photoracer18

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Posted 29 November 2018 - 03:22 PM

Its this mess that makes me like my Orion Argonaut (Intes MK 67) with its fixed optics and a Crayford on the VB as the only focusing mechanism. No increase in FL. Still waiting for Starlight to send me the adapter so I can switch to a 2" FT focuser in the back.



#37 Freezout

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Posted 30 November 2018 - 09:59 AM

Graffias79,

I have the same telescope. I use a 2" prism for now. I confirm that using 2" eyepieces can be nice even if the baffle of the telescope is 32mm. In several threads I made lately in Cloudy Nights the topic has been touched, and it appears that even with 32mm baffle opening, you can get a very nice TFOV of around 1.3 degrees with a 2" diagonal and eyepieces. The limit is the field stop of the eyepiece more than the baffle of teh telescope.

I use a 50mm Erfle and I enjoy it a lot!  

Just be careful if you want to add any kind of accessoires (ex: focuser), the light path might increase a lot. 

I observed that without prism (eyepiece directly in the 2" barrel of the visual back), my Erfle magnifies less than with the prism. But the prism doesn't change in any visible way the TFOV. 

 

My current prism is this one and works nicely (I want to replace it for an amici only for the correctly oriented view). To note: it has an exquisite mechanical quality with a twist-lock system integrated. APM made a very good job here. And for what it is, it's cheap.

https://www.apm-tele...nd-coating.html



#38 Freezout

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Posted 30 November 2018 - 10:09 AM

So what brands/models are good diagonals? I am a newbie so I don't have enough experience to know. We do have an ES 127mm Mak, and I just ordered a Baader 8-24mm zoom eyepiece for it. My stock diagonal is cheap plastic one with mirror. I am considering getting a prism. I notice some are fully "corrected" and some only fix the up/down but not the left/right.

To correct the left/right inversion, you will need an "amici" prism. It's my next project also...

Apparently it's a bad idea to take 45deg amici-prisms, they are fit for daylight use.

The amici-prisms I know are the following ones. Note: I don't own anyone but after the reviews I have been reading I would buy any of them without fear. I will myself take the Baader as it has the shortest light path.

 

1) Baader roof-prism. For this one you need to add some T2 adapters to have it connected to your telescope. It has a smaller aperture than the two others I will list.

https://www.baader-p...2-part-02).html

 

2) APM one. As said in my post #37 above, APM makes nice twist-lock clamps integrated on their prism. Markus Ludes, the boss of APM, says that his prism is better than all the others, for cheaper.

https://www.apm-tele...nd-coating.html

 

3) The one with an astro-price, also Baader:

https://www.baader-p...-r-coating.html

 

If you don't care about reversed right/left view, you have way more choice, in 2" or 1.25". I know only one, the APM one. I heared that Celestron makes good ones.



#39 RAKing

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Posted 30 November 2018 - 06:18 PM

You don't have to get too crazy with this stuff. lol.gif   Most designs give you 140-150mm of light path behind the baffle tube before you start to lose aperture or anything.

 

I have used a Baader SCT Clicklock on the back of my TEC 6 Mak with a small T-2 Baader prism if I want the shortest reasonable path and I also simply slip my A-P 2-inch Maxbright diagonal on there if I want to use 2-inch eyepieces. 

 

My longest eyepiece is the 2-inch Pentax XW 40mm and it gives me a beautiful wide view of things with no apparent vignetting.  I think the baffle tube might be cutting off some of the view, but I haven't done any drift timing to see exactly what my actual FOV is.  I just know that it is quite a bit wider than the 1.17 degrees I get with a Pentax XW30.

 

Before I bought my TEC 6, I owned an Orion 150 MCT and it showed wonderful views with the same, exact setup.

 

I think a 2-inch visual back (Baader Clicklock or etc.) with a 2-inch diagonal is fine for the Orion or SW 150 Maks.

 

Here's what the TEC backplate looks like and I think it is a reasonably compact setup:

 

Cheers,

 

Ron

 

TEC 6 Backplate.JPG

 



#40 Asbytec

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Posted 30 November 2018 - 07:08 PM

RAKing is right about adequate back focus, especially in the newer Orion 150 MCT. It was pulled from the market several years ago, and returned not long ago with a modified baffle design. Elwaine is right about about the longer focal length with a moving mirror focusing system. You're gonna be operating at a slower focal ratio, around f/13 or a bit more, and higher magnifications. 

 

So, the question is, the OP does not use 2" eyepieces yet wants a 2" diagonal for a future scope. Apparently to get a slightly wider FOV in the MCT. But, it's asking the MCT to do something it's not (really) designed to do. MCTs excel at lunar and planetary which do not require wild fields of view, only a nice focal length and high magnification. They operate in the high magnification realm, not the low power wider field realm.

 

So there is only a desire but no need for 2" eyepieces, anyway. A nice 1.25" eyepiece with a bit wider AFOV and good eye relief is fine. Nothing really wrong with 2" eyepieces, just saying the MCT is not really a low power wide field scope. Employ it where it excels at higher magnifications, especially on lunar and planetary. 

 

A 2" diagonal may better support heavy equipment for bino viewing, though, if that is in the cards. But, it will require quite a bit of back focus. I am not sure the MCT can handle that much back focus without vignetting. I defer to others who have tried it. I am certain my older Orion will not support that much back focus due to the very tight primary baffle - which is a good thing in all other cases. 

 

My $0.02...



#41 Freezout

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Posted 01 December 2018 - 01:01 AM

Hi Norme,
Yes a Mak will never show the 3+ degrees that a refractor or fast scopes can provide, but it can be the only telescope that one has outside for a session, or owns. It is then relevant to try to get the maximum out of it; you will agree that 1.2/1.3 degrees is better than 0.9!
Also: even just making planetary observation, it is comfortable to keep the target in view for longer (especially with a manual altaz). I love the Moon in large FOV!
Personally I do my best to keep 2" eyepieces compatibility on my Mak when I try different setups.
(Not to say that purchasing a nice wide field refractor never crossed my mind.......)

#42 Asbytec

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Posted 01 December 2018 - 01:24 AM

Hi Freeze, well, to me 0.9 and 1.3 are not much different. But, I do understand the allure of wider fields, big eyepieces, comfortable views, and longer drift times. I guess if one had a good set of 2" eyepieces for whichever scope, they would work just fine in a MCT, too. I guess I was just warning about expecting wide field vistas in a long focal length lunar and planetary scope. 



#43 JohnH

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Posted 01 December 2018 - 01:52 PM

My 45 degree Amici is from Vernonscope



#44 photoracer18

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Posted 04 December 2018 - 03:44 PM

Actually a 40mm 1.25 eyepiece in a 1.25" diagonal will yield only about 5x more in magnification than a 2" 56mm in a 2" diagonal. 3.3 mm exit pupil verses 3.6mm, not much difference for the added weight, and unless you have observe from a dark sky site you wont notice a difference. I have a 56mm 2" Meade, not an eyepiece Im impressed with to be honest. My old 60mm kellner does a better job, as does my 48mm Brandon in my refractors. Its a newer one, made in china bought at B&H last year.

The Chinese Meade 56mm SP is no match compared to the original 5-element smoothie or the 2nd gen 4-element Japanese model. But then again both those command used prices in the $120+ region. Other options are the TV 55mm Plossl and the University Optics 55mm Plossl. All of the later 4 are pretty good. I have owned and or used all of them. I currently have the UO 55.



#45 photoracer18

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Posted 04 December 2018 - 03:50 PM

So what brands/models are good diagonals? I am a newbie so I don't have enough experience to know. We do have an ES 127mm Mak, and I just ordered a Baader 8-24mm zoom eyepiece for it. My stock diagonal is cheap plastic one with mirror. I am considering getting a prism. I notice some are fully "corrected" and some only fix the up/down but not the left/right.

Every standard prism and mirror diagonal corrects up and down but not left-right. Corrected diagonals, either Porro or Amici prism based greatly lengthen the light path because they have up to 5 reflections instead of only one. The light bounces around in there until it manages to flip the image completely correct. All the reflections lose a little bit of light each time it is bounced.


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#46 bcm00re

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Posted 05 December 2018 - 04:56 PM

Thanks for all the info photoracer18.

#47 JohnH

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Posted 05 December 2018 - 07:01 PM

Every standard prism and mirror diagonal corrects up and down but not left-right. Corrected diagonals, either Porro or Amici prism based greatly lengthen the light path because they have up to 5 reflections instead of only one. The light bounces around in there until it manages to flip the image completely correct. All the reflections lose a little bit of light each time it is bounced.

Some of the reflections are total internal ones. Very small light loss




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