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Downsizing from C11 Edge to C8 Edge ???

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#1 bilgebay

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Posted 01 February 2013 - 05:21 AM

I've asked this question in the CCD Imaging & Processing forum but only got 3 serious comments so far although 230 people viewed the subject.

So, here I'm , asking the same, with hopes to get some more comments before acting.

I want to go down to C8 Edge from C11 Edge. My reasons are:

- Since I don't have a permanent setup, I am finding it quite cumbersome and risky to move this OTA in and out in my 2 storey warm room - observation terrace setup. I feel even more uncomfortable when I have the Hyperstar + CCD/DSLR hanging off of the corrector plate. I am keeping the dew shield on the scope during these transports to provide some sort of protection lest I should hit the camera against a door or a tree but this makes the scope even bulkier.

- I have acquired several other scopes after I purchased this scope. If you, please, look at my signature you can see these scopes. By the way, the scope list is in chronological order according to the purchase date. When I purchased my C11 Edge, the idea was to use this scope both for visual and imaging. But now, I have larger aperture scopes for visual observation. Additionally, I have ordered 2x Zambuto mirrors for my 12" Dob and 8" Newt. I am sure the 12" Zambuto mirror, coupled with a quality secondary and Feather Touch focuser + Paracorr II will give the C11 Edge a hard time.

- In the meantime, I have moved to CCD imaging from DSLR imaging and purchased an Atik 460 EX, which has a very convenient form/size which will not intrude into the light path of C8 when imaging in the Hyperstar configuration. So I don't need a C11 Edge just to make up for the bulkiness of the DSLR body.

- I am aware that the focal length will go down from 2800mm to 2032mm at f/10 and from 560mm at f/2 to 425mm. On the other hand I will have a wider FOV which I actually like.

Do you see a problem in this, other than losing some focal length, from an astro imagers point of view? I will have a much compromised performance if I want to use this scope visually, no doubt.... but this is not my primary concern now.

I have inserted the C8 Edge into the attached Brightness spreadsheet, which Rich (Starhawk) had kindly shared with me some time ago. C8 Hyperstar is shining against all the other scopes there, except for the C11 and C14 Hyperstars.

Some may find this suicidal but the spreadsheet is telling me otherwise. The brightness is still beating that of FSQ106 by a factor of 3 even when reduced to f/3,6 and the resolution is still way better than my average seeing values with C8. The only drawback is the reduced back focus, from 146mm to to 133mm but this is still plenty for all my imaging cameras at the moment. Here are some facts to compare:

C11
• Focal Ratio: f/2.0
• Focal Length: 560mm
• Maximum Usable Sensor Size: 27mm Diagonal (APS Format)
• DSLR Compatible
• Field of View (with 27mm sensor): 2.9 degrees
• Camera Adapter Threaded for 2" (48mm) Filters
• Backfocus (from mounting thread to focal plane): 59.7mm (2.35")
• Length (without camera adapter): 5.0"
• Diameter: 4.3
• Weight: 2.1 lbs
• OTA weight: 28 lbs

T2i – 137’ – 0.32”/pixel
Atik 460 – 77’ – 1.58”/pixel


C8
• Focal Ratio: f/2.1
• Focal Length: 425mm
• Maximum Usable Sensor Size: 27mm Diagonal (APS Format)
• Field of View (with 27mm sensor): 3.8 degrees
• Camera Adapter Threaded for 2" (48mm) Filters
• Backfocus (from mounting thread to focal plane): 39.8mm (1.57")
• Length (without camera adapter): 4.5"
• Diameter: 3.0"
• Weight: 1 lb.
• OTA weight: 14 lbs
T2i – 180’ – 0.44”/pixel
Atik 460 – 101’ – 2.2”/pixel


The actual weight of my C11 Edge, complete with the DSLR, Hyperstar, finder, etc is not less than 37 pounds.

I am looking forward to hearing your comments.

Thanks

Sedat

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#2 rmollise

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Posted 01 February 2013 - 09:17 AM

Depends on what your requirements are. If the field of the 8 matches what you want to image, go for it. The advantage of the C8 for imaging is that it gives a large image scale for smaller targets. Visually? The 11 wins, no doubt about that, but you can see one hell of a lot in a good old C8. ;)
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#3 WadeH237

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Posted 01 February 2013 - 09:20 AM

It doesn't sound crazy to me. For imaging, I tend to look at focal length as more important than aperture. Focal ratio can be a consideration, but since you are using Hyperstar, that's not the case in your situation.

One thing to consider with Hyperstar is the quality of the field. I have tried Hyperstar on both my C14 and my C8. I find the C8 to be far more sensitive to geometry and collimation than the C14. So much so that I've never been happy with the C8 in this configuration.

In my case, I believe that the reasons for the difference are the size of the imaging chip versus the size of the field. On my C14, I was using an ST-10, which has a small chip by today's standards. On my C8, I use a QHY8 Pro, which has a much larger APS-C sized chip. If I crop the C8 image down to ST-10 equivalent, it removes much of the problem areas. So I guess that my C8/Hyperstar/QHY-8 combination is just very unforgiving.

You have two advantages over me with regard to the C8. First, you are looking at an Edge HD scope, which by all account, comes from the factory very well aligned. I am using a 15 year old standard C8. And second, you've got a very good process for aligning and centering the secondary and corrector plate. I've spent some time trying to get mine perfect, but haven't quite got there yet.

Anyway, this is just my two cents and random thoughts.

-Wade
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#4 Eddgie

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Posted 01 February 2013 - 10:28 AM

Why not?

If you are Imageing, the only difference will be true field and image scale, and there are lots of targets that will benefit from having a bigger true field.

You can buy the scope based on the image scale you need for a given kind of target, or you can by the scope and pick the best targets for that image scale.

My bet is that either way, you get about the same number of targets. You'll just be looking for bigger targets in the 8" than you were in the 11". No big deal.

And if you aren't going to use the EdgeHD 11 for visual because you have bigger/better scopes for that, then dump it.

I love love love my EdgeHD 8". Funny thing is, I have only used it a few dozen since I have owned it.

But since owning it, I have used my 6" APO even less!!! If it fits in the field, it usually looks better in the EdgeHD 8", and the EdgeHD 8" is so much easier to take out than the 6" APO! Oh, I still love the 6" APO for summer Milky Way, but the EdgeHD 8" is fantastic for visual use.

Of course I use my C14 98% of the time, but hey, I don't image.

So, if you are covered visually, then by all means, drop down to the EdgeHD 8". They are superb scopes.
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#5 GlennLeDrew

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Posted 01 February 2013 - 10:48 AM

Don't get bogged down in analysis paralysis. Look at the key two or three features and weigh the systems based on these only. Often, the choice can (or perhaps should :grin:) be made by considering just one aspect.

#6 bilgebay

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Posted 01 February 2013 - 03:45 PM

Thank you Rod. As Eddgie is commenting down below, I will pick the targets that fits C8 best. I will have lots of options at 3 different focal ratios and 2-3 different cameras anyway.

Best

Sedat

#7 rmollise

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Posted 01 February 2013 - 04:24 PM

Again, Sedat, depends on what you are after, but for me, the C8 is my main imaging tool. The C11 just has a wee bit to much f/l most of the time...

#8 bilgebay

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Posted 01 February 2013 - 04:25 PM

Wade, thank you for your comments.

It doesn't sound crazy to me.



Glad to hear this :)

You have two advantages over me with regard to the C8. First, you are looking at an Edge HD scope, which by all account, comes from the factory very well aligned. I am using a 15 year old standard C8. And second, you've got a very good process for aligning and centering the secondary and corrector plate



If the corrector and the secondary is not already dead centered, I am sure I can sort this out again. This time, I may use my Howie Glatter laser and its attachments for checking and fine tuning the alignment.

The Hyperstar unit needs some tweaking as well for my method to be effective. Please see my thread on the subject which I have updated recently, some seven months after starting the thread

#9 bilgebay

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Posted 01 February 2013 - 04:30 PM

The C11 just has a wee bit to much f/l most of the time...


This is my conclusion after 2 1/2 years using C11 Edge.

Thanks

#10 bilgebay

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Posted 01 February 2013 - 04:35 PM

Ed, thank you very much. Your points are all very valid and in line with my assessment. I needed the reassurance of more experienced users before acting.

The moment I have a fixed setup at a location with very good seeing, I will buy a C14 Edge or whatever Celestron has at that time, a C18 Edge perhaps, for planetary work :)

Thanks again.

Sedat

#11 bilgebay

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Posted 01 February 2013 - 04:38 PM

Hi Glenn,

From time to time, analysis paralysis becomes inevitable for most of, doesn't it ? It is my turn now :)

Cheers

Sedat

#12 telfish

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Posted 01 February 2013 - 10:02 PM

How is the smaller rear opening of the c8 going to effect your imaging at prime. Will you get full chip coverage?

If so maybe the 9.25 would be a better choice.

#13 Patrick

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Posted 01 February 2013 - 11:50 PM

I recently acquired an EdgeHD 8" for imaging. Aside from cost, the main reason was the focal length issue. Also, the weight of the 8" is much less than the 11", making it a more portable scope.

I've been very interested in Hyperstar, but quite frankly I can't get past the simple fact that a short APO refractor can pretty much do the same job with less hassle. Of course the refractor won't be f/2, but you could get it down to f/5 or f/4 with a focal reducer. I'm jealous of your new camera purchase. I'd love to get one of the Sony 460 Ex's. :smirk:

Patrick

#14 mistyridge

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Posted 02 February 2013 - 01:41 AM

I sold my C11 and bought a EdgeHD C8 for similar reasons. The C11 was just to heavy and awkward for me to hoist up on the mount with my arthritic right shoulder. I have never looked back.

#15 bilgebay

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Posted 02 February 2013 - 02:49 AM

Well, according to Celestron's White Paper on Edge scopes, C8 Edge provides a 42 mm image circle, just like the other Edge scopes.

I guess I will be OK with the Atik 460EX but I have to see how well the
APS-C or KAF8300 is illuminated. According to the specs, they should be ok too.

Thanks for the heads up.

Sedat

#16 bilgebay

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Posted 02 February 2013 - 03:14 AM

Hi Patrick,

I'm glad to hear that you are happy with your C8.

I can tell you that Hyperstar is no hassle at all. I've been using it for over 2 years and never felt that way. I have scopes with f/5 speed but still HS is a lot faster than those, especially when shooting with 3nm NB filters. At f/2.1, C8 Hyperstar will be 5.5 times faster than my FSQ106. This is a big difference. Of course, FSQ provides very sharp images. I need to see the C8+HS combo's performance yet but my experience with C11+HS has been very positive so far.

Clear skies

Sedat

#17 bilgebay

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Posted 02 February 2013 - 03:16 AM

Hi Mike,

Thank you for sharing your experience. Great help.

Clear skies

#18 bilgebay

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Posted 02 February 2013 - 03:25 AM

I want to thank you all for your great contribution to my decision making process.

Today, I will place the order for a C8 Edge + AVX mount package as well as the C8 Hyperstar unit. Needless to say, a Feather Touch Microfocuser will be ordered too. I am considering to order cooling fans from Ed as well.

Thanks again. The stress is over now :)

#19 mmalik

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Posted 02 February 2013 - 05:52 AM

SCTs primarily being visual platforms, my vote will be for a premium APO (appropriate fl/aperture per your needs) given your inclination for imaging. APO will make a good visual platform as well. That would also mean NO to AVX. My suggestion would be to hold off; sorry, don't mean to make you stressed at the last minute but this package (including the mount) you talk about sounds iffy if you are buying it primarily for imaging. Thx

#20 telfish

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Posted 02 February 2013 - 09:17 AM

Well, according to Celestron's White Paper on Edge scopes, C8 Edge provides a 42 mm image circle, just like the other Edge scopes.

I guess I will be OK with the Atik 460EX but I have to see how well the
APS-C or KAF8300 is illuminated. According to the specs, they should be ok too.

Thanks for the heads up.

Sedat


Good keep us in touch with your experiences. The C8 Edge seems to be great value when you compare it to the C11 and C9.25 Edge scopes.

I shoot Hyperstar with an older C11 that I will either need to replace or re-coat soon. So I will be interested in your take on the new scope, especially as you are an engineer and a seasoned Hyperstar user.


Terry

#21 EFT

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Posted 02 February 2013 - 12:46 PM

The choice sounds perfectly reasonable to me. The C11HD has some definite advantages over the C8HD, but it has disadvantages as well, not the least of which is the size and weight.

#22 WarmWeatherGuy

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Posted 02 February 2013 - 01:26 PM

When using hyperstar (f/2) the camera blocks some of the starlight because the camera is usually larger than the secondary mirror. The amount of area that is blocked by the camera is about the same (in square mm, C8 versus C11) but will be more percentage-wise for the smaller scope. This means that the effective focal ratio won't be f/2 on the C8 and the C11. It might be f/3 for the C11 and f/5 for the C8 (as a crude example).

In the extreme, imagine doing hyperstar on a C5 where the camera blocks just about all the light entering the scope.

If you are not using hyperstar then you can get a focal reducer. A C11 with a focal reducer will have about the same field of view as a C8 without one. In this case your exposure times would need to be about half as long with the C11 versus the C8 (f/7 versus f/10).

#23 telfish

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Posted 02 February 2013 - 01:56 PM

I agree when using a DSLR or a large circular camera, however there are a number of cameras that are smaller than the diameter of the secondary on the market. I believe the OP has one of those.

#24 bilgebay

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Posted 02 February 2013 - 04:17 PM

SCTs primarily being visual platforms, my vote will be for a premium APO (appropriate fl/aperture per your needs) given your inclination for imaging. APO will make a good visual platform as well. That would also mean NO to AVX. My suggestion would be to hold off; sorry, don't mean to make you stressed at the last minute but this package (including the mount) you talk about sounds iffy if you are buying it primarily for imaging. Thx


Mike thank you.

The C8 Edge will ride on my Vixen New Atlux. This mount is capable of tracking perfectly with C11 Edge at 2800mm focal length and produce round stars. So, C8 is not a problem for this mount at all.

As for the VX mount, it is a lot of mount for the money. When purchased as a package with the C8, you save at least 100 bucks, if not more. I will be using it for visual observation. Of course, I will test its capabilities for imaging but I will not be relying on it for imaging.

Clear skies

#25 bilgebay

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Posted 02 February 2013 - 04:20 PM

Hi Terry,

I will most probably receive the scope during NEAF in April. You will have my report by the middle of May.

Best wishes






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