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Long refractor in-focus bummer (Takahashi TS-65)

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#1 Lentini

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Posted 27 October 2021 - 10:44 PM

So still getting to know my TS-65 f/15.3 refractor. Wicked sharp views. Great first impression. 
 

Tonight I was using Hyperions zooms with my Borg in binoviewers and a new Meade 4K zoom in the Tak. I have a WO correct image diagonal on the Tak. Nice views of Jupiter and Saturn, but I found that when I tried to zoom in on the Tak, it didn’t have enough in-focus for the higher mags. At 24mm, I could reach focus, but at some point I couldn’t focus as I adjusted the zoom. 
 

So I decided to grab some Orthos instead… The 12.5mm Tak Ortho was excellent. But the 7mm Celestron Ortho also couldn’t reach focus! I switched to a shorter tube on the Borg, and being so modular, it’s easy to adjust for all circumstances. But the 1973 Tak… What to do? 
 

I could skip the diagonal to get that in-focus back, but I enjoy the correct image view. And the angle with the diagonal.
 

Question for folks… Is there a component I can add to reduce that in-focus requirement?

 

Has anyone modified an old tube like this to add a draw-tube or reduce the tube length? 

 


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#2 photomagica

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Posted 27 October 2021 - 11:56 PM

Try a non-erecting diagonal. Sometimes an erecting diagonal needs a little more light path. 


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#3 MisterDan

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Posted 28 October 2021 - 12:57 AM

Call Harry (Siebert Optics).

 

https://www.siebertoptics.com/

 

One of his OCAs or focus adapters should solve the issue.  He can help you decide which solution best fits your needs.

 

His products are excellent.

 

Best wishes and luck.

Dan


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#4 Lentini

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Posted 29 October 2021 - 08:17 PM

I wonder if a Vernonscope 1.5x “Magic” Barlow on the scope side of my diagonal would extend that focal length? 



#5 MisterDan

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Posted 29 October 2021 - 11:24 PM

I wonder if a Vernonscope 1.5x “Magic” Barlow on the scope side of my diagonal would extend that focal length? 

Yes, Barlows will "extend" your focal point, but they will, of course, increase the scope's effective focal length.  If you have a typical/standard Barlow with a removable lens cell, its threads may indeed match those of your diagonal.  There are no hard/fast "rules of thumb" when it comes to "transplanting" those Barlow cells, but it's not uncommon for folks to report that their "shorty" Barlow lens cells yield ho-hum results, when "transplanted" to eyepiece barrels.  Long-ish/standard-length Barlow's, on the other hand, may "transplant" to eyepieces more effectively.  Since we're talking about diagonals, I would tend to expect standard- and longer-length Barlows (such as Tele Vue's 2x, Meade models 122 and/or 140) to do well.  However, their magnification factors may not change much, as the "lengths" of such Barlows may be comparable to the "lengths" of typical 1.25-inch diagonals.  Your Tak's effective focal length with a 2x Barlow cell installed in your diagonal's nosepiece may still end up right around 2000mm.

 

Keep in mind:  the Magic Barlow - when installed onto a 1.25-inch diagonal (instead of an eyepiece) - will yield a magnification factor closer to 2.

 

If you have a Barlow with a removable cell, give it a try!

 

Best wishes.

Dan



#6 Lentini

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Posted 31 October 2021 - 12:37 AM

Played with the Magic Barlow 1.5x installed in the diagonal tonight briefly. (I don’t have any other Barlows.)

 

It definitely pushed my focal point out… Much farther than I expected! It was 5” or so.

 

I didn’t have a quick way to judge what the mag was… If it was more than the 1.5x. 
 

spent some time on the Orion Nebula. A 24mm Pan was a pleasing view. 
 

I haven’t heard back from Harry at Siebert Optics. I guess I’d ideally want something close to zero mag that would push the length about 3 inches. But this Barlow does work. 


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