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Ags

1.25" diagonal annoyances

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I use the default Skywatcher cheapo diagonals with my two scopes, and they are intensely irritating because the locking screw is so far up the barrel the screw head pushes against the base of my wider eyepieces. I don't expect a diagonal upgrade to make any significant difference to views but what are my affordable options for two better diagonals? I would prefer prisms as they are less fragile than mirrors and I like the sound of 100% internal reflection. But mostly I just want my wider eyepieces to go into the diagonal straight, and to no longer feel the lock screw head grinding away at the base of my favorite eyepieces!

Edited by Ags

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39 minutes ago, Ags said:

the screw head pushes against the base of my wider eyepieces

Hi, you could consider replacing them with longer screws (ones that have a long, thin knob at the end rather than a short, wide one).

Diagonals collect a lot of dust etcetera, so they need regular cleaning. Dielectric mirrors are very hard, which makes them easy to clean without having to be too careful. That's why I prefer them.

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Ags, the Baader Zeiss spec prisms are the best diagonals I’ve ever used with TEC140 and C11. Both the 2” and the 1.25” outperform, to my eye, the top of the range Astro-Physics Dielectric mirror diagonal I previously used, in terms of contrast and scatter. I realise they are not budget options though ...  Bill Paolini has an informative review; from memory, I think he preferred the 1.25.

John E

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John E's suggestions are superb but come with quite large price tickets :smiley:

On a more affordable level, I have a Revelation / GSO 1.25" dielectric diagonal which works rather well for it's price (this is TS's version of this item):

https://www.teleskop-express.de/shop/product_info.php/info/p1771_TS-Optics-1-25--Zenitspiegel---99---Reflexion---Ringklemmung---CNC---1-12-Lambda.html

I do have some of the diagonal that John E lists and the Revelation is not shamed by them by any means :smiley:

While the prism type might be OK with your 102mm mak I'm not sure that they work so well with the ST80's ?

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The Baader Zeiss sounds very nice, but it is a bit too much for me. It would be a bit comical hanging off the back of an ST80 🤣

The TS one sounds more like my kind of thing. I've also looked at the Takahashi diagonal, it's only a few Euros more, and surely a Tak's good?

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If I understand correctly the screws that keep the eyepiece in grind into the ocular on the outside? I experienced this with stock Skywatcher diagonal on my 102 mak. With Tak prism no such issues. The funny thing is that since I started with observing Tak prism is the only thing that is permanent. All other things come and go.

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1 hour ago, Ags said:

The Baader Zeiss sounds very nice, but it is a bit too much for me. It would be a bit comical hanging off the back of an ST80 🤣

The TS one sounds more like my kind of thing. I've also looked at the Takahashi diagonal, it's only a few Euros more, and surely a Tak's good?

The Tak prism diagonal is good. It should work well with your 102 mak but I think prism diagonals (even very good ones) can introduce some issues when used with F/5 refractors which is why I had some doubts about your ST80.

Just for info, the Tak prism has a plastic body section which some find a little off putting. The performance is very good though and the twist compression fitting works well.

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Well... I need two ultimately, so I could get both 😀

@John, the issues with F5 refractors would be increased chromatic aberration?

Edited by Ags
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John, I never understood the issue with plastic body on Tak. I hardly notice it and overall the diagonal looks quality to me. It certainly is not a beast like white Baader 2" and similar so maybe that's an issue? It's petite? At the end of the day using Tak is so efortless, especially with Baader eyepieces with those threads on the neck. Only slight screw and it's fixed. On SSW though it's an issue....seems like infinite screwing...

Agnes, check Baader T-2 prism as well. It is really nice as well.

Edited by heliumstar
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25 minutes ago, John said:

Just for info, the Tak prism has a plastic body section which some find a little off putting. The performance is very good though and the twist compression fitting works well.

Agreed about the Tak prism, nice piece of kit. Regarding the twist clamp, I have found it can get caught in eye pieces with undercuts, such as my 24mm Panoptic. I had to out some insulating tape to fill the gap in order to prevent this, annoying when it happens.

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1 hour ago, Stu said:

Agreed about the Tak prism, nice piece of kit. Regarding the twist clamp, I have found it can get caught in eye pieces with undercuts, such as my 24mm Panoptic. I had to out some insulating tape to fill the gap in order to prevent this, annoying when it happens.

I agree Stu. The Tak twist clamp is OK but not perfect by any means. I much prefer the Baader click stop approach. Thats what I have on my Baader T-2 zeiss prism.

 

 

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1 hour ago, heliumstar said:

John, I never understood the issue with plastic body on Tak. I hardly notice it and overall the diagonal looks quality to me. It certainly is not a beast like white Baader 2" and similar so maybe that's an issue? It's petite? At the end of the day using Tak is so efortless, especially with Baader eyepieces with those threads on the neck. Only slight screw and it's fixed. On SSW though it's an issue....seems like infinite screwing...

Agnes, check Baader T-2 prism as well. It is really nice as well.

I don't mind "petite" at all. My Baader T-2 zeiss prism diagonal is petite IMHO and seems to suit the slender tube of the Tak FC-100DL well I feel :smiley:

 

takercole01.JPG

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1 hour ago, Ags said:

 

..... the issues with F5 refractors would be increased chromatic aberration?

Yes, thats what I've read. My prism is dedicated to my Tak FC-100DL F/9 though. I use the Revelation on the Tele Vue Ranger 70mm F/6.8 and it works well too.

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John, the whole setup is very nice :) and petite. And we all know the best poison comes in nice petite bottles :D

Edited by heliumstar
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Not too sure the bump in CA from a prism is going to affect the views in an ST80; it's never pointed at targets that would bring out CA anyway. I can understand the concern if the prism was going on something like an Esprit 80...

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Well made, top performing diagonal prism: three surfaces must be flat, smooth and precisely oriented with respect to each other and the optical axis. The internal reflection will be total. There will be partial reflection when the beam enters and exits the prism. Light loss and ghosting must be minimized by having the first and last surface coated. The light has to travel through the glass. Dispersion must be low, the glass must be homogeneous in composition throughout and free of bubbles and other inclusions.

Well made, top performing diagonal mirror: one surface must be flat, smooth and precisely oriented with respect the optical axis. The mirror must be coated. That's all.

I would expect that for a diagonal prism to performs as well as a diagonal mirror, the prism would be much more expensive to make. I probably could not afford a prism of the same quality as my TV enhanced Aluminium or my WO dielectric mirrors. Between these two, btw, I see no difference in image quality.

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Quite agree with John about price being an issue ... also that other diagonals can perform very well. So, if you can’t see any difference in the eyepiece, what the hey. 

No visible CA is contributed by the Baaders used with my TEC - that is f7 however.  I’ve got an ST80 somewhere, so I’ll give it a go with the 1.25 Baader - the scope itself is already quite ‘colourful’ though so if, as seems likely, any CA is apparent with that combo, I’d not be in a hurry to blame the prism. 

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On 10/10/2018 at 19:34, Ags said:

The Baader Zeiss sounds very nice, but it is a bit too much for me. It would be a bit comical hanging off the back of an ST80 🤣

The TS one sounds more like my kind of thing. I've also looked at the Takahashi diagonal, it's only a few Euros more, and surely a Tak's good?

I dug out my dusty ST80 and checked. You’re right - not comical exactly but not an easy fit and doesn’t look like a great match either.  Many other good options that others have suggested that don’t break the bank ...

John E

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