Additional lock points on SW 300P Flextube

[mitchelln]

Hi.

On my 300P Flextube, there are an additional set of truss locking holes 110mm back from the main ones. Anyone know what they are intended for? They obviously shorten the focal length slightly.

I'm going to try out some binoviewers and it struck me that these extra locking points may provide additional back focus.

Thanks!

[brantuk]

Don't touch them - especially if they have a piece of tape on them. They're tensioned to retain the ball bearing on a spring that locks the trusses in place when you raise the focuser box up to height. Resetting them to the right tension is a pig and if you undo the very short thread accidentally, the spring and ball bearing pop out and you wind up chasing them all over the floor lol. Hth

(They don't do anything to the focal length - but they do help retain the collimation)

[John]

Sounds like good advice from brantuk 

By the way, shortening the length of the tube would not shorten the focal length of the optical system. It would move the focal plane of the scope further outwards from the side of the tube though which might help binoviewers reach focus as, typically, then need around 100mm inwards focuser travel, which many newtonians don't have as standard.

[JamesF]

Don't touch them - especially if they have a piece of tape on them. They're tensioned to retain the ball bearing on a spring that locks the trusses in place when you raise the focuser box up to height. Resetting them to the right tension is a pig and if you undo the very short thread accidentally, the spring and ball bearing pop out and you wind up chasing them all over the floor lol. Hth

That's the second set of screws that are in the truss runners, isn't it?  Just below and to the side of the locking bolts?

I read the original posting to mean that there are a second set of holes in the truss poles themselves.

James

[Avocette]

Is it obvious whether the extra holes were drilled by, for instance, a previous owner? I'm thinking that they may look less 'manufactured' that other parts of the scope.

[Avocette]

By the way I'll be following your progress on the binoviewers idea with interest!

[AlexB67]

My 10 inch got the second holes too in the way James describes.  In fact a  week and a bit ago  I fell into that trap, It was dark. By mistake I locked the trusses using those holes. I could not get my eyepiece to focus, popped in another one, another one, the same. What on earth was going on, It was only the second time using the scope and thought  "wait, I am sure the scope was not this short before", :0) something is not right, "Hellooo" I said to myself,  then I realised the scope had locked in the lower holes

[Astro Imp]

Don't touch them - especially if they have a piece of tape on them. They're tensioned to retain the ball bearing on a spring that locks the trusses in place when you raise the focuser box up to height. Resetting them to the right tension is a pig and if you undo the very short thread accidentally, the spring and ball bearing pop out and you wind up chasing them all over the floor lol. Hth

(They don't do anything to the focal length - but they do help retain the collimation)

Sounds like your talking from experience.

[mitchelln]

Hi.

Seems to be some confusion There is an additional set of locking point holes in the trusses 110mm back from the main ones. So you can lock the tube at less than full height. They were present out of the box from new.

I tried a pair of Skywatcher binoviewers last night and with the tube fully extended. I could not reach focus without a barlow. I then shortened the tube length by locking back into the other holes. Binoviewers then easily reached focus without barlow. What is interesting is when I then extended the tube fully again and swapped in my 31mm Aspheric, it was perfectly in focus. Coincidence? I'm starting to suspect that Skywatcher have added the 2nd set of locking holes for this very purpose.

[Avocette]

I was hesitating about trying (buying) some binoviewers since I'd read that getting focus without the 1.6x Barlow was unlikely with typical Newts. One argument I've read is also that the lower priced BVs (SW, WO etc) have a field stop of around 20 mm which effectively limits the eyepieces to around 20mm of Plossl 52 degree AFOV. WIth your 300p flextube with 1500mm focal length and no Barlow you're still talking about 75x magnification as a lower limit which could certainly be more universally interesting than 120x. What eyepieces did you try using with the binoviewers?

[mitchelln]

Hi.

It was a couple of 20mm Revelation Astros.

Tempting way to go would be a 2nd Baader zoom

Sent from my GT-N7105 using Tapatalk

[brantuk]

Apologies folks - I though the OP was talking about the extra locking bolt holes behind the "T" bar truss locks - I must've misread the post. I actually don't have those holes indicated in the picture above on my 300P flextube. Mine only has the one set of holes in the end of the trusses, and I'm in the dark as to what the extra holes are for as well.

But yes - I did take the tapes off and undid the other bolts and wound up scrabbling on the floor looking for springs and ball bearings lol.

[mitchelln]

Apologies folks - I though the OP was talking about the extra locking bolt holes behind the "T" bar truss locks - I must've misread the post. I actually don't have those holes indicated in the picture above on my 300P flextube. Mine only has the one set of holes in the end of the trusses, and I'm in the dark as to what the extra holes are for as well.

But yes - I did take the tapes off and undid the other bolts and wound up scrabbling on the floor looking for springs and ball bearings lol.

How long ago did you get your 300P? Got mine in January. Perhaps it is something they had added. Turns out to be a useful little feature!

Glad you mentioned the bolts though. Whilst looking for what you were referring to, I noticed that one was nearly unscrewed. Saved me grubbing around on the floor for springs and ball bearings

[brantuk]

Mine is one of the original flextubes from when they first came out - so yes it could well be a new thing

[madsarmy]

I bought mine in June & it's only got the one.

[mitchelln]

How odd. I'll find the serial number on mine. Perhaps only one batch had them.

Sent from my GT-N7105 using Tapatalk

[AlexB67]

I got mine less than a month ago ( 10 inch ) from FLO.  I don't know how long it was in a warehouse and manufactured, but it is exactly as shown in the picture by Michelin, so I did wonder why the extra holes are there, as they seem to have no function .. best I could tell.

[TractionMan]

Got those extra holes on my dob as well. Might be a new feature then.

[stev74]

Interesting thread, I have an older 300P and don't have the extra holes but they would be handy as when I connect my Mintron camera with a focal reducer for some video astronomy I have to shorten the truss by roughly that much, it would be handy if I could get it the same each time instead of roughly guessing. I suspect that it is deliberate, as it would make sense for bino viewers, certain CCD camera's and probably DSLR's as well in 'movie mode' for the Moon and planets or single shot lunar work. 

[Avocette]

Hi.It was a couple of 20mm Revelation Astros. Tempting way to go would be a 2nd Baader zoom ;)Sent from my GT-N7105 using Tapatalk

Might be a touch wide to mount two zooms side by side and maintain your interpupillary distance, but nice idea. I may have to start drilling!

[mitchelln]

Might be a touch wide to mount two zooms side by side and maintain your interpupillary distance, but nice idea. I may have to start drilling!

I think it's fine. Baader have put a picture on their Maxbright binoviewers box with a pair of zooms. It must be a bit tight. I think weight might an issue though.

Any Flextube owners got any tips on attaching balancing weights? I've seen some minicab roof sign magnet on eBay. Alternatively I way thinking of some sort of shotgun cartridge type belt strapped round the mirror end which you could slip weights into.

[Stargazer_00]

Skywatcher produce binoviewers so it'd make sense for them to implement such a simple design change to allow for their BVs to work in the sopes that have an ability a variable focal length.

[Avocette]

Any Flextube owners got any tips on attaching balancing weights? I've seen some minicab roof sign magnet on eBay. Alternatively I way thinking of some sort of shotgun cartridge type belt strapped round the mirror end which you could slip weights into.

Haven't tried it myself yet but I've read of the use of a magnetic strip kitchen knife holder mounted on the tube and some steel weights to attach and/or slide to vary the balance.

[mitchelln]

Might try something like this

http://www.amazon.co.uk/WOODSIDE-PATROL-POUCHES-UTILITY-SECURITY/dp/B00D48130Q/ref=sr_1_4?s=sports&ie=UTF8&qid=1383314880&sr=1-4&keywords=utility+belt

I can drop weights into the pockets.

[Key]

Hi.

Seems to be some confusion There is an additional set of locking point holes in the trusses 110mm back from the main ones. So you can lock the tube at less than full height. They were present out of the box from new.

300P_locking_holes.jpg

I tried a pair of Skywatcher binoviewers last night and with the tube fully extended. I could not reach focus without a barlow. I then shortened the tube length by locking back into the other holes. Binoviewers then easily reached focus without barlow. What is interesting is when I then extended the tube fully again and swapped in my 31mm Aspheric, it was perfectly in focus. Coincidence? I'm starting to suspect that Skywatcher have added the 2nd set of locking holes for this very purpose.

Hi, I'm very interested in this: unfortunately my 250px flextube doesn't have the extra set of holes drilled into the truss tubes. Has anyone tried just tightening the lock at 110mm without holes? Is it safe to do this with the extra weight of a DSLR attached to the scope?

I've tried some basic DSLR astrophotography with the scope but achieving enough inwards travel on the standard focuser is a problem -  I'm hoping the shortened tube idea may avoid the expense of gambling that a low-profile focuser would be the answer. Will give it a try next time there's a break in the clouds!

Grateful for any ideas.

Cheers,

Key