How bring ASI174MM in focus with PST

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Jordan Konisky
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How bring ASI174MM in focus with PST

Post by Jordan Konisky »

An out-of-the-box ASI174MM camera does not reach focus with a Coronado 40 mm (400 focal length). For other ZWO cameras focus can be achieved with a PST with a 1.25 Low Profile Cover. The exception is the ASI174. The note on the ZWO website states: “PS: this new cover cannot hold the protect window of ASI174MM/MC, so you need an external 1.25 filter.” I understand why, but, as a newbie, have no idea how to accomplish this modification. Have perused many web sites and the ZWO forum but haven’t found a description of this solution. Are there alternative ways to bring this combination to focus? Could really need some help here and would appreciate suggestions.


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Re: How bring ASI174MM in focus with PST

Post by Montana »

Have you tried using a 1.6x or 2x Barlow to achieve focus?

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Re: How bring ASI174MM in focus with PST

Post by PDB »

Hello Jordan,

I don't have a ASI174 but had a look at the documentation: https://astronomy-imaging-camera.com/product/asi174mm
There might be a way shortening the backfocus by removing the T2 ring, but then you will need to find a nosepiece with inner T2 thread (the supplied one has outer T2 thread.
Asi.JPG
Asi.JPG (28.91 KiB) Viewed 4265 times
Regarding the AR window: if I read it correctly it is only a protective winwdow (protects sensor surface from dust and scratcher) and anti-reflection. No UV/IR filter.

As Alexandra said try a barlow. That usually helps.
It is not a good idea to use the ASI174 in prime focus of the PST (f/10) this will be way undersampled, bringing down the resolution to probably a 20 mm onjective.

PST resolution is ~3"
You need a sampling that is mininale half of that say 1.5"/pixel to get the full resolution.
Bringing the scope to ~f/20 will take care of that, so a 2x barrlow should do the trick.

Bad thing the solar disc will be bigger, and might not fit on the sensor for full disc without doing a mosaic.

Regards,

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Re: How bring ASI174MM in focus with PST

Post by Stumyatt »

Hello

I have the same issue as the poster above i have purchased the PST and also have a ASI174mm.

I have a standard 2x and 3x barlow but still unable to get back focus.

Do i need the the 2x barlow Coronado produce to enable backfocus?

Also i have been trying to find the low profile connector for the ASI174mm which ZWO used to produce any reason why its no longer available?

Thanks

Stu


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Re: How bring ASI174MM in focus with PST

Post by marktownley »

Stumyatt wrote: Sun Sep 25, 2022 6:18 am Hello

I have the same issue as the poster above i have purchased the PST and also have a ASI174mm.

I have a standard 2x and 3x barlow but still unable to get back focus.

Do i need the the 2x barlow Coronado produce to enable backfocus?

Also i have been trying to find the low profile connector for the ASI174mm which ZWO used to produce any reason why its no longer available?

Thanks

Stu
Welcome to the forum Stu!

Have you tried unscrewing the nosepiece from the barlow and screwing it onto the camera nosepeice?

Mark


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Re: How bring ASI174MM in focus with PST

Post by Rusted »

A shortened nosepiece is easily achieved with a junior hacksaw.
File or rub the cut edge on some abrasive paper to tidy it up and square the end.
This should allow filters, Barlow nosepieces and GPCs to screw into the nosepiece.
Ensure you remove all dust before you screw the shortened adapter into the camera.


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Re: How bring ASI174MM in focus with PST

Post by Montana »

I use my ASI174 on my PST with a 2x Celestron Ultima barlow. It works great with no focus issue ;)

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Re: How bring ASI174MM in focus with PST

Post by inhapi »

There are 3-D print files online to connect the ZWO camera line directly without barlow to the PST. A friend of mine didn't have much succes with them yet tough.


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