Achieving Focus with a Zenithstar 61mm and Quark Chromosophere

[Goose]

Please excuse my ignorance as perhaps there is an overly obvious answer, but I am having trouble figuring out backfocus when using an imaging train starting with a Williams Optics Zenithstar 61mm with the 61A flattener, a Quark Chromosophere, followed by a tilter an ASI174 camera. For the moment I am concerned only with achieving focus and less so with the FOV. I understand backfocus with a standard scope and camera but I'm confused about how the backfocus on the Zenithstar and the Quark coupled in this imaging train interact and how I should be compensating with spacers to achieve solar focus. Thanks for any help with this newbie question.
James S

[rsfoto]

Hi,

I would say your otpical train could look like this

Telescope > Quark > Flattener 61A > extension tube xxmm > tilter > Camera

May I ask what fort of Tilter you are referring to?

The 61A tilter for a M48x0.75mm thread is 67.7mm from which you deduct the 6.5mm of the ASI 174 = 61.2mm ring between flattener 61A and ASI 174 (I assume it is the normal non cooled version) and from 61.2 mm you need to deduct the thickness of the tilter and you get the necessary ring for it.

The Quark, if I remember well, has no backfocus necessities. I once had a Quark but it was blind and I returned and never ever again I pursued the Quark way.

But why do you want to use a Flattener which for me is not necessary for that tiny chip of the ASI 174. The chip is only 11.3x7.1mm and has a diagonal size of 13.35mm. Unfortunately there is no diagram report of the star shape without flattener.

I would say try it first without flattener and check the borders of the image.

[marktownley]

Ditch the flattener

[Goose]

Thanks for the advice. I'll get rid of the flattener. I had it in there for some night imaging and it may not have been necessary in any case with this particular camera. Its a ZWO tilter and I'll measure it to verify.

The optical train would then be Scope-Quark-ExtensionTube(s) -Tilter-Camera,
Again, excuse my (persistent) ignorance, but does one now establish the backfocus from the quark as if it did not exist?
In other words the backfocus would be measured from the end of the quark nearest the camera using the standard Zenithstar backfocus
(without flattener)?

Thanks again for your help. The Quark interface is something completely new to me.

[rsfoto]

Thanks for the advice. I'll get rid of the flattener. I had it in there for some night imaging and it may not have been necessary in any case with this particular camera. Its a ZWO tilter and I'll measure it to verify.

The optical train would then be Scope-Quark-ExtensionTube(s) -Tilter-Camera,
Again, excuse my (persistent) ignorance, but does one now establish the backfocus from the quark as if it did not exist?
In other words the backfocus would be measured from the end of the quark nearest the camera using the standard Zenithstar backfocus
(without flattener)?

Thanks again for your help. The Quark interface is something completely new to me.

As far as I know or remember one does not need extension tubes after the Quark because there is no specified backfocus.

5 minutes later. I checked some images and the camera goes right into the Quark 1.25" eye piece holder.

[Goose]

Thanks very much. Just to make sure I have this right then - I would have the scope (no flattener) followed by whatever extension tube length would be required to achieve focus assuming a camera were directly attached to the scope, followed by the quark and then with the camera plugged directly into the Quark? If the quark does not have a focus requirement I assume the focus would still have to be achieved at the scope end of things.
Again thanks for your help.

Jim S

[marktownley]

Quark is designed to work with a 2" diagonal which has optical path length of about 130mm. So, if you use an 80mm extension tube and rack the focuser out about 60mm you should be in the right ball park.

[Goose]

Thanks. That will be a great place to get started.