Prime focusing

[harleygirl]

Tried to photograph Jupiter this evening and failed miserably> I have a Skywatcher 102 and can find and focus on many objects using eyepieces and Barlow Lens combinations. As soon as I set up the DSLR (Nikon D3000) with T-ring + 2XBarlow lens directly into the diagonal, set the camera to manual and used a remote shutter release, I got absolutely nothing - totally black exposures despite varying exposure lengths! I can't figure out what's wrong - Jupiter & 4 moons pin sharp in the eyepiece but no luck on camera - help, please????

[ronin]

You will have to refocus with the camera attached.

If you have live view use the rear screen to get Jupiter focused, then press the remote shutter release.

May also be able to put a 5x barlow on for a bigger image, this could however shove the moons off the sensor.

Oh yes, Hello.

[Tinker1947]

You will when you sort out your focusing, you will find the images quiet poor in sharpness/quality, for Planets you would be better off using a web cam.....or if your camera supports video, try 1 minutes worth then stack the video,,,,

[harleygirl]

Thanks, both . The D3000 doesn't have live view, so I'll try with the other one (D7000) as that does. I didn't want to use the 'big' camera - a bit nervous of leaving the innards exposed. I can also shoot video with the D7000, so I'll have a go on Thursday when it's sposed to be clear.

[Tinker1947]

I put a freezer bag over the camera when its left out for any length of time, they have nice zips and do a good job of keeping the dew off.....This goes for the mount hand controller as well.....

[JamesF]

Which telescope is it that you have? I can think of three 102mm Skywatcher telescopes and I'm not even sure that list is exhaustive

James

[cantab]

If the scope is on target I don't see how you'd get a totally black exposure on a bright object like Jupiter just from being out of focus. I wonder if there's not some other issue also.

[harleygirl]

Hi James F - it's a SKYMAX-102 SynScanTM AZ GOTO 102MM (4") F/1300 COMPUTERISED MAKSUTOV-CASSEGRAIN - no problems aligning and slewing to particular objects - saw lots of cool stuff but 1st time I tried some photos

Cantab: the scope was on target with Jupiter & 4 moons clearly visble in a 25mm eyepiece, then a 10mm eyepiece - I'm pretty sure it was a focusing issue, as 1 out of the 6 images did image the scope (black spot in white circle). Must admit I got a better shot on Xmas day with my 70-300mm zoom, handheld after focusing on the full moon

[JamesF]

I think you're going to struggle a bit to get an image with the DSLR, but it should be possible.

Does the visual back (the bit the diagonal fits into) have a threaded outer edge on the 102? My 127 (the next size up from yours) does, and for imaging with my 450D I have a T-ring adaptor for the camera and that screws onto the visual back. I think it's a bit more reliable than putting the camera in the diagonal. If you don't want to faff about with screwing the adaptor to the visual back and you have a T-to-1.25" adaptor you could put that in the visual back instead of the diagonal.

When you have an eyepiece in the scope and you focus it (specifically for this sort of scope) what you're doing is moving the point at which the image is focussed into the correct position for the eyepiece. The point at which the image from the telescope is in focus is called the focal plane. If you then replace the eyepiece with a camera it will be a long way out because to be in focus the camera needs the focal plane to be at the same place as the camera sensor and for an eyepiece it may well be inside the top of the diagonal. In my EOS camera, that's 44mm behind the lens mounting flange. I imagine it will be similar for your Nikon. If you're too far out of focus the image is so faint that you might not be able to see it at all.

What I'd be tempted to do is to get the image in focus with an eyepiece using the diagonal, then remove the diagonal and eyepiece altogether and put the camera in the visual back, then take a photo, see how well it's focused, tweak the focus on the scope, take another and so on until you get it in focus. This is much easier to do with live view or with a Canon that's supported by something like AstroPhotography Tool, but I don't think the D3000 has live view so you're stuck with doing it the hard way. I'm guessing that with the T-adaptor in place, the focal plane will be in roughly the right position for the camera without the diagonal when an eyepiece is in focus with it.

James

[harleygirl]

Thanks, James, that makes complete sense and I'll try that

[JamesF]

Thanks, James, that makes complete sense and I'll try that

I'm pleased you think it does. I wasn't sure if it was at all clear what I meant

James

[Erquy]

Hii

I have exactly the same telescope and i have been facing the same issue: yes this a focus issue as when you change from ep to camera, you need to change a lot the focus to get it apparent. Even more with a barlow. Her is the way i proceed:

1) get it in the middle with 10mm ep. Make sure that the tescope follows well jupiter (when adjusting finish with up and right arrows, or down/left, not opposites). Change to camera (i have a canon eos 1100d with liveview) at prime focus (not through the diagonal) I use movrec to see live (not sure it support nikon) on my laptop and i set very high iso/long time and then you shall see the wide compltely unfocused jupiter (if low iso, you may simply not see it at all as too much unfocused. Focus. Adjust to get jupiter right in the middle. Then add the barlow. Keep highest iso (again if low iso you may not see it at all). Ajust focus. Then decrease the iso to get the color and details and further adjust focus

I am also in start up phase and you can find my attempts in my gallery (the best on jupiter is my 3 rd attempt, need to work the focus and camera setting and the avi treatment in registrax, but i am progressing. As mentioned above, a webcam is most likely better suited.

Hope you will managed

[ArmyAirForce]

Make sure that there isn't any flex in the mount/scope, otherwise the weight of the DSLR may droop the scope enough to loose the target from the frame. A DSLR is a great deal heavier than an eyepiece.

[Erquy]

Indeed. And with the barlow extension, the torque is even higher. With my canoneos 1100d, it is fine, even withe balow but i guess some 50or 100 grs more, it won t make it. Once using the diagonal + barlow, it could not manage to hold, but it was -12C and i think it makes it ever more sensitive at such low temp.