38 replies to this topic

[sahstim001]

Hello, I'm new to the forum (though I've been reading for some time, lots of great stuff on here). My wife and I are relatively new to astronomy, about 9 months now.

 

Some background:

Our first telescope is a Celestron Starhopper 8.

Basically when we were deciding which scope to buy we thought our biggest goal would be a nice view of Saturn. After doing research we decided an 8" would deliver the views we want, and it has been a good scope to us. Now our interest has spread into the world of DSO's, and we're planning to upgrade to a 12" (either Apertura AD12 or Zhumell Z12). Well today my wife asked 'what will Saturn look like in the 12"?' So I went back and looked at those same articles that lead us to 8", and I noticed that the views they claim with an 8" scope do not match our experience. I have attached one such image comparing a sumulated 4" on top and 8" on bottom. I also attached one of my images showing approximately what we see. Our view is better than the simulated 4", but well short of what it claims for 8".

 

1. Are we doing something wrong, or is the simulated view unrealistic? Could it be our collimation? We have a laser and collimation cap, but no Cheshire. 

 

2. I'd like to get a Cheshire to make sure our 12" performs at its best. It'll be an F/5. What are your recommendations? I've heard Celestron makes a good one, would that be a good choice? I also plan on trying the barlowed laser method. 

 

Your recommendations are appreciated! Thanks, all! 

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[Asbytec]

Actually, the 8" sim is pretty accurate from what I can see on my monitor. It pays to be cautious when comparing an image to visual, still...pretty accurate for intents and purposes of your question. 

 

Whenever the image is blurry, it's usually one of the usual suspects. The three "C's": Collimation, Cooling, and C'ing. Right now, Saturn is not well placed being low in the sky where seeing is most likely terrible. The image on the right is, well, about right. Seeing generally improves toward the zenith, so to get a good view of any planet you may have to wait until their next fly by. Save for Mars which is still fairly well placed high n the sky at sunset. Try that. 

 

A well collimated laser and collimation cap is a good combination. If you want a good Cheshire, then get a good one. Farpoint and Cat's Eye make good ones. There are others around, just don't skimp on good tools. A site tube or combo Cheshire and site tube is best for placing your secondary under the focuser, but the site tube duplicates the focuser axial alignment of your laser. The Collimation cap is similar to a Cheshire, so it's fine for aligning the primary already. So, you have the tools you need, and you can use the focuser draw tube as a reference for your secondary placement. 

Edited by Asbytec, 01 January 2021 - 05:47 PM.

[sahstim001]

Thanks for your reply!

Actually, we took this image back in July around midnight, so it would have been pretty high in the sky. Granted, they never got that high at my latitude, but they weren't close to the horizon.

 

Mars is another thing. I don't know what detail I'm supposed to see, but here's one of my pictures for Mars with the 8", and it represents about what I can see visually. Is this typical or is there a problem? 

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[ngc7319_20]

 

1. Are we doing something wrong, or is the simulated view unrealistic? Could it be our collimation? We have a laser and collimation cap, but no Cheshire. 

 

2. I'd like to get a Cheshire to make sure our 12" performs at its best. It'll be an F/5. What are your recommendations? I've heard Celestron makes a good one, would that be a good choice? I also plan on trying the barlowed laser method. 

 

Your recommendations are appreciated! Thanks, all! 

 

I think the simulated 8" image is pretty close. A good 8" under best conditions should be even better than the simulations.

 

Problem could be many things.... collimation, maybe the scope is warm and there are air currents in the tube, poor seeing / unstable atmosphere.  Could be problems with optical figure on the mirrors.  Maybe install a fan to cool the optics if there isn't one already.  Learn about star testing the optics.

 

Laser and collimation cap should get you pretty close already.  A Barlowed laser would help -- maybe you can add a lens to the laser you already have.  Cheshire will not improve planetary images beyond what is possible with what you have already.

Edited by ngc7319_20, 01 January 2021 - 05:53 PM.

[Starman1]

The 3 "C"s are most important for attaining a sharp image:

1) Collimation.  Unless you use high quality tools to collimate, every time you observe, you will have poor high power image quality, even if the optics are good.

2) Cooling.  As a mirror cools in the night air, it releases heat into its environment,  This heat forms a "boundary layer" in front of the mirror that acts a bit like a refractive element and modifies the image quality.

Until the mirror is cooled and the boundary layer disappears, high power images will not be good.  If the scope has a fan, use it.  If it doesn't have a fan, add one.  Or at least set the scope outside an hour and a half

before you plan to observe to let some of the heat in the mirror escape.

3) Conditions.  Basically, this is defined, for high power sharpness, as the turbulence in the atmosphere, or "Seeing".  This varies from night to night and even hour to hour.  Some places always have bad Seeing.

some things to remember:

• set up on grass or dirt instead of concrete or asphalt.  The paving materials bleed heat into the air around the telescope all night long.
• don't expect sharp images of a planet at high power when it is below 30° from the horizon (where the air is 2x the thickness of the air at the zenith.
• don't view at high powers directly above a roof.  Roofs bleed heat all night long and cause turbulence in the air above them.
• don't expect good Seeing right after a front has come through.  The air is usually steadier 1-2 days later.  Look at the stars.  If they're twinkling, that means bad Seeing.  Stagnant air often yields good Seeing.
• don't expect good Seeing if the jet stream is overhead.  Turbulence in the atmosphere means poor Seeing.

Right now, no one is getting a good view of Saturn.  It's been below 30° for quite a while now.  Mars, though small, is a better test.  If you cannot get a sharp high power image of Mars after cooling and collimation, then the atmosphere is to blame.  Be patient and view often and you will encounter a night of better Seeing.

Edited by Starman1, 01 January 2021 - 05:52 PM.

[Starman1]

Thanks for your reply!

Actually, we took this image back in July around midnight, so it would have been pretty high in the sky. Granted, they never got that high at my latitude, but they weren't close to the horizon.

 

Mars is another thing. I don't know what detail I'm supposed to see, but here's one of my pictures for Mars with the 8", and it represents about what I can see visually. Is this typical or is there a problem? 

That was 3 months before the opposition, and Mars was quite small.  The image reveals Mars was not high in the sky when you took the picture because atmospheric refraction 

tinted one side of the planet red.

The image is not in great focus, either.  Had you taken a movie of the planet instead of a single shot, you might have caught a few stills that were in better focus.

Edited by Starman1, 01 January 2021 - 05:56 PM.

[sahstim001]

That was 3 months before the opposition, and Mars was quite small.  The image reveals Mars was not high in the sky when you took the picture because atmospheric refraction 

tinted one side of the planet red.

The image is not in great focus, either.  Had you taken a movie of the planet instead of a single shot, you might have caught a few stills that were in better focus.

I'm sorry, let me clarify. The picture of Saturn was back in July. This picture of Mars is from October.

It could be that image wasn't the greatest, but every time I look at Mars it is consistently underwhelming in terms of surface detail, to the point where I don't even want to take the time to look at it. 

 

It seems like you guys are saying it could be a lot of things, maybe I just haven't had a good night for it yet, and I'm willing to be patient if that is so. We take the scope out about every 2 weeks. I just want to make sure I'm giving the equipment the best chance it can have instead of wanting to spend $$$ on bigger/more expensive equipment.

 

I'll definitely look into getting a good Cheshire, and I probably just need to get better at collimating. Like I said, we've only been at it for around 9 months.

 

Thanks for the help, everyone. 

[havasman]

I try to require myself to spend at least 1 year with a major new piece of gear before I go replace it to get "better" views. In that time I want to learn how to maximize that gear's capability and implement what I've learned. You've had so little time with your powerful instrument that there's little chance you have seen all it can do for your observing. Nor is it likely you have developed your observing skills to a point where you can yet see the limits of what it can do.

Collimation enables everything your scope can do. Becoming confident that your collimation processes are consistently yielding as near to perfect results as can be had is critical. I strongly recommend you bone up on the Barlowed laser collimation technique and work it to your advantage.

Learning the effect of conditions on your observing and becoming able to analyze your site's observing conditions is also a critical task.

If you're not getting your 8" Dob to perform as it should, it is pretty unlikely you will wring good performance from a larger scope.

Edited by havasman, 01 January 2021 - 06:17 PM.

[Asbytec]

 

Mars is another thing. I don't know what detail I'm supposed to see, but here's one of my pictures for Mars with the 8", and it represents about what I can see visually. Is this typical or is there a problem? 

That is about what I see, too. But I have pretty good seeing conditions most nights (being in the tropics with an oceanic air mass). The image is a little fuzzy, though, Mars should not be fuzzy like that. But, in general, that amount of detail, give or take depending on the three "C's", is a good approximation. Edit: and as Starman says, depending on Mar's distance form Earth. 

 

Below is about as good as it get's for me, but I was at fairly high magnification above 400x in descent seeing close to opposition when the image was pretty large. Plus, I had to wait for the better moments to capture everything I could possibly see. So, the sketch is not a snapshot, it's a composite of many lucky snapshots over time.

 

Edited by Asbytec, 01 January 2021 - 06:41 PM.

[bjulihn]

Hi sahstim001;

 

Welcome to CN. I'm not seeing anything here about how you took your images. Are they single shots, are they stacks, what post-processing did you use? I'm just gonna say that visually planets, no matter how big the aperture, tend to swim and be fuzzy except for brief moments of clarity. That is why most better planetary images are stacks in which a small percentage of a large number of frames are selected for use. Visually, planets need really good seeing to be fairly sharp.

 

Also, because planets are relatively bright but small, focal length is a bigger factor than aperture, in my opinion. The 1200mm focal length of the 8" Starhopper is somewhat limiting for planets. People going after planets, especially imagers tend to go for an SCT or something with more than 2000mm fl. A 12" Dob is a great instrument for DSO's, especially if you have access to a dark sky site for viewing. Good Luck!

[sahstim001]

Hi sahstim001;

 

Welcome to CN. I'm not seeing anything here about how you took your images. Are they single shots, are they stacks, what post-processing did you use? I'm just gonna say that visually planets, no matter how big the aperture, tend to swim and be fuzzy except for brief moments of clarity. That is why most better planetary images are stacks in which a small percentage of a large number of frames are selected for use. Visually, planets need really good seeing to be fairly sharp.

 

Also, because planets are relatively bright but small, focal length is a bigger factor than aperture, in my opinion. The 1200mm focal length of the 8" Starhopper is somewhat limiting for planets. People going after planets, especially imagers tend to go for an SCT or something with more than 2000mm fl. A 12" Dob is a great instrument for DSO's, especially if you have access to a dark sky site for viewing. Good Luck!

My pictures are just taken with a phone and a phone-eyepiece mount, fancy I know, don't judge  . I'll stack a few frames to remove some noise. Our pictures aren't our goal, we just take them to share with people what we can see, visual is our real goal. We almost got into AP, but then we realized if we were to spend the money to get a good setup we would rather have better visual views. We like seeing with our own eyes. Makes us feel connected to it. Basically I just shared these images to approximate what I see at the eyepiece.

 

Our interest has mainly shifted to DSO's, so we're looking forward to the 12". Our site is dark green on this map. I've seen Mag 5.5 stars at least, not bad I think considering our proximity to Chicago.

 

Thanks everyone for the input. I'll try to apply some of these suggestions before getting the 12" and see what improves. I think I need to do more research on collimation to make sure I'm getting it right. I just wanted to know if my views were a symptom of poor collimation, something in my control. As for what the sky gives me any night, I'll just take that as it comes. 

 

That is about what I see, too. But I have pretty good seeing conditions most nights (being in the tropics with an oceanic air mass). The image is a little fuzzy, though, Mars should not be fuzzy like that. But, in general, that amount of detail, give or take depending on the three "C's", is a good approximation. Edit: and as Starman says, depending on Mar's distance form Earth. 

 

Below is about as good as it get's for me, but I was at fairly high magnification above 400x in descent seeing close to opposition when the image was pretty large. Plus, I had to wait for the better moments to capture everything I could possibly see. So, the sketch is not a snapshot, it's a composite of many lucky snapshots over time.

 

Mars 17 Oct 2020 1300UTC.png

Wow, nice sketch! I look forward to seeing something like that.

Edited by sahstim001, 01 January 2021 - 07:10 PM.

[Sheol]

                        Those Saturn pics are nice, but a bit fuzzier than what I have often seen of Saturn in my 8 inch Dob. The image is smaller, but when seeing clears a bit, I get some beautiful views of my favorite planet. Mars was also very good this year!  I do regret that I have not gotten a chance to view the planets with my Orion 12 inch Truss tube Dob. Maybe a few days I can get a shot at Mars. Then again, I'm mostly DSOs, the 8 inch may be old but it works wonders on the Planets!

 

                                Clear Skies,

                                     Matt.

[sevenofnine]

Just something I've noticed on this forum. 12 inch solid tube Dobs are in the minority not because they are not good scopes but because they are so big, heavy and awkward to move. (think water heater ) A 10 inch seems to be the choice for size versus aperture. From there it's on to larger truss Dobs because they break apart into more manageable parts. Those scopes are usually taken to star parties at very dark skies. There they are amazing! Good luck with your decision.

[Asbytec]

 

Wow, nice sketch! I look forward to seeing something like that.

Thank you. You will. Collimate your scope, attend to thermal issues helping it cool to ambient, and pray for descent seeing not under the jet stream or low on the horizon. Observing planets can be challenging for man and machine. It requires we prep our scope for high resolution imaging and have favorable observing conditions. A lot of things have to come together to get the best high resolution images possible. Use the right magnification for your conditions, observe the planets higher in the sky, and pay attention to the image for a while.

 

I also agree your cell phone images are a bit more fuzzy than visual, the limb of the planet should be sharp much of the time and static cell phone images do not show softer detail than comes and goes as seeing conditions vary. Your eye can catch that detail. Saturn looks about right, except the limb and rings will be more crisp. However, the level of detail you show is fairly well represented for a quick image. Of course, better imaging equipment and processing will likely exceed our visual experience. So, somewhere between the two is probably about the best we can do visually.  

Edited by Asbytec, 02 January 2021 - 12:14 AM.

[Starman1]

On Mars, it also helps to have a filter that enhances the details on the planet, like a Baader Contrast Booster.

Details enhancement goes a long way toward making planetary views more rewarding.

Norme's drawing is fairly typical for an 8" aperture in decent seeing.

[JKowtko]

If it makes you feel any better, here's the best I have been able to do so far (I'm a newbie) with my Zhumell Z8 and ASI244mc, from the SF Bay Area ...

 

The photo was take on Nov 15, maybe 45-60 degrees off the horizon ...

 

 

 

The video was taken on Dec 22, pretty closet to Zenith ... using an SVBony 5x Barlow.

 

https://youtu.be/6ot-NwtNdoI

 

-- John

Edited by JKowtko, 02 January 2021 - 08:50 AM.

[sahstim001]

Just something I've noticed on this forum. 12 inch solid tube Dobs are in the minority not because they are not good scopes but because they are so big, heavy and awkward to move. (think water heater ) A 10 inch seems to be the choice for size versus aperture. From there it's on to larger truss Dobs because they break apart into more manageable parts. Those scopes are usually taken to star parties at very dark skies. There they are amazing! Good luck with your decision.

Yeah, i was going back and forth on truss vs solid tube. We decided that we are able to handle the cons of the solid (size, weight, transport), but the cons of the truss were more of a nuisance to us (setup, teardown, dewing, watching your breathing). Yes, those things can be mitigated as well, but for us solid seems the way to go. 

 

If it makes you feel any better, here's the best I have been able to do so far (I'm a newbie) with my Zhumell Z8 and ASI244mc, from the SF Bay Area ...

 

The photo was take on Nov 15, maybe 45-60 degrees off the horizon ...

 

 Mars007a.png

 

The video was taken on Dec 22, pretty closet to Zenith ... using an SVBony 5x Barlow.

 

https://youtu.be/6ot-NwtNdoI

 

-- John

 

That video is pretty representative of what we've seen of Mars, maybe a bit better. That picture is way better, but you probably stacked your good frames. 

[Starman1]

Yeah, i was going back and forth on truss vs solid tube. We decided that we are able to handle the cons of the solid (size, weight, transport), but the cons of the truss were more of a nuisance to us (setup, teardown, dewing, watching your breathing). Yes, those things can be mitigated as well, but for us solid seems the way to go. 

 

For 10" or smaller, perhaps.

But for 12" and larger, a truss is better:

• easier to transport
• lower center of gravity--more stable
• smaller rocker box for a much lighter base
• (almost always) larger altitude trunnions for less sensitivity to imbalance
• easier to customize the position of the focuser
• mirror is transported horizontal instead of vertical (on edge)

As for dew, breathing, body heat, there is really no difference with the tubed dob as long as you use a shroud.

Shrouds should be included with all truss dobs.

[Jon Isaacs]

For 10" or smaller, perhaps.

But for 12" and larger, a truss is better:

• easier to transport
• lower center of gravity--more stable
• smaller rocker box for a much lighter base
• (almost always) larger altitude trunnions for less sensitivity to imbalance
• easier to customize the position of the focuser
• mirror is transported horizontal instead of vertical (on edge)

As for dew, breathing, body heat, there is really no difference with the tubed dob as long as you use a shroud.

Shrouds should be included with all truss dobs.

 

 

I think one has to distinguish between commercial truss Dobs and custom/premium Dobs. Commercial Dobs tend to have small bearings and other issues, custom/premium Dobs have the large bearings and other advantages.

 

I agree with the 10 inch tube / 12 inch truss threshold.  My 10 inch is a Tube Dob, my 12.5 inch is a Truss but was a Tube Dob originally..  It's a flexible threshold but my 12.5 inch nests so has a 19"x20" footprint and is about 28 inches tall. The footprint is smaller than my 10 inch Dob and only 6 inches taller than the base. It takes up one passenger spot.

 

 

Jon

[SteveG]

If it makes you feel any better, here's the best I have been able to do so far (I'm a newbie) with my Zhumell Z8 and ASI244mc, from the SF Bay Area ...

 

The photo was take on Nov 15, maybe 45-60 degrees off the horizon ...

 

 Mars007a.png

 

The video was taken on Dec 22, pretty closet to Zenith ... using an SVBony 5x Barlow.

 

https://youtu.be/6ot-NwtNdoI

 

-- John

I would call that a great pic! I've never even tried imaging....

[vdog]

Shrouds should be included with all truss dobs.

  

[JKowtko]

That picture is way better, but you probably stacked your good frames. 

(sorry, I couldn't edit my post anymore so I'll have to reply in a new post ...)

 

Due to disk space limitation on my Macbook (and frankly some laziness) I've been taking sequences of only 100 photos and just kicking out a handful.  I used Lynkeos on the Mac, and didn't do much touching up (still not proficient with the image processing) So most of the raw frames look like the finished photo, just darker ... here's an example of one of them ...

 

 

I'm sure someone else could take my raw photo sequence and create a better finished product than I did (... but I like the idea that the photos are more representative of what you actually see through the scope

 

-- John

Edited by JKowtko, 06 January 2021 - 08:32 AM.

[sahstim001]

(sorry, I couldn't edit my post anymore so I'll have to reply in a new post ...)

 

Due to disk space limitation on my Macbook (and frankly some laziness) I've been taking sequences of only 100 photos and just kicking out a handful.  I used Lynkeos on the Mac, and didn't do much touching up (still not proficient with the image processing) So most of the raw frames look like the finished photo, just darker ... here's an example of one of them ...

 

Mars_raw.png

 

I'm sure someone else could take my raw photo sequence and create a better finished product than I did (... but I like the idea that the photos are more representative of what you actually see through the scope

 

-- John

In that case you are definitely getting better views of Mars than me. Hopefully if I apply the suggestions above my views will improve (been cloudy here, haven't had a chance).

And I also like pictures that represent what you see. That's mainly why I take them. 

[starbug]

Please allow me to add my 2 cents.

After just 9 Months I'd continue to use the 8" scope, and, if at all evolve the "backend" - Eyepieces (not very extensive), maybe some filters like UHC. 

Astronomy is a science of learning and patience. If you want to get "nice" views only, buy an ev-Scope or something similar, and sell the rest.

[sahstim001]

Please allow me to add my 2 cents.

After just 9 Months I'd continue to use the 8" scope, and, if at all evolve the "backend" - Eyepieces (not very extensive), maybe some filters like UHC. 

Astronomy is a science of learning and patience. If you want to get "nice" views only, buy an ev-Scope or something similar, and sell the rest.

I can appreciate that. Currently our main eyepieces are the Baader Hyperion Zoom MkIV and a 2" Orion Q70 38mm. We also have an Orion Ultrablock UHC filter and a Meade 3x barlow. 

But my main original concern was if collimation could be an issue, if my views were a symptom of me "doing it wrong". It seems like it could be, and it could be lots of other things.

You've all definitely given me a lot more to think about. I appreciate the advice!