29 replies to this topic

[Luckyhead11]

I just got my Sky-Watcher Evostar 72ED, and I connected my camera (Nikon D3500) to the end with a t-ring and a adapter. I can't seem to focus it on anything at all, not houses far away, or the moon. I couldn't even find the moon because of how unfocused it is. I'll try again with the moon tonight but I'm still wondering why I can't focus on anything at all.

 

(And yes I did turn the knobs on the sides to make the camera closer/farther from the lens, that made a very little difference)

[gnowellsct]

And post a pic of the setup.

[Luckyhead11]

Could this work?: https://www.amazon.c.../dp/B0BDV5652K/

[ButterFly]

You probably need extension tubes.  Try with an ordinary mirror diagonal in place in the mean time.  2" mirror diagonals add on the order of 100mm of extension.

 

The focal length is about 420mm on that scope, so measure 420 mm from the objective to the back of the scope.  That's where the objective focuses things from infinity.  That's where the camera sensor needs to be.  If you also wrap a white shopping bag onto the focuser, you will also be able to form an image on it, if the focuser can reach that far out.  You can estimate how much extension you need by pointing at the moon, then backing your hand away from the focuser until you see an image of the moon on your hand.

[gcardona]

See this topic.

[Luckyhead11]

You probably need extension tubes.  Try with an ordinary mirror diagonal in place in the mean time.  2" mirror diagonals add on the order of 100mm of extension.

 

The focal length is about 420mm on that scope, so measure 420 mm from the objective to the back of the scope.  That's where the objective focuses things from infinity.  That's where the camera sensor needs to be.  If you also wrap a white shopping bag onto the focuser, you will also be able to form an image on it, if the focuser can reach that far out.  You can estimate how much extension you need by pointing at the moon, then backing your hand away from the focuser until you see an image of the moon on your hand.

Those are extension tubes, the ones I linked.

[Sky King]

This thread has the info you need. The manual shows using a flattener, but you just want to focus your dslr with spacers for now. 

[Luckyhead11]

So will the things I linked work or not?

[BlueMoon]

So will the things I linked work or not?

They will work but you'll have vignetting due to the 1.25" diameter. A 2" diameter extension would work better. You need about 130mm of back focus to reach infinity. Another approach would be to use a 2" diagonal with a 2" extension tube to reach the 130mm needed.

 

I have a 72ED, the 0.85 focal reducer and DSLR. Before I bought the reducer I used this combination: (Left to right) Stellarvue 2" diagonal, Tele Vue 2" x 2" extension, Canon EOS DSLR to 2" nosepiece adapter.

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Edited by BlueMoon, 14 April 2024 - 04:58 PM.

[revans]

I just got my Sky-Watcher Evostar 72ED, and I connected my camera (Nikon D3500) to the end with a t-ring and a adapter. I can't seem to focus it on anything at all, not houses far away, or the moon. I couldn't even find the moon because of how unfocused it is. I'll try again with the moon tonight but I'm still wondering why I can't focus on anything at all.

 

(And yes I did turn the knobs on the sides to make the camera closer/farther from the lens, that made a very little difference)

You probably need 55mm of backfocus distance between telescope and camera.  One thing you can do is just put an eyepiece, say a 24, 25 or 26mm, in place of the camera and try to focus.  There isn't much difference between where the eyepiece will focus and where the camera will focus.  It is easier to find your focus point using an eyepiece and I find it at least gives me a ballpark distance to work with.  Sometimes I have to pull the eyepiece out of the receptacle while looking for focus and back away until I see focus achieved.  It will give you an idea of how much back space you need.

 

Rick

[ButterFly]

The focuser has M54 threads on it.  Get an M54 to M48 adapter, then M48 extension tubes.  Covert to M42 at the last step.  Ideally, you would want M54 extension tubes, but they're all short and expensive on Amazon.

[Luckyhead11]

My current setup is this:

 

Focuser -> https://www.amazon.c...yepiece-Adapter -> https://www.amazon.c...tible-Eyepieces -> Nikon D3500

 

What would It look like with your recommendations?

[Luckyhead11]

And post a pic of the setup.

Here they are, sorry for the low quality... I had to put them through a quality reducer so that CN would accept them :/

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[BlueMoon]

Unfortunately the links you provided don't work and give "Sorry. We couldn't find that page".

 

Here's the setup using the parts I posted earlier. The 2" diagonal and the 2" extender tube are necessary to get sufficient back focus for the camera.

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Edited by BlueMoon, 14 April 2024 - 08:06 PM.

[Luckyhead11]

Yeah thats weird try this:
 

1. Telescope -> https://www.amazon.c...13144135&sr=8-3 -> https://www.amazon.c...13144176&sr=8-3 -> Nikon D3500

[BlueMoon]

Ok. They parts themselves will work but won't solve your focus problem and will create a vignetting problem as well due to the 1.25" diameter. The first post in this thread demonstrates vignetting: https://www.cloudyni...ng-is-horrible/ and is something you need to avoid.

 

Your problem is that you can't move the camera back far enough to come to focus. That is why adding an extension tube along with a diagonal fixes the problem. The light path has to travel further through the diagonal and the extension tube to allow you enough back focus. The reason 2" parts are suggested is because they will give your camera better support. 

[PIEJr]

In order to determine roughly how much I'd need to achieve primary focus; I took my camera and handheld it back from the focuser portal. and got it roughly in focus.

Then looked and was surprised how far it was.

I ordered tubes to get that spacing, knowing I had a lot of adjustment in my refractors focuser to work with.

With my AT130mm, I even added my flip mirror box to get the draw tube deeper inside the telescope for a stiffer focuser support.

 

But doing some far fetched visual can get you in the ballpark for starting.

The stackable adaptors (Neewer in post 3 link) may not be enough to get you into primary focus.

You, like I did, may find you need some honkin long extensions.

 

I always reached for the 2" extensions to give my equipment the more robust and ridgid support.

My 1.25" extension was not a good choice for AP.

I even tried one of the telescoping extensions in 1.25".

 

Now, my imaging train is only 2" for as short as I can get away with, and all screwed together for rigidity.

From the start I've opted for Astro cameras. I did some work with my Nikon D3300. But did not want to eat up it's 150,000 shutter operation life expectancy for a task it was never intended (nor designed) to do.

Hence, why I've opted for dedicated Astronomy cameras. No moving parts.

 

If you do decide to get a dedicated Astronomy camera, I'd recommend you get a OSC version. (One shot color)

Then experiment with time.

 

Welcome to the Black Hole of Astrophotography.

Just throw your wallet in and succumb.   

[Luckyhead11]

In order to determine roughly how much I'd need to achieve primary focus; I took my camera and handheld it back from the focuser portal. and got it roughly in focus.

Then looked and was surprised how far it was.

I ordered tubes to get that spacing, knowing I had a lot of adjustment in my refractors focuser to work with.

With my AT130mm, I even added my flip mirror box to get the draw tube deeper inside the telescope for a stiffer focuser support.

 

But doing some far fetched visual can get you in the ballpark for starting.

The stackable adaptors (Neewer in post 3 link) may not be enough to get you into primary focus.

You, like I did, may find you need some honkin long extensions.

 

I always reached for the 2" extensions to give my equipment the more robust and ridgid support.

My 1.25" extension was not a good choice for AP.

I even tried one of the telescoping extensions in 1.25".

 

Now, my imaging train is only 2" for as short as I can get away with, and all screwed together for rigidity.

From the start I've opted for Astro cameras. I did some work with my Nikon D3300. But did not want to eat up it's 150,000 shutter operation life expectancy for a task it was never intended (nor designed) to do.

Hence, why I've opted for dedicated Astronomy cameras. No moving parts.

 

If you do decide to get a dedicated Astronomy camera, I'd recommend you get a OSC version. (One shot color)

Then experiment with time.

 

Welcome to the Black Hole of Astrophotography.

Just throw your wallet in and succumb.   

Yeahh, I was thinking ultimately about getting these:

https://www.amazon.c...1zcF9hdGY&psc=1

[Sky King]

From the rear of the focuser to the sensor in mm there is a number you need to figure out. In the thread I linked above the number for the 72ED is around 130mm. You already have 55mm with the camera, t-ring and t adapter you bought. Your scope also has the focuser travel to make up for being off by a few mm. Measure from the rear of the focuser. Anything inserted in the focuser itself is not counted in the 130mm. When you get it in focus write down what you used and take a picture so you will never have this problem again. 

Edited by Sky King, 15 April 2024 - 09:43 AM.

[Luckyhead11]

So I need to figure how far (in mm) my camera needs to be from the focuser for it to be in focus?

[BlueMoon]

So I need to figure how far (in mm) my camera needs to be from the focuser for it to be in focus?

Yep. You need a minimum of 130mm distance. The draw tube on my 72ED fully extends 40mm. Add to that 10 thickness of the stock 2" adapter on the end of the draw tube. So, 40 + 10 = 50mm. You need an additional 80mm to reach 130mm. So either a long 80mm 2" extension or a 2" diagonal and 2" extension. If you use the diagonal and extension tube I've been suggesting, then you'll have a bit over 130mm and that allows you some leeway for fine focusing. It also moves the weight of the camera closer to the focuser and lessens any flex. Cheers.

Edited by BlueMoon, 15 April 2024 - 11:42 AM.

[Luckyhead11]

The reason I don't want to go for a diagonal is because they are quite expensive :/ So I just figured that extension tubes would be the way to go. Another downside to extension tubes would be how back heavy the telescope would probably be.

 

So IN theory this would work:

https://www.amazon.c...T1zcF9hdGY&th=1 (Its just an 80mm version of the one I linked above)

Edited by Luckyhead11, 15 April 2024 - 11:56 AM.

[BlueMoon]

The reason I don't want to go for a diagonal is because they are quite expensive :/ So I just figured that extension tubes would be the way to go. Another downside to extension tubes would be how back heavy the telescope would probably be.

Yep, doing AP in not an inexpensive hobby to be sure. With either a long extension or the diagonal/extension combination, your scope will be heavy. However, and I'm not trying to rain on your parade, a long extension tube on the end of a draw tube that is fully extended will result in some flex and make it harder to center your target. So, either way there's a trade-off.

[Luckyhead11]

It is made of aluminum so it shouldn't bend unless I put pressure on it. My DSLR is about 3/4 of a pound.

 

Thanks for your help, I'll keep you updated!

[BlueMoon]

Thanks for your help, I'll keep you updated!

You bet and good luck with your imaging. Cheers.