Recommendations for erect image diagonal

[PatrickO]

I'm looking for recommendations for a 90° 1.25" erect image diagonal for lunar observation with my 8" SCT.

I've read that the Williams Optics one is good. Has anyone experience of it? Or of any others you would recommend or avoid.

Thanks, Patrick 

Edited March 20 by PatrickO

[Space Hopper]

This APM 2" seems to have a good reputation.

https://www.apm-telescopes.net/en/apm-2-inch-erect-image-prism-with-fast-lock-and-ultra-broadband-coating

[paulastro]

3 hours ago, PatrickO said:

I'm looking for recommendations for a 90° erect image diagonal for lunar observation with my 8" SCT.

I've read that the Williams Optics one is good. Has anyone experience of it? Or of any others you would recommend or avoid.

Thanks, Patrick 

If you mean  the William Optics 2inch 90 deg one (listed on 365 Astronomy) at just over £200, Ive had one for some years.  I bought it used, then it wasn't available again until comparatively recently.

It is MUCH better than any other I've used over the years (and I've tried and owned quite a few others) and can be used on powers up to around x125 (which others I've tried have not been able to do) and still have a good image. It gives a nice image  with good contrast and is very well made. I would recommend it if it's still of the same quality.

The best one is generally acknowledged as being the Badder/Zeiss 2 inch 90 deg version  that costs around £600!  FLO lists it but currently out of stock.  

This is the one I have

https://www.365astronomy.com/William-Optics-90-degree-Erecting-Prism?path=113_152_358

Edited March 19 by paulastro

[Space Hopper]

Perhaps worth mentioning that it's quite difficult to make one of these diagonals well. Well enough, and consistently well enough for high power astro use.

You only need to look inside one to see the complexity of the thing.

Hence the sky high price of the Badder BBHS 2" Amici.

With the more budget models you often see a bright diffraction spike through very bright stars etc.

I have the 'cheaper' Baader version ; it performs ok, only giving the big diffraction spike on something really bright like Venus or Sirius etc.

On Lunar though, theres no issues.

Let us know which one you go far and how it performs on your C8 🙂

 

 

[paulastro]

2 hours ago, Space Hopper said:

Perhaps worth mentioning that it's quite difficult to make one of these diagonals well. Well enough, and consistently well enough for high power astro use.

You only need to look inside one to see the complexity of the thing.

Hence the sky high price of the Badder BBHS 2" Amici.

With the more budget models you often see a bright diffraction spike through very bright stars etc.

I have the 'cheaper' Baader version ; it performs ok, only giving the big diffraction spike on something really bright like Venus or Sirius etc.

On Lunar though, theres no issues.

Let us know which one you go far and how it performs on your C8 🙂

 

 

Space Hopper.  When you say the cheaper one  do you mean the one below.

https://www.firstlightoptics.com/diagonals/baader-t-2-90-baader-astro-amici-prism-with-bbhs-coating.html

I was thinking of buying it ( or even  possibly the expensive one!) to replace the William Optics one I have.  I've never really been troubled much by the diffraction spike, but I would expect one or both of the Baaders to have a better overall performance and be ok on powers of over x125 or so.  Of course the cheaper one probably has too small a prism to accommodate my Celestron Ultima Edgel FF 30/70 and Baader Aspheric 36/72 without vignetting.

Can you tell me how the cheaper one performs on Jupiter/ Saturn/Mars on higher powers 

IfI bought the expensive one, I'd use it all the time and sell my ordinary Baader prism #2456095 to recoup some money.

Thanks, Paul

 

 

 

[Space Hopper]

Hi, and yrs, that looks like the same one at a similar price to mine. I think its the same catalogue number too.

One difference, mine is a few years older and is 'pre' the fancy BBHS coatings.

I also have the big 2" mirror version WITH the BBHS coatings and it performs very well indeed.

Regarding the AMICI : i haven't used it really on high power planetary : i always use my standard prism which has a 2.6x gpc 'permanently residing in it for high power planetary. This has a 'quick coupler on it that attaches on to my binoviewer, a Baader Mk5.

The reasons why i purchased the Amici were for terrestrial work with a smaller refractor, and also to help me on Lunar observations. I wanted to have a crack at 'the Lunar 100' and much prefer a correctly oriented image to aid identifications of craters etc.

I actually half considered the mega bucks Baader \Amici when they released it, but then some sense on my part kicked in. Nearly £600 on a diagonal is a bit crazy really.

I'm pleased with the 'cheaper' version though. One would assume the newer version with the posh coatings will perform even better.

The diffraction spike is only an issue on Venus really. And something really bright such as Sirius , Vega etc.

I don't think it will trouble you on the moon.

If you lived a bit closer to me, i'd happily lend it to you so you could try it out. 

The blue and white APM version is a good alternative though. I know a club member who uses one, and it performs very well.

 

[PatrickO]

12 hours ago, paulastro said:

If you mean  the William Optics 2inch 90 deg one (listed on 365 Astronomy) at just over £200, Ive had one for some years.  I bought it used, then it wasn't available again until comparatively recently.

It is MUCH better than any other I've used over the years (and I've tried and owned quite a few others) and can be used on powers up to around x125 (which others I've tried have not been able to do) and still have a good image. It gives a nice image  with good contrast and is very well made. I would recommend it if it's still of the same quality.

The best one is generally acknowledged as being the Badder/Zeiss 2 inch 90 deg version  that costs around £600!  FLO lists it but currently out of stock.  

This is the one I have

https://www.365astronomy.com/William-Optics-90-degree-Erecting-Prism?path=113_152_358

I'm thinking of the 1.25" one 

[michael.h.f.wilkinson]

I got a fairly cheap 1.25" 90 deg Amici prism from Teleskop Service for my DIY 14x70 finder, and it works well enough at low magnification. I have an Orion Optics (looks like a WO rebrand) 2" which works beautifully in wide-field views in my APM 80mm F./6 and Celestron C8), but degrades a  bit when pushing magnification (odd diffraction spikes). Haven't tried it on the moon, I should add.

[Highburymark]

2 hours ago, paulastro said:

Space Hopper.  When you say the cheaper one  do you mean the one below.

https://www.firstlightoptics.com/diagonals/baader-t-2-90-baader-astro-amici-prism-with-bbhs-coating.html

I was thinking of buying it ( or even  possibly the expensive one!) to replace the William Optics one I have.  I've never really been troubled much by the diffraction spike, but I would expect one or both of the Baaders to have a better overall performance and be ok on powers of over x125 or so.  Of course the cheaper one probably has too small a prism to accommodate my Celestron Ultima Edgel FF 30/70 and Baader Aspheric 36/72 without vignetting.

Can you tell me how the cheaper one performs on Jupiter/ Saturn/Mars on higher powers 

IfI bought the expensive one, I'd use it all the time and sell my ordinary Baader prism #2456095 to recoup some money.

Thanks, Paul

 

 

 

I have this one Paul - it’s superb. Only a tiny, almost imperceptible diffraction spike on very bright stars. Because they are difficult to make, there may be variations between different units, but I think the T2 Baader is the way to go if you want top quality without forking out for the very expensive 2”.

[stormioV]

Unless correct orientation through eyepiece is a must. I use this and find it excellent. https://shopatsky.com/products/mirror-image-field-map-of-the-moon

[paulastro]

1 hour ago, Space Hopper said:

Hi, and yrs, that looks like the same one at a similar price to mine. I think its the same catalogue number too.

One difference, mine is a few years older and is 'pre' the fancy BBHS coatings.

I also have the big 2" mirror version WITH the BBHS coatings and it performs very well indeed.

Regarding the AMICI : i haven't used it really on high power planetary : i always use my standard prism which has a 2.6x gpc 'permanently residing in it for high power planetary. This has a 'quick coupler on it that attaches on to my binoviewer, a Baader Mk5.

The reasons why i purchased the Amici were for terrestrial work with a smaller refractor, and also to help me on Lunar observations. I wanted to have a crack at 'the Lunar 100' and much prefer a correctly oriented image to aid identifications of craters etc.

I actually half considered the mega bucks Baader \Amici when they released it, but then some sense on my part kicked in. Nearly £600 on a diagonal is a bit crazy really.

I'm pleased with the 'cheaper' version though. One would assume the newer version with the posh coatings will perform even better.

The diffraction spike is only an issue on Venus really. And something really bright such as Sirius , Vega etc.

I don't think it will trouble you on the moon.

If you lived a bit closer to me, i'd happily lend it to you so you could try it out. 

The blue and white APM version is a good alternative though. I know a club member who uses one, and it performs very well.

 

Many thanks  that was very helpful.  I think in quality, the cheaper (smaller) one might be ok for me, but if I can't use it for sweeping with my 2 inch eyepieces (possible vignetting)  then that would  restrict the field with my 103 triplet to 2.3 degrees, instead of 3.0 or 3.7 degrees - I'll have to think about that as its half the price.

Whilst I agree that £600 is a lot for a prism/diagonal, it depends what you compare it with.  In our astronomy world some people will pay( and do) well over £600 for an eyepiece, £87  for anti vibration pads, £200 for counerweights and over £300 for some filters etc etc.

The reason I most want a better amici prism is that I have always resented having to put up with a mirror image view when using any ordinary diagram or prism.  It's not only annoying on the Moon and planets, but for any object or star field you look at you are not seeing reality, it's not what they really look like. Most people don't seem to be bothered by this, but if all telescopes had always given a right way round image and then someone had invented an optical system giving a mirror image people probably wouldn't put up with it!   (an inverted image is fine as it exists in reality, no upside down in the universe of course.)  Rant over 🤣.

Thanks for the APM prism heads up, but it may mot be as good as the Willuam Optics  2inch prism which I've used up to now. ( link in my first post in this thread)

Anyway, thanks again, I have somen thinking to do ☺️

[paulastro]

1 hour ago, Highburymark said:

I have this one Paul - it’s superb. Only a tiny, almost imperceptible diffraction spike on very bright stars. Because they are difficult to make, there may be variations between different units, but I think the T2 Baader is the way to go if you want top quality without forking out for the very expensive 2”.

Many thanks Mark.  That's very useful, I'll take it into consideration.  It may come down to how important it is to increase the field in my 103 from 2.3 to up to 3.7 degrees! I'm saying thus on the basis I'm assuming there will be some vignetting if I use a T2 2 inch nosepiece and 2 inch eyepiece clamp because of the smaller clear aperture in the T2 version..  Have you tried yours with 2 inch eyepieces Mark? 

 

 

Edited March 20 by paulastro

[Space Hopper]

All i can suggest is not to discount the APM version

https://www.apm-telescopes.net/en/apm-2-inch-erect-image-prism-with-fast-lock-and-ultra-broadband-coating

 

Is has a 46mm clear aperture meaning all your 2" eyepieces will do their thing and show NO vignetting.

And its a realistic price.

[Stu]

I have the 2” WO 45 deg erecting prism which I use occasionally for spotting purposes. I do find it is softer at higher power than a normal diagonal. I would suggest a Baader prism if you want to go down that that route.

Some years back @iPeace had a bit of a journey with these prisms, discovering that in one instance he obtained one that showed no spike at all if I recall correctly, probably due to perfect alignment. I can’t remember if he managed to get a second one as good, and he hasn’t been in the forum for some months now.

The Duplex Moon Atlas is a great resource for matching orientation to your scope if you are will to stick with left right reversed images.

https://www.firstlightoptics.com/books/duplex-moon-atlas-the-next-generation-lunar-atlas-by-ronald-stoyan.html

[paulastro]

17 minutes ago, Space Hopper said:

All i can suggest is not to discount the APM version

https://www.apm-telescopes.net/en/apm-2-inch-erect-image-prism-with-fast-lock-and-ultra-broadband-coating

 

Is has a 46mm clear aperture meaning all your 2" eyepieces will do their thing and show NO vignetting.

And its a realistic price.

Many thanks.  Apologies if I seemed dismisive in any way re the APM, I didn't mean to be. 

Your club member may think a lot of it, but I've no way of knowing what criteria are important to him.  Also, I've no way of trying one out so if I ordered one I'd be buying blind.  If I bought one and tried it out I might think its great.  If I didnt or it wasnt as good as the zwO I have, would they be willing to take it back?  Not all suppliers are as helpful as FLO and others I have used. The 46mm clear aperture is good, but then my WO version is 40 and shows no vignetting, the expensive Baader is 44, but this is not the only important thing.  The Baader literature gives persuasive reasons for buying it. as the APM one does, even more so. The main thing  has going for it is that it has an excellent reputation,  their other prisms are certainly very good.  

Are there any reviews of the APM version pr other information.?  I didn't know it existed before you mentioned it.

 

[Highburymark]

7 hours ago, paulastro said:

Many thanks Mark.  That's very useful, I'll take it into consideration.  It may come down to how important it is to increase the field in my 103 from 2.3 to up to 3.7 degrees! I'm saying thus on the basis I'm assuming there will be some vignetting if I use a T2 2 inch nosepiece and 2 inch eyepiece clamp because of the smaller clear aperture in the T2 version..  Have you tried yours with 2 inch eyepieces Mark? 

 

 

From my inexpert calculations, Paul, the XWA 20mm will vignette slightly with the Baader T2 amici prism, but not by much. The prism has an aperture of 32/33mm and the APM 20mm has a field stop of 34.8mm (according to Don Pensack) despite an advertised 37mm, which should mean you’ll barely notice the difference. I stand to be corrected on this - but it’s amazing how few eyepieces vignette with the Baader T2 diagonals (I also have the standard Zeiss prism and BBHS mirror). However, it does mean you’ll need a 2”/T2 clicklock ep holder for 2” eyepieces to attach to the prism.
 

[Highburymark]

5 hours ago, Stu said:

I have the 2” WO 45 deg erecting prism which I use occasionally for spotting purposes. I do find it is softer at higher power than a normal diagonal. I would suggest a Baader prism if you want to go down that that route.

Some years back @iPeace had a bit of a journey with these prisms, discovering that in one instance he obtained one that showed no spike at all if I recall correctly, probably due to perfect alignment. I can’t remember if he managed to get a second one as good, and he hasn’t been in the forum for some months now.

The Duplex Moon Atlas is a great resource for matching orientation to your scope if you are will to stick with left right reversed images.

https://www.firstlightoptics.com/books/duplex-moon-atlas-the-next-generation-lunar-atlas-by-ronald-stoyan.html

It was one of iPeace’s prisms I bought Stu. I was lucky to benefit from his experimentation. Certainly mine is 99% as sharp and detailed on the Moon as the standard Zeiss prism. 

[Stu]

24 minutes ago, Highburymark said:

From my inexpert calculations, Paul, the XWA 20mm will vignette slightly with the Baader T2 amici prism, but not by much. The prism has an aperture of 32/33mm and the APM 20mm has a field stop of 34.8mm (according to Don Pensack) despite an advertised 37mm, which should mean you’ll barely notice the difference. I stand to be corrected on this - but it’s amazing how few eyepieces vignette with the Baader T2 diagonals (I also have the standard Zeiss prism and BBHS mirror). However, it does mean you’ll need a 2”/T2 clicklock ep holder for 2” eyepieces to attach to the prism.
 

I agree, you actually don’t notice even quite significant vignetting so the T2 diagonals and prisms work surprisingly well even with longer focal length 2” eyepieces.

[paulastro]

1 hour ago, Highburymark said:

From my inexpert calculations, Paul, the XWA 20mm will vignette slightly with the Baader T2 amici prism, but not by much. The prism has an aperture of 32/33mm and the APM 20mm has a field stop of 34.8mm (according to Don Pensack) despite an advertised 37mm, which should mean you’ll barely notice the difference. I stand to be corrected on this - but it’s amazing how few eyepieces vignette with the Baader T2 diagonals (I also have the standard Zeiss prism and BBHS mirror). However, it does mean you’ll need a 2”/T2 clicklock ep holder for 2” eyepieces to attach to the prism.
 

Many thanks Mark. Mark, where did you get the XWA 20mm from?   My two 2 inch eyepieces are the Celestron 30mm/70 Ultima Edge FF and the Baader Asheric 36mm/72, also the Baader Star Diagonals Manual I printed off some years ago has the clear aperture of the Baader T2 Astro Amici-Prism with BBHS coating as 31 mm clear aperture.

I do agree that Baader T2 prisms don't vignette very easily.  My Baader T2 body with 'extra large BBHS Prism by Zeiss-standard short optical length' (34mm clear aperture, 38.5mm optical length) doesn't vignette with either of my 2 inch eyepieces.

I must admit, your own and Stu's comments have moved me in the direction of the T2 amici-prism for which I thank you both.

PS I could swap out the 2inch T2 Clicklock and 2inch nosepiece from my other prism.

 

Edited March 20 by paulastro

[Highburymark]

Oops - don’t know why I assumed you had the APM, and checking other websites, you’re right about the 31mm clear aperture. This is why I insert ‘I stand to be corrected’ on everything I write these days……..

[paulastro]

No problem Mark, I had to check  back to remind myself what I had written!  😊  

[Louis D]

14 hours ago, Highburymark said:

From my inexpert calculations, Paul, the XWA 20mm will vignette slightly with the Baader T2 amici prism, but not by much. The prism has an aperture of 32/33mm and the APM 20mm has a field stop of 34.8mm (according to Don Pensack) despite an advertised 37mm, which should mean you’ll barely notice the difference. I stand to be corrected on this - but it’s amazing how few eyepieces vignette with the Baader T2 diagonals (I also have the standard Zeiss prism and BBHS mirror). However, it does mean you’ll need a 2”/T2 clicklock ep holder for 2” eyepieces to attach to the prism.
 

You could probably only detect the vignetting of that combination by taking a photograph of an evenly lit sky or light colored wall through it and comparing it to one taken through a full 46mm or larger clear aperture diagonal.

[paulastro]

Patrick, thank you for starting this thread.  It so happened it was at a time I was thinking  of getting a better quality amici-prism to use on both of my refractors to use as my goto prism.  It's been useful for me and I hope I didn't  divert the thread from where you wanted to be ? apologies if I did.

I've ordered the Baader T2 90 deg Astro Amici-Prism with BBHS Coating #2456130 this morning.  I'll post my findings when I've had time to use it a few times.  Many thanks also to those who have added such helpful information to the thread.

[stormioV]

The Duplex Moon Atlas is a great resource for matching orientation to your scope if you are will to stick with left right reversed images.

https://www.firstlightoptics.com/books/duplex-moon-atlas-the-next-generation-lunar-atlas-by-ronald-stoyan.html

 

I do think this  recommended by Stu may be a better choice than the one I have and think I will be upgrading to this soon. My field map is really convenient/light. I often tuck  under arm or bend it over and tuck in in handles of mount.

 

Also, have you tried without diagonal and attached eyepiece directly to your ota. It can be a little uncomfortable but it may help on your final decision.

Edited March 23 by stormioV