Re: [APML] Manual guiding photo

["Bert Katzung" <katzung1@attbi.com>]

Roland:
I believe that any kind of tracking error will be *magnified* almost three
times by the longer focal length of the 135 mm lens compared to the 50 mm.
And if it's field rotation, the excellence of guiding will not help. You
have to be sure your polar alignment is good. You do have it on a wedge or
an equatorial mount, don't you?
Bert

Bert Katzung
katzung1@attbi.com
www.astronomy-images.com

----- Original Message -----
From: "MORVAN, Roland" <RMORVAN@STEIN-HEURTEY.FR>
To: <astro-photo@seds.org>
Sent: Thursday, May 09, 2002 11:43 AM
Subject: [APML] Manual guiding photo



Hello,


I am presently observing from Brazil for several months instead of observing
from France, and I enjoy southern sky for the first time.
In France I have a Meade Lx 200 and I use to take pictures of deep sky
objects in prime focus or in parallel with a 50 mm and a 135 mm telephoto
lens.

I came in Brazil ( isolated place with beautifull sky at 20 ° South
latitude)  with light material, i.e. a 115/900 mm scope that a friend of my
gave me and my 50 mm, 135 mm lenses to take pyggyback pictures of the
southern sky. The scope has no motor, so I have to guide manually by
following a star with a reticulated ocular.
My 50 mm is at f/1.7 and my 135 mm is at f/2.8 and I expose 5 min with the
50 mm and 10-15 min with the 135 mm witha  400 ASA film.

The pictures taken with the 50 mm are ok, but ALL pictures taken with the
135 mm have strar trails instead of points. I am not used with these kind of
problems with my motor driven LX 200.

My diagnostic is:

- Polar positioning error: the field rotation can cause star trails but I
should have the same trails with 50 mm focal length and 5 min exposure
compared with 135 mm focal length (same angular rotation),

- Mechanical flexure: with heavy (for this kind of scope)  135 mm lens , but
I tried several positionments of the camera to avoid flexure  but it is the
same in the pictures,

- Guiding error: according to what I heard, with a 135 mm, the guiding time
has to be at least 5 seconds maximum before we see trails in the negative. I
tried to guide continuously or each 3-5 seconds, so according to this point
I think that I made no mistake.


Anyody has  already seen these kind of problems ? How can I detect the cause
of this ? Can the trails direction or anything ele give clues ?


Thank you.

Roland.

--  APML Archives at <http://astro.umsystem.edu/apml/>  ---
             Unsubscribe at <majordomo@seds.org>




--  APML Archives at <http://astro.umsystem.edu/apml/>  ---
             Unsubscribe at <majordomo@seds.org>