Changing Focuser

[Rod-AR127 (Rod)]

I am going to buy a new focuser for my AR-127L frac.
The new focuser will need an adaptor or a new end piece made up for my ota to fit as the Hexafoc 2.5" is 82mm inside diameter, not a size that I've been able to find.

So, my main question is does the new focuser have to be the exact same distance from the front lens as the old focuser?

What happens if l move the focuser further away?

Old focuser is damaged, not repairable and not available new.

I've googled these questions and can't find anything, maybe a trip to the library is in the cards

Thanks.
Rod

[astro744]

Ideally you want the fully racked in position to be at the same distance and no further out otherwise you risk not being able to rack in far enough for eyepieces or accessories that require it, (binoviewer, long path diagonal come to mind). You want the focuser travel to be the same or close too so that the telescope will work as designed.

I did look up your ‘scope after your last thread and only found the Featherouch replacement which also required an adaptor to reduce the diameter from tube to focuser. Bresser sell both but the cost is nearly double that of the telescope!

[Rod-AR127 (Rod)]

As l suspected. Thankyou.
I'll try and get a new end piece for my ota made up ready to accept my chosen focuser. I will get the focuser first.
I will have to look through my friend's 130mm Newt before spending any money, after all, l have the EP,s, tripod and mount.
Maybe a 200mm plus Newt might be better?


I do like fracs though l.

[astro744]

This is what I found.

https://www.bresser.de/en/Astronomy/...h-2-5-HEX.html

And https://www.bresser.de/en/Astronomy/...TF2020BCR.html

A new OTA is 365 Euro. See https://www.bresser.de/en/Astronomy/...ical-Tube.html

You could buy another OTA for less than the Feathertouch! (Freight may be more though).

Note although ideally any new focuser is the same length you may have room to move in back focus with something different. You would have to measure at what point your current focuser is racked in for every eyepiece and accessory you own and are ever likely to own (the latter more difficult) and compare against any new focuser.

A 200mm Newtonian would give you a considerable boost in light gathering capability. Note though a Newt on an EQ Mount without rotating rings can be cumbersome as the eyepiece can end up in all sorts of positions including facing down (at an angle). Rotating rings are expensive though.

My first telescope was a 6” f5.5 Newtonian on a Vixen Polaris Mount (with extra counterweight). I got used to the awkward eyepiece angles but I didn’t have any heavy eyepieces back then to be worried about them falling out. There was no compression band on the focuser or safety undercut on any eyepiece either that I had although the eyepieces were light weight. I still have and use this telescope occasionally and have changed its focuser couple of times over the years.

Note Newtonians have far less travel in their focus range than refractors so using accessories such as Binoviewers (1x mode) or even cameras is not always possible (but not impossible with some designs). Every telescope is a compromise.

[Rod-AR127 (Rod)]

Yes l have seen the adaptor, feather touch and ota and their prices.
So this adaptor moves the focuser further back, this is now confusing me. Maybe the focuser has the range to accommodate that.
I guess l need to know the focal point of the objective lens and go from there.
Kind of highlights my inexperience in buying telescopes but that's ok, I'll wear that.
Looking at more the Bintel Crayford price range, no point putting racing tyres on a Datsun Sunny.

Anyways, l need to keep the focuser as close to the original position as possible, l think a new custom end piece and stock focuser will be the best.
IIS member in WA does custom stuff, already been in touch.

[astro744]

The adaptor with the Feathertouch probably puts it at the correct distance but cost is prohibitive. Standard Crayford from Bintel was my first thought but I think smallest is 86mm and you needed 81mm (3 3/16”) from an earlier thread I read, perhaps confirm this. Note the screws holding the focuser will have to line up in spacing and thread size/pitch. New focuser may not come with screws expecting old ones to fit, not sure.

If you have no luck in AU then try OS at http://www.scopestuff.com/ss_frc2.htm

I think it’s the same selection of sizes though but they may have some custom adaptors.

[astro744]

Contact Moonlite Focusers as they may have the correct adaptor or could possibly make one.

See https://focuser.com/products.php

[Rod-AR127 (Rod)]

Nope, I'll get a new end piece from the ota to the new focuser turned up by fellow IIS member, AFTER l buy a new suitable focuser.
The new focuser will be in the exact same position as the current one, just better.