MCT Secondary Baffle Mod
Posted 28 November 2013 - 08:25 PM
Posted 28 November 2013 - 08:58 PM
Posted 29 November 2013 - 12:36 AM
Posted 29 November 2013 - 02:05 AM
No problem. Do you infact do daylight spotting with the Mak? Now and again I like to take out the 70mm refractor to the shore and such. I'm promising myself to take the C6 too - but after seeing this - Ill wait till I flick it out.
Again a great set of revealing pics.
Posted 29 November 2013 - 02:09 AM
I plan on a shoot out after I complete both of mine. I will then compare the contrast from the C6 vs my 6 inch refractor. Seems many SCTs have gotten a bad wrap because of poor baffling.
I'm very interested in your results. The primary baffling on the pic you presented would appear to be throwing glare from its exterior . I suppose this could be wrapped in flocking too?
I look forward to your tests and pics.
Posted 29 November 2013 - 05:14 AM
My scope also has that ~2mm ring of unused secondary. I guess a nice rubber ring outta do the trick. That plus a few additional mods Don mentioned. I added a knife edge in the bottom of eyepiece insert tube of the diagonal just above the mirror. Eyepieces still fit with the barrels not quite reaching that deep into the diagonal and stopping just short of that knife edge. This seems to block scatter inside the diagonal eyepiece barrel from bouncing into the eyepiece itself. It's just an appropriately sized (square) rubber ring, too.
Ed, how did you mix your flat black paint. It's time to try some of that but am concerned about out-gassing, as well. Thanks in advance.
Posted 29 November 2013 - 10:55 AM
I have to believe at this point when folks have talked about their apo having the same contrast on deepsky nebula as much larger sct that the culprit here is all that off axis skyglow in the optical train bouncing off the baffles and such.
For the reflector Ive thought of have a black velvet insert opposite the focuser as a definitive black backdrop to the light one entering the eyepiece.
Posted 29 November 2013 - 12:23 PM
I'm sure the refractor guys talk about their baffling, but really the end result to contrast is a combination of lens scatter, sky glow, and internal reflections. We can't do much about the former two, but the latter we can get a handle on. So, that leaves sky glow and lens scatter with the latter being the only thing to boast about, optically anyway. In the tropics, atmospheric scattering (humidity plus aerosols) can be pretty hard on a guy especially with bright objects. But flocking and baffling gets rid of what we can get rid of, so it's worth the effort as Ed's images show. But, improvement's harder to see against dark skies and dim stars. Just knowing it's there, though, is nice when you turn your scope to Jupiter.
Posted 29 November 2013 - 10:39 PM
I then baked the parts in the oven at 200 degrees for 20 minutes to get them dry and hot before painting them. That was the easy part! Due to how smooth the primary baffle was on the inside, even after painting it with flat black, there were still small reflections from it. So, I went the way of Mr. Ed Holland and opted for a painted and rolled up tube of sandpaper of 180 grit. This most definitely did the trick! I also used a black marker around the edge of the primary mirror to blackened the reflective 45 degree edge.
This scope is so small it is hard to work on with all the rubber o-rings and washers. So it was a bit of a pain to put it back together. Not hard, just tedious. What was a pain was collimating the scope after a complete disassembly. I also found that the mirror was off center on the baffle slider and shimmed it with masking tape to center it and take up the slack on the baffle slider tube. So was all this work worth all the trouble? You bet! The little scope now star test better than it did before! There are also no more flares from bright stars, etc. And as Ed had shown, the contrast seems to be about four times better.
I know it's a little scope and that actually makes it worse, so don't jump into this mod if you have never done this kind of work before. I have rebuilt many scopes and binoculars and this was still a challenge for me. The good news is, I really love this little scope now!!
Tomorrow, I will try to post some images taken through the scope before and after the mods. Until then, here are some pictures of the C90 as I was doing the work...
Posted 29 November 2013 - 11:23 PM
I wait your results. Excellent. Thank you for posting, I might have to probe deeper and do some flat backing. Your baffle 'looks' darker. Really curious to know if there is a noticeable improvement.
Posted 30 November 2013 - 06:16 AM
Posted 30 November 2013 - 03:05 PM
- Zachrey likes this
Posted 30 November 2013 - 04:23 PM
Were those two pics taken on different days? They look so similar that you must have taken them at very nearly the same time, indeed, and not so many days apart (given the Sun's lowering declination.) And from pretty near the spot. I can detect only a slight difference in the placement of the vertical shadow near the bottom.
The contrast difference is most striking.
Posted 30 November 2013 - 04:28 PM
Posted 30 November 2013 - 05:32 PM
If the scene has uniform brightness, such as a patch of blank daytime sky, veiling glare increases brightness but does not alter contrast, for there was no contrast to begin with.
A nighttime sky is in a fashion different to the kind of daytime scene illustrated above. The latter sees the generally lesser 'shadow' zones affected most. A night sky is more like a vast shadow zone with a very much smaller collection of brighter highlights. Yet the same principle reigns. The veiling glare raises the brightness of the sky relatively more than it does for the brighter parts, thereby reducing contrast.
And the eye is primarily a contrast detector. Veiling glare afflicts all scenes having any intrinsic contrast, always lessening it.
Posted 30 November 2013 - 06:18 PM
Ok. The difference in contrast is huge. Well done. Especially for a scope like C90 ,which can easily used as a spotting scope, the mod is extremely successful. However, after reading Edgie's thread, I think also that in night time use the effect will be much less noticeable and probably insignificant,depending on the target. If anyone else decides to do similar flocking mod, it would be interesting to provide us with night time photos of landscape objects. Some poor light urban areas maybe, that can simulate better situations like while observing the moon or planets. Oh by the way excellent thread!!
If you look at my first picture showing the problem I was having, you will see flares off of almost any object, even 5 or 6 mag stars. The image is shown as an inset image. This was at night and it would happen in every image. So, it does make a huge difference at night because those flares are now gone!
They were shot a day apart within about 20 minutes of the same time of day. And the tripod was marked and in the same spot.
Posted 30 November 2013 - 06:31 PM
You got onto and finished that mod/enhancement in mighty short order! And good work it is. We amateurs fret and fuss over infinitely tinier differences than shown here; wander over to the refractor and eyepiece Forums to see what I mean.
Posted 30 November 2013 - 06:48 PM
After I took the pictures yesterday, I came in and pulled it down. I started cleaning and washing parts and once I had it all cleaned, I heated parts in the oven and went out back to paint. While they were drying, I took a break for dinner. After that, it took an hour or two to put it back together and get it collimated.
Posted 30 November 2013 - 10:17 PM
Glen, I find your results nothing short of astonishing, especially since the artifacts that troubled you are gone. Very well done. In your case, the results are definitely showing some improvement. In my case, I really do not notice much, if anything as Eddgie talks about, but I cannot escape the idea there has been improvement. And that's enough reason to pursue it, if one is so inclined. Seems I still have some room for additional improvement since this thread was revisited (thanks, Pete!)