Source for LongerT-2 Extension?

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DavidP
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Source for LongerT-2 Extension?

Post by DavidP »

I’m having a hard time finding longer( 4” ) T mount adapters for my Solar Spectrum filter. Anyone have a source?


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Re: Source for LongerT-2 Extension?

Post by marktownley »

What is it you need? a 4" long T2 extension tube?


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Re: Source for LongerT-2 Extension?

Post by DavidP »

Yes. A t-2 extension that is 80 to 100mm.
About 45 mm is the longest I’ve found


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Re: Source for LongerT-2 Extension?

Post by rsfoto »

DavidP wrote: Sun Jan 17, 2021 4:36 am I’m having a hard time finding longer( 4” ) T mount adapters for my Solar Spectrum filter. Anyone have a source?
See below ...

https://www.amazon.com/s?k=T2+extension ... _sb_noss_2

https://www.amazon.com/Astromania-Astro ... 041&sr=8-2


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Re: Source for LongerT-2 Extension?

Post by mdwmark »

Edmunds sells a 100mm Part number #65-969
What scope are you using where you need 100mm extension? Is this for the back side or the front of the telecentric?
The front, then the TZ4 sits about 48mm in front of prime focus. The best way to see what you need for an extension is put the telecentric on the scope without the filter , cut a plastic or paper tube 220mm long and tape a piece of paper on the back end as a screen. Now hold it on the back of the telecentric and move the focuser out till you see the solar disk focus on the paper screen.
Now measure how far you needed to move the focuser out. I like to have the focuser out no more then an 1" and make up the rest of the distance with an T2 tube.
If it is the back then, the TZ4 can be focused with an back focus of 150mm to 250mm and still work fine.
Mark W


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Re: Source for LongerT-2 Extension?

Post by marktownley »

DavidP wrote: Sun Jan 17, 2021 6:22 pm Yes. A t-2 extension that is 80 to 100mm.
About 45 mm is the longest I’ve found
Join 2 together?


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Re: Source for LongerT-2 Extension?

Post by DavidP »

Thanks all.
I will put the telecentric in and use the cardboard tube to find focus.
The need for a longer tube ( I can use more than one if needed) was a result of confusion about where the 4x telecentric should sit relative to the original focus. I had read original focus should be 93mm from the front lens which didn’t seem to be the case as I was messing with it. Mark’s suggestion of 48mm sounds more like what it wants.


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