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EAA with piggyback or on main CPC9.25

EAA SCT Equipment
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#1 Leafus

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Posted 19 June 2022 - 07:44 AM

I’m trying to decide my next path for EAA upgrading from afocal iPhone to a “proper” setup. I want to retain visual as a priority so I can look then take a photo. I’m not seeking perfect photographs. No AP or loads of computer work.

My latest thought is to piggy back a 4” frac with camera to the 925. Main scope for visual. Piggy-scope will be for EAA and plate-solve. With ASIAIR. So I can avoid a laptop. Colour cam is important to me, despite drawbacks.

I’m most interested in any recommendations you folks have about set up and if anyone uses similar.

I don’t want to spend to little on the piggy scope but not go Over the top.

Thanks in advance.

#2 Notdarkenough

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Posted 19 June 2022 - 10:49 AM

Sorry, but I don't quite understand what your question is. Are you curious if the C9¼ will do awesome EAA? It will.


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#3 Alien Observatory

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Posted 19 June 2022 - 11:19 AM

Yes I had that set up a couple of years ago and it worked very well.  I mounted a used TeleVue 101 on the 9.25, but some caution must be used as the Balance was off and it required an ADM Balance kit with 4 each 2.5 lb balance weights to work successfully.  

 

The TV 101 was 520 mm in focal length and it was used to replace the Hyperstar lens.  The used TV101 cost about the same as a new v4 Hyperstar and was more flexible as both scopes could be used at the same time.    Pat Utah smile.gif

Attached Thumbnails

  • CPC 9.25_TV 101.jpeg

Edited by Alien Observatory, 19 June 2022 - 11:26 AM.

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#4 Notdarkenough

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Posted 19 June 2022 - 01:22 PM

The TV 101 was 520 mm in focal length and it was used to replace the Hyperstar lens.  The used TV101 cost about the same as a new v4 Hyperstar and was more flexible as both scopes could be used at the same time.    Pat Utah smile.gif

I think you meant that the TV101 is used for widefield imaging instead of HyperStar, right? I sounds like you are suggesting the 101 can replace the HyperStar.

 

Regarding using the 101 as a piggyback, did you use it as a guidecam, or simply as a second OTA? I have seen folks using large APOs as guidecams as well as using them to image large DSOs, I just haven't seen anyone using a 101 as a guidecam. Thoughts?


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#5 MarkCosmos

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Posted 19 June 2022 - 02:06 PM

Yes I had that set up a couple of years ago and it worked very well.  I mounted a used TeleVue 101 on the 9.25, but some caution must be used as the Balance was off and it required an ADM Balance kit with 4 each 2.5 lb balance weights to work successfully.  

 

The TV 101 was 520 mm in focal length and it was used to replace the Hyperstar lens.  The used TV101 cost about the same as a new v4 Hyperstar and was more flexible as both scopes could be used at the same time.    Pat Utah smile.gif

 A little off topic Pat, but do you have any photos to share of how you have that tripod on some nice wheels? I’d very interested to see!
 

I’d like to use this style setup with my 9.25 and the new 80mm APO Triplet that I have ordered, how much weight can a CPC amount actually haul around and still be stable enough for EAA/AP? I have learned(after the fact) that capacity of my AVX wouldn’t be enough for the 9.25 by itself to do any “serious” imaging. Maybe I should have gotten the CPC and wedged it?


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#6 Alien Observatory

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Posted 19 June 2022 - 02:54 PM

I think you meant that the TV101 is used for widefield imaging instead of HyperStar, right? I sounds like you are suggesting the 101 can replace the HyperStar.

 

Regarding using the 101 as a piggyback, did you use it as a guidecam, or simply as a second OTA? I have seen folks using large APOs as guidecams as well as using them to image large DSOs, I just haven't seen anyone using a 101 as a guidecam. Thoughts?

Yes the 101 replaced my hyperstar.  I am on an Alt / Az mount so no guiding possible.  The stock finder scope (50 mm) could be used as a guide scope.  Pat Utah :)



#7 Alien Observatory

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Posted 19 June 2022 - 02:59 PM

 A little off topic Pat, but do you have any photos to share of how you have that tripod on some nice wheels? I’d very interested to see!
 

I’d like to use this style setup with my 9.25 and the new 80mm APO Triplet that I have ordered, how much weight can a CPC amount actually haul around and still be stable enough for EAA/AP? I have learned(after the fact) that capacity of my AVX wouldn’t be enough for the 9.25 by itself to do any “serious” imaging. Maybe I should have gotten the CPC and wedged it?

I tried a wedge with this set up, but I have no view of Polaris and it did not work out for me.  My skies went from Bortle 5/6 to 7/8 when the neighborhood (back yard) was built in the past 3 years (200 + homes, street lights...) so I no longer use the 9.25.   The wheels / frame is just a used JMI Standard Scope Buggy.   Pat Utah smile.gif

Attached Thumbnails

  • post-253189-0-40614600-1550197136_thumb.jpg

Edited by Alien Observatory, 19 June 2022 - 03:07 PM.

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#8 MarMax

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Posted 19 June 2022 - 05:07 PM

The main issue I've noticed when I put something larger (like an ED80 or bigger) on top of the CPC 1100 is the tracking is not as good. The assumption being that both setups are (neutrally) balanced. I'm going to try the ZenithStar 61mm on top of the CPC 1100 and see how it goes. IMO, even the ED80 was a bit much so hopefully the mount will track reasonably well with the 61mm up top.



#9 Alien Observatory

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Posted 19 June 2022 - 06:03 PM

Without balancing both Horz and Vert you will indeed get poor tracking with an additional telescope mounted on a SCT.   Pat Utah :)

 

https://www.cloudyni.../#entry10194479


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#10 MarMax

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Posted 19 June 2022 - 06:57 PM

Without balancing both Horz and Vert you will indeed get poor tracking with an additional telescope mounted on a SCT.   Pat Utah smile.gif

 

https://www.cloudyni.../#entry10194479

I have a similar setup with the weight rail on the bottom and also use the StarSense camera and the finder scope for additional weight if needed. With a full D plate on top there is also flexibility in locating the piggy back scope.


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#11 SchoolMaster

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Posted 20 June 2022 - 04:02 AM

Although different, I pit an 18" rail on top of my C8/Evo combination so I could set the 80ED back as far as possible and still clear the mount at zenith, for the best balance.

 

I now use an AT70ED and the even shorter, lighter, wider, better FPL53 AT60ED would work well too.  For EAA and wide-field, reduced aperture can largely be remedied by more exposure and/or longer subs.



#12 Leafus

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Posted 20 June 2022 - 05:43 AM

Sorry, but I don't quite understand what your question is. Are you curious if the C9¼ will do awesome EAA? It will.

I want to be able to instantly swap from visual to EAA is the main point. The EAA so I can see what the grey smudges of DSO actually look like in colour/detail.

 

I am also considering the alternative of a Baader Flip mirror and doing both the Visual and the EAA through the 925, but a lot of people say it's easier to do EAA with a short focal length Frac. So I started to also look at the option of keeping the 925 for the visual with just a diagonal/EP, and putting a smaller - say 3 or 4 inch frac scope in Piggy Back to handle the EAA side. I can then visually view first then take look via EAA (and take a souvenir snap-shot).

 

If I had the money, I'd probably get a Evscope to sit next to the visual 925 for DSO, but I don't have a spare few thousand so a 4 inch frac on top seemed to do something similar, with the ASIAIR would be a third of the cost of the Evscope and be modular.

 

For planetary EAA I would swap the camera to the 925 instead.

 

So my question was, is that a sensible setup. And the replies on here suggest it works: i just need to take care about balance and overall weight.

 

The second part of my question was what apperture/type/price of Frac would I need for good EAA results. Given the need for subs of less than 20seconds (to avoid trails with the alt-az) then I am thinking a fast scope is needed. Maybe F4.

 

Many thanks for all the replies.



#13 alphatripleplus

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Posted 20 June 2022 - 07:54 AM

 

The second part of my question was what apperture/type/price of Frac would I need for good EAA results. Given the need for subs of less than 20seconds (to avoid trails with the alt-az) then I am thinking a fast scope is needed. Maybe F4.

 

Many thanks for all the replies.

If you want to avoid bloated stars with a refractor, get a decent ED doublet (or better). There are several to choose from in the f/6 to f/7 range; you can go a bit faster by adding a reducer.  For example, I have a small AT72EDTII FPL53 doublet that I use at its native f/6 and also at about f/4.4 with a reducer. In addition, I have an AT130EDT f/7 triplet that I also use with a reducer at f/5.5 for EAA.

 

Fast, and well corrected refractors get fairly expensive as you increase aperture. I would recommend staying away from cheap achromats, as dealing with star bloat  due to chromatic aberration is hard. 


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#14 Leafus

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Posted 20 June 2022 - 08:11 AM

Fast, and well corrected refractors get fairly expensive as you increase aperture. I would recommend staying away from cheap achromats, as dealing with star bloat  due to chromatic aberration is hard. 

What counts as cheap?

 

I understand you recommendation to buy a minimum of a doublet (which makes sense), but what cost is a good new doublet? I makes it confusing when good brands such as Celestron churn out cheap stuff that's not great - so its hard to even just go off brand. Or is there a "safe" brand that only does good quality scopes.

 

I dislike buying things that are not good enough for purpose, so would prefer to wait and get something decent that works, rather than struggle with something poor quality.

 

I would be interested to know how much your 130 compares to the 72 for DSO objects (I'll use the 9.25 for lunar/planet/solar). I was tending towards a 4 inch frac, but if there's not much difference for DSO EAA with bigger apperture, then maybe getting a lighter weight, better quality 3 inch or 2.5inch would be the way to go.

 

Thanks.



#15 Jeff Lee

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Posted 20 June 2022 - 08:17 AM

I use a dual setup but have two EAA cameras (294/224) and the 4" is a great EAA scope especially using the .8 reducer. So yes you can do visual on one and EAA on the other if you want. But I really like two shots, one showing detail of the object and the other a widefield showing its surroundings.


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#16 alphatripleplus

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Posted 20 June 2022 - 08:32 AM

What counts as cheap?

 

I understand you recommendation to buy a minimum of a doublet (which makes sense), but what cost is a good new doublet?

I also have a cheap Orion ST80 that I use with a narrowband H-alpha filter, but the filter is not cheap, and narrowband captures are mostly limited to emission nebulae. The cost of a new 80mm f/5 achromat like the ST80 is around $200. A 80mm ED doublet will cost probably double that - for example, the AT80ED is around $420. An ED doublet with FPL53 glass will cost even more.

 

The Astrotech ED series of scope come in a variety of sizes. I have been happy with both my scopes (doublet and triplet).

 

As for comparison images, the AT72EDII is only 480mm in focal length at its native f/6, while the AT130EDT at f/7 has almost twice the focal length. On small targets like  galaxies, the longer focal length of the 130EDT will show more detail than the AT72EDII. If you want a wider field of view for DSOs, a small refractor will complement your 9.25, if you choose to use the 9.25 for EAA as well.

 

If you want a single scope for EAA, there is really no one size fits all for big and small targets - except maybe using a hyperstarred SCT at f/2, and at f/6.3 with a reducer, and maybe at f/10 for really small targets like planetary nebulae.


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#17 Leafus

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Posted 20 June 2022 - 08:41 AM

I should say, that my whole budget for adding EAA is about £1000 - £1200 - pretty much equates to upto 1500 dollars.

 

I was thinking of splitting it:

 

- ZWO294 (uncooled) - £700

- ASI AIR - can add later so not counting in initial budget. Initially connect to a laptop, but will add the ASIAIR plus later.

- 4 Inch APO circa £300-£500 including mounts I need to piggy back

 

I realise the split of camera to scope is perhaps tipped too far to the camera, but my reasoning is that the camera will have the biggest impact, and will also have to work with my CPC9.25 with planetary. 

 

The cheaper ZWO cameras seem to have low Megapixel count, and that does not sit right with me. Twenty years ago I had a 2Megapixel camera, and buying one now seems wrong.



#18 Leafus

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Posted 20 June 2022 - 08:54 AM

I also have a cheap Orion ST80 that I use with a narrowband H-alpha filter, but the filter is not cheap, and narrowband captures are mostly limited to emission nebulae. The cost of a new 80mm f/5 achromat like the ST80 is around $200. A 80mm ED doublet will cost probably double that - for example, the AT80ED is around $420. An ED doublet with FPL53 glass will cost even more.

 

The Astrotech ED series of scope come in a variety of sizes. I have been happy with both my scopes (doublet and triplet).

 

As for comparison images, the AT72EDII is only 480mm in focal length at its native f/6, while the AT130EDT at f/7 has almost twice the focal length. On small targets like  galaxies, the longer focal length of the 130EDT will show more detail than the AT72EDII. If you want a wider field of view for DSOs, a small refractor will complement your 9.25, if you choose to use the 9.25 for EAA as well.

 

If you want a single scope for EAA, there is really no one size fits all for big and small targets - except maybe using a hyperstarred SCT at f/2, and at f/6.3 with a reducer, and maybe at f/10 for really small targets like planetary nebulae.

Thanks Alpha, that really helps. There's so much to learn with this hobby. Which I like.

 

The bit I can't get my head around at the moment is how the Camera affects the image size. I mean, with a decent chip like in the ZWO294 would digital zoom keep decent resolution even with a short focal length. My iPhone has very wide angle, but you can zoom in a lot digitally after taking the image and still keep good resolution.

 

The cost of the 80mm doublet seems in budget and should not overload my CPC mount. I would be a bit worried about F7 with the 20second sub-limit due to the CPC alt-az mount.

 

The 130 would destroy my budget and likely bring my mount grinding to a halt in piggyback.



#19 alphatripleplus

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Posted 20 June 2022 - 09:42 AM

 

 

The bit I can't get my head around at the moment is how the Camera affects the image size. I mean, with a decent chip like in the ZWO294 would digital zoom keep decent resolution even with a short focal length. My iPhone has very wide angle, but you can zoom in a lot digitally after taking the image and still keep good resolution.

 

 

The physical size of the sensor and the focal length of the scope determine the field of view covered by an image - a big sensor will obviously cover a larger FOV than a small one, which will appear to give a "zoomed' image because of its smaller FOV. However, you can always crop the image from a large sensor camera to give a zoomed image.

 

What determines the level of detail you can actually see in any image (regardless of whether you are using a large or small sensor) is the image scale of the camera's pixels in arcsecs/pixel. The image scale depends on the sensor's pixel size in microns and the focal length of the scope, but NOT the physical size of the sensor. For example, if you have a large camera sensor consisting of  many 3 micron pixels and a small camera sensor with  fewer 3 micron pixels, they will each show the same level of detail because they both have 3micron  pixels, and so they have the same image scale. The big sensor will cover a wider field of view than the smaller sensor, but if you zoom in on the big sensor's FOV, you will see exactly the same level of detail as in the smaller sensor.

 

Digital zooming is equivalent to cropping - it won't improve the camera pixels' image scale to show finer detail. It will allow you to concentrate on part of a large image and see whatever detail the camera's pixels have captured.


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#20 Leafus

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Posted 20 June 2022 - 11:52 AM

The physical size of the sensor and the focal length of the scope determine the field of view covered by an image - a big sensor will obviously cover a larger FOV than a small one, which will appear to give a "zoomed' image because of its smaller FOV. However, you can always crop the image from a large sensor camera to give a zoomed image.

 

What determines the level of detail you can actually see in any image (regardless of whether you are using a large or small sensor) is the image scale of the camera's pixels in arcsecs/pixel. The image scale depends on the sensor's pixel size in microns and the focal length of the scope, but NOT the physical size of the sensor. For example, if you have a large camera sensor consisting of  many 3 micron pixels and a small camera sensor with  fewer 3 micron pixels, they will each show the same level of detail because they both have 3micron  pixels, and so they have the same image scale. The big sensor will cover a wider field of view than the smaller sensor, but if you zoom in on the big sensor's FOV, you will see exactly the same level of detail as in the smaller sensor.

 

Digital zooming is equivalent to cropping - it won't improve the camera pixels' image scale to show finer detail. It will allow you to concentrate on part of a large image and see whatever detail the camera's pixels have captured.

Right, thanks Alpha, I think I follow you. So the 2.1Mp cameras are likely on a small chip, so capture reduced FOV. The high Mp chips are generally larger, so capture more image/wider FOV, which if you crop it would then produce the same resolution image as the smaller chip. Assuming the pixel size is the same.

 

With a wide FOV scope, like a small 80mm frac, I assume I would need a big chip if I wanted to capture the whole FOV, but with a small chip I could still take just as high a resolution image (for the same camera pixel size) but just for a smaller part of the field of view.

 

For planetary, I understand that the small sensor is fine anyway.

 

Drawback would be that perhaps plate-solving would not work so well. I will still be able to easily centre the object, as I will have the 925 in visual mode at the same time (and hopefully both centred to each other).

 

I am not that concerned with really wide field photographs (I know I would miss some of the biggest DSO but only a few) - I often crop down to just the DSO anyway.

 

So I could perhaps start off by getting a cheaper camera than the 294, and spending more elsewhere, such as on a better quality piggyback scope.



#21 MarMax

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Posted 20 June 2022 - 12:34 PM

Here are three FOV's for the 9.25 as an example.

 

AA_9_25_FOVTest.jpg


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#22 alphatripleplus

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Posted 20 June 2022 - 12:40 PM

 

So I could perhaps start off by getting a cheaper camera than the 294, and spending more elsewhere, such as on a better quality piggyback scope.

That is a matter of preference. I started with a small 224MC and now I use a small 290MM mono - I will be moving to a larger sensor camera soon after many years of using small sensor cameras. Plate solving (if you get it to work) will be your friend if you have to deal with the small FOV that comes with a small sensor camera. Many people jump straight to a big sensor camera, as it simplifies the issues of finding a target, framing and fitting it into the FOV. 



#23 SchoolMaster

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Posted 20 June 2022 - 12:50 PM

You mentioned wide-field.  The AT60ED and AT72EDII are both decent FPL53 doublets, with a reducer, capable of f/4.8 and gives FOV even a 9.25 HyperStar cannot reach.  TS and other European vendors sell similar OTA.  I am always sorely tempted by a larger than 80mm doublet or triplet (115EDT, 125EDL) until I remind myself that for EAA, my C8, in one configuration or another, can cover that space.  It is only at the very wide-field end that I run out of reduction.

 

I would not buy a camera cheaper than the 533.  If you go uncooled, the PlayerOne SaturnC is the least expensive.  The 533 is the least expensive 'do it all" camera and modern too.  I think a two camera set up with a 290MM or 178MM for detail is a good choice.


Edited by SchoolMaster, 20 June 2022 - 01:19 PM.

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#24 Leafus

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Posted 20 June 2022 - 01:17 PM

MarMax: That's a great graphic. I can't believe the cameras are that different. Amazing.

Is that from a web-tool?

 

The fov with the 294 would be vast with the small piggy back frac, but that graphic also shows the FOV would be pretty good even with the straight 925, even without reducer for a lot of objects I want to look at. Would probably be even be better with the 925 for small DSO, than with a piggy back scope.

 

Alphatriple: I can see the big FOV would help locate objects. With my aim to do dual visual/EAA the EP view should help overcome problems finding the target, I would hope.

 

Schoolmaster: Excellent point that. With the 925 and an 80mm it would cover both for large objects and the small ones. I think that's convinced me I don't need to go over 80mm.

 

20 Second Subs?

So that just leaves me wondering whether with a reasonable 80mm Frac at say around F6 if I would end up with problems with the limited 20second subs the CPC will allow.

 

And with the cam swapped to the 925 for smaller DSO objects? I suppose a celestron reducer would be essential for those. Would it be enough though with only 20seconds maximum exposure?



#25 SchoolMaster

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Posted 20 June 2022 - 01:21 PM

It's astronomy.tools.

 

Look at this.

 

astronomy_tools_fov (51).png

 

AT60ED with 0.8 reducer down to unreduced C9.25.  Counting from the smallest, frame 4 is HyperStar.

 

This

 

astronomy_tools_fov (52).png

 

Adds a 80ED with and without reducer so you can see the overlap.


Edited by SchoolMaster, 20 June 2022 - 01:32 PM.

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