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2" vs 1.25" for EAA

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#1 millsbob

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Posted 19 July 2021 - 01:52 PM

i am currently using the gear in my signature, but planning to upgrade to a NexStar Evolution 8 once supply constraints ease. my eyes were never great, and now with age, EAA is really the only game in town. so i'm grateful that through many of you i discovered EAA in this forum *just* before i was about to invest in serious eyepieces!

 

i have no focal reducer as yet, just a .63x on order with Astronomics since February, but i was also looking at the always-on-the-horizon Night Owl .4x reducer. just last night i noticed that it's 2".

 

is there any benefit to me, given my current and prospective equipment, to moving up to 2" in general? or is it something i can treat as specific to the Night Owl for my purposes and just buy a 2" visual back for that? i guess the same question would apply to replacing the cheap barlow that came with my NexStar 6se, but it would be a safe assumption that 2" eyepieces are not in my future.

 

happy to hear any viewpoints or links to resources i should have consulted before asking!


Edited by millsbob, 19 July 2021 - 03:17 PM.


#2 photoracer18

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Posted 19 July 2021 - 02:09 PM

If its essentially a C-mount type of video camera it won't matter as the sensor is fairly small and even 1.25" won't cause any vignetting. Even many DSLRs only use a small part of the sensor for HD video. If however your camera uses a full sensor for video and it APS-C or FF you will need to use 2".



#3 GaryShaw

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Posted 19 July 2021 - 02:30 PM

Hi Bob

I have the same camera which, in fact is neither a ‘video’ camera, nor does it have a small sensor. It’s a very good, dedicated  Astro camera with a mid-size sensor and I believe it will benefit from 2”. I didn’t even know the 8” NextStars could come as 1.25 these days. I am a newtonian observer so see what the SCT observers have to say but I’d be surprised if anyone would suggest a 1.25 over 2” in this situation. 
Cheers

Gary

 

ps: Ever consider a 8” RASA? A way better 8” option for EAA in my view. 


Edited by GaryShaw, 19 July 2021 - 02:34 PM.

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#4 millsbob

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Posted 19 July 2021 - 03:15 PM

thank you for the thoughtful comments, Gary!

 

the NexStar 6 & 8 both come with a 1.25" visual back, although it can be replaced with a 2" fairly cheaply, i believe:

https://agenaastro.c...pter-93661.html

 

i have considered both RASA and Hyperstar. isn't the RASA restricted to f/2ish? would love to learn that i'm misunderstanding this, because a dedicated EAA rig is really what i'm after.



#5 millsbob

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Posted 19 July 2021 - 03:22 PM

oh, and forgot to add: one reason to address this Now is that i have the 1.25" .63 reducer on order, but if i should go primarily 2", it would be good to change that now rather than later! that way i'd only eat the cost of the 1.25" dielectric mirror diagonal i bought a few months ago.



#6 GaryShaw

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Posted 19 July 2021 - 04:02 PM

RASA is about F/2 which makes it perfect for the short exposure, ‘live’ feel that I believe EAA is really all about. There’s a lot of posts and chat in the CN community about how to utilize and manage the technology and, naturally, a lot of that relates to optimizing images. Some treat EAA as AP ‘lite’, but at its core, it seems to me it’s about maximizing what we can see, study, and better understand the incredible objects out there….

 

RASA pulls in so many photons that it speeds up the viewing process and provides stunning wide field views but lets us zoom in (digitally or with smaller sensor cameras) when we want to explore the detail, beauty and structure of nebulae, galaxies, clusters and Star fields. Even now, my finger hovers just above the RASA 11 ‘order button,. I don’t know how long I can hold out.

 

Cheers

Gary 



#7 GazingOli

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Posted 19 July 2021 - 04:03 PM

The C8 comes with a 2" thread - so the Celestron x6.3 reducer/corrector (which I would recommend) is also 2" - same thread on either side. Your camera got a 1,25" nosepiece, so you can use a 1,25" visual back (and some spacers in between for the correct distance to the reducer).

 

CS.Oli


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#8 alphatripleplus

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Posted 19 July 2021 - 04:07 PM

oh, and forgot to add: one reason to address this Now is that i have the 1.25" .63 reducer on order, but if i should go primarily 2", it would be good to change that now rather than later! that way i'd only eat the cost of the 1.25" dielectric mirror diagonal i bought a few months ago.

The f/6.3 reducer is NOT a 1.25 inch reducer - the standard SCT threads on the f/6.3 reducer are 2inch and 24threads per inch. I do not use the visual back when using a SCT (with or without a reducer) with an astro camera, but connect via a threaded connection to the camera. For example, I use a SCT thread to T-thread (M42) adapter to connect to my camera. Using threaded adapters, you'll have a more secure attachment than using a visual back, and less potential vignetting than with a 1.25 inch connection.


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#9 GazingOli

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Posted 19 July 2021 - 04:11 PM

The RASA 8 is more like a wide field scope!

 

For me f/6.3 works very well for EAA and you get much closer looks at the celestrial objects than you can with a RASA ( scope. The C8 is probably more easy to handle and you can get a Hyperstar anyway, if you want to try f/2. RASA scopes are restricted to f/2 and camera use - very specialized scope in my opinion.

 

Gary, why don't you buy a RASA?

 

CS.Oli


Edited by GazingOli, 19 July 2021 - 04:15 PM.

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#10 GaryShaw

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Posted 19 July 2021 - 04:12 PM

Hi Oli

He can remove the 1.25 nosepiece though and just go with the 2” connection as well. I recall when I first got my ASI294 about 3 years ago, I only had the 142 mm Schmidt newtonian and it only had a 1.25 drawtube so I kept the nosepiece on the camera and it worked just fine. Once I received my 200mm newtonian, it was set up for 2” and I removed the nosepiece for that scope. The added aperture and larger, 2”, optics path made a big difference. I just wonder if there is any reason to go with a more limited 1.25” when your system can also provide the 2” path. If there is, hopefully someone will chime in with that.

Gary 



#11 GazingOli

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Posted 19 July 2021 - 04:14 PM

that is correct. now when I bought the ASI294 I removed the nose piece, foregot that. Now I am using the M42 connection.

 

CS.Oli



#12 GaryShaw

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Posted 19 July 2021 - 04:22 PM

The RASA 8 is more like a wide field scope!

 

For me f/6.3 works very well for EAA and you get much closer looks at the celestrial objects than you can with a RASA scope. The C8 is probably more easy to handle and you can get a Hyperstar anyway, if you want to try f/2. RASA scopes are restricted to f/2 and camera use - very specialized scope in my opinion.

 

Gary, why don't you buy a RASA?

 

CS.Oli

All valid points for sure. I may be wrong but it seems that with decent resolution and a good monitor, the digital zoom can get you in closer. For small objects like PN’s, I would use either a camera with a smaller sensor or switch to my F4 newtonian….

 

RASA11…..could do it in a heartbeat but I resist increasing my consumption of ‘things’ and both of my current scopes are pretty fast. I’m also doing more variable star analyses and considering a move into exoplanet transit analysis. Neither needs that fast a scope…


Edited by GaryShaw, 19 July 2021 - 04:23 PM.


#13 millsbob

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Posted 19 July 2021 - 04:46 PM

thank you (again! umpteenth time) for saving my bacon, Errol/alphatripleplus!!!

 

so if were to order a better Barlow, should i be looking for a 2" then?

 

and should i stick with 2" for everything from here on out? what's the downside of that? cost?

 

and do i need one of these SCT to t-thread adapters then, i guess?

https://agenaastro.c...ad-adapter.html


Edited by millsbob, 19 July 2021 - 05:35 PM.


#14 GazingOli

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Posted 19 July 2021 - 05:40 PM

what do you want a barlow for? f/20 is rather unusual for EAA, it is more for planetary imaging.

 

CS.Oli



#15 GaryShaw

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Posted 19 July 2021 - 05:59 PM

I agree with Oli! 

 

I tried a barlow to increase my FL for viewing (with camera) planetary nebulae. Unfortunately I could never even reach focus with that Barlow. The folks at TS, in Munich area where my scope came from, are testing other Barlows to see if they can find one that works at F/4 with my optics.

 

Gary



#16 dave85374

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Posted 19 July 2021 - 06:15 PM

I have the Celestron Evolution 8, so when I started thinking about EAA three months ago my immediate thought went to putting a HyperStar 8 with the ASI294 mc Pro attached to it with the ASIAir Pro running the whole thing.  No problem pointing the system anywhere in the sky.  The only drawback if there is one is that the focal length is now 391mm which will not get you those breathtaking closeup shots you see out here though.  You can still zoom in with the IPAD using the pinch method and that works out rather nicely.

 

This system though added a few $$$ (HyperStar 6 for your scope would be $500 and it will accept one filter).  I use the Optolong L-Pro 2" and I get good results on Nebula's & galaxies.  Most of my shots are 8 seconds and the number depends on what I am looking at but are usually 30 shots.  I enjoy this much more than using eyepieces and the continual changing and refocusing.

 

I have talked to a guy in Mesa, AZ that has your scope and the setup I just mentioned other than the filter and he takes some nice photos. 

 

I have posted 6 photos on this months observing challenge (#29 & 30) if you want to look what my setup can do, and remember I am still learning since I have been at this less than 3 months.

 

Dave



#17 millsbob

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Posted 19 July 2021 - 06:24 PM

hmmm. i just took the visual back off my scope, and found what's in the picture below: a 1.25" threaded barrel extending ~6" into the OTA.

 

is this also true on the C8?

 

it's hard for me to see the justification for 2" anything on the end of that, but i'm happy to be educated.

 

ps: i did find a Very small but noticeable cobweb about 1/2" inside the opening there, so it was a useful experiment!

 

edited - 1.jpeg


Edited by millsbob, 19 July 2021 - 06:33 PM.


#18 millsbob

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Posted 19 July 2021 - 06:27 PM

what do you want a barlow for? f/20 is rather unusual for EAA, it is more for planetary imaging.

 

CS.Oli

i don't understand why EAA isn't applicable to planetary imaging, but yes, that is one of the things i was thinking of.



#19 millsbob

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Posted 19 July 2021 - 06:30 PM

I agree with Oli! 

 

I tried a barlow to increase my FL for viewing (with camera) planetary nebulae. Unfortunately I could never even reach focus with that Barlow. The folks at TS, in Munich area where my scope came from, are testing other Barlows to see if they can find one that works at F/4 with my optics.

 

Gary

Gary, i can understand that you'd have trouble reaching focus with the scopes you have in your sig.

 

i have a straight-up SCT, and have seen many photos by people using the same setup with a barlow for planetary work.



#20 alphatripleplus

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Posted 19 July 2021 - 08:30 PM

hmmm. i just took the visual back off my scope, and found what's in the picture below: a 1.25" threaded barrel extending ~6" into the OTA.

 

is this also true on the C8?

 

 

No, the C8 has a larger  primary baffle (which is what you are looking at). The C6 has only a 27mm diameter baffle, while the C8 has a 37 mm baffle. So with the C8 (and any larger SCTs) you are likely to get more vignetting of the light cone if you use only 1.25 inch connections. With a relatively large sensor camera like the 294MC that vignetting should be very noticeable with 1.25inch connections, even on larger SCTs. (With the C6 because of the primary baffle, you are probably getting vignetting on the 294MC regardless )


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#21 alphatripleplus

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Posted 19 July 2021 - 08:38 PM

i don't understand why EAA isn't applicable to planetary imaging, but yes, that is one of the things i was thinking of.

EAA does not involve any post-processing after capture - if you take that  extra step you've moved over to traditional imaging.

 

However, to get much beyond a blurry snapshot of a planet typical when doing EAA, you would have to take a stream of very short images, post-process the best images in the video clip using software like AutoStakkert!, which can then extract details to produce a final image. That is what planetary imagers do in the Major and Minor Planet Imaging Forum, and it is beyond the scope of a quick EAA snapshot. 


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#22 millsbob

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Posted 19 July 2021 - 08:43 PM

many thanks again for your patient explanations, Errol. there is so much to learn!


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#23 GazingOli

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Posted 20 July 2021 - 03:38 AM

The simplest and least expensive way to adapt the camera to the 8" SC is this: https://www.bresser....n-Tube-Set.html

 

It comes with an adaptor to the SC tube thread and you can adjust the distance between the sensor and the reducer to your needs.

 

I myself did it in a different way:

 

cameraadaption.jpg

 

just because I had all the parts in stock by chance.

 

I must admit that I do not care too much about the correct distance between reducer and sensor (which is supposed to be 12,5 mm as far as I remember). I just take care that the camera cannot colide with the bottom of the CPC mount fork. But I get decent results anyway:

 

M16 C8f6.3ASI294UH 15frames_120s_cropresized.jpg

 

some more are here: https://www.cloudyni...021/?p=11221014

 

The C8 is really a great scope for EAA if you want to get close to the objects - I love it!!!

 

CS.Oli


Edited by GazingOli, 20 July 2021 - 03:40 AM.

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#24 millsbob

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Posted 20 July 2021 - 11:34 AM

thanks, Oli -- unfortunately, Bresser don't seem to distribute in the US?

 

but shouldn't this work:

https://www.amazon.c...088R3VXYC&psc=1

 

or this:

https://agenaastro.c...ad-adapter.html

 

although it doesn't appear that either of those allow for rotating the camera.

 

or this?:

https://www.highpoin...z4aAn4tEALw_wcB


Edited by millsbob, 20 July 2021 - 11:44 AM.


#25 nic35

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Posted 20 July 2021 - 12:08 PM

MB

 

If your camera is cooled, you will want to get a celestron diagonal with interchangeable scope side barrels.  See https://www.celestro...d3fd9b64d&_ss=r.

 

Otherwise, on the evolution mount (and likely on your SE), the back of the camera will hit the mount and limit your maximum altitude to about 65 degrees.

 

In either instance you will likely need to move the OTA far forward in the mount.  Not an issue with the evolution, but I know nothing about the SE mounts.

 

This particular diagonal screws onto the back of the 0.63 reducer, and provides about the right mount of backfocus.

 

I'd opt for the version of the diagonal that has both scope side barrels, so you'll have a diagonal you can use with the 70-80mm ED scope you will invariably buy.  It will give you the wide field of hyperstar, at considerably less expense.

 

j


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