Beginning Astrophotography Focus Issues

[admin]

Ok,
this is my first foray into serious astrophotography... I am using a K200D Pentax DSLR on Bulb setting and clicking the remote button, holding it for about 10-50 seconds and checking what I took a pic of.

needless to say it was a failure to some extent. I was able to fix some balance / mount issues (I knew those screws were supposed to be tightened to stop up and down movements!!).

Ok here are some shots. As you can see (or not) that is sirius the star (brightest star I could see), in between phone / electric lines.



Ok I am using the mirror diagonal, a T-Adaptor hooked up to the mirror diagonal and then the DSLR screwed onto the T-Adaptor. I could not find a way to connect the T-adaptor to the ED100 tube directly but this maybe the focus issue.

Also I could see the out of focus star in the view finder, however I was not able to get it in focus. Maybe someone here could help

Telescope / Mount :

ED100 PRO
HEQ5PRO GOTO

Settings on camera:
ISO 1600
Bulb
Remote Control ON - 15.8 Seconds exposure time
MF
0.0 EV
F ---
sRGB
6 megapixels settings quality


thanks in advance for your patience
cheers

[Vinnie]

Looks more like Uranus

(no I'm not joking)

I'm not familiar with Pentax cameras, but is the mount the threaded version? ie does the lens of the camera thread into the body. If yes, I'm pretty sure I've got all the bits necessary to adapt the Pentax straight to the drawtube of the ED100.

If you ever decide to give me a postal address, I can chuck it in with the other stuff. With compliments .

[admin]

Ok this is my setup:


Thats the diagonal there connected to the T-adaptor. Actually the thing together is a monstrosity... no wonder there are focus issues... lol

And the T-adaptor for the Pentax DSLR :





And the ED 100 PRO Connector (i put the diagonal here):






let me know if you see anything weird.

cheers

[Carlos_dfc]

Sounds like a matter of not enough 'travel' on the focuser.

I've dabbled with attaching a SLR camera to an ED100 - and IIRC, I didn't have enough in-travel of the focus drawtube when using a diagonal.
In order to get focus I had to attach straight onto the drawtube as Vinnie mentions.
The diagonal effectively pushes the camera too far backwards

[Vinnie]

Whoa there Gus, You aint never gonna get in focus like that, as Carlos has pointed out.

The thing you are calling a T adaptor looks like an adaptor that you insert an Eyepiece into. Its way too long. The T adaptor is just a narrow ring, one end with T thread, the other with the bayonet or thread applicable to your camera body, and is only maybe 20mm long, or deep if you wish.

Again, does your Pentax use threaded lenses? As in when you take the lens off the camera body does it bayonet, or screw. If yes I have the correct adaptor here. Its one I picked up in a box of junk, and its carton is labelled "Pentax S, T- Mount Adaptor" but I don't have a Pentax camera to check it (being that there's no guarantee that whats in the box is actually what its supposed to be)

[SteveB]

This might get you into the right focus ballpark.

Take out an eyepiece, turn it upside down and look inside and you'll probably see the field stop ring. It's often close to the shoulder of the eyepiece body.
When the telescope is focused, the prime focused image is at that point. The eyepiece allows you to view that virtual image.

When you replace the eyepiece with a camera (for prime focus photography with no other lenses) you want that focus point to fall on the sensor.
The sensor is about 5mm from the back of the camera (it may be marked by a circle with a line through it). So, you need to wind the focus inwards by much further than you would normally consider.

Strictly speaking, the T-mount specification calls for the flange to sensor distance to be 55mm although I don't know if all adapters adhere to that.

Steve.

[Vinnie]

And to add to that, Steve, you can buy various M/F T threaded spacer rings to adjust that focal point


Gus, when you bought the scope, it shipped with a 2" to 1.25" adaptor so that you can use a 1.25" diag. This adaptor has a thread on the end where the 1.25" diag would go in. This is a T Thread. Then you get the correct T adaptor, which is a narrow ring, and attach one end to the camera body, the other to the 2" to 1.25" adaptor and then slip the whole setup straight into the focuser drawtube. This will position the front face of the camera body only about 25mm behind the end of the drawtube

[Vinnie]

Here is the adaptor and T Ring separated, and assembled

Camera body on one end, other end into focuser drawtube

The adaptor shown ships with all Synta 2" Crayfords. If its too long, you can buy shorter after market. If its two short, you can buy spacer rings after market. The actual T Ring is determined by your camera body. I have since checked and there are two different Pentax mounts, the "K" which is a bayonet, and the "S" which is a screw in.

[admin]

ok thanks to everyones help I think I figured it out , I can actually screw off the


bottom pentax connector (remove the long tube - its an adventure figuring out things with scopes - took me a week or so to find the hidden polarscope!).

The unscrewed piece is similar to Vinnies left piece in his 1rst picture. I screwed it onto the piece I have that is similar to Vinnies right piece in his 1rst picture. Actually as everyone said this fits directly onto the ED 100 where the diagonal is supposed to go. If I can see Sirius or another bright star, I will try this again tonite and document this more carefully.

Thanks again for the great input Karl, Steve and Vinnie I am learning every minute thanks to everyone.

cheers!

[Carlos_dfc]

Vin and Gus

That is the exact same part I used to attach my old Praktica 35mm camera to my ED
Only difference is that it screws straight into the Praktica's lens mount, without the need of an adaptor.





And here it is, on the end of the ED





Also very handy for snapshots of the Moon and Sun (with proper filtration of course) through my Dob (bigger image size due to longer focal length) - because I also have a Synta 2" Crayford on my Dob