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Focal reducers

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#1 mrflibbles

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Posted 17 May 2021 - 10:36 AM

I can't find the answer I'm looking for on Google or searching the forum, so forgive me if it has been asked.

In order for me to achieve focus with my mirrorless camera I need to have a 2x barlow. Do focal reducers work in the same way? Would I be able to achieve focus with a focal reducer mounting prime?

The reason I am asking is because doing test shots last night of the moon, I found that I barely fit the moon in frame.I know that some objects are very big, like andromeda galaxy for example, or the orion nebula.

Would it help to get a focal reducer? Or would I be better off unmounting my telescope and using my camera with a much smaller lens then my telescope, on my tacking mount? For example my 400mm 5.6 Canon lens, or my 100mm 2.8?

Is there such thing as a 0x barlow? Like no magnification, just a refocusing lens so that an slr can achieve focus "without" magnifying?

#2 brlasy1

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Posted 17 May 2021 - 11:07 AM

Mirrorless cameras sometimes need T-ring extenders to achieve focus.  Look on Amazon or various telescope vendor sites for a camera specific solution.



#3 mrflibbles

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Posted 17 May 2021 - 01:58 PM

Mirrorless cameras sometimes need T-ring extenders to achieve focus.  Look on Amazon or various telescope vendor sites for a camera specific solution.


I found that with my reflector. I need both a t-ring and a barlow. Without a barlow I am unable to achieve focus by just mounting prime, with a t-ring adapter alone.
 
With some objects this is too much magnification. I'm hoping to find a solution so that I don't have to unmount my telescope. My mirrorless camera weighs next to nothing but mounting my camera piggyback plus a camera lens,  would add so much weight it would be too much for the mount. So I am curious if anyone has had a chance to use a reducer, and still achieve focus.

Edited by mrflibbles, 17 May 2021 - 02:00 PM.

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#4 DubbelDerp

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Posted 17 May 2021 - 02:27 PM

So if you're using a Newtonian reflector designed for visual use, the problem is that a camera like this has the sensor buried in the camera body far enough that you can't rack the focuser inward enough for the focal plane to land on the sensor. DSLR cameras are even worse. One solution is to use a barlow, which moves the focal plane outwards so the camera can reach focus, but as you know increases magnification. Another solution is to move the primary mirror up the tube an inch or so, which moves the focal plane outwards enough to land on the camera sensor. Also not a great option if you don't like messing with your scope.

 

Some coma correctors do have the effect of moving the focal plane outwards, and may give you enough adjustment to focus with your camera. Otherwise a low profile focuser might do the trick. Take a look for newtonian coma correctors from your preferred vendor... that might be the best solution.


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#5 mrflibbles

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Posted 17 May 2021 - 02:43 PM

So if you're using a Newtonian reflector designed for visual use, the problem is that a camera like this has the sensor buried in the camera body far enough that you can't rack the focuser inward enough for the focal plane to land on the sensor. DSLR cameras are even worse. One solution is to use a barlow, which moves the focal plane outwards so the camera can reach focus, but as you know increases magnification. Another solution is to move the primary mirror up the tube an inch or so, which moves the focal plane outwards enough to land on the camera sensor. Also not a great option if you don't like messing with your scope.
 
Some coma correctors do have the effect of moving the focal plane outwards, and may give you enough adjustment to focus with your camera. Otherwise a low profile focuser might do the trick. Take a look for newtonian coma correctors from your preferred vendor... that might be the best solution.


Excellent, thank you for the idea. I will look into this. I do not want to mess with my primary mirror. I would rather I had too much magnification, than to risk at best ruining my warranty, or at worst breaking my telescope.


Near where I live there is a brick and mortar "telescope store" within a half an hours drive. I will see if they have any in stock that I can try out before I buy.

#6 DubbelDerp

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Posted 17 May 2021 - 03:00 PM

Just for example, the Baader MPCC is advertised as moving the focal plane outwards by approximately 10mm without increasing magnification. If you're close to being able to focus without the barlow, then this might give you what you need.


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#7 brlasy1

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Posted 17 May 2021 - 04:12 PM

Do you need more distance to achieve focus?  Mirrorless cameras need an extender, not just a t-ring.  Something like this:

 

 

Attached Thumbnails

  • Screen Shot 2021-05-17 at 4.09.49 PM.jpeg


#8 mrflibbles

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Posted 17 May 2021 - 08:24 PM

Do you need more distance to achieve focus?  Mirrorless cameras need an extender, not just a t-ring.  Something like this:

Actually I think the problem is I need less distance. I tried to move my camera further manually to see if I could get focus. I think the theory behind why the 2x barlow works is that it basically refocuses the light beams.
 
I think that is why some people go to the extreme to "move up" the primary mirror. So that you "lessen" the distance between the mirror and the camera. I could be wrong I don't fully understand the problem. 
 
This is what my adapter looks like

 

 

Attached Thumbnails

  • t adapter.jpg

Edited by mrflibbles, 17 May 2021 - 08:33 PM.

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#9 galacticinsomnia

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Posted 17 May 2021 - 10:43 PM

If you need to eliminate some of the space from between your camera sensor and your scope, you can do a neat trick with the EOS M.
I'm really into using various adapters outside their normal use.  But you can try this and you should have more than enough room for focusing natively :)

If getting closer to the sensor is the objective.

Get the EOS-M to C Mount Adapter 7.99

Get the C to 1.25" Adapter 11.99

Solution for under 20 bucks U.S.  :)

https://www.amazon.c...21308962&sr=8-4

https://www.amazon.c...21309005&sr=8-3

 

Clear Skies !!



#10 mrflibbles

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Posted 18 May 2021 - 05:36 PM

If you need to eliminate some of the space from between your camera sensor and your scope, you can do a neat trick with the EOS M.
I'm really into using various adapters outside their normal use.  But you can try this and you should have more than enough room for focusing natively smile.gif

If getting closer to the sensor is the objective.

Get the EOS-M to C Mount Adapter 7.99

Get the C to 1.25" Adapter 11.99

Solution for under 20 bucks U.S.  smile.gif

https://www.amazon.c...21308962&sr=8-4

https://www.amazon.c...21309005&sr=8-3

 

Clear Skies !!

Awesome, that does seem like a good solution. For 20$ it's worth a shot.

 

I'm not really sure why the t-adapter I have is so long. Maybe the retailers should state (not for Newtonian reflectors) Or sell a different adapter for newts. It would save quite a few people the trouble of finding out after the fact.

 

I bet "if I could" shave an inch or 2 off of that adapter I posted earlier: it would possibly achieve focus.

 

TYVM for the advice


Edited by mrflibbles, 18 May 2021 - 05:37 PM.

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#11 Lito

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Posted 26 May 2021 - 01:28 PM

Hi, 

 

I don't know what you ended up doing, I have a Canon EOS M3 and I use:

EOS-M to M42 adapter

then a M42 to T2 adapter

 

https://www.aliexpre...1176515984.html

 

https://www.aliexpre...1488713094.html

 

When I use a 1.25 nose it creates vignetting...


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#12 galacticinsomnia

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Posted 28 May 2021 - 05:47 PM

Hi, 

 

I don't know what you ended up doing, I have a Canon EOS M3 and I use:

EOS-M to M42 adapter

then a M42 to T2 adapter

 

https://www.aliexpre...1176515984.html

 

https://www.aliexpre...1488713094.html

 

When I use a 1.25 nose it creates vignetting...

Even better !!

Clear Skies!!


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#13 kathyastro

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Posted 28 May 2021 - 06:03 PM

The coma corrector is the best solution, because it will likely fix this issue as well as correcting another.  Without the CC, you need to reduce the distance to the camera. 

 

What kind of T-ring are you using?  A standard T-ring for a mirrorless camera adds considerable length to the light path because it needs to make up for the thinness of the camera body.  All standard T-rings are designed to make their respective cameras 55mm deep from the T-ring flange to the sensor.  A mirrorless camera therefore has no advantage over a DSLR on Newtonians!

 

There is something called a T-minus ring.  I know they are available for Sony mirrorless cameras; not sure about other brands.  It has the same connections as a standard T-ring, but the tube is much shorter than a standard T-ring.  That might get your camera close enough to focus.


Edited by kathyastro, 28 May 2021 - 06:03 PM.

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#14 galacticinsomnia

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Posted 28 May 2021 - 08:56 PM

The coma corrector is the best solution, because it will likely fix this issue as well as correcting another.  Without the CC, you need to reduce the distance to the camera. 

 

What kind of T-ring are you using?  A standard T-ring for a mirrorless camera adds considerable length to the light path because it needs to make up for the thinness of the camera body.  All standard T-rings are designed to make their respective cameras 55mm deep from the T-ring flange to the sensor.  A mirrorless camera therefore has no advantage over a DSLR on Newtonians!

 

There is something called a T-minus ring.  I know they are available for Sony mirrorless cameras; not sure about other brands.  It has the same connections as a standard T-ring, but the tube is much shorter than a standard T-ring.  That might get your camera close enough to focus.

That would be a very good option, and most likely work.  Finding a decent CC isn't hard, but 100-300 could be more than the scope?  Ouch.

Clear Skies !!




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