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Downsizing from C11 Edge to C8 Edge ???

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#26 bilgebay

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Posted 02 February 2013 - 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

#27 bilgebay

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Posted 02 February 2013 - 04:40 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).


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.

#28 Patrick

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Posted 02 February 2013 - 10:26 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).



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

Patrick

#29 GeneT

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Posted 02 February 2013 - 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.

#30 WarmWeatherGuy

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Posted 03 February 2013 - 02:51 AM


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.

#31 mmalik

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Posted 03 February 2013 - 08:29 AM

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).


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

#32 bilgebay

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Posted 03 February 2013 - 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

#33 mmalik

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Posted 03 February 2013 - 09:07 AM

That's little better. Thx

#34 Patrick

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Posted 03 February 2013 - 10:22 AM


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

#35 telfish

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Posted 03 February 2013 - 10:45 AM

Thanks.

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

Terry

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



#36 bilgebay

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Posted 07 February 2013 - 06:08 AM

Great! We can observe together if you come :)

Cheers

#37 ICit2

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Posted 06 December 2013 - 08:16 PM

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 :smirk:

#38 schinia

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Posted 07 December 2013 - 12:02 PM

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






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