Can you stack two tele-centric barlows?

[AndiesHandyHandies]

Hi

After looking at a post by Pupak I wondered if I should use an ordinary barlow and then a telecentric to reach 6x in my case.

Any difference between:

2x Barlow and 3x Telecentric

3x Telecentric and 2x Barlow

3x Telecentric and 2x Telecentric

If I start using my Mak 180 as well I expect a 2x Telecentric and Quark will work at F20 and 3600mm FL.

So on my 90mm F6.7 triplet should I use the 3x TE for F20 and 1800mm FL and PST DS and then add a 2x Barlow at the front for F40 and just Quark?

Cheers. Andrew.

[OlegLviv]

You have this set up and have barlows you can do it test, Petr showed to us him test and with him set up and all!

[marktownley]

I would have thoght a telecentric is designed to work by accepting a converging light cone to output a telecentric beam. So. if it received a telecentric beam on the input side then this is not the same. I don't know what it would output in this circumstance.

Try it.

[Sebastien Lebouc]

some years ago, I asked Oliver from Beloptik a customized TZ. (3,5x)
To achieve higher magnifications, he advised me to put a barlow before.

[Dennis]

some years ago, I asked Oliver from Beloptik a customized TZ. (3,5x)
To achieve higher magnifications, he advised me to put a barlow before.

Thats great, i will be doing this in front of a tz4-s to reach f/70, then lunt 40 etalon, then 36mm clear aperture daystar reducer until vignette. Curious of the contrast and field of view.. (bf between barlow and tz4-s)

[AndiesHandyHandies]

Hi

I looked in my Astronomy crystal cabinet for 1.25" barlows. And above.

1. Clave' 2x 'long' barlow. CV has a graph of barlow performance and the old 4X long 2" Barlow was flat until the far blue.

2. A 2" metal body long Chinese barlow Mark pointed out for us to buy.

3. A 2.5x Glasspath corrector.

4. Revelation astro 3x ED barlow. Now that is sharper in the centre than the 3x VK TE for visual use. Of course the very centre will be telecentric.

5. 2" Guan Sheng ED barlow. Messing about with 5" F7.5 Meade and it far enough back to give 4x, measured by drift method, this gave a good view with a PST mod. Like Pedros images at the time.

Collimated or telecentric should be best. And longer F nos are better provided enough aperture.

For daytime work the actual resolution must be less than theory. Provided any abberation is within the circle of confusion it will look sharp enough.

A few combinations to try. With a barlow and then a Tele-extender.

New Rumak 180 focuser and replaced Ioptron motor board will see that option back to try.

Cheers. Andrew.

[Merlin66]

This question came up some years ago.
I successfully stacked at the time two TV Powermates (x2.5) on my 90mm f10 refractor. Yes, it can be done.
Ken

[pupak]

If you do a simulation in Optgeo, it will become clear to you that it is unusable for solar purposes. A telecentric bundle emerges from the first element, not a convergent one as expected by the second element. In principle, it can no longer function properly. If the first element is Barlow, the output is still a convergent beam, only F is increased. If F is not significantly outside the design F of the telecenter, then it works correctly.
I have an F5 telescope, I will add a B2x, I will get an F10 and the TZ3x will work in optimal mode. This is not a problem for normal use, but you cannot combine two TCs on a solar system without the image quality suffering greatly.

[Dennis]

So this is what im getting with 2 apm 2.7 barlows in front of a Baader tz4-s and a lunt 40 etalon rear mounted (and Daystar reducer in the end +imx432). There is a layer of haze.
Contrast is ok, but its kind of blue or red shifted? How to fix it..

[Dennis]

And here we go again, but this time without the apm barlows. Just the tz4-s, lunt 40 etalon, imx432.

Not much difference to me, so this idea of putting a barlow in front of a telezentric to improve contrast didnt work (much).

My actual problem remains that the image appears off band and that i cant fix by adding another lunt 40. What do you think?

(have to admit its really fun to image like this, despite all)

[Dennis]

Edited result, single stack lunt 40 + tz4-s:

End of project.

[Geremia Forino]

much much better than the previous ones, am I wrong or have you already tried the tz4 with 40 etalon?

[Dennis]

much much better than the previous ones, am I wrong or have you already tried the tz4 with 40 etalon?

Its the first time i use a tz4 with a air spaced etalon. Before that i was using a Quark / Lunt 40 DS that works best for now.

I will try one more thing next time to get the single lunt 40 on band: instead of a Barlow i will add a 2.5x Powermate in front of the tz4-s.

[Dennis]

Today i added the Powermate 2.5 to the tz4-s and exchanged the lunt 40 for another one that was not that blue shifted.
First one with flats, no editing, just the presharpened output of Autostakkert.
Second one: No flats or editing, just the presharpened output of Autostakkert.


So to answer the topic question: yes you can stack telecentrics.

[Dennis]

Edited version, etalon at f/100 with reducer and imx432:

i think im getting there slowly.. i would say almost on band.

[marktownley]

HI Dennis,

Why are you using the sharpened feature in AS3? You are paying so much attention to detail in terms of the telecentrics and the f number the etalon see's etc but the sharpened function in As3 allows absolutely no control over outcome.

Mark

[Dennis]

HI Dennis,

Why are you using the sharpened feature in AS3? You are paying so much attention to detail in terms of the telecentrics and the f number the etalon see's etc but the sharpened function in As3 allows absolutely no control over outcome.

Mark

Hi Mark,
for tuning i usually just look on the live view (screen).
For quality estimation i mostly use the numbers in the *.as3 text files, if you mean this.

[Sebastien Lebouc]

For tuning I use the double limb effect. When it is null or limited to minimum, your are on band.

[Dennis]

For tuning I use the double limb effect. When it is null or limited to minimum, your are on band.

Yes, but for now it is all with a single stack etalon. I will try it with 2 lunt 40s later.

[AndiesHandyHandies]

Hi

I do not remember or know why I gravitated to stacking two Tele-centric barlows for 6x which gives me F40 from my 90mm F6.7 Triplet.
As James Martin IT guru says 'humans are meat machines'.

I had enough time to play with barlows and telecentrics for a bit today.

For full image at F20 I just need the VK 3x TE. There is scatter from the lens cell. I have a 10mm stop in a plastic Moon filter holder at the front. I have added two push in 10mm stops behind the first lens which helped. But I had to take the front lens out. Emery the shine off flat parts and black the inside of the cell before re-assembling. No reflections inside when pointing at the sky. I tried a cheap 'metal body' 2x Barlow on the front. This has very bad internal reflections. I have ordered a SH 1.25" Celestron Ultima 2x triplet Japanese glass barlow for possible use instead.

For higher power I have been stacking VK 3x TE and ES 2x TE. Which is optically not the best. I had a 1.25" Revelation Astro 3x ED barlow( Spotted by Mark) in stock to use with the ES 2x TE. This has some B3 180grit emery at the front already so I do not expect much more baffling work will be needed. Next little job.

I do have a 2" ES TE 2x barlow for use on the Mak180 F10 for F20.

Cheers. Andrew.

[AndiesHandyHandies]

You have this set up and have barlows you can do it test, Petr showed to us him test and with him set up and all!

Yep. Started on the testing phase.

Andrew.

[AndiesHandyHandies]

I would have thoght a telecentric is designed to work by accepting a converging light cone to output a telecentric beam. So. if it received a telecentric beam on the input side then this is not the same. I don't know what it would output in this circumstance.

Try it.

I will try the barlow then TE options. And then see what difference that makes.

Andrew.

[AndiesHandyHandies]

If you do a simulation in Optgeo, it will become clear to you that it is unusable for solar purposes. A telecentric bundle emerges from the first element, not a convergent one as expected by the second element. In principle, it can no longer function properly. If the first element is Barlow, the output is still a convergent beam, only F is increased. If F is not significantly outside the design F of the telecenter, then it works correctly.
I have an F5 telescope, I will add a B2x, I will get an F10 and the TZ3x will work in optimal mode. This is not a problem for normal use, but you cannot combine two TCs on a solar system without the image quality suffering greatly.

I seemed to have missed that fact!

Cheers. Andrew.

[AndiesHandyHandies]

And here we go again, but this time without the apm barlows. Just the tz4-s, lunt 40 etalon, imx432.

Not much difference to me, so this idea of putting a barlow in front of a telezentric to improve contrast didnt work (much).

My actual problem remains that the image appears off band and that i cant fix by adding another lunt 40. What do you think?

(have to admit its really fun to image like this, despite all)

Hi

My use of doubled up TE and or Barlows was to get the desired visual image scale:

1. Full disk which conveniently works with a PST Etalon DS at F20, DS too dim beyond that.

2. Longer focal length to see greater detail with the addition of better contrast.

I presume I will get a better quility image.

Cheers. Andrew.

[AndiesHandyHandies]

Today i added the Powermate 2.5 to the tz4-s and exchanged the lunt 40 for another one that was not that blue shifted.
First one with flats, no editing, just the presharpened output of Autostakkert.
Second one: No flats or editing, just the presharpened output of Autostakkert.


So to answer the topic question: yes you can stack telecentrics.

I was talking about stacking Telecentric barlows for a Quark or similar. As Pupak says its not going to work properly.

You seem to be stacking barlows and or telecentrics for Lunt air spaced etalons, as PST, where the longer resultant focal length is long and not too far off a collimated beam. This is more likely to work with only barlows before one telecentric. If a telecentric beam is falling on an etalon I assume the whole image will be off-band by the same amount due to the symmetry???

As a normal light cone increases in focal length the nearer you will be to collimated. Visually a PST mod at F28 with a barlow looked alright to me.

Cheers. Andrew.

[Dennis]

And here we go again, but this time without the apm barlows. Just the tz4-s, lunt 40 etalon, imx432.

Not much difference to me, so this idea of putting a barlow in front of a telezentric to improve contrast didnt work (much).

My actual problem remains that the image appears off band and that i cant fix by adding another lunt 40. What do you think?

(have to admit its really fun to image like this, despite all)

Hi

My use of doubled up TE and or Barlows was to get the desired visual image scale:

1. Full disk which conveniently works with a PST Etalon DS at F20, DS too dim beyond that.

2. Longer focal length to see greater detail with the addition of better contrast.

I presume I will get a better quility image.

Cheers. Andrew.

Hi Andrew,

from the perspective of light flux yes, it will get too dim at some point. And beyond f/40 contrast doesnt get much better, dependent on the Quark etalons fwhm.

Optically i didnt see problems though with 2 TE, no distortions, worked just like a barlow.

[AndiesHandyHandies]

HI

Had enough sun yesterday to try out combinations on the 90mm F6.7.

1.25" 3x VK TE gives me F20 and there is enough light to DS the PST etalon after it. Good contrasty view.

Tried 6x via 2x Clave' 'long barlow' with the VK 3x TE or a Revelation Astro 3x ED with the ES 2x TE at 1.25".
I found the proms were slightly sharper and brighter with the Clave'. Just need to do some blacking of the Clave'.

I actually got the Rumak 180 F10 with its new focuser out this morning. As intended for SC's will take nothing longer than a normal 2" nose piece.
So I tried the 2" ES TE and put the 2" Internal ERF and 1.25" T2 Baader straight in it. Of course went cloudy so more later.

Cheers. Andrew.