New AT 6" and 8" Classical Cassegrain
Posted 10 March 2021 - 04:37 AM
Posted 10 March 2021 - 06:08 AM
as I said. The secondary is restricted by its fixing ring. When it is bigger, for instance that it touches the baffle then fixing it without that ring would enlarge it to 55 mm. Then the baffle must be widened, there's spare for three more mm.
- Thandal likes this
Posted 10 March 2021 - 01:07 PM
@quilty; Wow! That would be an extraordinarily complicated amount of work to gain... what? Sure, if the (I presume unintentional) vignetting of the full aperture is a major issue it *might* be worth it. But at the price-point of these instruments, is it?
I haven't gone to the trouble of accurately measuring the size of my (Orion-branded) 8" CC, and I'm not sure I will. While it's interesting to know there might be something that could be done to improve it, (if desired) I probably wouldn't bother myself.
But thank you for describing how it *could* be done!
Edited by Thandal, 10 March 2021 - 01:08 PM.
Posted 10 March 2021 - 02:42 PM
That's what I'm asking. Aperture 150 instead of 138, CO 41 instead of 44%. Is it worth it? Could that be seen?
The price is no point to me. I think the scopes are worth it as soon as that improvement is considerable. Not too complicated. For me the challenge is to shorten the baffle without leaving ugly traces.
Somewhere in this thread I guess, there you'll find that your 8 inch scope in its real life is a 7.34 inch scope. The same thing on a larger scale.
Posted 11 March 2021 - 11:41 PM
Я не вижу здесь, чтобы вторичное зеркало ограничивалось стопорным кольцом. Край вторичного зеркала виден и свободен. Единственное, что мешает, - это отражение бленды линзы вторичного зеркала по краю этого зеркала.
Edited by Russkiy, 11 March 2021 - 11:42 PM.
- Gen 1:16 likes this
Posted 12 March 2021 - 03:59 PM
I don't understand where this fixing ring is located?
Posted 13 March 2021 - 05:09 AM
The secondary mirror is pressed at its circumference by a screwring to the baffle bottom. I' ve not yet removed ring and secondary to have a look under it. But this ring's inner diameter is 48 mm and propably the sec mirror is larger than that. My question is what can be seen on you pic?
Posted 13 March 2021 - 05:20 AM
Posted 13 March 2021 - 11:50 AM
Sorry, not in the next days. But if necessary I'll do later. That's why I didn't see what is on your pic. Me as well have the TS thing, but I remember the secondary baffle to look slightly different. In your photo on the right side, there's a gap and there might be another at the opposite side in order to screw or unscrew this ring. What puzzles me is that inside this ring there seems to be another, darker ring. When that's just a fotografic artefact, you can loose and remove that ring using the gaps (best with a hard plastic tool) by turning left and I think totally remove it. If the secondary itself is just pressed or additionally stuck to the baffle bottom I don't know.
Edited by quilty, 14 March 2021 - 02:24 AM.
Posted 13 March 2021 - 02:20 PM
Posted 14 March 2021 - 02:34 AM
I'm not at home so I cannot provide fotos of my own. But there is another slit or gap on opposite position of the one on the right side of your foto isn't it? What happens if you insert a tool and try and turn left (when you dare)?
I think your translating machine works fine.
Posted 14 March 2021 - 04:00 AM
Posted 14 March 2021 - 04:27 AM
I'm afraid when you want to know better you'll have to. The good thing: This one is very simple and it's hard to do wrong.
Posted 02 April 2021 - 02:25 AM
Not much of news, just my better seeing. Above I stated as reason why the 6 CC is so delicate about seeing that it's open and inhmogenous air can enter into the space between the mirrors. The effect might be amplified by the pointed light beam coming from the sec mirror. There's not much of experience about such short, open optics, that's why this maybe hasn't been cosidered yet.
Secondly the high extent of CO makes the vision still unstable. It widens the diffraction pattern (if there is any) and any poor seeing now sqirls that pattern into a mess. There's no need do disturb the pattern in the range of its dimension, to smear and fill the space between subsequent diffraction maxima is enough to produce the chaos. Strangely this doesn't seem to have been considered neither for there are many small and highly obstructed scopes out there in use for many years. The very similar RC scopes are supposed to be even more delicate to this regard (to avoid "dreadful").
I think both reasons work together.
By the way my operation entered the phase of concrete planning :-). I think there's no need to replace the cut section of the secondary baffle by a tin, appropriate shortening will do. (To the owners of an 8CC: I think it's worth it (if faisible), you will reduce your CO from 36% (if it is 67 mm diameter) to then 33%, which is quoted to be tolerable.
I'll let you know when successful. And then, if truth be told, what else would you expect me to declare but a great improvement? :-)
Edited by quilty, 02 April 2021 - 03:44 AM.
Posted 02 April 2021 - 06:22 AM
Hey Quilty, Still on this matter eh.
There will be little to gain from what you want to do and you may find the mirror behind the collar defective with a turned edge or scratched.
My advise is just sell it on the used market before you make it unsellable. Then buy yourself on the used market the largest newt primary set and put your energy towards building a 10"-12" Newtonian.
Then you will be happy and it will be worth the effort.
- eros312 and Terra Nova like this
Posted 05 May 2021 - 09:04 AM
yes, but it's over now. I've checked, The gain of secondary diameter is 1 mm maximum, which means the fixing ring takes no more than that. Not worth it.
Posted 05 May 2021 - 06:28 PM
I should try one out in my super steady seeing as i am still at over 80f at nite this time of year.
- eros312 and Terra Nova like this
Posted 10 May 2021 - 02:46 AM
It is simply necessary to take for granted that this telescope has an aperture of 138 mm instead of the stated 150 mm. For this money, such an aperture is not bad.
Edited by Russkiy, 10 May 2021 - 02:48 AM.
Posted 10 May 2021 - 02:44 PM
Its possible to pull the primary backand the final focus forward and use the full aperture of the 203mm model I've done this.
Having the primary forward and requiring the spacers at the back means the secondary is'nt big enough to cover the whole primary.
The larger screws need to be wound anti clockwise and the smaller then wound in on the primary adjustment to do this. Do them all the same ammount and the collimation is always close.
Posted 10 May 2021 - 02:47 PM
Pull the primary back and secondary won't be too small. works on the 8
How could this operation free up the 150mm aperture if the aperture is reduced due to the secondary mirror being too small?