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6" RC for imaging..?

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#26 XB-36

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Posted 15 September 2019 - 12:32 AM

After reading though this a bunch I bought my first AT6RC


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#27 Mert

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Posted 15 September 2019 - 04:11 AM

Hope to read how it goes with this nice OTA.


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#28 XB-36

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Posted 15 September 2019 - 08:05 PM

When it can it was way out of alignment. So, my dad and I started using a camera but found that that was getting annoying. My dad had the idea to use a diagonal so we could just use an eyepiece to culminate the telescope. He told me if it was going in the right direction as I turned the screws. We got it pretty close before the clouds moved in. Are there any problems with culminating this way? I will post a picture once I get a chance.

Clear Skies everyone


Edited by XB-36, 15 September 2019 - 08:09 PM.


#29 the Elf

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Posted 16 September 2019 - 03:04 PM

XB-36,

 

collimating. It is collimating. RCs are difficult to collimate. The simple way is to look in at the rear end and make everything concentrical as a starting point. This is not quite the truth because the optical center is not always the center of the mechanical outlines. After that point to a star, place it in the center and check the image when out of focus in both direction (focuser a bit too far in and a bit too far out). There should be a ring of even thickness. Turn the secondary screws (scope front). Beware, the star will move, you have to bring it back to the center after each tweak of the screws. This is probably good enough to have a sharp center spot. Getting the corners right is a bit more work:

https://www.deepskyi...ure_Ver_1.0.pdf

 

The CCD47 reducer is strongly recommended for beginner. A shorter focal length is easier to deal with, the system is faster and the camera moves closer to the scope. Though not the first choice for beginners I recommend off axis guiding if you exceed exposure times of about 2 minutes. The small RCs suffer from movement of the rear cell. Guiding with a guide scope cannot cure this and you have star trails. Short exposures on bright targets will work well with a guide scope. Unguided is not really an option. If you have a decent mount, 30 secs might work. Get a Bahtinov mask for focus and get Charles Bracken's book "The deep sky imaging primer". Good luck!


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#30 pfile

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Posted 16 September 2019 - 03:58 PM

i recently came across another PDF about RC collimation which is interesting... the author basically says to never try to star-collimate a GSO RC. he has a bench technique which he claims gets it spot on but like some methods it does require removing the baffle and also using the takahashi scope.

 

it's linked in the first post of this thread:

 

https://www.cloudyni...ng-frustration/

 

edit: the link at the top is broken but the OP re-linked it at the bottom of the thread.

 

rob


Edited by pfile, 16 September 2019 - 03:59 PM.

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#31 RJF-Astro

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Posted 16 September 2019 - 05:56 PM

Though not the first choice for beginners I recommend off axis guiding if you exceed exposure times of about 2 minutes. The small RCs suffer from movement of the rear cell. Guiding with a guide scope cannot cure this and you have star trails. Short exposures on bright targets will work well with a guide scope. 

But try before you buy, if you already have a guidescope. I use one with my 6" RC and I don't lose many frames to flexure, if any, including 4 minute subs narrowband.

 

Also, I collimated the RC with the DSI-method posted above, with no fancy collimation tools. It took me one evening and I have been pleased with the images ever since. Maybe they are not perfect, but they beat my ED refractors which is good enough for me now.


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#32 pfile

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Posted 16 September 2019 - 11:54 PM

yeah i think the 6 is easier to collimate with the DSI method thanks to the increased field curvature making the corner star shapes more obvious. with the 10" the star shapes at the edges of an 8300M can be subtle.

 

i had trouble with the external guidescope but that's because mine is trash. astro-physics makes a really nice guidescope bracket that also supports the guide camera which goes a long way toward reducing flexure.

 

rob


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#33 RJF-Astro

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Posted 17 September 2019 - 02:22 AM

Below is a picture of my RC6. I currently have the guidescope (ZWO 60mm) mounted on top, for balance. The ZWO bracket is not the best there is, but it is tight enough.

 

Not that I haven't thought about adding an off-axis guider. I have had it in my shopping basket for a few times now, but then I look at recent subs and see no reason to pull the trigger. Maybe my stars will improve, but I am also reluctant to fix anything if it isn't broken.

 

rc6.jpg



#34 the Elf

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Posted 17 September 2019 - 07:32 AM

RJF,

 

if you have good image quality with only 4 min NB there is no need to go for OAG. I take 10 to 15 min because I doubt the (mono modded) T3i can deal with 4 min NB subs. I must admit, I never tried.


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#35 XB-36

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Posted 17 September 2019 - 07:45 AM

My dad and I got the telescope perfectly collimated last night turns out that you should NOT use a diagonal. Now the telescope is working well and I can easily see M13, M32, and M31with a 20mm eyepiece. I will post some of my pictures soon.


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#36 XB-36

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Posted 18 September 2019 - 08:30 AM

After a night of astrophotography this is what I got. https://drive.google...iew?usp=sharing


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#37 Mert

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Posted 18 September 2019 - 01:24 PM

That's a good start, you might improve on this demanding target

using the best focus you can obtain!! ( on the shared version it

is a bit pixelated, maybe jpg compression? )

IMHO focussing the RC's ( I use the 8" version ) is demanding!!

 

Good job :waytogo:


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#38 XB-36

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Posted 18 September 2019 - 03:42 PM

It is hard to focus and the camera strap fell off of the camera (I had it laying on top of the camera) mid photo. lol.gif  as far as the focus goes I got it the best that I could. Do you have to use a focusing mask for the RC? I just got the vanes right on top of each other and the focus looked fine to me.

Clear Skies



#39 ram812

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Posted 18 September 2019 - 09:43 PM

   Hello, all! After  recovering from surgery I just couldn't wait to get back to CN. And, of course, I see a post on RC's and have to put my pennies worth in. I found it quite easy to collimate this little scope. I purchased the AT6RC before I went down (Literally) and didn't get to use it until I could actually move equipment up and down stairs. So, FWIW, it IS a neat little scope, but I have had to collimate it only ONCE since I first put it up. The secondary screws were gosh awful tight, but once I put it on a star and got a camera attached, it was quite easy. I know I'll never hear the end of it now, but the little scope has held up quite well. I'm just learning how to go from visual to photo in the dark without screwing anything else up. It is quite contrasty in pics. I've only taken a couple so far just to see and it is promising. That being said, I really would rather use my XT, truth be told, and have been thinking of just using the RC for planets and such stuff. F4 vs. F9 (Native) no contest for DSO. That is unless you really get all the ducks in a row. I'm getting impatient in my old age and like taking  pics  on the "Quick!" . So if you get this down, share it all as I'm still learning the in's and out's of stuffing that much focal in such a short tube. Camera tilt can and does happen so make sure everything is super tight. Good luck and clear skies!!!


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#40 RJF-Astro

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Posted 20 September 2019 - 01:29 AM

   Hello, all! After  recovering from surgery I just couldn't wait to get back to CN. And, of course, I see a post on RC's and have to put my pennies worth in. I found it quite easy to collimate this little scope. I purchased the AT6RC before I went down (Literally) and didn't get to use it until I could actually move equipment up and down stairs. So, FWIW, it IS a neat little scope, but I have had to collimate it only ONCE since I first put it up. The secondary screws were gosh awful tight, but once I put it on a star and got a camera attached, it was quite easy. I know I'll never hear the end of it now, but the little scope has held up quite well. I'm just learning how to go from visual to photo in the dark without screwing anything else up. It is quite contrasty in pics. I've only taken a couple so far just to see and it is promising. That being said, I really would rather use my XT, truth be told, and have been thinking of just using the RC for planets and such stuff. F4 vs. F9 (Native) no contest for DSO. That is unless you really get all the ducks in a row. I'm getting impatient in my old age and like taking  pics  on the "Quick!" . So if you get this down, share it all as I'm still learning the in's and out's of stuffing that much focal in such a short tube. Camera tilt can and does happen so make sure everything is super tight. Good luck and clear skies!!!

Hi there! You are right: F9 will never beat F4.7 for DSOs. That is why most imagers get a reducer for the RC6, such as the Astro Physics CCDT67 0.67x or the TS-Optics CCD47 (also 0.67x). That will make the RC6 an F6 scope at around 940mm at it's default setting.

 

In that way, the RC6 is still slower but it is also an easier scope to mount and guide compared to the XT (on the CGEM right?). But if you are about to get started on taking guided long exposures and all, both scopes can be difficult. A short, fast refractor of reflector might also be a good investment at this point.


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#41 the Elf

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Posted 20 September 2019 - 04:14 AM

Hi all,

I spent quite some time researching what options are available at a price below $2k for fast imaging optics and a focal length in the 1000mm range. Good fast refractors are very expensive. Fast refractors in that price range have a shorter focal lenght. Newts are fast for the price but often don't have enough back focus for DSLR users like me. The one great exception  seems to be the SkyWatcher 190MN. User "Acer" keeps on posting the most excellent images using that scope. Other also praise it. Like me a few people wrote that they ended up with a decision between the 190MN or the RC8 as Mert and I use it now. The RC (6 and 8) benefit or I should rather say "need" the reducer. I phoned TS and they did not exactly say the TS CCD47 is an exact copy of the AP CCDT67 but it is the same design and I guess it is made in the same chinese factory. I have been using it (the TS) with the RC6 pretty much from the start and a use it with the RC8 now. The quality is very good, no chromatic aberations, no astigmastism. Unlike flatteners this thing is reducing only and so tolerates a wide range of spacings to the sensor. By putting more or less spacers between reducer and camera the focus point can be moved in and out, depending on how much stuff one needs to add there (filter wheel, OAG). See my website for example images of both scopes. I spaced the RC6 down to 800mm fl for the Orion nebula. With the RC8 I am at 1100 now. In any case, the reducer is sunk in the draw tube. When just sliding in like an eyepiece this is very simple. I got the GSO RC6 via TS and they sold it with a Eur99 mono rail focuser that is poor and soon starts slipping. They sell the RC8 w/o focuser and offer a selection of four different focusers to be ordered seperately. I have the V-power now that is not too expensive, offers a rotator and a threaded connedtion at the rear. After some adapter battle I now have the reducer threaded inwards in the drawtube and an OAG and a T-ring outside. I use a mono modded T3i and the Baader protective T-ring that holds the filters (L, Ha, O-III) behind the OAG. It is a nice compact setup that I like very much and can recommend. The carbon tube does not react much on temperature changes, I refocus when temperature changes for more than 5°C.

I found the RC6 suffering from internal flex and thus started guiding via an OAG (there are two videos about OAG on my channel). As I got used to it I just continued using it with the RC8 and with my 65mm quad as well. I can't tell if the RC8 needs it, never checked the flex. As you can see on the photo there is just the DSLR quite close to the scope and the small pancace guide camera below. The finder scope on the tripod tray is used for star alignment only because with the small FOV the first star is sometimes not in the image. I take it of after alignment to save the weight.

 

Berlebach_low.jpg

 

Re focusing and mask: there is an online Bahtinov mask generator. My GF cut a mask from thin polystyrene (model railway stuff) with her dye cutter (Cricut) for me. You can see three small magnets on the secondary support of the scope and there is some self adhesive thin steel foil on the back of the mask so that it just drop it in the scope and it stays in place:

 

MagneticB_2.JPG MagneticB_4.JPG MagneticB_1.JPG

 

Here is Nico showing how to 3D-print B-masks:

https://www.youtube....h?v=a0Qk5jzsZfc

and this is the generator:

http://astrojargon.n...CookieSupport=1

 

Hope this helps someone making decisions or picking up ideas!


Edited by the Elf, 20 September 2019 - 04:23 AM.

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#42 ram812

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Posted 25 September 2019 - 01:09 PM

 Awesome info, here! Thanks for tips on reducers and this will be the next addition to my kit. RJF-ASTRO, the XT IS ungainly and a lot to handle, but after 2 years of testing different guide scopes and such, I've learned that it can and does a good job, good enough for me and my insatiable appetite I have for "Instant gratification"!. I see a high quality refractor in the future, and going monochrome also. Read $$$. This is why I enjoy CN, tons of info that helps us make an informed decision on purchases in the future. Thanks, all!


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#43 B. Hebert

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Posted 26 September 2019 - 02:16 AM

WHY isn't there a service or organized RC collimation party available anywhere?

 

I tried suggesting this to OPT but got no response.

 

Some might be willing to pay or travel to a star party where an experienced collimator would do their magic for pubic benefit or a price.



#44 WadeH237

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Posted 26 September 2019 - 06:37 AM

WHY isn't there a service or organized RC collimation party available anywhere?

Because collimation is a regular maintenance task on any reflecting telescope.  Every owner should know how to check and adjust collimation.  While some telescopes hold collimation better than others, all of them will need it sooner or later.  Also, a particular problem with having a service available to do it, would be that the scope would be at significant risk of losing collimation during the return trip to the owner.
 

Some might be willing to pay or travel to a star party where an experienced collimator would do their magic for pubic benefit or a price.

I've certainly helped people with collimation at star parties, and I'm happy to do it for anyone who asks.  The real value, though, is not in getting the scope collimated.  It's in learning to collimate the scope with the help of someone who's experienced.  I almost always make it a collaborative project between me and the scope owner.


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#45 ram812

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Posted 26 September 2019 - 11:35 AM

  I agree with the above post. The best way to learn is definitely hands on. Mirrors need cleaning, so collimation knowledge is a must. I enjoy collimating my scopes (I have 3 other reflectors in my closet that have "Special use" on them") and love to take things apart and put them back together. First time I did this the results were less than inspiring! But I got good, good enough that with proper care (Read EXCEPTIONAL) that when I bought my XT 10 (Factory collimated to perfection) I have NEVER had to take it apart (I check it every friggen time out,and star test confirm) and have handled it like a newborn baby for the past 5 years!. I'm highly confident that when I DO have to it will be a lot easier that my "Smaller reflectors" My other, smaller reflectors get handled lots more and they get the going over only when needed. Scopes vary scope to scope, on the frequency of need to collimate. This is largely due to the environment they are kept in and utilized. I believe that with the proper care most reflector mirrors only should be cleaned once every 10 years or so, anyway. Some folks are anal about it and they wear out the finish/coating way before their time. Too much of a good thing can be bad! So it all (IMHO) comes down to storage and things I've mentioned above. Too bad you're in so.Cal. or I'd meet with you and we'd get squared up real quick. grin.gif 



#46 the Elf

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Posted 27 September 2019 - 12:19 AM

Some scopes loose collimation when shipped or carried in a car. You have to collimate it at home. If an RC6 was collimated before it is quite likely you only need to adjust the secondary looking at an out of focus star in the image center. That's not a big deal. If the primary is off, that is a different story.




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