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Equipment Discussions >> Cats & Casses

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elwaine
Pooh-Bah


Reged: 06/18/06

Loc: Jupiter
Re: Edge HD Focal Reducer new [Re: elwaine]
      #3974758 - 08/10/10 12:58 PM

Bump

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Jeff Smith
professor emeritus


Reged: 04/06/10

Loc: Chicago
Re: Edge HD Focal Reducer new [Re: elwaine]
      #3974917 - 08/10/10 02:19 PM

Well, when I get a clear night, I'll test out my new Optec focal reducer system for you .

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Konihlav
Pooh-Bah


Reged: 03/05/09

Re: Edge HD Focal Reducer new [Re: Jeff Smith]
      #3974997 - 08/10/10 03:10 PM

that would be great Jeff I am interested too.

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elwaine
Pooh-Bah


Reged: 06/18/06

Loc: Jupiter
Re: Edge HD Focal Reducer new [Re: Jeff Smith]
      #3975029 - 08/10/10 03:27 PM

Thank you Jeff.

I hope to be able to use a Featertouch "shorty" Crayford, plus an AO-8 with my ST-8XME. I do not plan to use a color filter wheel. Total backfocus is approximately 5.75 to 6 inches. That will work fine for my Edge 9.25 without the Optec FR. But it seems to me that the backfocus with their filter in place is much more critical than the backfocus tequiremts for the scope at it's native f/10. I am also concerned about the central "hot spot."

Regards


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Peter in Reno
Postmaster
*****

Reged: 07/15/08

Loc: Reno, NV
Re: Edge HD Focal Reducer new [Re: elwaine]
      #3975049 - 08/10/10 03:35 PM

It would be best to test with a camera. Did Optec listed a required spacing distance specifically for EdgeHD? Since the EdgeHD has a flattener inside baffle tube, there may be a required distance between flattener and focal reducer AS WELL AS distance between focal reducer and camera.

I have a hard time seeing any focal reducer would work with EdgeHD with a flattener already installed inside the baffle tube. This is why I have not bought EdgeHD yet. Who would image all DSOs at F/10? And why is it taking Celestron so long to create a perfect focal reducer for all sizes EdgeHD?

Peter


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Konihlav
Pooh-Bah


Reged: 03/05/09

Re: Edge HD Focal Reducer new [Re: Peter in Reno]
      #3975113 - 08/10/10 04:10 PM

Peter in Reno: I have the same doubts and concerns about the spacing.

Anyway I decided to do DSO imaging at F/10 with large format CCD and binning 2x2 and/or 3x3 in the worst cases of bad seeing and objects low above horizon (we'll see later if it's feasible to do it this way or not) so I get the EdgeHD soon.


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elwaine
Pooh-Bah


Reged: 06/18/06

Loc: Jupiter
Re: Edge HD Focal Reducer new [Re: Konihlav]
      #3975483 - 08/10/10 07:23 PM

The distance from the back of the OTA to the plane of the camera sensor can be adjusted by getting longer or shorter spacing tubes, onto which one attaches his/her camera specific T-adapter. I don't see that as a problem. I'm more concerned about the apparent non-uniform image brightness. That sort of defeats the flat field design of the Edge, doesn't it?

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freestar8n
Post Laureate
*****

Reged: 10/12/07

Re: Edge HD Focal Reducer new [Re: elwaine]
      #3975513 - 08/10/10 07:37 PM

Hi-

Unfortunately there is a lot of confusion about what exactly "flat field" means. In an optical context - it means that the surface of best focus across the image lies in a plane. Note that does NOT mean the stars are small all the way across - it just means that the stars are at their best in a plane, and moving up or down in focus will make all stars worse everywhere.

You could have a flat field that had bad coma and astigmatism - and the stars looked terrible as you went out from center - but it would still be a flat field. You could also have what looks like a flat field with round stars across it - but in fact the field is curved and when you change focus, they get smaller in one area and bigger in another.

In the case of Edge HD, flat field means small, round stars across a large, flat ccd - as shown in images.

Now you are commenting on an issue of vignetting - which is yet something else. You could have a flat field with strong vignetting and it would still be a flat field.

In the case of Edge HD - it is designed to have a flat field with low vignetting at f/10. There is no reducer for it just yet - but if there is low vignetting at f/10, then I think you can expect some vignetting with a reducer. Since the field is already flat and well corrected, I don't think a reducer will enlarge the usable field much, but it will make the same angular field smaller and brighter through the faster f/ratio.

No matter what - some vignetting, and even pretty strong vignetting - will disappear with a good flat applied. But if the star shapes are bad - then there is no fix for that. So - vignetting is tolerable, but messed up stars are not.

Frank


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Jeff Smith
professor emeritus


Reged: 04/06/10

Loc: Chicago
Re: Edge HD Focal Reducer new [Re: Peter in Reno]
      #3975591 - 08/10/10 08:24 PM

Quote:

It would be best to test with a camera. Did Optec listed a required spacing distance specifically for EdgeHD? Since the EdgeHD has a flattener inside baffle tube, there may be a required distance between flattener and focal reducer AS WELL AS distance between focal reducer and camera.

I have a hard time seeing any focal reducer would work with EdgeHD with a flattener already installed inside the baffle tube. This is why I have not bought EdgeHD yet. Who would image all DSOs at F/10? And why is it taking Celestron so long to create a perfect focal reducer for all sizes EdgeHD?

Peter



As far as the spacing for the Edge HD and the Optec focval reducer, Jeff assured me that their combination of Canon tube and the Lepus f.r. is the correct spacing. He also suggested the Astro Physics 3.25" visual back to keep the whole thing tight. I have one on back order butin the mean time I have an old Celestron back that I am going to try out tonight. The skies are *BLEEP* tonight as are my skills but I can at least take an hour and a half of M51 and compare the results to my earlier attempts at f/10. I also have a new Astronomik CLS-CCD filter that I am going to try out tonight so my results will be a bit skewed.
The Optec unit is just a focal reducer. There is no field flattener built in to it. It is made for the Meade ACF and the Celestron Edge HD. I do believe that Celestron's focal reducer will be great when it comes out.


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elwaine
Pooh-Bah


Reged: 06/18/06

Loc: Jupiter
Re: Edge HD Focal Reducer new [Re: Jeff Smith]
      #3975786 - 08/10/10 09:58 PM

Hey Frank, that was very helpful Thank you!!!

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Jeff Smith
professor emeritus


Reged: 04/06/10

Loc: Chicago
Re: Edge HD Focal Reducer new [Re: elwaine]
      #3975867 - 08/10/10 10:41 PM

Too cloudy tonight. I'm not going to be able to test out the focal reducer yet.

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saadabbasi
Pooh-Bah


Reged: 08/23/09

Loc: 29N
Re: Edge HD Focal Reducer new [Re: Jeff Smith]
      #3976410 - 08/11/10 09:33 AM

I'm wondering about getting myself a C9.25 HD too, for some long focal length imaging. But yes, the F10 is very daunting and I would really like a reducer in the 0.63x range that brings the FL down to ~1500mm. I intend to use the reducer with my SBIG ST8300M and maybe with a 35mm DSLR. Will the Optec do the job? Or is it designed only for Canon DSLRs?

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PatHolland
Carpal Tunnel
*****

Reged: 10/11/09

Loc: Clever, Missouri
Re: Edge HD Focal Reducer new [Re: saadabbasi]
      #3976459 - 08/11/10 10:03 AM

Saad, I think it should work with any camera. I would think the only variable might be distance from the CMOS or CCD chip. It is possible that larger imaging chips may reveal more vignetting though.

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saadabbasi
Pooh-Bah


Reged: 08/23/09

Loc: 29N
Re: Edge HD Focal Reducer new [Re: PatHolland]
      #3976723 - 08/11/10 12:07 PM

Thanks for the response Pat. I ask about the 35mm format because I may buy a D700 used. The 35mm will provide rather wide views. However, am I correct in assuming that flat frames will removing vignetting completely? Or will the vignetting be so severe that flats cannot fix it?

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Micheal
sage


Reged: 02/28/10

Loc: Corona, CA
Re: Edge HD Focal Reducer new [Re: saadabbasi]
      #3981291 - 08/13/10 04:51 PM

I just got mine today but the camera adapter seems to be lost out there in internet land. Been trying to get optcorp to locatate it but I seem to be running into trouble there. So I am staring at this thing and trying to imagine how to set it up. Says right on the box Lens Assembly Mounted for use with 2" motorized focuser which I do not have and have no interest in. Looks like one end of this would fit into the visual back or focuser of the telescope but it is very short. The other end has a weird slanted beveled edge to it which I assume is so that it only works with other optec accessories. I'll post some photos shortly.

Edit: Just got off the phone with Optcorp.com and they said it is about 1.5 weeks away still for the camera adapter.

Posted the below thumbnails. Click them to blow them up.











Edited by Micheal (08/13/10 05:33 PM)


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GlennLeDrew
Postmaster
*****

Reged: 06/18/08

Loc: Ottawa, Ontario, Canada
Re: Edge HD Focal Reducer new [Re: Micheal]
      #3981892 - 08/13/10 11:34 PM

Michael,
Nice photos. Seeing as you're stuck with just staring at it for some time, how's about taking a measurement of the clear aperture? This would at least begin to give some idea of possible illumination characteristics at the focal surface once the lens-to-focus distance is known.

Thanks!


Larry (elwaine),
Frank (freestar8n) provided a most lucid explanation of the meanings of flat field and 'flat' illumination. (Thanks, Frank!) Until I'd read his post, I had copied a snippet of your text just prior, to which I'd planned to reply in like kind.


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PatHolland
Carpal Tunnel
*****

Reged: 10/11/09

Loc: Clever, Missouri
Re: Edge HD Focal Reducer new [Re: saadabbasi]
      #3982067 - 08/14/10 02:01 AM

Quote:

Thanks for the response Pat. I ask about the 35mm format because I may buy a D700 used. The 35mm will provide rather wide views. However, am I correct in assuming that flat frames will removing vignetting completely? Or will the vignetting be so severe that flats cannot fix it?




I don't know the answer but I am expecting my reducer to arrive any time now. Opt e-mailed me and told me it's on the way (no shipping info on the e-mail though). When I get mine in I'll test it with my XSi (26mm) andI'll post the results.


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elwaine
Pooh-Bah


Reged: 06/18/06

Loc: Jupiter
Re: Edge HD Focal Reducer new [Re: PatHolland]
      #3982268 - 08/14/10 08:00 AM

Flat frames should remove vignetting across the entire field. However, obtaing good flats is not as easy as getting a good master dark frame. There is a definite skill involved getting quality flats, but once one gets the knack, they will remove vignetting across the entire field and several other flaws as well.


Glenn,

I agree. Until I read his explanation I was confused about exactly what a flat field is.


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freemanpa
journeyman


Reged: 06/16/10

Re: Edge HD Focal Reducer new [Re: elwaine]
      #3985904 - 08/16/10 09:44 AM

Hi, sorry for the delay...I've been so busy with work and play that I haven't been out to CN for at least a week or two.

Anyway, the flat field will definitely resolve the vignetting. I have not yet tried to shoot at f/10 so I can't say with my EdgeHD 11" if it shows much vignetting. But my experience is that the FR on just about any OTA I've used will increase vignetting...leading to the certain need for flats.

A later post comments on the initial trickiness around getting good flats...I agree, but I was so determined to get flats (I know some folks who simply refuse to take 'em) that I learned quickly. On the DSLR, it's really not hard at all...just snap a flat and check for the histogram being near the center or at least away from either end. As I'm now also learning CCD photography, it's a bit more complex but I'm learning that too. And the biggest help for me was making my own flat-field boxes...one for the larger OTAs I own and one for the smaller refractors. I made it with foam-core board (white on inside, black on outside), lots of black duct tape (that stuff is great for so many "guy things"!) and four incandescent bulbs from Radio Shack. Oh, and a fair amount of hot-melt glue and a few other odds and ends from Home Depot. Cost me under $75, and most of that was the foam-core. Watch for sales on that. :-)


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Jeff Smith
professor emeritus


Reged: 04/06/10

Loc: Chicago
Re: Edge HD Focal Reducer new [Re: freemanpa]
      #3999680 - 08/22/10 05:11 PM

Well, good news and bad news.
Good news:I got mine and it works great. It really helped my efforts.
Bad news: I need to sell it. I'm selling some equipment because of a family emergency. If anybody is looking for a good deal on the focal reducer and Canon adapter let me know.

Edited by Jeff Smith (08/22/10 05:11 PM)


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