204 replies to this topic

[StefanBemmerl]

Thank you for your reply. The telescope has to stay on in any case, we had to put it on the mount with two people because it is such a heavy block. Yesterday it was constantly around 5 to 6 degrees Celsius all day, and there was hardly any difference at night. If it really comes from cooling down, I don't want to know what it's like when there are larger temperature differences. As I said, the adjustment was fine and the seeing was really good. My Newton, which cost less than 3000 euros, showed me an enormously better picture than the very expensive Mak. Jupiter wasn't wobbling in the Mak either, but it was a blurry spot with two stripes that couldn't be brought into focus. As I said, same as my C11. For such a large amount of money, I want to have something that works and doesn't require me to spend ages tinkering around with. I usually observe spontaneously, go out in the evening, open the roof and after 30 minutes my Newton is ready for use. To be honest, I'm pretty frustrated at the moment. I'll try it again this evening.

[deSitter]

Thank you for your reply. The telescope has to stay on in any case, we had to put it on the mount with two people because it is such a heavy block. Yesterday it was constantly around 5 to 6 degrees Celsius all day, and there was hardly any difference at night. If it really comes from cooling down, I don't want to know what it's like when there are larger temperature differences. As I said, the adjustment was fine and the seeing was really good. My Newton, which cost less than 3000 euros, showed me an enormously better picture than the very expensive Mak. Jupiter wasn't wobbling in the Mak either, but it was a blurry spot with two stripes that couldn't be brought into focus. As I said, same as my C11. For such a large amount of money, I want to have something that works and doesn't require me to spend ages tinkering around with. I usually observe spontaneously, go out in the evening, open the roof and after 30 minutes my Newton is ready for use. To be honest, I'm pretty frustrated at the moment. I'll try it again this evening.

I think you have to try the Reflectix jacket first. Everyone says that works. Fortunately it is a cheap and quick experiment, all you need is scissors and tape.

 

-drl

[StefanBemmerl]

What would be suitable for this, a sleeping mat?

[deSitter]

What would be suitable for this, a sleeping mat?

This stuff - if you can get it where you live. Just cut it to size and tape it in place. You can make it pretty later.

 

https://www.reflecti...ive-insulation/

 

-drl

[StefanBemmerl]

Thanks!

[deSitter]

Thanks!

The physics behind this is to prevent the heat from escaping (rapidly) through the tube wall, which is where you run into tube current problems.

 

Mylar was the preferred insulation during the Apollo missions. The lunar lander was covered with crinkly gold-covered Mylar - 10 or so layers of it - to control infrared radiation from the Sun. This is the reverse problem.

 

-drl

[StefanBemmerl]

I'll try it again if Markus agrees. I'm well aware of the principle, but I don't understand it when I think about yesterday. The telescope was outside all day at almost the same temperature. Maybe I should take off the heavy metal dew cap?

[deSitter]

I'll try it again if Markus agrees. I'm well aware of the principle, but I don't understand it when I think about yesterday. The telescope was outside all day at almost the same temperature. Maybe I should take off the heavy metal dew cap?

I think it is important to really understand the principle - radiative transfer of energy. An object will try to come into thermal equilibrium with its environment. It can do this by direct molecular transfer - the surrounding atmosphere and connection to the mount - or it can emit and absorb radiation, and this applies to everything out to infinity. What does a scope "see"? The metal tube it directly connected to outer space, which is at a temperature of 3 degrees Kelvin - -450F, -273C. That is, it will absorb almost nothing and lose - rapidly lose - its heat by attempting to come into thermal equilibrium with space. The bottom half of the tube will try to come into radiative equilibrium with the ground, chairs, yourself - which are 100s of degrees warmer. So the tube is caught in a thermal see-saw as you move it around - alternately frozen and baked.

 

There is an additional problem The tube gets so cold it develops a barrier to molecular transfer of heat. The boundary layer can be so cold that ice forms when the ambient temperature is higher than freezing. And it is very sticky - unless the wind is pretty stiff, that boundary layer will be stuck like glue to the outer wall of the tube. So you don't get much help from molecular heat exchange.

 

There are 4 solutions - you can insulate the interior of the tube, or the exterior of the tube, or you can make the tube of a material which naturally does not absorb or radiate - something like phenolic or spiral-bound paper. But in all cases the main problem is to prevent the tube from being caught in a thermal see-saw which ends up as big temperature differences on the INSIDE of the tube where the troublesome air lives.

 

The 4th solution is to actually heat the tube and fittings intelligently under control of thermocouples which monitor the temperatures.

 

If you leave the scope out, store it vertically so that the tube wall sees the sky as evenly as possible - and of course make sure it isn't in direct sunlight. Just because the Sun is out does not imply that space is any warmer than at night So the tube will do its thing during the day or night.

 

-drl

[saemark30]

Vahe,

Regarding Roland's 12" MAK story, is this with a 16T2 or 16T5 eyepiece?

Edited by saemark30, 06 February 2024 - 12:40 PM.

[JohnH]

I wouldn't give up to readily. Keep coming off of stuff ruins the view quite readily. I remember when my 6-in intes, I was looking at Mars during the 2003 opposition and I was concerned about a large streak of light coming off and I realized that was a heat plume from the baffle.

I had my Mak out and about last night for an hour and a half and it cooled down quite readily as I do leave it in an unheated garage when not in use and the temperature in there is comparable to the outdoors. Just moving it into the cool inside of my Observatory for an hour helped and it was pretty sharp right out of the starting gate.

The weather is looking pretty good again tonight so I may bring it out, and bring a guy down the road from me who owns a Questar three and a half inch

Edited by JohnH, 06 February 2024 - 12:54 PM.

[starman876]

That plume form the baffle on cold nights is so common in Maks and SCTs' and it really plays hell with image.

[deSitter]

That plume form the baffle on cold nights is so common in Maks and SCTs' and it really plays hell with image.

I suspect the baffle is modifying the air flow rather than being a direct source of trouble. It leaves a wake in falling air around it.

 

-drl

[clamchip]

In the past when I've owned telescopes with focal lengths in the 4000mm I have problems with

too much magnification, and I have bought 65mm and even 70mm fl eyepieces from Russell Optics.

I don't see a website but contact directly if you think you may be suffering similar symptoms:

https://makersrow.com/russell-optics

 

Robert

[starman876]

I suspect the baffle is modifying the air flow rather than being a direct source of trouble. It leaves a wake in falling air around it.

 

-drl

I have seen it in many compound scopes.  You defocus on a star and you can see the plume coming from the baffle.  It really screws up the image.   Thats why I dont take a compound scope out in the winter.     I used to play with my dobs and defocus on a star and put my hand near the end of the tube and watch the currents.    

 

I always wondered does the plume come from the baffle tube because of the warm eyepiece????  if you do not have electric focus could your hand heat up that end of the tube.   or any heat source near the back of the OTA be causing air currents.   A lot of SCT's have fans mounted on the back of the tube.  My old Meade 7" Mak has a fan.   

[clamchip]

I'll try removing my prism and give the focuser a gentle suck and see if the plume is disturbed.

My prism is in the focuser effectively damming the tube up but still it must be coming from the

baffle tube.

The SCT I highly suspect the secondary holder as the source of the plume but now after seeing

it in a Mak I'm not so sure.

The tube and rear cell cools faster than the baffle/primary mirror, maybe the baffle tube is creating

a current plume all by itself..

I used copper in my Mak for the baffle tube, it happened to be the size I needed. Now I'm

wondering if aluminum would be better. 

 

Robert

Edited by clamchip, 07 February 2024 - 01:22 AM.

[CHASLX200]

In the past when I've owned telescopes with focal lengths in the 4000mm I have problems with

too much magnification, and I have bought 65mm and even 70mm fl eyepieces from Russell Optics.

I don't see a website but contact directly if you think you may be suffering similar symptoms:

https://makersrow.com/russell-optics

 

Robert

Too much FL. You need a finder for scopes like that.  I may try a 8" Mak jack if i wanna face paying 3k or more. It is local.

[CHASLX200]

I have seen it in many compound scopes.  You defocus on a star and you can see the plume coming from the baffle.  It really screws up the image.   Thats why I dont take a compound scope out in the winter.     I used to play with my dobs and defocus on a star and put my hand near the end of the tube and watch the currents.    

 

I always wondered does the plume come from the baffle tube because of the warm eyepiece????  if you do not have electric focus could your hand heat up that end of the tube.   or any heat source near the back of the OTA be causing air currents.   A lot of SCT's have fans mounted on the back of the tube.  My old Meade 7" Mak has a fan.   

I take my eyep's outside to = scope temp.

[StefanBemmerl]

For me, everything is always outside in the observatory, so I don't have to put anything out beforehand. Unfortunately it was cloudy yesterday. Saturday it is supposed to become clear again and that is my last chance to return the telescope. I'm stuck with the 700 euro shipping costs, but I entered into this deal beforehand. I will isolate the tube until the weekend and am curious to see whether it will actually give me a different picture. I wanted a telescope to look into the back, otherwise I would be super happy with my Newton. But I would like to observe in a relaxed manner while sitting again and was hoping for a telescope that would give me the opportunity to have at least the same quality on the planet as my Newton.

[deSitter]

Vahe,

Regarding Roland's 12" MAK story, is this with a 16T2 or 16T5 eyepiece?

Does that make any difference? The view was far better through the Orthos. Case closed.

 

-drl

[deSitter]

For me, everything is always outside in the observatory, so I don't have to put anything out beforehand. Unfortunately it was cloudy yesterday. Saturday it is supposed to become clear again and that is my last chance to return the telescope. I'm stuck with the 700 euro shipping costs, but I entered into this deal beforehand. I will isolate the tube until the weekend and am curious to see whether it will actually give me a different picture. I wanted a telescope to look into the back, otherwise I would be super happy with my Newton. But I would like to observe in a relaxed manner while sitting again and was hoping for a telescope that would give me the opportunity to have at least the same quality on the planet as my Newton.

I have the same problem - my 10" Newtonian is getting too much to move around and I want to sit to observe. I might end up sending off my Newtonian and getting a 9.25" Celestron. My last hope is a shorter tripod for my Newtonian.

 

-drl

[clamchip]

I also have the same problem, I want to sit while observing, I always have preferred sitting. 

A newt is the amateur's instrument, how else are you going to reach these apertures?

But I must sit now more than ever and my big newt collects dust.

I would try your new M1212 during the daytime if possible. See how it performs on daytime

targets, a less hostile environment than nighttime.

Here's an example of one of my favorites, a cell tower 2-1/2 miles from my house. The red

arrow points to a perforated cylinder. Resolving the perforations is difficult. You want more

difficulty, there's plenty. Larger apertures I go for screw heads and wire connections.

Robert

 

Edited by clamchip, 07 February 2024 - 11:22 AM.

[StefanBemmerl]

Hello guys, today I'm going to the hardware store and buying insulation material. I will carry out another extensive star test on Saturday and, if necessary, photograph it intrafocally and extrafocally. What still surprises me is that the MC was outside for many hours and showed me a blurry ball at Jupiter and only 100x magnification. The image was calm, no streaks of air but spongy, muddy.

[rolo]

One thing that I found important in the Intes OTA design is the vents around the front meniscus to release inner OTA heat. When the scope is pointed upwards the heat has nowhere to go builds up and creates a distorting heat lens effect that may show as an oval diffraction pattern that may be creating an astigmatic effect preventing sharp focus. OTA heat is very slow moving and sometimes visible in the diffraction pattern as slow moving waves. Does your Mak have any venting holes around the front of the meniscus? Can you post some pics of the front and rear of the OTA?

 

Here's my old 10" f/12.5 APM/Wurth Mak, that was custom machined with rear vent holes for cooling. The most effective way to cool it down was facing down to release the heat through the rear. The fan didn't do much for cooling really. It was lined with cork insulation material that did nothing so I removed and flocked it instead. Also, note the push-pull screws on the rear cell for primary alignment. This scope was amazing on the planets with crisp, high contrast images that could rival my 12.5" f/6 Cave Newtonian. 

Also, since you previously asked, as far as a focal reducer I used a Celestron f/6.3 reducer to image the ring nebula and it did an excellent job. 

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Edited by rolo, 09 February 2024 - 12:07 AM.

[luxo II]

Rolo, looking at yours I’m stunned they managed to fit a fan in there at all without affecting the light path - in mine the gap between the primary mirror and the tube is under 5mm.

I’d also suspect the idea was originally to do with disrupting the boundary layer across the face of the primary - it’s far too small to have any significant thermal benefit.

But I’ve never seen anything to suggest there is an issue with the boundary layer on the primary…

Mine has a back with lots of holes as well, and a quartz primary. No ventilation around the front end. The other thing that has vents is the central baffle, which has knife-edge baffles machines inside, and its exterior has light - traps resembling stacked cones.

On mine the secondary mirror also has no baffle. Doesn’t seem to need one, either.

Edited by luxo II, 09 February 2024 - 01:34 AM.

[tim53]

That plume form the baffle on cold nights is so common in Maks and SCTs' and it really plays hell with image.

I find that this is a particularly vexing problem in planetary imaging.  If I don't use a star diagonal, the heat from the camera goes right up the baffle tube and makes a plume perpendicular to the ground.  If I put a star diagonal in before the camera, and orient it so the camera is on top, the plume disappears.

 

For my 9.25" in my observatory in Joshua Tree, I air condition the insulated observatory in summer months when it's hot outside, setting the temperature to the outside forecast for twilight.  But that wouldn't work in a cold climate, I suppose.

 

-Tim.