Attaching DSLR to telescope

[Dindsy]

Hi there,
I jsut want to see how people typically connect their DSLR to their telescope. I've been trying to do it with the Bintel camera adapter and a T-Ring. Using an Eyepiece in the Camera adapter. This assembly replaces the camera lens.
This seems to carry a few problems. A big one with focusing (been raising this in the Beginners section of this site). Also, there is no aperature controls so everything is done on manual.

I guess the big thing i seem to be getting is that people keep their lenses on. Is this right? How do you do it?

thanks

PS. I tired to attach an image of the camera adapter. Not sure what I've done so it may or may not appear.

[Dennis]

Hi Martin

There are two main methods used with a telescope in astro photography.

The first image shows the “Prime Focus” method.
The second image shows the “Eyepiece Projection” method.

For Prime Focus, you need a T2 adapter which fits the DSLR (without lens) to the telescope focuser.

I think your photo shows a device used for “Eyepiece Projection”.

Cheers

Dennis

[RB (Andrew)]

Originally Posted by Dindsy

Hi there,
I jsut want to see how people typically connect their DSLR to their telescope. I've been trying to do it with the Bintel camera adapter and a T-Ring. Using an Eyepiece in the Camera adapter. This assembly replaces the camera lens.
This seems to carry a few problems. A big one with focusing (been raising this in the Beginners section of this site). Also, there is no aperature controls so everything is done on manual.

I guess the big thing i seem to be getting is that people keep their lenses on. Is this right? How do you do it?

Dennis is spot on.

Just to clarify, you won't get aperture control because your scope becomes your lens therefore you use the camera in manual mode.

The other method you mention is piggyback photography in which you mount your camera and lens on top of your scope and use the scope/mount to track the movement of the stars while you expose thru your lens set at infinity.

[Dennis]

I should add the following.

Prime Focus
The telescope in the photos I posted is a Vixen 4 inch refractor with a focal length of 918mm (a focal ration of f9). In the 1st photo with the SLR connected to the focuser via a T2 ring, the telescope is acting like a “giant lens” with a focal length of 918mm.

This set up is the easiest to use and gives a Field Of View (FOV) of around 1½° x 1° so you can fit in around 3 full Moons. You would use this set up for nebulae like Orion M42.

Eyepiece Projection
You use an eyepiece (in my photo it is a 10mm Plossl) to literally project a magnified image onto the DSLR chip. This method is tough! The FOV is very small, typically less than 20 arc mins (2/3 size of a full Moon); the image is dim so it is hard to focus but before all of that, finding the object at such a high magnification is a challenge in itself, unless we are photographing something as big and bright as the Moon.

You really need a mount with drives to do Eyepiece Projection and stay sane.

Cheers

Dennis

[Dindsy]

Great Pictures Dennis,
You're exactly right. My piece is for Eye piece projection and that's what I'm doing. The T-ring is a separate piece.

I'm just having difficulty focusing. I've been trying to do some daylight shots of a distant tree just for easy experimenting. The camera viewfinder shows a nice sharp image but the shot on the camera LCD is a big blur.

For star shots I haven't had much better luck although the blur is less noticeable because they're stars and small. But I think I'm still getting the same blur.

Is this something obvious or is it related to the post below about focusing SLR/DSLR's ?? Can I compensate without the addon's discussed?

cheers

[Dennis]

Originally Posted by Dindsy

Great Pictures Dennis,
You're exactly right. My piece is for Eye piece projection and that's what I'm doing. The T-ring is a separate piece.

I'm just having difficulty focusing. I've been trying to do some daylight shots of a distant tree just for easy experimenting. The camera viewfinder shows a nice sharp image but the shot on the camera LCD is a big blur.

For star shots I haven't had much better luck although the blur is less noticeable because they're stars and small. But I think I'm still getting the same blur.

Is this something obvious or is it related to the post below about focusing SLR/DSLR's ?? Can I compensate without the addon's discussed?

cheers

Hi Martin

From your other post, the description reads like you are jumping in at the deep end, where even experts fear to tread…..

Using the DSLR (without lens) + Eyepiece Projection Adapter + Eyepiece gives you a highly magnified image, depending upon the focal length of the eyepiece used.

The stars may appear to be in focus on the viewing screen, but it is likely they will not be at the best focus, so in the final (> 3000x2000 pixel) image they will look blurred.

Also, if you press the shutter release manually, your contact with the release button is sufficient to knock the camera and ‘scope set up, which will trail or blur the stars, as will the vibrations of the DSLR mirror as it flips out of the way, unless you have a mirror lock up function.

If that is not enough, then it is likely that your mount (if it is tracking) would not be up to recording the star image as a dot for exposures of more than 2 or 3 seconds using eyepiece projection.

None of this is either operator or equipment error; it is just that you are pushing the envelope when using eyepiece projection.

Cheers

Dennis

[Dindsy]

Nothing like a challenge

I'm minimising some probs by using a shutter release cable and RA tracking on my EQ mount. But I do notice it's not hard to make the image wobble.

So, is the answer to use Prime focus method? Cos I tried that and all i see is fuzz. Like looking throught the viewfinder without a lens on.

For this set up I use the same adapter but without the eyepiece. Is the camera too far away in this instance? Do I need a shorter camera adapter to bring the camera right up to the focuser?

BTW my set up is: 6" Newtonian, f=1000mm, EQ3 mount with RA drive.

cheers

[Dennis]

Originally Posted by Dindsy

Nothing like a challenge

So, is the answer to use Prime focus method? Cos I tried that and all i see is fuzz. Like looking throught the viewfinder without a lens on.

For this set up I use the same adapter but without the eyepiece. Is the camera too far away in this instance? Do I need a shorter camera adapter to bring the camera right up to the focuser?

BTW my set up is: 6" Newtonian, f=1000mm, EQ3 mount with RA drive.

cheers

I think the answer is probably yes - do not use the long adapter. I have never used a Newtonian, but I understand that they do not have the large range of inward focus travel that SCTs and refractors have. This is known as insufficient back focus.

Typically, people mount the DSLR directly to the focuser with a low profile adapter and then have to wind the focuser almost all the way in. Some have even modified their ‘scopes by moving the prime mirror a little further up the tube, so the prime focus or point of focus extends sufficiently far outside the focus tube.

Cheers

Dennis

[Dindsy]

Thanks Dennis,

Many things answered.



cheers

[g__day (Matthew)]

Does a cable shutter release fix the bluring, or does the actual openning of the mechanism cause problems too?

I wonder if it does if it could be fixed by holding a matte black piece of cardborad just in from of the camera for say 10 seconds whilst the shutter cable releases - giving it time for vibrations to die down before you let any light into the CCD and only then do you drop the sheet and let light in?

[swannies1983 (Dan)]

You're correct. The movement of the mirror when the shutter is activated can also cause images to be blurry. Many cameras have a "mirror lock-up" option. This moves the mirror out of the light path. However, this means you cannot see anything through the viewfinder