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bilgebay
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Downsizing from C11 Edge to C8 Edge ???
      #5655598 - 02/01/13 05:21 AM Attachment (53 downloads)

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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rmollise
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Re: Downsizing from C11 Edge to C8 Edge ??? new [Re: bilgebay]
      #5655871 - 02/01/13 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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WadeH237
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Re: Downsizing from C11 Edge to C8 Edge ??? new [Re: bilgebay]
      #5655880 - 02/01/13 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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Eddgie
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Re: Downsizing from C11 Edge to C8 Edge ??? new [Re: bilgebay]
      #5656046 - 02/01/13 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.

Edited by Eddgie (02/01/13 10:48 AM)


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GlennLeDrew
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Re: Downsizing from C11 Edge to C8 Edge ??? new [Re: Eddgie]
      #5656101 - 02/01/13 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 ) be made by considering just one aspect.

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bilgebay
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Re: Downsizing from C11 Edge to C8 Edge ??? new [Re: rmollise]
      #5656613 - 02/01/13 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


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rmollise
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Re: Downsizing from C11 Edge to C8 Edge ??? new [Re: bilgebay]
      #5656679 - 02/01/13 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...

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bilgebay
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Re: Downsizing from C11 Edge to C8 Edge ??? new [Re: WadeH237]
      #5656683 - 02/01/13 04:25 PM

Wade, thank you for your comments.

Quote:

It doesn't sound crazy to me.




Glad to hear this

Quote:

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


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bilgebay
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Re: Downsizing from C11 Edge to C8 Edge ??? new [Re: rmollise]
      #5656694 - 02/01/13 04:30 PM

Quote:

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


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bilgebay
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Re: Downsizing from C11 Edge to C8 Edge ??? new [Re: Eddgie]
      #5656707 - 02/01/13 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


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bilgebay
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Re: Downsizing from C11 Edge to C8 Edge ??? new [Re: GlennLeDrew]
      #5656715 - 02/01/13 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


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telfish
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Re: Downsizing from C11 Edge to C8 Edge ??? new [Re: bilgebay]
      #5657232 - 02/01/13 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.


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Patrick
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Re: Downsizing from C11 Edge to C8 Edge ??? new [Re: telfish]
      #5657407 - 02/01/13 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.

Patrick


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mistyridge
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Re: Downsizing from C11 Edge to C8 Edge ??? new [Re: Patrick]
      #5657501 - 02/02/13 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.

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bilgebay
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Re: Downsizing from C11 Edge to C8 Edge ??? new [Re: telfish]
      #5657531 - 02/02/13 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


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bilgebay
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Re: Downsizing from C11 Edge to C8 Edge ??? new [Re: Patrick]
      #5657545 - 02/02/13 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


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bilgebay
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Re: Downsizing from C11 Edge to C8 Edge ??? new [Re: mistyridge]
      #5657546 - 02/02/13 03:16 AM

Hi Mike,

Thank you for sharing your experience. Great help.

Clear skies


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bilgebay
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Re: Downsizing from C11 Edge to C8 Edge ??? new [Re: bilgebay]
      #5657551 - 02/02/13 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


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mmalik
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Re: Downsizing from C11 Edge to C8 Edge ??? new [Re: bilgebay]
      #5657604 - 02/02/13 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

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telfish
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Re: Downsizing from C11 Edge to C8 Edge ??? new [Re: bilgebay]
      #5657745 - 02/02/13 09:17 AM

Quote:

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


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EFT
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Re: Downsizing from C11 Edge to C8 Edge ??? new [Re: bilgebay]
      #5658072 - 02/02/13 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.

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WarmWeatherGuy
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Re: Downsizing from C11 Edge to C8 Edge ??? new [Re: EFT]
      #5658151 - 02/02/13 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).


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telfish
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Re: Downsizing from C11 Edge to C8 Edge ??? new [Re: WarmWeatherGuy]
      #5658218 - 02/02/13 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.

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bilgebay
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Re: Downsizing from C11 Edge to C8 Edge ??? new [Re: mmalik]
      #5658433 - 02/02/13 04:17 PM

Quote:

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


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bilgebay
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Re: Downsizing from C11 Edge to C8 Edge ??? new [Re: telfish]
      #5658437 - 02/02/13 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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bilgebay
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Re: Downsizing from C11 Edge to C8 Edge ??? new [Re: EFT]
      #5658438 - 02/02/13 04:24 PM

Thank you Ed. This time I will not drill my OTA to implement my custom cooling system. I will buy your cooling fans

Thanks for developing such a nice product.

Sedat


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bilgebay
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Re: Downsizing from C11 Edge to C8 Edge ??? new [Re: WarmWeatherGuy]
      #5658462 - 02/02/13 04:40 PM

Quote:

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).




Thank you for your comments and the heads up.

Well, the camera I will be using in the Hyperstar configuration has a diameter of 60mm (Atik 460 EX). The secondary holder is of 69mm diameter. So the camera is not stealing any aperture. However, the C8 Hyperstar has a diameter of 3" according to the Starizona website. This means we will be increasing the central obscuration only by 6mm, which is negligible.

So, you can rest assured that I will be shooting at f/2

Using a T2i or a similar DSLR with C8 Hyperstar is out of question. Of course, seeing the fast developments in this field is quite promising. Canon EOS M is a very good example of how the form factor can diminish for the same APS-C size sensor. In the near future, using a DSLR can be quite possible.


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Patrick
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Re: Downsizing from C11 Edge to C8 Edge ??? new [Re: WarmWeatherGuy]
      #5659026 - 02/02/13 10:26 PM

Quote:

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).




The f/r does not change because of a larger CO...f/r= aperture / focal length.

Patrick


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GeneT
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Re: Downsizing from C11 Edge to C8 Edge ??? new [Re: bilgebay]
      #5659035 - 02/02/13 10:31 PM

Given your other telescopes, I believe it makes perfect sense to sell the C11 and get a C8. If you only owned a C11 and asked about moving to a C8, I would have thought--only if you can't handle the larger telescope, and need to move to something smaller. However, you have a 16 and a 12. After selling your 11, an 8 is the next place to be.

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WarmWeatherGuy
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Re: Downsizing from C11 Edge to C8 Edge ??? new [Re: Patrick]
      #5659315 - 02/03/13 02:51 AM

Quote:



The f/r does not change because of a larger CO...f/r= aperture / focal length.

Patrick




That is why I said effective focal ratio. The focal length and image size do not change but the image brightness changes and you need longer exposures. Effectively it is like a scope with a crummier focal ratio.


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mmalik
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Re: Downsizing from C11 Edge to C8 Edge ??? new [Re: WarmWeatherGuy]
      #5659506 - 02/03/13 08:29 AM

Quote:

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).




Quote:

That is why I said effective focal ratio. The focal length and image size do not change but the image brightness changes and you need longer exposures. Effectively it is like a scope with a crummier focal ratio.




I tend to agree; while you refer to it as a crummier in terms of extended “obstruction” DSLR causes; I would refer it as crummier in terms of its core design characteristics (i.e., means of reducing f-ratio in an already photographically compromised design of SCT [without getting into the debate of corrector stresses, spherical aberrations, collimation implications, etc.]). My point being, hypothetically speaking, if a DSLR were to transform into the size/shape of the central obstruction, I still think core characteristics of HyperStar make it a less than optimal imaging platform. I see the value of HyperStar in terms of crude video (web cam), but that’s about it; for sophisticated imagery, it makes for a make-shift solution.


Sedat, to use your image of C11..., I think C8 is going to "look" even more compromising, not to mention the image quality it may produce [I mean in comparison to an equivalent non-compromised system]. Thx


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bilgebay
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Re: Downsizing from C11 Edge to C8 Edge ??? new [Re: mmalik]
      #5659521 - 02/03/13 08:45 AM

Hi Mike,

That assumption is not true for the camera I will be using with this scope Mike.

For details of Atik 460EX, please see this page.

Sedat


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mmalik
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Re: Downsizing from C11 Edge to C8 Edge ??? new [Re: bilgebay]
      #5659547 - 02/03/13 09:07 AM

That's little better. Thx

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Patrick
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Re: Downsizing from C11 Edge to C8 Edge ??? new [Re: WarmWeatherGuy]
      #5659669 - 02/03/13 10:22 AM

Quote:



That is why I said effective focal ratio. The focal length and image size do not change but the image brightness changes and you need longer exposures. Effectively it is like a scope with a crummier focal ratio.




I'm not trying to nit pick here, but there is no such thing as effective focal ratio. That aside, I agree with you that letting something like a DSLR hanging over the secondary is not desirable. In Sadat's case he'll be fine with his 460EX. That's the camera I'd like too...drool!

Patrick


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telfish
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Re: Downsizing from C11 Edge to C8 Edge ??? new [Re: bilgebay]
      #5659708 - 02/03/13 10:45 AM

Thanks.

When I am next over sailing the turquoise coast I will look you up.

Terry

Quote:

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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bilgebay
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Re: Downsizing from C11 Edge to C8 Edge ??? new [Re: telfish]
      #5666505 - 02/07/13 06:08 AM

Great! We can observe together if you come

Cheers


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ICit2
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Reged: 01/17/11

Re: Downsizing from C11 Edge to C8 Edge ??? new [Re: bilgebay]
      #6238066 - 12/06/13 08:16 PM

Quote:

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




Well Sedat, not exactly. Check out page 17, 3rd paragraph of the Celestron EdgeHD "White Paper".

"Portability and affordability are the hallmarks of the EdgeHD 800. Although the 8-inch covers a 42mm image circle, we optimized its optics for the central 28mm area, the size of an APS-C chip in many popular digital SLR cameras."

So with a "C" chip a guy should be ok but it's the Edge 9.25 that optimized for the full 42mm and the Edge 11 comes in at 30mm optimization.

For the Edge 14, a beast of a scope requiring two strong men and a dog to put in the saddle, the story goes like this:

"In green light, the EdgeHD 1400 is diffraction-limited over a 28mm image circle, although atmospheric seeing enables it to display its full resolution only on the finest nights. Relative illumination is 100% across the central 16mm, and falls slowly to 83% in the extreme corners of a full-frame 35mm image sensor. We have seen excellent results when the 14-inch EdgeHD is used with a KAF-16803 CCD camera over a 50mm circle."

So, the image circle's optimization vary from scope to scope.

Richard
Soon to be wed to an Edge 8

Edited by ICit2 (12/06/13 08:26 PM)


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schinia
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Reged: 05/17/13

Loc: cape carteret,NC
Re: Downsizing from C11 Edge to C8 Edge ??? new [Re: ICit2]
      #6238916 - 12/07/13 12:02 PM

why ccd camera's system requirements only with PC's and not Apple products?

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