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AT72EDII threads etc...

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#1 bridgman

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Posted 14 March 2019 - 01:41 PM

User desertlens made a really helpful post recently talking about (among other things) focuser drawtube threads. My new AT72EDII just arrived (grin.gif) and I haven't seen much other information about threads, bolt sizes etc... for the scope so thought I would do a quick data dump here in case it helps others. Usual disclaimer - the information below is what I measured off a newly ordered sample, so older/newer scopes may be different.

 

Threaded holes on bottom of ring - 1xM6 centered, plus 2x unknown (smaller) 1/2" from center hole in each direction. I believe rail is attached with M6x16 bolts (not measured yet but they were just a bit shorter than M6x20) but I was able to attach new Vixen rail with M6x20 leaving ~1/8" to scope tube

 

Threaded hole on top of ring - 1xM6, no other holes. Flat area on top ring seems to be closer to scope tube than on bottom ring. I was able to mount original rail on top of rings (for future guide scope) using original screws, left ~1/8" to scope tube.

 

Focuser drawtube to rotator - M63, rotator male, drawtube female.

 

Rotator to 2" eyepiece holder - M54, rotator female / eyepiece holder male (found this interesting because reducer/flattener for SV70T seems to have M54 male on telescope end)


Edited by bridgman, 14 March 2019 - 01:42 PM.


#2 bridgman

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Posted 15 March 2019 - 02:54 PM

Update re: focuser - the red ring at the camera end of the focuser is actually two rings, one slightly wider than the other. Same orientation as the other threads - telescope end of each ring has male threads, camera end has female threads. Looks to be 68mm thread although I forgot to check thread pitch.

 

I was hoping it might turn out to be M63 like the back of the drawtube but it's definitely bigger - the threads on the small red ring are too big to engage the M63 thread at the back of the drawtube.



#3 Taylor

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Posted 16 March 2019 - 12:03 AM

This rotolock adapter that is M63 is directly screwed onto the rear of my AT72EDII draw tube.

 

https://agenaastro.c...t71-silver.html

 

Mine is the red version though, I bought the last one I could fine online from a Canadian dealer. I think WO stopped making the red ones. 

 

Love it. 


Edited by Taylor, 16 March 2019 - 12:04 AM.


#4 bridgman

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Posted 17 March 2019 - 04:53 PM

Thanks... I really do like Rotolocks and that seems like a great upgrade. There do seem to be a couple of red ones still available at Canadian dealers and I'm trying really hard not to buy one.

 

I figured that upgrading the visual back on the AT72 (which at least had a compression ring) didn't make sense while I still had a thumbscrew-only visual back on my old AT1010... so your post did lead to me ordering a similar Baader click-lock adapter for the Stellarvue. I had to guess at thread though... the thread at the end of an AT1010 focuser drawtube does not appear to be documented anywhere in the entire internet.

 

The great news is that upgrading the AT1010 allows me to go ahead with ordering a rotolock for the AT72 now. Nagging question remaining though is whether to get an M54 or M63 for the 72. If I go with an M63 I know now that it will fit the drawtube, but an M54 should fit the rotator which would be useful for imaging. Hmm...

 

EDIT - just answered my own question... if I upgrade to a rotolock it has to be the M63... 'cause if I kept the red focuser (M54) then I would have too much red back there smile.gif


Edited by bridgman, 17 March 2019 - 05:25 PM.


#5 bridgman

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Posted 21 March 2019 - 12:43 PM

This is the right amount of red IMO laugh.gif

 

IMG 20190321 132001

Edited by bridgman, 21 March 2019 - 12:43 PM.

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#6 bridgman

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Posted 03 April 2020 - 11:39 PM

One minor update - I got bored waiting for the rain to stop so checked to see if the threads on the back of my new AT115EDT (2020) were the same as the AT72EDII, since they looked pretty similar.

 

Confirmed that both the rotator and the visual back are independently interchangeable between the two scopes.

 

That tells me that an M54-threaded AT2FF flattener would be a wonderful addition to the AstroTech lineup, since it would thread into and work well with quite a few of their scopes AFAICS.


Edited by bridgman, 04 April 2020 - 05:55 PM.


#7 bridgman

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Posted 04 April 2020 - 05:56 PM

Found some more interesting info:

 

#1 - Apparently the AT2FF nosepiece unscrews via an M48 thread, so it's probably possible to just change the nosepiece to one with M54 male threads at the back of the 2" nosepiece, similar to what is being supplied with the AT72 and AT115 dedicated reducer/flatteners. In the meantime an M63 to M48 adapter would let you thread the AT2FF into the focuser drawtube, although you would lose the rotator:


https://www.cloudyni...at92/?p=9184335

 

#2 - since there is also an M48 female thread in the front of the AT2FF nosepiece (for filters) the same adapter should thread into the front of the nosepiece as well (further down the above thread)


#3 - in an earlier post in the same thread Michael mentioned that they would try to look into a threaded version of the AT2FF - that would be ideal but even a "buy an M54-threaded nosepiece" option would be great as well

 

#4 - Seems that there are M54-to-M48 adapters available as well (Agena) but both M54x1 and M54x0.75 are available - will need to figure out which pitch the AT scopes use at the back of the rotator. The M54x0.75 seems most likely - I did a rough check using M63x1 and M48x0.75 threads for comparison.

 

https://agenaastro.c...apter-m-03.html

 

My AT2FF is still on back-order anyways - but this means I can stop agonizing over whether I should have ordered a different flattener to get threads. Woot !!

 

I picked up a local (Starfield) 0.8x reducer/flattener last year so I could start imaging while waiting for the AT2FF - if I can figure out which thread pitch I might order an M54-to-M48 adapter and start by threading it into the front of the reducer/flattener nosepiece, but will need to confirm that the rig would be able to reach focus with the added length. It looks like the Starfield nosepiece might unscrew but I wasn't able to move it by hand.


Edited by bridgman, 04 April 2020 - 06:32 PM.


#8 bridgman

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Posted 06 April 2020 - 06:53 PM

I picked up a local (Starfield) 0.8x reducer/flattener last year so I could start imaging while waiting for the AT2FF - if I can figure out which thread pitch I might order an M54-to-M48 adapter and start by threading it into the front of the reducer/flattener nosepiece, but will need to confirm that the rig would be able to reach focus with the added length. It looks like the Starfield nosepiece might unscrew but I wasn't able to move it by hand.

Hmm... unless I can get the nosepiece off the Starfield reducer (and be sure the nosepiece still comes off the AT2FF) things look a bit iffy for a short term threaded solution.

 

I set up the AT72EDII + reducer + camera and checked where the focuser was when focusing at infinity-ish - infinity is hard because it's always cloudy/foggy so the best thing I have right now is distant trees. Focuser reading was just under 25mm.

 

The flattener nosepiece length (in case I have to thread into front of nosepiece) minus visual back depth (adapter will thread into focuser after removing visual back) is just over 20mm and the optical length of the M54 to M48 adapter is 4.9mm so might work, might not. It leaves me roughly zero extra in-focus to cover the difference between infinity-ish and infinity.

 

Using the SV M63 to M48 adapter (going into drawtube rather than rotator) should work with a bit of room to spare, but that means no rotator, and adding an M63-to-M63 rotator would cost at least as much space as the M63-M54 rotator that comes with the scope. 

 

I hate it when a plan doesn't quite come together. Might order the adapter anyways and hope that either the Starfield nosepiece comes off or the latest AT2FF nosepiece still comes off. Maybe next step should be seeing how much focus I have left on the AT115EDT... the focuser seems to come out about a foot on that one.

 

https://agenaastro.c...dapter-m09.html

 

EDIT - I did a quick test with camera + reducer in the AT115EDT visual back, but by the time I remembered to take off the lens cap I had lost most of the light. Focuser seemed to be out past 30mm anyways (vs 25mm on the AT72EDII) which is enough of a margin to make me feel OK about ordering the adapter.

 

EDIT 2 - ordered, along with a Baader T-ring which will hopefully eliminate the slop with my current (Celestron) T-ring. The bayonet lugs are a bit too short in the current ring so scope+ring can rotate back and forth a bit in the camera's mount. It's probably going to be a month or so before it arrives but will update when it does.

 

In the meantime I guess I can try to find some strap wrenches to see if the nosepiece on my current reducer/flattener really does come off. Vice grips seem a bit too aggressive.

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Edited by bridgman, 06 April 2020 - 09:17 PM.

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#9 Toddeo

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Posted 06 April 2020 - 07:28 PM

I have the Astro-Tech AT2FF. It has the 2" nose piece with a safety undercut- I can't see where you can unscrew the nosepiece?



#10 bridgman

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Posted 06 April 2020 - 07:48 PM

I read about it in the following thread... seemed to work for a couple of different people (it's a long thread):

 

https://www.cloudyni...38#entry9184335

 

My understanding is that the nosepiece has an M48x0.75 thread which goes into a standard filter thread in the front of the flattener body. That suggests you would not see a line on the nosepiece itself but around the outside where it joins up with the flattener body.

 

Another poster referred to the AT2FF nosepiece as an M48x0.75 extension tube, which makes sense because it has M48 female filter thread on the front.

 

Post #927 in the same thread (near top of page) has a picture of another reducer/flattener (which looks just like mine) with the two parts separated. I looked at it again then made another attempt to separate the parts on my reducer/flattener (a Starfield) with no success. I imagine it takes some gentle encouragement with strap wrenches or similar.

 

We should probably both check with Astronomics - I say both because your AT2FF is probably from a different batch than mine, since you have yours and I do not :)


Edited by bridgman, 06 April 2020 - 07:58 PM.


#11 bridgman

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Posted 07 April 2020 - 10:27 PM

Hmm, good news / bad news.

 

The good news is that I just remembered the focuser has an M68 thread followed by a reducer to M54. If I could add an M68 to M48 adapter that would save me a few mm, just enough to make the worst case scenario above work. The bad news is that I'm seeing first hints that the M54 thread may be 0.75mm pitch rather than the 1mm I ordered. It didn't look like 0.75mm under the light though.

 

Both the reminder and the suggestion about M54x0.75 came from the similar looking TSOptics rotator / visual back specs:

 

https://www.teleskop...M54-and-2-.html

 

Here is the M68-to-M48 adapter I first looked at:

 

https://www.teleskop...-engewinde.html

 

Hopefully I guessed right and the M54x1 adapter will fit the rotator. If it does, and if I can get the nosepieces off on my current reducer and the AT2FF then that's it. Either way, it looks like the M68 adapter should be a good fallback.

 

EDIT - so much for "hopefully"... I played with some more filters and confirmed that the M54 thread really looks more like 0.75mm than 1mm pitch. That means the TS rotator spec above also seems applicable to the AT rotator, and also means I should have ordered the M-03 adapter rather than the M-09 I linked to above.

 

https://agenaastro.c...apter-m-03.html

 

It's probably too late to catch the order at Agena but I emailed them just in case and asked if they could change it. EDIT - nope, shipped yesterday morning.

 

Separately, I found a shorter version of the M68x1 to M48x0.75 adapter which also included filter threads on the front (so there's some way to get a 2" filter into the imaging train) and ordered that as backup. I already have two AT scopes with the 2.5" focuser/rotator and who knows where that will end ?

 

https://www.teleskop...ort-design.html

 

In hindsight the WO Z73a flattener is looking pretty good but I sure had fun and learned a lot by going this route and I can use the adapters to get all the same benefits from my 0.8x reducer while I wait.

 

That said, just adding a ring of M54 threads to the back of the AT2FF nosepiece would give a very elegant solution with both 2" and threaded options, although with a bit of luck the M54- or M68-to-M48 adapters will also work out. I believe AT has a similar nosepiece on some of their reducer/flatteners already.


Edited by bridgman, 08 April 2020 - 12:18 PM.


#12 bridgman

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Posted 09 April 2020 - 10:59 PM

A couple more updates, one going right back to the start of the thread.

 

#1 - conflict between wanting to add a Rotolock to the AT72EDII and concern about "having too much red" (first world problems, huh ?)

 

Resolved this by realizing that a gold Rotolock would more-or-less match the fine-focus knob on the AT115EDT and ordering a Rotolock for that scope instead. That works since the AT72EDII was intended primarily as an imaging scope, with visual use (travel) secondary.

 

After making the decision, I had a belated "D'oh !!"  moment when I realized that if I had ordered a red Rotolock for AT72EDII there would not have been a "too much red" problem anyways because the red rings at the end of the focuser tube are part of the rotator, and that you have to remove the rotator in order to add an M63 Rotolock anyways. Sigh... World 1 Brain 0... again.

 

#2 - at the same time I was ordering the Rotolock, I noticed that the vendor also had a couple of Flat73a's in stock. I weakened and ordered one of those as well. I'm going to keep the AT2FF order open anyways... seems like it is a really versatile flattener and will end up being useful on other scopes as well. Besides, if I have two I can race them :D

 

#3 - the Flat73a needs a 48mm T-ring, and none were available locally. I found one in stock at Agena, so ordered it there along with the M54x0.75mm adapter I should have ordered previously. Also added a couple of short (3mm, 6mm) T-thread spacers so I can experiment with backfocus on the AT2FF when it comes in, and the 0.8 reducer/flattener I have already.

 

Here's where it gets a bit funny. On the first Agena buy I ordered the M54-to-M48 adapter along with a Baader T-ring (42mm) to use with my existing reducer/flattener and the AT2FF since the Celestron T-ring I had was loose in the camera bayonet mount (lugs too narrow ?). Agena noticed that I was ordering an M48 male thread and M42 female thread, put the order on hold, and emailed me to check if this was going to be a problem.

 

Just as I was about to hit "Buy" on this order I noticed that I was doing it again only the other way round - M42 T-thread spacers plus an M48 T-ring - so I added a "yeah I know these don't fit together" note.

 

>Both the reminder and the suggestion about M54x0.75 came from the similar looking TSOptics rotator / visual back specs:

 

EDIT - going back to M54x1 vs M54x0.75, I noticed that SV also sells a similar looking rotator/visual back combination, and it also has an M54x0.75mm thread at the back of the rotator, so it seems pretty likely that 0.75 is the way to go. I'll update again when the adapters start arriving (probably a month).


Edited by bridgman, 10 April 2020 - 02:07 PM.


#13 bridgman

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Posted 14 April 2020 - 12:12 PM

Huh... it worked.

 

First to arrive was the M68x1 to M48x0.75 adapter from TS. I noticed that the two red rings on the AT72EDII were getting stuck together a lot, so I hit the threads with a bit of beeswax as a first step.

 

Removed the second red ring and the visual back, leaving just the rotator and its M68 thread on the drawtube. The adapter threaded cleanly into the rotator; a bit less cleanly into the reducer/flattener but that's not a surprise since AFAICS no two M48x0.75 filter threads are alike. The reducer threaded on about 1-1/2 turns, which is less than I would like, but enough for an initial fitting.

 

The important thing to me was that the resulting rig seemed to focus as close to infinity as I could find out the back door, with a comfortable bit of in-focus (10-12mm) left over. I'll confirm that it really focuses to infinity if the clouds ever go away. Assuming it does, it's nice to know that we now have a threaded solution for reducers and flatteners even with generic products like the AT2FF and the 0.8x reducer in this photo.

 

The M54 adapters are probably still a couple of weeks away (mail vs courier), will see if we can still get infinity focus with that approach when they arrive. As long as the AT2FF nosepiece still unscrews then there's no concern about achieving focus even with M54; it's only when you thread into the end of the nosepiece that in-focus gets tight.

 

EDIT - hold on, we have a problem. Getting the M68 adapter *out* of the rotator is proving difficult, primarily since there is nowhere to hold onto it without damaging a thread. If I had something with a male M48x0.75 thread that was longer than a filter housing I could probably just thread it into the other side of the adapter (it's threaded for filters) since (assuming I'm thinking straight) tightening from the telescope side would unscrew the threads rather than tighten them. Good news is that I have at least one such thing on order (the Flat73a); bad news is that it's not here yet.

 

Guess I'll just quietly put it back together for now and hope everything works out.

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Edited by bridgman, 15 April 2020 - 11:24 AM.


#14 bridgman

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Posted 15 April 2020 - 11:26 AM

OK, guess I got lucky. I spent part of the night dreaming about different ways I could remove the adapter - mostly pincer-type pliers or clamps, or drilling a couple of holes so I could use a pin wrench to unscrew it. Yeah I have strange dreams smile.gif

 

Was tinkering with it a bit this morning looking to see how much room I had to grab the flat part of the adapter and noticed that this morning the reducer was able to thread on a bit further (2 full turns now). Tightened up the reducer on the adapter then tried gently unscrewing with a bit of wiggle, and sure enough the adapter threaded out of the focuser. I re-installed the visual back with the reducer nosepiece inserted and checked focus... looks like ~26mm on the tube markings with the reducer inserted into the visual back vs ~14mm with the reducer nosepiece threaded into the M68 adapter.

 

Not sure what I can do to prevent it sticking in the future, but will try a bit of beeswax where the flat surface of the adapter butts up against the corresponding surface in the focuser ring. I'm guessing at beeswax because I have seen a few suggestions re: candle wax - is there anything better for avoiding sticking on adapter threads ?


Edited by bridgman, 15 April 2020 - 11:27 AM.


#15 bridgman

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Posted 21 April 2020 - 07:53 PM

So the Flat73a showed up today... something to tinker with smile.gif

 

First interesting discovery is that the front part of the Flat73a is the same M63/M68/M54 rotator/adapter combination that the AT72EDII uses, only in black like the AT115EDT rather than black/red like the AT72EDII.

 

The main body of the Flat73a has M54x0.75 threads on the front, so you could thread just the main body of the flattener into the rotator/adapter of the AT72EDII if you wanted. That said, it's quicker and easier to unscrew the rotator/adapter/VB set from the AT72EDII and thread in the rotator/flattener Flat73a, and the M63x1 thread on the front of the rotator is easier to get started than the M54x0.75 thread you get by separating the Flat73a into two parts.

 

If you wanted to be paranoid about protecting threads you could unscrew everything at the M68x1 point between the rotator and adapter and have sacrificial HW protecting both the flattener and the focuser drawtube, but hey, who worries enough to think about things like that ?

 

Anyways, first pic is Flat73a main body (minus rotator/adapter) threaded into AT72EDII rotator/adapter (M54x0.75); second pic is stock Flat73a threaded into AT72EDII focuser drawtube (M63x1).

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Edited by bridgman, 21 April 2020 - 10:50 PM.

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#16 bridgman

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Posted 23 April 2020 - 06:59 PM

A box arrived today with a Blue Fireball M-03 adapter (M54x0.75 male to M48x0.75 male) among other adapter goodies.

 

The adapter threads cleanly into the M54x0.75 female thread at the camera end of the M63/M68/M54 rotator/adapter combo, ie into the second red ring. The M-09 adapter (M54x1) I ordered first has not arrived yet but when it does it is not going to work.

 

On the reducer/flattener side, it only screws in a couple of turns just like the M68 adapter I tested a few days ago. Looks like there might be a wonky thread in the front of the reducer/flattener nosepiece, although you would never notice it when only threading in filters. Anyways, a couple of turns seems to be enough for a solid connection.

 

Downsides of this approach are:

 

#1 - you lose the ability to thread a 2" filter into the front of the reducer/flattener, although since I am mostly using clip-in filters at the moment that is not a big issue and the M68 adapter tried previously did include filter threads

 

#2 - in-focus is *very* tight, seems like only a couple of millimeters when focused on "as close to infinity as I can get in a back yard with perpetually cloudy nights"... probably OK but the M68 option gave a lot more margin while still keeping the rotator in the path. The M63-M48 adapter from Stellarvue gives the most in-focus margin, but you lose the rotator

 

As long as the AT2FF nosepiece is still removable on future shipments then the in-focus issue is not a problem there. It's not clear if the nosepiece is removable on my Starfield reducer/flattener.

 

It's worth mentioning that this is a total non-issue for the new AstroTech reducer/flattener (ATRF72) from Astronomics since that is fully threaded from the start... only an issue for generic units like the AT2FF and ATR8, or my Starfield reducer/flattener. The ATRF72 also offers a 48mm T-thread on the back (like the Flat73a) rather than 42mm T which is an added bonus.

 

Anyways, in the same box was a WO 48mm T-ring for the Flat73a, so I set that up as well. The WO T-ring fits much more snugly into the T3i lens mount, with only a tiny bit of play and much more "friction" keeping movement from happening. With the inexpensive Celestron T2 ring the camera would almost rattle back and forth but you have to work hard to find any play with this T-ring.

 

The last thing in the box was a couple of T2 spacers - 3mm and 6mm. I suspect that I will get best results from the Starfield reducer/flattener plus AT72EDII with a bit of additional spacing between R/F and sensor but won't know without some testing.

 

First pic - Starfield reducer/flattener with Blue Fireball M-03 adapter threaded into M54x0.75 thread at back of rotator/adapter - very tight for focus. Compare with pic in post #13 using M68x1 adapter.

 

Second pic - Flat73a threaded into M63x1 thread at back of focuser drawtube - no nosepiece so focuser tube needs to be racked much further out

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Edited by bridgman, 23 April 2020 - 09:38 PM.


#17 okietwisterdan

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Posted 26 April 2020 - 06:54 PM

I have a question about the AT115EDT. My QHY183m will not come to focus even with the drawtube extended fully out. So I want to extend the 2 inch compression ring out further. So would I need an M54 .75 female to M54 .75 male extender?



#18 bridgman

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Posted 26 April 2020 - 07:12 PM

I have a question about the AT115EDT. My QHY183m will not come to focus even with the drawtube extended fully out. So I want to extend the 2 inch compression ring out further. So would I need an M54 .75 female to M54 .75 male extender?

Correct.

 

If you have trouble finding a suitable M54x0.75 extension (the longest I found in stock was the 8mm S-3E from Agena) then you could also use M63x1 or M68x1, inserting them either ahead of the rotator or between rotator and M68/M63 adapter respectively. That said, I didn't see much in the way of M68 or M63 extension tubes either.

 

How far do you need to extend in order to get focus ?

 

If the nosepiece of your camera uses M42x0.75 threads to attach to the camera another option would be to use M42x0.75 extension tubes, which are readily available.


Edited by bridgman, 26 April 2020 - 07:13 PM.


#19 okietwisterdan

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Posted 26 April 2020 - 07:21 PM

20mm would be good. My back focus to my flattener is correct, which is why I need more extension on the telescope side of the flattener. I could extend the two inch flattener tube, but I don't want to put more weight on the compression ring and create a tilt on the camera train.



#20 bridgman

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Posted 26 April 2020 - 07:45 PM

Ahh, sorry... didn't realize you had a flattener in the train. The lower case "atredt15" fooled me and I missed it... definitely ignore the M42 extensions then.

 

If you are not using the M48x0.75 threads at the front of the nosepiece for a filter then another easy option would be an M48x0.75 adapter to M54 or M68 and using the flattener nosepiece as an extension tube as in posts #16 and #13 respectively.

 

Hold on... at the risk of asking a dumb question, if you are using an ATREDT15 then it already has M54x0.75 threads at the back of the nosepiece, so presumably you could combine those with an M54 extension tube ? Or is the problem that the ID of an M54 extension tube is too small for the nosepiece ? If so then you could use an M63 or M68 extension tube.

 

https://agenaastro.c...20-2458202.html

 

If you are using the compression ring and nosepiece for ease of visual/imaging rather than removing the compression ring the M68 extension above should work both ways:

 

#1 - focuser drawtube -> M63 front of rotator -> M68 rear of rotator -> M68 extension -> M68 to M54 adapter -> M54 compression ring -> 2" nosepiece on flattener

 

#2 - focuser drawtube -> M63 front of rotator -> M68 rear of rotator -> M68 extension -> M68 to M54 adapter -> M54 thread at rear of nosepiece on flattener

 

I guess using the second option would require an additional ~15mm of extension tube... I guess maybe you're using the compression ring to get extra distance ?

 

Anyways, I'll shut up and listen some more laugh.gif


Edited by bridgman, 26 April 2020 - 08:03 PM.


#21 okietwisterdan

okietwisterdan

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Posted 27 April 2020 - 11:22 AM

Sorry, I should have explained better, while I do sometimes use the atred15, I have a no name nonreducing flattener as well. I believe it could be an older Explore Scientific FF, which are oddballs because the back focus on these older ones is supposedly 45mm not 55mm. I think this may be causing my focal point to be beyond the normal drawtube range.




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