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Brainstorm

Astrophotography (can't see a thing)

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I got my T-ring through the post and thought tonight would be a great night to try it out. Managed to get Andromeda galaxy in sight, so I put the T ring adaptor on and attached it to the camera. I tried in Live view; nothing.. I tried looking through the viewfinder; still nothing. Just pure black, the sort of thing you'd expect to see if the lens cap had been left on (it hadn't)... How am I supposed to focus on a plain black field of view?

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A friend of mine had the same problem. Except his camera was an advanced Nikon! Using a 6 inch F:10 telescope and the camera attached to the photo-adapter, he could NOT see anything through the viewfinder.

But trying to focus with the viewfinder is really not going to get you very far, anyway. The best way to focus such a setup is to look at something during the daytime that is a long ways away, and then don't change anything until you have a chance to try the setup under the stars. Then, finding the brightest star you can, take a 15-30 second shot at around ISO 800. You should see the image of the star on your preview screen. Use your magnifying tool to zoom in on the image, and see if it is focused, or not. It probably will not be, but it shouldn't be too far out of focus. Keep adjusting the focus knob just the smallest fraction of a turn one way and the other, until the viewed image is as sharp as you can make it.

Is your camera equipped with "live view" ? If so, the job becomes a bit easier, as you can switch that function on, and focus to the viewing screen. My friend uses a combination of "live view" and a computer screen to magnify the image even more!

My D-80 seems to be a lot brighter than his camera for some reason, but focusing through the viewfinder of a DSLR does NOT seem to be the easiest thing to do with just about any of them. I would LOVE to hear others input on this subject, myself.

Good luck!

Jim S.

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Jim's suggestion above is sound but in the end you can't focus really accurately by looking at an image of a star. It simply isn't possible. Your best bet is an inexpensive or DIY Bahtinov Mask (mine are from Morris Engraving). A simpler variant for starters is the Y mask which is very easy to make. They all Google productively, I think.

You train the scope first on a bright star at a similar elevation to your target then you go to your target ready focused. You can't take out the camera to find it though, which won't matter with Andromeda but is why most imagers use GoTo. You might think that taking out the camera and putting it back without touching the focus would leave you in focus. It won't!

Olly

ollypenrice's Photos

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I have used a cannon 40D on a 12" SCT. You wont see anything at all if you are too far out of focus initially.

Even after focussing you wont see anything but the brightest stars in the viewfinder and even less in live view.

Do a simple experiment during the day if you can. Focus on something like a tree of a post a long way away (NOT THE SUN), using an eyepiece. Then replace the eyepiece with the camera and work out which way and how far you need to adjust the focus to get focus with the camera. Falling back to this process will help when you are out there at night trying to work out why the hell you can see anything at all hehe.

In the evening Pick the brightest star you can see, then start adjusting the focus as required. Sometimes to start off when I cant see anything I take a 30 sec exposure, this will usnially start to show you any out of focus stars unless you are way way out.

Make a bahtinov mask. It realy helps get perfect focus every time.

regards

Edited by Technobill

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good morning

i have tried takeing photos during the day and it works well so thought i would try it at night and nothing have tried the advice below before just cant get it to work the down side i have is no live view and a canon 350d one question i have is do you use manual setting with mirror lock up as if takeing night shots of the stars or not please.

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Initialy when starting out I focused the DSLR on the moon and marked the draw tube where the focus point was, it just needed tweaking in live view to get focus, zooming in on a bright star and focusing for the tightest star.

As Olly said above I now use a homemade Y mask and focus with live view zoomed in to get the best focus possible.

I would then, with M31, up the ISO to 3200 and take a 5 sec exposures to line up M31 in the centre of the chip.

A lot easier now using Goto. Using CdC and EQMOD to perfectly align and sync bright stars around the target, then when I goto the object it is in the centre of the FOV.

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Initialy when starting out I focused the DSLR on the moon and marked the draw tube where the focus point was, it just needed tweaking in live view to get focus, zooming in on a bright star and focusing for the tightest star.

The moon makes a great target for getting your focus in the right ball park, particularly when it's not full so that you can see detail on the terminator. Then as everyone else has already suggested, fine tune on a bright star with a Bahtinov Mask.

Edited by r3i

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A friend of mine had the same problem. Except his camera was an advanced Nikon! Using a 6 inch F:10 telescope and the camera attached to the photo-adapter, he could NOT see anything through the viewfinder.

What exactly is an "advanced Nikon", and why would it differ from my Canon 7D?

Do you mean "advanced" as in modified for astrophotography?

But trying to focus with the viewfinder is really not going to get you very far, anyway. The best way to focus such a setup is to look at something during the daytime that is a long ways away, and then don't change anything until you have a chance to try the setup under the stars.

A couple of problems with this method, I don't do any astronomy from home, I always drive out to dark sky areas, away from light pollution. This would mean sitting with my setup in the middle of nowhere for hours on end waiting for the stars to become visible.

Secondly, due to my camera being a professional model, it has a magnesium body and is a lot heavier than the entry level DSLRs, the problem being that over time, the focus tube sinks into the telescope under the weight. Maybe I'd be better off buying a lightweight entry level DSLR, such as a 450D or something.

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I tried in Live view; nothing.
If it is like the Canon1000D you need to have the exposure set above 2secs or so (can't remember the exact figure, but BULB is certainly OK) to have live view at full sensitivity. You still need to be near to focus though, and to have a bright star (I can do the Synscan alignment through live view with a 4" scope - so stars of that brightness should be visible).

Ironically I find that to focus this way you need to turn the exposure right down (to a few hundredths of a sec) otherwise the stars are too bloated to be useful.

NigelM

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What exactly is an "advanced Nikon", and why would it differ from my Canon 7D?

The advanced Nikon is a hybrid DSLR but one which records video in HD RAW format - I think it's the D90 in the UK.

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I got my T-ring through the post and thought tonight would be a great night to try it out. Managed to get Andromeda galaxy in sight, so I put the T ring adaptor on and attached it to the camera. I tried in Live view; nothing.. I tried looking through the viewfinder; still nothing. Just pure black, the sort of thing you'd expect to see if the lens cap had been left on (it hadn't)... How am I supposed to focus on a plain black field of view?
Focus on a bright star.

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What exactly is an "advanced Nikon", and why would it differ from my Canon 7D?

Do you mean "advanced" as in modified for astrophotography?

A couple of problems with this method, I don't do any astronomy from home, I always drive out to dark sky areas, away from light pollution. This would mean sitting with my setup in the middle of nowhere for hours on end waiting for the stars to become visible.

Secondly, due to my camera being a professional model, it has a magnesium body and is a lot heavier than the entry level DSLRs, the problem being that over time, the focus tube sinks into the telescope under the weight. Maybe I'd be better off buying a lightweight entry level DSLR, such as a 450D or something.

Sorry, poor choice of words. By "advanced" I really meant "semi-professional" series of Nikons. I believe it is a D200 , but I am not sure. My camera is a D-80 which is a good amateur-grade , but not at the level of his camera. But for some reason or another, the viewfinder is brighter with my setup. No, his camera is not modified in any way, and the typical modification of removing the IR filter would NOT change the brightness of the viewing/focusing screen.

As for the use of the Batinov mask, I am sure that they are helpful, but I am not sure that they are totally necessary if you are very careful with your focusing technique, and check your work by using the magnification function in conjunction with your preview viewing screen. I will not argue that they do make the job easier and more certain ! Remember, however, that no matter how you check your focus, you ARE going to have to use stars as your target of focus! So whether you "wait for hours on end for the stars to become visible" or not, you will still be there when they DO ! So the argument seems to be a bit moot, to me!

Another thing you mention, the weight of the camera, is also a concern of his. His camera is fairly much larger and heavier than mine, and he does have to shift his telescope further forward and use a heavier counterweight when hooking it up to his mount. However, since he is using SCTs and I am using a dedicated telephoto lens , nieither of us have problems with weight as such causing any balance or focus shift issues. Maybe someone can suggest a focuser with better locking capabilities for your setup. It sounds like you could use something like that. Good luck.

Jim S.

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What exactly is an "advanced Nikon", and why would it differ from my Canon 7D?

Do you mean "advanced" as in modified for astrophotography?

A couple of problems with this method, I don't do any astronomy from home, I always drive out to dark sky areas, away from light pollution. This would mean sitting with my setup in the middle of nowhere for hours on end waiting for the stars to become visible.

Secondly, due to my camera being a professional model, it has a magnesium body and is a lot heavier than the entry level DSLRs, the problem being that over time, the focus tube sinks into the telescope under the weight. Maybe I'd be better off buying a lightweight entry level DSLR, such as a 450D or something.

The 450D is great as is the 1000D for AP. I think the new 1100D is going to be a winner as well.

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