Telescope Reviews: Downsizing from C11 Edge to C8 Edge ???

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Equipment Discussions >> Cats & Casses

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EFT
Vendor - Deep Space Products

Reged: 05/07/07

Loc: Phoenix, AZ

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
professor emeritus

Reged: 08/27/11

Loc: Orlando, FL 28° N, 81° W

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
super member

Reged: 11/17/10

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
Post Laureate

Reged: 11/06/08

Loc: Türkiye - Istanbul and Marmari...

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
Post Laureate

Reged: 11/06/08

Loc: Türkiye - Istanbul and Marmari...

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
Post Laureate

Reged: 11/06/08

Loc: Türkiye - Istanbul and Marmari...

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
Post Laureate

Reged: 11/06/08

Loc: Türkiye - Istanbul and Marmari...

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
Postmaster

Reged: 05/16/03

Loc: Franklin, Ohio

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
Ely Kid

Reged: 11/07/08

Loc: South Texas

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
professor emeritus

Reged: 08/27/11

Loc: Orlando, FL 28° N, 81° W

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
Carpal Tunnel

Reged: 01/13/12

Loc: USA

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
Post Laureate

Reged: 11/06/08

Loc: Türkiye - Istanbul and Marmari...

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
Carpal Tunnel

Reged: 01/13/12

Loc: USA

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
Postmaster

Reged: 05/16/03

Loc: Franklin, Ohio

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
super member

Reged: 11/17/10

Re: Downsizing from C11 Edge to C8 Edge ??? new