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Flattener back focus issue - TS 130 f7

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#1 welluca

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Posted 22 September 2020 - 02:16 AM

Greetings everyone,

 

so yesterday after a long journey my new telescope arrived (TS 130 F7, 910 mm)

I wanted to test it immediately and started to mount things.

 

Long story short I was not able to reach focus with my camera (6200mm, with ZWO Filterwheel)

 

The reducer is the one at this link (TSAPORED075)

Form the technical description:

 

♦ The corrector can be used on all refractors with focusers from 2.5". The required back focus is 180 mm from the connection thread. Suitable adaptations via M68 are available.
♦ The working distance from the M48x0.75 thread is 55 mm. Ideal for astro cameras and DSLR/SLR cameras.
♦ The corrector offers another thread on the camera side, which allows you to extend the working distance to 105 mm

 

I ordered it with the support of TS consultants

We focused on the 55mm. According to ZWO, the train to have 55mm is Camera-Wheel-2mm adapter-16.5mm extender

 

Image is out focus with the focuser attached to the telescope, get worse moving away from it

At this point I removed the 16.5 mm extender from ZWO. Image still out of focus but better.

In the night i removed the extender on the reducer (see part 'a' in the image, which by the way is 55mm), and put the camera manually closer to the reducer. I reach focus.

 

At this point my guess is that the 55mm is not from the M48x0.75 but from the intermediate thread of the reducer (see the image, where part 'a' and 'b' split there is a thread (I think M68)

 

What is the meaning of the first sentence 180mm from the connection thread? the m68 thread of the telescope?

 

I am in contact with TS but I am happy to hear from you too smile.gif

 

Thanks,

 

Luca

Attached Thumbnails

  • flat.jpg

Edited by welluca, 22 September 2020 - 02:18 AM.


#2 sg6

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Posted 22 September 2020 - 02:53 AM

Quite logically if "a" is 55mm it cannot be included in the train. That is all the separation that you should have and it is all in one item. So that just cannot be in there.

 

You say:

We focused on the 55mm. According to ZWO, the train to have 55mm is Camera-Wheel-2mm adapter-16.5mm extender

So according to ZWO you want 2mm adaptor and 16.5mm extender (unsure why this bit) So why have you added a 55mm extender that is not required. Basically why is the 55mm item "a" in there at all it makes no sense.

 

The 55mm will be from some face on the reducer. It cannot be specified from anywhere else only from the reducer. TS cannot say it is 55mm from a face on some arbituary unknown thickness extension that is added. You seem to have decided the M68 thread of the reducer and that makes some sense.

 

The 16.5mm extender I have no idea about. Exactly what is every item from Reducer to Camera and the order and the thickness each provides.

 

Assume you have a ZWO camera so 6.5mm, 2mm adaptor (8.5mm), and I think 20mm filter wheel (28.5), and 16.5 extender (45mm). Somewhere there either is or is needed another 10mm. If I recall ZWO have an 11mm "bit" at their cameras (sometimes) which if you have it in there makes 56mm - close to the 55mm requirement.

Is there by chance a 10mm thick M68-M48 adaptor in there? Is that what "a" is ?

 

But the 55mm will be from th reducer and nothing else, I guess the 180mm specification is pointless, seem to be saying the reducer from front to back is 125mm long. So what?


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#3 welluca

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Posted 22 September 2020 - 03:13 AM

Hello, 

let me elaborate a bit more

 

The reducer, as bought, it is as you see in the picture, with part 'a' and part 'b'

Telescope side has a M82 thread. On this side I've installed the adapter to connect it to the telescope

Camera side has a M48 thread (on the part 'a')

Between 'a' and 'b' there is a thread, which i guess is M68, but I am not sure

 

The technical data sheet of the reducer states

The working distance from the M48x0.75 thread is 55 mm. Ideal for astro cameras and DSLR/SLR cameras.

So for this reason I left the part 'a' on, because that's the only part with a M48. 

 

And for the ZWO train the image can explain better what i did. The 2mm is an adapter which has a 2mm light path

 

I hope this helps to clarify where my choices came from :D

 

 

 

 

 

Attached Thumbnails

  • ywo.png


#4 welluca

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Posted 23 September 2020 - 12:01 PM

So, I am happily writing this post with the problem solved, hopefully it will spare some terror to other people when they will google about their problem

 

TL;DR: the telescope tube was too long

 

I reached TS today at the phone, describing my tests trying to convince them that I am not totally silly and incapable

 

After checking the drawing he said that there is the possibility that the tube is too long and a piece should be removed

 

And so I did...

 

 

Attached Thumbnails

  • flat2.jpg
  • a.jpg



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