1.25” Diagonal Recommendations

[John]

I've used a 2 dielectric mirror diagonal with my F/9 Tak FC-100 with no diminishment of performance over the Baader T2 prism that I could see. Mind you it was my Astro Physics Maxbright diagonal which are pretty good performers.

I prefer the Baader T2 prism in the scope because I think it suits the scope better ergonomically and mostly I use 1.25" inch eyepieces with it.

 

[Littleguy80]

12 hours ago, Piero said:

Hi,

To do what I did, you need to screw the VIP barlow into this adapter https://www.baader-planetarium.com/en/baader-tak-adapter-m43-x-0.75--t-2-(t-2-part-12).html (Baader: # 2458199). The Barlow will be mounted in the right direction. The Tak M43 side is not used, instead the other side which is T2, is attached to the 2-to-1.25" adapter.

Also, the ring fixed on a 15mm spacer at the bottom can be removed. The spacer should be attachable to the end of your zoom directly, I believe.

Note that with this configuration, the VIP barlow is essentially used in T2/2" mode. This is what I want because mine is used only with my bigger zoom and docter. It might not be what you want. Said this, the VIP is highly configurable. For instance, with another 2-to-1.25" adapter installed on top, you can use your 1.25" eyepieces too.

Thank you! I didn't realise that you were using an additional adapter. I sat there with it in parts trying to put it together like a jigsaw puzzle! It didn't make any sense for the barlow element to be upside down but I couldn't find any other that it could be attached. Thanks for the tips advice on this

[johninderby]

The Baader T2 prisim works nicely with my Bresser Mak screwed directly to the SCT port with a T2 adaptor.

[Littleguy80]

18 hours ago, F15Rules said:

The Tak prism diagonal is very good. So is the Baader T2 prism (I have the non - Zeiss one). It has a 32mm aperture so less likely to vignette, and being prisms, both have a shorter light path than mirror diagonals.

The Baader T2 prism set is good value  at £95, and very flexible, and includes the excellent Baader focusing eyepiece holder on the eyepiece end and a 1.25" nosepiece on the scope end..

https://www.365astronomy.com/Baader-Prism-Diagonal-T-2-90-degree-32mm-Set.html

you can remove the latter to replace with a Baader 2"-T2 nosepiece if you wish😊.

Dave

Thanks Dave. These two make up my short list now! 

The Tak is the cheaper option (not words you hear often). I like the twist lock mechanism. It's only draw back vs the Baader is needing to use a reducer on the telescope side. My plan is to use one of my Baader click lock 2" - 1.25" adapters. My only slight concern is whether the barrel will go in too far for my to use my 2" filters in the adapter. Should be fine...I think!

The Baader ticks all the boxes but costs twice as much even without going for the Zeiss prism. I'd like to get it with the 2" nosepiece and click lock adapter. Without the 2"-1.25" adapter the optical path is kept to a minimum and can safely use my 2" filters on it. 

All I have I have to do now is make a decision 😛 

[johninderby]

4 minutes ago, Littleguy80 said:

 

All I have I have to do now is make a decision 😛 

 

[Piero]

16 minutes ago, Littleguy80 said:

Thank you! I didn't realise that you were using an additional adapter. I sat there with it in parts trying to put it together like a jigsaw puzzle! It didn't make any sense for the barlow element to be upside down but I couldn't find any other that it could be attached. Thanks for the tips advice on this

No problem!

[John]

FWiW I'm not that keen on the Tak collar for 1.25" accessories. It works but I feel the Baader twist lock system is more positive and makes it easier to both insert and remove accessories.

I use one of the Tak collars to hold my Baader T2 diagonal in place (it's fitted with a 1.25" barrel currently) but I'm glad that I have the Baader system on the eyepiece side, which is where things go in and out much more of course !

 

 

[F15Rules]

I think another factor might need to be considered here, in respect of the mirror vs prism debate..

I tend to only view on axis most of the time as I use a driven mount. So I should always be seeing the best possible image with the least aberrations. But I know that many of you use altazimuth or DOB push along mounts, so perhaps you would be more likely to see and aberrations such as lateral colour since you are looking at off-axis images much more?

See below a quote from "Handprint Astro.com"..

Finally, any eyepieces and/or Barlow's in the optical chain (and/or our own eye limitations, and/or seeing conditions on a given night) may add their own aberrations, whether on their own or when paired with Barlow's etc.

So I reckon it could be quite difficult to test this theoretically - the real test is what you see for yourself and that really means trying out variations and different products wherever possible.

As ever, much of this is subjective, and however helpful external advice may be (and it so often is!), In the end we have to judge for ourselves which setup/combination gives us the most pleasure.

To be sure, anything sitting behind a premium objective such as Tak, Televue, Tec, Lzos etc sure has a head start! 😀😀

Dave

Lateral Chromatic Aberration.Lateral or transverse chromatic aberration appears in off axis image areas. It occurs in images brought into perfect refractive focus because the lateral spectrum produced by dispersion is of different widths or magnifications in light arriving from opposite sides of the aperture.

 

Edited May 27, 2019 by F15Rules

[johninderby]

So the observer is the weak link in the observing chain. 🤔

[Piero]

Mm.. I am not convinced about that. Lateral chromatic aberration can be quite evident to spot and I don't see how the eye of an observer can introduce it.

It would be interesting to defocus and see whether the diffraction rings have marginal difference in colour between in and out focus, whether a prism or mirror diagonal is used.

If a doublet Tak is slightly undercorrected and the prism overcorrects this, then the in- and out- focus diffraction rings should be just white and identical in colour.

Has anyone took a note of such a star test?

[John]

1 hour ago, Piero said:

Mm.. I am not convinced about that. Lateral chromatic aberration can be quite evident to spot and I don't see how the eye of an observer can introduce it.

It would be interesting to defocus and see whether the diffraction rings have marginal difference in colour between in and out focus, whether a prism or mirror diagonal is used.

If a doublet Tak is slightly undercorrected and the prism overcorrects this, then the in- and out- focus diffraction rings should be just white and identical in colour.

Has anyone took a note of such a star test?

One of the things that I have noticed about my Tak and my LZOS triplet is that intra and extra focal colour is not present. Likewise at focus of course. My previous experience with ED doublets (FPL-51 and 53) is that a small amount of colour becomes visible around brighter targets intra and extra focus but this disappears at focus with the exception of the very brightest stars where a small splash of violet is still visible. The Tak uses the Baader T2 zeiss prism diagonal and the LZOS the AP Maxbright mirror. This is one of the more noticeable characteristics of the Tak and the LZOS triplet - they are, to my eye, true apochromats whereas the ED doublets are very close at focus but show that ED characteristic of small amounts of off focus CA.

I've done such star testing on axis though as thats where I believe reliable star testing should be done. Normally I'm using a wide angle eyepiece such as a Pentax XW but sometimes I use the Nagler zoom 2-4mm and even a 4mm HD ortho that I have. The results are consistent eyepiece to eyepiece.

Personally I doubt that Takahashi produce deliberately under or over corrected objectives assuming that the use of a suitable prism will correct this aberration. The optical tests that I've seen (independant mostly) would show this and it would have been a subject of great discussion regarding this marque. Also many Japanese observers like to use their scopes "straight though" without a diagonal.

I have found many chinese achromats that do have spherical aberration though. This is one of the main issues that the Aries Chromacor was designed to correct and the ones that I have used were noticably improved when such correction was applied, notably in their ability to perform at high powers.

I do also subscribe to the idea that the human eye can produce it's own false colour though because I've experienced it myself. Sometimes when viewing a bright target obliquely and sometimes even on axis when my observing eye gets tired and / or starts to water a little.

These days I also subscribe to the notion that repeatedly testing and comparing optics will eventually reveal some small flaw or other, because none are perfect, and certainly not my eyes and skies. I've tried to concentrate more on observing and enjoying which is why I'm not doing equipment reviews much now

 

 

 

[CraigT82]

Just one point to note on the Tak prism, which I've just discovered for myself, is that it doesn't have any filter threads on the nosepiece.

[Littleguy80]

This is a new subject for me so bare with me if I've misunderstood and am asking a silly question. The Equinox 80 is F6.2 and I haven't noticed any CA so far. I believe it's an APO so I shouldn't notice any? Does the F ratio mean that I may see some CA using a prism type diagonal?

[iPeace]

1 hour ago, Littleguy80 said:

The Equinox 80 is F6.2 and I haven't noticed any CA so far. I believe it's an APO so I shouldn't notice any? Does the F ratio mean that I may see some CA using a prism type diagonal? 

The following may or may not be helpful.

I've not managed to internalize what ATA mean nor how to recognize them when observing. So when I say "the view looks fine to me", it means no more than exactly that.

My Borg 71FL is F5.6. When I use it with a Tak prism...the view looks fine to me.

P.S. ATA = All Those Abbreviations

[Littleguy80]

6 minutes ago, iPeace said:

The following may or may not be helpful.

I've not managed to internalize what ATA mean nor how to recognize them when observing. So when I say "the view looks fine to me", it means no more than exactly that.

My Borg 71FL is F5.6. When I use it with a Tak prism...the view looks fine to me.

P.S. ATA = All Those Abbreviations

haha perfect, thanks Mike  

[Star Struck]

I have used a Baader prism and a Baader Zeiss prism with an Equinox 80 and never noticed any CA.

Both were 1.25 inch.

[Littleguy80]

6 minutes ago, Star Struck said:

I have used a Baader prism and a Baader Zeiss prism with an Equinox 80 and never noticed any CA.

Both were 1.25 inch.

Thank you. Could see much difference between the two in terms of optical performance?

[Star Struck]

To be honest, not really. Might just be that my eyesight has diminished with age.

The Zeiss has a shorter path length and hence offers more flexibility if you use bino viewers.

 

[steveex2003]

On 28/05/2019 at 13:26, Star Struck said:

I have used a Baader prism and a Baader Zeiss prism with an Equinox 80 and never noticed any CA.

Both were 1.25 inch.

Did you notice anything between the two prisms? Would you be confident of identying one over the other blind, so-to-speak?
I have a couple of Equinox's and find planetary views to be my leaning right now, where I read Prisms may have marginally improved performance. I have 2" ES and 1.25" WO dielectric diagonals and although I read of potential differences, I would have absolutely zero confidence in being able to differentiate between the two blind. 

[Star Struck]

To be honest, I cannot tell the difference between them as far as viewing was concerned. My eyesight is not that finely tuned and maybe I am not that fussy as an observer. I also have a Televue Everbrite 1.25 diagonal and cannot honestly say I can see the difference between that and the prisms.

There is a physical difference and by that I mean it is possible to hit the prism with the eyepiece barrel (or in my case binoviewer barrel) in the zeiss prism. You cannot do that with the T2 prism as there is a metal ring that stops it from happening.

[Highburymark]

The Equinox will display a very small amount of colour on bright objects in my experience, and I’ve not noticed any difference in that level between the following diagonals: Baader Zeiss T2 prism; Baader 2” dielectric; WO 2” and 1.25” dielectrics. It’s a terrific performer for an F/6.25, 80mm scope. No doubt the Tak 76 or 80mm triplets are better, but we’re only talking about fine margins here. For a 3” scope to remain sharp at 170x, I reckon it does pretty much everything demanded of it.

[Paz]

I have a tak diagonal and a baader t2 prism diagonal. The Baader gets used most these days because I can adjust fine focus with it, which saves having the weight of a dual speed focuser, it can take filters, and it's stronger.

The tak diagonal is still good, really small and light.

I generally use prism diagonals with my Maksutov and SCT, and generally mirrors with my faster scopes.

[Littleguy80]

Decision made. Here’s what I bought:

The eagle eyed amongst you will have noticed that this isn’t a 1.25” Diagonal  Whilst a lot more expensive, even at secondhand prices, than the diagonal, the Nagler Zoom gives me the short focal length zoom I wanted. It should work well with the dob too. 

I’m still thinking about a 1.25” diagonal. I like the Baader prism with the 2” nosepiece and Clicklock. The 2” diagonal really comes in handy with my 20mm APM HDC which is light enough to be used with the Equinox 80 and gives at 4 degree TFOV at 25x mag. All other eyepieces I’d use would be 1.25” format. I’ll persist with the 2” diagonal for now and see if I feel like I need/want the lighter 1.25” diagonal. 

As always, many thanks for all the advice and suggestions. Greatly appreciated  

[RT65CB-SWL]

I don't think you will be disappointed with the TeleVue Nagler 3-6mm zoom. I have had mine since they were released.

[John]

Small but lovely and really well made