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Delos 17.3---VERY Sad

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#51 ThreeD

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Posted 27 November 2012 - 01:38 AM

If it doesn't come to focus, it is not really an eyepiece. Swing and a miss from TV.

And as far as moving the mirror forward a tiny bit with collimation, 1. what does the scope's manufacturer say about that? 2. why should have screw around with that? Shouldn't the eyepiece work with commercially produced scopes as they are? I can see mickey mousing it with an eyepiece made from spare lenses you got from Surplus Shed or with a DIY scope, but not a "premium" "EP" on a Newt that works with ever other EP.

I've read of premium dob buyers cutting trusses to the proper length upon arrival of their scope. Loosening the collimation bolts a turn or two is nothing...

Are you sure the scope works with *every* other EP? Do you own every other EP and have you tried them all? I'm sure there are a few others out there that won't work in that scope too unless the mirror is moved forward -- and the numbers will be even larger if you want to use a barlow or a Paracorr as they both require more in-focus.

I know that to use my 31T5 Nagler with a Paracorr and have it achieve focus in my LB I need to make sure the mirror isn't pulled all the way back. I prefer to have my cell pulled back as it stiffens the cell and ensures it won't shift. However, I do need to run it relaxed just a bit to make that combination work. Luckily it's not enough to make it to where cell shift is a problem. Would you also claim that a Terminagler/Paracorr combination is a swing and a miss??
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#52 Stellarfire

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Posted 27 November 2012 - 02:30 AM

Just a reminder....TV website ep specs page gives fieldstop location referenced from the ep shoulder for all their current eps.

Use it and there will be no more surprises after ordering TV eps.

:cool:



Yes. By the way: According that TeleVue spec page, the new 14mm Delos will have the same field stop location like the 17.3mm Delos. All other Delos models are parfocal.

Stephan

#53 Sarkikos

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Posted 27 November 2012 - 07:16 AM

If there is not enough in-focus for an eyepiece, and you have an old-style tall focuser, you could upgrade to a low-profile. Or if you have a truss scope, you could shorten the trusses. Or you could raise the mirror in a tube scope. But then you might need to buy extensions for your other eyepieces...

Or you could return the eyepiece or sell it to someone else. Cut your losses, don't shorten the scope.

:grin:
Mike

#54 Jeff Morgan

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Posted 27 November 2012 - 10:01 AM

If it doesn't come to focus, it is not really an eyepiece. Swing and a miss from TV.

And as far as moving the mirror forward a tiny bit with collimation, 1. what does the scope's manufacturer say about that? 2. why should have screw around with that? Shouldn't the eyepiece work with commercially produced scopes as they are? I can see mickey mousing it with an eyepiece made from spare lenses you got from Surplus Shed or with a DIY scope, but not a "premium" "EP" on a Newt that works with ever other EP.


A relevant topic for me, since I just finished focus testing (trimming truss tubes) on my new project. Daylight focus on a distant hill works, star test is next.

Firstly, trimming tubes is not a big deal. Even if you have no tools a trip to the hardware store for a hacksaw, mitre box, and file will set you back about $25 and do an acceptable job. And if you have a table saw, it is a trivial job. I would prefer this solution over using the collimation screws or moving the mirror cell up the tube (for solid tube scopes).

A swing and a miss on the Delos 17.3 and 14? Hardly! They both appear to require just a bit less in-travel than the 31 Nagler, which is perhaps the most common maximum field sweepers you will find on Dobs today. If you can make the 31N focus, the 17.3/14 Delos should also focus.

As far as focus travel, most of us inflict that pain upon ourselves by selecting focusers with minimum travel distance. I just did it to myself also, buying a 1-1/2" travel focuser instead of the 2" travel I have used in previous builds. I can reach with the 31 Nagler and 14 Delos, and most of the rest of my eyepieces will reach focus within my focuser range, with one exception - the 48 Brandon. It requires an extension tube. Annoying, but not a show stopper. Had I chosen the 2" travel focuser, they would all reach with no extension tube but that is the nature of choices, no?

What would the manufacturer would say about moving the mirror forward? There is a reason those collimation screws are left that long ....

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#55 Sarkikos

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Posted 27 November 2012 - 10:12 AM

Firstly, trimming tubes is not a big deal. Even if you have no tools a trip to the hardware store for a hacksaw, mitre box, and file will set you back about $25 and do an acceptable job. And if you have a table saw, it is a trivial job. I would prefer this solution over using the collimation screws or moving the mirror cell up the tube (for solid tube scopes).


Trimming truss tubes should not be a problem. Resizing a solid tube - or moving a mirror up in tubes where the cell attaches directly to the tube end - can be a problem. Well, IS a problem for me with my lack of metal-working skills, metal-working equipment and the space for metal-working.

:grin:
Mike

#56 Starman1

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Posted 27 November 2012 - 10:43 AM

Jeff,

I seem to have an instinctive need to play with focus whenever I change eyepieces. Since I have a nice focuser, parfocal has never been an issue for me.


I agree. I never got this preoccupation with parfocality - is that a word? - in eyepieces. That factor flies well below my radar. I don't give a fig if my eyepieces are parfocal or not. I just don't get it. What's a focuser for?

On the other hand, it is not a good thing if an eyepiece needs more focus or less focus than my focuser will allow. I'd rather not deal with extensions and low-profile adapters.

Mike

One of the great things about the Paracorr, other than eliminating coma and flattening the field, is that it makes every eyepiece parfocal.
If one presets the Paracorr's tunable top before the next eyepiece is inserted, the amount of focuser travel to get to perfect focus is negligible.
All my eyepieces focus in +/- 1mm.
Or, one can insert the new eyepiece and focus using the tunable top.
Either way, each eyepiece will have its correct setting and the amount of focuser shift from one eyepiece to the next will be negligible.
The only reason it might not have been wise for me to use a focuser with <1/2" travel is that there may be accessories I don't yet have that wouldn't focus in that range. If I used binoviewers, for example, they are typically used without a Paracorr, and the focal position could be well away from where the Paracorr is positioned.

Oh, that and the Delos 17.3 and 14 require a little more in-travel of the Paracorr's tunable top than is allowed in the Paracorr design. There are a couple adapters that could work
to mitigate this.
However, this may not be enough in the Paracorr I. There, some experimentation would be necessary.
But, you'll be closer to parfocal than not using a Paracorr at all.

#57 dcoyle

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Posted 27 November 2012 - 10:54 AM

An OT moment, please.

Jeff, That is an amazing scope! What size and f/ is it?

Thanks,

Dan

#58 Scanning4Comets

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Posted 27 November 2012 - 10:57 AM

When I received my new crayford focuser I thought I needed an extension tube to reach focus for all of my eyepieces, but it turns out that the one I got can go outwards about another 1/4" so I was in business. Someone on here mentioned moving my mirror back a bit, so that helped as well.

I can now use ALL of my eyepieces without the extension tube and I was also awarded with another added bonus:

I can use my two extension tubes with filters attached to them, so when I need to use my 2" filters, I just plop the extension tube with Orion Ultrablock or 2" Polarizer, then add the eyepiece into the tube and I can still reach focus!

No more fumbling in the dark screwing filters onto eyepieces !!! I DESPISE doing that because half the time I try that, the threads don't catch or they will try to cross-thread. I have almost dropped the filters so many times when trying to screw them onto the barrels of my adapters.

I will never go back to screwing filters onto barrels ever again!

So, in relation to the original poster here, and others who think it is a bummer if you need to fiddle a bit in order to actually REACH FOCUS, consider yourselves lucky! Sometimes you can't get focus at all. A few twists of the collimation screws, or truss adjustments is half the fun in achieving focus sometimes!

:)

Cheers,

#59 Sarkikos

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Posted 27 November 2012 - 11:06 AM

Don,

One of the great things about the Paracorr, other than eliminating coma and flattening the field, is that it makes every eyepiece parfocal.
If one presets the Paracorr's tunable top before the next eyepiece is inserted, the amount of focuser travel to get to perfect focus is negligible.
All my eyepieces focus in +/- 1mm.
Or, one can insert the new eyepiece and focus using the tunable top.
Either way, each eyepiece will have its correct setting and the amount of focuser shift from one eyepiece to the next will be negligible.


I have not done this yet but it sounds like a worthy experiment for next New Moon at my dark site. So far, I haven't kept the Paracorr in the focuser consistently, but only use it now and then for specific eyepieces.

One problem that I've found when setting my Paracorr I for different eyepieces, is that the tuning knob sticks. Often I need to loosen both the tuning knob and the set screw that detains the 1.25" adapter in order to turn the tuning top. This is a PITA at a dark site.

Mike

#60 Sarkikos

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Posted 27 November 2012 - 11:33 AM

Mark,

I can use my two extension tubes with filters attached to them, so when I need to use my 2" filters, I just plop the extension tube with Orion Ultrablock or 2" Polarizer, then add the eyepiece into the tube and I can still reach focus!

No more fumbling in the dark screwing filters onto eyepieces !!! I DESPISE doing that because half the time I try that, the threads don't catch or they will try to cross-thread. I have almost dropped the filters so many times when trying to screw them onto the barrels of my adapters.

I will never go back to screwing filters onto barrels ever again!


Yep, I use that trick for 2" filters, too. It also allows you to keep the same filter on the scope and change eyepieces. A friend had a 2" filter wheel I thought about buying, but I thought again and decided not to. In a Dob, you'd probably need an OCA to come to focus, thereby halving the effective focal length of the eyepiece. That would ruin the whole idea of using low power eyepieces with a 2" filter. (The extra weight would also be a bear to deal with.)

But for medium-to-high power, a wheel for 1.25" filters is great. I have a wheel permanently loaded with DSO filters for trips to the dark site. Nothing like viewing M42 with a Baader Zoom on a filter wheel. You can immediately vary the image scale and the DSO filter as you wish.

That's one of the main reasons I don't have a Paracorr permanently installed in my focuser! :ubetcha:

:grin:
Mike

#61 Starman1

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Posted 27 November 2012 - 01:55 PM

Don,

One of the great things about the Paracorr, other than eliminating coma and flattening the field, is that it makes every eyepiece parfocal.
If one presets the Paracorr's tunable top before the next eyepiece is inserted, the amount of focuser travel to get to perfect focus is negligible.
All my eyepieces focus in +/- 1mm.
Or, one can insert the new eyepiece and focus using the tunable top.
Either way, each eyepiece will have its correct setting and the amount of focuser shift from one eyepiece to the next will be negligible.


I have not done this yet but it sounds like a worthy experiment for next New Moon at my dark site. So far, I haven't kept the Paracorr in the focuser consistently, but only use it now and then for specific eyepieces.

One problem that I've found when setting my Paracorr I for different eyepieces, is that the tuning knob sticks. Often I need to loosen both the tuning knob and the set screw that detains the 1.25" adapter in order to turn the tuning top. This is a PITA at a dark site.

Mike

There are 2 versions of the Paracorr 1 I see in the field: one has a thumbscrew you loosen and that is the only alignment screw between the tunable top and the Paracorr body. The newer version of the Paracorr 1 had 3 screws aligning the top to the body, and only one was loosened to turn the top. The second version is better able to hold its alignment and turn smoothly. The earlier version was sometimes difficult to turn with an eyepiece in place because the weight of the eyepiece could tilt the tunable top when the thumbscrew was loosened.
I got around that by simply supporting the weight of the eyepiece with my hand as I was turning the top and eyepiece together.
I can't think of why the setscrew in the adapter would have to be loosened, however. That's a mystery.

#62 Jeff Morgan

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Posted 27 November 2012 - 02:49 PM

An OT moment, please.

Jeff, That is an amazing scope! What size and f/ is it?

Thanks,

Dan


Thanks. The scope is obviously not complete, this photo was taken last week during focus testing. As you can see, I had quite a few tubes to trim :grin: But it does reach focus with the 31 Nagler and the 14 Delos. I start the ServoCAT install after lunch today and hope to have it operational by Thursday night. Finishing touches and debugging should take another month, but that can be accomplished between observing sessions.

The original concept was a 12.5" f/9 to replace a 12.5" f/6. I approached Carl Zambuto to do the mirror and he suggested that considering effort and investment I really should go up in aperture too. After some thought and reflection, I agreed. Based on cost, nightly temperature variation, and weight a 16" aperture was about the maximum I wanted. (Well, I want a 30" but we all know how that goes.) However the preliminary design on the 16" f/9 was rather ... intimidating.

Since 112" of focal length was about the most I was prepared to deal with, Viola! a 16" f/7.

#63 Sarkikos

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Posted 27 November 2012 - 04:43 PM

Don,

There are 2 versions of the Paracorr 1 I see in the field: one has a thumbscrew you loosen and that is the only alignment screw between the tunable top and the Paracorr body. The newer version of the Paracorr 1 had 3 screws aligning the top to the body, and only one was loosened to turn the top. The second version is better able to hold its alignment and turn smoothly. The earlier version was sometimes difficult to turn with an eyepiece in place because the weight of the eyepiece could tilt the tunable top when the thumbscrew was loosened.
I got around that by simply supporting the weight of the eyepiece with my hand as I was turning the top and eyepiece together.
I can't think of why the setscrew in the adapter would have to be loosened, however. That's a mystery.


My Paracorr has one thumbscrew in the tuning slot and one thumbscrew which secures the 2" eyepiece or 1.25" adapter inside the Paracorr. That's all. I know for a fact that if I only loosen the tuning slot thumbscrew, the tuning top will become tight and hang up about mid-range. This does not happen if an eyepiece or 1.25" adapter is not in the Paracorr.

However, if I also loosen the thumbscrew which secures the 2" eyepiece or 1.25" adapter, the tuning top can be turned easily. But then you have be aware that the eyepiece is not tightly secured in the Paracorr.

Other than this, the Paracorr works beautifully. But it definitely gets too tight to turn - or turns only with difficulty - if only the tuning slot thumbscrew is loosened. The thumbscrew which secures the eyepiece also needs to be loosened a little. I have no idea why. That's just the way it is.

Mike

#64 csrlice12

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Posted 27 November 2012 - 04:53 PM

My 13mmT1 had the opposite Problem. Too little outfocus unless i use the 1.25" adapter. Kind of scary holding that eyepiece with a single set screw on the end of the 1.25" barrel. But, it did work. putting it all the way in with the 2" barrel, I could not come to focus. I did later discover that if I put the "notch" in the 2" eyepiece where one of the two 2" focuser set screws are, it will "rest" on the set screw; and I tighten the other set screw and I can bring it into focus, but it is still at almost the max outfocus.

#65 Starman1

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Posted 27 November 2012 - 06:45 PM

Don,

There are 2 versions of the Paracorr 1 I see in the field: one has a thumbscrew you loosen and that is the only alignment screw between the tunable top and the Paracorr body. The newer version of the Paracorr 1 had 3 screws aligning the top to the body, and only one was loosened to turn the top. The second version is better able to hold its alignment and turn smoothly. The earlier version was sometimes difficult to turn with an eyepiece in place because the weight of the eyepiece could tilt the tunable top when the thumbscrew was loosened.
I got around that by simply supporting the weight of the eyepiece with my hand as I was turning the top and eyepiece together.
I can't think of why the setscrew in the adapter would have to be loosened, however. That's a mystery.


My Paracorr has one thumbscrew in the tuning slot and one thumbscrew which secures the 2" eyepiece or 1.25" adapter inside the Paracorr. That's all. I know for a fact that if I only loosen the tuning slot thumbscrew, the tuning top will become tight and hang up about mid-range. This does not happen if an eyepiece or 1.25" adapter is not in the Paracorr.

However, if I also loosen the thumbscrew which secures the 2" eyepiece or 1.25" adapter, the tuning top can be turned easily. But then you have be aware that the eyepiece is not tightly secured in the Paracorr.

Other than this, the Paracorr works beautifully. But it definitely gets too tight to turn - or turns only with difficulty - if only the tuning slot thumbscrew is loosened. The thumbscrew which secures the eyepiece also needs to be loosened a little. I have no idea why. That's just the way it is.

Mike

You have the original version, and the adapter tilts slightly when the tunable top thumb screw is loosened. That's why you have to loosen the adapter's set screw. It has to be able to "float" in the tunable top, which is now slightly off angle.
I would suggest you adjust the tunable top before you put the eyepiece into the Paracorr. I couldn't remember the settings for every eyepiece and didn't want to have a crib sheet by the scope (back when I had a hundred eyepieces), so I put a label-maker label on the side of each eyepiece with the correct setting for that eyepiece (which I had determined by focusing with the tunable top earlier) so I wouldn't have to remember at all.

#66 Starman1

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Posted 27 November 2012 - 06:49 PM

I had first light with my D17.3 tonight in my 8" F6 dob. To my great disappointment, it would NOT come to focus; I needed a mm or so more infocus I did not have. The D6 and 10 are close to parfocal and work fine in my little dob. Am I the only one who did not realize that the D17 was not even close to the other Deloi?

Gordon

There are other 1.25" eyepieces (like the Parks Gold Series 35) that require even MORE inward focuser movement. The answer is a thinner 1.25" adapter if you have a 2" focuser.
But if you have a 1.25" focuser, the answer is a little more complicated and either involves installing a lower-profile focuser or moving the primary mirror upward. Just about any solution will involve a slight change of balance in your scope.

#67 Starman1

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Posted 27 November 2012 - 06:53 PM

My 13mmT1 had the opposite Problem. Too little outfocus unless i use the 1.25" adapter. Kind of scary holding that eyepiece with a single set screw on the end of the 1.25" barrel. But, it did work. putting it all the way in with the 2" barrel, I could not come to focus. I did later discover that if I put the "notch" in the 2" eyepiece where one of the two 2" focuser set screws are, it will "rest" on the set screw; and I tighten the other set screw and I can bring it into focus, but it is still at almost the max outfocus.

When using a skirted 1.25"/2" eyepiece, that's how you're supposed to do it: the 1.25" adapter's thumbscrew fits in the slot in the 2" skirt and the screw on the 2" skirt tightens down on the adapter from outside the 2" barrel. Plenty of support that way.
You can tighten both screws, actually, making the fit quite solid.

#68 Sarkikos

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Posted 27 November 2012 - 08:48 PM

Don,

You have the original version, and the adapter tilts slightly when the tunable top thumb screw is loosened. That's why you have to loosen the adapter's set screw. It has to be able to "float" in the tunable top, which is now slightly off angle.


Just this evening I've solved this problem (= Televue design defect) for the most part by taking the tunable top off and carefully rubbing Super Lube on the opposing surfaces. Now the tunable top turns much more smoothly without having to loosen the set screw that secures the adapter/eyepiece. It also helps to pull up a bit on the tunable top as I turn it.

I would suggest you adjust the tunable top before you put the eyepiece into the Paracorr.


That would defeat the purpose of setting each eyepiece on-the-fly by using the tunable top to focus, as you were suggesting.

I couldn't remember the settings for every eyepiece and didn't want to have a crib sheet by the scope (back when I had a hundred eyepieces), so I put a label-maker label on the side of each eyepiece with the correct setting for that eyepiece (which I had determined by focusing with the tunable top earlier) so I wouldn't have to remember at all.


I hardly ever use the Paracorr at home. Here I usually have a binoviewer in the focuser instead. When I go to my dark site, I take along "only" about 30 eyepieces. I have the Paracorr settings for them on a cheat sheet, which I look at when I need to.

I never put any labels on my eyepieces. My sites tend to very dewy, and I don't want any labels sliding off and onto optical surfaces! Whenever I buy eyepieces, the first thing I do is take off all those "helpful" labels that previous owners have put on. I do put labels on filter cases, though.

:grin:
Mike

#69 sixela

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Posted 28 November 2012 - 05:05 AM

Thus creating a need for the Paracorr Type 3 that will be announced at NEAF much to the chagrin of those who invested in the Type 2 over the last year. :foreheadslap:


New 'enhanced' 2"-1.25" adapter:
http://www.sciencece...s/html/7396.htm

Been using it for years in similar situations.

Although in this case I'd possibly prefer to use this from Baader and turn the 17.3mm Delos into a 2" eyepiece:

http://www.teleskop-...info/p767_Ba...

You can remove the long set screw and use the recessed set screw (and a small hex wrench) instead. The length of the adapter is then just 1mm.

#70 Mirzam

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Posted 28 November 2012 - 08:17 AM

I have recent experience with the Astrosystems negative adapter and can offer a few observations.

1. The adapter has an internal compression ring rather than a bare set screw. This holds tall eyepieces like the D17.4 more securely. Not all negative adapters have this.

2. The D17.4 DOES fit into the recessed hole in the astrosystems adapter. My Pentax XWs also fit.

3. My version of the adapter seems to have a bit longer snout (50 mm) than the one shown in the earlier link. I bought mine from OPT a couple weeks ago. This is an issue for using the adapter in a Paracorr in that the adapter may not seat all the way into the Paracorr (it depends on the Paracorr setting if the tunable top is all the way out then it's okay).

I trimmed 3/8" off of the end of my adapter to allow it to seat all the way in. This is easily done with a hacksaw.

JimC

#71 Starman1

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Posted 28 November 2012 - 10:11 AM

Thus creating a need for the Paracorr Type 3 that will be announced at NEAF much to the chagrin of those who invested in the Type 2 over the last year. :foreheadslap:


New 'enhanced' 2"-1.25" adapter:
http://www.sciencece...s/html/7396.htm

Been using it for years in similar situations.

Although in this case I'd possibly prefer to use this from Baader and turn the 17.3mm Delos into a 2" eyepiece:

http://www.teleskop-...info/p767_Ba...

You can remove the long set screw and use the recessed set screw (and a small hex wrench) instead. The length of the adapter is then just 1mm.

TeleVue has designed an adapter for the 17.3 and 14 Delos that makes them parfocal in the Paracorr with all the other Delos eyepieces (which use the standard Paracorr adapter) and nearly all their 1.25" eyepieces. It might not make it into production unless we push them to do so (I gave a nudge), but it would end the discussion except for those scopes with 1.25" focusers with insufficient in-travel.
Alexis' 2nd link comes close, but to make the 17.3/14 Delos parfocal in the Paracorr, the adapter has to have a negative height, like the GSO or Astrosystems adapters.

#72 Starman1

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Posted 28 November 2012 - 10:13 AM

I have recent experience with the Astrosystems negative adapter and can offer a few observations.

1. The adapter has an internal compression ring rather than a bare set screw. This holds tall eyepieces like the D17.4 more securely. Not all negative adapters have this.

2. The D17.4 DOES fit into the recessed hole in the astrosystems adapter. My Pentax XWs also fit.

3. My version of the adapter seems to have a bit longer snout (50 mm) than the one shown in the earlier link. I bought mine from OPT a couple weeks ago. This is an issue for using the adapter in a Paracorr in that the adapter may not seat all the way into the Paracorr (it depends on the Paracorr setting if the tunable top is all the way out then it's okay).

I trimmed 3/8" off of the end of my adapter to allow it to seat all the way in. This is easily done with a hacksaw.

JimC

When the adapter is trimmed, does the setting selected come close to other 1.25" eyepieces?

#73 Mirzam

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Posted 28 November 2012 - 10:18 AM

It works fine now at the middle setting of the tunable top, which is where I usually leave the Paracorr.

There was a link way up the thread though that showed an Astrosystems adapter that looked shorter than mine. So maybe there is another version that does not need to be trimmed.

JimC

#74 Mirzam

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Posted 28 November 2012 - 10:27 AM

Looking at the Paracorr settings guide it appears that the lowest setting is recommended for the Delo 17.4. In any case, I've been using mine at the middle setting without obvious problems.

This makes sense I guess since the adapter recesses the eyepiece, much like having the Paracorr at a low setting.
JimC

#75 dcoyle

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Posted 28 November 2012 - 10:37 AM

When I ordered an astrosystems negative adapter, they informed me that the tall adapter was the old style and that they were now producing the short adapter.

Dan






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