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Can't bring DMK41 to focus.


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Been trying all day (between clouds) to get a sharp focus with the DMK41. It seems I can go either side of the focus position without obtaining a crisp image. I have tried the DMK with my Lunt 2" solar wedge and my Lunt LS60T with no success. I have tried a variety of 2"-1.25 adaptors to see if I can get the ccd closer to the focal point and even tried ising a short extender to move it out, but still no luck. Is this still a normal problem.

I have read that a low profile C mount adapter might help, but FLO is out of stock. Anything else I can try besides filing the hip of the DMK nosepiece and shortening it?

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Just to be clear - you do mention in your post that you can go either side of focus. I take it you mean that you approach focus, see the image improving then it gets worse again. If this is the case then different adapters aren't likely to solve it.

I have a Lunt 60 with diagonal and a DMk (618 chip) and have no trouble. There is plenty of room for focus either side. It is on scopes like the LS35T where in focus can be quite tight.

Ha viewing and imaging is quite dependent on lack of cloud for good detail. Is "between clouds" clear sky or there still being some wispy stuff present?

How was it holding up visually?

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I started today with the Omni 120mm XLT and the Lunt solar wedge. I uwanted to see what it was like for white light first before I mod it for the PST. I used a Baader clickstop zoom and although the focuser is not the best in the world, I did get nice clear views of the surface. I could not see much in the way of granulation, but the large sunspot coming into view near the limb was quite clear. The cloud was broken and whispy so the clear views were short lived. This is the first time using bothe the scope and wedge, so I know I need practice with both.

When I put in the DMK I had to refocus and could not find the same clarity as I was getting visually. Again, the cloud made it very difficult to focus and I never actually got time to take any frames. I kept trying to tweek the focus between the clouds hoping to hit the correct spot, but could not find it. I don't have an arsenal of barlows but tried the one that came with the Baader zoom. I still could not get it right.

Frustrated, I changed to the LS60T, and now you have mentoned it, I forgot to extend the drawtube a bit before I put in the DMK. I will try again tomorrow if the sun comes out to play.

This imaging lark isn't as easy as it appears. :smiley:

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I started today with the Omni 120mm XLT and the Lunt solar wedge. I uwanted to see what it was like for white light first before I mod it for the PST. I used a Baader clickstop zoom and although the focuser is not the best in the world, I did get nice clear views of the surface. I could not see much in the way of granulation, but the large sunspot coming into view near the limb was quite clear. The cloud was broken and whispy so the clear views were short lived. This is the first time using bothe the scope and wedge, so I know I need practice with both.

When I put in the DMK I had to refocus and could not find the same clarity as I was getting visually. Again, the cloud made it very difficult to focus and I never actually got time to take any frames. I kept trying to tweek the focus between the clouds hoping to hit the correct spot, but could not find it. I don't have an arsenal of barlows but tried the one that came with the Baader zoom. I still could not get it right.

Frustrated, I changed to the LS60T, and now you have mentoned it, I forgot to extend the drawtube a bit before I put in the DMK. I will try again tomorrow if the sun comes out to play.

This imaging lark isn't as easy as it appears. :smiley:

If it was easy, everyone would be doing it. Don't discourage. If it wasn't for the 10 hours flight seperating us, I would have gladly come over and show you :-)

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Hi Allan,

I use a DMK41 on my Lunt 60 and focus is not a problem, but you will need to extend the draw tube a little way. I would say distance from the back of the scope to edge of the diagonal is around 60mm for my DMK41, but it depends very much on how closely your DMK sits in the holder.

To focus, I usually start off with 50% magnification on the laptop screen so I can see as wide a field as possible. I then increase the magnification to around 100-125% and fine focus. Usually and unless seeing is superb, this looks a little fuzzy, but I try the best I can and then hope for the best. Usually I take around 1500 frames and stack about 300 - 500 depending on quality. This usually gets a fairly sharp picture. I have to let go of the focus knob after each adjustment and let the scope settle, there is too much hand vibration otherwise.

It is a lot of trial and error, try to keep the gain below 350, the frame rate as high as possible and go for around 80-90% on the histogram.

Generally, barlows only make the focus problem worse, unless you don't have enough inwards focus.

I hope this helps?

Robin

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If it was easy, everyone would be doing it. Don't discourage. If it wasn't for the 10 hours flight seperating us, I would have gladly come over and show you :-)

don't let a little thing like that stop you. :grin:

Robin; I have been looking for a way to zoom in with ICC, but never thought of actually just zooming the laptop screen. Doh!

I shot a few more avi's today and the results look better. We'll see how they stack. There was some beautiful proms this afternoon and I hope I've got something to show for my efforts. I was using the LS60T and tried a reducer screwed onto the end of the nosepiece to get a full disk, but deffinately did not have enough in focus for that to happen. Maybe I still need a shorter profile nosepiece on the DMK.

Still, it was a better day, and I got time to play. I found that turning up the exposure let me focus easier on the proms, but then I turned the exposure down a bit for the capture. Hope this works.

One thing that confuses me with ICC is saving the avi's. I can't find a way to automatically save the files when I stop the capture. I have to keep manually saving and renaming them so that I can take the next one without overwriting the one I have just taken. I would have thought the programme would have autosaved each avi when you press the stop button. Am I missing something.

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don't let a little thing like that stop you. :grin:

Robin; I have been looking for a way to zoom in with ICC, but never thought of actually just zooming the laptop screen. Doh!

I shot a few more avi's today and the results look better. We'll see how they stack. There was some beautiful proms this afternoon and I hope I've got something to show for my efforts. I was using the LS60T and tried a reducer screwed onto the end of the nosepiece to get a full disk, but deffinately did not have enough in focus for that to happen. Maybe I still need a shorter profile nosepiece on the DMK.

Still, it was a better day, and I got time to play. I found that turning up the exposure let me focus easier on the proms, but then I turned the exposure down a bit for the capture. Hope this works.

One thing that confuses me with ICC is saving the avi's. I can't find a way to automatically save the files when I stop the capture. I have to keep manually saving and renaming them so that I can take the next one without overwriting the one I have just taken. I would have thought the programme would have autosaved each avi when you press the stop button. Am I missing something.

It does have an autosaved and a auto-naming function. You certainly mised it. You need to set it up everytime, you open the ICC.

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Hi Allan,

In ICC, I vary the zoom on the capture window, not the whole screen. It is at the top and usually starts at 100%. I reduce this until the window scroll bars disappear.

As regards the save, something seems to be going wrong. I open the capture window, create a directory and then gve t a file name. When you press the record, it records and when you press stop it stops. If you press record again, it asks if you want to over-write, I select no, and then change the file name, like Sun-dd-mm-yy-0x5-1, -2, -1-prom etc.

To get the dll disc, I use a 0.5x focal reducer on a cut down nosepiece as they are threaded for 1.25" filters all the way down. With only a few millimetres of barrel my 0.5x FR gives about 0.8x, just big enough to get the full disc. I posted pics on here in another thread and will look out the link for you.

I did try a 0.5x FR on a standard nosepiece and that would focus as well, but the sun was a little too small. Perhaps if you post some photos of your setup with as close to focus as you can, I could compare them to mine?

Robn

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Robin, the method you use to save seems to be the same as mine. Very long winded, and when you are cloud dodging there is no time to mess about. I'll examine the menu's and see if I can find the autosave feature that Fogbound mentioned.

The nosepiece on my DMK has a sort of hip at near the top with a spacer above it. Without this i could drop down another 5mm. I will get another lower profile nosepiece soon and try that. I'm not sure cutting my DMK nosepiece will get me any closer.

Do I need to get the reducer nearer to the ccd, or the nosepiece lower down in the tube?

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Hi Allan,

I am not aware of an 'auto-save' function, I just set mine up at the start of the imaging session and then when it is right hit the 'record' button. The next time I hit record, I say no to over-write and set a new new name. If you don't like ICC, you can use any other imaging capture program that supports these camera, there are quite a few to choose from, both free and paid for.

The magnification or reduction ratio is dependent on the distance from the CCD to the FR or Barlow. The distance from FR or Barlow to the objective lens (scope) just changes the focus.

I hope this helps. Still trying to proceed my pics from this weekend, mostly away walking in Scotland.

Robin

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Robin, the method you use to save seems to be the same as mine. Very long winded, and when you are cloud dodging there is no time to mess about. I'll examine the menu's and see if I can find the autosave feature that Fogbound mentioned.

The nosepiece on my DMK has a sort of hip at near the top with a spacer above it. Without this i could drop down another 5mm. I will get another lower profile nosepiece soon and try that. I'm not sure cutting my DMK nosepiece will get me any closer.

Do I need to get the reducer nearer to the ccd, or the nosepiece lower down in the tube?

I will get you a screenshot when I get home.

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Thanks Fogboundturtle, but I have it sorted. Full auto saving with no delay. I even worked out how to do a fully automated long exposure sequence.

Thanks for the pointer.

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The magnification or reduction ratio is dependent on the distance from the CCD to the FR or Barlow. The distance from FR or Barlow to the objective lens (scope) just changes the focus.

Robin

I thought that would be the case. I turned my focus right out to all the way in. The image was getting smaller as I wound in, but then I ran out of movement. It seemed that I had to have more in focus travel to bring the image into focus. i'll keep trying till I find the answer.

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