Achieving focus on a (200) pds newtonian using a DSLR and 0.9x coma

[UKJay1971]

Long winded title - basically I am in the situation where my QHY camera has gone back to China for repair and so I am back using my DSLR. I tried setting up last night on my 200pds but couldn't find focus using my DSLR and coma corrector. I was wondering if anyone can give me some clues where it is - I expect it will be very close to the inner focal extreme of the focus tube as that is what pds scopes aim to do. I have no distant objects to work on in daylight and, of course, the one time I could do with the moon, it's two weeks away from being useful.

I have removed all elements from the focal tube other than the basic two screw locking collar and am slotting my camera and coma corrector into the tube.

[PeterCPC]

Bahtinov mask?

Peter

[UKJay1971]

I couldn't even find a star field! I lost patience with extension tubes which I don't think I need - trials of setting up an unfamiliar set-up in the dark

[tooth_dr]

A photo will be helpful. There is no reason why you shouldn’t be able to get focus 

[UKJay1971]

Hi - sorry, I'm not being clear. I am an experienced imager but haven't used my DSLR on this scope. Under time pressure I couldn't find focus quickly so I am just looking for advice where about roughly focus in on a 200PDS - does it need an extention tube or not? Is focus at the innermost travel of the focuser or outermost. Using liveview on a DSLR is a nightmare when compared to the luxury of a CMOS cooled camera on Sharpcap. I can figure it out myself but just thought, if someone could quickly help, then I'd ask.

[tooth_dr]

6 hours ago, UKJay1971 said:

Hi - sorry, I'm not being clear. I am an experienced imager but haven't used my DSLR on this scope. Under time pressure I couldn't find focus quickly so I am just looking for advice where about roughly focus in on a 200PDS - does it need an extention tube or not? Is focus at the innermost travel of the focuser or outermost. Using liveview on a DSLR is a nightmare when compared to the luxury of a CMOS cooled camera on Sharpcap. I can figure it out myself but just thought, if someone could quickly help, then I'd ask.

Jay, it'll be right in at the innermost travel of the focuser if it's anything like my 250 and 300.  Why don't you plug you camera into the USB and use liveview on the PC?

[UKJay1971]

Thanks

[tooth_dr]

6 minutes ago, UKJay1971 said:

Thanks

No bother. Hope you get sorted. 

[wimvb]

With my 150PDS and Baader cc, it's about 10 mm out. Since your cc is reducing, my guess is that it will be (almost) all the way in. I've also found that if you increase the cc to sensor distance past the optimum 55 mm, focus moves further out. I saw this when the distance to my asi camera was off. (I have no idea what this does to star shapes in the corners.) But if you can't achieve focus, you can always try adding a mm or so between cc and camera.

Again, my experience is with a Baader non-reducing cc on a sw 150PDS.

[UKJay1971]

2 hours ago, wimvb said:

With my 150PDS and Baader cc, it's about 10 mm out. Since your cc is reducing, my guess is that it will be (almost) all the way in. I've also found that if you increase the cc to sensor distance past the optimum 55 mm, focus moves further out. I saw this when the distance to my asi camera was off. (I have no idea what this does to star shapes in the corners.) But if you can't achieve focus, you can always try adding a mm or so between cc and camera.

Again, my experience is with a Baader non-reducing cc on a sw 150PDS.

Good idea - I have some spacers I can use

[UKJay1971]

Further than I thought!

[Adam J]

What was up with the QHY163 out of interest?

[UKJay1971]

The heated sensor window wasn’t working. Can’t wait to get it back - it’s a great camera

[Adam J]

On 12/9/2017 at 06:36, UKJay1971 said:

The heated sensor window wasn’t working. Can’t wait to get it back - it’s a great camera

Glad to hear it, would be interested to hear an account of your experience of returning the camera to QHY any costs and did you send it via a shop / which one. I am mulling getting one but I am nervous about them being in china. So if you could once you get it back then I will be grateful. I suspect there is nothing for me to be worried about mind you. 

[UKJay1971]

On 12/11/2017 at 10:59, Adam J said:

Glad to hear it, would be interested to hear an account of your experience of returning the camera to QHY any costs and did you send it via a shop / which one. I am mulling getting one but I am nervous about them being in china. So if you could once you get it back then I will be grateful. I suspect there is nothing for me to be worried about mind you. 

Sure - I got it from Bernard at Modern Astronomy and he has taken care of the return. This is after the aftersales team in China had FedExed me a spare part for free (had to pay like £4 import duty) just to see if that would work.