127 mac cass

[Willow127mm (Brad)]

Hi I was wondering if anyone can help me I have a 127 celestron mac cass not the best scope for AP but its all I have at the moment.
I have a canon 1100d and all connections.I cant seem to get an image in live view to centre targets and swapping EP for cam is problematic.I saw Forrest Tannaka do a nice photo of Andromeda by stacking alot of shorter frames and I was hoping to do the same with that and others I have had some good luck with the camera lens but wide angle gets old fast and I was hoping to target individual objects anyone got some advise on equipment ,flip mirrors,OAG,s ECT
Any help much appreciated

[raymo]

Hi Brad, Firstly, do you have an EQ mounted 127, or the Alt/Azimuth
mounted SLT127? You can get longer exposures with an EQ mounted one. Live View will only show bright objects, so find a bright star, and
magnify the Live View 10x, and focus until the star is as small as the
white star shown in the box at bottom right of the screen. Then shift to your target. As a budding imager start with bright objects that can be seen through the camera's viewfinder. You need to learn the basics of
AP before worrying about OAGs etc. A good first idea is to aim at the moon with the camera attached, screw the focuser right in or out, and count the turns back to when the moon is sharp, so when changing from EP to camera you can get approximate focus straight away. You are trying to run before you can walk. Get some passable single images
under your belt before worrying about stacking. Stacking is not just
combining images, you have to learn image processing too.
good luck.
raymo

[Willow127mm (Brad)]

Hi Raymo thanks for the reply I probably wasnt very clear in my last post I have done alot of moon shots and wide angle shots and even a few of orion but I was using a 4'' refractor witch had alot of aberation as the glass wasnt that good that was also a goto.
I hope to get EQ mount when poss but I am pretty much stuck with the SLT Celestron for now.
I know what I have isnt that good for imaging but I was hoping I could still take shots of the brighter objects without tracking.
Ive had some ok results stacking and Im getting the hang of processing
but I know Im very much a beginner in all aspects.
I just want some advise from people who know.
Is there any hope for this scope or should I sell it and slowly build up.
Its great for observing and the glass seems better than my meade but if I can only take photos of the moon than i think i will lose interest.
Thanks in advance for any help Brad

[raymo]

If you have the complete SLT 127, then it will of course track, but being an Alt/Az mount, it will suffer from field rotation, which will show up in your images.
This fact coupled with the fact that the Mak is very slow photographically
makes your setup less than ideal for AP. There are two types of AP that
your setup would be o.k. for. First, video imaging of the moon, sun [with
the appropriate filter], and planets, with a cheap webcam. Many of the best examples are done that way, stack 1000 or so frames in the usual way. Secondly, a few of the brightest DSOs could be imaged by stacking
a lot of exposures that are short enough to not show field rotation.
I imagine that the focal length of your Mak will limit you to around
30 sec exposures. Your scope being so slow, even brighter DSOs may be barely visible on individual frames, but will still be o.k. when they are stacked.
raymo

[Willow127mm (Brad)]

Hi Raymo firstly thanks greatly for your replys I rely appreciate it.
My scope is very complete and it works great as far as alignment goes.
I try to use the rule of 600 when trying to avoid star trailing and came up with 600\div by 1500 focal lenth =0.4 of a second which seemed questionable.Am I using the wrong sum?
You mentioned 30 second which seems more realistic will it be suitable with a 1500mm FL?
Also what DSO,s do you think are a good first up targets.
I was also wondering about imaging with EP inserted in an extension between the t ring and the rear of the OTA does it have a place in AP or should it be totally avoided.
I understand it is kinda the opposite to a focal reducer but I thought it could be helpful for planetary imaging as it gives more mag what do you think?
I have some images I have taken nothing great but I would love some critasism good or bad I feel that's the best way to learn.
The problem is I need a program to shrink my photos to fit any suggestions?
So to image DSO,s should I align the mount as well as possible then swap the EP for the canon and start shooting?
Also how many shots do you think 20 at 30sec with 5 to 10 darks or more or less also what ISO and WB do you advise I currently use Daylight WB and ISO between 1600 and 3200 but I do have a fair bit of LP were I live would a LP filter help for imaging?
Sorry to chew your ear off but Im sure you know how addictive this hobby can be.
THANX HEAPS Brad

[raymo]

I've just read your post, and will be glad to give you a full answer, but I am flat out tonight. Will answer tomorrow. If someone helps you in the meantime , so well and good.
raymo

[julianh72 (Julian)]

There's a good description of how to calculate the "pixel shift" due to field rotation on an Alt-Az mount as a function of your latitude, the position of the target in the sky, your sensor size (in pixels) and your exposure time here:
http://calgary.rasc.ca/field_rotation.htm

I have attached a spreadsheet which you can modify for your own location and equipment - if you can keep the exposure such that the "pixel shift" in the corners of the image is only 1 or 2 pixels in each frame, you should be able to get a nice series of frames which can be stacked successfully. 30-second exposures or thereabouts should be quite feasible for many targets - indeed, I generally get more pixel movement from telescope vibrations than from field rotation on my SLT mount.

[julianh72 (Julian)]

Originally Posted by Willow127mm

I try to use the rule of 600 when trying to avoid star trailing and came up with 600\div by 1500 focal lenth =0.4 of a second which seemed questionable.Am I using the wrong sum?

I believe the "Rule of 600" (and similar rules of thumb) is for eliminating star trails on fixed (non-tracking) cameras. With your camera mounted on a tracking Alt-Az mount, you have already dealt with the overall issue of stars trailing across a fixed field of view, but you still need to deal with "Field Rotation" - see my previous post.

[raymo]

Firstly Brad, As Julianh said, the rule is for fixed cameras, and at 1500mm
focal length, 0.4 secs would be about right, but it depends greatly on
which part of the sky you are imaging. The nearer to the celestial poles
you get, the longer the exposures you can use. You could use exposures at 80 degrees declination 6x longer than at 0 degrees declination.
Putting an EP between your camera and the scope is called eyepiece projection, and you can buy adaptors for that purpose. In your case it
would not be a good idea. Your scope is already very slow photographically, and it would become incredibly slow using that method. You would need horrendously long exposures. Planetary imaging is
normally done with a cheap webcam. It's very hard to get good images
with a DSLR.[unless using it's video function.]
Regarding imaging DSOs and anything else that is not very bright;
focus is everything; it has to be spot on, which is not easy to do unless
you have Live View, and/or a Bahtinov mask. If your camera has Live
View, do the align routine, and then direct it to a bright star as near as possible to your imaging target. Magnify the star 10x in Live View and
focus it until it is as small as the white star shown in the small box at bottom right of the screen. Lock the focuser and slew the scope to your target. At this early stage don't worry about darks. Enable the camera's
noise reduction feature[s], and it will take a dark after each exposure.
This of course halves the number of images you'll get in a session, but
at this stage it's not as if you'll be looking to get hundreds of images in a session. Daylight WB is fine. It is essential to find out how long your
exposures can be without star trailing. Take increasing length test shots
at very high ISO[6400 or higher] so the process doesn't take too long, until you see star elongation happening. Set your exposure time to
or just below the longest one that shows round stars, and start shooting
away at 3200 ISO. When you're getting consistent results drop to 1600.
Try stacking 10 subs, and if happy with that, 30-50 is good.
LP filter would help, but will rob you of some light, which is the last thing your slow scope needs. See if you can borrow one and try it.
Eta Carina, The Tarantula Neb, and the Orion Neb would be good first
targets.
I use Photoshop for downsizing, but it is probable that the software that came with your DSLR can do it.
raymo