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Sandancer10

2 x Barlow Lens causing problems

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Hi all

I am having a major problem with my new 2" Barlow and trying to get it to focus with my DSLR.  I have a 2" extention tube and have tried it both ways 1, putting that into the focusser then the Barlow and finally the camera. 2, putting the Barlow in the focusser then the extention into the camera - and I still can't focus properly.  It seems there is enough back focus (I think) but not enough between the Barlow and the focusser.  Should I buy another 2" extention or will it not work anyway. 

Strangley, if I want to just view through the ep with the Barlow I get focus although not pin sharp.

At my wits end :eek:

Brenda

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Hi all

I am having a major problem with my new 2" Barlow and trying to get it to focus with my DSLR. I have a 2" extention tube and have tried it both ways 1, putting that into the focusser then the Barlow and finally the camera. 2, putting the Barlow in the focusser then the extention into the camera - and I still can't focus properly. It seems there is enough back focus (I think) but not enough between the Barlow and the focusser. Should I buy another 2" extention or will it not work anyway.

Strangley, if I want to just view through the ep with the Barlow I get focus although not pin sharp.

At my wits end :eek:

Brenda

I have similar issues, I can get focus with the r/a in place but not if I just put the Barlow and dslr into the focuser so interested to hear what the solution is, I suspect it is a series of adapters. this is with a sw 80ed pro.

Sent from my Nexus 7 using Tapatalk 4

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Barlows are useful if you need more inwards focus.

James

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No a Barlow will move the focus point OUT.

That is one of the solutions for newts that don't have enough in focus to reach focus with a dSLR.

The order should be

focuser --> extension(if needed) --> Barlow --> camera.

But you don't say what scope you have? If it's a newt then I would be surprised if you needed the extension at all. But you might...

If you have a refractor then it is almost certainly not far enough out, you can test this if you have a 2" diagonal. You can use that to increase the position of the camera relative to the focuser. The order above is correct for all scopes.

During the day I would setup in a position where I can see something a long long way away - the further the better. Start with nothing attached and add in a eyepiece and align so that you can see something a house or tree or telegraph pole etc.

Then remove the eyepiece and add in the camera and make sure it focuses, then add in the Barlow re bearing that the focus will move out. So if you are already close to fully out on the focuser you will need an extension tube for sure.

If you cannot get focus add in the extension tube and or diagonal and see what happens. If at this point you cannot find focus remember to start fully wound in and slowly turn the focuser, as you increase F ratio the image will become darker as the magnification is increased and sometimes the focus point will be quite narrow and if you tune the focuser too fast you could easily miss it.

If that fails then what I would do is undo the thumb screws that hold the camera/Barlow from the extension tube and I would start to pull out the Camera/Barlow from the focuser tube - trying really hard to keep it in line - keep pulling it out and IMO you will eventually see the image come to focus.

That will tell you how much more of an extension tube you'll need.

HTH

Cheers

Ant

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Thanks for that Ant. I'm using the kit in my signature and I spent most of yesterday afternoon doing what you suggested. It was at that point I realised I have a problem as I had tried focussing on Jupiter on the last clear night we had, Tuesday I think, and I couldn't get it into focus at all with my DSLR. I havn't tried taking it out of the focusser though so I will give that a go. I am arguing with myself whether to buy a CCD now instead and go down that route. I do want to do that at some point so I'm not sure if I sort this out I'm then giving myself another headache? The thing is that I would really like to be able to make the DSO images bigger so that I don't need to crop the photo's so much and therefore lose quality. Any ideas would be much appreciated.

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Annoyingly when I replied last night for some reason your sig wasn't showing (must have been something odd with the iPad).

My first piece of advice is to not use a Barlow for DSO imaging. It will make things bigger on the chip but it will also double your F ratio of the scope which will quadruple your exposure times. Combine that with the fact that it will also make guiding harder. In my opinion your opening yourself up to a whole world of pain.

That said if none of us did anything that was hard where would we be today?

Your scope is nice and fast and you can get some lovely results with it. There are people using exactly your scope and the results are really really nice. Yes it has a larger FOV but instead of changing it, pick targets that are a good size match for your FOV.

There are loads of galaxies and clusters that will look fantastic in your setup.

One thing you can try is to attach the Barlow (lense cell) directly to the 2" T adapter. Not all barlows have lens cells that unscrew but a lot do. If yours does, unscrew it and screw it into the T ring. This will give a reduced effect (mine is around 1.4x) but will also move the focus point out less.

A Barlow with a removable lens cell will look a little like this

Cheers Ant

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Good advice again Ant.  I just checked the Barlow and it does unscrew so I will give that a go and see if I can get it into focus.  

I know what you're saying about FOV, but of my particular favourite is the Orion Nebula and it looks quite small on the photo's I've taken.  With all of them I've had to crop quite a bit and even using Photoshop to enlarge the image in small increments it still seems to cause problems in creating a sharp decent size pic.

I know I need to do more research on my targets as at the moment I am just trying to capture the most photographed galaxies, and being disappointed with the results.  I thought if I could use a Barlow it might help with the size of the image, but I know trying to keep the image perfectly still is another whole ball game.  When I did manage to get something relatively close in focus with it (about 30 meters) I wasn't struck with the quality, but this is a learning curve and I enjoy a challenge. Who said AP was going to be easy? But, it has its own rewards and that's why I absolutely love the hobby.

Will keep you posted on my progress.

:smiley:

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M42 is around 85' x 60' so around 1 and a half degrees by a degree.

Assuming you have a 300D (I've used that camera as an example as I have one :)), the standard FOV is roughly 100 x 70', so in fairness that would seem the perfect scope/camera combination for M42.

Post up your results in the imaging section, you may find you just need some longer subs to get the outer areas. Give me a nudge when you posted them up - I miss most threads now that there are so many lol.

Cheers

Ant

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The good thing about a barlow which has a lens which unscrews is:

If you need more outward focus you can remove the lens and just use the empty barrel to give you extra sturdy length.

If you need more inwards focus, just use as it (but this will increase the magnification).

James

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Success!!  I tried unscrewing the Barlow and when I put the lens in it fell to the bottom of the focusser -ooh er, but I retreived it and thought I'll just put it part way in and bingo I managed to focus.  I wouldn't have discovered focus but for that happy accident.  Now I'm happy and can't wait to check it out when we get some clear skies.

:smiley:  :smiley:  :smiley:

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