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Being such a controversial subject, I guess the most straight foreword thing to do is to do a test.
Two (almost) identical telescopes, one with buffles and the other floacked and some test chart (like those for resolution and contrast tests) placed at distance to be viewed through the scopes. This way the contrast could be judged directly for both situations, with a camera or with naked eye.

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A cost-benefit analysis would also be useful, not necessarily in terms of money spent, but in time and effort invested.

Clear Skies,
Mike

--------------------
Celestron 10" f5 Newt on 1stBase (DSO)
Zhumell 8" f6 Newt, Bosma 6" f12 MCT (NSO)
6" f5 Newt, 130ST, 4.5" f4.4 Ball w/GLP, ST80 w/Crayford (RFTs)
C4-R (NSO/DS)
90mm f13 MCT (Luna/DS)
SkyMaster 25x100, 15x70
Zhumell 20x80
Barska XWA 10x50, 8x40
OptiView LPR 10x50
Const View 2.3x40
BV-125C
CG5, 2 drv / CG4, 2 drv, wood legs, ScopeStuff saddle / CG3, 1 drv
SV AZ / 501HDV on Bogen 055XB / P+ on Oberwerk
QuikFinder, Telrad
Orion Dynamo Pro 12, Dew-Not
Have GLP and not afraid to use it!

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I do use a flocked, foot-long cylindrical light shield on the sky-end of my OTA, but I don't consider that a baffle.

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It is one, though. It's not an OTA ring baffle, but it's a baffle nonetheless.

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Agreed. I'll just have to keep that in mind during these discussions.

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In a *Newt*, I actually have serious doubts that many baffles (except the light shield, a flocked baffle just in front of the primary or on the mirror box, a baffle between focuser and secondary and on some scopes the shroud, which is actually helpful on truss scopes for other reasons than baffling) actually do anything useful.

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Also agreed. And in one form or another, I do use all these baffles in my 10" Newt. However, I do see some of the newer reflecting scopes designed for astrophotography ("astrographs") have many built-in baffles along the OTA. If I were to buy a scope with these baffles already installed I certainly wouldn't mind, because if designed correctly they should improve the image *somewhat*, but I would never attempt it myself.

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In fact (as Mark correctly points out) a baffle that's installed where none should live actually hurts if it kicks a tube current into the light path.

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Yes, of course, there's always the tube currents to consider, especially for lunar and planetary work.

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Flocking is complementary to baffles. Actually, flocking also only works because it uses the same principles as baffling but on a smaller scale.

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In Newts, at least, I would say that baffles are complementary to flocking. But we weren't talking about Newts. In refractors, flocking would be complementary to baffles, yes indeed.

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But in a refractor, there's no question that a tube wall in the shadow of a baffle or unseen (because the unlit side of a baffle is in front of it) is darker than a flocked tube wall. No need for fancy theories, it's just Plain Common Sense.

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Yessir.

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But again, baffling requires precision and application of theory,

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Gosh, fancy that. Something which you actually have to design. Surely that's something we must all strive to avoid, especially in the "ATM, Optics and DIY" forum.

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Well, in fact I do tend to avoid that as much as possible. I'm a DIYer, not an ATMer. I try to improve the scopes that I buy that others have designed, not design my own scope. I'll leave that to the ATMers in this forum.

Cheers,
Mike

--------------------
Celestron 10" f5 Newt on 1stBase (DSO)
Zhumell 8" f6 Newt, Bosma 6" f12 MCT (NSO)
6" f5 Newt, 130ST, 4.5" f4.4 Ball w/GLP, ST80 w/Crayford (RFTs)
C4-R (NSO/DS)
90mm f13 MCT (Luna/DS)
SkyMaster 25x100, 15x70
Zhumell 20x80
Barska XWA 10x50, 8x40
OptiView LPR 10x50
Const View 2.3x40
BV-125C
CG5, 2 drv / CG4, 2 drv, wood legs, ScopeStuff saddle / CG3, 1 drv
SV AZ / 501HDV on Bogen 055XB / P+ on Oberwerk
QuikFinder, Telrad
Orion Dynamo Pro 12, Dew-Not
Have GLP and not afraid to use it!

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This is pretty much what I did but I placed the baffle flush on the inner wall of the OTA at the focuser hole, not out in the OTA. I am reluctant to put anything else out into the initial light path to the primary.

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This is pretty much what I did but I placed the baffle flush on the inner wall of the OTA at the focuser hole, not out in the OTA. I am reluctant to put anything else out into the initial light path to the primary. It is bad enough that the diagonal, spider vanes, and sometimes the focuser tube are out there. And at least in my focuser, the focuser tube is quite a bit smaller in diameter than the focuser hole itself, so the drawing is not entirely applicable in that respect. At any rate, how would you even place a longitudinally-aligned baffle out in the OTA? Would you suspend it from a diagonal spider vane? There is also the possibility of the baffle dropping onto the primary. I would prefer not to.

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Not following this argument. A baffle on the focuser is just a piece of something with a hole in it, attached to the tube or the focuser plate, that vignettes the incoming light beam from the secondary. It doesn't hang in the light path or fall onto the primary. Common sense should make it easy to build, as it can be done in any of a number of ways, just like a filter drawer.

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The "light trap box" was written up by Harold Suiter somewhere (sorry) in regards to minimizing stray light in a solar scope. It's a box that sits on the opposite side of the focuser, black or flocked inside, and any light that goes into it doesn't easily come out.

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Well, Suiter IS the man. This LTB sounds like it would make sense in a solar scope, where there is no lack of available light from the object. But IMHO it does not sound like something that would help in a scope used for finding faint fuzzies. Wouldn't it be better to just flock opposite the diagonal and be done with it? Why put another possible obstruction in the light path? But thanks for the concept. I had never heard of an LTB. I'll look it up and do more research.

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Again, not following this argument. It's on the other side of the tube from the focuser, and sticks out of the tube, a little box that occupies the space where you can see past the secondary through the focuser. It's better than flocking, and would work on any newt.

Best,
Mark

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It's not in the light path in the illustration (updated). :rofl:

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Oh, it's not in the light path NOW. I could have sworn it was before ... Fine, if the focuser baffle can be positioned a bit out from the inner wall of the OTA, as long as it is securely attached to the OTA and is just outside the light path, I have no problem with it.

Mike

--------------------
Celestron 10" f5 Newt on 1stBase (DSO)
Zhumell 8" f6 Newt, Bosma 6" f12 MCT (NSO)
6" f5 Newt, 130ST, 4.5" f4.4 Ball w/GLP, ST80 w/Crayford (RFTs)
C4-R (NSO/DS)
90mm f13 MCT (Luna/DS)
SkyMaster 25x100, 15x70
Zhumell 20x80
Barska XWA 10x50, 8x40
OptiView LPR 10x50
Const View 2.3x40
BV-125C
CG5, 2 drv / CG4, 2 drv, wood legs, ScopeStuff saddle / CG3, 1 drv
SV AZ / 501HDV on Bogen 055XB / P+ on Oberwerk
QuikFinder, Telrad
Orion Dynamo Pro 12, Dew-Not
Have GLP and not afraid to use it!

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Not following this argument. A baffle on the focuser is just a piece of something with a hole in it, attached to the tube or the focuser plate, that vignettes the incoming light beam from the secondary.

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Yes, and that's basically what mine is, except that it is flush with the inner surface of the OTA so that there will be no chance of it vignetting the intial incoming rays from the sky-end of the tube. My OTA has an enclosed primary cell and the inner surface of the OTA is rather close to the primary, so there's not a lot of wiggle room to have a baffle jutting out into the OTA without cutting off some incoming rays. Of course, I can imagine how it could be done, and I may experiment with that, but I don't think I'll do it as my very next DIY project.

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It doesn't hang in the light path or fall onto the primary. Common sense should make it easy to build, as it can be done in any of a number of ways, just like a filter drawer.

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Oh, you might be surprised. I did have at least one conversation with a nice chap in England who did have a focuser baffle suspended from a diagonal vane! I believe I've conversed with at least one other individual who did something similar. I hate to say it, but I think this is a Eurpopean thing, not that there's anything wrong with that. Different viewpoints help you to think creatively.

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Again, not following this argument. It's on the other side of the tube from the focuser, and sticks out of the tube, a little box that occupies the space where you can see past the secondary through the focuser. It's better than flocking, and would work on any newt.

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Not following me? I'm not following you! Then we must be headed in opposite directions. I've searched for "Light Box Trap" in various ways on the internet and haven't found anything enlightening. (I've found plenty of info on "light boxes" for astrophotography, but that's something else. Not interested AT ALL.) Suiter wrote an article for S&T a while back involving a gizmo like this in a solar scope, as you said, but I haven't seen a picture of the gizmo or a good description of it. From your description here, it sounds as if the box would be coming out of a hole cut in the area of the OTA which faces the "back" side of the secondary. If that is the case, I don't see how that would do anybody any good. Just flock the area and save the effort of cutting the hole! (Your use of the term "tube" may be confusing here. It is ambiguous. It can refer to either the focuser tube or the OTA.)

Mike

(Me after my attempt to understand the Light Trap Box.)

--------------------
Celestron 10" f5 Newt on 1stBase (DSO)
Zhumell 8" f6 Newt, Bosma 6" f12 MCT (NSO)
6" f5 Newt, 130ST, 4.5" f4.4 Ball w/GLP, ST80 w/Crayford (RFTs)
C4-R (NSO/DS)
90mm f13 MCT (Luna/DS)
SkyMaster 25x100, 15x70
Zhumell 20x80
Barska XWA 10x50, 8x40
OptiView LPR 10x50
Const View 2.3x40
BV-125C
CG5, 2 drv / CG4, 2 drv, wood legs, ScopeStuff saddle / CG3, 1 drv
SV AZ / 501HDV on Bogen 055XB / P+ on Oberwerk
QuikFinder, Telrad
Orion Dynamo Pro 12, Dew-Not
Have GLP and not afraid to use it!

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it sounds as if the box would be coming out of a hole cut in the area of the OTA which faces the "back" side of the secondary. If that is the case, I don't see how that would do anybody any good.

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Sorry there's no easy online reference to explain it. It's just a better way of absorbing light - it doesn't just sit opposite the secondary, it occupies all of the far side of the tube that can be seen through the focuser. If there's no effective baffle for the focuser, and you can see more than the secondary through the focuser, you need to make what you can see absorb stray light if you don't want to see that light affect the contrast in the EP. A "light trap" is likely not needed for ordinary use, but if you're trying to extract every last bit of performance, it might be useful.

More generally, if you can't see any sources (or potential sources) of stray light through the focuser than there won't be any stray light getting into the focuser. It doesn't matter where light goes that won't be seen. Truss dobs can be fully baffled and immune to stray light without shrouds. Mel Bartels gives some good information on doing that and checking it to see that it works, and I highly recommend what he has to say about it, because it works.

Bottom line, the only thing you should be able to see through the focuser is what the telescope's pointed at. Do that and there won't be any stray light interference, it's that simple.

Best,
Mark

Edited by mark cowan (10/06/09 09:58 PM)

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Yes, and that's basically what mine is, except that it is flush with the inner surface of the OTA so that there will be no chance of it vignetting the intial incoming rays from the sky-end of the tube.

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Oh, you might be surprised.

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I hate to say it, but I think this is a Eurpopean thing,

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From your description here, it sounds as if the box would be coming out of a hole cut in the area of the OTA which faces the "back" side of the secondary. If that is the case, I don't see how that would do anybody any good.

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It's better than flocking, that's all. Because it uses baffling on a large scale (rather than on an uncontrolled microscale, like flocking does).

On the other hand, reflectivity for a flocked surface isn't that big when you look at it from the normal of the surface, so it's probaby overkill.

--------------------

400mm f/4.46 self made Dobsonian on Tom Osypowski equatorial platform
Orion Starblast (114mm f/4 reflector, Alt/Az)

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Yes, and that's basically what mine is, except that it is flush with the inner surface of the OTA so that there will be no chance of it vignetting the intial incoming rays from the sky-end of the tube.

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There's no "except". Mark doesn't disagree it's sound placement

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So do you think that my placement and design of the focuser baffle is a good use of baffling? It just seemed to make sense to me, and it does appear to improve contrast in the images. Of course, it's difficult to tease out the individual contributions of the OTA flocking, the focuser baffle, and the light shield. I just know that my visual experience at the eyepiece has improved.

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I'm not surprised. These baffles are more effective at negating the need for larger baffled (light shields) at the other end of the UTA or tube.

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But the light shield is so easy to make, it would be a shame not to use one on a Newt or most any scope. Ease of design and implementation is an important factor that should not be ignored. I never ignore it! Light shields are especially useful when observing at a site where there is much ambient light and direct glare, e.g., most suburban yards. They also provide excellent dew protection for the objective or corrector lens, or for the diagonal in the case
of Newts.

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But personally, I think it's penny wise but pound foolish to put in an extra vane in the light path (and one that's very thick for off-axis objects). Unless a lightweight design is *the* primary design consideration.

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Agreed. I wouldn't do it.

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I hate to say that the first examples of combined curved vanes and baffles that I've seen originate from the US. I've even seen them on CN.

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I did say that the observation was from my own limited experience.

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From your description here, it sounds as if the box would be coming out of a hole cut in the area of the OTA which faces the "back" side of the secondary. If that is the case, I don't see how that would do anybody any good.

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It's better than flocking, that's all. Because it uses baffling on a large scale (rather than on an uncontrolled microscale, like flocking does).

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I certainly would like to see a visual illustration of the "light box trap." If it does entail cutting a hole in the side of my OTA, it's not gonna happen! But I might consider eyeballing the area of the OTA that is visible when looking through the focuser tube, and perhaps setting up baffles around that limited area. Just a thought.

Clear Skies,
Mike

--------------------
Celestron 10" f5 Newt on 1stBase (DSO)
Zhumell 8" f6 Newt, Bosma 6" f12 MCT (NSO)
6" f5 Newt, 130ST, 4.5" f4.4 Ball w/GLP, ST80 w/Crayford (RFTs)
C4-R (NSO/DS)
90mm f13 MCT (Luna/DS)
SkyMaster 25x100, 15x70
Zhumell 20x80
Barska XWA 10x50, 8x40
OptiView LPR 10x50
Const View 2.3x40
BV-125C
CG5, 2 drv / CG4, 2 drv, wood legs, ScopeStuff saddle / CG3, 1 drv
SV AZ / 501HDV on Bogen 055XB / P+ on Oberwerk
QuikFinder, Telrad
Orion Dynamo Pro 12, Dew-Not
Have GLP and not afraid to use it!

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But the light shield is so easy to make, it would be a shame not to use one on a Newt or most any scope. Ease of design and implementation is an important factor that should not be ignored. I never ignore it! Light shields are especially useful when observing at a site where there is much ambient light and direct glare, e.g., most suburban yards. They also provide excellent dew protection for the objective or corrector lens, or for the diagonal in the case
of Newts.

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Alexis didn't say it replaced the light shield (needed) he said it allows for a smaller light shield. This is useful for several reasons - on large fast dobs the light cone is steep, and hence the view out past the secondary is also steep, which calls for a large light shield that then catches the wind and generally gets in the way. Using a focuser baffle reduces this part in size - it's certainly what I'm planning to do in producing commercial ultralight ultrafast dobs.

But maybe this is semantics - if by "light shield" you mean a tube extension - I mean a circular baffle (often with a hole in the center) attached to the far side of the truss OTA opposite the focuser. Tube extensions are very useful, but not needed or practical on truss dobs.

I'll give a practical example about baffling, though due to the CN TOS I can't name names. At the last Oregon Star Party a well known optician attended on a road trip of several star parties, with his 30" f/4.5 (or so) motorized commercial scope design, which I got to try out. Lifetime best view of M92 (one of my favorite globs), so I knew it was good, but that was straight overhead. During the day due to the dust devils and wind he'd taken the shroud off, but the scope wasn't baffled properly for use without the shroud. Later that evening he dialed up the Lagoon and Veil Nebulae, without the shroud. I didn't recognize them! The contrast was so poor with stray light around the grounds getting into the focuser that the field was just stars, with "oh yeah! A hint of nebulosity!". My 8" planetary with its flocked solid tube far outperformed this 30" on these targets.

Best,
Mark

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So do you think that my placement and design of the focuser baffle is a good use of baffling?

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But the light shield is so easy to make, it would be a shame not to use one on a Newt or most any scope.

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If it does entail cutting a hole in the side of my OTA, it's not gonna happen!

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Then it's not going to happen. It's a way of making sure that the relevant part of the tube opposite the focuser (which you necessarily must see to have anything but a point sized fullt illuminated field) is in fact itself baffled, i.e. obscured by shadows.

But as I said, in general, if you flock the opposite of the UTA it's probably good enough. Yes, in sunlight you still can see a difference betwene a flocked surface and one in the shadow, but if you're looking at the Sun *a lot more* light still goes to the focal plane the correct way than is reflected by the flocked surface (seen on its normal).

And when the Sun's up, atmospheric scattering (i.e. the blue background sky) is going to make a lot more veiling glare than anything that a light trap can catch. Which is why most of us don't try to observe faint nebulae when the Sun is up .

The only condition I think a light trap could actually make a difference is when the full moon is up and you're still trying to observe other objects. But an ad-hoc baffle preventing moonlight from hitting the tube wall opposite the focuser seems a perfectly fine idea, even if it's a friend of yours holding up a cardboard.

And yes, even that is baffling (and I should think your friend will also be baffled when you ask him to hold up the cardboard ).

--------------------

400mm f/4.46 self made Dobsonian on Tom Osypowski equatorial platform
Orion Starblast (114mm f/4 reflector, Alt/Az)

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that you'd baffle be able to baffle my tube in anything under a few days.

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Flocking wins

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It's not a contest; as I said, baffling and flocking is complementary (you baffle what you can -- easily -- and you flock what you cannot baffle, which for some definitions of "easily" may be everything that is relevant when you have no "easy" baffles).

Understanding things, by the way, could have saved you quite some effort, because if you fully flocked a Newt's tube you probably flocked parts of the tube that could almost never contribute anything to veiling glare.


--------------------

400mm f/4.46 self made Dobsonian on Tom Osypowski equatorial platform
Orion Starblast (114mm f/4 reflector, Alt/Az)

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Alexis didn't say it replaced the light shield (needed) he said it allows for a smaller light shield. This is useful for several reasons - on large fast dobs the light cone is steep, and hence the view out past the secondary is also steep, which calls for a large light shield that then catches the wind and generally gets in the way.

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Using a focuser baffle reduces this part in size - it's certainly what I'm planning to do in producing commercial ultralight ultrafast dobs.

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But maybe this is semantics - if by "light shield" you mean a tube extension - I mean a circular baffle (often with a hole in the center) attached to the far side of the truss OTA opposite the focuser. Tube extensions are very useful, but not needed or practical on truss dobs.

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Unless I say otherwise, I am always speaking from the viewpoint of an owner of solid-tube Newts. So when I say "light shield" I mean "tube extension." I don't have a truss tube. But if I were to buy a reflector larger than 10", I would definitely get a truss tube. I do see a 14" or even up to a 16" or 17" in my future. One of the limiting factors, for me, would be that I do not want to have to stand to look in the eyepiece. If I have to stand, the scope's too big! It's better to know someone else with a scope that big and to just take a peek now and then.

Clear Skies,
Mike

--------------------
Celestron 10" f5 Newt on 1stBase (DSO)
Zhumell 8" f6 Newt, Bosma 6" f12 MCT (NSO)
6" f5 Newt, 130ST, 4.5" f4.4 Ball w/GLP, ST80 w/Crayford (RFTs)
C4-R (NSO/DS)
90mm f13 MCT (Luna/DS)
SkyMaster 25x100, 15x70
Zhumell 20x80
Barska XWA 10x50, 8x40
OptiView LPR 10x50
Const View 2.3x40
BV-125C
CG5, 2 drv / CG4, 2 drv, wood legs, ScopeStuff saddle / CG3, 1 drv
SV AZ / 501HDV on Bogen 055XB / P+ on Oberwerk
QuikFinder, Telrad
Orion Dynamo Pro 12, Dew-Not
Have GLP and not afraid to use it!

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A rule of thumb that I have heard for refractors is that the length of the dew/light shield should be ideally up to 2.5x the diameter of the objective.

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I just limit the length of the shield to about a foot and be done with it.

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A foot is still more than 150mm (and even with light material, it makes a difference of several hundred grams, which does have quite an impact on the positioning of the bearings on the mirror box (because of the lever) even though I have large bearings.

And without actually evaluating the focuser baffling, *you* won't even know whether a foot is enough (it depends on the profile of the focuser and the placement of the focal plane).

--------------------

400mm f/4.46 self made Dobsonian on Tom Osypowski equatorial platform
Orion Starblast (114mm f/4 reflector, Alt/Az)

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Let's see - for my current 400mm Dob UTA build, I have the choice of either making a hole 50mm rather than 70mm somewhere (so that it baffles part of the unwanted light) and making a light shield that's 150mm long, or making a light shield that's 1000mm long...

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I would go with the 150mm long light shield, if I were you. Remember, I am speaking from the refractor/Mak/binocular/moderately-sized-solid-tube-Newt world. What I should do isn't necessarily what someone with a 16" truss tube should do. If I had a big truss tube scope I'd look for different solutions than I'm currently implementing, also.

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By the way, the UTA has been made minimal; it's just large enough to mount the spider and to prevent it from hitting the ground with the UTA placed on the ground. That's why I need to pay attention to baffling.

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I just limit the length of the shield to about a foot and be done with it.

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A foot is still more than 150mm (and even with light material, it makes a difference of several hundred grams, which does have quite an impact on the positioning of the bearings on the mirror box (because of the lever) even though I have large bearings.

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To compensate for several hundred grams on my 10" solid tube Newt, all I have to do is shift the scope down in the rings a bit or place a little magnetic or other weight at the lower end of the tube. No big deal, and well worth the protection from dew and glare provided by the dew/light shield.

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And without actually evaluating the focuser baffling, *you* won't even know whether a foot is enough (it depends on the profile of the focuser and the placement of the focal plane).

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I know from experience that the view is better with the shield than without. A rule of thumb is good enough until I can get around to a closer evaluation and fine tuning. Also, I haven't experienced dew on the diagonal mirror since using the shield, so that is an added benefit I don't want to do without.

Mike

--------------------
Celestron 10" f5 Newt on 1stBase (DSO)
Zhumell 8" f6 Newt, Bosma 6" f12 MCT (NSO)
6" f5 Newt, 130ST, 4.5" f4.4 Ball w/GLP, ST80 w/Crayford (RFTs)
C4-R (NSO/DS)
90mm f13 MCT (Luna/DS)
SkyMaster 25x100, 15x70
Zhumell 20x80
Barska XWA 10x50, 8x40
OptiView LPR 10x50
Const View 2.3x40
BV-125C
CG5, 2 drv / CG4, 2 drv, wood legs, ScopeStuff saddle / CG3, 1 drv
SV AZ / 501HDV on Bogen 055XB / P+ on Oberwerk
QuikFinder, Telrad
Orion Dynamo Pro 12, Dew-Not
Have GLP and not afraid to use it!

Post Extras: