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Removing new Mods

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Re: Maksutov 180/1800 Modification?

Post by marktownley » Thu May 09, 2019 4:05 pm

Lenses you've listed sound wrong to me; the rumak is f10. The pst etalon is 20mm diameter. This then needs a -200mm fl lens to collimate the beam, that would need a 20mm entrance pupil. You would need a 2" -200mm lens that you stop down to 20mm.
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Re: Maksutov 180/1800 Modification?

Post by AndiesHandyHandies » Fri May 10, 2019 8:45 am

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Re: Maksutov 180/1800 Modification?

Post by marktownley » Fri May 10, 2019 1:28 pm

AndiesHandyHandies wrote:
Fri May 10, 2019 8:45 am
Hi

Its the longest fl length lens I can find. For minimising abberations.

Also I am not restricted by the original PST 5mm blocking filter at the back and the backfocus of 200mm in the PST black box.

Its effectively a Combo as the PST aperture is not restricted by the 20mm clear aperture filters.

I am just using the etalon part from the PST in a full mod.

Andrew.
The PST etalon has 20mm clear aperture regardless of configuration it is used in.

To minimise aberrations the focal ratio of the scope, collimating and refocusing lens need to be identical.

You've got a lot more energy with a 180mm aperture than a 110mm aperture to risk damage to scope and also eyesight.

I would wholeheartedly recommend a full aperture ERF. Would also like to point out that the advice given on this forum, or the forum itself cannot be responsible if mods go wrong and do not work as expected.
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Re: Maksutov 180/1800 Modification?

Post by christian viladrich » Fri May 10, 2019 6:31 pm

Hi,

The rationale is as follows :
- Let's call F and D the focal length and diameter of the telescope. For your Mak F/D = 10.
- Let's call d the diameter of the etalon and of the collimating lens. We will come back latter to the case where the diameters of etalon and lens are different.
- Let's call f the absolute value of the focal lens of the collimating lens.

We need to have F/D = F/d, otherwise :
- if F/D > f/d, there is vigneting with the etalon. In other words, only part of the etalon is used => the field of view (more precisely the sweet spot on Ha line) is reduced.
- if F/D < f/d, there is vigneting in the lens (or mirror) of the telescope. In other words, this is just as if you were using a smaller telescope.
So, the optimal is to have F/D = f/d.

Now, let's assume the diameter of the collimating lens (d') is greater that the diameter of the etalon (d). This is not an issue as long as you still have F/D = f/d. There, this is the diameter of the etalon which matters, not the diameter of the lens.

If we have the diameter of the lens (d') smaller that the diameter of the etalon (d), then ... this would be a very bad idea since this would reduce the diamter of the sweet spot.

The other important point is that the collimating lens is to be placed at the distance "f" ahead of the focus of the telescope. You have to check if this is indeed feasible.

I understand you already have a PST ? If so, you already have the whole package (etalon, negative and positive collimating lenses). Why change the collimating lenses ?
Christian Viladrich
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Re: Maksutov 180/1800 Modification?

Post by AndiesHandyHandies » Sat May 11, 2019 9:25 am

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Re: Maksutov 180/1800 Modification?

Post by Valery » Sat May 11, 2019 4:10 pm

All your math valid for only one single point on the sun disk. But the sun is not a point. The sun heat will hit the collimation lens cell, the wall of the baffle, when you will observe the edge of the sun (proms, spiculaes or AR at the near limb) the sun heat will hit the secondary baffle, the main baffle, the collimation lens cell. Internal air turbulence is guaranted.
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Re: Maksutov 180/1800 Modification?

Post by AndiesHandyHandies » Sun May 12, 2019 9:18 am

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Re: Maksutov 180/1800 Modification?

Post by AndiesHandyHandies » Thu May 16, 2019 3:54 pm

Hi Christian,

I have gone back to my attempt to graph the Maksutov 180/1800. Complicated diagram.

I overlooked the parallel beam out of the lens was bigger than the 20mm PST aperture so vignettes as you point out.

Anyway I have found a -200 2" lens from Laser 2000 in the UK

https://www.laser2000.co.uk/product/slb ... 00---700nm

I have been working on reducing other telescopes FL for EAA astronomy and I have sneaked macro-lenses larger than a 2" focusser by using a 48mm to larger size adapter in front of the focusser tube, you have to take the focusser off of course.
On a Optic star 80mm F4 refractor turning down 48-49mm adapters for a 49mm nominal macro-lens allowed it to sneak down the relaxed tolerences in its focusser.

So I can do the same on the Mak focusser, having the bottom of the focusser turned out for the 50mm lens holder on an adapter to 48mm.

Then I can put a 48mm UV-IR or Baader 35nm behind the collimating lens and like in the Vixen the reflected light goes back out as it came in with no dangerous hot spot.

I tried my PST in my 127mm refractor for the first time today. Using a 2x ED Barlow attached to the PST AOK T2 adapter I had made via a 48mm to T2 adapter.

To start with I had a 2" Baader 35nm 150mm before the Barlow, a Omega Bobs 40nm ERF in the collimator lens holder in the front of the PST and a 1.25" Belpotik UV-IR on KG3 on the front of my 25MM Clave'.

I did not want to fiddle about with the 20mm collimator lens as in the Vixen 110 adapter and a fiddly fit.

It reached focus despite having no collimator lens, if not the collimator might have given me enough back focus.

Amazingly it worked without a collimator lens. First saw the sphericules on first focus, a very nice sharp prominence on the bottom left for me and the umbra and pen-umbra on the spot to its top right. On a par with the view I had through RodAstros set up.

I also removed the Baader 35nm and that seemed OK as well.

So I confident my scheme for the Vixen 110 will work on the Mak 180 with a bigger 2" collimator lens in front of a 2" UV-IR or Baader 35nm.

Andrew.

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Re: Maksutov 180/1800 Modification?

Post by marktownley » Thu May 16, 2019 5:50 pm

Hi Andrew.

Unless i'm missing something here; you're using a 2" collimator with the 2" ERFs, the free aperture of the PST etalon is only 20mm so either you're going to get an effective 20mm field stop aperture in that 2" beam. Or, you're only using the central 20mm of the ERF and collimator lens in which case you're concentrating 180mm beam down into a 20mm beam on the centre of a filter. I think that will pop it.

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Re: Maksutov 180/1800 Modification?

Post by AndiesHandyHandies » Thu May 16, 2019 9:50 pm

Hi Mark,

You are right that even a 2" -200mm f lens will only use the middle 20mm at F10.

Andrew
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Re: Maksutov 180/1800 Modification?

Post by Valery » Fri May 17, 2019 12:41 am

Andy, when will you understand that your math does not reflects the reality?

Try to place the edge of the sun in the center of the FOV (imaging - you observe a prominence). Then the secondary baffle will be at fire from the primary mirror, the main baffle will be at the fire too. They are black anodized and will be overheated and will loose their black anodizing quickly.

I have experimented with 2" Baader 7nm Ha filter in the C11 telescope. Cracked. And the telescope full of smoke when the sun was off-center.


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Re: Maksutov 180/1800 Modification?

Post by Valery » Fri May 17, 2019 12:46 am

Mark,

I found this thread hazardous, especially for not very experienced users. And what Andy offers is more hazardous than were propaganded by Apollo Lasky here and there. He was banned here and there.

I'd offer Andy to experiment with his equipment at his own risk without propaganda here.


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Re: Maksutov 180/1800 Modification?

Post by Astrophil » Fri May 17, 2019 7:00 pm

Something to consider.

I own telescopes that I don't think of as disposable so when entering into Solar imaging it was important for me to make sure the setup used was safe for me and the equipment. I tested different full aperture energy rejection filters to see how they performed. Below are two images taken with a thermal camera showing the temperature of a paper screen at the axial port of a 6" Maksutov. Temperature readings of the hottest ERF was taken after 2 minutes with the sun centered. The scope was capped before the paper burned. The cooler EFR produced a stable temperature at 163°.

This scope utilizes a reflective spot on the meniscus with no secondary baffle to heat. Under no circumstances would I subject my equipment to unfiltered, concentrated solar radiation.

Hope that helps,

Phil
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Re: Maksutov 180/1800 Modification?

Post by AndiesHandyHandies » Fri May 17, 2019 8:45 pm

Hi

I am not using the Mak without filters.

Andrew.
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Re: Maksutov 180/1800 Modification?

Post by AndiesHandyHandies » Sat May 18, 2019 7:27 am

Hi

Looking around:

viewtopic.php?f=4&t=24356&p=218951&hili ... al#p218951

Many years ago at the RTMC, I was shocked to see a 10" SCT without an ERF and a Daystar filter aimed at the sun, it was Jen making tests using just a 2" UV/IR filter in front of the filter, it stayed aimed to the sun for a couple of days without any harm to the scope or the filter.

Andrew
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Re: Maksutov 180/1800 Modification?

Post by krakatoa1883 » Sat May 18, 2019 9:38 am

Astrophil wrote:
Fri May 17, 2019 7:00 pm
I tested different full aperture energy rejection filters to see how they performed.
what a large difference in T between the hottest and the coldest ERF...

A very interesting experiment indeed, is the hottest ERF you tested still safe at the etalon or would it require additional filtering ?
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Re: Maksutov 180/1800 Modification?

Post by Astrophil » Sat May 18, 2019 2:01 pm

Yes, the difference in temperature was surprising. I did not test my Maksutov scope without any full aperture filter for obvious reasons. The Quark Combo used showed no signs of damage using the hotter ERF. The Combo incorporates a reflective blocking filter as it's first element. However, images taken with the cooler ERF are superior.

Another point to consider is the back reflections. A point of concentration located near the ERF filter melted regions of a 3D printed cell when the Sun was positioned off axis using the hotter ERF.

Is the hotter ERF safe for this etalon? Without long term or accelerated aging tests performed it would be hard for me to say. If I were selling etalons I might say sure, what do have to loose? I am only relating my experience using a Maksutov telescope. Other telescope designs will be different. You will find that full aperture filters or smaller off axis ERFs are recommended for Maks and SCTs.

Remember heat and temperature are not the same thing.

Phil

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Re: Maksutov 180/1800 Modification?

Post by marktownley » Sat May 18, 2019 2:04 pm

This topic has received a lot of attention with several experienced members of the forum contacting me to express concern about the whole concept of using the 180/1800 in this way.

I'm not directly familiar with this particular scope so I had a google of it. I'm guessing it's a scope like this one Andy? https://www.avaruus.fi/foorumi/index.php?topic=7476.0

My main concern with the concept you propose is the thermal management of the design. Putting the ERF where you suggest will still have the full force of energy on the secondary. This will heat up, and will expand, it may well crack the corrector plate and also the secondary. Like Valery says the baffle is also at risk too. 428F is pretty hot!

As with the feeling of others I would not recommend this modification in this way at all. A full aperture ERF is the best solution at these apertures.
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Re: Maksutov 180/1800 Modification?

Post by krakatoa1883 » Sat May 18, 2019 3:30 pm

marktownley wrote:
Sat May 18, 2019 2:04 pm
As with the feeling of others I would not recommend this modification in this way at all. A full aperture ERF is the best solution at these apertures.
I totally agree, Mark, however Astrophil's experiment raises an interesting point as it seems that front ERFs can be quite different each other. How one can be sure that a given ERF is doing its job in terms of safety for the observer and the equipment ?
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Re: Maksutov 180/1800 Modification?

Post by Astrophil » Sat May 18, 2019 5:56 pm

There are yellow glass, red glass, Baader D-ERF, and Aries D-ERF that I'm aware of. Dielectric coated filters are the coolest. Listen to Valery on this subject.

Phil

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Re: Maksutov 180/1800 Modification?

Post by marktownley » Sun May 19, 2019 7:02 am

Astrophil wrote:
Sat May 18, 2019 5:56 pm
Listen to Valery on this subject.
Absolutely. He has more experience than probably anyone else on the planet when it comes to large aperture solar systems using mirrors.
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Re: Maksutov 180/1800 Modification?

Post by krakatoa1883 » Sun May 19, 2019 9:00 am

Astrophil wrote:
Sat May 18, 2019 5:56 pm
There are yellow glass, red glass, Baader D-ERF, and Aries D-ERF that I'm aware of.
I am aware too there are all these ERFs, which ones were the subject of your test ?
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Re: Maksutov 180/1800 Modification?

Post by marktownley » Sun May 19, 2019 9:34 am

Astrophil wrote:
Sat May 18, 2019 5:56 pm
There are yellow glass, red glass, Baader D-ERF, and Aries D-ERF that I'm aware of.
I've got a couple of Beloptik tri-bands, and Frederic at Airy Labs make a Ha ERF for C9.25.
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