ETX TECHNICAL TIPS
Jump to the start of today's update
15 October 2000
From: firstname.lastname@example.org (Colony Oaks)
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.
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: email@example.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.
Subject: Re: ETX-125 baffle tube question ... Sent: Tuesday, February 3, 2009 08:59:10 From: "P. Clay Sherrod" (firstname.lastname@example.org) 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 http://www.arksky.org/ ----- 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 opinion? Cheers, 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 reckless. Dr. Clay
Return to the top of this page.
Go back to the Tech Tips page.
Go back to the ETX Home Page.