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Edge HD 1100 Adapter: Which one for CCD camera, and BF question

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#1 John Verderame

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Posted 12 July 2018 - 06:11 PM

I purchased a used Edge 1100 HD not long ago.  It came with the DSLR T-Adapter, part #93646, and a small visual back.  Then I read the Edge HD "White Paper," all about how important it is to get the right back focus distance.  No problem with the T-Adapter for my Nikon DSLR, but for the life of me, I cannot figure out what adapter I'm supposed to use for my ZWO ASI290MC.  Do I use that same adapter and just screw the ZWO body onto it?  Not according to the diagram on p. 15 of the White Paper.  There, there is a drawing of a mystery adapter for use with CCD cameras.  No part numbers are given, and I have tried and tried to figure out what that adapter is.  According to the diagram, the flow is:  Reducing ring > Small T-Adapter > T-to-1.25" Adapter > Astrocamera.

 

Until I heard about the White Paper, I was just imaging using a GSO Crayford focuser screwed onto the back of the OTA and getting some nice images, but not real crisp, and I was attributing that mainly to seeing issues.  So, another question I (and a friend who also just bought an Edge 1100 HD) had was, How much is the image degraded if my imaging sensor falls too much inside or outside the recommended 5.75" sweet spot for back focus?

 

Any help appreciated, especially if you have a photo of that train of adapters from OTA to camera (or part numbers).

 

Thanks!

John


Edited by John Verderame, 12 July 2018 - 11:52 PM.


#2 John Verderame

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Posted 13 July 2018 - 10:29 AM

I've contacted Celestron directly with my questions.  Will post response here, if helpful.  Guess not too many others have come up against these issues, or this is the wrong place to have posted?  Since my friend, who just purchased the same scope and is an advanced amateur astronomer, had the same questions I figured it wasn't just me.  Any suggestions, or redirection to other discussions that might be helpful, would be appreciated.



#3 andicus

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Posted 13 July 2018 - 12:13 PM

I don't have the answer, but will be watching this thread, as I may have a similar setup, down the road.



#4 jpbutler

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Posted 13 July 2018 - 01:07 PM

that t adapter is set up to work with a dslr which has an inherent 55mm of backfocus.

your asi 290 has 12.5mm backfocus if it is the uncooled version. 

so you need 42.5mm of m42 adapters added to your imaging train.

 

the cooled version, according to the zwo documentation has 17.5mm backfocus so you would  need to add 37.5mm.

agena astro has a buttload of adapters.

 

john


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#5 John Verderame

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Posted 13 July 2018 - 01:23 PM

Thanks, John!

 

Uncooled.  I understand the DSLR adapter and how to use that and about the 55mm and all, but just to be clear, you're saying yes, use the large T-adapter for the DSLR and add 42.5mm to that?  If it's that simple, I wish the diagram had shown it that way.  They seem to show some other adapter as the primary one (see p. 15 of the White Paper), then a secondary, smaller but similar, adapter (which I guess would be the M42).

 

Also, do you know the answer to the back focus question?  If I'm a little too far off one way or another from that 5.75" sweet spot, is it going to make a huge difference in the quality of the image?



#6 John Verderame

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Posted 13 July 2018 - 02:02 PM

Sorry to be dense, John, but still not quite sure which adapters you're referring to after doing more research.  I can't come up with a single or combo of adapters that comes to 42.5mm.  There must be some Celestron part or parts I'm missing here.  I do hope they get back to me and clarify it some.



#7 Endymion

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Posted 13 July 2018 - 03:21 PM

John,

  Two of these https://agenaastro.c...-t2-ext-21.html in series would get you close enough.  If needed you could add a 0.5mm spacer between them to get the exact 42.5 mm.  

 

John


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#8 Endymion

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Posted 13 July 2018 - 03:28 PM

Here are some spacer rings.  https://agenaastro.c...r-ring-set.html



#9 jpbutler

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Posted 13 July 2018 - 03:37 PM

Hi get these adapters:

 

zwo 16.5mm m48 to m42(t2) adapter: https://agenaastro.c...8-extender.html

zwo 21mm m42(t2) adapter: https://agenaastro.c...-t2-ext-21.html

Blue Fireball 5mm m42(t2) spacer https://agenaastro.c...-extension.html

 

 

No guarantees here, but this is what I would do.

 

John

 

 

 

 

 

 

Attached Thumbnails

  • 20180713_163440.jpg


#10 John Verderame

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Posted 13 July 2018 - 03:49 PM

Hi John,

 

Thanks for the link.  I did see those, but of course, there's only one available! bawling.gif  And I was not sure if that was "the one."  Fortunately, or not, we're in monsoon season, so it's not looking real hopeful for doing any imaging in the near future, but Agena's pretty good about getting new stock in so I'll check with Manish there to see if they'll have more on hand soon.

 

So, are you saying add two of those to the DSLR extension then?  Again, if it's that simple, I wish the White Paper had made that clear, because, again, it does not show the DSLR T-adapter in the picture for using a CCD camera.  But it seems the suggestion to add those adapters is on the money.



#11 John Verderame

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Posted 13 July 2018 - 03:58 PM

John Butler,

 

Just saw your picture.  Guess you just added that as I was posting.  Ok, I think both Johns have provided the answer here.  I will wait to hear from Celestron to see if they have anything to add, but can see where what you're proposing would work, but still don't quite understand why Celestron doesn't come out and just say it and picture it as simply as you both did, rather than showing an apparently different adapter for CCD cameras in the White Paper.



#12 John Verderame

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Posted 13 July 2018 - 04:08 PM

Also, hate to harp on it, but do any of you guys have any info on image degradation if you're not close enough to that 5.75 inch mark?  Or is that for another thread under another topic?

 

Thanks as always for the great help and responses here.


Edited by John Verderame, 14 July 2018 - 09:36 AM.


#13 ckhorne

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Posted 13 July 2018 - 04:34 PM

I use a 290MM and 290MC on my Edge 11HD.  From my understanding, the reason for the specific backspacing is because the image plane is curved, and by placing the camera at the distance specified, you've reached optimal focus and the flattest image plane.

 

A corrector / field flattener can correct this; in the case of the HD line, the corrector is built into the internal baffle tubes, resulting in a nearly (but not quite perfect) image plane.

 

True_Astrograph_Quality.png?149635430862

 

(Image from Celestron's own page on HD optics)

 

What's important is that, the larger the sensor, the more critical this curvature is. The C11 can illuminate up to a 42mm circle, supporting a full frame 35mm camera (a huge sensor in the AP world). If you look at the diagram above, note that the sensor's best placement is so that it averages out the curvature over the entire area. This means that the larger your sensor, the more critical the backspacing.

 

The sensor on the 290 is small - 6.46mm diagonal, to be exact. At this size, the curvature of the image plane won't have much effect because the sensor is only in the very center.  It matters even less if you're doing planetary imaging, and using only the very very center of the already small sensor.

 

To summarize, while it's always recommended to put the sensor at exactly the 146mm spec, it's not near as critical for the small sensors.

 

Personally, I have an image train for my AS1600 which is exactly at 146mm, and I have a separate image train for my 290mm (focal extender -> flip mirror -> ADC -> filter wheel -> ASI290MM. I've never even bothered to measure the backfocus, and I've always had good results. 

 

I wouldn't worry about it too much - esp. if you add a barlow or focal extender in front of the camera. Focus and precise collimation will be much more important than backfocus.


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#14 John Verderame

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Posted 13 July 2018 - 04:58 PM

<<It matters even less if you're doing planetary imaging, and using only the very very center of the already small sensor.>>

 

Wow, excellent post!  And pretty much explains it.  I was thinking because of the Edge's field curvature correction that the back focus distance for the ZWO was not absolutely critical, but you have turned my "hunch" into a factual explanation as to why it's apparently not, at least for planetary.

 

Well, once the clouds clear here, I'm really looking forward to putting some of this to the test and seeing how my images improve.  I've waited all my life to take a good photo of Mars, and that's why I'm after these answers, 'cuz I just want to get it right when the next opportunity arises!

 

Thanks again to all of you.



#15 jpbutler

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Posted 13 July 2018 - 05:05 PM

sorry about leading you down the wrong path. I have never done planetary and only think in terms of dso's.

 

john



#16 John Verderame

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Posted 13 July 2018 - 05:17 PM

John, don't understand.  How did you lead me down the wrong path?  In fact, I just ordered one of the 21mm adapters from Agena.  They only had one.  So now I'm looking for another.  I think two of those is what I need.  If not, I'll keep experimenting.

 

Really appreciate your help and suggestions!

 

John



#17 ckhorne

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Posted 13 July 2018 - 06:52 PM

sorry about leading you down the wrong path. I have never done planetary and only think in terms of dso's.

 

john

Every camera will work optimally at the exact focal distance. But I'm not sure that the difference between the perfect 146mm backspacing and being a little off will be measurably different.


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#18 Endymion

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Posted 13 July 2018 - 07:00 PM

John, don't understand.  How did you lead me down the wrong path?  In fact, I just ordered one of the 21mm adapters from Agena.  They only had one.  So now I'm looking for another.  I think two of those is what I need.  If not, I'll keep experimenting.

 

Really appreciate your help and suggestions!

 

John

I think he meant you don't need the M48 to M42 adapter.  The Celestron DSLR T-Adapter, part #93646 has a T2 thread (M42) and the ASI should have a M42 thread (all 3 of mine do).   So you just need the 2 x 21 mm and maybe a spacer.

 

John



#19 Endymion

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Posted 13 July 2018 - 07:11 PM

Shows in stock here:  https://telescopes.n...1mm-length.html



#20 John Verderame

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Posted 13 July 2018 - 07:13 PM

I think he meant you don't need the M48 to M42 adapter.  The Celestron DSLR T-Adapter, part #93646 has a T2 thread (M42) and the ASI should have a M42 thread (all 3 of mine do).   So you just need the 2 x 21 mm and maybe a spacer.

 

John

Yes, they do have that standard thread.  Had already checked that out.  Thanks for the clarification, assuming that's what John meant.  I got the last 21mm Agena had, apparently, and some other suppliers I usually use are out of stock, so I put up a want ad on CN for the other.



#21 John Verderame

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Posted 13 July 2018 - 07:18 PM

Thanks.  Did see that one, but with almost $10.00 shipping being the cheapest for a tiny metal ring, if I'm not mistaken, I'd rather not!  Agena had same price, free shipping.  And I had to get some other items, so was hoping to throw the second one in.  Was told they may not have them in stock again for a few weeks.



#22 jpbutler

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Posted 13 July 2018 - 07:20 PM

I think he meant you don't need the M48 to M42 adapter.  The Celestron DSLR T-Adapter, part #93646 has a T2 thread (M42) and the ASI should have a M42 thread (all 3 of mine do).   So you just need the 2 x 21 mm and maybe a spacer.

 

John

Yes that is what I meant.

 

John


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#23 John Verderame

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Posted 13 July 2018 - 07:26 PM

I've forwarded this thread to my friend, who's also a CNer, and I'm sure he too will appreciate the information you guys have provided, so thanks yet again.



#24 Endymion

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Posted 13 July 2018 - 07:44 PM

I see what he meant.   If you want planetary and not DSOs, the DSLR T-adapter and the 2x21mm extension are not what you need.  They are designed for DSO imaging.   For planetary, you will need a Barlow (2.5x should be fine with your pixel size on the ASI).  Then you hook things up so:

 

C11EdgeHD -> Star Diagonal -> Barlow -> Barlow 1.25" adapter, ZWO 1.25 to T2 adapter, ZWO ASI 290.

 

You will get images with the DSO setup on planetary but you will be disappointed with the resolution without the Barlow.

 

 

Here's what it looks like together and then broken into pieces:

 

IMG 7307
 
IMG 7309

 

Note that the star diagonal is there because it gets you close to the correct focus point but it isn't critical as it would be for large sensor DSO work.  

 

 

John


Edited by Endymion, 13 July 2018 - 08:07 PM.


#25 John Verderame

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Posted 13 July 2018 - 09:26 PM

John, that seems a bit complicated. I have been using my GSO Crayford focuser, a Barlow, and then the camera, so probably pretty close to what you're recommending there, but I'm wondering what you use to attach that diagonal to the scope and if that increases the length of the light path even more.  Also, I'd rather not use a diagonal if possible, so as to not introduce more glass and more possibility of error into the light path.  Just being picky, I know.  I'm sure your setup works fine.

 

However, I just took another look at p. 15 of the White Paper, and it was like a light went on.  Kind of a, "Why didn't I see this before" epiphany.

 

The Edge 800 uses a "small T-adapter."  For some reason, with the 925 and above, it is not clear that that is the SAME "small T-adapter" that you need to use for CCD cameras, but it suddenly hit me: Wait, that looks like the exact same adapter that's used on the 800.

 

Now, if you look up that part, here for example https://agenaastro.c...cope-93644.html  you will see that it specifies the Edge 800 ONLY, and nothing about the larger Edge SCTs.  In fact the Celestron site itself does no such thing.  Hence, the confusion.  Was there a similar, but somehow different, part for the Edge 1100?  That's what the uncertainty was.

 

Well...  Apparently not.  The images on p. 15 of the WP for the 800 adapter and the CCD adapter for the 925, 1100, and 1400 are the SAME.  Apparently "small T-adapter" for the 800 is the same as "small T-adapter" for the other sizes.  Why that's not made clear, I don't quite understand.  Now there's the question of the T-to-1.25" adapter, but I believe that one will be easier to figure out.

 

I think we've got it finally.




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