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MikeWilson

Will a QHY5 work with the Starlight Express OAG?

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As the title says :-)

Hello everyone,

I'm just looking at ways to reduce weight and flex and to simplify my setup. I'm strongly thinking about upgrading my 2"x4 BrightStar filter wheel to something that blocks out ambient light a little better (this has only been a problem when using a super bright EL panel for flats). The SX filter wheel looks perfect for the job.

Now SX also have an OAG that works with the filter wheel. I have a QHY5 though and I'm wondering if this camera works with that OAG. If it does, I suspect that I will have a solid and reliable system for guiding my 8" CF Quattro.

Any ideas? I can't find anything on Google and I contacted Martin at FLO who suggested posting here...

I'm also very interested in hearing from people with first hand experience of either the SX filter wheel or the SX OAG.

All the best,

Mike

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I'm also very interested in hearing from people with first hand experience of either the SX filter wheel or the SX OAG.

I use an SX filter wheel and the SX OAG.

I have had the filter wheel for over a year. It is loaded with Astronomik LRGB plus Ha, OIII and SII 1.25" filters. It works fine. I use it from within Maxim. Can't really say anymore about it - its a filter wheel and it works.

I am a recent user of the SX OAG. It is made to carry the Lodestar camera which uses a C thread to connect to the OAG. If you are intending to use a QHY5 then you will need a C to T thread adaptor - preferably just a ring as you don't really want to start adding adaptors to your main camera to achieve focus.

As for usage then it is one of the best moves I made I think. I have used a number of guiding setups in the years I have been messing with imaging and have always suffered with drift. Now I have none - I could stack my subs now without registration.

For example ...

oagalign.jpg

The SX setup, filter wheel and OAG WITH the Lodestar is very good. However I would really check out focusing distances with any adaptor before you purchase it to ensure you can get both your main and guide camera parfocal without yards of adaptors. Furthermore I "think" the SX OAG will possibly not illuminate the whole of the QHY5 CCD. Not sure on that - more questions - speak to a dealer.

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Less weight and dimensions would give a filter drawer from TS, although if you change filter requently it may be less handy than a wheel.

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@riklaunim: Thanks for the suggestion. I'm intrigued and might go this route although I don't expect much saving in weight or complexity compared to say, a manual Brightstar filter wheel.

@Komet: That's remarkable. Thank you for sharing your results. I think that if you can get it working - OAG is certainly the way to go for life. You've got some incredible results - I've always had a tiny bit of drift (solved with registering but it makes the stars very very slightly elongated).

My main concern with using the QHY5 is getting the spacing correct. Especially as I have a coma corrector at the end of the optical train.

So:

Coma Corrector ---> Filter Wheel (inc filter) ---> t-thread extension ---> CCD.

If I had the SX OAG, crucially I need to find out how much back focus it would introduce from the coma corrector.

Do you have any pictures of your SX filter wheel and OAG installed?

Thanks again for sharing.

All the best,

Mike

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My main concern with using the QHY5 is getting the spacing correct. Especially as I have a coma corrector at the end of the optical train.

So:

Coma Corrector ---> Filter Wheel (inc filter) ---> t-thread extension ---> CCD.

If I had the SX OAG, crucially I need to find out how much back focus it would introduce from the coma corrector.

Do you have any pictures of your SX filter wheel and OAG installed?

A number of thoughts. What camera are you going to be using with this? If its a DSLR then you may well need 2" filters for a start to reduce vignetting. I know when I tried a 1000D Canon I got quite pronounced vignetting when it was peering through the filter wheel. I may be wrong though - DSLR users will be a far better sector to ask on that score (didn't like DSLR imaging I'm afraid). If it is a DSLR and you have to use an extension tube then of course the thickness of the filter wheel and any OAG can be removed from the length of that tube. Also it would be better in front of the wheel as otherwise you would be moving the CCD away from the filters making any vignetting problem worse!

This makes fitting any OAG easier as you won't need long extension tubes fitted to the OAG mounting to get parfocal with the main camera. As long as the distance to both chips is the same from say the corrector then it should work.

This is my setup below. I use an IMG2Pro CCD (which is very similar to an SX H9) so its CCD surface is roughly where an SC CCD surface should be so the Lodestar is will within the focusing range.

The Lodestar is focused by moving the mount it is screwed to up and down a square tube and then located in place with a small grub screw. I have however added a C extension tube to it so the mount is further down the pickoff tube. I didn't need to do this though.

The long bolt with the gnurled plastic head is used to adjust the pick off mirror in the OAG.

To attach a QHY5 you will need an adaptor - a C female to T male if such a thing exists.

cam1.jpg

cam2.jpg

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Thanks Mick for the detailed explanation and images.

I'm using a QHY8L, which is currently mounted to a Brightstar filter wheel:

IMG_8245.jpg

You're using a Mak-Newt which essentially has no need for a coma corrector. As I'm using a coma corrector, I'm concerned that the spacing between the Baader MPCC's glass and the QHY5's CCD may not be able to reach the rather exact 55mm +/- 1mm required. It's possible that since we're just guiding, that some incorrect spacing might not matter too much?

I am indeed using 2" filters.

This makes fitting any OAG easier as you won't need long extension tubes fitted to the OAG mounting to get parfocal with the main camera. As long as the distance to both chips is the same from say the corrector then it should work.

I've contacted Starlight Xpress regarding the spacing, just to ask for some measurements but they haven't responded yet.

The Lodestar is focused by moving the mount it is screwed to up and down a square tube and then located in place with a small grub screw. I have however added a C extension tube to it so the mount is further down the pickoff tube. I didn't need to do this though.

How much focusing adjustment movement is possible in that OAG focusing mechanism?

To attach a QHY5 you will need an adaptor - a C female to T male if such a thing exists.

Another good point!

All the best,

Mike

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You're using a Mak-Newt which essentially has no need for a coma corrector. As I'm using a coma corrector, I'm concerned that the spacing between the Baader MPCC's glass and the QHY5's CCD may not be able to reach the rather exact 55mm +/- 1mm required. It's possible that since we're just guiding, that some incorrect spacing might not matter too much?

The imaging and guiding cameras will need to be parfocal anyway so the main issue is the imaging camera's sensor to MPCC distance. On the SX filter wheel with their OAG installed, the backfocus with 'T' adapters is 42mm so you will need a sensor to mounting face distance on the imaging camera and guide camera of no more than 13.0 mm +/- 1.0mm.

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The imaging and guiding cameras will need to be parfocal anyway so the main issue is the imaging camera's sensor to MPCC distance. On the SX filter wheel with their OAG installed, the backfocus with 'T' adapters is 42mm so you will need a sensor to mounting face distance on the imaging camera and guide camera of no more than 13.0 mm +/- 1.0mm.

Thanks Steve!

I think that can be accomplished (as long as the C female to T male adapter isn't very big. I think the distance between the threads of the QHY5 and the sensor is about 10mm, so there's not a lot to play with.

On the SX filter wheel with their OAG installed, the backfocus with 'T' adapters is 42mm

Just to clarify, does this mean that the backfocus through the SX filter wheel and up the OAG is also 42mm?

All the best,

Mike

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How much focusing adjustment movement is possible in that OAG focusing mechanism?

I would think (without disturbing mine) there is about 10mm of movement

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Just to clarify, does this mean that the backfocus through the SX filter wheel and up the OAG is also 42mm?

Not necessarily - because there is no 'fixed point of reference' for the turret's position.

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Thanks all,

The SX solution is to buy the lot, wheel, camera and OAG. I'm now looking at the TS OAG with the SX filter wheel... It's a shame that there's no wiki to compare reviews and tech specs. Maybe I'll make one.

All the best,

Mike

---

- Sent from my mobile using TapaTalk (so please excuse bad grammar & spelling!) :-)

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No good asking me Mikey - SX H9, SX FW, SX OAG :):D

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I use a SXH9, SX filter wheel, SX OAG and a DMK21.

So there is a chance that it will, but I can't guarantee that it will.

Ant

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Thanks chaps!

The SX system does look good but the whole lot is rather expensive.

The DMK21 has a C-thread which helps. If a QHY5 + T-to-C adapter can be done with the same amount of back focus then I think it might work.

Why SX couldn't use t-threads or supply t-adapters for the OAG, I don't know!

I'm considering the SX filter wheel with a thin TS OAG. That looks like it could work.

All the best,

Mike

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But they do, they have rings for T thread (both male and female versions) , SCT and Takahashi thread.

Here's one for example : Robtics | Starlight Xpress female T-draad adapter voor filterwiel of OAG

-- Hans

Hi Hans,

That's interesting thanks for the heads up! Although there's no data on thickness and I'm still waiting on SX Express to get back to me (honestly - I've been waiting & chasing weeks for a reply). Plus, it's 5 weeks before SX Express actually have any stock too - I wonder why so many people rate them so highly when their replies and delivery speed is lacking!

Does anyone else do a decent electric filter wheel and OAG combination for a Newtonian?

All the best,

Mike

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