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Baader T-2 prism Diagonals - differences?

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#1 vkhastro1

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Posted 18 October 2013 - 07:51 AM

Baader makes 2 different non-amici T-2 prism star diagonals.
The 32mm version (lower priced - $129.00) and the more expensive 34mm
Zeiss version. The mm measures clear prism aperture.
1. the 32mm version is supposed to have about 96% transmission and the Zeiss version is closer to 99% transmission. In actual field use is there a perceivable difference?
2. The 32mm version is shorter in actual back focus length than the Zeiss version. What are the actual back focus lengths of each version?
3. Comparing the information and advantages/disadvantages of these 2 versions - price, transmission, back focus length - what is the best diagonal to use with a Baader maxbright binoviewer and Baader Mark V binoviewer?
I presently own a Celestron C8 Edge and C14 Edge. I have both the Baader Maxbright and Mark V binoviewers on separate Baader Zeiss 34mm prism star diagonals.
Final question -should I invest in purchasing the Baader 32mm version for maximizing the Baader maxbright binoviwer use with the Celestron C8 Edge?

#2 Eddgie

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Posted 18 October 2013 - 08:01 AM

You can't really see the difference in transmission. Compared to Max Mirror, view is identical.

The actual light path length varies with the focal length of the telescope and I believe that it is stated for f/5. I believe that for slower focal length scopes, it is a bit longer than stated.

You don't need the bigger prism optically, and the light path savings is not enough to really make much difference, but of course the standard prism is much less expensive.

I use the standard prism and find it to be excellent so have never felt like I needed to spend more.

If you can afford the Zeiss though, hey, why not? Then you know you have the best.

#3 mgwhittle

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Posted 24 October 2013 - 07:06 PM

I got the Zeiss. If I did it again I would get the Baader 32mm version and save a bit of cash. As Eddgie said, I don't think there is a true visible difference at the eyepiece.

#4 axle01

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Posted 24 October 2013 - 10:37 PM

Just got a Baader Zeiss to mate up with my Denkmeier Binotron 27 with one of their dovetail adapters.

I have the best bino and I didn't want to compromise so I got the Zeiss, first light this Sat night.

#5 tomcody

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Posted 25 October 2013 - 08:50 AM

T2-1C = 37mm
T2-1 B = 41 mm
I can see a small difference in between the two (same with the Maxbrights and MarkV's) . As you own both binos, Whatever difference you can see between them? is what you will notice with the diagonals.
As to buying one? unless 4mm savings in backfocus is very important to your setup? I would not bother.
Rex

#6 tomcody

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Posted 25 October 2013 - 12:29 PM

Final question -should I invest in purchasing the Baader 32mm version for maximizing the Baader maxbright binoviwer use with the Celestron C8 Edge?

Just an idea, if you want to optimize the C8HD? you could try attaching the binos directly to the C8HD without a diagonal, with a good mount ( either Alt-az or gem , it should be possible to view that way, heck binocular guys do it all the time with big binos, and the back focus should be about perfect.
Rex

#7 Eddgie

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Posted 25 October 2013 - 01:04 PM

Final question -should I invest in purchasing the Baader 32mm version for maximizing the Baader maxbright binoviwer use with the Celestron C8 Edge?


Yes.

And if you really want to make it as excellent as possible, use either the Baader 10mm SCT to T2, or at lest the 15mm SCT to T2.

Suppose you are using a 1.25" diagonal (and if you are using a 2", loose it as fast as possible, it is not a good configuration).

But lets suppose that you are using a 1.25" diagonal and a 1.25" visual back.

The standard 1.25" visual back is about 35mm in light path.

the standard 1.25" diagonal is about 65mm in lighth.

By going to the T2 Prism (either one) and the 15mm SCT to T2 (won't work on the C14), you will shave 30mm for the eyepiece holder, and another 20mm for the 1.25" visual back.

This will do two things for you. First, if you cut 50mm off, you reduce the focal length by 150mm. In the EdgeHD 8", that makes your true field quite a bit bigger and for lowest power the field will be not only bigger, but slightly brighter as well.

And, once the light path goes over 165mm (at least in two of the three EdgeHD 8" scopes that I know have been measured), the aperture is reduced by about 2.5mm for every mm of light path.

Even with the setup in the picture (T2 standard prism with 10mm connector and Mark V), my EdgeHD 8" is only working at 7.85" of aperture.

Before I did the light path reduction, aperture was 7.4"

My light path is now at 171mm. With a Maxbright/T2 and the 10mm connector, you would get full aperture.

I am willing to sacrifice .15" of aperture for the much bigger prisms though. Even 28mm field stop eyepecies work fine with the Mark Vs, but the ES 20/68 were the lowest power wide fields I could use with the Maxbright.

For the C14, not so critical. Aperture reduction does not start until 200mm of back focus, so Mark V and T2 prism, Zeiss Prism, or Max T2 Mirror all work fine.

But my own advice is to keep it as short as possible for the EdgeHD 8".

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#8 Eddgie

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Posted 25 October 2013 - 01:08 PM

The previous picture is the 10mm Connector (total of 171mm of light path with the 10mm/Standard Prism/Mark V).

the problem with this diagonal is that it does not allow for easy rotation. I use it on a Alt-Az mount (8SE) so don't need to be able to rotate the diagonal.

The 15mm though has a collar like a standard SCT diagonal, so it allows you to rotate the diagonal the same way. For GEM mounting, this would be better, but I don't think it is as secure as I would like. If the bino is tilted off to the right when viewing close to the horizon, the BV can cause it to break free, rotating the BV down with heart stopping suddenness.

In fact, I changed to the 8SE just so I could move to the 10mm connector (but also because it was lighter, though not as stable as the CG5).

Anyway, here is a picture of the 15mm connector.

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#9 Kent10

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Posted 26 March 2014 - 10:16 PM

I see in the original post transmission of the Baader 32mm Prism is 96% and the Baader Zeiss 34mm is 99%. Does anyone know where this information is located and if it is true. I haven't been able to confirm this anywhere online. Thanks.

#10 Eddgie

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Posted 27 March 2014 - 06:28 AM

I have never seeen this published either.

Getting better than 96% transmission with a Prism is pretty easy though so I would think that the standard prism is at least this good and perhaps better.

Also, these figures can be misleading even when they are published.

The question is how was the transmission measured.

It is possible (and likely) that the Zeiss has a broader range of transmission (more wavelenths) than the standard prism and maybe in green, they are the same.

But you don't know until you see a full range transmission graph.

So, never seen this figure published, and unless you see the entire spectrum figures, one would not necessarily have a complete picture of performance.

#11 Kent10

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Posted 27 March 2014 - 08:49 AM

Thanks Ed. I just ordered the standard prism because the Zeiss has been out of stock for a while.

#12 Eddgie

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Posted 27 March 2014 - 09:35 AM

I have been using the standard and I own the Maxbright mirror.

It is almost impossible for me personally to tell the difference between any of these and the best 2" diagonal I own.

I think most of the differences that the expert eyepiece testers see when they do that kind of thing is so subtle that I would never see it.

I used to expact to see some meaningful difference after reading all kinds of eyepiece/diagonal reviews, and I never saw them myself.

I remember when Dielectrics first came out.. People were raving about how much better they were.

I could never see it.

And now, it seems that all the rage is the Baaader Prism.

But people can spend their money however they like.

I have been more than happy with the standard prism, and if you don't get caught up in all the hype, you can be too.

#13 Hesiod

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Posted 27 March 2014 - 12:24 PM

Both prisms are good, in my opinion the "Zeiss" has a tiny advantage because it shows a bit less scattering; but when coupled to the Maxbright (which by itself has more scatter than both prism together) I can not see any difference.

#14 Jeff B

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Posted 28 March 2014 - 09:43 AM

Say, I've a Baader T2 prism that visually has a line in it and displays a spike on stars. Annoying so I've parked it. Which one is that?

Jeff

#15 Eddgie

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Posted 28 March 2014 - 09:45 AM

You have the Amici. While the Baader Amici is perhaps the best Amici on the market, it is not usually a good idea to use these for astronomy use because as you have seen, they can have a bright spike.

Great for daytime, but not the best choice for night time.

#16 Mark9473

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Posted 28 March 2014 - 02:07 PM

Well the Baader T2 amici is the best choice for night time viewing if you need upright non-mirrored views. It's no slouch optically; easily beat a standard mirror diagonal for detail and contrast on Jupiter, despite the diffraction spike.

But if you don't need the upright non-mirrored image then by all means get a regular star diagonal.

#17 Jeff B

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Posted 28 March 2014 - 11:06 PM

Thanks guys, I've got both. I'll give "Spike" another try.

#18 REC

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Posted 31 March 2014 - 02:18 PM

Ed, I have been following your recommendations for a while and I keep reading that the 1.25" diagonal is a better setup than a 2" rear configuration, of which I am using. It seems to be a lot sturdier than my 1.25" back and diagonal.

The 2" back I have is 35mm long and has 2 set screws that holds the 2" diagonal pretty well and secure. The 1.25" back is only 1 screw and I'm afraid the diagonal would slip.

So I have shied away from the Baader setup you use as I thought it was pretty costly at $250, but I just read your post from last year and I realize that you are using the basic T-2 prism at a cost of $129...that is more reasonable for me to try.

So, is this all I would need for my Meade LS-8 and Denk 2 P/S BV?

1. 10mm back that screws directly to the Baader T2 prism for $29?

2. Baader T2 prism diagonal $129.00

3. Denk dovetail adapter - $29.00

Thanks,

Bob

#19 Eddgie

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Posted 31 March 2014 - 02:54 PM

Yes, this is all you need, but Denk does not make a dovetail adapter for the Denk II. Only for the Binotron.

To use the Denk II, you are going to have to have an adapter made. It will need male thread on the Denk end, and T2 female on the other end.

Precise Parts I think makes these for $98.

I was having one made by a forum member in Canada for $60 for a Denk II, but I sold the Denk II and no longer need it. If you want it, I can arrange to have him take the money from you and ship the adapter to you when they are finished (he was having a batch of them made).

But the only dovetail connector that Denkmeier makes at this point (that I am aware of) is for the Binotron and it will not fit the Denk II.

So you still need a part to do that. Otherwise, as long as you have standard SCT port on the back, all you need is the 10mm SCT to T2 connector and the T2 diagonal.

#20 REC

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Posted 31 March 2014 - 05:07 PM

Ed, thanks for your reply.

I did get an email from Russ today and he confirmed what you said, only has them for the Binotron as it is a different size thread. I guess I could use the Baader diagonal with a 1.25" tube and use the same nosepice in the Denk, or maybe take you up on the Canada guy and just get that dovetail piece and thanks for your offer!

All and all, that is the best idea for reducing the back focus, right. I think you told me once that my 2" configuration was over 250mm and working at f/2600 vs. native f/2000...loss of light and aperture ect. Here's what it looks like now.

Bob

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