RASA 8 Camera Adapters, Filters and Back Focus

[@astronorthwet636]

Just got my 8" RASA yesterday. I need all the information I can find on this kind of stuff. Great informative video. Thanks!

[@jeffrh]

Scott, Glad you liked the video. One word about the back focus numbers I'm using. These are all for Mallincam DS series cameras that have 17.5 mm of back focus. If your using another brand of cameras. Then you will need to find out that number to calculate the correct back focus for your camera. ZWO cameras can be used with the Filter Slider from Starizona. They sell everything needed to get to the correct back focus needed for those cameras.

[@omaracosta3542]

This is great info, just purchased a RASA 8 and this video comes in at the perfect time... Thx for taking the time to explain and show this process.

[@jeffrh]

Thanks Omar... Hope the Filter Wrench's showed up OK!

[@MCDanyification]

This is one of the most useful Videos about the RASA 8" !!!! Because back focus is so crucial with this system it helps a lot. THX sir.!!!

[@jeffrh]

Thanks, Daniel Celestron has just come out with some spacer made for various cameras. Here's a link: www.celestron.com/products/m42-spacer-kit

[@claude77573]

Great video! Thank you for your contribution! If I can add an additional comment, I noticed the clear filter was in place when the adapter was installed. Page 16 of the RASA White Paper says "Because the RASA’s optics are designed for a single 2mm thick filter in the optical path, if you wish to use another filter, remove the internal clear glass filter located inside the RASA’s tilt collar. If two filters are in the optical path at the same time, the RASA’s performance will be affected."

[@jeffrh]

Claude, Yes, I read that also. I don't have the cleanest observation conditions and didn't see that much of a difference between that big clear glass in or out. So I decided to keep it in to help protect the optical glass behind it. It does affect the backfocus. I have 3D printed spaces that I can use to nail the backfocuswhen I change filters. I have found that the back focus is more important than if the glass is in or out. I could also be out to lunch.... ;-) I now have a RASA 11 and also leave that glass in place. Doesn't seem to be doing anything that makes me run for cover... I might be over compasating a little. Better safe than sorry works for me... Just need to keep an eye on the backfocus which I see when a plate solve happens.

[@claude77573]

For what it's worth, a filter will add 1/3 of the thickness of the filter to the back focus length (which the RASA 8 Celestron manual also refers to as the flange focal distance). So a 2mm thick filter would add .67mm of backfocus / flange focal distance. For a reference, see the Cloudy Nights article titled "RASA 8 Baader adapters".

[@jeffrh]

Thanks fr the info...

[@timothymaurer6720]

Hey Jeff...great info here. Couple of questions for you. First, do you need to use your paper shim with the Artesky adapter too? I know the Celestron m45 needs it but was hoping the flange diameter of the Artesky was a little larger and wouldn't need any shimming. Second, when I measure/calculate the thickness of my Celestron m45 adapter, I get 2.5mm optical thickness. I do this by measuring the adapter with a 7.5mm extension and then just subtracting the extension out (10-7.5=2.5) since that seems more accurate (and easier) that measuring that dip on the top of the adapter. I would add that I remove the paper compression ring on the bottom of the adapter since I would prefer metal on metal contact between my surfaces. Anyway. good stuff. Thanks again!

[@jeffrh]

Timothy, I no longer have the RASA 8... I upgraded to an RASA 11 shortly after making this video. My quess would be that the Artesky Adapter is very close in size to the Celestron Adapters. So my guess today would be yes... One of the things they fixed with the newer RASA's I believe is the adapters have a beveled edge on the top of the adapter that the collar ring would center on. I left the compression paper alone as that helps to keep the camera from spinning after it is tightened. I never saw any tilt from that surface being uneven. Thanks for the measuring tip... Lots of ways to do these things... ;-)

[@ericgrossman7248]

Hi Jeff. Great video! I am currently having focus issues with my RASA 8. I am using the Starizona filter slider and no other spacers. I measure the back focus at 30 mm. Could that be causing my focus issue? How exact does back focus need to be? Thanks.

[@jeffrh]

Eric, The total back focus for the RASA 8" is 28.73 mm. Using the supplied T2 camera adapter and a 7.5 mm spacer gets you just about there. Now add in the 17.5 mm for a Mallincam DS series camera and you get 28.5 mm. Using the Starizona Filter Slider on the 8' will not work unless you're using a ZWO camera and there are only a few that can work with it. If you're using a Mallincam camera DS series. The back focus for those is 17.5 mm and the filter slider has the same 17.5 mm. If you add those up you get 35 mm with just those two pieces. Now add in the supplied camera adapter from Celestron and your way over 28.73 mm the RASA 8 needs. I hope this helps...

[@srikanthmeg]

When using the Artesky RASA 8 adapter - Did you had to remove clear glass from Celestron to use the Artesky adapter?

[@jeffrh]

The Artesky RASA 8 adapter was purchased for a Mallincan DS16cTEC camera that has a backfocus of 17.5 mm. With that camera and the Artesky adapter. I was able to achieve the correct backfocus and use 2" filters. You are suppose to remove the clear glass protective window when you add a filter. I never did and had no problems with my images or getting the correct focus. I think the filter adds around 1 mm or so of additional backfocus to the system. The Artesky adapter comes with a spacer that sits in between the camera and the adapter. I can't remember how thick it was. Could have been about 1 mm which if you removed that and keep the clear glass window in would keep the backfocus in the correct area. I no longer own the RASA 8 or the Artesky adapter and this is from memory. Hope it helps...

[@ACEOFSPACE2000]

Thanks for the info well done

[@jeffrh]

Thanks, If you have a RASA 8. You'll love the FOV!

[@selrahcarev]

Hi ! just got my RASA 8" with an ASI2600MC Pro and unfortunately I can plug my filters with it, then I saw the artesky adapter, could you confirm me if the rasa + artesky + 7,5mm spacer + ASI is ok ? do you like the artesky piece ? Want to order it for a l pro and l enhance 2" Thank you !!

[@jeffrh]

Selrah, I'm talking about Mallincam cameras when I'm talking about back focus needed. Their DS series camera has a back focus of 17.5 mm. If the ASI260MC you have has a back focus of 17.5 mm. Then yes, the Artskey RASA 8 adapter will work with that camera. If the back focus is less. Then you would need to add a spacer to make up the distance...

[@SIGP229TPOC]

Great info, and great video. Thanks for doing this! Question, do you have a link for that paper you purchased? I tried a 3D printed ring, but never could get the right size and never really fit.

[@jeffrh]

Thanks Chris, Not quite sure what paper your talking about. Could you give me a time in the video where I'm talking about that paper?

[@SIGP229TPOC]

@@jeffrh @12:44

[@jeffrh]

@@SIGP229TPOC OK, Thanks for that time code... That is some black paper that I got at an AC Moores Art Store. They are no longer in Buffalo. The paper is very similar to Business Card Stock in thickness. Hope this helps you out.

[@SIGP229TPOC]

@@jeffrh Much appreciated!

[@jimtaylor5802]

Convinced that many of the tilt issues are from installing the camera while horizontal - I’ve gotten the best results while the rasa is vertical…

[@LiveSteamMad]

C mount camera adapter included with RASA, not 1.25" adapter

[@jeffrh]

I got the C Mount & 1.25 which is why I showed it to the Group. Maybe Celestron has changed what they ship with the scope now? Last I looked, the Celestron site showed the 1.25 adapter in what's included. That was maybe 2 months ago.

[@nkondrashov]

Breathing on filters is not good for them - coating can be damaged.. mold can grow..

[@jeffrh]

Thanks for the heads up. One of my many bad habits. I have bulbs all over the place to..