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Equipment Discussions >> Cats & Casses

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BKBrown
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Reged: 08/23/09

Loc: Northern Virginia, USA
Re: Edge HD Focal Reducer new [Re: bilgebay]
      #5938930 - 06/24/13 11:40 PM

Hi Sedat,

I am a C11 Edge owner and am very interested in the AP CCDT67. Could you post information for the complete train to give us an idea of what we would need to pick up for DSLR imaging with the CCDT67? I would be much obliged sir! Thanks

Clear Skies,
Brian


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bilgebay
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Reged: 11/06/08

Loc: Türkiye - Istanbul and Marmar...
Re: Edge HD Focal Reducer new [Re: BKBrown]
      #5939021 - 06/25/13 12:46 AM

Hi Brian,

Please see page 15 of this thread. You will find all the details from that page onwards.

Best wishes


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bilgebay
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Reged: 11/06/08

Loc: Türkiye - Istanbul and Marmar...
Re: Edge HD Focal Reducer new [Re: freestar8n]
      #5939266 - 06/25/13 08:06 AM

Quote:

Ok - I get 0.46"/pixel which is very similar, and I see little vignetting. I can't tell the exact percentage without having bias frames to subtract, so that I know where the "zero" is. But both images appear to be dominated by skyglow so I don't think it matters much and there is just gradual vignetting toward the corners - which is what I expected with that size sensor.

So - they both seem ok to me in terms of vignetting.

Frank




Hi Frank, thank you.

Here is the Bias and here is the Flat raw files.

I don't have the bias for the M13 frame unfortunately.

Meanwhile I have asked Jerry about his imaging train. I will share his answer with you. Or maybe he can chime in here too.

Clear skies


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Jerry Lodriguss
Vendor


Reged: 07/19/08

Loc: Voorhees, NJ
Re: Edge HD Focal Reducer new [Re: bilgebay]
      #5939585 - 06/25/13 11:46 AM

Hi Sedat,

I used AstroTortilla to plate solve the image and the focal length came out to 1963mm and f/7.0257695 with the Celestron focal reducer.

On my test of the Celestron focal reducer:

I was using a JMI electronic focuser on the back of the Celestron focal reducer. The focuser has a 2 inch opening.

Next came a Lumicon OAG with a 2 inch opening.

Then came a regular t-mount adapter.

Then the camera.

I also shot some frames with the Celestron 146mm T-mount adapter on the back of the focal reducer.

This is the setup that Celestron sells to be used with the focal reducer.

The vignetting was the same.

So, even if it were the t-mount that caused the vignetting, this is the way Celestron made it to be used.

But I do not think it was the t-mount because the vignetting was present before the t-mount because that is the location of the OAG pickoff prism, and the vignetting was so severe at this point, I could not find a star to guide on, even with a 10 second exposure in the Lodestar.

I measured the vignetting by examining average pixel values in the debayered linear file in Images Plus before stretching, so I don't know why there is any discrepancy.

Also, as far as using flats, flats may solve the difference in brightness between the center and corners of the frame, but they do not solve the problem of lost signal-to-noise ratio as you move from the center to the corners.

And the biggest problem for me is that the vignetting was so severe with my OAG that I could not find a guidestar with a 10 second exposure in the Lodestar.

This alone made it essentially unusable for me.

Perhaps another OAG with a pickoff prism that could be moved farther into the light cone would solve this problem, but might introduce another problem of prism shadowing in the image. And, again, while flats would seem to solve this problem, they don't fix the s/n issue in the shadowed area.

Jerry


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freestar8n
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Reged: 10/12/07

Re: Edge HD Focal Reducer new [Re: Jerry Lodriguss]
      #5939924 - 06/25/13 02:44 PM

Hi Jerry-

I don't have a consistent set of files for analysis, but if Sedat's bias is similar to yours, at ISO 1600, and if the approximate value after deBayering is similar, then both have a background of about 2020. That means your vignetting is about 1/3 from corner to center and Sedat's is about 1/4.9. In other words, your corner is at about 67% and his is at about 80%, or 13% difference. I think both would be hard to tell after applying a flat - especially since it is a corner measurement and the transition is gradual.

I don't know what would be going on with the oag, but if you have some basic measurements of the system it should be easy to tell if there is any expected vignetting just based on geometry. The f/7 cone is well defined and it should appear to come from an exit pupil that is about 280mm in diameter and 2000mm away.

I think that everything on the Edge reducer is larger than on the AP reducer - mainly the front and rear openings. Isn't that correct? So it would be very hard to understand why there would be more vignetting in the Edge version.

Are you sure the OAG was focused properly when you looked for a guidestar? I do oag with a normal c11 and a normal f/6.3 reducer and have no trouble - but I use the primary focuser and have just the reducer, oag, filter wheel, and ccd.

Frank


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freestar8n
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Reged: 10/12/07

Re: Edge HD Focal Reducer new [Re: freestar8n]
      #5940208 - 06/25/13 05:47 PM Attachment (42 downloads)

Here's a scale diagram of the back end of the system with the reducer in place. This assumes D=280, bf=146, f=1960, aps-c diag=26.8, clear diam=42, rear lens of focal reducer is drawn at 60mm.

For an f/7 beam coming from an exit pupil 280mm in diameter 1960mm away, a rear lens 60mm diameter gives a fully illuminated 42mm diameter field. For a 26.8mm diagonal field, the opening needed on the reducer is then reduced to 45.6mm. As long as nothing after the reducer is smaller than 45.6mm diameter, there should be no vignetting across the entire diagonal of the 350D sensor. There may be a slight reduction in illumination due to normal cosine effects - but not vignetting per se.

Assuming I drew this right, of course. But the math is just simple geometry.

Of course the actual optical path is changed from f/10 to f/7 by the reducer - but as far as the optical system seen by the sensor - it is just an f/7 beam going out to an exit pupil 280mm diameter.

Frank


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BKBrown
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Reged: 08/23/09

Loc: Northern Virginia, USA
Re: Edge HD Focal Reducer new [Re: bilgebay]
      #5940389 - 06/25/13 07:59 PM

Quote:

Hi Brian,

Please see page 15 of this thread. You will find all the details from that page onwards.

Best wishes




Thanks Sedat!

Brian


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Jerry Lodriguss
Vendor


Reged: 07/19/08

Loc: Voorhees, NJ
Re: Edge HD Focal Reducer new [Re: freestar8n]
      #5940393 - 06/25/13 08:05 PM

Hi Frank,

Quote:

Are you sure the OAG was focused properly when you looked for a guidestar?




Yes, the Lodestar had been previously parfocalized with the camera.

Jerry


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bilgebay
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Reged: 11/06/08

Loc: Türkiye - Istanbul and Marmar...
Re: Edge HD Focal Reducer new [Re: Jerry Lodriguss]
      #5940842 - 06/26/13 02:25 AM

Frank, maybe there is an internal choke point on the Edge reducer ? Jerry's image train shouldn't cause any severe light fall off.

AP documentation states that the CCDT67 will provide 30mm fully illuminated image circle at 0.675x reduction ratio. At $165, it is real value for the money. The only drawback is the shortened back focus but what remains is still plenty for many of us. Especially the DSLR users won't have any problem at all.

I cannot wait for this weekend to start my tests on the C8 Edge!


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freestar8n
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Reged: 10/12/07

Re: Edge HD Focal Reducer new [Re: bilgebay]
      #5940862 - 06/26/13 02:57 AM

Hi Sedat and Jerry-

For the full illuminated 42mm circle you would need the big, wide t-adapter for Edge925 and higher, the 93646 version. It has a large base to accommodate the 60mm rear lens on the reducer. Any 2" components or regular t-size tubing would definitely constrict. I just measured the ID of a normal t-adapter tube and it is only 37mm - and if that were near the back of the reducer it would vignette an aps-c sensor.

As you go farther back from the reducer toward the sensor you can have normal t-sized adapters involved - but for example the 2" oag would be constricting. Based on my diagram a 2" ID should not be a problem for the aps-c, but if the ID gets below 46mm or so, then there could be vignetting.

I always recommend not adding a focuser to an sct for deep sky imaging - and just use robofocus on the primary. The 2" OAG might be too small for that reducer and that might explain the lack of guidestars. You should be able to tell if it is blocked just by looking in the guide port when exposed to the blue sky. It may be adjustable.

I think the AP reducer might be very cost effective for Edge when used with a smaller sensor like the aps-c - but I would be very surprised if it is in any way superior - especially with a full size chip like in a Canon 5dii. The vignetting is limited by the size of the rear lens, which is 60mm in the Edge reducer. The AP is only designed for a 29mm circle, as opposed to 42mm for Edge. And it also has to keep the stars well corrected out that extra distance - and I think that is why the Edge version is so much bigger and heavier.

Frank


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wolfman_4_ever
Pooh-Bah


Reged: 07/15/11

Loc: El Segundo, Ca, So. Cal
Re: Edge HD Focal Reducer new [Re: freestar8n]
      #5940877 - 06/26/13 03:26 AM

Maybe you have a bad reducer?

Someone on a yahoo group received an HD11 reducer with severe vignetting and had it replaced.


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bilgebay
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Reged: 11/06/08

Loc: Türkiye - Istanbul and Marmar...
Re: Edge HD Focal Reducer new [Re: wolfman_4_ever]
      #5941011 - 06/26/13 08:14 AM

Dave this is a very important information. I would really like to see other Edge1100 reducer owners share their experiences with us.

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bilgebay
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Loc: Türkiye - Istanbul and Marmar...
Re: Edge HD Focal Reducer new [Re: bilgebay]
      #5941052 - 06/26/13 08:46 AM

Hi Frank,

I agree with the points you put forth in your latest post.

Here is the components I am using in my image train with this reducer

1 - Lacerta OAG or Wide T-mount
2 - Baader Hyperion fine tuning ring - 28mm
3 - A-P CCDT67 reducer

The OAG has a wide opening too



Below you can see the reducer coupled to the 28mm fine tuning ring then to EOS-to-48mm adaptor



and this shows the ADASCTLC large visual back that I use for attaching the image train to the scope



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Thomas27
member


Reged: 02/24/10

Re: Edge HD Focal Reducer new [Re: bilgebay]
      #6077518 - 09/12/13 05:57 PM

Hey Guys,

Looking for some input here. I want to get a reducer for my 9.25.

My options are the optec or the AP CCDT67.

The optec looks easy as there are only 2 pieces i need to get but i don't like the fact that there are no threads on it and am a little confused on how it fits together.

I like how the CCDT67 fits together but am unsure of the parts i need for it to work properly with my scope.

ADASCTL + CCDT67 + 20mm spacer maybe?

any help would be appreciated.

thanks.


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frobi6852
member


Reged: 07/11/11

Re: Edge HD Focal Reducer [Re: Thomas27]
      #6078255 - 09/13/13 06:00 AM

Quote:

Hey Guys,

Looking for some input here. I want to get a reducer for my 9.25.

My options are the optec or the AP CCDT67.

The optec looks easy as there are only 2 pieces i need to get but i don't like the fact that there are no threads on it and am a little confused on how it fits together.

I like how the CCDT67 fits together but am unsure of the parts i need for it to work properly with my scope.

ADASCTL + CCDT67 + 20mm spacer maybe?

any help would be appreciated.

thanks.




I have the Optec reducer for my 8" EdgeHD it comes with the reducer and a dovetail for my camera. The reducer screws into the rear cell and the dovetail mounts to the reducer via 3 hex screws


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end
sage


Reged: 08/31/11

Loc: Houston, Texas, USA
Re: Edge HD Focal Reducer new [Re: frobi6852]
      #6096812 - 09/23/13 01:13 PM

I'd just like to add a data point here. To preface, I only received the X0.7 reducer for EdgeHD 1100 a little while ago and every night thereafter has been poor due to clouds. Therefore the results I have are not yet complete.

To add another caveat, I'm using the new Celestron OAG with this setup. First the good news:

I plate solved two images. One taken with the reducer and one without. Everything else about the setup was identical (both used the Celestron OAG and a Canon 60Da).

With reducer:
Pixel scale: 0.45 arcsec/pixel
Field width: 38.92 arcminutes
Field height: 25.93 arcminutes

Without reducer:
Pixel scale: 0.32 arcsec/pixel
Field width: 27.42 arcminutes
Field height: 18.28 arcminutes

This gives an actual focal reduction of:

based on width: X0.7045
based on height: X0.7050

Which is probably within the expected error for the system, but I will continue to test this as the weather permits.

My concern, as others here have expressed is with vignetting. The design of the OAG is such that it attaches to the standard SCT thread and not to the large aperture provided by the C9.25, 11 and 14. This results in an immediate constriction of the light cone after the reducer. I haven't had a chance yet to properly quantify the vignetting caused by this, but I will compare this to the vignetting caused by the standard t-adapter as soon as the clouds permit.
Considering the large number of adapters provided in the OAG setup, this seems like a poor choice to me. I may end up fabricating a more appropriately sized adapter because otherwise I really like the new OAG.


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Wmacky
Carpal Tunnel
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Reged: 11/24/07

Loc: Florida
Re: Edge HD Focal Reducer new [Re: end]
      #6106792 - 09/29/13 12:00 AM

Hey Sedat, how are those C8 Edge reducer tests coming along?

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bilgebay
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Reged: 11/06/08

Loc: Türkiye - Istanbul and Marmar...
Re: Edge HD Focal Reducer new [Re: Wmacky]
      #6111451 - 10/01/13 03:41 PM

Still in the queue for the final tests.

I couldn't convince myself to sacrifice the very little time I had for testing the reducer instead of imaging. I have imaged with my FSQ all this summer and the results are more than perfect.

Meanwhile, have you seen any images taken with the Celestron reducer ? If it is delivering tight and round stars without too much vignetting, I'd rather buy it instead of spending my precious nights with trials and errors.

Clear skies


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end
sage


Reged: 08/31/11

Loc: Houston, Texas, USA
Re: Edge HD Focal Reducer new [Re: bilgebay]
      #6111683 - 10/01/13 06:22 PM

My findings for the C11 reducer is that it too provides good star shape and only minor vignetting. In contrast, unfortunately, the use of the new Celestron OAG with the reducer results in substantial vignetting. There is a discussion on the "Team Celestron" web page now about this. My guess is that the fix will be a modified version of the adapter that goes between the 3.3" back of the C11 and the OAG. For some reason the one that ships with the OAG was designed only with small OTAs with the traditional SCT threads in mind and thus the light cone is substantially constricted. Really a mind boggling oversight in my opinion.

Nevertheless, I think this will be a fixable problem and expect at this point that my primary setup is likely to soon be my EdgeHD1100 running at 1960mm, f/7. Crossing my fingers that this will be a good stable platform for the foreseeable future!!


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bilgebay
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Re: Edge HD Focal Reducer new [Re: end]
      #6112596 - 10/02/13 08:10 AM

end, thank you for the update on the C11 reducer and OAG.

Any C8 users ? I 'd love to have some first hand information.

Clear skies


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