Backspacing specification on new equipment

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Blue
Posts: 4
Joined: Tue Feb 04, 2020 12:13 am

Backspacing specification on new equipment

Post by Blue » Wed Feb 05, 2020 7:55 pm

Hi all, I have been using an ASI294MC Pro camera for about a year and I am looking to update. If budget permits I was considering going to the top with a mono ASI6200, filter wheel and new OAG.

One thing I have not found written down, the combination if ASI6200, 7 position 2" filter wheel, OAG and tilt plate is stated as adding up to 55mm back focus distance, but is that a physical distance from the face of the tilt plate (When fitted to the mew M68 OAG) to the sensor, or does it include an allowance for the effect of filters on that distance, and does it include an allowance for the sensor chamber window?

On the new telescope I am waiting for delivery on it may require me to have a new tilt plate machined to avoid the use of any thread adapters as with the normal 55mm spacing requirement of most field flatteners I would be likely to end up at least 1mm over spaced with the M48 to M55 adapter I will require. If the 55mm of the tilt plate, OAG, filter and camera combination is a physical distance I might just get away with it once filters and the sensor window are taken in to account.

Katherine.Tsai
Posts: 520
Joined: Fri Dec 07, 2018 10:24 am

Re: Backspacing specification on new equipment

Post by Katherine.Tsai » Fri Feb 07, 2020 3:44 pm

Blue wrote:
Wed Feb 05, 2020 7:55 pm
Hi all, I have been using an ASI294MC Pro camera for about a year and I am looking to update. If budget permits I was considering going to the top with a mono ASI6200, filter wheel and new OAG.

One thing I have not found written down, the combination if ASI6200, 7 position 2" filter wheel, OAG and tilt plate is stated as adding up to 55mm back focus distance, but is that a physical distance from the face of the tilt plate (When fitted to the mew M68 OAG) to the sensor, or does it include an allowance for the effect of filters on that distance, and does it include an allowance for the sensor chamber window?

On the new telescope I am waiting for delivery on it may require me to have a new tilt plate machined to avoid the use of any thread adapters as with the normal 55mm spacing requirement of most field flatteners I would be likely to end up at least 1mm over spaced with the M48 to M55 adapter I will require. If the 55mm of the tilt plate, OAG, filter and camera combination is a physical distance I might just get away with it once filters and the sensor window are taken in to account.
A physical distance from the face of the tilt plate.

Blue
Posts: 4
Joined: Tue Feb 04, 2020 12:13 am

Re: Backspacing specification on new equipment

Post by Blue » Wed Feb 12, 2020 1:48 am

Great thank you. I assumed that it was a physical distance so for instance for a ASI6200 with filter wheel and the sensor chamber window I would need to allow approximately another 1mm.

I had the manufacturer turn the camera side threads on the field flattener deeper to increase the back spacing allowed from their standard 55mm as if I require any other spacers I would have been in trouble.

Katherine.Tsai
Posts: 520
Joined: Fri Dec 07, 2018 10:24 am

Re: Backspacing specification on new equipment

Post by Katherine.Tsai » Wed Feb 12, 2020 9:45 am

But it will not too much effect on the image train since it can tolerate 1 or 2mm difference.

Blue
Posts: 4
Joined: Tue Feb 04, 2020 12:13 am

Re: Backspacing specification on new equipment

Post by Blue » Wed Feb 12, 2020 10:04 pm

Thanks, I was wanting to keep the options open to really fine tune it as I am considering buying a full frame camera such as the ASI6200 to go with the new scope as it has a 43mm corrected image circle. I have seen from a friends similar scope that the last little bit of field correction at the edges can literally come down to 0.5mm error in the spacing.

Katherine.Tsai
Posts: 520
Joined: Fri Dec 07, 2018 10:24 am

Re: Backspacing specification on new equipment

Post by Katherine.Tsai » Thu Feb 13, 2020 6:52 am

Maybe you can add some thin spacer to fine adjust the back focus.

Blue
Posts: 4
Joined: Tue Feb 04, 2020 12:13 am

Re: Backspacing specification on new equipment

Post by Blue » Fri Feb 14, 2020 5:22 am

That will not be a problem, I have plenty of spacers, once I am sure of the exact spacing I need I will have an adapter machined to suit. I will temporarily be using my new scope with my existing ASI294MC Pro but I am hoping to get enough money together to change later this year to an ASI6200MM with filter wheel and off axis guider.

Katherine.Tsai
Posts: 520
Joined: Fri Dec 07, 2018 10:24 am

Re: Backspacing specification on new equipment

Post by Katherine.Tsai » Fri Feb 14, 2020 9:26 am

That's great.:)

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