Weasner's Astrophotography Tips Page

ASTROPHOTOGRAPHY - TIPS
Last updated: 8 November 2010

This page documents astrophotography comments, tips, and photos. Contributions welcome. Be certain to see the other articles on the main Astrophotography page.

Subject:	ETX Camera Drive
Sent:	Friday, November 5, 2010 07:26:39
From:	delarcombe@netidea.com (delarcombe@netidea.com)
I don't know if you have seen this application of the ETX mount to
photography.  It is from John Macdonald in the Victoria Chapter of RASC.

http://www.members.shaw.ca/wjm890131/JAlbum-web/ETX%20Camera%20Mount.htm

Thanks for the help.

Dennis Larcombe
Kaslo BC
presently east of Edmonton, Alberta

Subject:	etx 125
Sent:	Sunday, August 29, 2010 10:40:21
From:	Charles Eye (nitesky3@sbcglobal.net)
Hi Mike, Chuck here, I tried that hat trick with the d70 attached to
scope but if its not one thing its something else? I have several trees
around here and about a 15 minute window from around midnight to work
with Jupiter between the trees before it gets to high for the camera not
to touch the base. I gave up on the hat trick set exposure for different
times and this is the best I could do. I"ll just keep trying this trial
and error procedure....  it is fun attempting this... oh by the way,
after your suggestion of resetting, calibrating and training the scope
is working great..... Chuck

Mike here: I adjusted the "levels" in your image. Cloud bands appear! Remember, post-processing your images can dramatically improve the images, even when you think there is nothing useful there.

Subject:	etx 125
Sent:	Thursday, August 26, 2010 13:28:43
From:	Charles Eye (nitesky3@sbcglobal.net)
As far as taking pictures of Jupiter, been very difficult focusing
mainly due to the way the view finder of the nikon d70 camera is made.
The moon though is quite different, it focuses quite easily with no
problems what so ever and that is probably due to being much brighter??
I'm going to try again tonight for Jupiter pics, only thing I know to do
is just take somewhat out of focus, trip the shutter with camera remote,
turn focus knob on scope and snap another, turn focus know a little more
and keep doing this for about 15 or 20 frames, one of them has to be
focused huh?  Thanks again and you have a good clear night.......  Chuck

Mike here: Yes, focusing is challenging (no matter what the camera). Right now, you can use the moon as the focus target and then slew to Jupiter. The focus will be the same (unless the ETX mirror shifts), so don't change it. Also, you should use the "Hat Trick" Technique (discussed on the Helpful Information: Astrophotography page) to avoid image blur due to the camera mirror movement. Also, you might want to see the Hartmann Mask articles on that page was well. And there is also the "Bahtinov Mask" and the Stiletto Focuser, both reviewed on the Accessory Reviews: Astrophotography page.

And:

Thanks for the reply and info. I forgot to mention that am trying
something a little different, I am going to put a 2x converter between
the camera and the scope [no telescope lens, just camera] to make what
should be a 3800mm lens, I use the converter mainly for my 500mm camera
lens......  Chuck

Mike here: That should work. But the increase in magnification will result in more blurring from movement. By the way, on my LX200-ACF I have combined a 2X Barlow Lens with a 3X TeleXtender, for a combined 6X increase in magnification at prime focus. Works great on the moon with my D70 DSLR.

And:

Yes, I have been wondering about the extra magnification. I wanted to
ask if you accept pics through this kind of mail if so I thought I'd
send any results to share with you.....  Chuck

Mike here: See the "Electronic Mail Etiquette and Submittal Guidelines" on the ETX Site home page.

And and more:

Hello, I tried that hat trick with Jupiter, I can't seem to move fast
enough before picture is just too bright. Will be some trial and error
with this one, I'm sure I need to learn more about my camera and using
it. I did get and attaching a fairly decent pic of the moon though with
that 3,800mm set up using the 2x converter..  have a good day.  Chuck

Mike here: It takes practice. Also, be certain to use a low ISO setting on the camera when photographing the moon, especially when near full phase. And one other technique is to adjust the "levels" and image sharpening using editing software:

Subject:	Novice Trying Astrophotography
Sent:	Monday, August 23, 2010 07:55:03
From:	Ted Trostle (tctrostle@gmail.com)
I have found an old adapter that attaches my Canon A560 digital camera
to my ETX-125. From what I have read this camera may not provide the
quality shots other cameras do. But it is what I have and I have been
advised I can program it using the CHDK software....more on that later.

What I would like to ask could some one share a series of shots that
need staked, processed, etc.. so I could practice the stacking and
processing using Photoshop ?

Mike here: Using Photoshop to stack is a bit of a pain. Use AstroStack, Registax, Keith's Image Stacker, or Lynkeos. For more information on stacking and processing, see the Helpful Information: Astrophotography page.

Subject:	autostar drive problem for astrophotography
Sent:	Friday, April 9, 2010 05:04:47
From:	Posma Net (posmanet@web.de)
As you can see on the pictures i am using an ETX OTA on an Meade DS
Mount with Autostar. (Just like the DSX ones.) I have connected my Canon
DSLR with Meade T2-adaptor. This ist fairly good balanced for the mount
as no movement occurs when loosening the upper clamp.

On the M50-picture you can see the problem i am expieriencing with my
autostar. This picture ist taken with 240 seconds exposure. I am using
remote control and mirror lock-up with the camera so that vibrations
cannot be the reason. Vibrations would look more like blur on such long
time exposures anyway. Every long time exposure with the autostar looks
like this, with this kind of "slow tremor" over both axes. The object
always stays in my FOV for over hours, (i.e. telescope is aligned good)
but seems to jitter slowly in place. When i replaye the DS with the old
ETX-RA forks on a wedge (all other conditions the same) this problem
does not occur.

Is it possible that the drives' resolution is not sufficient for long
time exposures? Du you have any ideas what else could be the reason for
my problem?

Thanks!
Posma Net

Mike here: Certainly, the DS mount is not up to doing such long exposures at prime focus. Any vibration at all will appear in the images. Depending on what surface the tripod is mounted on, even vibrations from a slight breeze, or even just walking around, will be magnified up through the less than sturdy tripod. You will either need to get a better mount for the OTA or use shorter exposures (and stack them).

And:

thanks for your suggestions. But i don't think that vibrations are the
reason for this kind of trouble.

I want to show you another three images. You can see in ds_9minutes.jpg
that the autostar drives almost draw a "fiddly" rentacle over 9 minutes.
Approximately every minute there seems to be a small jerk in the system
that leads to a slightly brighter spot in the picture.

In comparison, in the jumpingaround_30seconds.jpg you can see "real"
vibrations caused by me jumping around the tripod during exposure. Just
like i suspected in my first e-mail, this leads to a kind of blur in the
picture instead of the zigzag track caused by the autostar drives. In
addition, the blur is not as big as in the ds_9minutes picture.

The third picture shows a picture with the ETX in the old fork-mount,
not perfectly aligned (this logically leads to the stars drawing a
straight line). There is no zigzag- or rentacle track here... it has to
be caused by the autostar (drives).

The three images can be compared directly as they were taken in the same
windless night inbetween half an hour at the same wind-protected
location. The tripod was the same aluminium one for all three pictures
and all pictures were taken focal with the same DSLR on ETX OTA.

Again, thanks for your personal support and your great online
collection!
Posma Net

Mike here: What you are likely seeing is from two sources: tracking in Alt/Az and Periodic Error. This affects all drives, even on the higher-end, expensive, telescopes. If you place the mount in a polar position, instead of Alt/Az, you can reduce the tracking problems as the drives have to use less movement to compensate for the Earth's rotation. As to Periodic Error, there isn't much you can do about that with the AutoStar #494 that comes with the DS mount. You might want to consider a wedge of some sort (you'll likely have to make your own) if you really want to do long duration astrophotography. Otherwise, you will see "field rotation" during the exposure, resulting in star trailing around the center of the field.

And:

This makes sense to me. There must be some kind of periodic error due to
resolution limitations in movement. Too sad that it affects tracking
that much. Thanks Mike!

Yes i have tried that (putting DS on wedge) some time ago, with negative
results: The DS mount has a construction-conditioned overwheight to its
backside. (The dec axis can be balanced.) Thus the RA drive's clutch is
slipping and proper tracking is not possible. Maybe some kind of
counterweight on the mount's front can solve this problem, but there
seems to be no easy way to attach one without drilling holes or
something, besides loads of plastic parts in this aera.

Clear skies!
Posma Net

Mike here: There are several counterweight designs on the Helpful Information: Astrophotography page that don't require drilling holes. Howecer, keep in mind that small mounts like the DS and ETX are not designed for long duration astrophotography. Yes, you can do some types of astrophotography, such as piggyback and prime focus (for a few seconds or if lucky, a few minutes) but afocal and eyepiece projection will be the most challenging due to the high magnifications involved. Keep in mind that not only are you magnifying the object, you are also magnifying any tracking variations or vibrations in the mount.

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