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ETX125 and 2" accessories

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#1 Escher

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Posted 25 June 2012 - 09:19 AM

Just wondering - can the drive base in the 125 tolerate a 2" diagonal and large 2" E.P.?

Just curious if I could use my larger EP's and diagonal from my 7"... But I assume the drive would be sorely inadequate... correct?

#2 Mike Cook

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Posted 25 June 2012 - 09:41 AM

It probably depends on the total weight of the EP and diagonal. The ETX is really nose heavy by default, so that may help counter the weight in the back. If it feels too heavy and the clutch has a hard time holding it without excess force, it probably is too much. Another issue is hitting the base when slewing up to zenith.

#3 *skyguy*

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Posted 25 June 2012 - 10:00 AM

Another possible issue ... the camera port is only press-fitted into the rear of the scope. Who knows how much weight it can hold until it "pops" out! However ... I have attached my 2" diagonal with 2" eyepieces to the rear of my ETX-125 without any problems. I was even able to increase my maximum FOV from .9 degrees to 1.25 degrees.

#4 Escher

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Posted 25 June 2012 - 10:09 AM

Interesting.... I'm planning to pick up a 125 soon as a travel scope and will have to give this a try...

That camera port has always bugged me... I wish there was an aftermarket rear cell you could swap on the OTA and get rid of that plastic mess..

#5 Mike Cook

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Posted 26 June 2012 - 10:57 AM

Yes there's also that chance of popping out the camera port. It hasn't happened to me while using a Canon Rebel XT DSLR and T ring / adapter, but it was always on my mind. Another alternative is a 1.25" to 2" eyepiece adapter and try it on the top port. Not sure if there would be any vignetting issues with a 2" eyepiece though.

#6 pogobbler

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Posted 27 June 2012 - 09:47 PM

Another thing to consider is whether the 2" diagonal would clear the drive base when the telescope is pointed perpendicular to the base. Though I realize Meade wanted to largely replicate the Questar design, I do wish they'd have gone with a conventional SCT port, 1.25", or 2" visual port on the scope.

#7 Darenwh

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Posted 06 December 2012 - 10:41 AM

Another possible issue ... the camera port is only press-fitted into the rear of the scope. Who knows how much weight it can hold until it "pops" out! However ... I have attached my 2" diagonal with 2" eyepieces to the rear of my ETX-125 without any problems. I was even able to increase my maximum FOV from .9 degrees to 1.25 degrees.



OK, How did you do it... How did you expand the Max FOV?
Thanks,
Daren

#8 *skyguy*

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Posted 06 December 2012 - 02:43 PM

Hey Daren,

See the information in the right-hand column on the Siebert Optics site:

http://www.siebertop...ceadapters.html

Many EXT owners claim a wider field can't be achieved because of the restricted 35mm. SCT-adapter opening in the rear photo-port. However, with right eyepiece it does work.

Jim

#9 Escher

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Posted 06 December 2012 - 03:41 PM

Just to close the loop on this a bit...

Forget adapters - contact Jim Wegat for his ETX125 back conversion - its the *ONLY* really good way to go. Rock solid, machined and has a standard SCT thread. It was designed for the Terabeam scopes and is drop in on the standard 125's.

Jim's a great guy and I can get you his contact info if you are interested.

#10 moynihan

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Posted 06 December 2012 - 03:57 PM

Just to close the loop on this a bit...

Forget adapters - contact Jim Wegat for his ETX125 back conversion - its the *ONLY* really good way to go. Rock solid, machined and has a standard SCT thread. It was designed for the Terabeam scopes and is drop in on the standard 125's.

Jim's a great guy and I can get you his contact info if you are interested.


He is doing these again? :)

#11 Escher

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Posted 06 December 2012 - 10:57 PM

A couple of months ago he told me he was and to send folks his way if they were interested in the 125 size adapter.

#12 Christopher Erickson

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Posted 07 December 2012 - 04:29 AM

The widest possible unobstructed, non-vignetted true field of view in the ETX 90/105/125 scopes is achieved with a 1.25" Televue Panoptic 24 eyepiece. The now-discontinued, Japanese-made Celestron Ultima 35 (Plossl design) in 1.25" was about 1/3 the price of the Pan-24 and gave the basic same true field of view, but in a smaller apparent field of view.

The field stop diameters in the ETX 90/105/125 Maksutov compound optical design makes 2" eyepieces highly-obstructed and vignetted.

And 40mm 1.25" eyepieces are not worth the money for visual observing because they give the same true field of view as a typical 32mm Plossl, but in a much tinier image.

Simply being able to mechanically-mount a 2" diagonal and 2" eyepieces to an ETX scope is not nearly the same as actually getting the light benefits and field of view of a 2" field stop.

FWIW, the Panoptic 24 gives beautiful, sharp, wide-angle views in the ETX scopes that is impossible to beat. Unfortunately it has a price tag to match!

But if you ever get one, it will instantly become your favorite eyepiece and will rarely be taken off of your scope.

I hope this helps.

#13 *skyguy*

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Posted 07 December 2012 - 11:30 AM

"The field stop diameters in the ETX 90/105/125 Maksutov compound optical design makes 2" eyepieces highly-obstructed and vignetted."

Theoretically this may be true, but in actual use ... using the right eyepiece ... vignetting is not noticeable and the FOV increase is substantial. For my ETX-125, I've experienced a true increase in the FOV from 55 arc-minutes (1.25" eyepiece) to 75 arc-minutes (2" eyepiece) without any detectable vignetting.

And 40mm 1.25" eyepieces are not worth the money for visual observing because they give the same true field of view as a typical 32mm Plossl, but in a much tinier image.

I wouldn't write-off the 40mm eyepiece as being worthless for use in the ETX. True, the image scale is smaller in the 40mm eyepiece .. however, the exit pupil is larger than in the 32mm eyepiece (2.6mm vs 2.1mm). This larger exit pupil will give the observer a better chance to see the very faintest nebulosity at the extreme edges in deep-sky objects. This certainly is not always the case ... but, the 40mm is the first eyepiece ... and usually the last one I grab ... when I'm out observing with my ETX.

Jim

#14 Jaimo!

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Posted 08 December 2012 - 10:41 AM

Theoretically this may be true, but in actual use ... using the right eyepiece ... vignetting is not noticeable and the FOV increase is substantial. For my ETX-125, I've experienced a true increase in the FOV from 55 arc-minutes (1.25" eyepiece) to 75 arc-minutes (2" eyepiece) without any detectable vignetting.



What eyepiece are you using? and what is the maximum TFOV you are able to achieve?

It has been a while since I have owned an ETX, but going to a 2" eyepiece, you are limited to the diameter of baffle. It will act as an effective field stop and in the ETX you cannot achieve more than 1° TFOV. The Maksutov is a great scope and optical system, but it does have it's limitations, like any other scope. If you desire a wider field of view, don't invest in 2" accessories for the ETX, and put that money toward a good pair of binoculars or a short tube 80mm f/5 scope.

Jaimo!

#15 *skyguy*

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Posted 08 December 2012 - 01:03 PM

Theoretically this may be true, but in actual use ... using the right eyepiece ... vignetting is not noticeable and the FOV increase is substantial. For my ETX-125, I've experienced a true increase in the FOV from 55 arc-minutes (1.25" eyepiece) to 75 arc-minutes (2" eyepiece) without any detectable vignetting.



What eyepiece are you using? and what is the maximum TFOV you are able to achieve?

It has been a while since I have owned an ETX, but going to a 2" eyepiece, you are limited to the diameter of baffle. It will act as an effective field stop and in the ETX you cannot achieve more than 1° TFOV. The Maksutov is a great scope and optical system, but it does have it's limitations, like any other scope. If you desire a wider field of view, don't invest in 2" accessories for the ETX, and put that money toward a good pair of binoculars or a short tube 80mm f/5 scope.

Jaimo!


I use a surplus military 2" eyepiece that has a 40mm field lens and a 37mm eye lens. Theoretically, it should not work but in reality it does ... don't ask me why. The true FOV is increased to 1.25 degrees without any noticeable vignetting.

#16 Christopher Erickson

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Posted 08 December 2012 - 01:34 PM

Theoretically this may be true, but in actual use ... using the right eyepiece ... vignetting is not noticeable and the FOV increase is substantial. For my ETX-125, I've experienced a true increase in the FOV from 55 arc-minutes (1.25" eyepiece) to 75 arc-minutes (2" eyepiece) without any detectable vignetting.



What eyepiece are you using? and what is the maximum TFOV you are able to achieve?

It has been a while since I have owned an ETX, but going to a 2" eyepiece, you are limited to the diameter of baffle. It will act as an effective field stop and in the ETX you cannot achieve more than 1° TFOV. The Maksutov is a great scope and optical system, but it does have it's limitations, like any other scope. If you desire a wider field of view, don't invest in 2" accessories for the ETX, and put that money toward a good pair of binoculars or a short tube 80mm f/5 scope.

Jaimo!


I use a surplus military 2" eyepiece that has a 40mm field lens and a 37mm eye lens. Theoretically, it should not work but in reality it does ... don't ask me why. The true FOV is increased to 1.25 degrees without any noticeable vignetting.


My speculation is simply that the vignetting and other field distortions aren't bad enough to be objectionable to your eye. No problem with that. Everyone, of course, has different perceptions and standards.

I still vote for the Televue Panoptic-24.

Once you get a Pan-24, those 1.25" 40mm Plossls and Rube Goldberg 2" setups will stay in the box and never be put on your ETX scope ever again.

#17 *skyguy*

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Posted 08 December 2012 - 04:23 PM

Theoretically this may be true, but in actual use ... using the right eyepiece ... vignetting is not noticeable and the FOV increase is substantial. For my ETX-125, I've experienced a true increase in the FOV from 55 arc-minutes (1.25" eyepiece) to 75 arc-minutes (2" eyepiece) without any detectable vignetting.



What eyepiece are you using? and what is the maximum TFOV you are able to achieve?

It has been a while since I have owned an ETX, but going to a 2" eyepiece, you are limited to the diameter of baffle. It will act as an effective field stop and in the ETX you cannot achieve more than 1° TFOV. The Maksutov is a great scope and optical system, but it does have it's limitations, like any other scope. If you desire a wider field of view, don't invest in 2" accessories for the ETX, and put that money toward a good pair of binoculars or a short tube 80mm f/5 scope.

Jaimo!


I use a surplus military 2" eyepiece that has a 40mm field lens and a 37mm eye lens. Theoretically, it should not work but in reality it does ... don't ask me why. The true FOV is increased to 1.25 degrees without any noticeable vignetting.


My speculation is simply that the vignetting and other field distortions aren't bad enough to be objectionable to your eye. No problem with that. Everyone, of course, has different perceptions and standards.

I still vote for the Televue Panoptic-24.

Once you get a Pan-24, those 1.25" 40mm Plossls and Rube Goldberg 2" setups will stay in the box and never be put on your ETX scope ever again.


Without a doubt, the TV Panoptic 24mm is an exceptional eyepiece ... I often use my TV Nagler 16mm on the ETX125. However at $300 for the Panoptic ... I'll stick with the 1.25" 40mm Plossls and Rube Goldberg 2" setups. ;)

#18 cavefrog

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Posted 09 December 2012 - 12:52 AM

A couple of months ago he told me he was and to send folks his way if they were interested in the 125 size adapter.


so how about some contact info? why do you not just put it up? you said he asked you to send people. what better place to advertise by word of mouth so to say.

Theo

#19 REC

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Posted 09 December 2012 - 09:59 AM

I use a Meade 24mm SWA with mine. ES has the same ow for about $200, but both come up used sometimes.

#20 Jaimo!

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Posted 09 December 2012 - 07:00 PM

Theoretically this may be true, but in actual use ... using the right eyepiece ... vignetting is not noticeable and the FOV increase is substantial. For my ETX-125, I've experienced a true increase in the FOV from 55 arc-minutes (1.25" eyepiece) to 75 arc-minutes (2" eyepiece) without any detectable vignetting.



What eyepiece are you using? and what is the maximum TFOV you are able to achieve?

It has been a while since I have owned an ETX, but going to a 2" eyepiece, you are limited to the diameter of baffle. It will act as an effective field stop and in the ETX you cannot achieve more than 1° TFOV. The Maksutov is a great scope and optical system, but it does have it's limitations, like any other scope. If you desire a wider field of view, don't invest in 2" accessories for the ETX, and put that money toward a good pair of binoculars or a short tube 80mm f/5 scope.

Jaimo!


I use a surplus military 2" eyepiece that has a 40mm field lens and a 37mm eye lens. Theoretically, it should not work but in reality it does ... don't ask me why. The true FOV is increased to 1.25 degrees without any noticeable vignetting.


I doubt you are actually getting 1.25° TFOV, while mathematically possible, in practice I would believe it is quite less. If you have the time, I'd be interested in your results if you made a few measurements using the "drift method" with couple of different eyepieces. An eyepiece with a max field for 1.25" barrel: 32mm Plössl, 40mm Plössl or 24mm SWA - all which yield ~0.9° TFOV; and also measurements with your 1.25° TFOV setup; also, the 26mm Meade 4000 Super Plössl that come with the scope as a standard. This could be very helpful for the entire ETX community as this subject as been brought up many times over the years, experimentally you could put this issue to rest in one evening. I would do it, but I got rid of my ETX about a year ago.

Here is a good link for information on using the drift method. http://www.astrobuys...om/paul/fov.htm

What do you think?
Jaimo!

#21 Escher

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Posted 15 December 2012 - 01:42 AM

Just trying to honor his wishes - I dont know if he wants his address made public for the time being.

#22 *skyguy*

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Posted 16 December 2012 - 11:40 AM

I doubt you are actually getting 1.25° TFOV, while mathematically possible, in practice I would believe it is quite less. If you have the time, I'd be interested in your results if you made a few measurements using the "drift method" with couple of different eyepieces. An eyepiece with a max field for 1.25" barrel: 32mm Plössl, 40mm Plössl or 24mm SWA - all which yield ~0.9° TFOV; and also measurements with your 1.25° TFOV setup; also, the 26mm Meade 4000 Super Plössl that come with the scope as a standard. This could be very helpful for the entire ETX community as this subject as been brought up many times over the years, experimentally you could put this issue to rest in one evening. I would do it, but I got rid of my ETX about a year ago. Here is a good link for information on using the drift method. http://www.astrobuys...om/paul/fov.htm What do you think? Jaimo!

Jaimo,

The chances of me getting out in the winter to do a FOV test using the drift method ranges from zero to none. I live in a snow belt area and lake effect clouds pretty much "closes out" any observing from mid-November through early March. :(

However, I did set up a FOV test inside my home. First, I determined mathematically the FOV of my 1.25" - 40mm. (29mm. field stop) and 2" - 32mm. (39mm. field stop) eyepieces when used on ETX-125.

Theoretical FOV results:

1.25" - 40mm .... 52.2 arc-minutes (0.87 degrees)
2.00" - 32mm .... 70.8 arc-minutes (1.18 degrees)

Next, I positioned a yard stick 42.6' from the ETX-125. Using the 1.25" - 40mm eyepiece, the reading was 8" ... and for the 2.00" - 32mm eyepiece, the reading was 10.1" ... with no discernible vignetting along the edge. Doing the math:

Actual FOV Results:

1.25" - 40mm .... 54 arc -minutes (.9 degrees)
2.00" - 32mm .... 68.4 arc-minutes (1.14 degrees)

Also, theoretical FOV from photo port (27mm opening) .... 48.6 arc-minutes (.81 degrees)

My conclusions ... The theoretical and actual FOVs in the 1.25" - 40mm are essentially the same. The actual FOV in the 2.00" - 32mm eyepiece falls slightly short of the theoretical FOV. However, the use of the 2" - 32mm eyepiece does represent an actual increase in the viewing area of 62% ... over the maximum realized with an 1.25" eyepiece. Vignetting is also an important issue and although none was noticed during testing, almost all optical systems suffer from this problem. Was testing during the daytime and not at infinity focus a factor? I don't know the answer. Also, why does a 2.00" eyepiece seem to work well in the ETX-125 when the optical train is restricted by the 27mm opening in the photo port? Any comments, thoughts or ideas on this test are certainly welcomed. BTW, here's a shot of my EXT-125 set up for use with 2.00" eyepieces:

Attached Files



#23 Pentax Syntax

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Posted 19 December 2012 - 10:10 PM

Interesting. I have observed that a 2" diagonal and eyepieces do increase the field but I see some vignetting with a 30 Pentax XW and Meade 30 QX Wide angle. The system is still useful though. Thanks for posting.

#24 Jaimo!

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Posted 07 January 2013 - 11:16 PM

Excellent work Skyguy! Sorry it has taken me so long to get back...

Jaimo!






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