32 replies to this topic

[parnassian]

Hello all,

 

From other threads I've found out that a Celestron Reducer/Corrector requires a 105mm distance from the end of the FR to the imaging sensor of the camera / autoguider OAG.

 

I have a FR and a Meade OAG and most of the sites don't seem to have a plain jane SCT female to SCT male extension.

 

Off the various sites, I tried different combos of T2, M42, and M48 adapters and I come up with nothing.

 

Maybe someone creative here can help me figure out how to complete this image chain properly with the correct back focus lengths.

 

Here's the image I took of the parts in question.

 

- Michael

Attached Thumbnails

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Edited by parnassian, 04 December 2024 - 04:51 AM.

[Astrojensen]

Why have you shown such a large distance between the reducer and the off-axis guider? The distance you have shown is the TOTAL distance needed from the reducer to the sensor - and the sensor comes AFTER the off-axis guider. 

 

See this thread for examples: https://www.cloudyni...focal-reducer/ 

 

 

Clear skies!

Thomas, Denmark

[parnassian]

The OAG height is 7cm, so that still has me scratching my head to find a 3cm SCT F to M adapter.

The handful of sites I've gone through don't even seem to have a piece like that.

 

Unless, I use an astromania SCT retractable male to T2 female and add a short compatible barrel to it, (T2 back to SCT) I still come up short.

 

- Michael

Edited by parnassian, 04 December 2024 - 05:25 AM.

[parnassian]

I read the other post and brought up the SCT/T2 challenge because the Meade OAG is a SCT size connector, and to convert back from T2 to SCT seems hard to find. That would have solved the problem easily.

 

- Michael

Edited by parnassian, 04 December 2024 - 05:42 AM.

[Astrojensen]

I don't understand what it is you're trying to achieve. What combination of camera, reducer and off-axis guider are you trying to create? Why can't you just use a T2 extension tube between the off-axis guider and the camera, and then an extension tube in the off-axis guider to reach focus? That was how it was done in the good ol' SLR days. 

 

 

Clear skies!

Thomas, Denmark

[parnassian]

I thought my ask was simple.

 

The OAG connects to the FR, no problem, but doesn't clear 105mm.

It's an SCT female to male extension that I'm asking about if it exists, after a few hours search of looking for it.

 

If it doesn't, what parts do I need to make the appropriate length from the OAG to FR.

Both are SCT, so I don't understand why you're bringing up T2 after I mentioned I couldn't find the appropriate combo.

 

I get it that you probably a revered old timer around here. I don't think what I'm asking about was mind bending.

 

Your smug posts scares away new comers who are trying to understand how this stuff works, especially since I started this hobby a few month's ago.

 

I'm the type of individual who researches first on my own so that I don't look foolish.

Yes, I google and gpt first before I ask questions.

 

However, how you're approaching this post is discouraging.

 

Obviously I might not know as much about astronomy as you do, and you're making making a clear case of posting your comments that way.  

 

- Michael 

[Astrojensen]

My intention was not to be smug or any such thing, but to help. 

 

And I need some info to be able to do so. It's not clear to me, why you need to increase the distance from the reducer to the off-axis guider, when the off-axis guider is meant to be mounted directly onto the reducer, and the working distance between the camera and the reducer is then adjusted with T2 extension tubes between the off-axis guider and the camera. If it is done the other way around, you will not be able to reach focus on the guiding camera.  

 

Does the off-axis guider not have SCT threads on the front and T2 at the rear? The ones I can find on the net are of this design. 

 

 

Clear skies!

Thomas, Denmark

Edited by Astrojensen, 04 December 2024 - 07:25 AM.

[Tapio]

Well, Thomas was trying to help and he had a fair point.
You can have extension before OAG or after, and it's easier to have them after.
I've read that Meade OAG normally is supplied with an 43mm T extension.
Not sure you need that, or different length. Depends on the camera you have (which we don't know what is it).
You know the OAG itself takes some optical space.

I tried to find relevant image/document but found only this old one.
Maybe it's helpful.

http://www.company7....educerp.112.pdf

[Migwan]

Sorry, but Idon't see a smug post here.  I do see one that is rife with condemation.

[gpaunescu]

Just to notice: 105 should be from last optical element (in this case reducer) until the camera sensor.

So you need to know the optical path of the diagonal, in order to subtract from 105.

[bignerdguy]

FYI the distance from the focal reducer to the camera sensor is measured starting from the back of the FR not the front. I asked Celestron and that was what they advised me.  I have also tried this on my camera setup and they are right as i have set it up as measured from the back oft the FR and the stars are all pinpoints from edge to edge where as if i use the front then they have slight football shapes.  Also for the OAG you wont take into account the OAG camera spacing initially, what you do is get the main camera focused THEN worry about the OAG camera spacing and focus. You may or may not need to use extension tubes on it if it turns out to be too close or if not that far off, just back the camera out a little from the focus tube before you secure it and try to focus it.  Essentially you want to match the OAG camera spacing to the main camera AFTER the main camera is focused.

 

Also attach the OAG directly to the back of the FR and then use extension tubes for the main camera as needed.

Edited by bignerdguy, 04 December 2024 - 08:27 AM.

[Tapio]

FYI the distance from the focal reducer to the camera sensor is measured starting from the back of the FR not the front. I asked Celestron and that was what they advised me. I have also tried this on my camera setup and they are right as i have set it up as measured from the back oft the FR and the stars are all pinpoints from edge to edge where as if i use the front then they have slight football shapes. Also for the OAG you wont take into account the OAG camera spacing initially, what you do is get the main camera focused THEN worry about the OAG camera spacing and focus. You may or may not need to use extension tubes on it if it turns out to be too close or if not that far off, just back the camera out a little from the focus tube before you secure it and try to focus it. Essentially you want to match the OAG camera spacing to the main camera AFTER the main camera is focused.

Also attach the OAG directly to the back of the FR and then use extension tubes for the main camera as needed.

What is back and what is front of focal reducer?
Anyway the measurement is from the shoulder of the male threads of reducer.

[bignerdguy]

What is back and what is front of focal reducer?
Anyway the measurement is from the shoulder of the male threads of reducer.

Here is the email I got from Celestron:

 

From: Celestron Support <ustechsupport@celestron.com>
Sent: Tuesday, September 17, 2024 4:55 PM
To: Brian 
Subject: [#25210] Need back focus distance

Hello Brian,

The Celestron 94175 F/6.3 Reducer/Corrector has a back focus distance of approximately 105 mm (about 4.13 inches).
This measurement starts from the back of the Reducer/Corrector, specifically from the base of the threads where the accessory attaches to the telescope, not from the glass element itself.

Thank you,

Justin

[parnassian]

Okay, maybe I was a touch raw sensitive at 3am in the morning after looking for so long for an SCT barrel.

 

But, what I know about the connector on the FR has an SCT male and the OAG has a matching female SCT and I need to use some type of extender, which for the life of me I can't seem to find on most of the astro hardware sites mentioned here.

 

That was the original ask, and it would the correct length from FR lens to either the autoguider or camera sensor.

 

I was thinking from originally posting that this is probably a "not a new" item that someone's overcome before and I was hoping to tap into that collective knowledge.

 

To take it further perhaps someone can post a link of what I'm looking for, since this subject has been address by many before me.

 

To that I'm grateful and any additional time I'm not rooting blind to find that part is most appreciated.

My apologies for the early morning sass.

 

- Michael    

[parnassian]

If you can allow me to present another pic.

I'm looking for a 4cm SCT barrel to extend apart the 2x pieces for proper length back focus.

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Edited by parnassian, 04 December 2024 - 12:53 PM.

[Astrojensen]

But is it SCT threads on that end, too, or T2? My guess (and, according to the Meade catalogue) is T2, as the threads appear to be much smaller than the SCT threads at the front. 

 

 

Clear skies!

Thomas, Denmark

[parnassian]

I was thinking that too, but I was incorrect when I started to adapt assorted pieces laying around..

The part of the OAG that mates up with the FR is SCT.

It's on the opposite end which the camera lens will be adapted to a T2 male connecter.

 

Most of the places starting with Amazon, High Point, Agena, Astronomics and Starizona didn't seem to list one their online catalogs. That's why I turned here at CN thinking someone has solved this already.  

 

- Michael   

[bignerdguy]

The camera side of the Meade OAG is T-threaded.  You only need a T-Thread extender to make it fit a camera.  However that also depends on what Camera you plan to use.  If it is a dedicated Astro-camera, those might need an extender.  If you plan to use a DSLR be aware that the distance to the sensor also has to take into account the camera body since the sensor also sits down inside the body a ways.  For example i have a Canon 60D and the distance from the front of the lens connector to the sensor is 44mm.  i needed to take that into account when figuring the max distance i need to have the camera attached at.  As you have a Canon T7 listed in your signature section if you plan to use that camera with this setup you will need to figure in the same 44mm depth to your calculations.  This means from the back of the FR to the camera body you have exactly 61mm to work with.  It can be a few mm higher or lower but not too many or you will get streaked/football shaped stars.

[bignerdguy]

Here is my setup.  In this image i have the same FR, a SCT to T-thread adapter (SCT Visual back adapter), a Astronomik CLS T-Threaded light pollution filter, and a Canon T-ring plus the camera.  Everything but the camera works out to be roughly 63-64mm and still gives me great star shapes.

 

Edited by bignerdguy, 04 December 2024 - 02:29 PM.

[parnassian]

@bignerdguy, nice setup, but. don't forget I have a Meade OAG in the image train and it's a SCT connection. I'm pointing this out as I'm trying to put proper distance between the twp pieces so that the autoguider is also at 105mm. The camera side should be straightforward as indeed it's T2.

I'll keep researching this until I figure it out and find this elusive adapter/barrel. Thanks guys who had helped.

I'm confident there's an SCT to SCT connector out there. I haven't found it yet.

- Michael

Edited by parnassian, 04 December 2024 - 05:47 PM.

[Daveatvt01]

In full disclosure, I have never used an OAG. But as I understand it, the spacing for the guiding camera does not need to be exact.

The back spacing for the main camera is critical for best stars to the corner of a relatively large sensor so it should be close to spec as possible.

However the guider has a relatively small sensor and even if corners show some coma or other aberrations it's not a big deal. As long as the guider can reach focus I think you'll be ok.

Hopefully someone with firsthand knowledge can chime in?

 

Good luck!

[WadeH237]

I'm pointing this out as I'm trying to put proper distance between the twp pieces so that the autoguider is also at 105mm. The camera side should be straightforward as indeed it's T2.

Even if you find an SCT threaded extension, it's likely that you won't be able to make it work.

 

If I were setting this up, I would get the OAG as close to the reducer/corrector as possible, and then I would add a T2 extension between the OAG and camera to make the spacing be 105mm.  I would then focus the main camera with the SCT's focus knob.  That would give you the proper setup for the main camera.  At this point, the guide camera may be too close to the OAG to focus, so you may need to add a C-mount extension between the OAG and the guide camera...but it's likely you won't need any extension there.

 

The problem with what you are trying to do, is that any extension between the reducer/corrector and the OAG will also be adding spacing between the scope and the guide camera, which is bad.  You cannot push the guide camera closer to the scope than the OAG's guide camera port.  If your SCT extension is long enough, the OAG itself will prevent the guide camera from getting close enough to achieve focus.

[WadeH237]

In full disclosure, I have never used an OAG. But as I understand it, the spacing for the guiding camera does not need to be exact.

When you set up an OAG, you adjust spacing for the main camera only.  Once you have the main camera in focus with the proper spacing, then you adjust the guide camera for focus.  You don't care about spacing for the guide camera, but it's critical that it has enough freedom to move into the precise position for focus.

[parnassian]

@Daveatvt01 ..

 

my gosh if that rings true, then I can leave the OAG connected straight to the FR and worry only about extending out to a camera sensor using T2.

I distinctly remember reading that OAG and camera, both have to be a close proximity (of equal distance) for the autoguider to be effective and I'll look for that abstract of info.

 

It solves a world of problems as a F-to-M SCT extension hunt is similar to a needle in a haystack. 

[parnassian]

The problem with what you are trying to do, is that any extension between the reducer/corrector and the OAG will also be adding spacing between the scope and the guide camera, which is bad.  You cannot push the guide camera closer to the scope than the OAG's guide camera port.  If your SCT extension is long enough, the OAG itself will prevent the guide camera from getting close enough to achieve focus.

This sounds like you've encountered this and I'm running in the same challenges. Tonight I'll keep the OAG directly attached to the FR and cross-fingers the autoguide will work in that configuration and jump on amazon to buy a T2 extension for the camera sensor so it's spaced 105mm from the FR lens.

 

At some point, perhaps I'll "upgrade" to a more modern OAG that has a more versatile compatibility. There's not much that I can do with the FR, but to keep it on the SCT, but the image train after that can be resolved at some point with newer parts.

 

Short of beating a dead horse, am I understanding that an autoguider doesn't require 105mm spacing even if there's a FR in the chain?

Edited by parnassian, 04 December 2024 - 08:55 PM.