Author Topic: Cooldown times (APO refractor vs Newtonian reflector)  (Read 381 times)

pelotwollgar

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Cooldown times (APO refractor vs Newtonian reflector)
« on: December 28, 2017, 11:56:45 PM »
Hello...

I've read contradictory statements regarding this so wanted to check here.

Assuming aperture size is the same, which type would you say requires less "cooldown" time:

- An APO doublet or a reflector?
- What about a triplet vs a reflector?

And let's say an 80-120mm APO vs 8"-12" dob?

Thanks guys!

Alex



imasatex

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Re: Cooldown times (APO refractor vs Newtonian reflector)
« Reply #1 on: December 29, 2017, 04:31:23 PM »
Alex:

In general, refractors are more thermally stable than reflectors. Not only do refractors cool faster but they are less affected by the cooling process so they perform closer to their potential while cooling.

But just because a scope has not reached thermal equilibrium, it does not mean the scope is unusable, it will still give good views, it's just that it wont provide the best possible views at higher magnfication.

Jon

Akida Holland

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Re: Cooldown times (APO refractor vs Newtonian reflector)
« Reply #2 on: December 30, 2017, 06:15:01 AM »
IME for DSO's I find minimal issues with thermals in mirrors, however Planetary/Lunar is a different story sometimes requiring Boundary Layer fans for optimal potential with a Mirror.

Jared Morgan

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Re: Cooldown times (APO refractor vs Newtonian reflector)
« Reply #3 on: January 03, 2018, 04:29:52 PM »
Quote

Assuming aperture size is the same, which type would you say requires less "cooldown" time:

Well, if aperture is the same it will get tricky...a 6" Newt will cool pretty quickly compared to other larger reflectors. A 6" apo will likely take some time compared to smaller apo refractors. Even my 110mm ED takes some time to adjust, although perhaps 1/3 the time that the 10" Dob does for best view planetary--of course the Dob is putting up better views nearly the entire time and far better in a fraction of that time.

I don't think anyone has much feel for cool down of an 8 or 10" apo vs. an 8 or 10" Dob/Newt.

tamamatte

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Re: Cooldown times (APO refractor vs Newtonian reflector)
« Reply #4 on: January 04, 2018, 09:28:33 AM »
In choosing a scope there are much more important considerations than cool-down time. The fields of view, range of magnifications, transportability, suitability for AP or other specialized mode and other factors are more useful factors. Cool-down is just something you learn to deal with in your scope. There are strategies that can be applied.As above, it has limited impact on many observations.

Your local conditions impact an answer to your Q. What's ambient? What's storage temp for the scope? What's the expected temp range of change over a session? For some folks at some times of the year storage temp can closely = ambient and little change will occur over a night.

grumepinod

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Re: Cooldown times (APO refractor vs Newtonian reflector)
« Reply #5 on: January 04, 2018, 03:42:03 PM »
No help, but I don't know of anyone that waits and that includes me. Every one I know of will take the scope out, set it up and get prepared then just gets viewing. The scope(s) get as much cool down as it takes to get ready to put eye to eyepiece.

The cool down time seems to be one of those academic values. The mirror/lens may have attained a better shape after an hour but the purpose is to use the scope to view things.

Worst case you could be saying:
I was waiting for the scope to cool down and missed Betelguese going nova.

calbeyrefrows

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Re: Cooldown times (APO refractor vs Newtonian reflector)
« Reply #6 on: January 08, 2018, 03:53:46 AM »
My scopes live in a well ventilated, unheated garage so they are close to ambient temperature most of the time, so this is not something I have to deal with generally.

Is the question one of interest, or a concern about how long it will take before you can use the scope?

Waiting time to use the scope is near zero, as far as know.  As long as there is no fogging or condensation due to humidity you can take the scope out of the house and use it.   What I read on the forums is that you might see is an improved high power view over time.

If the house is 70 degrees and it is 60 to 80 degrees outside I am not sure that is enough to be a major issue, but others can better advise. If it is 70 in the house and 20 degrees outside then the thermal adjustment will likely be more of a consideration.

What is your concern?

tradunjuwa

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Re: Cooldown times (APO refractor vs Newtonian reflector)
« Reply #7 on: January 08, 2018, 01:00:57 PM »
Quote
In choosing a scope there are much more important considerations than cool-down time. The fields of view, range of magnifications, transportability, suitability for AP or other specialized mode and other factors are more useful factors. Cool-down is just something you learn to deal with in your scope. There are strategies that can be applied.As above, it has limited impact on many observations.

Your local conditions impact an answer to your Q. What's ambient? What's storage temp for the scope? What's the expected temp range of change over a session? For some folks at some times of the year storage temp can closely = ambient and little change will occur over a night.

I know about that.  I've taken all those aspects into consideration for a variety of different types of scopes and scope sizes with different eyepieces and barlows. Last thing to consider was cooldown times so I came here to ask.

As for temps... Room temperature ( = scope temp) would be about 70-75F. Maybe a bit lower during the winter.
Average winter temps are around 35F. Guessing the temps during winters would be 65F room and 20F outside (15-30F)... Not sure... might be a bit higher room temps as well as outside temps. While I'm typing this (8:00 PM) it's 77F outside, but it will drop by a few degrees in the next couple of hours for sure. I'd do most of my observing between midnight and 2 AM. During the summer the difference would be small, but winters are a different story.

inovilmei

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Re: Cooldown times (APO refractor vs Newtonian reflector)
« Reply #8 on: January 09, 2018, 08:53:29 AM »
Quote
My scopes live in a well ventilated, unheated garage so they are close to ambient temperature most of the time, so this is not something I have to deal with generally.

Is the question one of interest, or a concern about how long it will take before you can use the scope?

Waiting time to use the scope is near zero, as far as know.  As long as there is no fogging or condensation due to humidity you can take the scope out of the house and use it.   What I read on the forums is that you might see is an improved high power view over time.

If the house is 70 degrees and it is 60 to 80 degrees outside I am not sure that is enough to be a major issue, but others can better advise. If it is 70 in the house and 20 degrees outside then the thermal adjustment will likely be more of a consideration.

What is your concern?

No major concern, just wondering, so I know what to expect and to take that into consideration when choosing a first scope in the near future.

I know Maks are the worst when it comes to thermal adjustment. Love their compact size and the fact they are great for planets even in a light polluted city. But the planets will be pretty low for the next couple of years, so not sure if a Mak would be the way to go at this moment. Not the best for DSOs because of narrow FOV.

APO refractors (cost aside), wide FOV, crisp high-contrast images, lower cooldown, no collimation, eyepiece position, great on planets, but smaller aperture size does not make them so great for DSOs. Considering a smaller size one (80mm or so) for it's super nice FOV, but not sure it will be good at all in the city. 150mm might be somewhat decent for urban viewing but the price of $6k or so just for the OTA... ouch!

Mabe 12" dob would be best in this case. I still don't know. Would like something portable which I could take out of the city from time to time. Collapsible 12" dob is still very big. I could put it in my small car, but not much more would fit in after it, if you know what I mean.  Guess it would be OK for urban viewing.

SCTs not available here.

Just bored a bit and thinking out loud... forgive me.

Chad Fithian

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Re: Cooldown times (APO refractor vs Newtonian reflector)
« Reply #9 on: January 10, 2018, 12:03:19 AM »
Quote
Quote

My scopes live in a well ventilated, unheated garage so they are close to ambient temperature most of the time, so this is not something I have to deal with generally.

Is the question one of interest, or a concern about how long it will take before you can use the scope?

Waiting time to use the scope is near zero, as far as know.  As long as there is no fogging or condensation due to humidity you can take the scope out of the house and use it.   What I read on the forums is that you might see is an improved high power view over time.

If the house is 70 degrees and it is 60 to 80 degrees outside I am not sure that is enough to be a major issue, but others can better advise. If it is 70 in the house and 20 degrees outside then the thermal adjustment will likely be more of a consideration.

What is your concern?

No major concern, just wondering, so I know what to expect and to take that into consideration when choosing a first scope in the near future.

I know Maks are the worst when it comes to thermal adjustment. Love their compact size and the fact they are great for planets even in a light polluted city. But the planets will be pretty low for the next couple of years, so not sure if a Mak would be the way to go at this moment. Not the best for DSOs because of narrow FOV.

APO refractors (cost aside), wide FOV, crisp high-contrast images, lower cooldown, no collimation, eyepiece position, great on planets, but smaller aperture size does not make them so great for DSOs. Considering a smaller size one (80mm or so) for it's super nice FOV, but not sure it will be good at all in the city. 150mm might be somewhat decent for urban viewing but the price of $6k or so just for the OTA... ouch!

Mabe 12" dob would be best in this case. I still don't know. Would like something portable which I could take out of the city from time to time. Collapsible 12" dob is still very big. I could put it in my small car, but not much more would fit in after it, if you know what I mean.  Guess it would be OK for urban viewing.

SCTs not available here.

Just bored a bit and thinking out loud... forgive me.
There is nothing inherently wide field about an APO refractor.  Field of view is based on focal length, magnification and the apparent field of view of the eyepiece. Any short focal length scope will give you a wide field of view, refractor or reflector.  SCTs and Maks tend to be long focal length scopes so they are typically not considered wide FOV scopes.

A 400 mm FL Newtonian and a 400 mm FL refractor will have the same field of view with the same eyepiece.

FL Scope / FL eyepiece = Magnification

AFOV eyepiece / magnification = FOV

Note that there is no consideration of what type of scope is involved.

ndesevtenzio

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Re: Cooldown times (APO refractor vs Newtonian reflector)
« Reply #10 on: January 11, 2018, 06:13:39 AM »
Quote
There is nothing inherently wide field about an APO refractor.  Field of view is based on focal length, magnification and the apparent field of view of the eyepiece. Any short focal length scope will give you a wide field of view, refractor or reflector.  SCTs and Maks tend to be long focal length scopes so they are typically not considered wide FOV scopes.A 400 mm FL Newtonian and a 400 mm FL refractor will have the same field of view with the same eyepiece.

FL Scope / FL eyepiece = Magnification

AFOV eyepiece / magnification = FOV

Note that there is no consideration of what type of scope is involved.
Sorry, I was referring to the APOs mostly between f-5 and f-7.

Mike Brown

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Re: Cooldown times (APO refractor vs Newtonian reflector)
« Reply #11 on: January 12, 2018, 04:03:03 AM »
As long as you know it, that is all that matters.

Jaimeylos Chiessa

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Re: Cooldown times (APO refractor vs Newtonian reflector)
« Reply #12 on: January 12, 2018, 05:54:09 AM »
Quote
In the winter going from 70 inside to 35 outside I've found the following:
80mm refractor 10-15 min
100mm refractor 15 min
130mm refractor 30-40 min
All of those are doublets. Tripliets would take more time.
6 in reflector 45-1hr 15 min
10 in reflector 1hr 30min - 2hr
A fan on the mirror can cut that down in half.
That sounds about right to me. Note that cooldown time increases with aperture more rapidly for refractors than for reflectors -- just as cost does. That's presumably because big refractors necessarily have fairly thick lenses, whereas big reflectors can get by with pretty thin mirrors, assuming the mount is well designed.
Also, there's a huge variation depending on the design of the particular telescope. For instance, reflectors whose tubes are open on both ends cool much faster than ones whose bottoms are blocked off. For reflectors in particular, cooldown time depends a lot on the wind. Having a stiff breeze blowing through the tube is as good as or better than a fan.

Cooldown time is surprisingly insensitive to the temperature differential between inside and out, since most of the cooldown time is probably spent on the last 10 degrees of adjustment. However, if the temperature outside is falling rapidly (very common in the Western U.S.!), a big reflector with poor ventilation may never really catch up at all.

Derek Vail

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Re: Cooldown times (APO refractor vs Newtonian reflector)
« Reply #13 on: January 12, 2018, 12:24:35 PM »
Quote
Quote

My scopes live in a well ventilated, unheated garage so they are close to ambient temperature most of the time, so this is not something I have to deal with generally.

Is the question one of interest, or a concern about how long it will take before you can use the scope?

Waiting time to use the scope is near zero, as far as know.  As long as there is no fogging or condensation due to humidity you can take the scope out of the house and use it.   What I read on the forums is that you might see is an improved high power view over time.

If the house is 70 degrees and it is 60 to 80 degrees outside I am not sure that is enough to be a major issue, but others can better advise. If it is 70 in the house and 20 degrees outside then the thermal adjustment will likely be more of a consideration.

What is your concern?

No major concern, just wondering, so I know what to expect and to take that into consideration when choosing a first scope in the near future.

I know Maks are the worst when it comes to thermal adjustment. Love their compact size and the fact they are great for planets even in a light polluted city. But the planets will be pretty low for the next couple of years, so not sure if a Mak would be the way to go at this moment. Not the best for DSOs because of narrow FOV.

APO refractors (cost aside), wide FOV, crisp high-contrast images, lower cooldown, no collimation, eyepiece position, great on planets, but smaller aperture size does not make them so great for DSOs. Considering a smaller size one (80mm or so) for it's super nice FOV, but not sure it will be good at all in the city. 150mm might be somewhat decent for urban viewing but the price of $6k or so just for the OTA... ouch!

Mabe 12" dob would be best in this case. I still don't know. Would like something portable which I could take out of the city from time to time. Collapsible 12" dob is still very big. I could put it in my small car, but not much more would fit in after it, if you know what I mean.  Guess it would be OK for urban viewing.

SCTs not available here.

Just bored a bit and thinking out loud... forgive me.
I think you would be very happy with a 10" dob. Fitted with a coma corrector and high quality eyepieces, I get refractor-like views. Where I live, winter cool-down on my 10" dob is about 1 hour. As stated, this only affects high power viewing. If you live in a cold climate, a cooling fan will help greatly.

Where do you live?

belmadeasus

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Re: Cooldown times (APO refractor vs Newtonian reflector)
« Reply #14 on: January 13, 2018, 11:59:44 AM »
Quote
I think you would be very happy with a 10" dob. Fitted with a coma corrector and high quality eyepieces, I get refractor-like views. Where I live, winter cool-down on my 10" dob is about 1 hour. As stated, this only affects high power viewing. If you live in a cold climate, a cooling fan will help greatly.

Where do you live?
I live here.