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Pete Presland

Lunt 50 focus issues resolved (sort of)

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Finally getting somewhere with the focus issues with the Lunt 50mm. Using the ASI 120mm focus is pretty easy to get by removing the nosepiece from the camera and the eyepiece holder from the B600 diagonal. Then the camera screws directly in to the diagonal. the diagonal is then withdrawn from the focuser approx 10mm

post-5271-0-08842000-1440365981_thumb.jp

It is slightly trickier when trying to increase the image scale. When the x2.5 Powermate is fitted for some reason I am unable to achieve focus with it where the eyepiece would be. I am though able to achieve it if I use an extension (empty barlow) and the Powermate between the diagonal and focuser. Even this is only possible only if I withdraw the tubes a little from each other approx180mm from focuser to diagonal.

Unfortunately due to the sag this gives horrible newtons rings, but at least its a start.

post-5271-0-33338300-1440366016_thumb.jp

I can not help thinking a scope that is marketed with a filter (B600) which is aimed at imagers ought to be set up better for that purpose. It doesn't look like the DMK21 is going to be usable with the current set up.

Obviously these are just my own personal opinions and would be happy to here any others on the subject.

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Hello Pete,

Thanks for the description and photos. Good to hear you have the ASI 120MM working with the Lunt 50/B600.

I would be interested to hear if anyone has success with the DMK21 - I haven't got into imaging with my Lunt 50 yet, so it would be helpful to know which cameras work with it.

Go well!

Jeremy

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Another update on the Lunt focus issues, especially with DMK21au618. Finally managed to get the DMK21 focused with the Powermate. Approximately 165mm distance was needed to gain focus, as shown below.

post-5271-0-66183800-1442001644_thumb.jp

Today I did an experiment with a couple of thick elastic band and no nosepiece on the camera or adapter on the diagonal. I managed to get focus fairly easy with focuser/diagonal out around a combined 40mm.

With this in mind I have ordered a very short adapter  http://www.ebay.co.uk/itm/321757913944?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT it should arrive early October all the way from China. I just need to shorten the DMK nosepiece as well.

I am hoping that because I have had the focuser out 40mm then it should focus comfortably with this set up.

post-5271-0-26326800-1442001670_thumb.jp

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Another update on the Lunt 50 focus issues. With some recent experiment's, I figured I could use a shallow M42 adapter and get focus with the DMK21au618. so I bought this adapter from a well known website http://www.ebay.co.uk/itm/New-M42-to-1-25-1-25-inch-Adaptor-anodized-aluminum-Telescope-Adapter/321757913944?_trksid=p3693.c100102.m2452&_trkparms=ao%3D1%26asc%3D20140212121249%26meid%3D21c7d84ba9df46639f10ab588419dd74%26pid%3D100102%26 The quality is pretty good the brass compression ring could be better, but it functions fine.

The one on the left is the Lunt supplied adapter 30mm deep, the one on the right is 18mm deep.

post-5271-0-42444000-1442772917_thumb.jp

Once attached focus was easily achievable. The last job is to replace the cut down camera nosepiece which has an undercut and no flange on it, with a straight flanged version. As the undercut and lack of flange is not allowing the camera to sit square

post-5271-0-02269900-1442772886_thumb.jp

Hopefully this will be helpful info to other Lunt users in the future.

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I also have the Lunt LS50 and an ASI120MM camera. Following reading this thread, I decided to do some experimenting of my own. I started off following your lead, and used an extension in the focusser, then x2 barlow, then the diagonal and got focus ok at about 170mm distance. As I didn't have any suitable extensions, I ended up using an adapter from a vacuum cleaner!

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I then decided I would try the camera at native FL, but mounted in the 1.25in eyepiece holder.  Knowing I had to reduce the length of the optical train somewhere, I took the 1.25in nosepiece off the front of the diagonal, and used the M42 threaded part of a T-ring to thread the diagonal directly onto the thread on the focusser. The camera was screwed to the thread on the end of the 1.25in eyepiece holder. I was able to achieve focus with no slop or sag in the system.

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After that, I wondered if my x2 TAL barlow would fit in the traditional position after the diagonal, with the camera in the barlow and focus. It did, although the camera nosepiece was too long and bottomed out in the barlow. For testing, I took the nosepiece off again, and used elastic bands to hold the camera on the end of the barlow.

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So, I knew I could get focus now, but what about tilt? Would that push the camera too far back to focus?

I found a small piece of wood, and cut it into a cube about 5mm on each side. This was popped into the front face of the camera, jacking up one side against the barlow. Yes, I could still focus, and the Newton Rings had gone too!

So armed with this knowledge, I need to fine tune my spacings, make a tilt adapter and buy another T-ring so I don't have to keep pinching the one from my OAG!

Overall, a sucessful Sunday of experimentation.
 

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I recently purchased a Lunt 50/B600 and to that I'm slightly disappointed at the measures required to gain focus while using my DMK21AU618, has anyone seen a statement from Lunt on focus or the lack of it. 

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I recently purchased a Lunt 50/B600 and to that I'm slightly disappointed at the measures required to gain focus while using my DMK21AU618, has anyone seen a statement from Lunt on focus or the lack of it.

I emailed lunt regarding the focus problems and the fact their scope which retails at the best part of £1,000, has a focuser that at best is poor, including a screw that constantly comes loose. So far not even the courtesy of a reply.

Sent from my GT-N7100 using Tapatalk

Edited by bunnygod1
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I know this is now a bit of a "blast from the past", but having just been in receipt
of a NEW Lunt LS50THa, this has pointed me more rapidly in the right direction! :)

Visually, I discovered that my Baader Hyperions "work" fine within the focus limits.
(Yeah, yeah - I know. But I suspect they are still good enough at f/7. lol) I am now
resigned to the fact that I am limited (by eyesight?) as a visual Astronomer anyway.

Adapters are always difficult to buy with confidence, but as a VIDEO Astronomer,
I mention the following T2 to C/CS Adapter which enabled me to *at least test* 
the imaging capabilities with my current Watec (video) Cameras:

http://www.teleskop-express.de/shop/product_info.php/info/p2838_Adaptor-T2-female-on-C-Mount-male---only-4mm-length.html

I suspect this would work with DMK cameras? (It only adds 4mm to optical path)!
N.B. I "pad out" the nose of the Watec Camera with 3x5mm C-thread extenders...

Today, I 'm about to try out my ASI 120MC (colour). Who knew I needed B&W? :D
If the "Sun Gods" permit, I might just try out Eyepiece Projection with a Hyperion... 

Edited by Macavity
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That focuser looks identical to the one on the Altair 60mm guide scope and I'm having trouble with it just using a Loadstar, took it apart and it's a pretty poor design not really up to the abuse Petes thrown at it :)

Dave

Edited by Davey-T
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You certainly need a sunny day (OK so far!) and a driven equatorial.
An "Astronomers Life" is ever about thread sizes and compatibilities?
In favour of Lunt, it is at least, fairly "modular" - So you can fiddle... :p

Forced to sell a PST prior to investigation, so thought I go different! :D

 

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That is certainly a thin adapter,  I will take a closer look when I get home. My solar imaging equipment is languishing in the back of the car, as the promised clear skies haven't got to biggleswade. It's raining as I type!

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2 hours ago, Davey-T said:

That focuser looks identical to the one on the Altair 60mm guide scope and I'm having trouble with it just using a Loadstar, took it apart and it's a pretty poor design not really up to the abuse Petes thrown at it :)

Dave

The replacement that finally arrived wasn't much better either,  but I guess have got use to the idiosyncratic ways of working with it. I will upgrade though is something better is produced. 

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On 2/23/2016 at 15:46, bunnygod1 said:

I thought one was being developed.

 

On 2/23/2016 at 14:14, Davey-T said:

What happened to the Moonlight Focuser plan ?

Dave

 

Yep that was me folks.  I can update you in as far as this:  I have sent off my focuser to Ron at Moonlite, it was measured up and after some difficulties Ron said he thought he had a solution to getting a moonlite version designed.  I have lost contact with him sadly and no longer seem to get email replies, which seems uncharacteristic as we seemed to have a steady thread of conversation over the first 6 months but then nothing :( 

 

I am personally a bit concerned as to if he is actually well and okay ?  Does anyone know about this ?  

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