Last updated: 3 February 2009

ETX-125EC Baffle Modification

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15 October 2000
From: colonyoaks@fingercompanies.com (Colony Oaks)

Hello, I'm an ETX125 owner.

I just thought I'd let you in on a little experiment of mine. This was extremely risky on my part but I had to try. First I'll explain my reason for doing this. The ETX is my first real telescope ever and I really looked forward to high power views of Saturn and Jupiter. So on a fairly steady night I tried it out and was disappointed in the sharpness of the views produced. I have read a few times that the central obstruction of an ETX is almost 40% making it more of a general purpose scope and not so much a dedicated planetary scope. The review in sky and telescope pointed out the secondary light baffle was far to large to produce truely sharp high power planetary images.

Well after serveral tries at sharp images with different eyepeices and on different nights I gave up. I then weighted the risk and tried a crazy idea. I removed the secondary baffle and sliced it in half!! Reducing it's outer most width by half. The results were slightly sharper images at over 300x and up. When I say slightly, I mean I was just able to notice the difference. Saturn was ever so slighter crisper and Jupiters belts showed more definition. Enough so that I was satisfied the experiment worked.

One side effect of this is that during the day, and possibly while viewing the moon (hasn't been in the sky for a while) there is some light leakage when viewing a scene when the soundings are uniformly bright. Nothing for me to worry about since this scope is never used during the day. (I tried it just for this experiment). I suspect the moons light is a narrow enough beam to be blocked by the baffle.

So far everthing seems to have worked perfectly. I got my tiny extra bit of resolution, and all it cost was a slight halo while veiwing daytime objects. That's cool with me.

Added later:

I wrote concerning my experimental reduction of the secondary light baffle:

>One side effect of this is that during the day, and possibly while viewing the moon (hasn't been in the
>sky for a while) there is some light leakage when viewing a scene when the soundings are uniformly

Ok so today I took my scope outside during the day again to confirm that there is light leakage. This time I was unable to notice any leakage at all, and the halo was gone. I then tried to cause leakage on purpose by looking at a bright patch of sky just in and outside of the field of view. But I was unable to see the halo of the other day. My only guess is that on my first attempt the halo was a fluke reflection, or that the sweet spot for light leakage is extemely small. One thing I did notice, the zoom eyepeice I just bought seems to snap to focus at high powers better after the baffle was reduced, even during the day... :)

I'll let you know how the moon looks as soon as it come out.

Mike here: Remember, this will invalidate any warranties and is not for the faint-hearted. Neither myself nor the submitter is responsible for damage this tip may cause.

Subject:	 Re: Update on my experiment
Sent:	Friday, October 13, 2000 23:08:47
From:	colonyoaks@fingercompanies.com (Colony Oaks)
Final word on my experimantal reduction of the secondary light bafle on
my ETX 125

I finally got to view the full moon and it looked just as nice as I
thought it would. I put the moon just out of the field of view and there
was a glare, but there would be a glare on any scope so that doesn't
prove much. The important thing being the moon was very sharp and
resolved even at 475x. (the highest I can go with my current eyepeices).

After looking at Jupiter again I had to admit it looked slightly better
than it did before the experiment. But was it sharp enough? No, not
enough for me...LOL. I guess what I really need is my own personal
Hubble telescope..ha ha. I'm not sure if I will ever be totally happy
with any ground based telescope I could ever hope to afford. There's so
much I wanna see and I have to live with the fact I just won't be able
to see it with my own eyes. That's something every one who ever looked
up had to deal with at one time or another I guess.

Still, my little 125 gets me closer than I was without it. That is
something, isn't it? :)

Thank you Mr.Weasner.

Start of today's update
Subject:	Re: ETX-125 baffle tube question ...
Sent:	Tuesday, February 3, 2009 08:59:10
From: "P. Clay Sherrod" (drclay@tcworks.net)
Subject: Re: ETX-125 baffle tube question ...

Absolutely not....whoever came up with that oddity is playing with folks.
The computer-generated baffle that is in there is absolutely a perfect
match for optimal optical performance.

Dr. Clay
Arkansas Sky Observatories
MPC H45 - Petit Jean Mountain South
MPC H41 - Petit Jean Mountain
MPC H43 - Conway West

	----- Original Message ----- 
	From: "Mike H"
	Dr. Clay:
	Somewhere I read that shortening the baffle tube by half improved
	contrast in the EXT-125.  I can't find the epistle which I think was
	on Weasner's site.  Have you seen this also, and do you have an
	Mike H

And some additional information:

That is an incredible assumption; if anything, shortening a baffle tube
will REDUCE contrast considerably.   Both baffles are carefully matched
to the shape of the focal light cone as well as the diameter of the
optics (set of 3) and they are actually precisely sized to accept the
maximum light cone without permitting extraneous light....thus reducing
contrast and limiting magnitude.

What this is saying is exactly the opposite of the purpose of a light
baffle in the first place.

One thing that should never be modified in the catadioptic telescope,
whether Meade, Celestron or whatever, is the baffle tubes.  They are the
size they are because a professional optician with a superior computing
program determined optimal light control.

Honestly suggesting to cut off a light baffle is misleading and

Dr. Clay

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