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20-second Sub limit for EAA with CPC925 alt-az. A problem?

Catadioptric DSO EAA SCT
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#1 Leafus

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Posted 21 June 2022 - 06:48 AM

I'm looking at buying my first proper EAA setup. 

 

I've read a lot on the maximum sub exposure limit for Alt-Az mounts and whether that is a problem for EAA and a lot of what I read is contradictory, so it would be great to get some real-life feedback on this.

 

I realise the question is deceptively simple, and the factors/variables involved are complex. But on a practical level I know it works, but to what extent? What imaging situations/objects will not be possible?

 

My current assumption is:

 

- Lunar/Solar/Planets - Yes - easily

- Brighter DSO - yes

- Fainter DSO - this is the question.

 

I guess a reducer is going to be important to the answer. I am also looking at an F5/6 80mm Piggy-Frac.

 

From what I've read the following is relevant:

 

A) SUB-exposure limit: The 20 second limit is a rule of thumb and varies with latitude, the direction the scope points and the altitude. I found a great table on: https://telescopemou...-great-results/

 

B) Guiding: What?? Guiding?? On an alt-az? I had read that "no you can't, and that is the end of discussion" but another article on the above site suggests you can. I could use an OAG.

 

BUT is it really necessary?

Has Anyone here tried it?

 

Article is at: https://telescopemou...ount-with-phd2/

Okay, its about their mount, but suggest is it would work with other alt-az.

 

C) Camera Rotator: This is an intriguing idea. The big observatory scope are alt-az and rotate, so no doubt its possible. But is it necessary.

 

D) Reducer for the 925: I saw one called Night Owl at 0.4 but that seems too optimistic and most people seem to use the Celestron 0.63.

 

E) Plate-solving - this seems to be widely regarded as important.

 

I should add that I am competent, but not too patient, with technology, so my ideal answer to this thread is "Yes you can get good results for 90% of objects (either with a piggyback 80mm frac, or my CPC925) without all the extra hassle or guide/rotators/etc."

 

I look forward to hearing your opinions. Thank you in advance.


Edited by Leafus, 21 June 2022 - 07:12 AM.

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#2 nic35

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Posted 21 June 2022 - 07:17 AM

Here's a good article on the exposure limits imposed by an alt-az mount. As you say, it depends mostly on where you are pointed in the sky.  https://telescopemou...-great-results/

 

Many folk get perfectly acceptable results with their Evolution mounts, so it can be done.

 

Guiding not necessary.

 

Rotator not necessary. 

 

The night owl reducer (is it in stock ?)  is designed for a camera with a 16mm diagonal sensor, Perfect for the ASI533,but not so good for the 23mm diagonal ASI294.   

 

The 0.63 works well with virtually all cameras and is much less expensive.

 

There's a learning curve with most of this stuff, unless you opt for a stellina, or one of its variants. They are set it up, plug it in and off you go. But they are not very flexible when it comes to changing out scopes, etc. And they tend to be expensive if you already have gear, as you do.

 

Then there's the ASIAir plus, which simplifies a lot of activity.  It essentially replaces you computer, and relies on a wireless connection to a tablet or smartphone for control/viewing. But it works only with ZWO cameras. It is not quite as feature rich (as I understand) as some general purpose EAA software like SharpCap.

 

You get the most flexibility out of something like SharpCap, but some find it complicated, and it has a learning curve.

 

good luck

 


Edited by nic35, 21 June 2022 - 07:18 AM.

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#3 Xio1996

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Posted 21 June 2022 - 07:31 AM

Hi Leafus,

 

There are lots of very knowledgeable people on this forum that can give you much better answers than me. Having said that this is my experience with a lowly CPC-800.

 

I don't really worry about field rotation. My subs are from 2 to 15 seconds normally, depending upon the DSO. Last night my subs were 6s and 12s because that seemed to work. I have gone longer 20,30,40 seconds just for the fun of it. However, I get far too impatient waiting for those images to appear, so I keep it fast and as near to real-time as I can. I do have a column in the excellent Astroplanner software. This shows the maximum exposure for an object at its current location based on how many pixels I want to smear at the edge of the FOV. It is interesting to look at but really just tells me East and West and not too high are best. 

 

I don't use guiding, as again my exposures are short and it all seems too much hassle to set-up and maintain. Like you though I do remember reading that it was possible to do with Alt-Az mount. With my set-up and philosophy it is not necessary.

 

Rotators - No experience, but again just needed for longer sub exposures (framing?). So are they necessary for EAA?

 

On focal reducers I use the Celestron F6.3 reducer and alter the spacing to try and tune it to my scope's optics. I know some forum members, very successfully stack 2 reducers to get F4 and below.

 

I have found EAA simply amazing and it reignited my love for observing the universe. I just like to keep it simple and speedy. I hope you manage to build a set-up that suits your needs and you have some amazing observing sessions.

 

Have fun

 

Pete


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#4 Leafus

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Posted 21 June 2022 - 07:37 AM

Thanks Nic. 

 

I just saw the Night Owl mentioned. Probably would be very tricky to find in England anyway.

 

I'll definitely be getting the ASIAIR as funds allow. So would be looking at a ZWO camera. Colour and non-cooled. Both those you mention look good. It would mainly be for DSO but will be pointed at Planets when they are back up higher/evening.

 

The article you link is great and where I got most of the information. But it does not go into much detail on what objects the "20 Second" sub-limit would not allow. It mentions surface brightness, but I cannot see that number in SkySafari so I am not sure how to apply the guidance. I would hope to be able to see far more than the top 20 brightest DSO, and that is really what my question is:

 

"In practice, how limiting is the Exposure Length limit for an alt-az mount."



#5 Leafus

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Posted 21 June 2022 - 07:43 AM

Xio1996: Thanks Pete. Sounds like we have a similar outlook on EAA. Short Exposure is best. Interesting that you are able to keep most of your exposures so short. I'll take a look at that software you mention. I have been trying to find some web-tool were you can input equipment (scope/reducer/camera) and it will tell you the sub-exposure need for that object.

 

I have been playing around with an afocal iPhone, and have been using far longer shutter speeds than I should have, assuming Dark=Long Shutter speed.



#6 Tfer

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Posted 21 June 2022 - 08:05 AM

My main scope is a CPC1100.  ALT/AZ configuration.

 

I've yet to find a reason to go longer than 10 seconds on my subs.  I’ve viewed galaxies with it that are below magnitude 21 during my standard 20 minute total integration time. 
 

Get a 0.63 reducer and the largest sensor you can afford, and you’re off to the races. 


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#7 Leafus

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Posted 21 June 2022 - 08:16 AM

My main scope is a CPC1100.  ALT/AZ configuration.

 

I've yet to find a reason to go longer than 10 seconds on my subs.  I’ve viewed galaxies with it that are below magnitude 21 during my standard 20 minute total integration time. 
 

Get a 0.63 reducer and the largest sensor you can afford, and you’re off to the races. 

That is very encouraging as you have the same f-ratio as my 925 so I should be able to do the same. 

 

It all gets very confusing when I come across an AP thread that's saying a 300s sub is not enough. Though I guess it apples and oranges, as AP is to get a 100% quality photo whereas EAA is to get 95%(?) but quickly.

 

I'm hoping a lot of DSO are achievable in under 5 minutes to get me to 80%, which would do fine for me.



#8 GaryShaw

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Posted 21 June 2022 - 08:23 AM

 

"In practice, how limiting is the Exposure Length limit for an alt-az mount."

Hi 

I spent my first few years of EAA observing using an 8” F4 Newtonian on an AZ mount and encountered no limitations to my observations and casual imaging - especially when using Sharpcap’s live stacking which is the primary sw in use for EAA.  You probably know that SC rotates and translates sequential images as it stacks them so modest offsets between images, whether due to rotation or poor tracking, are compensated by SC.

 

 

Even while using dual band filters and 12-20 second exposures for viewing nebulae at high altitudes, I did not find rotation to be a problem. My interest is mainly in ‘observing’ quality rather than chasing ‘image’ quality, so minor elongation of stars at the edges of my FOV are immaterial to me and totally not worth obsessing over. Others, viewing EAA as ‘AP lite’, may feel differently of course. Bear in mind also, that I’m working at F4 and you’ll be working a bit slower at gathering photons so you’ll experience more minor exposure limitations.

 

If you’re thinking eventually of AP ( which includes all solar system observing/imaging) you would, of course, be using an EQ mount ( or AZ and wedge) which is not subject to rotation. I’ve transitioned to EQ mounts since my interests have expanded to include variable star and exoplanet imaging and these require quite precise tracking. So, you might want to keep in mind the possible directions that your own interests may take you over time.

 

Equipped with a crystal ball, I might have started out with a high quality EQ mount. EAA has been one of the most rewarding pursuits of my life so far and I hope you enjoy a fast, fun ride up the learning curve. 

Gary 
 


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#9 Tfer

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Posted 21 June 2022 - 08:29 AM

Don’t read AP threads.

That’s like asking a thoracic surgeon about splinting a broken finger.

I can view thousands of DSOs with my first sub.

Everything after that is just smoothing noise and adding more photons.
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#10 MunichAtNight

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Posted 21 June 2022 - 08:59 AM

Hello Leafus!

 

You are asking the right things! wink.gif

 

 

...

 

A) SUB-exposure limit: The 20 second limit is a rule of thumb and varies with latitude, the direction the scope points and the altitude. I found a great table on: https://telescopemou...-great-results/ ....

I work with this table and the values are more or less correct. Based on my experience and on this table your thumb is in generally to big! lol.gif  20 seconds is challenging. But I worked already with 16 seconds exposure times. But in most cases I work with 2, 4, 8 s.

 

Some weeks ago I did the Little Pinwheel, NGC 3184 which is to my understanding with a magnitude of ~ 14 some how faint ...

 

NGC3184 ALL Stack 2342frames 9368s WithDisplayStretch
 
  • Teleskop: Skywatcher 200 PDS, 1,000 mm, 5", f/5
  •     Mount: Skywatcher AZ-EQ5 GT
  •     Camera: ZWO ASI 294MC
  •     Software: Sharpcap Pro 4.0.8785.0
  •     Total time: 9368s | Frames: 2342 | 4s | Gain: 400
  •     Data: 4144 x 2822 pixel
  •     Darks: Sharpcap 4.0 PRO
  •     Flats: Sharpcap 4.0 PRO
  •     Optic: Baader Mark MK-III
  •     Filter: none
  •     Date: 2022-04-21 | Time: 00:13 UTC | Outdoor: 8.3 °C
Here a cutout of the above photo
 
NGC3184 cutout Stack 2342frames 9368s WithDisplayStretch
 
Stacking time was almost 2 and half hour. Without guiding! I didn't had here a problem with field rotation and I never had a need for guiding. But possible problems by field rotation are based where the object is located and how big it is, too.
 
When doing the Rosette Nebulae, field rotation did steal some part I would have liked to be kept!
 
RosetteNebula All Stack 678frames 5424s WithDisplayStretch
  • Teleskop: Skywatcher 130 PDS, 650 mm, 5", f/5
  •     Mount: Celestron Nextstar
  •     Camera: ZWO ASI 294MC
  •     Total time: 5424 s | Frames: 678| 8s | Gain: 400
  •     Data: 4144 x 2822 pixel
  •     Darks: Sharpcap 4.0 PRO
  •     Flats: Sharpcap 4.0 PRO
  •     Optic: Baader MK-III Coma Corrector
  •     Filter: Altair Quad Band
  •     Date: 2022-03-01 | Time: 22:06 UTC | Outdoor: 3,3 °C

In such a case there are several thing which might be done as single action or in combination:

  • Shorter focal length by shorter telescope or reducer
  • Camera which wider field / bigger sensor, for example instead of a ASI294MC an ASI2600MC
  • Camera field rotator.

 

C) Camera Rotator: This is an intriguing idea. The big observatory scope are alt-az and rotate, so no doubt its possible. But is it necessary.

e.

I just bought a Pegasus Falcon rotator. It is just waiting for finishing 3D-printed adapters and for Clear skies!

 

To be honest, I have only the idea such a rotator might help from case to case, but as you can see with my two examples, it might be helpful but is it necessary? I hope I am able to find out! Any way the rotator will be helpful to rotate the field of view by software. Which is very smart when working remote with the EAA setup.

 

MunichATNight - Ewald


Edited by MunichAtNight, 21 June 2022 - 09:00 AM.

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#11 Leafus

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Posted 21 June 2022 - 11:09 AM

GaryShaw: Very interesting about the exposure times you mention. The f/4 is much faster than even a reduced CPC925 but even so it all seems manageable with the Alt-Az. And if I get a faster smaller scope to piggy back the CPC then even better.  I am more of your view of EAA as an observing tool (though I like a photo for a souvenir too) for objects I can't see in detail/colour otherwise (Nebula particularly), but it needs to be quick and without too much aggravation - particularly not too much aggravation.

 

Tfer - I totally agree. I will keep away from AP threads. Viewing on first sub sounds good to me.

 

But I could be drawn to the APlite-side if I could do photos like MunichAtNight.

 

 

MunichAtnight: Awesome photographs. I am astonished at how an alt-az can take such amazing photographs. I would likely not have the patience for such long tracking, and darks/flats/etc, but if images like that are possible I can see a change of mind coming about. Thank you for sharing your experience and photographs.



#12 steveincolo

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Posted 21 June 2022 - 11:36 AM

 

Hello Leafus!

 

You are asking the right things! wink.gif

 

 

I work with this table and the values are more or less correct. Based on my experience and on this table your thumb is in generally to big! lol.gif  20 seconds is challenging. But I worked already with 16 seconds exposure times. But in most cases I work with 2, 4, 8 s.

 

Some weeks ago I did the Little Pinwheel, NGC 3184 which is to my understanding with a magnitude of ~ 14 some how faint ...

 

 
 
  • Teleskop: Skywatcher 200 PDS, 1,000 mm, 5", f/5
  •     Mount: Skywatcher AZ-EQ5 GT
  •     Camera: ZWO ASI 294MC
  •     Software: Sharpcap Pro 4.0.8785.0
  •     Total time: 9368s | Frames: 2342 | 4s | Gain: 400
  •     Data: 4144 x 2822 pixel
  •     Darks: Sharpcap 4.0 PRO
  •     Flats: Sharpcap 4.0 PRO
  •     Optic: Baader Mark MK-III
  •     Filter: none
  •     Date: 2022-04-21 | Time: 00:13 UTC | Outdoor: 8.3 °C
Here a cutout of the above photo
 
 
 
Stacking time was almost 2 and half hour. Without guiding! I didn't had here a problem with field rotation and I never had a need for guiding. But possible problems by field rotation are based where the object is located and how big it is, too.
 
When doing the Rosette Nebulae, field rotation did steal some part I would have liked to be kept!
 
 
  • Teleskop: Skywatcher 130 PDS, 650 mm, 5", f/5
  •     Mount: Celestron Nextstar
  •     Camera: ZWO ASI 294MC
  •     Total time: 5424 s | Frames: 678| 8s | Gain: 400
  •     Data: 4144 x 2822 pixel
  •     Darks: Sharpcap 4.0 PRO
  •     Flats: Sharpcap 4.0 PRO
  •     Optic: Baader MK-III Coma Corrector
  •     Filter: Altair Quad Band
  •     Date: 2022-03-01 | Time: 22:06 UTC | Outdoor: 3,3 °C

In such a case there are several thing which might be done as single action or in combination:

  • Shorter focal length by shorter telescope or reducer
  • Camera which wider field / bigger sensor, for example instead of a ASI294MC an ASI2600MC
  • Camera field rotator.

 

I just bought a Pegasus Falcon rotator. It is just waiting for finishing 3D-printed adapters and for Clear skies!

 

To be honest, I have only the idea such a rotator might help from case to case, but as you can see with my two examples, it might be helpful but is it necessary? I hope I am able to find out! Any way the rotator will be helpful to rotate the field of view by software. Which is very smart when working remote with the EAA setup.

 

MunichATNight - Ewald

 

Pegasus has a couple links to nice AP shots taken with a Dob and the Falcon rotator.  Looking forward to seeing yours in action!



#13 azcubs76

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Posted 21 June 2022 - 11:54 AM

I would look at one of the zero amp glow cameras like the 533mc or 585mc. Depending on the telescope you may be able to get away with taking no darks or flats which simplifies it a bit. I got the asi294mc for the increased sensor size but I'd probably get a 533mc if I did it over again. Flats are an absolute necessity with the 294mc in my C8@f6.3 due to vignetting. It's better in the 80mm but I still do darks and flats as the improvement is worth the small hassle.

 

I started EAA on a GEM mount then switched to an Alt-Az and have never gone back. Tracking and field rotation have never been enough of an issue to worry about for me. I can do 30s exposures (longer on the 80mm) with no issues but I rarely go higher than 15s and only if using filters.


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#14 MunichAtNight

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Posted 21 June 2022 - 01:07 PM

Hello!

 

 


But I could be drawn to the APlite-side if I could do photos like MunichAtNight.

 

 

MunichAtnight: Awesome photographs. I am astonished at how an alt-az can take such amazing photographs. I would likely not have the patience for such long tracking, and darks/flats/etc, but if images like that are possible I can see a change of mind coming about. Thank you for sharing your experience and photographs.

But it isn't AP- all my photos are saved inside Sharcap "As seen" - which produces png files I convert with IrfanView 1:1 to JPG. Otherwise forum admin will send me to the hell of data! wink.gif

 

Thanks for the positive feedback! The most of my photos are done with a Celestron Nexstar with an awful backslash and f/5 newton 130 PDS ( 5 " mirror ) so no miracle. Only some patient!

 

 

MunichAtNight - Ewald


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#15 SchoolMaster

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Posted 21 June 2022 - 02:26 PM

A second vote here for the 533MC Pro as a first camera, it can do pretty much everything and quite well and should have good 'legs'.

 

The longest capture I have ever sine is 45 minutes of 20 secs and I really can't keep my mental focus for that long.  15 20 20, to maybe 30 is my limit at the moment, although now I have an EQ mount I'm going to try 30 and 60 sec suns to see what I can get with the reduced (I hope) Gain.



#16 Tfer

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Posted 21 June 2022 - 05:26 PM

Hello!

 

 

But it isn't AP- all my photos are saved inside Sharcap "As seen" - which produces png files I convert with IrfanView 1:1 to JPG. Otherwise forum admin will send me to the hell of data! wink.gif

 

Thanks for the positive feedback! The most of my photos are done with a Celestron Nexstar with an awful backslash and f/5 newton 130 PDS ( 5 " mirror ) so no miracle. Only some patient!

 

 

MunichAtNight - Ewald

OP should check out the Gallery and What Have You Seen Lately threads.

 

Modern cameras and calibration frames have made getting 80% of AP the norm. 


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#17 MunichAtNight

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Posted 29 June 2022 - 12:23 AM

Hello!

 

Pegasus has a couple links to nice AP shots taken with a Dob and the Falcon rotator.  Looking forward to seeing yours in action!

I got today the 3D printed adapter for the falcon rotator to fit!

 

Here a invisible adapter for thread M42 to M54

falcon-skywatcher-03-mini.jpg

 

I added a filter drawer, too.

falcon-skywatcher-01-mini.jpg

 

Waiting for clear skies!

falcon-skywatcher-02-mini.jpg

 

Here screen shots from Sharpcap and the falcon Windows software

screenshot-sharpcap.jpg

 

screenshot-falcon-windows.jpg

 

MunichAtNight - Ewald


Edited by MunichAtNight, 29 June 2022 - 12:31 AM.

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#18 Leafus

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Posted 29 June 2022 - 06:06 AM

Munich at Night: Wow - that rotator is way bigger than I expected. Looks like it could rotate the whole OTA.

 

It will be interesting to know how well it works. 



#19 dave85374

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Posted 29 June 2022 - 01:46 PM

If you don't mind spending $$$$ you could always purchase a HyperStar to make your camera a VERY fast (F1.9) camera.  It will make your telescope a wide field scope. My Evolution 8 went from 2032 mm to 391 mm and all my shots are 8 sec which are then stacked.  Real small DSO's are tough to see, but you can zoom into them, though because of the reduced size/magnification though.  That is what I started with and am very happy.

 

+1 on the 533, I have the 294.  You can look at my photographs in my gallery out here.

 

I try not to read or follow articles that mainly mention something that I don't own so as to not get confused but I definitely look at the photos posted just to see how mine relate to what someone else is getting.  The ASIAir Pro or + is definitely easier to start with but there are things that you can't really do with it as in adjusting the color in some way or another.  That said if you think you might like to do AP sometime down the line I would get a different system so you wouldn't have to start over with the learning.  At my age I didn't think I wanted or would ever change to something different so I went with the AAP.


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#20 Jared

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Posted 29 June 2022 - 05:58 PM

I'm looking at buying my first proper EAA setup. 

 

I've read a lot on the maximum sub exposure limit for Alt-Az mounts and whether that is a problem for EAA and a lot of what I read is contradictory, so it would be great to get some real-life feedback on this.

 

I realise the question is deceptively simple, and the factors/variables involved are complex. But on a practical level I know it works, but to what extent? What imaging situations/objects will not be possible?

 

My current assumption is:

 

- Lunar/Solar/Planets - Yes - easily

- Brighter DSO - yes

- Fainter DSO - this is the question.

 

I guess a reducer is going to be important to the answer. I am also looking at an F5/6 80mm Piggy-Frac.

 

From what I've read the following is relevant:

 

A) SUB-exposure limit: The 20 second limit is a rule of thumb and varies with latitude, the direction the scope points and the altitude. I found a great table on: https://telescopemou...-great-results/

 

B) Guiding: What?? Guiding?? On an alt-az? I had read that "no you can't, and that is the end of discussion" but another article on the above site suggests you can. I could use an OAG.

 

BUT is it really necessary?

Has Anyone here tried it?

 

Article is at: https://telescopemou...ount-with-phd2/

Okay, its about their mount, but suggest is it would work with other alt-az.

 

C) Camera Rotator: This is an intriguing idea. The big observatory scope are alt-az and rotate, so no doubt its possible. But is it necessary.

 

D) Reducer for the 925: I saw one called Night Owl at 0.4 but that seems too optimistic and most people seem to use the Celestron 0.63.

 

E) Plate-solving - this seems to be widely regarded as important.

 

I should add that I am competent, but not too patient, with technology, so my ideal answer to this thread is "Yes you can get good results for 90% of objects (either with a piggyback 80mm frac, or my CPC925) without all the extra hassle or guide/rotators/etc."

 

I look forward to hearing your opinions. Thank you in advance.

1) If you are trying to have fun with EAA and, perhaps, go a little deeper than you can with an eyepiece, maybe even ad a little color to your observing, then 20s (or whatever is the appropriate limit for the part of the sky where you are observing) should be just fine. You will gain some weird triangular dark wedges around the edges of your image as livestacking auto-rotates sub exposures for stacking. For most subjects, that's no big deal at all. Something that fills the frame? You'll lose the edges. 

2) You asked whether alt-az is OK for fainter objects. How faint? And how bad is your light pollution? If you are talking about getting a pleasing result on something like M101, no worries. If you are talking about capturing the Integrated Flux Nebula in EAA format, forget about it.

3) I wouldn't consider guiding with an alt-az mount. It's theoretically possible as long as you are guiding on the center of the imaging frame, but it is always going to be sub-optimal since it can't possibly correct for rotation, and you are just as likely to make things worse as you are to make them better (by choosing a guide star that is off center). Generally speaking, if your mount can't track well enough to generate reasonably round stars at 20s, it's probably not going to guide very well in any event. 

4) Good camera rotators are a great idea. Bad ones are... Not so wonderful. I have only ever tried bad ones (from some years ago). Wish I could say more, but no experience with recent products.

5) I have used the old Celestron 0.63 reducer on a range of SCT's over the years. It is not very good by modern standards even if it is still the "reference" just because it has been around so long. I haven't tried any others so can't speak to them.

6) Plate solving is a freaking miracle in terms of throughput. It dramatically reduces the time between targets. Even if your mount is accurate enough to put your subject on the sensor after you slew halfway across the skies without resorting to a finder scope and a star chart, it performs the centering in just a few seconds as opposed to the couple of minutes it typically took by hand. Is it critical? No, but it's really, really pleasant. I equate it to electric windows in a car. No, you don't need it at all, but it's super nice and once you have it you can't imagine going back to life without it. 

 

In summary, I don't see the 20s limit as much of a barrier to EAA enjoyment. I have no idea whether the CPC9.25 tracks well enough for decent stars at 20s, but if it does you should be fine. 


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#21 MarMax

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Posted 29 June 2022 - 06:57 PM

Guiding

I've recently started guiding with the CPC 1100 and find it to be very helpful. It does not reduce field rotation but it does keep the object centered.

 

Sub-Exposure

I'm typically using 15 seconds or less but 30 seconds does work with the CPC Alt-Az mount.

 

NGC 6888 last night with 20 x 30 second exposures

NGC6888_Hyp_183_g18_LeN_20F_600S_NoEdit_06292022s.jpg

 

Reducer

An f/6.3 is recommended to provide versatility in your kit.

 

Plate Solving

A definite yes to make your life easier and especially if you decide to Guide. A guide/finder scope will make alignments and plate solving a piece of cake.


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#22 Leafus

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Posted 30 June 2022 - 12:06 PM

dave85374: I'd love to get the hyperstar, but my wife is only just forgiving me for spending thousands on the scope, and the unexpectedly many accessories required for it, a few months back for my birthday. My current aim is to add the camera, reducer etc, in the next few months, then maybe later...

 

jared: thanks for the detailed response. Yes, you hit the nail on the head: fun, quick, more detail, more colour and more objects are my aim.

 

My sky is Bortle 4 - in theory - though at the moment there is no night at all with the summer equinox only just passed. The sky brightness, without moon, measured at inner city levels a few nights back (with the Dark Sky Meter app). As actual nights return I'm hoping that many more objects will come out to play.

 

I've just bought a Astronomik UHC filter, which might bring some more things out visually and with the iPhone (my camera until I get the proper Astronomy Camera).

 

The 925 CPC mostly gets things in frame even at high mag Eyepiece. Not dead centre but if you can actually see the object then its usually there. At the moment I can't even see a lot nebula (last session the cocoon) even though the scope was right on it - hence I'll try the filter - but when night returns I hope I will be able to see a lot of the fainter objects, and more with a camera. At low mag the scope gets things pretty central, though I have noticed the centring can wander a little. But 20second is not issue at all. Plate solving will help a lot and can't wait for that. Its so much better trying to view a DSO when you now it is there, rather than doubting if the object is even in frame.

 

marmax: Interesting you put up the Crescent Nebula, as that was the other nebula I could not see in visual or with the iPhone last session. Next day, I actually plate matched my image online (stars were visible but no nebula), and it came back with the image being in the correct location for the crescent, but just capturing the middle third in the bottom right corner. I went back to image on my phone and used the built in editing buttons, and managed to boost up the nebulosity, but it looked all over the place, so I thought it must be phantom noise, so I gave up. But looking at your image now, I had another look and when I boosted it again with the iPhone photo tools, it came up with the right shaped nebulosity (it matched yours) around the double star in the correct place. So it was actually the crescent in my image, not rogue noise. Amazing really.

 

That was one 10 second sub. Doesn't look anywhere near as nice as yours, but it's encouraging I can get something in bright skies, with no filter, no stacks and very short exposure, and with just an iPhone looking down the EP. I'm looking forward to trying that Astronomik UHC filter. It will keep me going until I get the proper kit.

 

The good thing is that things will just keep getting better for me, since I started out on this hobby mid May. Starting at the "worst" time of year has that benefit at least.

 

Thanks all. Leafus




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