ASI1600MM + 2" EFW + M68 OAG < 55mm back focus possible?

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rosswalker
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Joined: Fri Apr 05, 2019 11:49 pm

ASI1600MM + 2" EFW + M68 OAG < 55mm back focus possible?

Post by rosswalker » Tue Jun 23, 2020 6:27 am

Hello,

I'm preparing for the move to full frame. I've ordered a set of Chroma 2" filters and am about to order the ZWO 2" large filter wheel and M68 OAG. Until I have the funds to purchase the ASI6200 mono I wish to use my 1600mm Pro. The imaging train is to be used with a reducer that has the standard 55mm of back focus. The reducer is the Askar f/3.9 reducer with an M48 male thread on the camera side.

Looking at the ZWO docs this seems doable (around 49mm of BF taken), but just in case, I would like to confirm that the 1600MM + 2" EFW + M68 OAG + all adapters will indeed fit within the 55mm BF requirement. Also, are all the required adapters included with the EFW and OAG to do this? Finally, can the 1600MM be bolted to the EFW?

The focal reducer specs are at the bottom of this page:

http://www.askarlens.com/index.php/wap/ ... 5/192.html

Thank you,

Ross

rosswalker
Posts: 7
Joined: Fri Apr 05, 2019 11:49 pm

Re: ASI1600MM + 2" EFW + M68 OAG < 55mm back focus possible?

Post by rosswalker » Thu Jun 25, 2020 2:34 am

Replying to myself, but I'm sure there will be others using 1600MMs and wishing to do the "slow upgrade" to 2 inch filters like I am, so I hope this post is useful.

This question is holding up a roughly $2k order to ZWO; I can't really proceed with the order unless I know this is going to work.

After reading various ZWO docs it does seem possible to have an imaging train with ASI1600MM + 2" EFW + M68 OAG with less than 55mm of back focus:

The 2" EFW has an M54 female connection on the camera side, while the ASI1600MM has an M42 male. So I need an M54 male to M42 female adapter to connect the EFW to the ASI1600. The EFW indeed comes with an M54 male to M42 female adapter, so that gets the camera connected to the EFW, and the adapter takes up zero backfocus. I hope ZWO staff will let me know if this is not possible for some reason. I will probably also need a 6mm M42 spacer in-between the 1600 and EFW to keep the OAG cam and imaging cam parfocal.

The M68 OAG bolts onto the 2" EFW.

I then bolt on the ZWO M54 tilt adapter (purchased separately) to the M68 OAG. The M54 tilt adapter has an M54 female connector on the scope side. My reducer has an M48 male connection, so I need an M54 male to M48 female adapter. The 2" EFW comes with this adapter, and it takes up zero back focus. That completes the imaging train.

My calcs suggest the total back focus without the 6mm M42 spacer is 49mm, so well within the 55mm backfocus spec of the reducer.

So, what do you think ZWO? Can you confirm that this is possible, and at the same time have the guide cam and imaging cam par-focal? Is there something I am not considering?

Thank you,

Ross

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Support@ZWO
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Re: ASI1600MM + 2" EFW + M68 OAG < 55mm back focus possible?

Post by Support@ZWO » Tue Jul 07, 2020 4:19 pm

Hi Ross,
1600MMPro(17.5mm)+2"EFW(20mm)+M68OAG(17.5mm)+M54 tilter(5mm)=60mm, it can connect but exceeds 55mm back focus.
Location:lon=120.6 lat=31.3
Suzhou China

rosswalker
Posts: 7
Joined: Fri Apr 05, 2019 11:49 pm

Re: ASI1600MM + 2" EFW + M68 OAG < 55mm back focus possible?

Post by rosswalker » Fri Jul 10, 2020 9:41 am

Hello,

Thanks for the reply.

1600MMPro(17.5mm)

The 1600MM has only 6mm of backfocus, and I believe it can connect directly to the EFW using the M42 to M54 adapter supplied with the EFW. Is that not correct?

The 2" EFW has an M54 female thread on the camera side, yes?

Cheers,

Ross

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Support@ZWO
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Joined: Mon Apr 24, 2017 10:08 am

Re: ASI1600MM + 2" EFW + M68 OAG < 55mm back focus possible?

Post by Support@ZWO » Tue Jul 14, 2020 8:55 am

rosswalker wrote:
Fri Jul 10, 2020 9:41 am
Hello,

Thanks for the reply.

1600MMPro(17.5mm)

The 1600MM has only 6mm of backfocus, and I believe it can connect directly to the EFW using the M42 to M54 adapter supplied with the EFW. Is that not correct?

The 2" EFW has an M54 female thread on the camera side, yes?

Cheers,

Ross
1. Yes
2. Yes.
Location:lon=120.6 lat=31.3
Suzhou China

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