Quick question - DSLR mount

[ThunderStorm]

I got a Canon 600D and do I need to buy a T-Mount adaptor to hook that to my dob eye piece?

[Dennis]

Hi Alan

For Prime Focus photography, just check that your Dob will allow sufficient “in-focus” with a DSLR attached. I understand that the focuser on Newtonian telescopes sometimes bottom out. That is, even when racked all the way in, the image in the DSLR has not yet come to focus.

Some users have solved this with using low profile focusers, low profile adapters, etc. whereas others have raised the Primary Mirror up the tube so the light cone extends further out of the focuser.

For eyepiece projection (the DSLR pointing into the eyepiece) there are special adapters that fit on the focuser and you can screw the DSLR baseplate onto the adapter to hold it steady, although a DSLR is quite heavy for this technique and may have a vignetted field of view unless you can get the camera lens very close to the eyepiece.

I suspect that attaching a DSLR plus lens to the eyepiece of a Dobsonian (eyepiece projection photography) would dramatically affect the balance of the tube. Additionally, the image of the brighter objects (such as our Moon and the Planets) would be so highly magnified that it might also be quite challenging keep the object in the field of view.

Cheers

Dennis

[MrB]

As Dennis has said, in-focus could be an issue, as might the % illuminated field. Dob Newtonians are usually built for visual observing. A Newtonian built for photography is known as an astrograph.
If you are able to reach focus, then yes you will need a T-mount adapter, you will also need an EOS to M42 adaptor.
This will get you started however you will see Coma (elongated stars at the corners of the photo) at some stage, if the photography bug bites, you may want to purchase a coma corrector which essentially replaces the t-mount, you will still need the EOS adapter.

[raymo]

With Skywatcher Newts [including Dobs] you do not require a T-adaptor.
You unscrew the barrel on the focuser that 1.25" eyepieces slide into, and the T ring screws directly onto the exposed male thread for prime focus work. The weight of a DSLR is not a real problem, as a simple counterweight can be devised. My 30mm 2" eyepiece is heavier than my Canon 1100D, and the load is even heavier when I add the 1.5x barlow.
raymo

[Misplaced]

Hi Raymo,

The advice I've been given for the Skywatcher I'm looking to purchase is that it does require an adaptor. This advice was from Andrews Communications.

Confused?:shrug:

[raymo]

you do not need a T- adaptor with a SW Newt. If you look at a T- adaptor
you will see that one end slides into the focuser, and the other has a male
thread on it. That male thread is the same as the one on the SW focuser that is revealed when the barrel for 1.25" eyepieces is unscrewed. That thread is almost flush with the open end of the focuser. When the T-ring
[not T-adaptor] is screwed onto the male thread the camera is hard up against the focuser, which is where it has to be in order to come to prime focus. If you introduce a T-adaptor between the T-ring and the focuser,
the camera cannot come anywhere near focus. When a Canon DSLR is
at prime focus, the focuser is only racked out around 10mm. The SW focuser/adaptor setup is a bit confusing, and many new owners have
thought that their scopes cannot come to prime focus, until told how
to do it by various IIS members.
raymo

[Misplaced]

Cheers Raymo - I shall go back to them and ask why I need the adaptor and use your explanation if that is ok?

Mis

[raymo]

That's o.k. It is of course possible that the latest available tubes have a
different focuser arrangement, but I doubt it very much, they've been
the same for many years. I am taking some pics to show how it works,
and will post them very shortly. I suggest you have a look at them before
contacting Andrews again, so you have a better idea of what you are talking about.
raymo

[ThunderStorm]

T-Ring...T-Adapter?
Looking forward to your photos. :)

[Misplaced]

I shall await the pictures.
Mis

[raymo]

O.K. Loosen off the 2 knurled knobs at positions 2 o'clock and 6 o'clock in
pic 1. Remove the eyepiece holder/adaptor assembly so you are left with the open end of the focuser as in pic 2. Separate the 2 parts of the assembly you removed from the focuser.[ pic 3, ] so you end up with
pic 4. Attach the disc with the male thread to your T-ring as shown in
pic 5. Attach the T-ring/ adaptor assembly to your camera. Attach the camera to the focuser as shown in pic 6. Rotate the camera to desired position, and nip up the 2 knurled knobs that you earlier loosened off.
Sounds a bit of a pain, but after you have done it once or twice you can do it in about 30 seconds, or even less.
Pic 6 shows the focuser in approx. the position that it is in when at prime focus. If you want to know what a T-adaptor looks like you will find a pic of one on Andrews website.
raymo

[Misplaced]

They are great thanks Raymo.

I have sent you a PM.

Mis

[ThunderStorm]

So I need to buy a T-ring (connect to DSLR) and a T-mount (connect T-ring to focuser)?

[omegacrux]

Yes you need a t-ring should mount like the pic below , mine does to a skywatcher dob
But I need the adapter to mount it to my refractor

Edit , t-ring should mount straight to the focuser minus the ep holders


David

[ThunderStorm]

Oh...for a dob you only need a T-ring?

[astro744]

Some clarification on astro-photography methods with DSLR and telescope:

1. Piggyback: Camera with lens rides on top of telescope using suitable bracket with 1/4-20 screw for camera. Great for wide field photography.

2. Prime focus: Camera without lens is attached to the telescope. The telescope is the lens whether it is refractor or reflector. First a T-Ring that matches your camera body must be used. The T ring converts your camera body bayonet mount to T2 female thread. Then a T2-adapter that has a T2 male thread screws into the T-ring. The other end is either a 2" nose-piece that slips into the focuser. (1.25" is also available but will vignette with cameras with larger sensors). e.g. if you telescope is 200mm dia./f5 then you have a 1000mm f5 telephoto 'lens'.

3. Eyepiece projection: The camera with lens removed and T-ring added screws onto a special eyepiece projection adapter. This adapter holds an eyepiece inside and the focal length of eyepiece and distance to film plane determines the effective focal length of the system. This method was popular in the film days for photographing planets and close-ups of the Moon. It is not used much anymore due to video astronomy offering far better results for planetary and Luna. Some eyepiece projection adapters were variable with a sliding upper body. Note only small narrow body 1.25" eyepieces with a short upper section could be used with this method.

4. Afocal: The camera with lens is placed via a suitable bracket (or hand held if steady enough for bright objects) in front of the eyepiece. The eyepiece used is typically 32 to 40mm or so with good eye relief to avoid vignetting. The zoom feature of the camera can be used to enlarge the object. Again this method is best for the Moon and planets and using small compact digital cameras.

Note I've not seen a Skywatcher Newtonian focuser but from what others have said it appears that it has a T2 male threaded adapter. It is also possible to get a 2"-1.25" adapter with T2 male thread. However I particularly do not like these as you could easily damage your field lens on say a 2" Nagler if you happened to forget to remove the 2"-1.25" T2 threaded adapter from the focuser.

Note often the problem with prime focus on a standard focuser is that you cannot rack in enough and hence the need for a low profile focuser, (or first try and release the primary mirror springs all the way and then tighten only enough to get collimation). The Skywatcher system overcomes this with a different design. I have a Tectron focuser with two upper bodies; one visual standard rack & pinion and then another photographic for prime focus photography. You simply undo two nylon screws, remove the visual and add the photographic body to get the camera much lower. This focuser is not made anymore that I know of.

[omegacrux]

Yup just a t-ring that is matched to your camera there not expensive $30ish
The last picture below shows that

David

[raymo]

Astro 744, SW Newts do not need a T-adaptor. The T-ring screws directly
onto the focuser, as shown in the last pic below.
raymo

[ThunderStorm]

I am using Canon DSLR 600D.

I found these on eBay:
- just T-ring
http://www.ebay.com.au/itm/DSLR-Camera-Mount-Adapter-T-Ring-for-Canon-EOS-M42x0-75mm-for-Telescope-New-/150879143355?pt=AU_Cameras_Telescop es_Binoculars&hash=item23211905bb&_uhb=1

The pictures did not show there are threads to fit the focuser. Or just plug it into the focuser? Looks not locked secure?

- or do I need this?
http://www.ebay.com.au/itm/Metal-1-25inch-Mount-Adapter-1-65inch-T-Ring-Adapter-for-Canon-EOS-Cameras-New-/161241315103?pt=AU_Cameras_Telescop es_Binoculars&hash=item258abb371f&_uhb=1

It has the 1.25inch adaptor to fit into the focuser.

[omegacrux]

Its hard to see but there's a very fine thread on the t-ring
So the top one you listed should be fine
The one with the 1.25 nosepiece might not reach focus due to the extra length.

David

[raymo]

If your Newt is a skywatcher you only need the top one [T-ring].
If it is another brand, you could very well need the bottom one
[T- adaptor] as well.
raymo

[omegacrux]

Here you go just screw the 1.25 out exposing the thread an t-ring screws here

David

[ThunderStorm]

Mine is Skywater dob, so will buy the T-ring only then. Thanks.
:)

[ThunderStorm]

Thanks for the photo, all clear now.
:)

[ThunderStorm]

Hi David,

I looked at my Skywatcher 10in dob and removed 1.25in eyepiece (and also the 2 inch-to-1 inch adapter) from the focuser, there is no thread for me to screw in the T-ring.

Eidt - is the 2 inch-to-1 inch adapter a single piece? Or can I dis-assemble into 2 pieces?

[omegacrux]

Hi
the 1.25 adapter nosepiece unscrews from that 2in bit that has the two thumbscrews exposing the thread that can be seen at the base of the 1.25 nosepiece

David

[omegacrux]

It looks like a single piece
Care needed with these fine thread made out of alloy make sure you line em up properly , don't want to cross tread them !
See to the right there's the thread you need
Sorry about pic quality I reduce'd it a bit too much

David

[omegacrux]

Here's what to expect
10in flexdob
Lumix gf3
Last night focus is not easy really need a dual speed focuser
I also put up a pic with the ed80 in begginars sec see the difference

David

[raymo]

My Photos and explanation at the beginning of this thread showed quite clearly how to do it. You just unscrew the barrel that the 1.25" eyepieces
slide into from the adaptor that is held in the focuser by the two knurled knobs, and screw the T-ring onto the male thread on the adaptor.
raymo

[Forgey]

Hi Alan, if it helps i've taken a pic of how i connect my 600D to the dob. Unscrew the 1 1/2 adapter and and the t-ring screws straight onto that.

[ThunderStorm]

I know what's happening:
My 2in-to-1.25in adapter has a "ring" and "eyepiece-like" part.
I unscrewed the eyepiece-like part can see the "ring" that has thread on it.
So finally I think I got it.

What you guys have the 2in-to-1.25in adapter look like? Just the ring or 2-part adapter?

[omegacrux]

Post 11, pic 3-4 of Raymo's post shows what needs to be done just copy and match yours to his pics

David

[ThunderStorm]

I found something on eBay, one T2 adaptor is thicker and one other is thinner, not sure if the thinner is the same.

Thinner one:
http://www.ebay.com/itm/M42-Lens-to-Canon-EOS-Adapter-Ring-4-Rebel-XSi-T1i-T2i-/290762705159?pt=US_Filter_Rings_Hol ders&hash=item43b2cec907

Thicker one:
http://www.ebay.com.au/itm/New-T2-T-MOUNT-T-ring-adapter-for-Canon-Eos-1D-5D-III-7D-50D-/281154656430?pt=AU_Cameras_Photogra phic_Accessories&hash=item41761f98ae

[raymo]

The first one [thinner] is a different thing altogether; it's purpose is to
let you put Pentax M42 lenses onto your Canon EOS camera.
You need the second [thicker] one, which will screw directly onto the thread you mentioned in your previous post. I had assumed that you already had a basic T-ring.
raymo

[glend]

If you have Modular Hyperion EPs you can (using a cheap T-thread adaptor from Baader, product #2958080 available from Agena Astro) screw the EP directly to the camera T-thread adaptor. I have a Hyperion 13mm EP and it attached directly to my Canon 450d. You get the benefit of the magnification from the EP. TO my knowledge this only works with the modular Hyperion EPs.

[MrB]

To expand on Ray's reply... While both systems are M42, the lens mount version of the M42 thread(by Zeiss but commonly known as Praktica or Pentax mount) has 1.0mm thread pitch, while the T2 thread pitch is 0.75mm.
They will start to screw together for about half a turn, but attempting to force these two systems together will lead to damage.

[ThunderStorm]

So I should buy the thicker one?

[astro744]

The thinner one is called a body mount. They are used to convert a lens of one make for use on a camera of a different make.

When I first started astrophotography I had a Praktica camera that has M42 screw lenses. I bought a Praktica M42 T-ring and T2 adapter. Yes the threads are the same but the pitch is different.

Later I bought a Nikon FE2 and rather than buy a Nikon T-ring, I bought a Praktica M42 to Nikon body mount. This body mount was quite thin and also had a small correcting lens to account for the thickness of the body mount to ensure proper focus (also ensures focus at infinity lines up with the infinity index). The body allowed me to use M42 screw lenses on my Nikon. However, I eventually got some Nikkor lenses and then simply used the body mount with the Praktica T-ring and T2 adaptor when doing astrophotography. I removed the small corrective lens as it was not needed for prime focus astrophotography.

Unless you have use for a body mount, get the thicker T-ring.

[SingleWord]

Thanks for all replies.
I'll go for the thicker one then. :)