Imaging with a C8 - newbie advice requested...

[bowery]

Hello all,

I'm new to the forum. I have a C8 which I enjoy visually and now I want to move on to imaging. I've done a few (poor) attempts, and have some questions. I'm not guiding (yet), just using the mount's guiding. I want to spend some money improving my rig, but need advice on what would help me more. Thanks in advice everyone!

1) Would a focal reducer help me achieve MORE with shorter exposures? From what I understand, SCT's are kind of slow, and focal reducers concentrate light "faster"? I've heard Celestron's focal reducer (F/10 to F/6.3) makes exposures x3 faster... is that true?

2) Star trailing. I get nasty trails due to poor alignment really quick. Quick as in 30 seconds. Is this normal (see photo below, 10 30 second exposures? I assume improving scope alignment is the only solution? I have read about off-axis guiders. Does anyone have a decent tutorial on that?

3) Focus. I'm focusing with a 2'' crayford on the back of the scope, as I hated the SCT's focus knob. I assume this + a Hartmann mask is as good as it gets? My images always come out blurry...

4) imaging itself. I'm using a Canon 60Da, not attached to a laptop as i'm a remote location. 

Last, but not least, my observing spot is close to the sea. Could humidity really affect my focus? I find all my images to be super blurry when compared with other people's. See below an M42 as a reference...

Again thanks in advance, I really want to improve my skills but need some newbie help I guess!

[lensman57]

Hello all,

I'm new to the forum. I have a C8 which I enjoy visually and now I want to move on to imaging. I've done a few (poor) attempts, and have some questions. I'm not guiding (yet), just using the mount's guiding. I want to spend some money improving my rig, but need advice on what would help me more. Thanks in advice everyone!

1) Would a focal reducer help me achieve MORE with shorter exposures? From what I understand, SCT's are kind of slow, and focal reducers concentrate light "faster"? I've heard Celestron's focal reducer (F/10 to F/6.3) makes exposures x3 faster... is that true?

2) Star trailing. I get nasty trails due to poor alignment really quick. Quick as in 30 seconds. Is this normal (see photo below, 10 30 second exposures? I assume improving scope alignment is the only solution? I have read about off-axis guiders. Does anyone have a decent tutorial on that?

3) Focus. I'm focusing with a 2'' crayford on the back of the scope, as I hated the SCT's focus knob. I assume this + a Hartmann mask is as good as it gets? My images always come out blurry...

4) imaging itself. I'm using a Canon 60Da, not attached to a laptop as i'm a remote location. 

Last, but not least, my observing spot is close to the sea. Could humidity really affect my focus? I find all my images to be super blurry when compared with other people's. See below an M42 as a reference...

m42small.jpg

Again thanks in advance, I really want to improve my skills but need some newbie help I guess!

Hi,

With your C8 a reducer is a must, it will reduce the focal length by a factor of 0.63 and it will make imaging faster, but still it will have focal length of about 1200mm+. a bit long for wide field imaging but good for galaxies. Guiding this scope will be challenge though. You can use your 60da with a T adapter to do imaging but you have to get the backfocus of the reducer right, I think for celestron is around 110mm from flange to sensor, a 55mm spacer will be necessary. The crayford focuser may have to come off though. For imaging the collimation has to be spot on too

A.G

PS: humidity, temprature and seeing conditions  will all have an effect on your focusing.

[bowery]

Thanks lensman. Just one question. Now I have scope-crayford-tadapter-camera. Can you tell me where does the Reducer go in this setup, and the spacer? Never had problems with the crayford as, combining the crayford and the SCT's focusing knob, I have a huge margin to play with... I was hoping to keep the crayford IN with the reducer...

[lensman57]

Thanks lensman. Just one question. Now I have scope-crayford-tadapter-camera. Can you tell me where does the Reducer go in this setup, and the spacer? Never had problems with the crayford as, combining the crayford and the SCT's focusing knob, I have a huge margin to play with... I was hoping to keep the crayford IN with the reducer...

Hi,

The Reducer is designed to be screwed on to the flange on the back of the rear cell, this is a design requirement. You then screw the spacer onto back of the reducer and the camera with the T adapter on to the of the spacer. Celestron makes a dedicted spacer for this purpose . As for guiding people use an off axis guider for SCTs as this is a more rigid set up than a guidescope but it has its shortcomings too. If you go for an OAG then the back focus of the  OAG has to be taken into account. It is best if you take the scope to a reputable dealer so every thing could be measured up correctly.

A.G

See the attached.