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Best APO/Triplet correctors and focusers?


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I'm possibly going to be getting a 130 f6.6 APO triplet soon, but it comes with a 2" focuser. So far, the highest quality corrector I have found seems to need at least a 2.5" focuser (Here) or even a 3.5" (Here). I have an APS-C sensor at current so these would allow me to bring the scope down to a more reasonable f4.95 while also being extremely sharp out to full frame distance, with barely any vignetting across a full frame sensor, let alone my APS-C one. But this also makes me wonder if there are stronger reducing correctors I could use, that would allow me to take the scope even faster for my camera?

The other thing was to do with replacement focusers in general. It seems rack & pinion is very popular, and having googled it, it seems many actually have a strong distain for crayfords, even the mighty diamondtrack not free from criticism from many! Yet R&P would suffer backlash and leave me at risk of having to set backlash compensation settings precisely on my EAF? Are there any particularly good 3" focusers that would fit on the back of such a telescope without mechanical issues?

I come from the land of mirrors as it stands so I am not well read up on refractors, but I have finally had enough of cheap newtonians and the many problems they have that I am unable to solve!

Any help and suggestions welcome : D

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58 minutes ago, Louis D said:

If cost and weight is no object (and if Don is still making them), the Clement focuser would probably work for you with the appropriate adapter.  It's natively a 3" focuser.

Sadly I am working under an aim to reduce weight if possible. My current 200mm f4 newt is about 8.5kg with tube rings, while this refractor is only 6.5 with rings AND guidescope! That also looks like it'd be bigger than the whole 130mm scope! Thanks for the link though!

57 minutes ago, iantaylor2uk said:

I use a hotech SCA 1x flattener on my Tak 102 TSA and it works for refractors between f/5 and f/8

Ah, I hadn't considered looking at hotech! I'll give them a looksies now.

Thanks!

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2 hours ago, pipnina said:

I'm possibly going to be getting a 130 f6.6 APO triplet soon, but it comes with a 2" focuser. So far, the highest quality corrector I have found seems to need at least a 2.5" focuser (Here) or even a 3.5" (Here). I have an APS-C sensor at current so these would allow me to bring the scope down to a more reasonable f4.95 while also being extremely sharp out to full frame distance, with barely any vignetting across a full frame sensor, let alone my APS-C one. But this also makes me wonder if there are stronger reducing correctors I could use, that would allow me to take the scope even faster for my camera?

The other thing was to do with replacement focusers in general. It seems rack & pinion is very popular, and having googled it, it seems many actually have a strong distain for crayfords, even the mighty diamondtrack not free from criticism from many! Yet R&P would suffer backlash and leave me at risk of having to set backlash compensation settings precisely on my EAF? Are there any particularly good 3" focusers that would fit on the back of such a telescope without mechanical issues?

I come from the land of mirrors as it stands so I am not well read up on refractors, but I have finally had enough of cheap newtonians and the many problems they have that I am unable to solve!

Any help and suggestions welcome : D

You also have to consider the tube side fitting diameter, the focuser size on the tube side and probable adapter that connects the two. If your tube is not one of the 'common brand' sizes it may be difficult to find an off the shelf adapter. So you need an adapter for the focuser you buy, that fits your tube and focuser, they aren't cheap, you may also need to consider backfocus depending if you have any gizmos in your light path eg Riccardi M82 . Its a non trivial consideration so you need to plan things out before buying

I bought an APM 3.7" R&P to replace the 2" Crayford Feathertouch on my TMB 115mm. Due to the diameter of the Krupex tube there were no off the shelf adapters despite contacting APM and Starlight Instruments plus others. They suggested an expensive custom jobbie and wanted me to send the whole scope overseas to be measured! In the end I measured it myself , designed an adapter and 3d printed it. It fits

Nothing wrong with the 2" Feathertouch just that it wasn't easy to attach a M82 Riccardi to. The Feathertouch 3.5" isn't worth 2.5x the price of the APM 3.7" (if you can find one)

Edited by billhinge
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On 22/09/2022 at 21:43, billhinge said:

You also have to consider the tube side fitting diameter, the focuser size on the tube side and probable adapter that connects the two. If your tube is not one of the 'common brand' sizes it may be difficult to find an off the shelf adapter. So you need an adapter for the focuser you buy, that fits your tube and focuser, they aren't cheap, you may also need to consider backfocus depending if you have any gizmos in your light path eg Riccardi M82 . Its a non trivial consideration so you need to plan things out before buying

I bought an APM 3.7" R&P to replace the 2" Crayford Feathertouch on my TMB 115mm. Due to the diameter of the Krupex tube there were no off the shelf adapters despite contacting APM and Starlight Instruments plus others. They suggested an expensive custom jobbie and wanted me to send the whole scope overseas to be measured! In the end I measured it myself , designed an adapter and 3d printed it. It fits

Nothing wrong with the 2" Feathertouch just that it wasn't easy to attach a M82 Riccardi to. The Feathertouch 3.5" isn't worth 2.5x the price of the APM 3.7" (if you can find one)

This is a quote from the seller. Do the measurements seem similar to other scopes, do these numbers help indicate if it's possible to easily switch focuser or not really? Cheers

Quote

The Tube has a fixed flange on the back with 2.867" or 72.9mm. As I understand it there's a connector for the Moonlight focuser and the
Feathertouch. The adapter for the skywatcher I would include, so you can sell that focuser in case you upgrade.

 

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