c8 focusing situation

wucheeyiun · Post by **wucheeyiun** » Wed Apr 20, 2005 9:46 pm

I like to share with fellow forumer regarding astrophotography problem.

Finally i got my visual back, slip into c8 and put on d70,
i could get a clear view from the view finder, but somehow the picture taken is BLUR or unfocus.

Similarly, when i use the eyepiece, the clarity from the c8 ia alot better then the c4r, however, I don't have the problem with my c4r, as some of the posting you all saw i took is sharp, but i am not able to schieve the same sharpness with the c8, same camera.

has it had to do with the complex image baffling within the c8, visual back etc or what i need is like a focal reducer?

Or the mount is too shaky, its a clone gp vixen.

What could be the problem? Care to give comments?

kayheem · Post by **kayheem** » Wed Apr 20, 2005 10:55 pm

Perhaps you could post a sample of your pics so we can take a look.

I am not sure about the D70, but you could try a mirror lockup if it does have one. This will reduce the vibrations which will be magnified in the C8, seeing the F.L. is 2030mm. With the 1.5X crop factor, we are looking at about 3000mm F.L. on the D70.

Kay Heem

Post by **weixing** » Thu Apr 21, 2005 12:08 am

Hi,
I think Kayheem is right... this may be cause by the camera mirror when the shutter open. With a 3000mm focal length as kayheem mention, you need a shutter speed of around 1/3000s(theoretically) to totally get pass the vibration cause by the mirror. I've seen quite a few complaint on this in photography forum... same blur image.

Have a nice day.

tanguan2001 · Post by **tanguan2001** » Thu Apr 21, 2005 10:39 am

What was the exposure time? 3 potential problems - focus, vibration, or tracking - so would need to know exp time and see the pic to locate the problem.

By the way, focussing by eye through the viewfinder is usually not good enough - except perhaps for the moon.

TG

wucheeyiun · Post by **wucheeyiun** » Thu Apr 21, 2005 12:15 pm

Dear all,
I notice a lot of vibration on the scope when i tap very lightly on it, this could be due to insufficent counterweight as the top of scope is heavier then the bottom, i will be getting a 3.7 kg weight to augment the current situation and report the findings
Also when i put the scope on the table and shoot across the building, when i tap the scope lightly, there were no vibration. Hopefully i am on the right track, if not got to change tripod.
Will post pictures soon.

MooEy · Post by **MooEy** » Thu Apr 21, 2005 1:48 pm

counterweights are suppose to balance the scope, not likely to reduce vibrations. in fact, adding more counterweights will cause the cg to be higher and shake even more. dun be too bothered about the mount if u are not going to fork out $$ to buy a much bigger mount.

~MooEy~

kochu · Post by **kochu** » Thu Apr 21, 2005 2:05 pm

Hi Wu ,

If I remember correctly last sunday I saw your scope mounted on Aluminium tripod outstreched quite high to clear the height of the balcony wall. Such a set up especially if is windy is bound to be shaky for photography.

Kochu/21-4-05

ariefm71 · Post by **ariefm71** » Thu Apr 21, 2005 2:06 pm

Also when i put the scope on the table and shoot across the building, when i tao the scope lightly, there were no vibration. Hopefully i am on the right track, if not got to change tripod.

You can try to use my portable pier if you want.
http://www.singastro.org/viewtopic.php?t=1490

Post by **weixing** » Thu Apr 21, 2005 8:15 pm

Hi,
To test whether is your problem cause by the vibration of your SLR mirror when shutter is release, point your scope at a far away object or building during day time. Put your mount as low as possible. Focus carefully and take a few images when there is no wind. This will remove the tracking error (since there is no tracking) and vibration cause by the wind. Look at the images, if the sharpness of images is inconsistence, I think it is cause by the SLR mirror when you release the shutter. If the blurness is consistence, try refocus and shoot again.

Anyway, I still think it is cause by the vibration of the SLR mirror when the shutter is release, because normally the tracking error and vibration cause by the wind won't show up on moon image, because the shutter speed is usually quite fast.... unless a very strong wind blow directly at you or your tripod leg is extend too high.

Happy imaging and have a nice day.

wucheeyiun · Post by **wucheeyiun** » Thu Apr 21, 2005 10:06 pm

bad moon shot,
f10, prime focus. Plenty vibration.
speed 1/30, ISO 800.

SingAstro

c8 focusing situation

c8 focusing situation

Shaky pics