People are asking the connect methods of ASI2600MM Pro: How to use it with the new 36mm EFW? How to reach the 55mm back focus distance? What accessories I need and can I add the original OAG or OAG-L into my imaging train?

To get all of the answers of these questions, you need to read this instruction.


1. The Basic Connection Solution:

No filter wheel or filter drawer in this solution, only adapters or the original OAG.

Suitable for telescope up to f/4.8

APS-C format cooled camera - 55mm back focus length solution


You can change the T2-M48 16.5mm into the original OAG. But please note that the OAG will block the sensor in a bit if the thread of the end side of your telescope is M42.


2. Using 36mm EFW:

This solution can be divided into 3 cases: with the original OAG and adapters, or with the OAG-L, or with adapter only.

1) With the original OAG or adapters:

Suitable for telescopes up to f/5.4

APS-C format camera + 36mm EFW + OAG


In this case, the connection method can be very convenient with the use of threads. You can take the full advantage of the accessories you have. A few notes:

– The original OAG can be replaced to T2-M48 16.5mm extender;

– The original 36mm EFW and new 36mm EFW will both work;

– T2-T2 2mm adapter can be found in the package of 36mm EFW;

– The back focus distance in this case is 56mm;

– Like we mentioned above, the original OAG will block the sensor in a bit if the thread of the end side of your telescope is M42.


2)With OAG-L:

Suitable for telescopes up to f/4.2



You can leave the adapters aside and directly connect the new 36mm EFW to the camera via screws in this case, the distance from the sensor and the filter will also be much closer. A few notes:

– The M42 sensor tilt adapter attached to the camera need to be taken off;

– The original OAG can not be replace to OAG-L, but if you have the M68 OAG, you can also use the M68 OAG instead;

– This method does not support the telescopes with M42 threads at the end side.

– M48/54/68 sensor tilt adapter can be bought separately.


3)No OAG, with adapter only:

连接M42M-M48F-22.5L和36mm EFW-英文

This method only supports the telescopes with M42 or M48 threads at the end side。 The M42M-M48F 22.5mm extender needs to be bought separately.


3. Using 2” EFW:

Being the same as Solution #2, this solution can be divided into 2 cases: with the original OAG and adapters, or with the OAG-L.

1) With the original OAG or adapters:

APS-C format cooled camera + 2inch EFW

– The back focus distance in this case is 56mm;
APS-C format cooled camera + 2inch EFW + OAG

– The back focus distance in this case is 56mm;


2)With OAG-L:


This method is quite similar to Solution #2 → 2), so we do not go into details here.


4. Using 2” Filter Drawer:

APS-C format cooled camera + OAG

APS-C format cooled camera + M42 filter drawer

APS-C format cooled camera + M42 filter drawer + OAG

Above the 4 solutions for the ASI2600MM Pro APS-C camera to reach the 55mm back focus length. Indeed there are more than 4 solutions in total, but these are what we most recommend. If you have any questions about this guide, please do contact us, we are glad to help!

100 Responses to [ASI2600 Guide] 4 Connection methods to get 55mm back focus length
  1. Avatar

    Hi, the screws that come with the 2″ filter wheel to attach direct to the asi2600 don’t seem to be long enough due to them tapering out at the top. Am I missing something or do I need to buy extra screws?


  2. Avatar

    Hi Sara,

    Is it possible to leave the tilt plate installed on the 2600MM Pro and then attach it to the new 7×36 mm EFW using the screw holes closest to the opening?

    I could then attach the T2 to M48 16.5 mm adapter to the telescope side of the EFW to connect to a scope with M48.

    This would total to 54 mm and then add 1 mm allowance for the filter (I am using Chroma 3 mm filters). That would then put the set-up at 55 mm and potentially reduce light leaks on the camera side.

    For the telescope side – could four of the screws provided with the EFW be used to seal those holes (or use electrical tape I suppose).

    Basically , solution 2.1 above, without using the 2 mm T2-T2 adapter.

    Thank You!


  3. Avatar

    Does option 2.3 with no OAG and 36mm filter wheel have a focal ratio limit and would this work with no vignetting at F/3.75? What is the distance to filter with new 36mm filter wheel attached with and without tilt plate? Thanks


  4. Avatar

    Which adapter do I need between my Asi2600mm Pro/filter wheels

    and my Nikon lens (Nikkor)?


  5. Avatar

    I have a Canon manual lens, 50 mm f1:8, with the FD bayonet mount.
    Is there a way to attach this lens to a ASI 174mm camera.
    I guess it needs a canon body mount and a tube which extends the length by the correct amount.
    Thank you.


  6. Avatar

    Hello ZWO

    I have the OAG-L and a 21mm Filter Drawer – from what I can work out, is it impossible to get 55mm back focus, only can get 56mm back focus?

    OAG-L = 17.5mm
    Filter Drawer = 21mm
    Tilt plate = 5mm
    2600MC = 12.5mm

    Total = 56mm

    Is there any other way to achieve this?

    Thank you


  7. Avatar

    I am trying to attach a 5×2″ ZWO filter wheel to the asi2600. Unfortunately, my EFW didn’t ship with a T2/T2 adapter, so I decided to try attaching directly to the camera with screws (taking off the front tilt bracket).

    My question is, are you supposed to be able to get 4 screws in when attaching directly to the camera this way? I can easily reach the lower two screws (below the camera sensor) by rotating an empty filter slot over them. But the top two holes are not reachable in this way, and are basically at the edge of the wheel. Is there some trick I am missing here? Am I supposed to remove the entire filter wheel from the device? If so, how do I do this? Or are two screws supposed to be sufficient? I could not find any instructions on this entire installation process.


  8. Avatar

    Can I connect ZWO ASI2600 MM on CELESTRON RASA8?


  9. Avatar

    I have a 102mm f5.1 refractor and a 10inch f5 newtonian. I currently use a asi1600mm pro cool and a zwo 36mm efw with a asi290mm mini for guiding. I use m48 connectors to the telescope. Will i be able to use a asi2600 with this set up?


  10. Avatar

    Hi – I am using the 2600MM with the 7×2 filter wheel. The standard set of connections give me 56mm backfocus. Any ideas how to achieve the 55mm backfocus? Here is what I have so far:

    ASI2600MM – with tilt plate (17.5mm) + 7×2 Filter wheel (20mm) + M54-M48 adapter (2mm) + M48 extender (16.5mm) = 56mm

    Even if I remove the tile plate – it’d be

    ASI2600MM – without tilt plate (12.5mm) + 7×2 Filter wheel (20mm) + M54-M48 adapter (2mm) + M48 extender (16.5mm) = 51mm

    Any advice? Or should I not use the 7×2 filter wheel (which forces me to use the 2mm M54 to M48 adapter) and switch to 7x36mm filter wheel instead (that would be a bummer).



  11. Avatar

    I setup my ASI2600 on a Stellarvue 80mm (f/6, 480FL) using method 3.2, using the M68 OAG-L, 2″ EFW, and a M54 thread plate on the telescope side. However, I am getting about 15% tilt on images. Is this the wrong setup to use or how do I correct for the tilt?


  12. Avatar

    I set up the ASI 2600 MM with the 68mm OAG using the instructions in Section 3-2 (with OAG-L) and my ASI 290 mini guide camera can’t come to focus. It’s close but stars are slightly out of focus/donuts. I have the guide camera all the way into the OAG focuser and backing it out a bit just makes it worse. Should this setup be functional with the ASI 2600 mm/OAG-L/2×7″ EFW? OTA is an 8″ SCT running at f/7.



    • Avatar

      Please make sure the distance of guide camera to the prism and image camera to the prism are equal.
      You’d better do it at day time to make sure imaging camera and guiding camera can reach focus at the same position.


  13. Avatar

    If i want use with the Asi2600mc a barlow lense, how i should this connect?


  14. Avatar

    I’m a bit confused with you specs.

    I want to use the asi2600mm with my f/4 scope
    Connection is M48 from coma corrector.
    May I use the 7*36mm filter wheel and standard Oag?
    Or do I have to use the OAG-L, with the 36mm filterwheel, or even more, the 2″ filter wheel with the Oag-L?

    Thanks a lot for your help.


  15. Avatar

    We regret to say that we can only provide some standard connection methods.


  16. Avatar

    What is the connection solution for a RASA8 – Starizona filter holder and the ASI2600


  17. Avatar

    Where do I purchase a m42 male m48 female extender as In example 3 above? The extender is 22.5 mm in length. Do you have a item number?


  18. Avatar

    Let’s say I have a fast astrograph that is faster than f/4.2.
    What are my options for the ASI2600? No filters, no OAG possible?


  19. Avatar

    Hello, I have a newton 250Quattro F4, what filter wheel should I buy if I want the camera 2600mm? And what method should I use for the backfocus? Thank you


  20. Avatar

    Is it possible to remove the tilt adapter from the 2600mm, mount the new 36mm filter wheel directly to the camera, then mount the tilt adapter directly to the scope side of the filter wheel?

    This would bypass the OAG in option #2 and then require a custom length adapter from the tilt adapter to the Focal Reducer.
    If this is possible, what size and threads are on the tilt adapter? M48?

    Thank you.




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