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4" Achro Frac with Binoviewers


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All of the fracs I've had seem to have focusers that have focuser out-travel to spare - My AR-127L would come to focus with all of my EPs without a diagonal in the Jap style straight through. It was amusing until my neck gave up.

All of those same fracs with a 2" diagonal, brought pretty much every EP I tried to focus after about an inch or so of out travel, so unless these things are either 1) a Japanese conspiracy, or 2) designed in isolated ignorance of binoviewers, there's 4" of pointless travel - For my purposes, at least.

So, does anybody have, or know of a half decent 4" frac that actually uses a good amount of focuser out-travel when just using a diagonal?

The reason I ask is that if there is and it's a circa F10 focal ratio, then it seems to me, to be eminently suitable candidate for BV use without the 1.6x Barlow nose-piece that stuffs up lower magnifications, but would be handy to use for higher mags.

Yes, my SCT does exactly this, but I feel the need (again) for a circa 1000mm FL scope in my armoury and at 4", it'll be light (and short) enough for the Minitower. At the moment, I'm contemplating getting something - AR-102L, Tal 100RS, etc - and cutting the OTA down, because they're so cheap.

I'd like to do something less drastic if possible though!

Russell

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wondering into dark territory Russ? :D

Well i dont want to recommend any "half diecent" frac.Thats just not my way of doing things.Also remember that all telescopes where built and designed before binoviewers came into play as such there are NONE of the earlier ones who will work stright out of the box,unless,there are some things what could be modified without any drastic changes.But i dont know of any.

Question is about the diagonal you are using.Standard 2" diagonal will introduce quite a long light pass and this is purely the reason why not many use them for binoviewers.I had one and it didnt work for me either and i got a prism now.Option on this one:get a 1.25" prism or if you are feeling generous like me,get a Baader-Zeiss 2" prism.This will drastically shorten your light pass and might give you a chance of reaching focus without the need of barlow.If this doesnt help,well that only leaves you with one option: introduce your OTA to hacksaw blade.You will need to chop off about 100mm of your OTA to be able to use binos in native9will need to measure your light pass to get accurate chopping length).Is it worth it or no,will be up to you to decide.I love binoviewing and if that would be my only option,i would go for it.Again:YOU DECIDE.

As for scope recommendation,here is my take.

i would personally sell that Bresser AR 127 and get a Skywatcher 100 ED and chop it :D Your bresser should fetch about 150-200 squid where s/h 100 ED`s are about 250.Alternatively,i would also be tempted by TAL100RS,but again its a chopping block for that scope too.If money is an issue,there will be nothing wrong by using your Bresser and adopt(chop) it for use in binos.

best of luck buddy

Gaidis

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I'm a keen refractor chopper. All my refractors apart from a Tak Sky90 which had nothing left to chop, have been chopped for either binoviewers or PST mods for Ha use, Nominally a 30 minute job and just an extension piece needed for "normal" use. Be careful to note the position of the eyepiece end baffle before chopping.   :smiley: 

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wondering into dark territory Russ? :D

Well i dont want to recommend any "half diecent" frac.Thats just not my way of doing things.Also remember that all telescopes where built and designed before binoviewers came into play as such there are NONE of the earlier ones who will work stright out of the box,unless,there are some things what could be modified without any drastic changes.But i dont know of any.

Question is about the diagonal you are using.Standard 2" diagonal will introduce quite a long light pass and this is purely the reason why not many use them for binoviewers.I had one and it didnt work for me either and i got a prism now.Option on this one:get a 1.25" prism or if you are feeling generous like me,get a Baader-Zeiss 2" prism.This will drastically shorten your light pass and might give you a chance of reaching focus without the need of barlow.If this doesnt help,well that only leaves you with one option: introduce your OTA to hacksaw blade.You will need to chop off about 100mm of your OTA to be able to use binos in native9will need to measure your light pass to get accurate chopping length).Is it worth it or no,will be up to you to decide.I love binoviewing and if that would be my only option,i would go for it.Again:YOU DECIDE.

As for scope recommendation,here is my take.

i would personally sell that Bresser AR 127 and get a Skywatcher 100 ED and chop it :D Your bresser should fetch about 150-200 squid where s/h 100 ED`s are about 250.Alternatively,i would also be tempted by TAL100RS,but again its a chopping block for that scope too.If money is an issue,there will be nothing wrong by using your Bresser and adopt(chop) it for use in binos.

best of luck buddy

Gaidis

Dark territory? Not at all; although I appreciate 4" aperture ain't going to be the brightest thing going!

Alas dear Sir, the AR-127L long since departed Williams Towers, to fund the SCT. Had I still had that and it's yard of focuser, I'd still have the EXOS 2 Goto which could handle it, hence the current restriction to a lighter 100mm. I really liked that scope though and the minimal CA it had didn't really fuss me alongside the colour free ES Triplet. 

It would take some soul searching to buy anything Synta though, but it would be an easy chop. A straight cut on a tube and drilling three holes isn't exactly going to be taxing, but that holds true for a fair few fracs. The thing is, I've battled with Synta focusers enough in my life and a BV plus EPs isn't light.

On that note, I keep looking a Nightfisher's Starwave 102 F11. You know that's going to have good optics and a good strong focuser and the price is decent, but collection only is killing it. That and the fact that it's only another £60 to the TS badged version brand new, if you consider that comes with a 50mm finder holder and is delivered to your door.

The TAL obviously is on the radar. It can still be found for under £250 new and has the requisite yard long focuser draw tube. That focuser is R&P too, which I like. There's also the fact that the TAL is, in some ways, the Alfa Romeo of refractors - You aren't a petrol head unless you've owned one and I haven't. Seriously tempting.

Russell

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Well, the soul didn't take much searching when a Celestron C100ED-R cropped on UKABS for £200. You can't ignore that sort of value!

Cheers for the help chaps. :)

Russell

Nice one Russ :) I saw that one come up and nearly went for it also, great price for an 100ED! I ended up going for the 80 quid Celestron 102mm f/10 xlt instead. Our similar kit list continues :grin: 

Interesting thought about chopping the tube for BV's, hmm?   

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Well, for £200 it's going to be hard to resist getting the hacksaw out, but it may have to wait until I find out which focuser it has. As far as I am aware C100 EDs had a screw on focuser and chopping the tube will remove the thread.So that will require a new focuser (TS Monorail?) and that will have to wait a month or two.

Russell

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Russell. Chopping a tube with a screw fit is a 2 chop job. cut the tube ahead of the threaded portion then cut the remaining length of the shortening. Split this second bit and remove enough so that it will fit inside the main tube and then join the threaded section to it. The joins can be by screws or bonding. Care is needed of course to make sure the faces are square. Saves buying a new focuser.   :smiley:

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Good idea Peter and something I've done with rainwater down-pipe. The handy thing is that the split section helps square the two tube ends to each other too. The only thought that crosses my mind is what a two-chop might do to internal baffle positions? I guess you don't want to effectively move one of the rear, smaller aperture baffles up the OTA due to vignetting - Or is it not that critical? If it is, I suppose it's probably easy enough just to knock the offending baffle out.

I'll have look-see before I plan anything definitive. The version I've bought has an R&P focuser, which (looking at old threads on here and else where) some can't wait to replace whilst others have had great success in tuning up with tactical Teflon strips. If it does turn out to be rubbish, I've got a suspicion that just chopping the threaded section of barrel off might make fitting a TS Monorail easier, as it seemed to require an adaptor from Agena Astro, that they no longer make.

Russell

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  • 1 month later...

Update. :)

I lasted about two sessions with the risible Celestron R&P (no wonder Crayfords took off!) before I weakened and bought a TS Monorail focuser to fit a 96mm internal diametre OTA. For once, the problem that followed wasn't a Synta issue. No, digital vernier calipers showed the TS focuser to have a 97mm outside diameter. Give me strength.

Well, I might have chopped the unsightly external thread off the OTA myself, but I was not equipped to turn 0.5mm radius off the focuser. It was suggested by those in the know, that Graham at Astrotech could perform such surgery and as luck would have it, my work is halfway to his abode. I dropped the focuser OTA adaptor and the OTA tube with him yesterday and he has just sent me these. 

gallery_10522_3803_15097.jpg

gallery_10522_3803_91516.jpg

looking good and with the TS Monorail being 40mm shorter than the R&P, plus the additional 10mm+ of lost thread, this should be bang in the right region for the Binoviewer. If not, I'll sacifice a touch more tube.

It might be a challenge to achieve enough out-focus for a diagonal and EP, but for that, we have extension tubes. :)

Russell

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Nice one Russ. I had a Meade AR127 awhile back which I chopped 4" off the tube with so I could comfortably use unbarlowed binoviewers with. It gave superb views. I have an old 6" F8 in the loft which I keep threatening to do something similar with

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Interesting stuff - thanks for the pics Russell.

This is probably a dumb question but if you shorten the tube of a refractor but use the same focuser, is there a risk that the inner end of the refractor drawtube, as it's now further along the optical path of the scope, intercepts the light cone a bit and causes some vignetting ?.

Or are focuser drawtubes generally wide enough to allow for this ?

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Nice one Russ :) I was a little worried how hard it would be to make the new focuser fit neatly, but all is looking very good indeed. Please post some pics with the new focuser in situ if you get a chance :) 

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John, it's certainly not a dumb question and it was one I considered.

I think that  vignetting would be a possibility under exactly the circumstances you describe, but I guess it varies scope to scope.

In the case of the very shallow light cone of a F9-10 scope, I think you would have to chop one heck of a lot off. The rear most internal knife edge baffle in the OTA, is only just over 2" in diameter. As best I can tell, the lengthy focuser draw tube stops and inch or so short of that, with the focuser fully racked in, so there's certainly room to spare. In the case of the TS Monorail and what I've done, the EP end of the draw tube may now be 2" closer to the objective, but the draw tube itself is also at least 2" shorter, so it's certainly a non-issue in this scope.

I guess one may have to be a bit more exacting if such surgery were performed to a F7 or shorter scope, due to the steeper light cone. However, as the only real reason to do this is for binoviewing and even an uber BV like the Binotron 27 with OCS 37 has a clear aperture (which is well ahead of the binoviewer) of 37mm, I imagine a small amount of vignetting of the light cone may pass un-noticed. Indeed, as more vanilla fayre, such as TV Bino View (!) and down with 1.25" threaded amplifiers, etc, you've got an even greater margin for a bit of clipping. By the time you get to the trinket I'm using, you dream of clipping issues!

Just returning to the case of the ubiquitous Synta 4" F9, I actually suspect it's baffles, or at least the foremost one is undersized, or should that be over? Even with a diagonal in and the original focuser racked out beyond where any of my EPs focus, I could see a bright ring of reflected light from the OTA wall behind the lens cell, with my eye placed centrally. It was so bright, it's one of the few times I've actually felt compelled to flock, rather than just doing so because cloud has bred boredom. 

Russell

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Nice one Russ :) I was a little worried how hard it would be to make the new focuser fit neatly, but all is looking very good indeed. Please post some pics with the new focuser in situ if you get a chance :)

Will do when I get it home. I'll post some pics of the old v new to illustrate what I was explaining above too.

Then I'll move on to considering tarting this up for some serious bling. At what this scope has cost and considering that these mods make it worth less, I suspect there will be no point in ever selling it, so I may as well make it really mine. For some reason, I'm considering having all of the paint (internal and external) stripped from the OTA and then chroming it and dew shield, followed by repainting the interior in some sort of very black. I imbibe at the local on Friday night with a Hell's Angel. If you've seen the quality of chrome on his self restored Harleys (one over-winters in his living room!) it's hard to resist....

It turns out that the light nights of summer breed boredom in much the same measure as cloudy ones....

Russell

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Will do when I get it home. I'll post some pics of the old v new to illustrate what I was explaining above too.

Then I'll move on to considering tarting this up for some serious bling. At what this scope has cost and considering that these mods make it worth less, I suspect there will be no point in ever selling it, so I may as well make it really mine. For some reason, I'm considering having all of the paint (internal and external) stripped from the OTA and then chroming it and dew shield, followed by repainting the interior in some sort of very black. I imbibe at the local on Friday night with a Hell's Angel. If you've seen the quality of chrome on his self restored Harleys (one over-winters in his living room!) it's hard to resist....

It turns out that the light nights of summer breed boredom in much the same measure as cloudy ones....

Russell

Thanks Russ, I'm sure we'll all enjoy seeing the pics, but no rush :)

lol go for it! infact I can probably find a picture of what it might look like in chrome! When I started a thread showing my efforts to pimp out a C80ED in carbon wrap, one guy showed me a picture of a C80ED he chromed. Looked really nice! Slightly Moonrakered if that's a word.

Check out the pics second post down:

http://stargazerslounge.com/topic/169539-cosmetically-challenged-celestron-ed80/page-2

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