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Can I have a dual rokinon 135 setup with one imaging system?

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#1 Startoucher 101

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Posted 14 October 2024 - 11:29 AM

Hello everyone! Has anyone tried to make a dual refractor setup(in my case I want a rokinon 135 setup) but with one imaging system? Is that possible and if yes, how can this be accomplished?4

 

Cleas skies everyone!



#2 The0s

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Posted 22 October 2024 - 12:31 AM

No - you'd need two cameras. Trying to precisely focus the light from two telescopes (especially fast camera lenses) onto one sensor, while probably technically possible, is way too difficult to be worth the effort - I'm sure some people have tried, but I've yet to hear of anyone actually getting a dual setup like this to work. It's a lot easier to just buy a camera for each lens (or simply buy a faster lens - the Rokinon 135mm f/1.8 is 2 times faster than the f/2, so it's effectively the equivalent of 2 of the regular Rokinons).


Edited by The0s, 22 October 2024 - 12:32 AM.


#3 drmikevt

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Posted 22 October 2024 - 06:48 AM

By 'imaging system' do you mean 1 camera or 1 mount system with 2 telescopes/lenses and 2 cameras?  

 

The second is possible and there are some programs that have built in functionality for this.  The only one that I'm familiar with is Voyager with the Array add-on.  I think NINA can also do this, but someone more familiar would have to say for sure.



#4 Der_Pit

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Posted 22 October 2024 - 07:35 AM

The second is possible and there are some programs that have built in functionality for this.  The only one that I'm familiar with is Voyager with the Array add-on.  I think NINA can also do this, but someone more familiar would have to say for sure.

Latest KStars development version also adds support for this, so it should be in the next stable release.



#5 Helyis

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Posted 22 October 2024 - 07:51 AM

No - you'd need two cameras. Trying to precisely focus the light from two telescopes (especially fast camera lenses) onto one sensor, while probably technically possible, is way too difficult to be worth the effort - I'm sure some people have tried, but I've yet to hear of anyone actually getting a dual setup like this to work. It's a lot easier to just buy a camera for each lens (or simply buy a faster lens - the Rokinon 135mm f/1.8 is 2 times faster than the f/2, so it's effectively the equivalent of 2 of the regular Rokinons).


F1.8 is not 2x faster than F2, it is almost the same.

#6 calypsob

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Posted 22 October 2024 - 08:56 AM

F1.8 is not 2x faster than F2, it is almost the same.


To calculate how much faster an f/1.8 aperture is compared to f/2, we look at the relationship between f-stops. The formula for the amount of light entering through an aperture is proportional to the square of the f-stop ratio.

The ratio of light between two f-stops is:

\[
\left( \frac{\text{f-stop 1}}{\text{f-stop 2}} \right)^2
\]

In this case, the comparison is between f/1.8 and f/2:

\[
\left( \frac{2}{1.8} \right)^2 = \left( 1.111 \right)^2 \approx 1.235
\]

This means f/1.8 allows approximately **23.5% more light** than f/2. Hence, f/1.8 is about 23.5% faster in terms of light-gathering capability than f/2.

#7 Helyis

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Posted 22 October 2024 - 11:15 AM

To calculate how much faster an f/1.8 aperture is compared to f/2, we look at the relationship between f-stops. The formula for the amount of light entering through an aperture is proportional to the square of the f-stop ratio.

The ratio of light between two f-stops is:

\[
\left( \frac{\text{f-stop 1}}{\text{f-stop 2}} \right)^2
\]

In this case, the comparison is between f/1.8 and f/2:

\[
\left( \frac{2}{1.8} \right)^2 = \left( 1.111 \right)^2 \approx 1.235
\]

This means f/1.8 allows approximately **23.5% more light** than f/2. Hence, f/1.8 is about 23.5% faster in terms of light-gathering capability than f/2.


That's a much longer way to say "almost the same" ;)
  • Startoucher 101 likes this

#8 Der_Pit

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Posted 23 October 2024 - 09:27 AM

That's a much longer way to say "almost the same" wink.gif

If you are getting a 25% reduction of your salary, that is almost the same as before!?

 

SCNR



#9 bbasiaga

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Posted 23 October 2024 - 10:00 AM

You can run side by side scopes/cams on a single mount.  NINA does have a mode where it can link the sessions, so that dithering on the guided scope does not happen in the middle of an exposure on the other scope.   I have not done this, just heard Cuiv talk about it on the YT.  

 

I think the ZWO driver limits you to two cameras at a time ( I could be wrong).   So you might check in to other driver limitations.  You may need different brands of EAF, guide cam or something to avoid confusion there. 

 

 

 

Brian



#10 Helyis

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Posted 23 October 2024 - 10:29 AM

If you are getting a 25% reduction of your salary, that is almost the same as before!?

 

SCNR

I wouldn't like that for sure! lol.gif

 

But as far as it comes to aperture, yeah, it is mainly insignificant in the real world.

 

First, it is not guaranteed that the full aperture is usable, for the mere reason of optical quality. If you end up stopping them both down to F2.8 for decent stars across your field, it is of no use.

 

Then, it also doesn't mean you are truly getting 25% more light at the end of the lens. The T-stop reading would be much better at quantifying this. Oh, and faster most likely means more vignetting too

.

On top of that, it is not even guaranteed that the microlens array on the sensor is capable of translating this 25% more light into 25% more light reaching the actual photosite, since this additional light comes at a steeper angle. The same goes for filters as well.

 

And even if all of this was negligible, the SNR boost you get from 25% more light would be only around 11%. I'd bet we have way more difference across our image due to vignetting, and we never notice.

 

I stand by my point, that's negligible. smile.gif




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