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Evo 6 or Evo 8

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#26 donstim

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Posted 03 May 2019 - 11:58 PM

Hi Dave,
Yep, you are right on all counts. I must have been editing my post to say it wasn't true EAA when you were writing yours, but I am hoping to get better with live stacking in SharpCap to at least get close to what I ended up with since I didn't do much with GIMP.

It was 10-12 minutes max stacking time at f/10,which isn't completely unreasonable for near live viewing in my opinion, but f/2 would be great!

Here is a link to the processed image https://photos.app.g...RviA32yFHzw9N56 and here's the EAA SharpCap image:
https://photos.app.g...kkdA1ULKPaxqxb8

Edited by donstim, 04 May 2019 - 03:11 PM.


#27 crn3371

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Posted 04 May 2019 - 12:49 PM

Ordering the Evo 8 this weekend. With regards to imaging, can someone explain to me, or point me to a tutorial, on what a basic imaging train using a 6.3 reducer and zwo asi224mc would look like. I think the FR screws on to the back of scope in place of the visual back, but after that I’m confused. Do I then attach the visual back directly to the reducer, then insert the cameras nosepiece into the visual back? Are other spacers or adapters needed? This can be frustrating, I’m used to being the “know it all” in the room, feeling kind of helpless with all of this.

#28 roelb

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Posted 04 May 2019 - 05:38 PM

yes f/6.3 FR screwed onto scope

to obtain 0.63 focal reduction you need to have 105 mm spacing between the end of the f/6.3 FR and the sensor

(take into account the backfocus distance of 12.5 mm of the ASI224MC)

 

the ASI224MC comes with a 1.25" to T2 nosepiece of 29 mm, so you need an additional 64 mm spacer(s)

if you use 1.25" spacers, they can be inserted into the Visual Back which is screwed onto the f/6.3 FR

 

if you use T2 spacers, you need a SC female to T2 male adapter screwed onto the f/6.3 FR,

and the additional "T2 spacers" to obtain the necessary focus distance

 

with this image train you will hit the mount base, so the tilt angle is limited (about 60°)

to avoid this you have to limit the image train length for the Evo 8 to about 152 mm

the focus distance is then limited to about 83 mm and the focal reduction is about 0.68

 

(see http://www.wilmslowa...rmulae.htm#FR_b to calculate focal reduction)

 

you can also avoid collision using a 0.5 FR (focus distance 50 mm)

or using two f/6.3 FR's: 

Stacking 2x f_6.3.JPG


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#29 barbarosa

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Posted 04 May 2019 - 05:44 PM

"It is the distance from the reducer to the sensor that sets the amount of reduction." This is true for all reducers, though different reducers can have a different working distance.  "For the Celestron f/6.3 reducer the distance is about 105mm. You would need to add something like the Celestron T adapter, and the appropriate t extender (s) to make up the full 105mm." (Repetentis bona gerunt.)

 

Rear port<---f/6.3 reducer<-- Celestron T adapter <-- T extension(s)<--T ring on the front of the 224

 

Rear port<---f/6.3 reducer<--visual back<-- 1/25" prism diagonal (not a mirror or 2" diagonal)<--1.25" nose piece (included with ZWO camera)<-- T ring on the front of the camera.

 

Rear port<---f/6.3 reducer<--visual back<--1.25"nose piece<--T extension tube(s)<--T ring on camera.

 

The Celestron f/6.3 is a more complex lens than the simple doublets of the .5x reducers. It reduces and corrects the image making for a better focused field with better stars at the edges. I haven't used the Mallincam product but it has had some favorable comment. 

 

The inexpensive reducers like some of these generally have the advantage of a shorter working distance and a lower price.

 

People also sometimes stack or use two reducers to get below f/5. This involves some experimentation with spacing.  Some are pleased with the result and some are not. I think i tried most variations and in the end decided that the optical artifacts detracted too much.



#30 descott12

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Posted 04 May 2019 - 06:59 PM


Here is a link to the processed image https://photos.app.g...RviA32yFHzw9N56 and here's the EAA SharpCap image:
https://photos.app.g...kkdA1ULKPaxqxb8

That processed image looks really great. You really must be good at processing if you started with the EAA image.



#31 crn3371

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Posted 05 May 2019 - 10:04 PM

Is there an appreciable downside in having the diagonal in the imaging train? Certainly would give me more camera options. For example, I’m considering the QHY version of the 224, and it’s long cylindrical form factor may not allow zenith unless using the diagonal.

#32 Rickster

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Posted 05 May 2019 - 11:45 PM

Although it will, in theory, reduce the quality of the image, I couldn't tell the difference when I used a diagonal with an 8" SCT (in order to get clearance).



#33 crn3371

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Posted 06 May 2019 - 09:34 AM

Although it will, in theory, reduce the quality of the image, I couldn't tell the difference when I used a diagonal with an 8" SCT (in order to get clearance).


That’s good to know, certainly gives one a lot more options. I’m assuming that David’s recommendation on using a prism diagonal has to do with the prism producing less light scatter over a mirror diagonal. Is the stock Celestron diagonal a mirror, or a prism?

#34 Rickster

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Posted 06 May 2019 - 10:20 AM

I used this 2 inch dielectric mirror diagonal that threaded directly to the focal reducer.  https://www.astronom...l-for-scts.html



#35 donstim

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Posted 06 May 2019 - 09:16 PM

That’s good to know, certainly gives one a lot more options. I’m assuming that David’s recommendation on using a prism diagonal has to do with the prism producing less light scatter over a mirror diagonal. Is the stock Celestron diagonal a mirror, or a prism?

Based on this :  https://www.cloudyni...omparison-r2877 the stock Celestron diagonal is a prism.

 

That processed image looks really great. You really must be good at processing if you started with the EAA image.

Thanks, but actually I'm not.  It was very basic black/gray level setting/stretching.  (I'm not sure if I could repeat it exactly again, though!)  Because it was so basic, I am hoping I can do it directly in SharpCap in the future.  The only thing I have to check on is whether you can identify a specific point or area in the image in SharpCap to identify as black like you can in GIMP.  That may result in some black level clipping that wouldn't be acceptable for AP, but I'm fine with that for EAA (if such processing during LiveStacking with SharpCap still qualifies as EAA).

 

Ordering the Evo 8 this weekend. With regards to imaging, can someone explain to me, or point me to a tutorial, on what a basic imaging train using a 6.3 reducer and zwo asi224mc would look like. I think the FR screws on to the back of scope in place of the visual back, but after that I’m confused. Do I then attach the visual back directly to the reducer, then insert the cameras nosepiece into the visual back? Are other spacers or adapters needed? This can be frustrating, I’m used to being the “know it all” in the room, feeling kind of helpless with all of this.

There were some good detailed answers given to this, but I also gave a simplified answer in my earlier post.  Yes, you can attach the visual back directly to the reducer, then the necessary spacers, then the cameras nosepiece.  As I explained in my earlier post, all I needed was an additional 5 mm spacer to add to the 16.5 mm and 21 mm spacers supplied with the ASI 294 MC Pro camera. Or, instead of the visual back, you can use a T-thread adapter as explained by Roel and David, or as shown in this picture I pilfered from someone else on this site (sorry I cannot provide a proper attribution!) (Note:  This diagram may have a camera with a different amount of back focus to the camera sensor than yours and the total back focus you should aim for is 105 mm.)

Attached Thumbnails

  • Spacers for f6.3 focal reducer.png

Edited by donstim, 06 May 2019 - 09:19 PM.

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#36 crn3371

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Posted 06 May 2019 - 10:50 PM

Can’t get any more clearer than that. Thanks. Now, if I were to substitute a diagonal into the imaging train, is there a formula for measuring the light path of the diagonal? I’ve downloaded a chart which shows the optical length of assorted diagonals but I haven’t seen any kind of formula. Is there one, or do you have to go off of mfgr specs?

Edit:
The chart I downloaded is from the diagonal link in your post. It seems there is no hard formula for determining the length of the light path.

Edited by crn3371, 06 May 2019 - 11:02 PM.


#37 donstim

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Posted 08 May 2019 - 08:08 PM

I re-measured the distance from the focal reducer glass to the ZWO camera body and found I had made a rather large error.  I had not accounted for the fact that the visual back snugs right up to the edge of the focal reducer inside of the attachment rings, so I was measuring from the wrong beginning point. It turns out I need 18mm of additional spacing over and above the nose piece, 16.5mm and 21mm extensions, and T2 extender that came with the camera.  Fortunately, the Astronomic spacers package I bought from Amazon includes 10mm and 8mm extenders.  So, I swapped out the 5mm I had in there before and replaced it with the 10mm and 8mm.  So, now I have the reducer, the visual back plus 1.25" nose piece (33mm), the 10mm extender, the 8 mm extender, the 21mm extender, the 16.5 extender, and the 11mm T2 adapter in attached to the camera, which with its 6.5mm back focus gives me the 105mm back focus for the Celestron .63x focal reducer.

 

It is not entirely clear to me how to measure or compute the distance when using the diagonal (to avoid hitting the mount base for objects higher than about 60 degrees), but using only the nose piece and T2 adapter for the camera, it appears to me that the distance is more than 105mm.  It will be interesting to see how that works out.



#38 Rickster

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Posted 08 May 2019 - 09:04 PM

To measure the diagonal, just figure the added distance along the centerline.  It doesn't need to be precise. 

 

If you want to verify how you have done, submit an image to http://nova.astrometry.net/upload for plate solving.  In the results you will see the pixel scale in arc seconds per pixel.  Compare that to what https://astronomy.to.../field_of_view/ predicts for your combination. 

 

Again, this is like hand grenades.  You only need to be close.


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#39 crn3371

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Posted 09 May 2019 - 01:39 PM

Thanks to all for your help. Evo 8 ordered and on it’s way.


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