Prism or mirror diagonal best for solar Ha?

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Prism or mirror diagonal best for solar Ha?

Post by Highbury Mark » Wed Jan 06, 2021 1:15 pm

This is perhaps a rather technical question, but one that’s been on my mind for a while, so am hoping someone on the forum might be able to answer.
Are there any advantages to using a prism or mirror diagonal for solar observing?
With conventional night astronomy, the general advice is that prisms are better for slower scopes, while mirrors are recommended for faster scopes, to minimise false colour. But what about Ha solar?
My set up is two 70mm front mounted solar filters attached to a TV85 refractor (F/7), a Baader T2 prism diagonal, and a binoviewer, which I use for 95% of observing. Although I have a selection of diagonals,I use the Baader T2 prism for solar as it has the shortest light path, and is the only diagonal which lets me achieve focus. I’m very happy with the views, which are sharp up to 120-130x under good conditions. But I wonder if there would be any benefits (transmission, sharpness?) from using a T2 mirror diagonal instead?


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Re: Prism or mirror diagonal best for solar Ha?

Post by Ljungmann » Wed Jan 06, 2021 4:50 pm

I use a Takahashi 1.25" prism diagonal. The filters are 0.6A Quantum (former ATM) and 0.3A SolarSpectrum. Refractors and a 8" Baader Triband SCT. I have tested a number of mirror diagonals and I will say that the Takahashi gives you observations with 0 reflections. World class. The Baaders prism diagonals are among the best too.



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Re: Prism or mirror diagonal best for solar Ha?

Post by marktownley » Wed Jan 06, 2021 6:09 pm

Highbury Mark wrote:
Wed Jan 06, 2021 1:15 pm
Are there any advantages to using a prism or mirror diagonal for solar observing?
Personally I don't think it will make a scrap of difference. Try it and see. Buy a prism from somewhere that allows you return and give it a go.


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Re: Prism or mirror diagonal best for solar Ha?

Post by Highbury Mark » Wed Jan 06, 2021 8:08 pm

Thanks guys. I shall happily continue using my current Baader diagonal and not fret further.
That Takahashi prism seems to be highly rated. As an owner of two Takahashi scopes, I can’t work out why the prism is the only Tak accessory that doesn’t require a second mortgage. In fact it’s a positive bargain. Glad to hear it’s delivering the goods with the Daystar/Solar Spectrum filters.


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Re: Prism or mirror diagonal best for solar Ha?

Post by marktownley » Wed Jan 06, 2021 8:17 pm

I'm in the process of working towards a new (mod/setup?) for this year that for my visual work will involve the Baader T2 prism diagonal, I think it will be a couple of months maybe before I get one (other bits to trickle in first), but I think will work just fine. The reason I am going this route is because of the shorter optical path compared to a 2", but, gives 'fixed' screw thread connections compared to a 1.25" diagonal.


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Re: Prism or mirror diagonal best for solar Ha?

Post by Highbury Mark » Wed Jan 06, 2021 10:11 pm

marktownley wrote:
Wed Jan 06, 2021 8:17 pm
I'm in the process of working towards a new (mod/setup?) for this year that for my visual work will involve the Baader T2 prism diagonal, I think it will be a couple of months maybe before I get one (other bits to trickle in first), but I think will work just fine. The reason I am going this route is because of the shorter optical path compared to a 2", but, gives 'fixed' screw thread connections compared to a 1.25" diagonal.
Sounds intriguing Mark. I liked the look of your Lunt 50/Quark double stack set up - great images too. I am all-T2 now with my three scopes (and three diagonals). Particularly helpful as I binoview a lot and need to keep light paths short. It’s incredibly robust and user friendly.


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Re: Prism or mirror diagonal best for solar Ha?

Post by DeepSolar64 » Thu Jan 07, 2021 2:47 am

I have never thought about that since my blocking filter diagonal doesn’t give me that choice on Ha. HM, where is the blocking filter in your setup? Straight-through?


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Re: Prism or mirror diagonal best for solar Ha?

Post by Highbury Mark » Thu Jan 07, 2021 11:30 am

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Yes - straight through James. It’s a neat system but it adds another 35mm to the light path which I could do without - the blocking filter has the blue tape around it


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Re: Prism or mirror diagonal best for solar Ha?

Post by DeepSolar64 » Thu Jan 07, 2021 5:00 pm

HM,
I would have guessed a straight-through BF. That's a nice looking setup too!! I also love the focuser on the TV-85. A close friend of mine has one and I like the focuser better than any other I have used.

While not Ha my little Orion70 white light refractor has a mirror diagonal. The scopes FL is F7.1.

James


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Re: Prism or mirror diagonal best for solar Ha?

Post by Highbury Mark » Thu Jan 07, 2021 6:58 pm

Yes, the focuser needs to be reasonably good for binoviewing. I believe the TV85 focuser is a Starlight (though this was denied by David Nagler at the last ‘Astrofest’ in London - I think he was protecting the supremacy of the TeleVue name - lovely guy though).
Something I haven’t tried yet is to use the TV85/SF70 without a diagonal. Now the Sun’s so low I should give it a go - though diagonals are so good these days that I can’t imagine I’d perceive any difference.
I’ve just googled the Orion 70mm white light scope - what a cool addition to your solar armoury. Orion’s not so popular over here - don’t seem to be stocked by UK retailers, though they do advertise mail order in the astro mags.
Although 99% of my observing has been Ha in recent years, I’m really looking forward to some WL sessions in 2021. Just as compelling as Ha on those rare days when we have decent activity and good seeing.


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Re: Prism or mirror diagonal best for solar Ha?

Post by marktownley » Thu Jan 07, 2021 7:49 pm

What are the ep's you are using there Mark?


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Re: Prism or mirror diagonal best for solar Ha?

Post by Highbury Mark » Thu Jan 07, 2021 8:29 pm

marktownley wrote:
Thu Jan 07, 2021 7:49 pm
What are the ep's you are using there Mark?
They’re Panoptic 24s Mark. For years I bleated on about only needing TV Plossls and orthos for solar (and the Pentax XF zoom - such a great solar eyepiece). But after getting some wider binoviewers, I bought a second Panoptic 24 in the summer, and they are terrific. 65x-ish with this scope (with 2.6x GPC/barlow), they are excellent for solar binoviewing. Possibly a notch less sharp than the best orthos, but they frame the full disc so well - and they’re good with less than perfect seeing. It’s always fun when you’re showing someone the Sun for the first time to place the disc outside the field of view and then let it slowly drift in.


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Re: Prism or mirror diagonal best for solar Ha?

Post by DeepSolar64 » Fri Jan 08, 2021 6:42 am

Highbury Mark wrote:
Thu Jan 07, 2021 6:58 pm
Yes, the focuser needs to be reasonably good for binoviewing. I believe the TV85 focuser is a Starlight (though this was denied by David Nagler at the last ‘Astrofest’ in London - I think he was protecting the supremacy of the TeleVue name - lovely guy though).
Something I haven’t tried yet is to use the TV85/SF70 without a diagonal. Now the Sun’s so low I should give it a go - though diagonals are so good these days that I can’t imagine I’d perceive any difference.
I’ve just googled the Orion 70mm white light scope - what a cool addition to your solar armoury. Orion’s not so popular over here - don’t seem to be stocked by UK retailers, though they do advertise mail order in the astro mags.
Although 99% of my observing has been Ha in recent years, I’m really looking forward to some WL sessions in 2021. Just as compelling as Ha on those rare days when we have decent activity and good seeing.

Though inexpensive the Orion 70mm Solar Telescope has been a real performer, no it won't quite equal the similar sized Astro-Tech AT72EDII using the wedge but the difference is on most days not that much. That's surprising since the Altair wedge alone costs more than the Orion scope does! With the Orion 70, bang for the buck certainly applies here! It certainly sounds like Orion needs a European distributor.

Given some good active regions white light can be very educational and fun. And certainly much cheaper than doing Hydrogen-Alpha. And unlike CaK you can visually see it!!


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Re: Prism or mirror diagonal best for solar Ha?

Post by Highbury Mark » Fri Jan 08, 2021 3:01 pm

Now we’re talking about white light James, I was surprised to see how expensive the Baader wedge is in the States - almost as much as a Lunt 50 and more than a PST!!
While you get cheaper Lunt and Coronado prices, we get cheaper Baader and Solarscope prices.


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Re: Prism or mirror diagonal best for solar Ha?

Post by DeepSolar64 » Fri Jan 08, 2021 5:12 pm

Yes the Baader wedge is expensive here. That’s one reason I opted for the Altair wedge. I have been really satisfied with it.


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Re: Prism or mirror diagonal best for solar Ha?

Post by Highbury Mark » Fri Jan 08, 2021 6:15 pm

DeepSolar64 wrote:
Fri Jan 08, 2021 5:12 pm
Yes the Baader wedge is expensive here. That’s one reason I opted for the Altair wedge. I have been really satisfied with it.
Doubt anyone could see any difference between the two. I saw a small improvement in views, particularly at high magnification, when I moved from Baader film to the wedge. But comparing the Lacerta wedge to the Baader, I couldn’t perceive any advantage in the Baader


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Re: Prism or mirror diagonal best for solar Ha?

Post by DeepSolar64 » Fri Jan 08, 2021 7:01 pm

Highbury Mark wrote:
Fri Jan 08, 2021 6:15 pm
DeepSolar64 wrote:
Fri Jan 08, 2021 5:12 pm
Yes the Baader wedge is expensive here. That’s one reason I opted for the Altair wedge. I have been really satisfied with it.
Doubt anyone could see any difference between the two. I saw a small improvement in views, particularly at high magnification, when I moved from Baader film to the wedge. But comparing the Lacerta wedge to the Baader, I couldn’t perceive any advantage in the Baader
A friend of mine opted for the Lacerta wedge over the Altair and Baader models because of the brewster angle concept? Does this give any advantage over other wedges as claimed?


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Re: Prism or mirror diagonal best for solar Ha?

Post by Merlin66 » Sat Jan 09, 2021 7:22 am

Only if you want to use polarized filters to attenuate the light throughput.


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Re: Prism or mirror diagonal best for solar Ha?

Post by Highbury Mark » Sat Jan 09, 2021 3:53 pm

Yes - it’s just the polarisation feature that distinguishes the Lacerta wedges. They are very solidly made too.


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Re: Prism or mirror diagonal best for solar Ha?

Post by SimonM » Sat Jan 09, 2021 9:13 pm

The Lacerta USP is a more effective polarised output but the disadvantage is it is not 90 degrees.

So if you look up at the sun, you have to also look up and any perceived advantage is lost by getting an uncomfortable view (neck-ache)?

If it doesn’t have the filters required e.g. Solar Continuum and ND3.0 then that is extra costs on top.



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Re: Prism or mirror diagonal best for solar Ha?

Post by DeepSolar64 » Mon Jan 11, 2021 7:01 am

SimonM wrote:
Sat Jan 09, 2021 9:13 pm
The Lacerta USP is a more effective polarised output but the disadvantage is it is not 90 degrees.

So if you look up at the sun, you have to also look up and any perceived advantage is lost by getting an uncomfortable view (neck-ache)?

If it doesn’t have the filters required e.g. Solar Continuum and ND3.0 then that is extra costs on top.
The main reason I did not choose the Lacerta wedge is the less than 90 degree angle would make it hard to use when the Sun is high in the sky in the summer months. I could buy an extra polarizing filter if needed to rival the polarization control of the brewster concept. I am also not nuts about the open bottom of the wedge. It can let dirt/dust in.


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Re: Prism or mirror diagonal best for solar Ha?

Post by Highbury Mark » Mon Jan 11, 2021 6:15 pm

Three great solar mysteries to ponder:

Why is the corona so hot?
Why is there a new solar cycle every 11 years?
Why isn’t the Meade Herschel Wedge badged Coronado?


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Re: Prism or mirror diagonal best for solar Ha?

Post by DeepSolar64 » Mon Jan 11, 2021 7:19 pm

Highbury Mark wrote:
Mon Jan 11, 2021 6:15 pm
Three great solar mysteries to ponder:

Why is the corona so hot?
Why is there a new solar cycle every 11 years?
Why isn’t the Meade Herschel Wedge badged Coronado?
WoW, I have never thought of that last one.


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