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Bresser 127 Mak, f/15; Two Baffling Qs

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#51 fcathell

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Posted 30 July 2018 - 03:31 PM

Here is the new baffle - 18mm long and 44mm diameter at the flared end.  I also roughed up the inside wall so no grazing angle flare. This will give me about a 36% obstruction and no annular light leakage at any angle with a 90* diagonal.  I think this will be a good compromise. With no baffle I would have a 34.5% obstruction due to the aluminized spot.  Another 1.5% should be inconsequential (I think!).

 

 

 

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#52 Joe1950

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Posted 30 July 2018 - 03:58 PM

Very similar to my efforts, Frank! I think we're on the same page.

 

 

The reduced baffle will be right at about 35%. The entire baffle was long and flared out quite a lot to 52mm or 41% CO.

 

So, I think for astro use this will be a good place to be.

 

 

 


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#53 fcathell

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Posted 30 July 2018 - 04:05 PM

Here is the removed part of the baffle with a penny for reference.

 

Frank

 

 

 

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#54 Asbytec

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Posted 30 July 2018 - 06:34 PM

You guys are amazing. Nice work.

I think my baffle would have been 11mm tall. No annulus you say? Yea, I think that's a great mod.

Doing the math, from 40% to 35% takes you from 0.7 to 0.77 peak intensity and closer to 0.8. That's about 10% improvement in peak intensity and reduced diffraction effects.

Edited by Asbytec, 30 July 2018 - 06:40 PM.

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#55 fcathell

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Posted 30 July 2018 - 06:37 PM

You should see what I've done to some old AM ham radio transmitters. Even I don't like to look inside any more.  The funny thing is they still work!

 

FC


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#56 Joe1950

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Posted 30 July 2018 - 06:44 PM

I'm a ham too, Frank. W2DI. No equipment though.

 

Those AM transmitters were beasts. The ones with plate modulation had those big, heavy transformers. Nice sounding though.

 

Hobbies are nice, but too expensive for me. I mean, I have deep pockets. Just nothing in them!  frown.gif

 

 

Norme, I just guessed at the baffle. Too much work to run the math or ray trace. lol.gif



#57 fcathell

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Posted 30 July 2018 - 07:13 PM

Joe - I was K3YAZ, originally from near Ocean City, MD. I changed my call last year to W7YAZ after being in AZ for 23  years. I initially messed with some of the big boat anchors (Valiant, DX-100, etc) but they were ball busters.  I now use a couple of old Hallicrafters HT-40s.  One still uses the screen modulation but I substituted a 6LW6 (largest sweep tube ever made) in for the 6DQ5 final and jacked the plate voltage to 750Vdc.  Works great with about 40W carrier.  The other I plate modulated with an old Eico 730 - about 50W carrier. More fun than SSB IMO.  Enough of that now! Back to observing the higher frequency photons!

 

By the way, I re-tested the Mak with the artificial star and that "flaring" effect on the diffraction pattern is greatly diminished.  I can't figure out what causes that. When looking through the scope from the back, it's obvious that the CO is smaller. I hope I can try it tonight before the clouds move in. 

 

Frank


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#58 JimFR

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Posted 30 July 2018 - 08:06 PM

The net can ping us across the globe in a fraction of a second but there’s something magical about a radio signal bouncing off the ionosphere.  Never got to ham but built several of my own antennas for CB at the time when it was at it’s peak.

 

I have some work now to do on my mak.  Maybe not pull the secondary baffle but it needs flocking badly and the glue they used to mount it is shiny and clear and I can see it in the reflections.


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#59 Joe1950

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Posted 30 July 2018 - 08:40 PM

Those were He-Man rigs, Frank! Big tubes and high plate voltages... kept you real honest with the covers off!

 

Jim, I recall a few times when conditions were at their peak hearing signals both short and long path, with an echo like sound as a result of the different distances. Some sunspot cycles were extraordinary and 10/11 meters easily went worldwide with very moderate power.

 

It seems like the last two cycles have been weak ones, especially the last one.

 

 

I checked with a look through without the eyepiece and the light is not sneaking in at any angle with the diagonal. So, I think I'll keep it there. A little less CO makes you feel better about things grin.gif

 

Jim, good flocking goes a long way. Its a lot of work, but certainly worth the trouble. The Bresser is not too bad with reflections off the main tube or inside the baffles. they have a ridge type surface that isn't as reflective as some I've seen. 

 

It could be better and I may get into flocking as some point. I want to see if I can lessen the focus shift and the focus recoil. It isn't too bad, but annoying. There is some of that Asian gorilla grease inside and it may be too stiff. I don't know.


Edited by Joe1950, 30 July 2018 - 08:42 PM.


#60 Asbytec

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Posted 30 July 2018 - 09:00 PM

By the way, I re-tested the Mak with the artificial star and that "flaring" effect on the diffraction pattern is greatly diminished.  I can't figure out what causes that. 

 

Frank

That's an interesting development, Frank. Might have to find my baffle and readdress it. 


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#61 Redbetter

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Posted 30 July 2018 - 11:19 PM

Joe,

 

Since your scope and mine are a little different than the Orion/SW Maks, I wonder if a slightly different approach might optimize things.  You noted that the baffle actually is on the mirrored center.  So perhaps the solution would be to cut both ends of the baffle (and/or perhaps shave away 1mm of wall thickness on the inner wall next to the secondary spot in addition.)  This would/might provide maximum illumination from the secondary spot, while still baffling the annulus around to some minimal value. 

 

The difficulty is in making precision cuts square and getting the baffle adhered so that it sits centered and flush.  I admit it scares me away from the project so far.  Mine gives good images despite the baffle, so I am not in a rush to modify it.  I might get the urge next year when Jupiter comes around again--I want something like that to test it on for fine planetary detail on good nights.  Of course Jupiter will be in the muck the next two years... 

 

If I had a second baffle cone I wouldn't be as hesitant to modify the one I have.  What was the original height of the cone?  That could be used along with the diameter on both ends (and thickness) to choose where to make a cut on the bottom end.


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#62 fcathell

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Posted 30 July 2018 - 11:48 PM

Red - I sort of took a guess on mine, essentially cut it in half length wise. It was a rough cut at first.  I used a buzz saw attachment on my dremmel tool. I held the baffle in a vice and worked around it after marking an even cut band with a magic marker. I then took the piece I was going to use and started working it in a circular motion on a flat piece of medium sand paper then went to a finer grit piece. I kept working it until it was even and smooth on the cut end.  I was surprised at well it came out. I also sanded the inside to rough it up to avoid grazing angle glare reflections.  It is about 18 mm long now. I cleaned the "fuzzy" glue off the baffle and the periphery of the aluminized spot on the corrector with a Q-tip and alcohol. To replace the new, shorter baffle I used 5 small spots of super glue placed around the bottom of the baffle. As Joe mentioned, the bottom edge is about 3mm thick, so there is plenty of room for the drops of glue.  I eyeballed it and placed it evenly on the aluminized section and then put a small weight on the polished end of the baffle.  I let it sit for about 30 minutes and it came out just fine. There is certainly less obstruction than before and it is noticeable looking through the rear of the scope.  I just need some clear skies to test it. 

 

Frank


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#63 Redbetter

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Posted 31 July 2018 - 12:07 AM

Frank,

 

I have wondered about what adhesive would be best, especially since it is on the mirrored spot and it might be necessary to remove it at some point.  I assume this is the type formulated for glass rather than standard?

 

It might off gas for awhile. 


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#64 Asbytec

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Posted 31 July 2018 - 12:40 AM

Double sided tape?
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#65 Joe1950

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Posted 31 July 2018 - 12:58 AM

That’s a good thought, Red! It would expose more mirror doing it that way.

 

The thickness of the baffle goes from a maximum of about 3mm at the base to about 1 or less at the top/wide end. The length was about 43-44mm. I also used the middle point and the two pieces are each 41mm with 1 or 2mm between. 

 

I dont know what the illumination was with the full baffle vs. without any. With the half as I have it, the same amount of secondary is exposed. I didn’t think there was any issue with it as it was originally.

 

Anyway, I’ll see what I can determine with the arrangement as it is now. Thanks!

 

Added: I used a thin layer of clear silicone to attach it. Appears to grab well.


Edited by Joe1950, 31 July 2018 - 01:02 AM.

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#66 Redbetter

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Posted 31 July 2018 - 01:35 AM

The length was about 43-44mm. I also used the middle point and the two pieces are each 41mm with 1 or 2mm between. 

 

I am trying to figure the angle.  When you say length, do you mean the hypotenuse or the height of the baffle?  I assume the "41mm" above is actually 21mm from cutting it in half?



#67 Joe1950

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Posted 31 July 2018 - 04:16 AM

I measured the height, Red.

 

My math is a little off. Each remaining piece is 21mm high. Combined 42mm plus whatever a common hacksaw would take; I’m thinking a millimeter or 2. Probably 2mm because I sanded the piece I used smooth and flat. So the final combined height would likely be 44mm.

 

Hope that helps. Thanks.


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#68 Joe1950

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Posted 31 July 2018 - 05:09 AM

I took a couple photos, straight on as I could get them and lined everything up in Inkscape. Made some angle measures and the angle of the cone came very, very close to

 

10° off the Y axis (vertical)

 

on both sides.

 

The top is 52 mm across.

 

The bottom is 37 mm across

and the cone at that point is

3 mm thick.

So the clear aperture would be 31 mm.

 


Edited by Joe1950, 31 July 2018 - 05:18 AM.

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#69 fcathell

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Posted 31 July 2018 - 08:37 AM

I used the more viscous version of the Gorilla superglue.  I found it works better than the really "wet" types.  It doesn't out-gas as bad either. I actually let it "dry" for several hours before re-assembling the scope.

 

It appears Joe's baffle was even longer (height) than mine. Mine was 40mm before cutting it.  Now the baffle is 18mm high. I got beat by the clouds again last night.

 

Frank


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#70 Joe1950

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Posted 31 July 2018 - 09:14 AM

We're definitely on the same page, Frank!

 

For whatever reason, I never had much luck with any kind of superglue. I may have a tendency to use too much. But when it gets on my fingers, it works, well, Super!

 

So I used the clear silicone and let it set well overnight and the connection is good. Everything back together and I did the flashlight test to make sure nothing was adversely affected...

 

 

From the 4" mark to the 9" mark is the stated 5", or 127mm.

 

Plus the CO shadow reads just about right at 1-11/16" or 1.6875" or 43mm or 34% or there abouts. I actually measured 44mm across the baffle giving 34.6%, but why split hairs.

 

It's down from 41% and I'm sure I won't even notice that difference of 6 or 7% anyway. 

 

I really need a good Metric scale!

 

 

So I too will have to get a viewing session on Jove and some stars. It may need collimation after all the jostling, but once I secured the primary baffle retaining ring, it has been right on, no matter what I do.

 

Very good, thanks!

 

 

Added: Frank, this is definitely the largest baffle, relative to the scope aperture I've ever seen. I had to fix a creeping secondary baffle on an ETX 90 and I looked at one on a C-90 and they were both much more shallow - being wider than they were high.


Edited by Joe1950, 31 July 2018 - 09:21 AM.

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#71 fcathell

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Posted 31 July 2018 - 01:11 PM

I've had a C90 Mak apart in the past, and it definitely has a more shallow baffle.  In fact the C90 Mak had exactly a 34% obstruction using the flashlight test. I think the ETX90 was about the same. It seems that the 127 Maks have the worst "stock" central obstruction due to that baffle and certainly contribution of the undersized primary mirror in the Synta version. Oh well, they do give sharper images on average than most of the similar SCTs I've owned.

 

Frank 


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#72 Joe1950

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Posted 31 July 2018 - 01:30 PM

I’m very pleasantly surprised by the images they show. I had a newer C5 and it had good optics. It came in at about 40% CO also.

 

I have one of those used C’tron go to mounts also, Frank. Works pretty good. Cost about $75 or so from Wing and Sons. I’ll use the 127 on that also.

 

 

Frank, I recall reading a post on the Weisner ETX site about a young lady who had problems with the baffle migration the early units had. She wrote into a forum with (I believe) Dr. Sherrod, an expert with the ETX-90 and other models.

 

Anyway, she fixed the baffle (which is made of metal, by the way on the 90) back in place with super glue. The entire secondary frosted over with the outgass of the stuff. Probably the real liquidy type that had the strong odor and outgass. 

 

I dont think there there was anything suggested to do at that point.


Edited by Joe1950, 31 July 2018 - 01:39 PM.


#73 fcathell

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Posted 31 July 2018 - 02:22 PM

Wow - interesting about that lady with that ETX baffle creep thing.  The superglue I used didn't have that highly volatile, penetrating odor and was a more heavy, thick type of superglue.  I only used 5 tiny drops.  I think some people over do it with superglue.  It's curing requirement is anaerobic and requires only a small amount to do the job.  I'll keep an eye on mine but so far, no issues.

 

By the way, I also have one of those older C'tron GT goto mounts from Wing & Sons.  I made an offer on Ebay for $60 and got it for that plus shipping.  It works great and I've even put my C6 on it but that is definitely pushing it. The 127 Mak does fine and I typically use an RD finder with the scope with that mount.

 

Frank


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#74 fcathell

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Posted 31 July 2018 - 04:18 PM

Maybe I should start this as a new thread, but since we're on the topic of Maks, baffles, modifications, etc, I have been really annoyed with the stuff I used to try to flock my primary baffle tube in the 127 Mak.  I can't remember where I got it because I've had a sheet of it for some time.  Here's the problem; since the fuzzy felt part has a stiffer, paper backing, I have found that if you don't cut it exactly (the circumference when rolled up) such that the edges come together precisely when inserted into the baffle tube, the edges will lift slightly (from attempting to straighten out) if you cut it too short and the thing will buckle if you are over. Even with a very slight amount of lifting, I get light showing between the paper side and the baffle wall, and this has caused some weird effects for bright stars near the edge of the field. I tried another approach today after finding a piece of non-backed felt from Michael's art store. The "sheet" of felt was $0.99, so I felt (no puns) it was worth a try. It seemed like it may be a little thick and I wondered if it would "mold" to the wall of the tube without sagging and/or act similar to the paper backed felt material.  I carefully cut it, rolled it up and then inserted it into the baffle tube from behind.  It went in fine as long as you roll it tight and then it unrolls once it's in the baffle. I then took a smooth wood dowel about 15mm in diameter and carefully inserted into the center of the baffle tube and proceeded to push or "iron" the felt against the baffle wall. It worked perfectly and it seems to be holding just fine under the pressure of it own slight stiffness. I've had it in there for a few hours and it is not lifting or buckling in any way. There is some slight vignetting if you move your head from side to side when looking into the back but with your eye close to center axis, the entire mirror plus a little is visible.  This material sure has zero reflectivity even with bright incoming light at a grazing angle. I am very happy about how this worked out and will update any potential issues.  Has anyone else done similar or had issues with the commercial paper backed flocking material when used in Mak primary baffles?

 

Thanks,

 

Frank     


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#75 Joe1950

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Posted 31 July 2018 - 06:28 PM

When I had the Celestron C-90, I did the baffle mod, which was really needed for that scope, Frank.

 

A lot of people used sandpaper painted black but I got some non adhesive flock from Edmund Optics, which is about 15 minutes from here.

 

It is the thinnest flock a group of us tested and without the adhesive it was easy to manipulate.

 

I was just lucky to get it right where the ends butted and kept it round in the tube. Plus the tube is smaller in the 90mm.

 

It's hit or miss and I was trimming just a little at a time with one of those paper trimmers. I just happened to hit it right which is odd for me.

 

I'm glad the felt worked. I have a couple sheets of that also.




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