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Inward focus problem


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I have a Baader wedge that I use with my ED100 for solar observing but have a problem in that some of my longer focal length EPs cannot reach focus due to a lack of inward focus travel.

These EPs can reach focus if I use the standard eyepiece/diagonal adapter on the end of the focus tube but I don't like doing that as I end up with £1000 worth of kit hanging on two cheap knurled screws. For dark observing my Baader Clicklock adapter replaces the standard fitting and I can achieve focus no problem. The problem comes from the extra few millimeters of light path within the Baader wedge when compared with a normal diagonal.

All I need is about 3-5mm more inward travel :huh:

One potential solution I have thought of is to take a hacksaw to the draw tube on the ED100 and cut 5mm off the threaded end. That would take the scope side face of the Clicklock (and therefore the EP) 5mm farther up the lightpath when the tube is fully inside the focuser.

Has anyone tried this?

Am I about to ruin £400 worth of refractor?

Is there a better solution?

All advice greatly appreciated.

Derek

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its not unusual for refractors to be cut down to deal with infocus issues.

Never done it myself mind you but i imagine with the right tools and skills its simple enough

Most normally cut the OTA tube not the focuser.

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its not unusual for refractors to be cut down to deal with infocus issues.

Never done it myself mind you but i imagine with the right tools and skills its simple enough

Most normally cut the OTA tube not the focuser.

That is all good to hear. Never thought of cutting the OTA, which makes much more sense as a larger adjustment could be made to give more flexibility.

Luckily my father in law is an engineer by trade so he will know how to do this properly and will have the correct tools.

Thanks

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Normally Bino Viewers casue the issue, and some OTAs are either designed with that usage in mind and an only be used without a binoviewr with a diagonal or an extension. Some scopes are also starting to come with changable OTA sections to allow differing configurations to suit various tasks, pretyy good idea.

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I think that the solution for bino viewrs rather than cutting can be to use a barlow before the viewers, some come supplied with one too, now not all of them tell you this though.

However i feel that if your using bino viewers in a smaller refractor (quiet often the choice) barlowing it is not the general idea as your looking for widefield low mag views.

I hope you get it all sorted to your satisfaction.

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One aspect is that if you came to selling the scope later you would reduce the value.

For all I like refractors the mention that "We cut a chunk off it" would mean forget any deal/sale.

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I've just thought of another potential solution for my particular problem which is to file down another few mm of the bottom of the draw tube so that it goes slightly further into the focuser/OTA.

I only need about 3mm and more than that is available from the part of the tube that is left outside the focuser when it is all the way in so this might just be enough without the need for major surgery.

Thanks for your help. Much appreciated.

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One aspect is that if you came to selling the scope later you would reduce the value.

For all I like refractors the mention that "We cut a chunk off it" would mean forget any deal/sale.

Yes, that is ringing in my ears.

I might actually buy a second hand Evostar 120 Achro and do it to that rather than chopping up a scope I just paid £400 for :wink:

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Funny old world. If I bought a 2nd hand scope that had been shortened to accept a binoviewer with no focus issues I would see it as a + whereas many seem to see it as having been damaged.  :smiley:

It is a funny world in that respect Peter. Having been a "watcher" of the used astro market for many years I've noticed that modified scopes, even if nicely done, seem to take longer to sell and seem to command a lower price than bog standard ones.

I think there is a low profile Baader adapter for Synta scopes:

http://www.teleskop-express.de/shop/product_info.php/info/p3588_Baader-Adapter-from-M68-and-M60-to-2----length-only-12mm.html

It's compression ring rather than twist lock though. I guess the twist lock mechanism requires a certain length of barrel in order to function ?

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I have that low profile adapter, John, it arrived from 365Astronomy this morning :smile:

It is slightly slimmer than the ClickLock and a very solid piece of kit so I want to keep it but I still need to find a few mm more inward travel.

I think the safest option in terms of not damaging the scope or the value is to trim 3-5mm off the threaded end of the draw tube with a good quality hacksaw. If I mess that up I can easily replace the focuser without having damaged the scope.

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I dont know that scope bit with my old 130 I thought I only needed a big of inward focus and then took out the hacksaw and three jobs later I had to take that much off my rack and pinion was no more and had to manually push in and out to get focus. Just be very sure you dont need to take much off, I had to just buy a new scope mine was that bad.

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Sorry, should have been more specific - the EPs I cannot use in the current set-up are 13mm, 17mm & 21mm Ethos and 31mm Nagler. All of them seem to only need a few mm more :sad:

I should have read your kit list :)

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